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Sample records for superconducting kondo alloys

  1. Superconductivity in the Kondo lattice model

    Energy Technology Data Exchange (ETDEWEB)

    Bodensiek, Oliver; Pruschke, Thomas [Institute for Theoretical Physics, University of Goettingen, Friedrich-Hund-Platz 1, D-37077 Goettingen (Germany); Zitko, Rok [Institute for Theoretical Physics, University of Goettingen, Friedrich-Hund-Platz 1, D-37077 Goettingen (Germany); Jozef Stefan Institute, Jamova 39, SI-1000 Ljubljana (Slovenia)

    2011-07-01

    We study the Kondo lattice model with an additional attractive interaction among the conduction-band electrons by means of dynamical mean-field theory in combination with the numerical renormalization group method. In the normal phase we observe a strong dependency of the low-energy scale on the attractive interaction. Thus, there exists a delicate interplay between the attractive interaction and the antiferromagnetic Kondo exchange, which results in a critical interaction, above of which the Fermi surface collapses because the spins become effectively decoupled from the conduction electrons. Additionally, we allow for a s-wave superconducting phase, which appears to be split at the point of the underlying Fermi surface collapse. We discuss the interplay between attractive interaction an Kondo exchange and its pertinence to phonons in heavy fermion physics.

  2. Superconductivity of heavy fermions in the Kondo lattice model

    Energy Technology Data Exchange (ETDEWEB)

    Sykora, Steffen [IFW Dresden (Germany); Becker, Klaus W. [Institut fuer Theoretische Physik, Technische Universitaet Dresden (Germany)

    2015-07-01

    Understanding of the origin of superconductivity in strongly correlated electron systems is one of the basic unresolved problems in physics. Examples for such systems are the cuprates and also the heavy-fermion metals, which are compounds with 4f and 5f electrons. In all these materials the superconducting pairing interaction is often believed to be predominantly mediated by spin fluctuations and not by phonons as in normal metals. For the Kondo-lattice model we present results, which are derived within the Projective Renormalization Method (PRM). Based on a recent study of the one-particle spectral function for the normal state we first derive an effective Hamiltonian which describes heavy fermion quasiparticle bands close to the Fermi surface. An extension to the superconducting phase leads to d-wave solutions for the superconducting order parameter in agreement with recent STM measurements.

  3. Charge Kondo effect in negative-U quantum dots with superconducting electrodes

    Science.gov (United States)

    Fang, Tie-Feng; Guo, Ai-Min; Lu, Han-Tao; Luo, Hong-Gang; Sun, Qing-Feng

    2017-08-01

    Recent experimental realization of superconducting quantum dot devices with intradot attraction U [Nature (London) 521, 196 (2015), 10.1038/nature14398; Phys. Rev. X 6, 041042 (2016), 10.1103/PhysRevX.6.041042] offers unique opportunities to study the charge Kondo effect in a superconducting environment. In such devices pseudospin flips are caused by two tunneling processes. One is the cotunneling of normal electrons which generates near-gap Kondo resonances in the single-electron spectral density. This negative-U charge Kondo effect is more robust than the conventional spin Kondo effect against the suppression by the superconductivity. The other tunneling is the mean-field Cooper-pair tunneling which produces a zero-energy bound state in the pair spectral density. Interesting crossover physics from the strongly-correlated Kondo screening to the mean-field polarization of local pseudospin is demonstrated. Due to the interplay of these two tunnelings, the supercurrent is suppressed for intermediate couplings, but it can increase to the unitary limits both in the strong and weak coupling regimes. We obtain the magnetic field-dependent supercurrent which is consistent with the key experimental findings.

  4. Superconductivity of composite particles in a two-channel Kondo lattice.

    Science.gov (United States)

    Hoshino, Shintaro; Kuramoto, Yoshio

    2014-04-25

    Emergence of odd-frequency s-wave superconductivity is demonstrated in the two-channel Kondo lattice by means of the dynamical mean-field theory combined with the continuous-time quantum Monte Carlo method. Around half filling of the conduction bands, divergence of an odd-frequency pairing susceptibility is found, which signals instability toward the superconductivity. The corresponding order parameter is equivalent to a staggered composite-pair amplitude with even frequencies, which involves both localized spins and conduction electrons. A model wave function is constructed for the composite order with the use of symmetry operations such as charge conjugation and channel rotations. Given a certain asymmetry of the conduction bands, another s-wave superconductivity is found that has a uniform order parameter. The Kondo effect in the presence of two channels is essential for both types of unconventional superconductivity.

  5. Overscreened Kondo effect, (color) superconductivity and Shiba states in Dirac metals and quark matter

    CERN Document Server

    Kanazawa, Takuya

    2016-01-01

    We study the interplay between the Kondo effect and (color) superconductivity in doped Dirac metals with magnetic impurities and in quark matter with colorful impurities. We first point out that the overscreened Kondo effect arises in the normal state of these systems. Next the (color) superconducting gap is incorporated as a mean field and the phase diagram for a varying gap and temperature is constructed nonperturbatively. A rich phase structure emerges from a competition of effects unique to a multichannel system. The Kondo-screened phase is shown to disappear for a sufficiently large gap. Peculiarity of quark matter due to the confining property of non-Abelian gauge fields is noted. We also investigate the spectrum of sub-gap excited states, called Shiba states. Based on a model calculation and physical reasoning we predict that, as the coupling of the impurity to the bulk is increased, there will be more than one quantum phase transition due to level crossing among overscreened states.

  6. Superconducting Pairing Correlations near a Kondo-destruction Quantum Critical Point in Cluster Impurity Models

    Science.gov (United States)

    Cai, Ang; Pixley, Jedediah; Si, Qimiao

    Heavy fermion metals represent a canonical system to study superconductivity driven by quantum criticality. We are particularly motivated by the properties of CeRhIn5, which shows the characteristic features of a Kondo destruction quantum critical point (QCP) in its normal state, and has one of the highest Tc's among the heavy fermion superconductors. As a first step to study this problem within a cluster-EDMFT approach, we analyze a four-site Anderson impurity model with the antiferromagnetic spin component of the cluster coupled to a sub-Ohmic bosonic bath. We find a QCP that belongs to the same universality class as the single-site Bose-Fermi Anderson model. Together with previous work on a two-site model, our result suggests that the Kondo destruction QCP is robust as cluster size increases. More importantly, we are able to calculate the d-wave pairing susceptibility, which we find to be enhanced near the QCP. Using this model as the effective cluster model of the periodic Anderson model, we are also able to study the superconducting pairing near the Kondo-destruction QCP of the lattice model; preliminary results will be presented.

  7. Kondo effect from a Lorentz-violating domain wall description of superconductivity

    CERN Document Server

    Bazeia, D; Mota-Silva, J C

    2016-01-01

    We extend recent results on domain wall description of superconductivity in an Abelian Higgs model by introducing a particular Lorentz-violating term. The temperature of the system is interpreted through the fact that the soliton following accelerating orbits is a Rindler observer experiencing a thermal bath. We show that this term can be associated with the {\\sl Kondo effect}, that is, the Lorentz-violating parameter is closely related to the concentration of magnetic impurities living on a superconducting domain wall. We also found that the critical temperature decreasing with the impurity concentration as a non-single valued function, for the case $T_K

  8. Foundations of heavy-fermion superconductivity: lattice Kondo effect and Mott physics

    Science.gov (United States)

    Steglich, Frank; Wirth, Steffen

    2016-08-01

    This article overviews the development of heavy-fermion superconductivity, notably in such rare-earth-based intermetallic compounds which behave as Kondo-lattice systems. Heavy-fermion superconductivity is of unconventional nature in the sense that it is not mediated by electron-phonon coupling. Rather, in most cases the attractive interaction between charge carriers is apparently magnetic in origin. Fluctuations associated with an antiferromagnetic (AF) quantum critical point (QCP) play a major role. The first heavy-fermion superconductor CeCu2Si2 turned out to be the prototype of a larger group of materials for which the underlying, often pressure-induced, AF QCP is likely to be of a three-dimensional (3D) spin-density-wave (SDW) variety. For UBe13, the second heavy-fermion superconductor, a magnetic-field-induced 3D SDW QCP inside the superconducting phase can be conjectured. Such a ‘conventional’, itinerant QCP can be well understood within Landau’s paradigm of order-parameter fluctuations. In contrast, the low-temperature normal-state properties of a few heavy-fermion superconductors are at odds with the Landau framework. They are characterized by an ‘unconventional’, local QCP which may be considered a zero-temperature 4 f-orbital selective Mott transition. Here, as concluded for YbRh2Si2, the breakdown of the Kondo effect concurring with the AF instability gives rise to an abrupt change of the Fermi surface. Very recently, superconductivity was discovered for this compound at ultra-low temperatures. Therefore, YbRh2Si2 along with CeRhIn5 under pressure provide a natural link between the large group of about fifty low-temperature heavy-fermion superconductors and other families of unconventional superconductors with substantially higher T c, e.g. the doped Mott insulators of the perovskite-type cuprates and the organic charge-transfer salts.

  9. Foundations of heavy-fermion superconductivity: lattice Kondo effect and Mott physics.

    Science.gov (United States)

    Steglich, Frank; Wirth, Steffen

    2016-08-01

    This article overviews the development of heavy-fermion superconductivity, notably in such rare-earth-based intermetallic compounds which behave as Kondo-lattice systems. Heavy-fermion superconductivity is of unconventional nature in the sense that it is not mediated by electron-phonon coupling. Rather, in most cases the attractive interaction between charge carriers is apparently magnetic in origin. Fluctuations associated with an antiferromagnetic (AF) quantum critical point (QCP) play a major role. The first heavy-fermion superconductor CeCu2Si2 turned out to be the prototype of a larger group of materials for which the underlying, often pressure-induced, AF QCP is likely to be of a three-dimensional (3D) spin-density-wave (SDW) variety. For UBe13, the second heavy-fermion superconductor, a magnetic-field-induced 3D SDW QCP inside the superconducting phase can be conjectured. Such a 'conventional', itinerant QCP can be well understood within Landau's paradigm of order-parameter fluctuations. In contrast, the low-temperature normal-state properties of a few heavy-fermion superconductors are at odds with the Landau framework. They are characterized by an 'unconventional', local QCP which may be considered a zero-temperature 4 f-orbital selective Mott transition. Here, as concluded for YbRh2Si2, the breakdown of the Kondo effect concurring with the AF instability gives rise to an abrupt change of the Fermi surface. Very recently, superconductivity was discovered for this compound at ultra-low temperatures. Therefore, YbRh2Si2 along with CeRhIn5 under pressure provide a natural link between the large group of about fifty low-temperature heavy-fermion superconductors and other families of unconventional superconductors with substantially higher T c, e.g. the doped Mott insulators of the perovskite-type cuprates and the organic charge-transfer salts.

  10. Magnetic susceptibility of Dirac fermions, Bi-Sb alloys, interacting Bloch fermions, dilute nonmagnetic alloys, and Kondo alloys

    Science.gov (United States)

    Buot, Felix A.; Otadoy, Roland E. S.; Rivero, Karla B.

    2017-03-01

    Wide ranging interest in Dirac Hamiltonian is due to the emergence of novel materials, namely, graphene, topological insulators and superconductors, the newly-discovered Weyl semimetals, and still actively-sought after Majorana fermions in real materials. We give a brief review of the relativistic Dirac quantum mechanics and its impact in the developments of modern physics. The quantum band dynamics of Dirac Hamiltonian is crucial in resolving the giant diamagnetism of bismuth and Bi-Sb alloys. Quantitative agreement of the theory with the experiments on Bi-Sb alloys has been achieved, and physically meaningful contributions to the diamagnetism has been identified. We also treat relativistic Dirac fermion as an interband dynamics in uniform magnetic fields. For the interacting Bloch electrons, the role of translation symmetry for calculating the magnetic susceptibility avoids any approximation to second order in the field. The expressions for magnetic susceptibility of dilute nonmagnetic alloys give a firm theoretical foundation of the empirical formulas used in fitting experimental results. The unified treatment of all the above calculations is based on the lattice Weyl-Wigner formulation of discrete phase-space quantum mechanics. For completeness, the magnetic susceptibility of Kondo alloys is also given since Dirac fermions in conduction band and magnetic impurities exhibit Kondo effect.

  11. Superconductivity in Metals and Alloys

    Science.gov (United States)

    1963-02-01

    sintered material (Reed, Gatos , LaFleur, and Roddy, 1962). It has great importance for any materials work, since generalizations based only on stoichio...1961),Phys. Rev. Letters 6, 597. Goodman, B. B., (1962) IBM J. Research and Development 6, 63. Gor’kov, L. P., (1960), Soy . Phys. JETP 10, 998...34Superconductivity in Metals and Alloys-Technical Documentary Report No. ASD-TDR-62-269, Contract No. AF 33(616)-640 5. Reed, T. B., Gatos , H. C., LaFleur, W. j

  12. Superconductivity and magnetic order in La--Ce alloys

    Energy Technology Data Exchange (ETDEWEB)

    Wollan, J.J.; Finnemore, D.K.

    1971-03-01

    Superconductivity and magnetic order have been studied both above and below the Kondo temperature for the La--Ce system. Electrical resistivity measurements on La 0.2, 1.0, 2.0, 3.2, and 4.0 wt. percent Ce have been made from 0.060 to 20.0K.

  13. Enhanced superconductivity, Kondo behavior, and negative-curvature resistivity of oxygen-irradiated thin films of aluminium

    Science.gov (United States)

    Sinnecker, E. H. C. P.; Sant'Anna, M. M.; ElMassalami, M.

    2017-02-01

    We followed the evolution of the normal and superconducting properties of Al thin films after each session of various successive oxygen irradiations at ambient temperature. Such irradiated films, similar to the granular ones, exhibit enhanced superconductivity, Kondo behavior, and negative-curvature resistivity. Two distinct roles of oxygen are identified: as a damage-causing projectile and as an implanted oxidizing agent. The former gives rise to the processes involved in the conventional recovery stages. The latter, considered within the context of the Cabrera-Mott model, gives rise to a multistep process which involves charges transfer and creation of stabilized vacancies and charged defects. Based on the outcome of this multistep process, we consider (i) the negative-curvature resistivity as a manifestation of a thermally assisted liberation of trapped electric charges, (ii) the Kondo contribution as a spin-flip scattering from paramagnetic, color-center-type defects, and (iii) the enhancement of Tc as being due to a lattice softening facilitated by the stabilized defects and vacancies. The similarity in the phase diagrams of granular and irradiated films as well as the aging effects are discussed along the same line of reasoning.

  14. Dressed topological insulators. Rashba impurity, Kondo effect, magnetic impurities, proximity-induced superconductivity, hybrid systems

    Energy Technology Data Exchange (ETDEWEB)

    Posske, Thore Hagen

    2016-02-26

    Topological insulators are electronic phases that insulate in the bulk and accommodate a peculiar, metallic edge liquid with a spin-dependent dispersion. They are regarded to be of considerable future use in spintronics and for quantum computation. Besides determining the intrinsic properties of this rather novel electronic phase, considering its combination with well-known physical systems can generate genuinely new physics. In this thesis, we report on such combinations including topological insulators. Specifically, we analyze an attached Rashba impurity, a Kondo dot in the two channel setup, magnetic impurities on the surface of a strong three-dimensional topological insulator, the proximity coupling of the latter system to a superconductor, and hybrid systems consisting of a topological insulator and a semimetal. Let us summarize our primary results. Firstly, we determine an analytical formula for the Kondo cloud and describe its possible detection in current correlations far away from the Kondo region. We thereby rely on and extend the method of refermionizable points. Furthermore, we find a class of gapless topological superconductors and semimetals, which accommodate edge states that behave similarly to the ones of globally gapped topological phases. Unexpectedly, we also find edge states that change their chirality when affected by sufficiently strong disorder. We regard the presented research helpful in future classifications and applications of systems containing topological insulators, of which we propose some examples.

  15. A sourcebook of titanium alloy superconductivity

    CERN Document Server

    Collings, E W

    1983-01-01

    In less than two decades the concept of supercon­ In every field of science there are one or two ductivity has been transformed from a laboratory individuals whose dedication, combined with an innate curiosity to usable large-scale applications. In the understanding, permits them to be able to grasp, late 1960's the concept of filamentary stabilization condense, and explain to the rest of us what that released the usefulness of zero resistance into the field is all about. For the field of titanium alloy marketplace, and the economic forces that drive tech­ superconductivity, such an individual is Ted Collings. nology soon focused on niobium-titanium alloys. They His background as a metallurgist has perhaps given him are ductile and thus fabricable into practical super­ a distinct advantage in understanding superconduc­ conducting wires that have the critical currents and tivity in titanium alloys because the optimization of fields necessary for large-scale devices. More than superconducting parameters in ...

  16. Spin-glass, antiferromagnetism and Kondo behavior in Ce2Au1-CoSi3 alloys

    Indian Academy of Sciences (India)

    Subham Majumdar; E V Sampathkumaran; St Berger; M Della Mea; H Michor; E Bauer; M Brando; J Hemberger; A Loidl

    2002-05-01

    Recently, the solid solution Ce2Au1-CoSi3 has been shown to exhibit many magnetic anomalies associated with the competition between magnetic ordering and the Kondo effect. Here we report high pressure electrical resistivity of Ce2AuSi3, ac susceptibility () and magnetoresistance of various alloys of this solid solution in order to gain better knowledge of the magnetism of these alloys. High pressure resistivity behavior is consistent with the proposal that Ce2AuSi3 lies at the left-hand side of the maximum in Doniach’s magnetic phase diagram. The ac data reveal that there are in fact two magnetic transitions, one at 2 K and the other at 3 K for this compound, both of which are spin-glass-like. However, as the Co concentration is increased, antiferromagnetism is stabilized for intermediate compositions before attaining non-magnetism for the Co end member.

  17. A theoretical study of the spin glass-Kondo-magnetic disordered alloys in the presence of a random field

    Science.gov (United States)

    Magalhaes, S. G.; Zimmer, F. M.; Coqblin, B.

    2012-12-01

    We study here the influence of a random applied magnetic field on the competition between the Kondo effect, the spin glass phase and a ferromagnetic order in disordered cerium systems such as CeNi1-xCux. The model used here takes an intrasite Kondo coupling and an intersite random coupling; both the intersite random coupling and the random magnetic field are described within the Sherrington-Kirkpatrick model and the one-step replica symmetry breaking procedure is also used here. We present phase diagrams giving Temperature versus the Kondo exchange parameter and the random magnetic field makes decrease particularly the importance of the spin glass and ferromagnetic phases.

  18. Unconventional superconductivity in low density electron systems and conventional superconductivity in hydrogen metallic alloys

    Science.gov (United States)

    Kagan, M. Yu.

    2016-06-01

    In this short review, we first discuss the results, which are mainly devoted to the generalizations of the famous Kohn-Luttinger mechanism of superconductivity in purely repulsive fermion systems at low electron densities. In the context of repulsive- U Hubbard model and Shubin-Vonsovsky model we consider briefly the superconducting phase diagrams and the symmetries of the order parameter in novel strongly correlated electron systems including idealized monolayer and bilayer graphene. We stress that purely repulsive fermion systems are mainly the subject of unconventional low-temperature superconductivity. To get the high temperature superconductivity in cuprates (with T C of the order of 100 K) we should proceed to the t-J model with the van der Waals interaction potential and the competition between short-range repulsion and long-range attraction. Finally we note that to describe superconductivity in metallic hydrogen alloys under pressure (with T C of the order of 200 K) it is reasonable to reexamine more conventional mechanisms connected with electron-phonon interaction. These mechanisms arise in the attractive- U Hubbard model with static onsite or intersite attractive potential or in more realistic theories (which include retardation effects) such as Migdal-Eliashberg strong coupling theory or even Fermi-Bose mixture theory of Ranninger et al. and its generalizations.

  19. Superconducting state parameters of indium-based binary alloys

    Indian Academy of Sciences (India)

    A M Vora; Minal H Patel; P N Gajjar; A R Jani

    2002-05-01

    Our well-recognized pseudopotential is used to investigate the superconducting state parameters viz; electron–phonon coupling strength , Coulomb pseudopotentialµ *, transition temperature c, isotope effective exponent and interaction strength 0 for the In1-Zn and In1-Sn binary alloys. We have incorporated six different types of local field correction functions, proposed by Hartree, Taylor, Vashistha–Singwi, Ichimaru–Utsumi, Farid et al and Sarkar et al to show the effect of exchange and correlation on the aforesaid properties. Very strong influence of the various exchange and correlation functions is concluded from the present study. The comparison with other such theoretical values is encouraging, which confirms the applicability of our model potential in explaining the superconducting state parameters of binary mixture.

  20. Unexpected observation of spatially separated Kondo scattering and ferromagnetism in Ta alloyed anatase TiO2 thin films.

    Science.gov (United States)

    Sarkar, T P; Gopinadhan, K; Motapothula, M; Saha, S; Huang, Z; Dhar, S; Patra, A; Lu, W M; Telesio, F; Pallecchi, I; Ariando; Marré, D; Venkatesan, T

    2015-08-12

    We report the observation of spatially separated Kondo scattering and ferromagnetism in anatase Ta0.06Ti0.94O2 thin films as a function of thickness (10-200 nm). The Kondo behavior observed in thicker films is suppressed on decreasing thickness and vanishes below ~25 nm. In 200 nm film, transport data could be fitted to a renormalization group theory for Kondo scattering though the carrier density in this system is lower by two orders of magnitude, the magnetic entity concentration is larger by a similar magnitude and there is strong electronic correlation compared to a conventional system such as Cu with magnetic impurities. However, ferromagnetism is observed at all thicknesses with magnetic moment per unit thickness decreasing beyond 10 nm film thickness. The simultaneous presence of Kondo and ferromagnetism is explained by the spatial variation of defects from the interface to surface which results in a dominantly ferromagnetic region closer to substrate-film interface while the Kondo scattering is dominant near the surface and decreasing towards the interface. This material system enables us to study the effect of neighboring presence of two competing magnetic phenomena and the possibility for tuning them.

  1. Kondo effect in quantum dots and molecular devices

    Institute of Scientific and Technical Information of China (English)

    JIANG Lang; LI Hongxiang; HU Wenping; ZHU Daoben

    2005-01-01

    Kondo effect is a very important many-body phenomenon in condensed matter physics,which explains why the resistance increases as the temperature is lowered (usually <10 K) in dilute magnetic alloy, and why the conductance increases as temperature is decreased in quantum dots. This paper simply introduces equilibrium and non- equilibrium Kondo effects in quantum dots together with the Kondo effect in quantum dots with even number of electrons (when the singlet and triplet states are degenerate). Furthermore, Kondo effect in single atom/molecular transistors is introduced, which indicates a new way to study Kondo effect.

  2. 19 September 2011 - Japan Science and Technology Agency President K. Kitazawa visiting the LHC superconducting magnet test hall with engineer M. Bajko; the ATLAS visitor centre with Collaboration Former Spokesperson P. Jenni and Senior Scientist T. Kondo; signing the guest book with Adviser R.Voss and Head of International Relations F. Pauss.

    CERN Multimedia

    2011-01-01

    19 September 2011 - Japan Science and Technology Agency President K. Kitazawa visiting the LHC superconducting magnet test hall with engineer M. Bajko; the ATLAS visitor centre with Collaboration Former Spokesperson P. Jenni and Senior Scientist T. Kondo; signing the guest book with Adviser R.Voss and Head of International Relations F. Pauss.

  3. Discovery of a superconducting high-entropy alloy.

    Science.gov (United States)

    Koželj, P; Vrtnik, S; Jelen, A; Jazbec, S; Jagličić, Z; Maiti, S; Feuerbacher, M; Steurer, W; Dolinšek, J

    2014-09-05

    High-entropy alloys (HEAs) are multicomponent mixtures of elements in similar concentrations, where the high entropy of mixing can stabilize disordered solid-solution phases with simple structures like a body-centered cubic or a face-centered cubic, in competition with ordered crystalline intermetallic phases. We have synthesized an HEA with the composition Ta34Nb33Hf8Zr14Ti11 (in at. %), which possesses an average body-centered cubic structure of lattice parameter a=3.36  Å. The measurements of the electrical resistivity, the magnetization and magnetic susceptibility, and the specific heat revealed that the Ta34Nb33Hf8Zr14Ti11 HEA is a type II superconductor with a transition temperature Tc≈7.3  K, an upper critical field μ0H_c2≈8.2  T, a lower critical field μ0Hc1≈32  mT, and an energy gap in the electronic density of states (DOS) at the Fermi level of 2Δ≈2.2  meV. The investigated HEA is close to a BCS-type phonon-mediated superconductor in the weak electron-phonon coupling limit, classifying it as a "dirty" superconductor. We show that the lattice degrees of freedom obey Vegard's rule of mixtures, indicating completely random mixing of the elements on the HEA lattice, whereas the electronic degrees of freedom do not obey this rule even approximately so that the electronic properties of a HEA are not a "cocktail" of properties of the constituent elements. The formation of a superconducting gap contributes to the electronic stabilization of the HEA state at low temperatures, where the entropic stabilization is ineffective, but the electronic energy gain due to the superconducting transition is too small for the global stabilization of the disordered state, which remains metastable.

  4. Exact Nonequilibrium Transport in the Topological Kondo Effect

    Science.gov (United States)

    Béri, B.

    2017-07-01

    A leading candidate for the experimental confirmation of the nonlocal quantum dynamics of Majorana fermions is the topological Kondo effect, predicted for mesoscopic superconducting islands connected to metallic leads. We identify an anisotropic, Toulouse-like, limit of the topological Kondo problem where the full nonequilibrium conductance and shot noise can be calculated exactly. Near the Kondo fixed point, we find novel asymptotic features including a universal conductance scaling function and fractional charge quantization observable via the Fano factor. In the universal regime, our results apply for generic anisotropy and even away from the Kondo limit as long as the system supports an emergent topological Kondo fixed point. Our approach thus provides key new qualitative insights and exact expressions for quantitative comparisons to future experimental data.

  5. Superconductivity in the amorphous phase of topological insulator Bi x Sb100-x alloys

    Science.gov (United States)

    Barzola-Quiquia, J.; Lauinger, C.; Zoraghi, M.; Stiller, M.; Sharma, S.; Häussler, P.

    2017-01-01

    In this work we investigated the electrical properties of rapidly quenched amorphous Bi x Sb{}100-x alloys in the temperature range of 1.2 K to 345 K. The resistance reveals that for a broad range of different compositions, including that for the topological insulator (TI), a superconducting state in the amorphous phase is present. After crystallization and annealing at an intermediate temperature, we found that in pure Bi and Bi x Sb{}100-x alloys with composition corresponding to the TI, the superconductivity persists, but the transition shifts to a lower temperature. The highest superconducting transition temperature {T}{{C}0} was found for pure Bi and those TI’s, with a shift to low temperatures when the Sb content is increased. After annealing at a maximum temperature of T = 345 K, the samples are non-superconducting within the experimental range and the behavior changes from semiconducting-like for pure Bi, to metallic-like for pure Sb. Transition temperature {T}{{C}0} of the amorphous Bi x Sb{}100-x alloys have been calculated in the BCS-Eliashberg-McMillan framework, modified for binary alloys. The results can explain the experimental results and show that amorphous Bi x Sb{}100-x exhibits a strong to intermediate electron-phonon coupling.

  6. Structure and superconducting transition in splat-cooled U–T alloys (T = Mo, Pd, Pt)

    Energy Technology Data Exchange (ETDEWEB)

    Kim-Ngan, N.-T.H., E-mail: tarnawsk@up.krakow.pl [Institute of Physics, Pedagogical University, Podchorazych 2, 30-084 Krakow (Poland); Paukov, M. [Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 12116 Prague (Czech Republic); Sowa, S.; Krupska, M. [Institute of Physics, Pedagogical University, Podchorazych 2, 30-084 Krakow (Poland); Tkach, I.; Havela, L. [Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 12116 Prague (Czech Republic)

    2015-10-05

    Highlights: • Splat-cooled U–6 at.% Mo, U–5 at.% Pd, U–5 at.% Pt alloys become superconducting below 1 K. • U–5 at.% Pd and U–5 at.% Pt reveal only one resistivity jump at T{sub c}. • Two distinguishable resistivity drops were observed for U–6 at.% Mo. • A broad maximum was observed at T{sub c} in the specific heat. • Those splats consist of two phases having orthorhombic α- and cubic γ-U structure. - Abstract: U–T (T = Mo, Pd, Pt) alloys were prepared by splat cooling technique and characterized by X-ray diffraction. The resistivity and specific heat measurements were performed down to 0.3 K to study their superconductivity. The superconducting transition in the alloy with 6 at.% Mo (U–6%Mo) revealed by a smooth decrease below 1.5 K and a sharp drop at 0.6 K in the resistivity, while a single sharp drop was revealed at T{sub c} ≈ 0.8 K for those with 5 at.% Pd and Pt doping (U–5%Pd and U–5%Pt). With applying magnetic fields, the resistivity drops move to lower temperatures. The superconductivity transitions were revealed by only one broad peak at T{sub c} in the C(T) curves.

  7. Study of the {delta}-Al/Ag superconducting alloy for TES applications

    Energy Technology Data Exchange (ETDEWEB)

    Gastaldo, L. [Department of Physics, University and INFN of Genoa, Via Dodecaneso 33, 16146 Genoa (Italy) and Kirchhoff-Institut fuer Physik, Universitaet Heidelberg, INF 227, 69120 Heidelberg (Germany) and Technische Universitat Munchen, E15 James Franck Strasse, D-85748 Garching (Germany)]. E-mail: loredana.gastaldo@ge.infn.it; Gallinaro, G. [Department of Physics, University and INFN of Genoa, Via Dodecaneso 33, 16146 Genoa (Italy); Gatti, F. [Department of Physics, University and INFN of Genoa, Via Dodecaneso 33, 16146 Genoa (Italy); Pergolesi, D. [Department of Physics, University and INFN of Genoa, Via Dodecaneso 33, 16146 Genoa (Italy); Gomes, M. Ribeiro [Department of Physics, University and INFN of Genoa, Via Dodecaneso 33, 16146 Genoa (Italy); Repetto, P. [Department of Physics, University and INFN of Genoa, Via Dodecaneso 33, 16146 Genoa (Italy); Dussoni, S. [Department of Physics, University and INFN of Genoa, Via Dodecaneso 33, 16146 Genoa (Italy); Valle, R. [Department of Physics, University and INFN of Genoa, Via Dodecaneso 33, 16146 Genoa (Italy); Manfrinetti, P. [INFM and Dipartimento di Chimica e Chimica Industriale via Dodecaneso 33, 16146 Genova (Italy); Chincarini, A. [Department of Physics, University and INFN of Genoa, Via Dodecaneso 33, 16146 Genoa (Italy)

    2006-04-15

    Despite the general discard in using Al/Ag alloys as transition edge sensors (TES), primarily due to the persistent instability of these devices, further investigations were conducted on the metallic diffusion processes based on the phase diagram of these systems for periods of more than 9 months. The results demonstrated the formation of a stable superconducting inter-metallic alloy at the sample interface showing an HCP lattice corresponding to the {delta}-Al/Ag phase alloy. Furthermore, the transition temperature of the alloy depends on the material stoichoimetry and can vary from about 80 mK to more than 100 mK. In this paper, we suggest the R and D continuation of Al/Ag inter-metallic {delta}-phase as homogeneous stable films for TES applications.

  8. Superconductivity

    CERN Document Server

    Poole, Charles P; Farach, Horacio A

    1995-01-01

    Superconductivity covers the nature of the phenomenon of superconductivity. The book discusses the fundamental principles of superconductivity; the essential features of the superconducting state-the phenomena of zero resistance and perfect diamagnetism; and the properties of the various classes of superconductors, including the organics, the buckministerfullerenes, and the precursors to the cuprates. The text also describes superconductivity from the viewpoint of thermodynamics and provides expressions for the free energy; the Ginzburg-Landau and BCS theories; and the structures of the high

  9. Theoretical investigation of superconductivity in MgB2-xCx alloys

    Science.gov (United States)

    Sharma, Gargee; Sharma, Smita

    2016-05-01

    In this paper we investigated the superconducting properties of MgB2-xCx alloys where x is the concentration (0.0, 0.03, 0.11 and 0.20). The superconducting state parameters, namely, the electron-phonon coupling strength (λ), Coulomb pseudopotential (μ*), transition temperature (Tc), isotope effect exponent (α) and interaction strength (NoV) of MgB2-xCx alloys have been investigated in the BCS-Eliashberg-McMillan framework, as modified for MgB2-xCx alloys. Pseudo ions with average properties have been considered to replace different types of ions in the system. It is observed that all the superconducting parameters go on decreasing as the concentration of C is increased. The magnitudes of λ and Tc indicate that MgB2-xCx is strong-to-intermediate coupling superconductor. It is also observed that Tc is composition dependent. Present computations yield almost linear variation of Tc with concentration x of C in the MgB2-xCx system, which is in agreement with the experimental data. A linear Tc equation is proposed by fitting the present results.

  10. Kondo Physics and Unconventional Superconductivity in the U Intermetallic U2PtC2 Revealed by NMR

    Energy Technology Data Exchange (ETDEWEB)

    Mounce, Andrew M. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Thompson, Joe David [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2015-12-17

    The set of slides begins by discussing the topic NMR of heavy fermion superconductors under the topics heavy fermion materials, superconductivity, and nuclear magnetic resonance. The history of these phenomena is sketched, with particular mention made of CeCu2Si2, UPt3, and UBe13. Unconventional superconductivity, which is non-phonon mediated superconductivity, presents a high Tc (up to ~150 K), and involves a more complicated spin/orbital wave function. The presentation then goes on to give experimental NMR results for U2PtC2 and Pu-115’s.

  11. Flux Pinning in Superconducting Niobium-Titanium Alloys

    Science.gov (United States)

    McKinnell, James Charles

    1990-01-01

    By studying Nb-Ti alloys from Nb44wt%Ti to Nb62wt%Ti the low field (2T) current density has been raised from 6500A/mm^2 (4.2^ circK) with standard Nb46.5wt%Ti to 7400A/mm ^2 with Nb58wt%Ti. When standard processing sequences were used, the alloys containing more than 46.5wt%Ti exhibited non-uniform microstructures following a precipitation heat treatment and the hardness rose from 200 DPN to over 300 DPN. By increasing the cold work prior to heat treatment the non-uniform precipitation was avoided. The amount of cold work needed prior to heat treatment to suppress non-uniform precipitation increased as the Ti content of the alloy increased. The volume fraction of precipitate produced during a given heat treatment also increased as the Ti content of the alloy increased. As the Ti content increased, the peak in the reduced pinning force curve shifted from b = 0.5 to b = 0.25. In order to determine whether the change in the flux pinning properties was due to the change in microstructure or due to enhanced Delta H_{c} pinning as the Ti content was increased, a set of wires with similar microstructures was developed. Their flux pinning behavior showed that the higher Ti alloys have pinning force curves which peak at progressively lower reduced fields. Thus Delta H_{c} pinning becomes the dominant pinning mechanism as the Ti content is increased.

  12. Superconductivity

    CERN Document Server

    Thomas, D B

    1974-01-01

    A short general review is presented of the progress made in applied superconductivity as a result of work performed in connection with the high-energy physics program in Europe. The phenomenon of superconductivity and properties of superconductors of Types I and II are outlined. The main body of the paper deals with the development of niobium-titanium superconducting magnets and of radio-frequency superconducting cavities and accelerating structures. Examples of applications in and for high-energy physics experiments are given, including the large superconducting magnet for the Big European Bubble Chamber, prototype synchrotron magnets for the Super Proton Synchrotron, superconducting d.c. beam line magnets, and superconducting RF cavities for use in various laboratories. (0 refs).

  13. Kondo screening of the spin and orbital magnetic moments of Fe impurities in Cu

    Science.gov (United States)

    Joly, L.; Kappler, J.-P.; Ohresser, P.; Sainctavit, Ph.; Henry, Y.; Gautier, F.; Schmerber, G.; Kim, D. J.; Goyhenex, C.; Bulou, H.; Bengone, O.; Kavich, J.; Gambardella, P.; Scheurer, F.

    2017-01-01

    We use x-ray magnetic circular dichroism to evidence the effect of correlations on the local impurity magnetic moment in an archetypal Kondo system, namely, a dilute Cu:Fe alloy. Applying the sum rules on the Fe L2 ,3 absorption edges, the evolution of the spin and orbital moments across the Kondo temperature are determined separately. The spin moment presents a crossover from a nearly temperature-independent regime below the Kondo temperature to a paramagneticlike regime above. Conversely, the weak orbital moment shows a temperature-independent behavior in the whole temperature range, suggesting different Kondo screening temperature scales for the spin and orbital moments.

  14. Development of a persistent superconducting joint between Bi-2212/Ag-alloy multifilamentary round wires

    Science.gov (United States)

    Chen, Peng; Trociewitz, Ulf P.; Davis, Daniel S.; Bosque, Ernesto S.; Hilton, David K.; Kim, Youngjae; Abraimov, Dmytro V.; Starch, William L.; Jiang, Jianyi; Hellstrom, Eric E.; Larbalestier, David C.

    2017-02-01

    Superconducting joints are one of the key components needed to make Ag-alloy clad Bi2Sr2CaCu2O8+x (Bi-2212) superconducting round wire (RW) successful for high-field, high-homogeneity magnet applications, especially for nuclear magnetic resonance magnets in which persistent current mode operation is highly desired. In this study, a procedure for fabricating superconducting joints between Bi-2212 RWs during coil reaction was developed. Melting temperatures of Bi-2212 powder with different amounts of Ag addition were investigated by differential thermal analysis so as to provide information for selecting the proper joint matrix. Test joints of 1.3 mm dia. wires heat treated in 1 bar flowing oxygen using the typical partial melt Bi-2212 heat treatment (HT) had transport critical currents I c of ˜900 A at 4.2 K and self-field, decreasing to ˜480 A at 14 T evaluated at 0.1 μV cm-1 at 4.2 K. Compared to the I c of the open-ended short conductor samples with identical 1 bar HT, the I c values of the superconducting joint are ˜20% smaller than that of conductor samples measured in parallel field but ˜20% larger than conductor samples measured in perpendicular field. Microstructures examined by scanning electron microscopy clearly showed the formation of a superconducting Bi-2212 interface between the two Bi-2212 RWs. Furthermore, a Bi-2212 RW closed-loop solenoid with a superconducting joint heat treated in 1 bar flowing oxygen showed an estimated joint resistance below 5 × 10-12 Ω based on its field decay rate. This value is sufficiently low to demonstrate the potential for persistent operation of large inductance Bi-2212 coils.

  15. Superconductivity and mesoscopic physics in planar and cylindrical films of gold-indium alloy

    Science.gov (United States)

    Zadorozhny, Yuri Kostyantinovich

    Superconducting properties of planar and cylindrical thin films of Au 0.7In0.3 alloy have been investigated by electrical transport measurements at low temperature and in the presence of applied magnetic field. The films were grown on flat substrates and on insulating fibers of sub-micron diameter, respectively, by sequential deposition and interdiffusion of alternating gold and indium layers. The primary focus of the study was the effects of disorder, sample size, sample topology, and quantum interferences on the superconducting properties of these samples. Structural and compositional analysis and transport measurements were carried out, which showed that the films were granular, with varying local indium concentrations, apparently corresponding to several distinct alloy phases. This variation, in turn, led to the variation in the local amplitude of the superconducting order parameter, and in the local superconducting transition temperature (Tc). In planar films, the presence of disorder in the sample leads to a broad superconducting transition regime, typically with a gradual resistance drop at the onset of the transition, followed by a more abrupt one as the temperature is lowered. At the lowest temperatures in transition regime, deviations from the behavior expected in Kosterlitz-Thouless-Berezinskii (KTB) vortex-antivortex pair unbinding model were found in the I-V characteristics of the films. This deviation could originate from vortex-antivortex pair unbinding by quantum tunneling rather than thermal activation. Magnetoresistance oscillations in cylindrical Au0.7In 0.3 films at low temperatures were also studied. In the high-temperature part of the superconducting transition regime, the resistance oscillated with a period of h/2e in the unit of the enclosed magnetic flux, as expected for Little-Parks effect. Unlike the cylindrical samples discussed above, which were mechanically and thermally anchored, superconducting Au0.7In0.3 cylinders used in the early

  16. Superconductivity

    Science.gov (United States)

    1989-07-01

    SUPERCONDUCTIVITY HIGH-POWER APPLICATIONS Electric power generation/transmission Energy storage Acoustic projectors Weapon launchers Catapult Ship propulsion • • • Stabilized...temperature superconductive shields could be substantially enhanced by use of high-Tc materials. 27 28 NRAC SUPERCONDUCTIVITY SHIP PROPULSION APPLICATIONS...motor shown in the photograph. As a next step in the evolution of electric-drive ship propulsion technology, DTRC has proposed to scale up the design

  17. Electronic properties and superconductivity of rapidly quenched Al-Si alloys

    Energy Technology Data Exchange (ETDEWEB)

    Chevrier, J.; Pavuna, D.; Cyrot-Lackmann, F.

    1987-12-15

    We present detailed studies of electronic properties of Al-Si alloys prepared in a nonequilibrium state by means of rapid solidification. The quenched alloys exhibit an enhanced superconducting transition temperature up to 6.2 K in an Al--Si 30 at. % alloy as well as an increased thermal slope of resistivity. Using differential scanning calorimetry, a large enthalpy variation (..delta..H = 4.1 kJ/mole for Al--Si 30 at. %) has been measured during the irreversible transition from the non- equilibrium state to the equilibrium one. This is mainly attributed to the energy difference between the metallic state of silicon atoms trapped in fcc aluminum matrix during quenching and the usual covalent state of silicon precipitates in an equilibrium state. This large energy difference is presented as the origin of a lattice instability which softens the phonon spectrum and gives rise to a stronger electron-phonon coupling. This appears to be a characteristic property of nonequilibrium Al-Si solid solutions, which is associated with the metallic state of silicon atoms. An interpretation of the T/sub c/ enhancement is proposed for both Al-Si and Al-Ge alloys based on the phonon softening in these nonequilibrium crystalline alloys.

  18. Spin Relaxation in Kondo Lattice Systems with Anisotropic Kondo Interaction

    Science.gov (United States)

    Belov, S. I.; Kutuzov, A. S.

    2016-12-01

    We study the influence of the Kondo effect on the spin relaxation in systems with anisotropic Kondo interaction at temperatures both high and low as compared with the static magnetic field. In the absence of the Kondo effect, the electron spin resonance linewidth is not narrowed in the whole temperature range due to the high anisotropy of the Kondo interaction. The Kondo effect leads to the universal energy scale, which regulates the temperature and magnetic field dependence of different kinetic coefficients and results in a mutual cancelation of their singular parts in a collective spin mode.

  19. Corrected Kondo temperature beyond the conventional Kondo scaling limit

    Science.gov (United States)

    Li, ZhenHua; Wei, JianHua; Zheng, Xiao; Yan, YiJing; Luo, Hong-Gang

    2017-05-01

    In the Kondo systems such as the magnetic impurity screened by the conduction electrons in a metal host, as well as the quantum dots connected by the leads, the low energy behaviors have universal dependence on the T/T\\text{K}0 or eV/{{k}\\text{B}}T\\text{K}0 , where T\\text{K}0 is the conventional Kondo temperature. However, it was shown that this scaling behavior is only valid at low-energy; this is called the Kondo scaling limit. Here we explore the extention of the scaling parameter range by introducing the corrected Kondo temperature T K, which may depend on the temperature and bias, as well as the other external parameters. We define the corrected Kondo temperature by scaling the local density of states near the Fermi level, obtained by accurate hierarchy of equations of motion approach at finite temperature and finite bias, and thus obtain a phenomenological expression of the corrected Kondo temperature. By using the corrected Kondo temperature as a characteristic energy scale, the conductance of the quantum dot can be well scaled in a wide parameter range, even two orders beyond the conventional scaling parameter range. Our work indicates that the Kondo scaling, although dominated by the conventional Kondo temperature in the low-energy of the Kondo system, could be extended to a higher energy regime, which is useful for analyzing the physics of the Kondo transport in non-equilibrium or high temperature cases.

  20. Corrected Kondo temperature beyond the conventional Kondo scaling limit.

    Science.gov (United States)

    Li, ZhenHua; Wei, JianHua; Zheng, Xiao; Yan, YiJing; Luo, Hong-Gang

    2017-02-20

    In the Kondo systems such as the magnetic impurity screened by the conduction electrons in a metal host, as well as the quantum dots connected by the leads, the low energy behaviors have universal dependence on the [Formula: see text] or [Formula: see text], where [Formula: see text] is the conventional Kondo temperature. However, it was shown that this scaling behavior is only valid at low-energy; this is called the Kondo scaling limit. Here we explore the extention of the scaling parameter range by introducing the corrected Kondo temperature T K, which may depend on the temperature and bias, as well as the other external parameters. We define the corrected Kondo temperature by scaling the local density of states near the Fermi level, obtained by accurate hierarchy of equations of motion approach at finite temperature and finite bias, and thus obtain a phenomenological expression of the corrected Kondo temperature. By using the corrected Kondo temperature as a characteristic energy scale, the conductance of the quantum dot can be well scaled in a wide parameter range, even two orders beyond the conventional scaling parameter range. Our work indicates that the Kondo scaling, although dominated by the conventional Kondo temperature in the low-energy of the Kondo system, could be extended to a higher energy regime, which is useful for analyzing the physics of the Kondo transport in non-equilibrium or high temperature cases.

  1. Screening-Dependent Study of Superconductivity in 3d-Transition Metals Binary Alloys Superconductors

    Institute of Scientific and Technical Information of China (English)

    Aditya M. Vora

    2009-01-01

    In the present article, we report the screening-dependent study of the superconducting state parameters (SSPs), viz. electron-phonon coupling strength A, Coulomb pseudopotential μ*, transition temperature Tc, isotope effect exponent a, and effective interaction strength NoV of 3d-band transition metals binary alloys superconductors have been made extensively in the present work using a model potential formalism and employing the pseudo-alloy-atom (PAA) model for the first time. Five local field correction functions proposed by Hartree (H), Taylor (T), Ichimaxu-Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) are used in the present investigation to study the screening influence on the aforesaid properties. The present results of the SSPs obtained from H-screening are found in qualitative agreement with the available experimental data wherever exist.

  2. Possible "Magnéli" Phases and Self-Alloying in the Superconducting Sulfur Hydride

    Science.gov (United States)

    Akashi, Ryosuke; Sano, Wataru; Arita, Ryotaro; Tsuneyuki, Shinji

    2016-08-01

    We theoretically give an infinite number of metastable crystal structures for the superconducting sulfur hydride HxS under pressure. Previously predicted crystalline phases of H2S and H3S have been thought to have important roles for experimentally observed low and high Tc, respectively. The newly found structures are long-period modulated crystals where slablike H2S and H3S regions intergrow on a microscopic scale. The extremely small formation enthalpy for the H2S -H3S boundary indicated by first-principles calculations suggests possible alloying of these phases through the formation of local H3S regions. The modulated structures and gradual alloying transformations between them not only explain the peculiar pressure dependence of Tc in sulfur hydride observed experimentally, but also could prevail in the experimental samples under various compression schemes.

  3. Resistivity and anomalous superconducting transition in Ti/sub 1-x/Fe/sub x/ alloys (0

    Energy Technology Data Exchange (ETDEWEB)

    Prekul, A.F.; Shcherbakov, A.S.; Volkenshtein, N.V.

    1976-11-01

    It has been established that in the region of ..beta..-solid solutions Ti--Fe alloys simultaneously display superconductivity and a nonmetallic type of temperature dependence of their resistivity. The alloys are found to be divided distinctly into two groups, with low- and high-temperature minima on the rho (T) curve. Both groups of alloys exhibit anomalously wide resistive transitions into the superconducting state.

  4. INVESTIGATION OF EMPIRICAL LAWS FOR SUPERCONDUCTIVITY OF ALLOY AND COMPOUND SUPERCONDUCTORS

    Institute of Scientific and Technical Information of China (English)

    刘隆鉴; 章壮健

    2001-01-01

    By studying the average effect of the electronegativity of alloy and compound superconductors, some empirical laws are found. The average value of the electronegativity of alloy superconductors x is from 1.3 to 1.9, most of which is concentrated in the region 1.5 < x < 1.8. The x of many higher Tc superconductors is nearly 1.60. All these characteristics are similar to element superconductors. The average value of the electronegativity η of positive valence elements in oxide superconductors is from 1.3 to 1.6, and the average effect of an electronegativity of zero on every element is from 1.75 to 2.00. The mean of η and is from 1.5 to 1.8. When both η and are near the limit value (1.3 or 1.6 and 1.75 or 2.00), the material has a very low Tc, even is non-superconductive. The η of other compound superconductors is either too high or too low, and the is too low so that the Tc of these superconductors is quite low.Studying the average effect of the electronegativity of non-superconducting compounds further confirms the laws.

  5. Superconductivity

    CERN Document Server

    Ketterson, John B

    2008-01-01

    Conceived as the definitive reference in a classic and important field of modern physics, this extensive and comprehensive handbook systematically reviews the basic physics, theory and recent advances in the field of superconductivity. Leading researchers, including Nobel laureates, describe the state-of-the-art in conventional and unconventional superconductors at a particularly opportune time, as new experimental techniques and field-theoretical methods have emerged. In addition to full-coverage of novel materials and underlying mechanisms, the handbook reflects continued intense research into electron-phone based superconductivity. Considerable attention is devoted to high-Tc superconductivity, novel superconductivity, including triplet pairing in the ruthenates, novel superconductors, such as heavy-Fermion metals and organic materials, and also granular superconductors. What’s more, several contributions address superconductors with impurities and nanostructured superconductors. Important new results on...

  6. Correlations between Kondo clouds in nearly antiferromagnetic Kondo lattices

    Energy Technology Data Exchange (ETDEWEB)

    Kiselev, M.N. E-mail: kiselev@physik.uni-wuerzburg.de; Kikoin, K.A

    2004-05-01

    We discuss a novel fluctuational mechanism explaining the physics of nearly antiferromagnetic Kondo lattices (KL). The effective action for KL model is expressed in terms of Bose operators responsible for paramagnetic excitations and semi-bosonic fields describing the dynamic Kondo clouds created by conduction electrons around local spin. The gauge invariant resonance valence bond theory of interacting Kondo clouds describes the spin liquid with strong critical fluctuations imitating itinerant fluctuation magnetism of Moriya type.

  7. Exchange coupling and superconductivity in light rare earth alloys and superlattices

    CERN Document Server

    Deen, P P M

    2003-01-01

    The complementary techniques of X-ray magnetic resonant scattering, neutron and X-ray diffraction and SQUID magnetometry have been employed to explore rare earth superlattices and thin films. In particular, this thesis concerns the complex magnetism of Cerium, exchange coupling in Nd/Pr superlattices and the interplay between magnetism and superconductivity in Gd/La superlattices. Molecular beam epitaxy enables the growth of high quality single-crystal structures that do not occur in nature with tailor-made physical properties. Fundamental problems in condensed matter physics can therefore be addressed. Through a study of CeY and CeLu alloys, the origin of diffuse scattering and intermediate valence behaviour observed in CeHo alloys was determined. XMRS was able to probe the behaviour of Ce in various environments. A higher energy resonance, indicative of intermediate valence behaviour, is present for the Lu and Ho based alloys but not for those containing Y. Since the lattice parameters of CeLu closely match...

  8. Superconductivity

    CERN Document Server

    Poole, Charles P; Creswick, Richard J; Prozorov, Ruslan

    2014-01-01

    Superconductivity, Third Edition is an encyclopedic treatment of all aspects of the subject, from classic materials to fullerenes. Emphasis is on balanced coverage, with a comprehensive reference list and significant graphics from all areas of the published literature. Widely used theoretical approaches are explained in detail. Topics of special interest include high temperature superconductors, spectroscopy, critical states, transport properties, and tunneling. This book covers the whole field of superconductivity from both the theoretical and the experimental point of view. This third edition features extensive revisions throughout, and new chapters on second critical field and iron based superconductors.

  9. Lateral manipulation and interplay of local Kondo resonances in a two-impurity Kondo system

    Energy Technology Data Exchange (ETDEWEB)

    Ren, Jindong; Wu, Xu; Guo, Haiming, E-mail: hmguo@iphy.ac.cn; Pan, Jinbo; Du, Shixuan; Gao, Hong-Jun [Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Luo, Hong-Gang [Center for Interdisciplinary Studies and Key Laboratory for Magnetism and Magnetic Materials of the MoE, Lanzhou University, Lanzhou 730000 (China); Beijing Computational Science Research Center, Beijing 100084 (China)

    2015-08-17

    The atomic-scale spatial relationship of a two-impurity Kondo system has been determined at varying lateral distance by scanning tunneling microscopy (STM) and spectroscopy. The localized spins of two cobalt magnetic adatoms that are placed on different electrodes of an STM form two individual Kondo singlet states, each showing quite different Kondo coupling, i.e., the tip-Kondo with low Kondo temperature and the sample-Kondo with high Kondo temperature. The differential conductance dI/dV spectra show the continuous changes of the resonance peak feature when approaching the Kondo tip laterally to the local sample-Kondo impurity on the surface. The result indicates a notable interplay between these two Kondo systems. We propose a convolution model based on the q factor of the sample-Kondo (q{sub s}) and tip-Kondo (q{sub t}) to interpret the change of various tunneling channels and the evolution of the experimental spectra.

  10. The Spin Glass-Kondo Competition in Disordered Cerium Systems

    Science.gov (United States)

    Magalhaes, S. G.; Zimmer, F.; Coqblin, B.

    2013-10-01

    We discuss the competition between the Kondo effect, the spin glass state and a magnetic order observed in disordered Cerium systems. We present firstly the experimental situation of disordered alloys such as CeNi1 - xCux and then the different theoretical approaches based on the Kondo lattice model, with different descriptions of the intersite exchange interaction for the spin glass. After the gaussian approach of the Sherrington-Kirkpatrick model, we discuss the Mattis and the van Hemmen models. Then, we present simple cluster calculations in order to describe the percolative evolution of the clusters from the cluster spin glass to the inhomogeneous ferromagnetic order recently observed in CeNi1 - xCux disordered alloys and finally we discuss the effect of random and transverse magnetic field.

  11. Vortex-glass transformation within the surface superconducting state of β-phase Mo1-x Re x alloys

    Science.gov (United States)

    Sundar, Shyam; Chattopadhyay, M. K.; Sharath Chandra, L. S.; Rawat, R.; Roy, S. B.

    2017-02-01

    We have performed an experimental study on the temperature dependence of electrical resistivity ρ(T) and heat capacity C(T) of the Mo{}1-xRe x (x=0.20,0.25) alloy superconductors in different magnetic fields. In the presence of applied magnetic field, the electrical resistivity of these alloys goes to zero at a temperature well above the bulk superconducting transition temperature obtained with the help of heat capacity measurements in the same magnetic field. Our study indicates the presence of a surface superconducting state in these alloys, where the flux lines are pinned in the surface sheath of the superconductor. The configuration of the flux lines (two-dimensional pancake-like) in the surface sheath is understood in the realm of the flux-spot model. Experimental evidence in support of the surface mixed-state state or ‘Kulik vortex-state’ and the occurrence of a vortex-liquid to vortex-glass transition is presented.

  12. Consequences of Kondo exchange on quantum spins

    OpenAIRE

    Delgado Acosta, Fernando; Hirjibehedin, Cyrus F.; Fernández Rossier, Joaquín

    2014-01-01

    When individual quantum spins are placed in close proximity to conducting substrates, the localized spin is coupled to the nearby itinerant conduction electrons via Kondo exchange. In the strong coupling limit this can result in the Kondo effect — the formation of a correlated, many body singlet state — and a resulting renormalization of the density of states near the Fermi energy. However, even when Kondo screening does not occur, Kondo exchange can give rise to a wide variety of other pheno...

  13. Magnetically induced QCD Kondo effect

    Science.gov (United States)

    Ozaki, Sho; Itakura, Kazunori; Kuramoto, Yoshio

    2016-10-01

    The "QCD Kondo effect" stems from the color exchange interaction in QCD with non-Abelian property, and can be realized in a high-density quark matter containing heavy-quark impurities. We propose a novel type of the QCD Kondo effect induced by a strong magnetic field. In addition to the fact that the magnetic field does not affect the color degrees of freedom, two properties caused by the Landau quantization in a strong magnetic field are essential for the "magnetically induced QCD Kondo effect"; (1) dimensional reduction to 1 +1 -dimensions, and (2) finiteness of the density of states for lowest energy quarks. We demonstrate that, in a strong magnetic field B , the scattering amplitude of a massless quark off a heavy quark impurity indeed shows a characteristic behavior of the Kondo effect. The resulting Kondo scale is estimated as ΛK≃√{eqB }αs1 /3exp {-4 π /Ncαslog (4 π /αs)} where αs and Nc are the fine structure constant of strong interaction and the number of colors in QCD, and eq is the electric charge of light quarks.

  14. A Maximally Supersymmetric Kondo Model

    Energy Technology Data Exchange (ETDEWEB)

    Harrison, Sarah; Kachru, Shamit; Torroba, Gonzalo; /Stanford U., Phys. Dept. /SLAC

    2012-02-17

    We study the maximally supersymmetric Kondo model obtained by adding a fermionic impurity to N = 4 supersymmetric Yang-Mills theory. While the original Kondo problem describes a defect interacting with a free Fermi liquid of itinerant electrons, here the ambient theory is an interacting CFT, and this introduces qualitatively new features into the system. The model arises in string theory by considering the intersection of a stack of M D5-branes with a stack of N D3-branes, at a point in the D3 worldvolume. We analyze the theory holographically, and propose a dictionary between the Kondo problem and antisymmetric Wilson loops in N = 4 SYM. We perform an explicit calculation of the D5 fluctuations in the D3 geometry and determine the spectrum of defect operators. This establishes the stability of the Kondo fixed point together with its basic thermodynamic properties. Known supergravity solutions for Wilson loops allow us to go beyond the probe approximation: the D5s disappear and are replaced by three-form flux piercing a new topologically non-trivial S3 in the corrected geometry. This describes the Kondo model in terms of a geometric transition. A dual matrix model reflects the basic properties of the corrected gravity solution in its eigenvalue distribution.

  15. Holographic Kondo and Fano Resonances

    CERN Document Server

    Erdmenger, Johanna; O'Bannon, Andy; Papadimitriou, Ioannis; Probst, Jonas; Wu, Jackson M S

    2016-01-01

    We use holography to study a $(1+1)$-dimensional Conformal Field Theory (CFT) coupled to an impurity. The CFT is an $SU(N)$ gauge theory at large $N$, with strong gauge interactions. The impurity is an $SU(N)$ spin. We trigger an impurity Renormalization Group (RG) flow via a Kondo coupling. The Kondo effect occurs only below the critical temperature of a large-$N$ mean-field transition. We show that at all temperatures $T$, spectral functions of certain bosonic operators exhibit a Fano resonance, which in the low-$T$ phase is a large-$N$ manifestation of the Kondo resonance. Such Fano resonances are characteristic features of RG flows between $(0+1)$-dimensional fixed points, and are thus distinct from those observed for example in quantum dots.

  16. Thermoelectric power of Kondo insulators

    OpenAIRE

    佐宗, 哲郎

    2002-01-01

    Thermoelectric power (TEP) of the Kondo insulators is investigated theoretically within the framework of the dynamical mean field theory. It is found that the temperature dependence of the Seebeck coefficient changes from the ordinary behavior S(T) ∝ T−1 in semiconductors to S ∝ T at low temperatures due to the finite imaginary part of the electron self-energy in the Kondo insulators with strong correlation. Realistic models for YbB12 and FeSi based on the band calculations are also studied....

  17. Spatially dependent Kondo effect in Quantum Corrals

    Science.gov (United States)

    Rossi, Enrico; Morr, Dirk K.

    2007-03-01

    We study the Kondo screening of a single magnetic impurity placed inside a quantum corral consisting of non-magnetic impurities on the surface of a metallic host system. We show that the spatial structure of the corral's eigenmodes leads to a spatially dependent Kondo effect whose signatures are experimentally measurable spatial variations of the Kondo temperature, TK, and of the critical Kondo coupling, Jcr. Moreover we find that the screening of the magnetic impurity is accompanied by the formation of multiple Kondo resonances with characteristic spatial patterns that provide further experimental signatures of the spatially dependent Kondo effect. Our results demonstrate that quantum corrals provide new possibilities to manipulate and explore the Kondo effect.

  18. Topological confinement and superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Al-hassanieh, Dhaled A [Los Alamos National Laboratory; Batista, Cristian D [Los Alamos National Laboratory

    2008-01-01

    We derive a Kondo Lattice model with a correlated conduction band from a two-band Hubbard Hamiltonian. This mapping allows us to describe the emergence of a robust pairing mechanism in a model that only contains repulsive interactions. The mechanism is due to topological confinement and results from the interplay between antiferromagnetism and delocalization. By using Density-Matrix-Renormalization-Group (DMRG) we demonstrate that this mechanism leads to dominant superconducting correlations in aID-system.

  19. Upper critical fields and superconducting transition temperatures of some zirconium-base amorphous transition-metal alloys

    Science.gov (United States)

    Karkut, M. G.; Hake, R. R.

    1983-08-01

    Superconducting upper critical fields Hc2(T), transition temperatures Tc and normal-state electrical resistivities ρn have been measured in the amorphous transition-metal alloy series Zr1-xCox, Zr1-xNix, (Zr1-xTix)0.78Ni0.22, and (Zr1-xNbx)0.78Ni0.22. Structural integrity of these melt-spun alloys is indicated by x-ray, density, bend-ductility, normal-state electrical resistivity, superconducting transition width, and mixed-state flux-pinning measurements. The specimens display Tc=2.1-3.8 K, ρn=159-190 μΩ cm, and |(dHc2dT)Tc|=28-36 kG/K. These imply electron mean free paths l~2-6 Å, zero-temperature Ginzburg-Landau coherence distances ξG0~50-70 Å, penetration depths λG0~(7-10)×103 Å, and extremely high dirtiness parameters ξ0l~300-1300. All alloys display Hc2(T) curves with negative curvature and (with two exceptions) fair agreement with the standard dirty-limit theory of Werthamer, Helfand, Hohenberg, and Maki (WHHM) for physically reasonable values of spin-orbit-coupling induced, electron-spin-flip scattering time τso. This is in contrast to the anomalously elevated Hc2(T) behavior which is nearly linear in T that is observed by some, and the unphysically low-τso fits to WHHM theory obtained by others, for various amorphous alloys. Current ideas that such anomalies may be due to alloy inhomogeneity are supported by present results on two specimens for which relatively low-τso fits of Hc2(T) to WHHM theory are coupled with superconductive evidence for inhomogeneity: relatively broad transitions at Tc and Hc2 current-density-dependent transitions at Hc2 and (in one specimen) a J-dependent, high-H (>Hc2), resistive "beak effect." In the Zr1-xCox and Zr1-xNix series, Tc decreases linearly with x (and with unfilled-shell average electron-to-atom ratio in the range 5.05previous results for these systems and contrary to the Tc vs behavior of both amorphous and crystalline transition-metal alloys formed between near neighbors in the Periodic Table. Upper

  20. Changes in cluster magnetism and suppression of local superconductivity in amorphous FeCrB alloy irradiated by Ar+ ions

    Science.gov (United States)

    Okunev, V. D.; Samoilenko, Z. A.; Szymczak, H.; Szewczyk, A.; Szymczak, R.; Lewandowski, S. J.; Aleshkevych, P.; Malinowski, A.; Gierłowski, P.; Więckowski, J.; Wolny-Marszałek, M.; Jeżabek, M.; Varyukhin, V. N.; Antoshina, I. A.

    2016-02-01

    We show that сluster magnetism in ferromagnetic amorphous Fe67Cr18B15 alloy is related to the presence of large, D=150-250 Å, α-(Fe Cr) clusters responsible for basic changes in cluster magnetism, small, D=30-100 Å, α-(Fe, Cr) and Fe3B clusters and subcluster atomic α-(Fe, Cr, B) groupings, D=10-20 Å, in disordered intercluster medium. For initial sample and irradiated one (Φ=1.5×1018 ions/cm2) superconductivity exists in the cluster shells of metallic α-(Fe, Cr) phase where ferromagnetism of iron is counterbalanced by antiferromagnetism of chromium. At Φ=3×1018 ions/cm2, the internal stresses intensify and the process of iron and chromium phase separation, favorable for mesoscopic superconductivity, changes for inverse one promoting more homogeneous distribution of iron and chromium in the clusters as well as gigantic (twice as much) increase in density of the samples. As a result, in the cluster shells ferromagnetism is restored leading to the increase in magnetization of the sample and suppression of local superconductivity. For initial samples, the temperature dependence of resistivity ρ(T) T2 is determined by the electron scattering on quantum defects. In strongly inhomogeneous samples, after irradiation by fluence Φ=1.5×1018 ions/cm2, the transition to a dependence ρ(T) T1/2 is caused by the effects of weak localization. In more homogeneous samples, at Φ=3×1018 ions/cm2, a return to the dependence ρ(T) T2 is observed.

  1. Developing Kondo lattice coherence and quantum criticality in YbRh{sub 2}Si{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Wirth, Steffen; Seiro, Silvia; Geibel, Christoph; Steglich, Frank [MPI for Chemical Physics of Solids, Dresden (Germany); Kirchner, Stefan [MPI for Physics of Complex Systems, Dresden (Germany); Krellner, Cornelius [Goethe University Frankfurt (Germany); Si, Qimiao [Rice University, Houston, Texas (United States)

    2015-07-01

    Hybridization is a fundamental concept in strongly correlated electron physics. In heavy fermion metals, it may result in the generation of low-energy scales that can give rise to quantum criticality and unconventional superconductivity. An important techniques that helped shaping our understanding of nonlocal correlations - magnetic and superconducting - has been tunneling spectroscopy (STS) with its unique ability to give local, microscopic information that directly relates to the one-particle Green's function. We investigated YbRh{sub 2}Si{sub 2}, an archetypal heavy fermion metal. Quantum criticality is discussed in terms of an antiferromagnetic instability and a Kondo break-down of the heavy quasiparticles. STS studies identified a hybridization-induced gap-like feature of the tunneling conductance. Here we focus on the evolution of the Kondo lattice. While the Kondo lattice starts forming already at the single-ion Kondo temperature, lattice Kondo effects dominate only at much lower temperatures. This establishes a hierarchy of energy scales. Finite-temperature signatures of the QCP are observed in field-dependent STS. Our findings are augmented by band structure calculations and transport measurements.

  2. Theory of superconductivity

    CERN Document Server

    Crisan, Mircea

    1989-01-01

    This book discusses the most important aspects of the theory. The phenomenological model is followed by the microscopic theory of superconductivity, in which modern formalism of the many-body theory is used to treat most important problems such as superconducting alloys, coexistence of superconductivity with the magnetic order, and superconductivity in quasi-one-dimensional systems. It concludes with a discussion on models for exotic and high temperature superconductivity. Its main aim is to review, as complete as possible, the theory of superconductivity from classical models and methods up t

  3. Influence of nonmagnetic disorder on specific heat and electrical resistivity in Kondo lattice system CePd{sub 1−x}Ge{sub x}In

    Energy Technology Data Exchange (ETDEWEB)

    Gnida, D., E-mail: d.gnida@int.pan.wroc.pl [Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 50-950 Wrocław (Poland); Dominyuk, N.; Zaremba, V. [Inorganic Chemistry Department, Ivan Franko Lviv National University, Kyryla and Mephodiya Str. 6, 79005 Lviv (Ukraine); Kaczorowski, D. [Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 50-950 Wrocław (Poland)

    2015-02-15

    Highlights: • Interplay of Kondo and RKKY interactions in the presence of nonmagnetic disorder. • Suppression of the coherent Kondo state by nonmagnetic impurities. • Observation of quantum interference phenomena in Ce-based Kondo system. • Coexistence of incoherent Kondo effect and Altshuler-Aronov quantum correction. - Abstract: The alloy system CePd{sub 1−x}Ge{sub x}In with 0.1⩽x⩽0.4 was investigated by means of heat capacity and electrical resistivity measurements. Its low-temperature behavior has been found to be governed by the interplay of Kondo effect and Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions in the presence of atomic disorder in nonmagnetic atoms sublattice. The coherent Kondo state, observed for CePdIn, gradually vanishes with increasing the Ge-content. The incoherent Kondo state, which characterizes Ge-rich alloys, appears very sensitive to applied magnetic field. The observed systematic changes in the temperature- and field-dependent electrical transport in CePd{sub 1−x}Ge{sub x}In manifest the important role of quantum correction due to electron-electron interactions in weakly localized regime.

  4. Numerical study of Kondo impurity models with strong potential scattering: - reverse Kondo effect and antiresonance -

    OpenAIRE

    Kiss, Annamaria; Kuramoto, Yoshio; Hoshino, Shintaro

    2011-01-01

    Accurate numerical results are derived for transport properties of Kondo impurity systems with potential scattering and orbital degeneracy. Using the continuous-time quantum Monte Carlo (CT-QMC) method, static and dynamic physical quantities are derived in a wide temperature range across the Kondo temperature T_K. With strong potential scattering, the resistivity tends to decrease with decreasing temperature, in contrast to the ordinary Kondo effect. Correspondingly, the quasi-particle densit...

  5. Competition between Quadrupole and Magnetic Kondo Effects in Non-Kramers Doublet Systems

    Science.gov (United States)

    Kusunose, Hiroaki; Onimaru, Takahiro

    2015-03-01

    We discuss possible competition between magnetic and quadrupole Kondo effects in non-Kramers doublet systems in cubic symmetry. The quadrupole Kondo effect leads to non-Fermi-liquid (NFL) ground state, while the magnetic one favors ordinary Fermi-liquid (FL) ground state. In terms of the j-j coupling scheme, we argue that the orbital fluctuation must develop in the vicinity of the NFL-FL boundary. A change of temperature dependence of the f-electron entropy in both the FL and NFL regimes is demonstrated by the Wilson's numerical renormalization-group (NRG) method on the basis of the extended two-channel Kondo exchange model. We present implications to PrT2X20 (T=Ti, V, Ir; X=Al, Zn) systems which exhibit both quadrupole ordering and peculiar superconductivity. We discuss how the magnetic field lifts the non-Kramers degeneracy. Our model also represents the alternative FL state accompanied by a free magnetic spin, as a consequence of stronger competition between the magnetic and the quadrupole Kondo effects.

  6. Möbius Kondo insulators

    Science.gov (United States)

    Chang, Po-Yao; Erten, Onur; Coleman, Piers

    2017-08-01

    Heavy fermion materials have recently attracted attention for their potential to combine topological protection with strongly correlated electron physics. To date, the ideas of topological protection have been restricted to the heavy fermion or `Kondo' insulators with the simplest point-group symmetries. Here we argue that the presence of nonsymmorphic crystal symmetries in many heavy fermion materials opens up a new family of topologically protected heavy electron systems. Re-examination of archival resistivity measurements in the nonsymmorphic heavy fermion insulators Ce3Bi4Pt3 and CeNiSn reveals the presence of a low-temperature conductivity plateau, making them candidate members of the new class of material. We illustrate our ideas with a specific model for CeNiSn, showing how glide symmetries generate surface states with a novel Möbius braiding that can be detected by ARPES or non-local conductivity measurements. One of the interesting effects of strong correlation is the development of partially localization or `Kondo breakdown' on the surfaces, which transforms Möbius surface states into quasi-one-dimensional conductors, with the potential for novel electronic phase transitions.

  7. Fractionalized Fermi liquid in a Kondo-Heisenberg model

    Science.gov (United States)

    Tsvelik, A. M.

    2016-10-01

    The Kondo-Heisenberg model is used as a controllable tool to demonstrate the existence of a peculiar metallic state with unbroken translational symmetry where the Fermi surface volume is not controlled by the total electron density. I use a nonperturbative approach where the strongest interactions are taken into account by means of exact solution, and corrections are controllable. In agreement with the general requirements formulated by T. Senthil et al. [Phys. Rev. Lett. 90, 216403 (2003), 10.1103/PhysRevLett.90.216403], the resulting metallic state represents a fractionalized Fermi liquid where well defined quasiparticles coexist with gapped fractionalized collective excitations. The system undergoes a phase transition to an ordered phase (charge density wave or superconducting), at the transition temperature which is parametrically small in comparison to the quasiparticle Fermi energy.

  8. Mott-Kondo insulator behavior in the iron oxychalcogenides

    Science.gov (United States)

    Freelon, B.; Liu, Yu Hao; Chen, Jeng-Lung; Craco, L.; Laad, M. S.; Leoni, S.; Chen, Jiaqi; Tao, Li; Wang, Hangdong; Flauca, R.; Yamani, Z.; Fang, Minghu; Chang, Chinglin; Guo, J.-H.; Hussain, Z.

    2015-10-01

    We perform a combined experimental-theoretical study of the Fe-oxychalcogenides (FeO C h ) series La2O2Fe2O M2 (M =S , Se), which are among the latest Fe-based materials with the potential to show unconventional high-Tc superconductivity (HTSC). A combination of incoherent Hubbard features in x-ray absorption and resonant inelastic x-ray scattering spectra, as well as resistivity data, reveal that the parent FeO C h are correlation-driven insulators. To uncover microscopics underlying these findings, we perform local density approximation-plus-dynamical mean field theory (LDA+DMFT) calculations that reveal a novel Mott-Kondo insulating state. Based upon good agreement between theory and a range of data, we propose that FeO C h may constitute an ideal testing ground to explore HTSC arising from a strange metal proximate to a novel selective-Mott quantum criticality.

  9. Performance of titanium oxide-polymer insulation in superconducting coils made of Bi-2212/Ag-alloy round wire

    Science.gov (United States)

    Chen, Peng; Trociewitz, Ulf P.; Dalban-Canassy, Matthieu; Jiang, Jianyi; Hellstrom, Eric E.; Larbalestier, David C.

    2013-07-01

    Conductor insulation is one of the key components needed to make Ag-alloy clad Bi2Sr2CaCu2O8+x (Bi-2212/Ag) superconducting round wire (RW) successful for high field magnet applications, as dielectric standoff and high winding current densities (Jw) directly depend on it. In this study, a TiO2-polymer insulation coating developed by nGimat LLC was applied to test samples and a high field test coil. The insulation was investigated by differential thermal analysis (DTA), thermo-gravimetric analysis (TGA), scanning electron microscopy (SEM), dielectric property measurement, and transport critical current (Ic) property measurement. About 29% of the insulation by weight is polymer. When the Bi-2212/Ag wire is fully heat treated, this decomposes with slow heating to 400 ° C in pure O2. After the full reaction, we found that the TiO2 did not degrade the critical current properties, adhered well to the conductor, and provided a breakdown voltage of more than 100 V, which allowed the test coil to survive quenching in 31.2 T background field, while providing a 2.6 T field increment. For Bi-2212/Ag RW with a typical diameter of 1.0-1.5 mm, this ˜15 μm thick insulation allows a very high coil packing factor of ˜0.74, whereas earlier alumino-silicate braid insulation only allows packing factors of 0.38-0.48.

  10. Anisotropic Kondo lattice without Nozieres exhaustion effect

    Energy Technology Data Exchange (ETDEWEB)

    Kiselev, M.N. [Physics Department, Arnold Sommerfeld Center for Theoretical Physics and Center for Nano-Science, Ludwig-Maximilians Universitaet Muenchen, 80333 Munich (Germany)]. E-mail: kiselev@physik.uni-wuerzburg.de; Kikoin, K. [Ben-Gurion University of the Negev, Beer-Sheva, 84105 (Israel)]. E-mail: kikoin@bgumail.bgu.ac.il

    2006-05-01

    The properties of layered Anderson/Kondo lattices with metallic electrons confined in 2D xy planes and local spins in insulating layers forming chains in z direction are studied. Each spin possesses its own 2D Kondo cloud, so that the Nozieres' exhaustion problem does not arise. The excitation spectrum is gapless both in charge and spin sectors. Possible experimental realizations of the model are briefly discussed.

  11. Emergence of anisotropic heavy fermions in antiferromagnetic Kondo lattice CeIn3 revealed by photoemission

    Science.gov (United States)

    Zhang, Yun; Lu, Haiyan; Zhu, Xiegang; Tan, Shiyong; Chen, Qiuyun; Feng, Wei; Xie, Donghua; Luo, Lizhu; Zhang, Wen; Lai, Xinchun; Donglai Feng Team; Huiqiu Yuan Team

    One basic concept in heavy fermions systems is the entanglement of localized spin state and itinerant electron state. It can be tuned by two competitive intrinsic mechanisms, Kondo effect and Ruderman-Kittel-Kasuya-Yosida interaction, with external disturbances. The key issue regarding heavy fermions properties is how the two mechanisms work in the same phase region. To investigate the relation of the two mechanisms, the cubic antiferromagnetic heavy fermions compound CeIn3 was investigated by soft x-ray angle resolved photoemission spectroscopy. The hybridization between f electrons and conduction bands in the paramagnetic state was observed directly, providing compelling evidence for Kondo screening scenario and coexistence of two mechanisms. The hybridization strength shows slight and regular anisotropy in K space, implying that the two mechanisms are competitive and anisotropic. This work illuminates the concomitant and competitive relation between the two mechanisms and supplies some evidences for the anisotropic superconductivity of CeIn3

  12. Kondo-like zero-bias conductance anomaly in a three-dimensional topological insulator nanowire

    Science.gov (United States)

    Cho, Sungjae; Zhong, Ruidan; Schneeloch, John A.; Gu, Genda; Mason, Nadya

    2016-02-01

    Zero-bias anomalies in topological nanowires have recently captured significant attention, as they are possible signatures of Majorana modes. Yet there are many other possible origins of zero-bias peaks in nanowires—for example, weak localization, Andreev bound states, or the Kondo effect. Here, we discuss observations of differential-conductance peaks at zero-bias voltage in non-superconducting electronic transport through a 3D topological insulator (Bi1.33Sb0.67)Se3 nanowire. The zero-bias conductance peaks show logarithmic temperature dependence and often linear splitting with magnetic fields, both of which are signatures of the Kondo effect in quantum dots. We characterize the zero-bias peaks and discuss their origin.

  13. Kondo Destruction in RKKY-Coupled Kondo Lattice and Multi-Impurity Systems

    Science.gov (United States)

    Nejati, Ammar; Ballmann, Katinka; Kroha, Johann

    2017-03-01

    In a Kondo lattice, the spin exchange coupling between a local spin and the conduction electrons acquires nonlocal contributions due to conduction electron scattering from surrounding local spins and the subsequent RKKY interaction. It leads to a hitherto unrecognized interference of Kondo screening and the RKKY interaction beyond the Doniach scenario. We develop a renormalization group theory for the RKKY-modified Kondo vertex. The Kondo temperature TK(y ) is suppressed in a universal way, controlled by the dimensionless RKKY coupling parameter y . Complete spin screening ceases to exist beyond a critical RKKY strength yc even in the absence of magnetic ordering. At this breakdown point, TK(y ) remains nonzero and is not defined for larger RKKY couplings y >yc. The results are in quantitative agreement with STM spectroscopy experiments on tunable two-impurity Kondo systems. The possible implications for quantum critical scenarios in heavy-fermion systems are discussed.

  14. Superconducting Metallic Glass Transition-Edge-Sensors

    Science.gov (United States)

    Hays, Charles C. (Inventor)

    2013-01-01

    A superconducting metallic glass transition-edge sensor (MGTES) and a method for fabricating the MGTES are provided. A single-layer superconducting amorphous metal alloy is deposited on a substrate. The single-layer superconducting amorphous metal alloy is an absorber for the MGTES and is electrically connected to a circuit configured for readout and biasing to sense electromagnetic radiation.

  15. Kondo peak splitting and Kondo dip in single molecular magnet junctions

    Energy Technology Data Exchange (ETDEWEB)

    Niu, Pengbin, E-mail: 120233951@qq.com [Institute of Solid State Physics, Shanxi Datong University, Datong 037009 (China); Shi, Yunlong; Sun, Zhu [Institute of Solid State Physics, Shanxi Datong University, Datong 037009 (China); Nie, Yi-Hang [Institute of Theoretical Physics, Shanxi University, Taiyuan 030006 (China); Luo, Hong-Gang [Center for Interdisciplinary Studies & Key Laboratory for Magnetism and Magnetic Materials of the MoE, Lanzhou University, Lanzhou 730000 (China); Beijing Computational Science Research Center, Beijing 100084 (China)

    2016-01-15

    Many factors containing bias, spin–orbit coupling, magnetic fields applied, and so on can strongly influence the Kondo effect, and one of the consequences is Kondo peak splitting (KPS). It is natural that KPS should also appear when another spin degree of freedom is involved. In this work we study the KPS effects of single molecular magnets (SMM) coupled with two metallic leads in low-temperature regime. It is found that the Kondo transport properties are strongly influenced by the exchange coupling and anisotropy of the magnetic core. By employing Green's function method in Hubbard operator representation, we give an analytical expression for local retarded Green's function of SMM and discussed its low-temperature transport properties. We find that the anisotropy term behaves as a magnetic field and the splitting behavior of exchange coupling is quite similar to the spin–orbit coupling. These splitting behaviors are explained by introducing inter-level or intra-level transitions, which account for the seven-peak splitting structure. Moreover, we find a Kondo dip at Fermi level under proper parameters. These Kondo peak splitting behaviors in SMM deepen our understanding to Kondo physics and should be observed in the future experiments. - Highlights: • We study Kondo peak splitting in single molecular magnets. • We study Kondo effect by Hubbard operator Green's function method. • We find Kondo peak splitting structures and a Kondo dip at Fermi level. • The exchange coupling and magnetic anisotropy induce fine splitting structure. • The splitting structures are explained by inter-level or intra-level transitions.

  16. Continuous Time Quantum Monte Carlo simulation of Kondo shuttling

    Science.gov (United States)

    Zhang, Peng; Assaad, Fakher; Jarrell, Mark

    2010-03-01

    The Kondo shuttling problem is investigated by using the Continuous Time Quantum Monte Carlo method in both the anti-adiabatic limit φTK and the intermediate regime φ˜TK, where φ is the phonon modulation frequency and TK is the Kondo temperature. We investigate the potential emergence of Kondo effect or Kondo breakdown as a function of the phonon modulation frequency and electron-phonon coupling. This research is supported by grant OISE-0952300.

  17. 28 May 2010 - Japanese Ambassador H. Ueda visiting the LHC superconducting magnet test hall with CERN Technology Deputy Department Head L. Rossi.

    CERN Multimedia

    Maximilien Brice

    2010-01-01

    CERN-HI-1005088 02 Japanese Ambassador H. Ueda (right) visiting the LHC superconducting magnet test hall with Technology Deputy Department Head L. Rossi(left). H. Ueda is accompanied by KEK and ATLAS Collaboration T. Kondo (centre).

  18. Kondo effect in low-carrier systems

    Energy Technology Data Exchange (ETDEWEB)

    Hager, R.; Bulla, R. [Theoretische Physik III, Elektronische Korrelationen und Magnetismus, Univ. Augsburg (Germany)

    2007-07-01

    Recent experiments on dilute U impurities in semiconducting CaB{sub 6} show typical Kondo phenomena with a Kondo temperature T{sub K}{approx}2 K (G.A. Wigger e.t al., Europhys. Lett. 68, 685 (2004)). This observation is rather unusual for magnetic moments due to 5f electrons because of the large hybridization between impurities and the conduction electrons. We perform numerical renormalization group calculations for an Anderson impurity model with a, low concentration of conduction electrons, believed to be the relevant model for (U,Ca)B{sub 6}. We present results for thermodynamic and dynamic quantities for various carrier concentrations and investigate the crossover from mixed-valent to Kondo behaviour upon decreasing the filling of the conduction band. (orig.)

  19. Kondo effect in molecules with strong correlations

    Energy Technology Data Exchange (ETDEWEB)

    Kuzmenko, Tetyana [Department of Physics, Ben-Gurion University, P.O. Box 653, Beer-Sheva 84105 (Israel)]. E-mail: tetyana@bgumail.bgu.ac.il; Kikoin, Konstantin [Department of Physics, Ben-Gurion University, P.O. Box 653, Beer-Sheva 84105 (Israel); Avishai, Yshai [Department of Physics, Ben-Gurion University, P.O. Box 653, Beer-Sheva 84105 (Israel)

    2005-04-30

    A theory of Kondo tunneling through molecules adsorbed on metallic substrate is constructed and the underlying physics is exposed. It is shown that in the case of weak chemisorption the sandwich-type molecules manifest a novel type of Kondo effect that has not been observed in magnetically doped bulk metals. The exchange Hamiltonian of these molecules unveils unusual dynamical SO(n) symmetries instead of conventional SU(2) symmetry. These symmetries can be experimentally realized and the specific value of n can be controlled by gate voltage.

  20. Kondo lattice without Nozieres exhaustion effect.

    Energy Technology Data Exchange (ETDEWEB)

    Kikoin, K.; Kiselev, M. N.; Materials Science Division; Ben-Gurion Univ. of the Negev; Ludwig-Maximilians Univ.

    2006-01-01

    We discuss the properties of layered Anderson/Kondo lattices with metallic electrons confined in 2D xy planes and local spins in insulating layers forming chains in the z direction. Each spin in this model possesses its own 2D Kondo cloud, so that the Nozieres exhaustion problem does not occur. The high-temperature perturbational description is matched to exact low-T Bethe-ansatz solution. The excitation spectrum of the model is gapless both in charge and spin sectors. The disordered phases and possible experimental realizations of the model are briefly discussed.

  1. Kondo tunneling through real and artificial molecules.

    Science.gov (United States)

    Kikoin, K; Avishai, Y

    2001-03-05

    When an asymmetric double dot is hybridized with itinerant electrons, its singlet ground state and lowly excited triplet state cross, leading to a competition between the Zhang-Rice mechanism of singlet-triplet splitting in a confined cluster and the Kondo effect (which accompanies the tunneling through quantum dot under a Coulomb blockade restriction). The rich physics of an underscreened S = 1 Kondo impurity in the presence of low-lying triplet-singlet excitations is exposed and estimates of the magnetic susceptibility and the electric conductance are presented, together with applications for molecule chemisorption on metallic substrates.

  2. Theory of scanning tunneling spectroscopy: from Kondo impurities to heavy fermion materials

    Science.gov (United States)

    Morr, Dirk K.

    2017-01-01

    Kondo systems ranging from the single Kondo impurity to heavy fermion materials present us with a plethora of unconventional properties whose theoretical understanding is still one of the major open problems in condensed matter physics. Over the last few years, groundbreaking scanning tunneling spectroscopy (STS) experiments have provided unprecedented new insight into the electronic structure of Kondo systems. Interpreting the results of these experiments—the differential conductance and the quasi-particle interference spectrum—however, has been complicated by the fact that electrons tunneling from the STS tip into the system can tunnel either into the heavy magnetic moment or the light conduction band states. In this article, we briefly review the theoretical progress made in understanding how quantum interference between these two tunneling paths affects the experimental STS results. We show how this theoretical insight has allowed us to interpret the results of STS experiments on a series of heavy fermion materials providing detailed knowledge of their complex electronic structure. It is this knowledge that is a conditio sine qua non for developing a deeper understanding of the fascinating properties exhibited by heavy fermion materials, ranging from unconventional superconductivity to non-Fermi-liquid behavior in the vicinity of quantum critical points.

  3. Nonequilibrium Transport through a Spinful Quantum Dot with Superconducting Leads

    DEFF Research Database (Denmark)

    Andersen, Brian Møller; Flensberg, Karsten; Koerting, Verena

    2011-01-01

    We study the nonlinear cotunneling current through a spinful quantum dot contacted by two superconducting leads. Applying a general nonequilibrium Green function formalism to an effective Kondo model, we study the rich variation in the IV characteristics with varying asymmetry in the tunnel...

  4. Fabrication of Nb{sub 3}Al superconducting wires by utilizing the mechanically alloyed Nb(Al){sub ss} supersaturated solid-solution with low-temperature annealing

    Energy Technology Data Exchange (ETDEWEB)

    Pan, X.F. [National Engineering Laboratory for Superconducting Material, Western Superconducting Technologies (WST) Co., Ltd., Xi’an 710018 (China); Superconducting Materials Center, Northwest Institute for Nonferrous Metal Research, Xi’an 710016 (China); Yan, G., E-mail: gyan@c-nin.com [National Engineering Laboratory for Superconducting Material, Western Superconducting Technologies (WST) Co., Ltd., Xi’an 710018 (China); Superconducting Materials Center, Northwest Institute for Nonferrous Metal Research, Xi’an 710016 (China); Qi, M. [Superconducting Materials Center, Northwest Institute for Nonferrous Metal Research, Xi’an 710016 (China); Cui, L.J. [National Engineering Laboratory for Superconducting Material, Western Superconducting Technologies (WST) Co., Ltd., Xi’an 710018 (China); Chen, Y.L.; Zhao, Y. [Key Laboratory of Magnetic Levitation Technologies and Maglev Trains (Ministry of Education of China), Superconductivity and New Energy R and D Center, Southwest Jiaotong University, Chengdu 610031 (China); Li, C.S. [Superconducting Materials Center, Northwest Institute for Nonferrous Metal Research, Xi’an 710016 (China); Liu, X.H. [National Engineering Laboratory for Superconducting Material, Western Superconducting Technologies (WST) Co., Ltd., Xi’an 710018 (China); Feng, Y.; Zhang, P.X. [National Engineering Laboratory for Superconducting Material, Western Superconducting Technologies (WST) Co., Ltd., Xi’an 710018 (China); Key Laboratory of Magnetic Levitation Technologies and Maglev Trains (Ministry of Education of China), Superconductivity and New Energy R and D Center, Southwest Jiaotong University, Chengdu 610031 (China); Liu, H.J. [Institute of Plasma Physics, Chinese Academy of Sciences (CAS), Hefei 230031 (China); and others

    2014-07-15

    Highlights: • This paper reported superconducting properties of the powder-in-tube Nb{sub 3}Al wires. • The Nb{sub 3}Al wires were made by using Nb(Al){sub ss} supersaturated solid solution powders. • The Cu-matrix Nb{sub 3}Al superconducting wires have been successfully fabricated. • The transport J{sub c} of Nb{sub 3}Al wires at 4.2 K, 10 T is up to 12,700 A/cm{sup 2}. - Abstract: High-performance Nb{sub 3}Al superconducting wire is a promising candidate to the application of high-field magnets. However, due to the production problem of km-grade wires that are free from low magnetic field instability, the Nb{sub 3}Al wires made by rapid heating, quenching and transformation (RHQT) are still not available to the large-scale engineering application. In this paper, we reported the properties of the in situ powder-in-tube (PIT) Nb{sub 3}Al superconducting wires, which were made by using the mechanically alloyed Nb(Al){sub ss} supersaturated solid solution, as well as the low temperature heat-treatment at 800 °C for 10 h. The results show that Nb{sub 3}Al superconductors in this method possess very fine grains and well superconducting properties, though a little of Nb{sub 2}Al and Nb impurities still keep being existence at present work. At the Nb{sub 3}Al with a nominal 26 at.% Al content, the onset T{sub c} reaches 15.8 K. Furthermore, a series of Nb{sub 3}Al wires and tapes with various sizes have been fabricated; for the 1.0 mm-diameter wire, the J{sub c} at 4.2 K, 10 T and 14 T have achieved 12,700 and 6900 A/cm{sup 2}, respectively. This work suggests it is possible to develop high-performance Cu-matrix Nb{sub 3}Al superconducting wires by directly using the Nb(Al){sub ss} supersaturated solid-solution without the complex RHQT heat-treatment process.

  5. Transport across two interacting quantum dots: bulk Kondo, Kondo box and molecular regimes

    Science.gov (United States)

    Costa Ribeiro, Laercio; Hamad, Ignacio; Chiappe, Guillermo; Victoriano Anda, Enrique

    2014-03-01

    We analyze the transport properties of a double quantum dot device with both dots coupled to perfect conducting leads and to a finite chain of N non-interacting sites connecting both of them. The inter-dot chain strongly influences the transport across the system and the local density of states of the dots. We study the case of small number of sites, so that Kondo box effects are present. For odd N and small coupling between the inter-dot chain and the dots, a state with two coexisting Kondo regimes develops: the bulk Kondo due to the quantum dots connected to leads and the one produced by the screening of the quantum dots spins by the spin in the finite chain. As the coupling to the inter-dot chain increases, there is a crossover to a molecular Kondo effect, due to the screening of the molecule spin by the leads. For even N the two-Kondo temperatures regime does not develop and the physics is dominated by the usual competition between Kondo and antiferromagnetism. We finally study how the transport properties are affected as N is increased. We used exact multi-configurational Lanczos calculations and finite U slave-boson mean-field theory. The results obtained with both methods describe qualitatively and also quantitatively the same physics.

  6. Transport properties of fully screened Kondo models

    NARCIS (Netherlands)

    Hörig, Christoph B M; Mora, Christophe; Schuricht, Dirk

    2014-01-01

    We study the nonequilibrium transport properties of fully (exactly) screened Kondo quantum dots subject to a finite bias voltage or a finite temperature. First, we calculate the Fermi-liquid coefficients of the conductance for models with arbitrary spin, i.e., its leading behavior for small bias vol

  7. The Kondo tip decorated by the Co atom

    Science.gov (United States)

    Feng, Wei; Liu, Qin; Lai, Xinchun; Zhao, Aidi

    2016-11-01

    The Kondo effect of single Co adatoms on Ru(0001) is detected with two different kinds of co-decorated tip (Kondo tip) by using low temperature scanning tunneling microscopy and scanning tunneling spectroscopy. We call the relatively separated two magnetic impurities in the tunneling region ‘two Kondo system’ to distinguish it from the ‘two-impurity Kondo system’. We find that the artificially constructed Kondo tips can be generally categorized into two types of Kondo resonances, which have distinct Fano line shapes with quantum interference factor |q| ≫ 1 and |q| ∼ 1, respectively. The tunneling spectra of six constructed two Kondo systems can be well fitted by summing the two Fano resonances of the two subsystems and a linear background. More interestingly, by extracting the amplitudes of the two Fano resonances in the spectra, we find that the electron transmission of such a two Kondo system in the tunneling region is dominated by the quantum interference of the Kondo tip, which is directly related to the geometric configuration of the adsorbed Kondo atom on the tip.

  8. Dynamical symmetries in Kondo tunneling through complex quantum dots.

    Science.gov (United States)

    Kuzmenko, T; Kikoin, K; Avishai, Y

    2002-10-07

    Kondo tunneling reveals hidden SO(n) dynamical symmetries of evenly occupied quantum dots. As is exemplified for an experimentally realizable triple quantum dot in parallel geometry, the possible values n=3,4,5,7 can be easily tuned by gate voltages. Following construction of the corresponding o(n) algebras, scaling equations are derived and Kondo temperatures are calculated. The symmetry group for a magnetic field induced anisotropic Kondo tunneling is SU(2) or SO(4).

  9. Competing Kondo Effects in Non-Kramers Doublet Systems

    OpenAIRE

    Kusunose, Hiroaki

    2016-01-01

    In non-Kramers Kondo systems with a quadrupolar degrees of freedom, an ordinary magnetic Kondo effect can compete with the quadrupolar Kondo effect. We discuss such competition keeping Pr$T_{2}$Zn$_{20}$ ($T$=Ir, Rh) and Pr$T_{2}$Al$_{20}$ ($T$=V, Ti) in mind, where the $\\Gamma_{3}$ non-Kramers crystalline-electric-field (CEF) doublet ground state is realized in Pr$^{3+}$ ion with $(4f)^{2}$ configuration under cubic symmetry. The quadrupolar Kondo effect can be described by the two-channel K...

  10. Kondo force in shuttling devices: dynamical probe for a Kondo cloud.

    Science.gov (United States)

    Kiselev, M N; Kikoin, K A; Gorelik, L Y; Shekhter, R I

    2013-02-08

    We consider the electromechanical properties of a single-electronic device consisting of a movable quantum dot attached to a vibrating cantilever, forming a tunnel contact with a nonmovable source electrode. We show that the resonance Kondo tunneling of electrons amplifies exponentially the strength of nanoelectromechanical (NEM) coupling in such a device and make the latter insensitive to mesoscopic fluctuations of electronic levels in a nanodot. It is also shown that the study of a Kondo-NEM phenomenon provides additional (as compared with standard conductance measurements in a nonmechanical device) information on retardation effects in the formation of a many-particle cloud accompanying the Kondo tunneling. A possibility for superhigh tunability of mechanical dissipation as well as supersensitive detection of mechanical displacement is demonstrated.

  11. The Correlated Kondo-lattice Model

    OpenAIRE

    Kienert, J.; Santos, C.; Nolting, W.

    2003-01-01

    We investigate the ferromagnetic Kondo-lattice model (FKLM) with a correlated conduction band. A moment conserving approach is proposed to determine the electronic self-energy. Mapping the interaction onto an effective Heisenberg model we calculate the ordering of the localized spin system self-consistently. Quasiparticle densities of states (QDOS) and the Curie temperature are calculated. The band interaction leads to an upper Hubbard peak and modifies the magnetic stability of the FKLM.

  12. Kondo Effect at a Quantum Critical Point

    Science.gov (United States)

    Ramazashvili, Revaz; Coleman, Piers

    1998-03-01

    The Kondo effect in a metal on the verge of a zero-temperature magnetic instability provides a fascinating example of interference between local and long-range correlations. (A. I. Larkin and V. I. Mel'nikov, Sov. Phys. JETP 34, 656 (1972)) (P. Coleman and A. M. Tsvelik, cond-mat/9707003) (A. Sengupta, cond-mat/9707316) We discuss possible consequences of this interference, including the breakdown of the Fermi liquid state.

  13. Kondo effects in triangular triple quantum dots

    Science.gov (United States)

    Oguri, Akira; Numata, Takahide; Nisikawa, Yunori; Hewson, A. C.

    2009-03-01

    We study the conductance through a triangular triple quantum dot, which is connected to two noninteracting leads, using the numerical renormalization group (NRG). It is found that the system shows a variety of Kondo effects depending on the filling of the triangle. The SU(4) Kondo effect occurs at half-filling, and a sharp conductance dip due to a phase lapse appears in the gate-voltage dependence. Furthermore, when four electrons occupy the three sites on average, a local S=1 moment, which is caused by the Nagaoka mechanism, is induced along the triangle. The temperature dependence of the entropy and spin susceptibility of the triangle shows that this moment is screened by the conduction electrons via two separate stages at different temperatures. The two-terminal and four-terminal conductances show a clear difference at the gate voltages, where the SU(4) or the S=1 Kondo effects occur[1]. We will also discuss effects of deformations of the triangular configuration, caused by the inhomogeneity in the inter-dot couplings and in the gate voltages. [4pt] [1] T.Numata, Y.Nisikawa, A.Oguri, and A.C.Hewson: arXiv:0808.3496.

  14. Changes in cluster magnetism and suppression of local superconductivity in amorphous FeCrB alloy irradiated by Ar{sup +} ions

    Energy Technology Data Exchange (ETDEWEB)

    Okunev, V.D., E-mail: okunev@mail.fti.ac.donetsk.ua [Donetsk Physiko-Technical Institute, Ukrainian Academy of Sciences, av. Nauki 46, 03028 Kiev (Ukraine); Samoilenko, Z.A. [Donetsk Physiko-Technical Institute, Ukrainian Academy of Sciences, av. Nauki 46, 03028 Kiev (Ukraine); Szymczak, H.; Szewczyk, A.; Szymczak, R.; Lewandowski, S.J.; Aleshkevych, P.; Malinowski, A.; Gierłowski, P.; Więckowski, J. [Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw (Poland); Wolny-Marszałek, M.; Jeżabek, M. [Institute of Nuclear Physics, Polish Academy of Sciences, Krakow (Poland); Varyukhin, V.N. [Donetsk Physiko-Technical Institute, Ukrainian Academy of Sciences, av. Nauki 46, 03028 Kiev (Ukraine); Antoshina, I.A. [Obninsk State Technical University of Atomic Energy, 249020 Obninsk (Russian Federation)

    2016-02-01

    We show that cluster magnetism in ferromagnetic amorphous Fe{sub 67}Cr{sub 18}B{sub 15} alloy is related to the presence of large, D=150–250 Å, α-(Fe Cr) clusters responsible for basic changes in cluster magnetism, small, D=30–100 Å, α-(Fe, Cr) and Fe{sub 3}B clusters and subcluster atomic α-(Fe, Cr, B) groupings, D=10–20 Å, in disordered intercluster medium. For initial sample and irradiated one (Φ=1.5×10{sup 18} ions/cm{sup 2}) superconductivity exists in the cluster shells of metallic α-(Fe, Cr) phase where ferromagnetism of iron is counterbalanced by antiferromagnetism of chromium. At Φ=3×10{sup 18} ions/cm{sup 2}, the internal stresses intensify and the process of iron and chromium phase separation, favorable for mesoscopic superconductivity, changes for inverse one promoting more homogeneous distribution of iron and chromium in the clusters as well as gigantic (twice as much) increase in density of the samples. As a result, in the cluster shells ferromagnetism is restored leading to the increase in magnetization of the sample and suppression of local superconductivity. For initial samples, the temperature dependence of resistivity ρ(T)~T{sup 2} is determined by the electron scattering on quantum defects. In strongly inhomogeneous samples, after irradiation by fluence Φ=1.5×10{sup 18} ions/cm{sup 2}, the transition to a dependence ρ(T)~T{sup 1/2} is caused by the effects of weak localization. In more homogeneous samples, at Φ=3×10{sup 18} ions/cm{sup 2}, a return to the dependence ρ(T)~T{sup 2} is observed. - Highlights: • The samples at high dose of ion irradiation become more homogeneous. • Gigantic increase in density of the samples (twice as much) is observed. • Ferromagnetism in large Fe–Cr clusters is restored. • Ferromagnetism of Fe–Cr clusters suppresses local superconductivity in them. • The participation of quantum defects in scattering of electrons is returned.

  15. Method and system for controlling chemical reactions between superconductors and metals in superconducting cables

    Energy Technology Data Exchange (ETDEWEB)

    Shen, Tengming

    2016-11-15

    A method, system, and apparatus for fabricating a high-strength Superconducting cable comprises pre-oxidizing at least one high-strength alloy wire, coating at least one Superconducting wire with a protective layer, and winding the high-strength alloy wire and the Superconducting wire to form a high-strength Superconducting cable.

  16. Textured tape substrates from binary copper alloys with vanadium and yttrium for the epitaxial deposition of buffer and superconducting layers

    Science.gov (United States)

    Khlebnikova, Yu. V.; Rodionov, D. P.; Egorova, L. Yu.; Suaridze, T. R.

    2016-05-01

    The structure of tapes of binary Cu-0.6 wt % V and Cu-1 wt % Y alloys and texturing process of them in the course of cold deformation by rolling to 99% and subsequent recrystallizing annealing have been studied. The possibility of achieving the perfect cube texture in thin tapes made from binary copper-based alloys with vanadium and yttrium additions has in principle been shown. This opens the prospect of using them as substrates when manufacturing tapes of second-generation high-temperature superconductors. Optimum annealing conditions for the studied alloys have been determined, which have made it possible to produce the perfect biaxial texture with a content of cube {001} ± 10° grains on the surfaces of textured tapes of more than 95%.

  17. Observation of orbital two-channel Kondo effect in a ferromagnetic L10-MnGa film

    Science.gov (United States)

    Zhu, Lijun; Woltersdorf, Georg; Zhao, Jianhua

    2016-09-01

    The experimental existence and stability of the fixed point of the two-channel Kondo (2CK) effect displaying exotic non-Fermi liquid physics have been buried in persistent confusion despite the intensive theoretical and experimental efforts in past three decades. Here we report an experimental realization of the two-level system resonant scattering-induced orbital 2CK effect in a ferromagnetic L10-MnGa film, which is signified by a magnetic field-independent resistivity upturn that has a logarithmic and a square-root temperature dependence beyond and below the Kondo temperature of ~14.5 K, respectively. Our results not only evidence the robust existence of orbital 2CK effect even in the presence of strong magnetic fields and long-range ferromagnetic ordering, but also extend the scope of 2CK host materials from nonmagnetic nanoscale point contacts to diffusive conductors of disordered alloys.

  18. Kondo Effect in a Single Electron Transistor

    Science.gov (United States)

    Goldhaber-Gordon, David

    1998-03-01

    When a field-effect transistor is made very small, and electrons in the channel are separated from those in the leads by tunnel junctions, the transistor turns on and off every time an extra electron is added to the channel. The droplet of electrons confined in the channel of such a single-electron transistor (SET) interacts with electrons in the leads. This is in close analogy to an impurity atom interacting with the delocalized electrons in a metal, the traditional system for studying the Kondo effect.(Y. Meir, N.S. Wingreen, and P.A. Lee. PRL) 70, 2601 (1993) I will discuss measurements on a new generation of SETs that display all the aspects of the Kondo effect:(D. Goldhaber-Gordon, Hadas Shtrikman, D. Mahalu, D. Abusch-Magder, U. Meirav, and M.A. Kastner. To be published in Nature). a spin singlet forms between a localized electron in the channel and delocalized electrons in the leads, causing an enhancement of the zero-bias conductance, when the number of electrons on the artificial atom is odd but not when it is even. The system can be studied out of equilibrium by applying a voltage between the two leads, an impossible procedure in bulk Kondo systems. The spin singlet is altered by applying such a voltage or a magnetic field or by increasing the temperature, all in ways that agree with predictions. In addition, the tunability of an SET allows study of the system over a range of parameters not easily accessible to previous calculations or experiments.

  19. Alloy

    Science.gov (United States)

    Cabeza, Sandra; Garcés, Gerardo; Pérez, Pablo; Adeva, Paloma

    2014-07-01

    The Mg98.5Gd1Zn0.5 alloy produced by a powder metallurgy route was studied and compared with the same alloy produced by extrusion of ingots. Atomized powders were cold compacted and extruded at 623 K and 673 K (350 °C and 400 °C). The microstructure of extruded materials was characterized by α-Mg grains, and Mg3Gd and 14H-LPSO particles located at grain boundaries. Grain size decreased from 6.8 μm in the extruded ingot, down to 1.6 μm for powders extruded at 623 K (350 °C). Grain refinement resulted in an increase in mechanical properties at room and high temperatures. Moreover, at high temperatures the PM alloy showed superplasticity at high strain rates, with elongations to failure up to 700 pct.

  20. Superconductivity fundamentals and applications

    CERN Document Server

    Buckel, Werner

    2004-01-01

    This is the second English edition of what has become one of the definitive works on superconductivity in German -- currently in its sixth edition. Comprehensive and easy to understand, this introductory text is written especially with the non-specialist in mind. The authors, both long-term experts in this field, present the fundamental considerations without the need for extensive mathematics, describing the various phenomena connected with the superconducting state, with liberal insertion of experimental facts and examples for modern applications. While all fields of superconducting phenomena are dealt with in detail, this new edition pays particular attention to the groundbreaking discovery of magnesium diboride and the current developments in this field. In addition, a new chapter provides an overview of the elements, alloys and compounds where superconductivity has been observed in experiments, together with their major characteristics. The chapter on technical applications has been considerably expanded...

  1. Competing Kondo Effects in Non-Kramers Doublet Systems

    Science.gov (United States)

    Kusunose, Hiroaki

    2016-06-01

    In non-Kramers Kondo systems with quadrupolar degrees of freedom, an ordinary magnetic Kondo effect can compete with the quadrupolar Kondo effect. We discuss such competition keeping PrT2Zn20 (T = Ir, Rh) and PrT2Al20 (T = V, Ti) in mind, where the Γ3 non-Kramers crystalline-electric-field (CEF) doublet ground state is realized in a Pr3+ ion with a (4f)2 configuration under cubic symmetry. The quadrupolar Kondo effect can be described by the two-channel Kondo model, which leads to the local non-Fermi-liquid (NFL) ground state, while the magnetic Kondo effect favors the ordinary local Fermi-liquid (FL) ground state. On the basis of the minimal extended two-channel Kondo model including the magnetic Kondo coupling as well, we investigate the competition and resulting thermodynamics, and orbital/magnetic and single-particle excitation spectra by Wilson's numerical renormalization group (NRG) method. There is a first-order transition between the NFL and FL ground states. In addition to these two states, the alternative FL state accompanied by a free magnetic spin appears in the intermediate temperature range, which eventually reaches the true NFL ground state, as a consequence of the stronger competition between the magnetic and quadrupolar Kondo effects. In this peculiar state, the magnetic susceptibility shows a Curie-like behavior, while the orbital fluctuation exhibits the FL behavior. Moreover, the single-particle spectra yield a more singular behavior. Implications to the Pr 1-2-20 systems are briefly discussed.

  2. Recent developments in superconducting materials including ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Tachikawa, Kyoji

    1987-06-01

    This report describes the history of superconduction starting in 1911, when the superconducting phenomenon was first observed in murcury, until the recent discovery of superconducting materials with high critical temperatures. After outlining the BCS theory, basic characteristics are discussed including the critical temperature, magnetic field and current density to be reached for realizing the superconducting state. Various techniques for practical superconducting materials are discussed, including methods for producing extra fine multiconductor wires from such superconducting alloys as Nb-Ti, intermetallic Nb/sub 3/Sn compound and V/sub 3/Ga, as well as methods for producing wires of Nb/sub 3/Al, Nb/sub 3/(Al, Ge) and Nb/sub 3/Ge such as continuous melt quenching, electron beam irradiation, laser beam irradiation and chemical evaporation. Characteristics of superconducting ceramics are described, along with their applications including superconducting magnets and superconducting elements. (15 figs, 1 tab, 19 refs)

  3. Applied superconductivity

    CERN Document Server

    Newhouse, Vernon L

    1975-01-01

    Applied Superconductivity, Volume II, is part of a two-volume series on applied superconductivity. The first volume dealt with electronic applications and radiation detection, and contains a chapter on liquid helium refrigeration. The present volume discusses magnets, electromechanical applications, accelerators, and microwave and rf devices. The book opens with a chapter on high-field superconducting magnets, covering applications and magnet design. Subsequent chapters discuss superconductive machinery such as superconductive bearings and motors; rf superconducting devices; and future prospec

  4. Entanglement Entropy in a Holographic Kondo Model

    CERN Document Server

    Erdmenger, Johanna; Hoyos, Carlos; Newrzella, Max-Niklas; Wu, Jackson M S

    2015-01-01

    We calculate entanglement and impurity entropies in a recent holographic model of a magnetic impurity interacting with a strongly coupled system. There is an RG flow to an IR fixed point where the impurity is screened, leading to a decrease in impurity degrees of freedom. This information loss corresponds to a volume decrease in our dual gravity model, which consists of a codimension one hypersurface embedded in a BTZ black hole background in three dimensions. There are matter fields defined on this hypersurface which are dual to Kondo field theory operators. In the large N limit, the formation of the Kondo cloud corresponds to the condensation of a scalar field. The entropy is calculated according to the Ryu-Takayanagi prescription. This requires to determine the backreaction of the hypersurface on the BTZ geometry, which is achieved by solving the Israel junction conditions. We find that the larger the scalar condensate gets, the more the volume of constant time slices in the bulk is reduced, shortening the...

  5. Kondo effect and mesoscopic fluctuations

    Indian Academy of Sciences (India)

    Denis Ullmo; Sébastien Burdin; Dong E Liu; Harold U Baranger

    2011-11-01

    Two important themes in nanoscale physics in the last two decades are correlations between electrons and mesoscopic fluctuations. Here we review our recent work on the intersection of these two themes. The setting is the Kondo effect, a paradigmatic example of correlated electron physics, in a nanoscale system with mesoscopic fluctuations; in particular, we consider a small quantum dot coupled to a finite reservoir (which itself may be a large quantum dot). We discuss three aspects of this problem. First, in the high-temperature regime, we argue that a Kondo temperature K which takes into account the mesoscopic fluctuations is a relevant concept: for instance, physical properties are universal functions of /K. Secondly, when the temperature is much less than the mean level spacing due to confinement, we characterize a natural cross-over from weak to strong coupling. This strong coupling regime is itself characterized by well-defined single-particle levels, as one can see from a Nozières Fermi-liquid theory argument. Finally, using a mean-field technique, we connect the mesoscopic fluctuations of the quasiparticles in the weak coupling regime to those at strong coupling.

  6. Kondo effect in organometallic complexes with vibrating ligand shells

    Energy Technology Data Exchange (ETDEWEB)

    Kiselev, M.N. [Institut fuer Theoretische Physik und Astrophysik, Universitaet Wuerzburg, 97074 (Germany)]. E-mail: kiselev@physik.uni-wuerzburg.de; Kikoin, K. [Physics Department, Ben-Gurion University, Beer-Sheva 84105 (Israel); Wegewijs, M.R. [Institut fuer Theoretische Physik-Lehrstuhl A, RWTH Aachen, 52056 Aachen (Germany)

    2007-03-15

    We investigate transport through a mononuclear rare-earth metal-organic shell complex with strong tunnel coupling between the shell and two electrodes. The ground state of this molecule is a singlet while the first excited state is a triplet. We show that modulation of the tunnel barrier due to a molecular distortion which couples to the tunneling induces the Kondo effect, provided the discrete vibrational energy compensates the singlet/triplet gap. We discuss also the possibility of tuning the phonon-induced Kondo tunneling by external magnetic field and the finite bias Kondo anomaly.

  7. The effect of Ce dilution on the ferromagnetic ordering and Kondo behavior of CeRuPO

    Science.gov (United States)

    Noorafshan, M.; Nourbakhsh, Z.

    2017-03-01

    The structural, electronic and magnetic properties and Kondo behavior of Ce1-xLax RuPO (x=0, 0.25, 0.5, 0.75 and 1) alloys are investigated using density functional theory by utilizing Wien2k package. The exchange-correlation potential is treated with the generalized gradient approximation (GGA). Moreover, the GGA+U approach (where U is the Hubbard correlation term) is employed to treat the f-electrons properly. We also present a comparative study between the electronic structure and magnetic properties of these alloys within GGA and GGA+U approaches. The calculated lattice parameters and bulk moduli of these alloys as a function of x are in the best agreement with Vegard's linear rule. The total and partial electron density of states and linear coefficient of electronic specific heat of these alloy within GGA and GGA+U are investigated and compared. The effect of La substitution on the Kondo behavior of CeRuPO compound is investigated.

  8. Proximity effect induced by Kondo interaction in a network composed of YBCO and spin density wave

    Science.gov (United States)

    Maity, S.; Ghosh, Ajay Kumar

    2015-10-01

    The possibility of the proximity effect mediated by Kondo interaction in YBCO embedded in system of diluted magnetic spin ordering has been studied. An YBCO sample is selected in which both metal to insulator transition and superconducting state exist in the different ranges of temperature. The intergranular network of the bulk Y-123 has been modified by the inclusion of YMnO3 which has a well defined magnetic structure depending on temperature. The current-voltage measurements have been carried out in pure Y-123 at several temperatures. At the same set of temperatures the current-voltage curves in presence of YMnO3 have been studied. The role of the diluted spin magnetic ordering in tuning proximity effect and conduction property in binary systems is associated with reduced coherence length in the normal region.

  9. Kondo Screening and Fermi Surface in the Antiferromagnetic Metal Phase

    Science.gov (United States)

    Yamamoto, Seiji; Si, Qimiao

    2006-03-01

    We address the Kondo effect deep inside the antiferromagnetic metal phase of a Kondo lattice Hamiltonian with SU(2) invariance. The local- moment component is described in terms of a non-linear sigma model. The Fermi surface of the conduction electron component is taken to be sufficiently small, so that it is not spanned by the antiferromagnetic wavevector. The effective low energy form of the Kondo coupling simplifies drastically, corresponding to the uniform component of the magnetization that forward-scatters the conduction electrons on their own Fermi surface. We use a combined bosonic and fermionic (Shankar) renormalization group procedure to analyze this effective theory and study the Kondo screening and Fermi surface in the antiferromagnetic phase. The implications for the global magnetic phase diagram, as well as quantum critical points, of heavy fermion metals are discussed.

  10. Nonequilibrium electron transport through quantum dots in the Kondo regime

    DEFF Research Database (Denmark)

    Wölfle, Peter; Paaske, Jens; Rosch, Achim

    2005-01-01

    Electron transport at large bias voltage through quantum dots in the Kondo regime is described within the perturbative renormalization group extended to nonequilibrium. The conductance, local magnetization, dynamical spin susceptibility and local spectral function are calculated. We show how the ...

  11. Quantum Entanglement in the Two Impurity Kondo Model

    CERN Document Server

    Cho, S Y; Cho, Sam Young; Kenzie, Ross H. Mc

    2005-01-01

    In order to quantify quantum entanglement in two impurity Kondo systems, we calculate the concurrence, negativity, and von Neumann entropy. The entanglement of the two Kondo impurities is shown to be determined by two competing many-body effects, the Kondo effect and the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, $I$. Due to the spin-rotational invariance of the ground state, the concurrence and negativity are uniquely determined by the spin-spin correlation between the impurities. It is found that there exists a critical minimum value of the antiferromagnetic correlation between the impurity spins which is necessary for entanglement of the two impurity spins. The critical value is discussed in relation with the unstable fixed point in the two impurity Kondo problem. Specifically, at the fixed point there is no entanglement between the impurity spins. Entanglement will only be created (and quantum information processing (QIP) be possible) if the RKKY interaction exchange energy, $I$, is at least severa...

  12. Non-Fermi liquid picture and superconductivity in heavy fermion systems

    Energy Technology Data Exchange (ETDEWEB)

    Sykora, Steffen [IFW Dresden, D- 01171 Dresden (Germany); Becker, Klaus W. [Department of Physics, TU Dresden, D-01069 Dresden (Germany)

    2013-07-01

    We study the S = 1/2 Kondo lattice model which is widely used to describe heavy fermion behavior. In conventional treatments of the model a hybridization of conduction and localized f electrons is introduced by decoupling the Kondo interaction. However, such an approximation has the detrimental effect that a breaking of a local gauge symmetry is imposed which implicates that the local f occupation n{sub i}{sup f} is no longer conserved. To avoid such an artifact, we treat the model in an alternative approach based on the Projective Renormalization Method (PRM). Thereby, within the conduction electron spectral function we identify the lattice Kondo resonance as an almost flat incoherent excitation near the Fermi surface which is composed of conduction electron creation operators combined with localized spin fluctuations. This leads to a new concept of the Kondo resonance without having to resort to a symmetry breaking and Fermi liquid theory. Based on this new picture we develop a microscopic theory for superconductivity in heavy fermion systems. Thereby we study the momentum-dependence of the superconducting order parameter for singlet as well as triplet pairing. We show that in particular the triplet pairing components are strongly affected by the incoherent excitations found to be responsible for the Kondo resonance.

  13. Schwinger boson approach to the fully screened Kondo model.

    Science.gov (United States)

    Rech, J; Coleman, P; Zarand, G; Parcollet, O

    2006-01-13

    We apply the Schwinger boson scheme to the fully screened Kondo model and generalize the method to include antiferromagnetic interactions between ions. Our approach captures the Kondo crossover from local moment behavior to a Fermi liquid with a nontrivial Wilson ratio. When applied to the two-impurity model, the mean-field theory describes the "Varma-Jones" quantum phase transition between a valence bond state and a heavy Fermi liquid.

  14. Evidence of Kondo effect in organic radical nanoassemblies

    Science.gov (United States)

    Rashidi, Mohammad; Mullegger, Stefan; Fattinger, Michael; Koch, Reinhold

    2012-02-01

    The outstanding spatial resolution of low temperature (LT) scanning tunneling microscopy (STM) and spectroscopy (STS) enables to probe the frontier orbital electronic structure of single magnetic molecules and clusters adsorbed on substrates. Here, we study self-aligned nanostructures of (spin-1/2) hydrocarbon radicals on a metal surface by means of LT-STM and STS. Pronounced involvement of surface state electrons is observed in the frontier molecular orbital (MO) resonances. An empty hybrid state closely above the substrate Fermi level exhibits the characteristic properties of surface Kondo effect reported for similar systems in the literature. By identifying three electronic states as hybrids of molecular orbitals and surface state electrons (two of them directly related to the Kondo effect), we are able to present a modified picture of the surface Kondo effect. It is based on a valence-bond model, where the bonding state represents Kondo's virtual bound state and the antibonding state is the so called 'Kondo resonance' reported in STM studies of the surface Kondo effect. Furthermore, double occupation of the originally singly unoccupied MO by tunneling electrons leads to the third state well above the Fermi level due to Coulomb repulsion as described by the Anderson model.

  15. Two strongly correlated electron systems: the Kondo mode in the strong coupling limit and a 2-D model of electrons close to an electronic topological transition; Deux systemes d'electrons fortement correles: le modele de reseau Kondo dans la limite du couplage fort et un modele bidimensionnel d'electrons au voisinage d'une transition topologique electronique

    Energy Technology Data Exchange (ETDEWEB)

    Bouis, F

    1999-10-14

    Two strongly correlated electron systems are considered in this work, Kondo insulators and high Tc cuprates. Experiments and theory suggest on one hand that the Kondo screening occurs on a rather short length scale and on the other hand that the Kondo coupling is renormalized to infinity in the low energy limit. The strong coupling limit is then the logical approach although the real coupling is moderate. A systematic development is performed around this limit in the first part. The band structure of these materials is reproduced within this scheme. Magnetic fluctuations are also studied. The antiferromagnetic transition is examined in the case where fermionic excitations are shifted to high energy. In the second part, the Popov and Fedotov representation of spins is used to formulate the Kondo and the antiferromagnetic Heisenberg model in terms of a non-polynomial action of boson fields. In the third part the properties of high Tc cuprates are explained by a change of topology of the Fermi surface. This phenomenon would happen near the point of optimal doping and zero temperature. It results in the appearance of a density wave phase in the under-doped regime. The possibility that this phase has a non-conventional symmetry is considered. The phase diagram that described the interaction and coexistence of density wave and superconductivity is established in the mean-field approximation. The similarities with the experimental observations are numerous in particular those concerning the pseudo-gap and the behavior of the resistivity near optimal doping. (author)

  16. Composite conductor containing superconductive wires

    Energy Technology Data Exchange (ETDEWEB)

    Larson, W.L.; Wong, J.

    1974-03-26

    A superconductor cable substitute made by coworking multiple rods of superconductive niobium--titanium or niobium--zirconium alloy with a common copper matrix to extend the copper and rods to form a final elongated product which has superconductive wires distributed in a reduced cross-section copper conductor with a complete metallurgical bond between the normal-conductive copper and the superconductor wires contained therein is described. The superconductor cable can be in the form of a tube.

  17. How does a Kondo impurity respond to its local environment?

    Science.gov (United States)

    Heinrich, Andreas

    2008-03-01

    The interplay between localized electrons on a magnetic atom and the conducting electrons in a metal can lead to intriguing many-body ground states such as the Kondo effect. When a spin is Kondo screened by conduction electrons the entire spin system performs a complicated dance that results in the formation of a spin singlet at sufficiently low temperature. For simplicity, most theoretical considerations of Kondo screening focus on magnetic impurities with the lowest possible spin S = 1/2. Such systems can be studied experimentally in exquisite detail and with great control using quantum dots in semiconductor heterostructures or carbon nanotubes. However, in Kondo systems consisting of localized magnetic atoms, the spin is often larger, making the Kondo effect richer and more complex. Here we use the imaging and spectroscopy capabilities of a scanning tunnelling microscope to study how the Kondo screening of a known high-spin atom is determined by its local environment. Co and Ti atoms were deposited on a thin insulating layer (Cu2N) on a copper substrate. We study the influence of external magnetic fields, crystalline magnetic anisotropy, as well as spin-coupling to surrounding atomic spins on the Kondo effect that forms on the Co or Ti atoms. We find that the anisotropy of the crystalline field quenches the high-spin system of Co (S = 3/2) into an effective S = 1/2 Kramers doublet. Surprisingly, much of the impact of these environmental factors on the complex many-body ground state can be understood simply through their effects on the energy levels of the unscreened spin.

  18. Low cost, formable, high T(sub c) superconducting wire

    Science.gov (United States)

    Smialek, James L. (Inventor)

    1991-01-01

    A ceramic superconductivity part such as a wire is produced through the partial oxidation of a specially formulated copper alloy in the core. The alloys contain low level quantities of rare earth and alkaline earth dopant elements. Upon oxidation at high temperature, superconducting oxide phases are formed as a thin film.

  19. Superconducting transistor

    Science.gov (United States)

    Gray, Kenneth E.

    1979-01-01

    A superconducting transistor is formed by disposing three thin films of superconducting material in a planar parallel arrangement and insulating the films from each other by layers of insulating oxides to form two tunnel junctions. One junction is biased above twice the superconducting energy gap and the other is biased at less than twice the superconducting energy gap. Injection of quasiparticles into the center film by one junction provides a current gain in the second junction.

  20. Superconductivity and superconductive electronics

    Science.gov (United States)

    Beasley, M. R.

    1990-12-01

    The Stanford Center for Research on Superconductivity and Superconductive Electronics is currently focused on developing techniques for producing increasingly improved films and multilayers of the high-temperature superconductors, studying their physical properties and using these films and multilayers in device physics studies. In general the thin film synthesis work leads the way. Once a given film or multilayer structure can be made reasonably routinely, the emphasis shifts to studying the physical properties and device physics of these structures and on to the next level of film quality or multilayer complexity. The most advanced thin films synthesis work in the past year has involved developing techniques to deposit a-axis and c-axis YBCO/PBCO superlattices and related structures. The in-situ feature is desirable because no solid state reactions with accompanying changes in volume, morphology, etc., that degrade the quality of the film involved.

  1. Two stages of Kondo effect and competition between RKKY and Kondo in Gd-based intermetallic compound

    Energy Technology Data Exchange (ETDEWEB)

    Vaezzadeh, Mehdi [Department of Physics, K.N.Toosi University of Technology, P.O. Box 15875-4416, Tehran (Iran, Islamic Republic of)]. E-mail: mehdi@kntu.ac.ir; Yazdani, Ahmad [Tarbiat Modares University, P.O. Box 14155-4838, Tehran (Iran, Islamic Republic of); Vaezzadeh, Majid [Department of Physics, K.N.Toosi University of Technology, P.O. Box 15875-4416, Tehran (Iran, Islamic Republic of); Daneshmand, Gissoo [Department of Physics, K.N.Toosi University of Technology, P.O. Box 15875-4416, Tehran (Iran, Islamic Republic of); Kanzeghi, Ali [Department of Physics, K.N.Toosi University of Technology, P.O. Box 15875-4416, Tehran (Iran, Islamic Republic of)

    2006-05-01

    The magnetic behavior of Gd-based intermetallic compound (Gd{sub 2}Al{sub (1-x)}Au{sub x}) in the form of the powder and needle, is investigated. All the samples are an orthorhombic crystal structure. Only the compound with x=0.4 shows the Kondo effect (other compounds have a normal behavior). Although, for the compound in the form of powder, with x=0.4, the susceptibility measurement {chi}(T) shows two different stages. Moreover for (T>T{sub K2}) a fall of the value of {chi}(T) is observable, which indicates a weak presence of ferromagnetic phase. About the two stages of Kondo effect, we observe at the first (T{sub K1}) an increase of {chi}(T) and in the second stage (T{sub K2}) a new remarkable decrease of {chi}(T) (T{sub K1}>T{sub K2}). For the sample in the form of needles, the first stage is observable only under high magnetic field. This first stage could be corresponds to a narrow resonance between Kondo cloud and itinerant electron. The second stage, which is remarkably visible for the sample in the form of the powder, can be attribute to a complete polarization of Kondo cloud. Observation of these two Kondo stages could be due to the weak presence of RKKY contribution.

  2. AC Conductance Through a Vibrating Molecular Dot in Kondo Regime

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    In the present paper, by applying the Lang-Firsov canonical transformation and the so-called non-crossing approximation technique, we investigate the joint effects of the electron-phonon interaction and an external alternating gate voltage on the transport of a quantum dot system in the Kondo regime. We find that, while the satellite Kondo resonant peaks appear in both the averaged local density of states and the differential conductance, the main Kondo peak at the Fermi energy is greatly suppressed. These results confirm the previous ones derived by other methods, such as the equation of motion solution. Furthermore, based on the picture of virtual transition between quasi-eigenstates in the system, we also give a slightly different explanation on these phenomena.

  3. Surface Kondo Impurities in the Slave-Boson Approach

    Science.gov (United States)

    Anda, Enrique; Vernek, Edson

    2005-03-01

    Transport properties of magnetic impurities on surfaces have captured a great deal of attention lately. Atom manipulation and topographic imaging techniques using scanning tunneling microscope have confirmed some theoretical predictions on Kondo physics and at the same time revealed other interesting behavior in these systems. For example, experiments have reported unexpectedly high Kondo temperatures for multi-impurity and molecular structures on metallic surfaces. Motivated by these experimental results we apply slave boson techniques for finite Coulomb interaction (finite U) to study the transport properties of magnetic impurities on a metallic surface in the Kondo regime. We report here on our studies of the role of fluctuations on the slave boson number for the case of one impurity on metallic surfaces. We compare our results to other theoretical approaches and to experimental results. Supported by CAPES-Brazil and NSF-IMC and NSF-NIRT.

  4. Hydrogen-induced Kondo effect for Co/Pt(111)

    Energy Technology Data Exchange (ETDEWEB)

    Dubout, Quentin; Calleja Mitja, Fabian; Etzkorn, Markus; Lehnert, Anne; Claude, Laurent; Gambardella, Pietro; Brune, Harald [Ecole Polytechnique Federale de Lausanne (EPFL), Lausanne (Switzerland)

    2011-07-01

    We present 0.4 K Scanning Tunneling Spectroscopy (STS) results on hydrogenated Co adatoms on Pt(111). Molecular H dosage creates two Co-H adsorption complexes with comparable abundance. Type I displays very large (40 %) inelastic conductance steps that originate from vibrations, as evidenced by their shift when substituting H by D. Type II displays smaller (5 %) conductance steps at higher energies, again due to H vibrations, together with a large conductance peak at the Fermi level. This feature is attributed to the Kondo effect. Its splitting in magnetic fields up to 8 Tesla identifies the Co-H complex as a S = 1/2 system, whereas clean Co/Pt(111) has a spin of 1 and shows no Kondo effect. H-adsorption has been reported to quench the Kondo effect, here we show that it can produce it.

  5. Fermionology in the Kondo-Heisenberg model: the case of CeCoIn5

    Science.gov (United States)

    Zhong, Yin; Zhang, Lan; Lu, Han-Tao; Luo, Hong-Gang

    2015-09-01

    The Fermi surface of heavy electron systems plays a fundamental role in understanding their variety of puzzling phenomena, for example, quantum criticality, strange metal behavior, unconventional superconductivity and even enigmatic phases with yet unknown order parameters. The spectroscopy measurement of the typical heavy fermion superconductor CeCoIn5 has demonstrated multi-Fermi surface structure, which has not been studied in detail theoretically in a model system like the Kondo-Heisenberg model. In this work, we take a step toward such a theoretical model by revisiting the Kondo-Heisenberg model. It is found that the usual self-consistent calculation cannot reproduce the fermionology of the experimental observation of the system due to the sign binding between the hopping of the conduction electrons and the mean-field valence-bond order. To overcome such inconsistency, the mean-field valence-bond order is considered as a free/fitting parameter to correlate them with real-life experiments as performed in recent experiments [M.P. Allan, F. Massee, D.K. Morr, J. Van Dyke, A.W. Rost, A.P. Mackenzie, C. Petrovic, J.C. Davis, Nat. Phys. 9, 468 (2013); J. Van Dyke, F. Massee, M.P. Allan, J.C. Davis, C. Petrovic, D.K. Morr, Proc. Natl. Acad. Sci. 111, 11663 (2014)], which also explicitly reflects the intrinsic dispersion of local electrons observed in experimental measurements. Given the fermionology, the calculated effective mass enhancement, entropy, superfluid density and Knight shift are all in qualitative agreement with the experimental results of CeCoIn5, which confirms our assumption. Our result supports a d_{x^2 - y^2 }-wave pairing structure in the heavy fermion material CeCoIn5.

  6. Charge Aspects of Composite Pair Superconductivity

    Science.gov (United States)

    Flint, Rebecca

    2014-03-01

    Conventional Cooper pairs form from well-defined electronic quasiparticles, making the internal structure of the pair irrelevant. However, in the 115 family of superconductors, the heavy electrons are forming as they pair and the internal pair structure becomes as important as the pairing mechanism. Conventional spin fluctuation mediated pairing cannot capture the direct transition from incoherent local moments to heavy fermion superconductivity, but the formation of composite pairs favored by the two channel Kondo effect can. These composite pairs are local d-wave pairs formed by two conduction electrons in orthogonal Kondo channels screening the same local moment. Composite pairing shares the same symmetries as magnetically mediated pairing, however, only composite pairing necessarily involves a redistribution of charge within the unit cell originating from the internal pair structure, both as a monopole (valence change) and a quadrupole effect. This redistribution will onset sharply at the superconducting transition temperature. A smoking gun test for composite pairing is therefore a sharp signature at Tc - for example, a cusp in the Mossbauer isomer shift in NpPd5Al2 or in the NQR shift in (Ce,Pu)CoIn5.

  7. Spiral Magnetic Order in the One-Dimensional Kondo Lattice

    Institute of Scientific and Technical Information of China (English)

    LIU Zhen-Rong; LI Zheng-Zhong; SHEN Rui

    2001-01-01

    The effects of c-f (conduction-f electrons) hybridization on the spiral spin magnetism in the one dimensional Kondo lattice are studied. By using the mean-field approximation, a close set of equations of the Green's functions with arbitrary wave vector Q for the spiral ordering of spins is deduced. The magnetic phase boundary between the spiral magnetism and ferromagnetism has been calculated approximately. From our qualitative results, one can find that the ferromagnetic region is enlarged due to the c f hybridization. Moreover, some new results reflecting the Kondo effect, such as the modified dispersion relation and the weakening of the localized magnetic moments are also obtained.

  8. Quadrupolar Kondo effect in uranium heavy-electron materials?

    Science.gov (United States)

    Cox, D. L.

    1987-01-01

    The possibility of an electric quadrupole Kondo effect for a non-Kramers doublet on a uranium (U) ion is a cubic metallic host is demonstrated by model calculations showing a Kondo upturn in the resistivity, universal quenching of the quadrupolar moment, and a heavy-electron anomaly in the electronic specific heat. With inclusion of excited crystal-field levels, some of the unusual magnetic-response data in the heavy-electron superconductor UBe13 may be understood. Structural phase transitions at unprecedented low temperatures may occur in U-based heavy-electron materials.

  9. Indications of a Quantum Critical Point in Bi2Sr2CaCu2O8+δ Using a Local Kondo Effect

    Science.gov (United States)

    Calleja, Eduardo; Dai, Jixia; Arnold, Gerald; Gu, Genda; McElroy, Kyle

    2014-03-01

    A complete understanding of the complex phase diagrams that are present in high temperature superconductors remains elusive. While there is an overwhelming amount of experimental data on the existence and interplay of the phases present in high Tc superconductors from local probes, much of the existing data only looks at the charge degree of freedom of the material. By substituting Fe atoms for Cu atoms in the CuO plane of Bi2Sr2CaCu2O8+δ (Bi2212), we gain the ability to access the spin degree of freedom since the Fe atoms retain their magnetization below the superconducting transition temperature. This leads to a local Kondo effect which can be observed using Spectroscopic-Imaging Scanning Tunneling Microscopy (SI-STM) and the local Kondo temperature can be extracted from spectra via a theoretical model. We show that the examination of this local Kondo temperature across local and sample average doping leads to the observation of a change in the quasiparticle spin degree of freedom at a quantum critical point (QCP) with a nominal hole doping of roughly 0.22, in agreement with other probes. The observation of the QCP in Bi2212 with this new method to access the spin degree of freedom helps to unravel some of the mystery behind the complex phase diagram of Bi2212.

  10. Superconductivity of Ta{sub 34}Nb{sub 33}Hf{sub 8}Zr{sub 14}Ti{sub 11} high entropy alloy from first principles calculations

    Energy Technology Data Exchange (ETDEWEB)

    Jasiewicz, K.; Wiendlocha, B.; Korben, P.; Kaprzyk, S.; Tobola, J. [AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, Al. Mickiewicza 30, 30-059, Krakow (Poland)

    2016-05-15

    The Korringa-Kohn-Rostoker method with the coherent potential approximation (KKR-CPA) is applied to study the first superconducting high entropy alloy (HEA) Ta{sub 34}Nb{sub 33}Hf{sub 8}Zr{sub 14}Ti{sub 11} (discovered in 2014 with T{sub c}=7.3 K), focusing on estimations of the electron-phonon coupling constant λ. The electronic part of λ has been calculated using the rigid muffin-tin approximation (RMTA), while the phonon part has been approximated using average atomic mass and experimental Debye temperature. The estimated λ=1.16 is close to the value determined from specific heat measurements, λ=0.98, and suggests rather strong electron-phonon coupling in this material. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  11. Superconducting electronics

    NARCIS (Netherlands)

    Rogalla, Horst

    1994-01-01

    During the last decades superconducting electronics has been the most prominent area of research for small scale applications of superconductivity. It has experienced quite a stormy development, from individual low frequency devices to devices with high integration density and pico second switching

  12. Kondo cloud of single heavy quark in cold and dense matter

    CERN Document Server

    Yasui, Shigehiro

    2016-01-01

    The Kondo effect is a universal phenomena observed in a variety of fermion systems containing a heavy impurity particle whose interaction is governed by the non-Abelian interaction. At extremely high density, I study the Kondo effect by color exchange in quark matter containing a single heavy (charm or bottom) quark as an impurity particle. To obtain the ground state with the Kondo effect, I introduce the condensate mixing the light quark and the heavy quark (Kondo cloud) in the mean-field approximation. I estimate the energy gain by formation of the Kondo cloud, and present that the Kondo cloud exhibits the resonant structure. I also evaluate the scattering cross section for the light quark and the heavy quark, and discuss its effect to the finite size quark matter.

  13. Kondo cloud of single heavy quark in cold and dense matter

    Science.gov (United States)

    Yasui, Shigehiro

    2017-10-01

    The Kondo effect is a universal phenomena observed in a variety of fermion systems containing a heavy impurity particle whose interaction is governed by the non-Abelian interaction. At extremely high density, I study the Kondo effect by color exchange in quark matter containing a single heavy (charm or bottom) quark as an impurity particle. To obtain the ground state with the Kondo effect, I introduce the condensate mixing the light quark and the heavy quark (Kondo cloud) in the mean-field approximation. I estimate the energy gain by formation of the Kondo cloud, and present that the Kondo cloud exhibits the resonant structure. I also evaluate the scattering cross section for the light quark and the heavy quark, and discuss its effect to the finite size quark matter.

  14. Kondo effect of D\\xAFs and D\\xAFs* mesons in nuclear matter

    Science.gov (United States)

    Yasui, Shigehiro; Sudoh, Kazutaka

    2017-03-01

    We study the Kondo effect for D¯s and D¯s* mesons as impurity particles in nuclear matter. The spin-exchange interaction between the D¯s or D¯s* meson and the nucleon induces the enhancement of the effective coupling in the low-energy scattering in the infrared region, whose energy scale of singularity is given by the Kondo scale. We investigate the Kondo scale in the renormalization group equation at nucleon one-loop level. We furthermore study the ground state with the Kondo effect in the mean-field approach, and present that the Kondo scale is related to the mixing strength between the D¯s or D¯s* meson and the nucleon in nuclear matter. We show the spectral function of the impurity when the Kondo effect occurs.

  15. Kondo effect for electron transport through an artificial quantum dot

    Institute of Scientific and Technical Information of China (English)

    Sun Ke-Wei; Xiong Shi-Jie

    2006-01-01

    We have calculated the transport properties of electron through an artificial quantum dot by using the numerical renormalization group technique in this paper.We obtain the conductance for the system of a quantum dot which is embedded in a one-dimensional chain in zero and finite temperature cases.The external magnetic field gives rise to a negative magnetoconductance in the zero temperature case.It increases as the external magnetic field increases.We obtain the relation between the coupling coefficient and conductance.If the interaction is big enough to prevent conduction electrons from tunnelling through the dot,the dispersion effect is dominant in this case.In the Kondo temperature regime,we obtain the conductivity of a quantum dot system with Kondo correlation.

  16. Characterization of a correlated topological Kondo insulator in one dimension

    Science.gov (United States)

    Hagymási, I.; Legeza, Ö.

    2016-04-01

    We investigate the ground state of a p -wave Kondo-Heisenberg model introduced by Alexandrov and Coleman with an Ising-type anisotropy in the Kondo interaction and correlated conduction electrons. Our aim is to understand how they affect the stability of the Haldane state obtained in the SU(2)-symmetric case without the Hubbard interaction. By applying the density-matrix renormalization group algorithm and calculating the entanglement entropy we show that in the anisotropic case a phase transition occurs and a Néel state emerges above a critical value of the Coulomb interaction. These findings are also corroborated by the examination of the entanglement spectrum and the spin profile of the system which clarify the structure of each phase.

  17. Kondo-effect of substitutional cobalt impurities at copper surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Wahl, P; Diekhoener, L; Schneider, M A; Kern, K [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstr. 1, D-70569 Stuttgart (Germany); Seitsonen, A P [IMPMC, CNRS and Universite Pierre et Marie Curie, 4 Place Jussieu, Case 115, F-75252 Paris (France)], E-mail: wahl@fkf.mpg.de

    2009-11-15

    The influence of the coordination on the Kondo temperature of a magnetic impurity at a noble metal surface and the line shape observed in low temperature scanning tunneling spectroscopy (STS) is investigated for single cobalt atoms adsorbed on and embedded in copper surfaces. Surprisingly, the Kondo temperature for substitutional cobalt atoms is almost the same as that of adatoms on the Cu(100) surface. This is in stark contrast to the behaviour observed at the Cu(111) surface. DFT calculations reveal that in the case of Cu(100) the coupling of the spin of the cobalt atom to the conduction band is not substantially increased by the incorporation of the cobalt atom. At the same time the observed line shape differs strongly from what is observed on adatom systems.

  18. The strong coupling Kondo lattice model as a Fermi gas

    CERN Document Server

    Östlund, S

    2007-01-01

    The strong coupling half-filled Kondo lattice model is an important example of a strongly interacting dense Fermi system for which conventional Fermi gas analysis has thus far failed. We remedy this by deriving an exact transformation that maps the model to a dilute gas of weakly interacting electron and hole quasiparticles that can then be analyzed by conventional dilute Fermi gas methods. The quasiparticle vacuum is a singlet Mott insulator for which the quasiparticle dynamics are simple. Since the transformation is exact, the electron spectral weight sum rules are obeyed exactly. Subtleties in understanding the behavior of electrons in the singlet Mott insulator can be reduced to a fairly complicated but precise relation between quasiparticles and bare electrons. The theory of free quasiparticles can be interpreted as an exactly solvable model for a singlet Mott insulator, providing an exact model in which to explore the strong coupling regime of a singlet Kondo insulator.

  19. Toward a new microscopic framework for Kondo lattice materials

    Science.gov (United States)

    Lonzarich, Gilbert; Pines, David; Yang, Yi-feng

    2017-02-01

    Understanding the emergence and subsequent behavior of heavy electrons in Kondo lattice materials is one of the grand challenges in condensed matter physics. From this perspective we review the progress that has been made during the past decade and suggest some directions for future research. Our focus will be on developing a new microscopic framework that incorporates the basic concepts that emerge from a phenomenological description of the key experimental findings.

  20. Tunable Kondo Effect of a Three-Terminal Transport Quantum Dot Embedded in an Aharonov-Bohm Ring

    Institute of Scientific and Technical Information of China (English)

    CHEN Xiong-Wen; SHI Zhen-Gang; WU Shao-Quan; SONG Ke-Hui

    2006-01-01

    @@ We theoretically investigate the Kondo effect of a three-terminal transport quantum dot (QD) embedded in an Aharonov-Bohm ring in the Kondo regime by means of the one-impurity Anderson Hamiltonian.

  1. Conductance fingerprint of Majorana fermions in the topological Kondo effect

    Science.gov (United States)

    Galpin, Martin R.; Mitchell, Andrew K.; Temaismithi, Jesada; Logan, David E.; Béri, Benjamin; Cooper, Nigel R.

    2014-01-01

    We consider an interacting nanowire/superconductor heterostructure attached to metallic leads. The device is described by an unusual low-energy model involving spin-1 conduction electrons coupled to a nonlocal spin-1/2 Kondo impurity built from Majorana fermions. The topological origin of the resulting Kondo effect is manifest in distinctive non-Fermi-liquid (NFL) behavior, and the existence of Majorana fermions in the device is demonstrated unambiguously by distinctive conductance line shapes. We study the physics of the model in detail, using the numerical renormalization group, perturbative scaling, and Abelian bosonization. In particular, we calculate the full scaling curves for the differential conductance in ac and dc fields, onto which experimental data should collapse. Scattering t matrices and thermodynamic quantities are also calculated, recovering asymptotes from conformal field theory. We show that the NFL physics is robust to asymmetric Majorana-lead couplings, and here we uncover a duality between strong and weak coupling. The NFL behavior is understood physically in terms of competing Kondo effects. The resulting frustration is relieved by inter-Majorana coupling which generates a second crossover to a regular Fermi liquid.

  2. Thermopower of few-electron quantum dots with Kondo correlations

    Science.gov (United States)

    Ye, Lvzhou

    2015-03-01

    The thermopower of few-electron quantum dots is crucially influenced by on-dot electron-electron interactions, particularly in the presence of Kondo correlations. We present a comprehensive picture which elucidates the underlying relations between the thermopower and the spectral density function of two-level quantum dots. The effects of various electronic states, including the Kondo states originating from both spin and orbital degrees of freedom, are clearly unraveled. With these insights, we have exemplified an effective and viable way to control the sign of thermopower of Kondo-correlated quantum dots. This is realized by tuning the temperature and by selecting the appropriate level spacing and Coulomb repulsion strength. Such a physical picture is affirmed by accurate numerical data obtained with a hierarchical equations of motion approach. Our understandings and findings provide useful insights into controlling the direction of electric (heat) current through a quantum dot by applying a temperature (voltage) gradient across the two coupling leads. This may have important implications for novel thermoelectric applications of quantum dots. The support from the Natural Science Foundation of China (Grants No. 21033008, No. 21233007, No. 21303175, and No. 21322305) and the Strategic Priority Research Program (B) of the CAS (XDB01020000) is gratefully appreciated.

  3. Observation of the frozen charge of a Kondo resonance

    Science.gov (United States)

    Desjardins, M. M.; Viennot, J. J.; Dartiailh, M. C.; Bruhat, L. E.; Delbecq, M. R.; Lee, M.; Choi, M.-S.; Cottet, A.; Kontos, T.

    2017-04-01

    The ability to control electronic states at the nanoscale has contributed to our modern understanding of condensed matter. In particular, quantum dot circuits represent model systems for the study of strong electronic correlations, epitomized by the Kondo effect. We use circuit quantum electrodynamics architectures to study the internal degrees of freedom of this many-body phenomenon. Specifically, we couple a quantum dot to a high-quality-factor microwave cavity to measure with exceptional sensitivity the dot’s electronic compressibility, that is, its ability to accommodate charges. Because electronic compressibility corresponds solely to the charge response of the electronic system, it is not equivalent to the conductance, which generally involves other degrees of freedom such as spin. Here, by performing dual conductance and compressibility measurements in the Kondo regime, we uncover directly the charge dynamics of this peculiar mechanism of electron transfer. The Kondo resonance, visible in transport measurements, is found to be ‘transparent’ to microwave photons trapped in the high-quality cavity, thereby revealing that (in such a many-body resonance) finite conduction is achieved from a charge frozen by Coulomb interaction. This freezing of charge dynamics is in contrast to the physics of a free electron gas. We anticipate that the tools of cavity quantum electrodynamics could be used in other types of mesoscopic circuits with many-body correlations, providing a model system in which to perform quantum simulation of fermion-boson problems.

  4. End view of ISR Superconducting Quadrupole in its cryostat

    CERN Multimedia

    1977-01-01

    This view shows the cold mass of the prototype ISR Superconducting Quadrupole suspended to the outer vacuum tank by means of titanium alloy rods.The heat shield wrapped with superinsulation can also be seen. See also photo 7702690X.

  5. Kondo hybridisation and the origin of metallic states at the (001) surface of SmB6

    NARCIS (Netherlands)

    E. Frantzeskakis; N. de Jong; B. Zwartsenberg; Y.K. Huang; Y. Pan; X. Zhang; F.X. Zhang; L.H. Bao; O. Tegus; A. Varykhalov; A. de Visser; M. Golden

    2013-01-01

    SmB6, a well-known Kondo insulator, has been proposed to be an ideal topological insulator with states of topological character located in a clean, bulk electronic gap, namely, the Kondo-hybridization gap. Since the Kondo gap arises from many-body electronic correlations, SmB6 would be placed at the

  6. Kondo hybridisation and the origin of metallic states at the (001) surface of SmB6

    NARCIS (Netherlands)

    Frantzeskakis, E.; de Jong, N.; Zwartsenberg, B.; Huang, Y.K.; Pan, Y.; Zhang, X.; Zhang, F.X.; Bao, L.H.; Tegus, O.; Varykhalov, A.; de Visser, A.; Golden, M.

    2013-01-01

    SmB6, a well-known Kondo insulator, has been proposed to be an ideal topological insulator with states of topological character located in a clean, bulk electronic gap, namely, the Kondo-hybridization gap. Since the Kondo gap arises from many-body electronic correlations, SmB6 would be placed at the

  7. Superconductivity in compensated and uncompensated semiconductors.

    Science.gov (United States)

    Yanase, Youichi; Yorozu, Naoyuki

    2008-12-01

    We investigate the localization and superconductivity in heavily doped semiconductors. The crossover from the superconductivity in the host band to that in the impurity band is described on the basis of the disordered three-dimensional attractive Hubbard model for binary alloys. The microscopic inhomogeneity and the thermal superconducting fluctuation are taken into account using the self-consistent 1-loop order theory. The superconductor-insulator transition accompanies the crossover from the host band to the impurity band. We point out an enhancement of the critical temperature Tc around the crossover. Further localization of electron wave functions leads to the localization of Cooper pairs and induces the pseudogap. We find that both the doping compensation by additional donors and the carrier increase by additional acceptors suppress the superconductivity. A theoretical interpretation is proposed for the superconductivity in the boron-doped diamond, SiC, and Si.

  8. Superconductivity in compensated and uncompensated semiconductors

    Directory of Open Access Journals (Sweden)

    Youichi Yanase and Naoyuki Yorozu

    2008-01-01

    Full Text Available We investigate the localization and superconductivity in heavily doped semiconductors. The crossover from the superconductivity in the host band to that in the impurity band is described on the basis of the disordered three-dimensional attractive Hubbard model for binary alloys. The microscopic inhomogeneity and the thermal superconducting fluctuation are taken into account using the self-consistent 1-loop order theory. The superconductor-insulator transition accompanies the crossover from the host band to the impurity band. We point out an enhancement of the critical temperature Tc around the crossover. Further localization of electron wave functions leads to the localization of Cooper pairs and induces the pseudogap. We find that both the doping compensation by additional donors and the carrier increase by additional acceptors suppress the superconductivity. A theoretical interpretation is proposed for the superconductivity in the boron-doped diamond, SiC, and Si.

  9. Method of forming low cost, formable High T(subc) superconducting wire

    Science.gov (United States)

    Smialek, James L. (Inventor)

    1989-01-01

    A ceramic superconductivity part, such as a wire, is produced through the partial oxidation of a specially formulated copper alloy in a core. The alloys contains low level of quantities of rare earth and alkaline earth dopant elements. Upon oxidation at high temperatures, and superconducting oxide phases are formed as a thin film.

  10. Phonon-assisted and magnetic field induced Kondo tunneling in single molecular devices

    Energy Technology Data Exchange (ETDEWEB)

    Kikoin, K [School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978 (Israel); Kiselev, M N [The Abdus Salam International Centre for Theoretical Physics, Trieste (Italy)

    2007-12-15

    We consider the Kondo tunneling induced by multiphonon emission/absorption processes in magnetic molecular complexes with low-energy singlet-triplet spin gap and show that the number of assisting phonons may be changed by varying the Zeeman splitting of excited triplet state. As a result, the structure of multiphonon Kondo resonances may be scanned by means of magnetic field tuning.

  11. Two-channel Kondo effect and renormalization flow with macroscopic quantum charge states.

    Science.gov (United States)

    Iftikhar, Z; Jezouin, S; Anthore, A; Gennser, U; Parmentier, F D; Cavanna, A; Pierre, F

    2015-10-08

    Many-body correlations and macroscopic quantum behaviours are fascinating condensed matter problems. A powerful test-bed for the many-body concepts and methods is the Kondo effect, which entails the coupling of a quantum impurity to a continuum of states. It is central in highly correlated systems and can be explored with tunable nanostructures. Although Kondo physics is usually associated with the hybridization of itinerant electrons with microscopic magnetic moments, theory predicts that it can arise whenever degenerate quantum states are coupled to a continuum. Here we demonstrate the previously elusive 'charge' Kondo effect in a hybrid metal-semiconductor implementation of a single-electron transistor, with a quantum pseudospin of 1/2 constituted by two degenerate macroscopic charge states of a metallic island. In contrast to other Kondo nanostructures, each conduction channel connecting the island to an electrode constitutes a distinct and fully tunable Kondo channel, thereby providing unprecedented access to the two-channel Kondo effect and a clear path to multi-channel Kondo physics. Using a weakly coupled probe, we find the renormalization flow, as temperature is reduced, of two Kondo channels competing to screen the charge pseudospin. This provides a direct view of how the predicted quantum phase transition develops across the symmetric quantum critical point. Detuning the pseudospin away from degeneracy, we demonstrate, on a fully characterized device, quantitative agreement with the predictions for the finite-temperature crossover from quantum criticality.

  12. Superconductivity of an oxide film on the surface of Bi(1-x)Sb(x) alloy single crystals produced by electrochemical oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Alfeev, V.N.; Aminov, B.A.; Brandt, N.B.; Vasina, S.IA.; Damaskin, B.B. (Moskovskii Gosudarstvennyi Universitet, Moscow (USSR))

    1989-10-01

    A study is made of the volt-ampere characteristics of point contacts produced by the mechanical compression of the electrochemically oxidized Bi(1-x)Sb(x) single crystals. Volt-ampere characteristics of the Josephson type have been observed at temperatures below Tc=6-8 K, indicating that the oxide films have superconducting properties at these temperatures. In a magnetic field, Mersereau oscillations, typical of a Josephson transition net, are observed in the contact region. In an external microwave field, the volt-ampere characteristics exhibit a structure related to the occurrence of Shapiro steps.

  13. From four- to two-channel Kondo effect in junctions of XY spin chains

    Directory of Open Access Journals (Sweden)

    Domenico Giuliano

    2016-08-01

    Full Text Available We consider the Kondo effect in Y-junctions of anisotropic XY models in an applied magnetic field along the critical lines characterized by a gapless excitation spectrum. We find that, while the boundary interaction Hamiltonian describing the junction can be recasted in the form of a four-channel, spin-1/2 antiferromagnetic Kondo Hamiltonian, the number of channels effectively participating in the Kondo effect depends on the chain parameters, as well as on the boundary couplings at the junction. The system evolves from an effective four-channel topological Kondo effect for a junction of XX-chains with symmetric boundary couplings into a two-channel one at a junction of three quantum critical Ising chains. The effective number of Kondo channels depends on the properties of the boundary and of the bulk. The XX-line is a “critical” line, where a four-channel topological Kondo effect can be recovered by fine-tuning the boundary parameter, while along the line in parameter space connecting the XX-line and the critical Ising point the junction is effectively equivalent to a two-channel topological Kondo Hamiltonian. Using a renormalization group approach, we determine the flow of the boundary couplings, which allows us to define and estimate the critical couplings and Kondo temperatures of the different Kondo (pair channels. Finally, we study the local transverse magnetization in the center of the Y-junction, eventually arguing that it provides an effective tool to monitor the onset of the two-channel Kondo effect.

  14. From four- to two-channel Kondo effect in junctions of XY spin chains

    Energy Technology Data Exchange (ETDEWEB)

    Giuliano, Domenico, E-mail: domenico.giuliano@fis.unical.it [Dipartimento di Fisica, Università della Calabria, Arcavacata di Rende I-87036, Cosenza (Italy); INFN, Gruppo collegato di Cosenza, Arcavacata di Rende I-87036, Cosenza (Italy); Sodano, Pasquale, E-mail: pasquale.sodano02@gmail.com [International Institute of Physics, Universidade Federal do Rio Grande do Norte, 59078-400 Natal, RN (Brazil); Departemento de Física Teorica e Experimental, Universidade Federal do Rio Grande do Norte, 59072-970 Natal, RN (Brazil); Tagliacozzo, Arturo, E-mail: arturo.tagliacozzo@na.infn.it [INFN, Gruppo collegato di Cosenza, Arcavacata di Rende I-87036, Cosenza (Italy); Dipartimento di Fisica, Università di Napoli “Federico II”, Monte S. Angelo-Via Cintia, I-80126 Napoli (Italy); CNR-SPIN, Monte S. Angelo-Via Cintia, I-80126 Napoli (Italy); Trombettoni, Andrea, E-mail: andreatr@sissa.it [CNR-IOM DEMOCRITOS Simulation Center, Via Bonomea 265, I-34136 Trieste (Italy); SISSA and INFN, Sezione di Trieste, Via Bonomea 265, I-34136 Trieste (Italy)

    2016-08-15

    We consider the Kondo effect in Y-junctions of anisotropic XY models in an applied magnetic field along the critical lines characterized by a gapless excitation spectrum. We find that, while the boundary interaction Hamiltonian describing the junction can be recasted in the form of a four-channel, spin-1/2 antiferromagnetic Kondo Hamiltonian, the number of channels effectively participating in the Kondo effect depends on the chain parameters, as well as on the boundary couplings at the junction. The system evolves from an effective four-channel topological Kondo effect for a junction of XX-chains with symmetric boundary couplings into a two-channel one at a junction of three quantum critical Ising chains. The effective number of Kondo channels depends on the properties of the boundary and of the bulk. The XX-line is a “critical” line, where a four-channel topological Kondo effect can be recovered by fine-tuning the boundary parameter, while along the line in parameter space connecting the XX-line and the critical Ising point the junction is effectively equivalent to a two-channel topological Kondo Hamiltonian. Using a renormalization group approach, we determine the flow of the boundary couplings, which allows us to define and estimate the critical couplings and Kondo temperatures of the different Kondo (pair) channels. Finally, we study the local transverse magnetization in the center of the Y-junction, eventually arguing that it provides an effective tool to monitor the onset of the two-channel Kondo effect.

  15. Bonding theory for metals and alloys

    CERN Document Server

    Wang, Frederick E

    2005-01-01

    Bonding Theory for Metals and Alloys exhorts the potential existence of covalent bonding in metals and alloys. Through the recognition of the covalent bond in coexistence with the 'free' electron band, the book describes and demonstrates how the many experimental observations on metals and alloys can all be reconciled. Subsequently, it shows how the individual view of metals and alloys by physicists, chemists and metallurgists can be unified. The physical phenomena of metals and alloys covered in this book are: Miscibility Gap between two liquid metals; Phase Equilibrium Diagrams; Phenomenon of Melting. Superconductivity; Nitinol; A Metal-Alloy with Memory; Mechanical Properties; Liquid Metal Embrittlement; Superplasticity; Corrosion; The author introduces a new theory based on 'Covalon' conduction, which forms the basis for a new approach to the theory of superconductivity. This new approach not only explains the many observations made on the phenomenon of superconductivity but also makes predictions that ha...

  16. Critical quasiparticles in single-impurity and lattice Kondo models

    Science.gov (United States)

    Vojta, M.; Bulla, R.; Wölfle, P.

    2015-07-01

    Quantum criticality in systems of local moments interacting with itinerant electrons has become an important and diverse field of research. Here we review recent results which concern (a) quantum phase transitions in single-impurity Kondo and Anderson models and (b) quantum phase transitions in heavy-fermion lattice models which involve critical quasiparticles. For (a) the focus will be on impurity models with a pseudogapped host density of states and their applications, e.g., in graphene and other Dirac materials, while (b) is devoted to strong-coupling behavior near antiferromagnetic quantum phase transitions, with potential applications in a variety of heavy-fermion metals.

  17. Influence of local spin polarization to the Kondo effect

    Institute of Scientific and Technical Information of China (English)

    LI Huan; GUO Wei

    2007-01-01

    We use the spin non-degenerate single impurity Anderson model to investigate the influence of the local spin polarization to the Kondo effect. By using the Schrieffer-Wolff transformation, we obtain a generalized s-d exchange Hamiltonian, which describes the interaction between a polarized local spin and conduction electrons. In this case, the singlet is no longer an eigenstate as shown by variational calculations where the splitting of the local energy △= εd↑ - εd↓ can be arbitrarily small. The local spin polarization generates the instability of the singlet ground state of the S = 1/2 s-d exchange model.

  18. Non-equilibrium Kondo effect in double quantum dot

    Energy Technology Data Exchange (ETDEWEB)

    Kiselev, M.N. E-mail: kiselev@physik.uni-wuerzburg.de; Kikoin, K.A.; Molenkamp, L.W

    2004-05-01

    We investigate theoretically a non-equilibrium transport through a double quantum dot (DQD) in a parallel geometry. It is shown that the resonance Kondo tunneling through a parallel DQD with even occupation and singlet ground state may arise at a strong bias, which compensates the energy of singlet/triplet excitation. Using the renormalization group technique we derive scaling equations and calculate the differential conductance as a function of an auxiliary DC-bias for parallel DQD being in a regime described by SO(4) symmetry.

  19. Photoexcited electron dynamics in Kondo insulators and heavy fermions

    OpenAIRE

    Demsar, Jure; Thorsmolle, Verner K.; Sarrao, John L.; Taylor, Antoinette J.

    2005-01-01

    We have studied the photoexcited carrier relaxation dynamics in the Kondo insulator SmB6 and the heavy fermion metal YbAgCu4 as a function of temperature and excitation level. The dynamic response is found to be both strongly temperature dependent and nonlinear. The data are analyzed with a Rothwarf-Taylor bottleneck model, where the dynamics are governed by the presence of a narrow gap in the density of states near the Fermi level. The remarkable agreement with the model suggests that carrie...

  20. Local Moment Formation and Kondo Effect in Defective Graphene

    OpenAIRE

    Cazalilla, M. A.; Iucci, A.; Guinea, F.; Neto, A. H. Castro

    2012-01-01

    We study the local moment formation and the Kondo effect at single-atom vacancies in Graphene. We develop a model accounting for the vacancy reconstruction as well as non-planarity effects induced by strain and/or temperature. Thus, we find that the dangling $\\sigma$ orbital localized at the vacancy is allowed to strongly hybridize with the $\\pi$-band since the scattering with the vacancy turns the hybridization into singular function of the energy ($\\sim [|\\epsilon| \\ln^2 \\epsilon/D]^{-1}$, ...

  1. Superconducting Microelectronics.

    Science.gov (United States)

    Henry, Richard W.

    1984-01-01

    Discusses superconducting microelectronics based on the Josephson effect and its advantages over conventional integrated circuits in speed and sensitivity. Considers present uses in standards laboratories (voltage) and in measuring weak magnetic fields. Also considers future applications in superfast computer circuitry using Superconducting…

  2. The role of short-range magnetic correlations in the gap opening of topological Kondo insulators

    Science.gov (United States)

    Ramos, E.; Franco, R.; Silva-Valencia, J.; Foglio, M. E.; Figueira, M. S.

    2017-08-01

    In this article we investigate the effects of short-range anti-ferromagnetic correlations on the gap opening of topological Kondo insulators. We add a Heisenberg term to the periodic Anderson model at the limit of strong correlations in order to allow a small degree of hopping of the localized electrons between neighboring sites of the lattice. This new model is adequate for studying topological Kondo insulators, whose paradigmatic material is the compound SmB6 . The main finding of the article is that the short-range antiferromagnetic correlations, present in some Kondo insulators, contribute decisively to the opening of the Kondo gap in their density of states. These correlations are produced by the interaction between moments on the neighboring sites of the lattice. For simplicity, we solve the problem on a two dimensional square lattice. The starting point of the model is the 4f-Ce ions orbitals, with J=5/2 multiplet in the presence of spin-orbit coupling. We present results for the Kondo and for the antiferromagnetic correlation functions. We calculate the phase diagram of the model, and as we vary the Ef level position from the empty regime to the Kondo regime, the system develops metallic and topological Kondo insulator phases. The band structure calculated shows that the model describes a strong topological insulator.

  3. Competition between Kondo effect and RKKY physics in graphene magnetism

    Science.gov (United States)

    Allerdt, A.; Feiguin, A. E.; Das Sarma, S.

    2017-03-01

    The cooperative behavior of quantum impurities on two-dimensional (2D) materials, such as graphene and bilayer graphene, is characterized by a nontrivial competition between screening (Kondo effect) and Ruderman-Kittel-Kasuya-Yosida (RKKY) magnetism. In addition, due to the small density of states at the Fermi level, impurities may not couple to the conduction electrons at all, behaving as free moments. Employing a recently developed exact numerical method to study multi-impurity lattice systems, we obtain nonperturbative results that dramatically depart from expectations based on the conventional RKKY theory. At half filling and for weak coupling, impurities remain in the local moment regime when they are on opposite sublattices, up to a critical value of the interactions when they start coupling antiferromagnetically with correlations that decay very slowly with interimpurity distance. At finite doping, away from half filling, ferromagnetism is completely absent and the physics is dominated by a competition between antiferromagnetism and Kondo effect. In bilayer graphene, impurities on opposite layers behave as free moments, unless the interaction is of the order of the hopping or larger.

  4. Kondo route to spin inhomogeneities in the honeycomb Kitaev model

    Energy Technology Data Exchange (ETDEWEB)

    Das, S. D.; Dhochak, K.; Tripathi, V.

    2016-07-01

    Paramagnetic impurities in a quantum spin liquid give rise to Kondo effects with highly unusual properties. We have studied the effect of locally coupling a paramagnetic impurity with the spin-1/2 honeycomb Kitaev model in its gapless spin-liquid phase. The ( impurity) scaling equations are found to be insensitive to the sign of the coupling. The weak and strong coupling fixed points are stable, with the latter corresponding to a noninteracting vacancy and an interacting, spin-1 defect for the antiferromagnetic and ferromagnetic cases, respectively. The ground state in the strong coupling limit in both cases has a nontrivial topology associated with a finite Z(2) flux at the impurity site. For the antiferromagnetic case, this result has been obtained straightforwardly owing to the integrability of the Kitaev model with a vacancy. The strong-coupling limit of the ferromagnetic case is, however, nonintegrable, and we address this problem through exact-diagonalization calculations with finite Kitaev fragments. Our exact diagonalization calculations indicate that the weak-to-strong coupling transition and the topological phase transition occur rather close to each other and are possibly coincident. We also find an intriguing similarity between the magnetic response of the defect and the impurity susceptibility in the two-channel Kondo problem.

  5. Phase diagram of the bosonic Kondo-Hubbard model

    Energy Technology Data Exchange (ETDEWEB)

    Foss-Feig, Michael; Rey, Ana Maria [JILA, National Institute of Standards and Technology, and University of Colorado, Boulder, Colorado 80309 (United States)

    2011-11-15

    We study a bosonic version of the Kondo lattice model with an onsite repulsion in the conduction band, implemented with alkali-metal atoms in two bands of an optical lattice. Using both weak- and strong-coupling perturbation theory, we find that at unit filling of the conduction bosons the superfluid-to-Mott-insulator transition should be accompanied by a magnetic transition from a ferromagnet (in the superfluid) to a paramagnet (in the Mott insulator). Furthermore, an analytic treatment of Gutzwiller mean-field theory reveals that quantum spin fluctuations induced by the Kondo exchange cause the otherwise continuous superfluid-to-Mott-insulator phase transition to be first order. We show that lattice separability imposes a serious constraint on proposals to exploit excited bands for quantum simulations, and discuss a way to overcome this constraint in the context of our model by using an experimentally realized nonseparable lattice. A method to probe the first-order nature of the transition based on collapses and revivals of the matter-wave field is also discussed.

  6. Holographic optical traps for atom-based topological Kondo devices

    Science.gov (United States)

    Buccheri, F.; Bruce, G. D.; Trombettoni, A.; Cassettari, D.; Babujian, H.; Korepin, V. E.; Sodano, P.

    2016-07-01

    The topological Kondo (TK) model has been proposed in solid-state quantum devices as a way to realize non-Fermi liquid behaviors in a controllable setting. Another motivation behind the TK model proposal is the demand to demonstrate the quantum dynamical properties of Majorana fermions, which are at the heart of their potential use in topological quantum computation. Here we consider a junction of crossed Tonks-Girardeau gases arranged in a star-geometry (forming a Y-junction), and we perform a theoretical analysis of this system showing that it provides a physical realization of the TK model in the realm of cold atom systems. Using computer-generated holography, we experimentally implement a Y-junction suitable for atom trapping, with controllable and independent parameters. The junction and the transverse size of the atom waveguides are of the order of 5 μm, leading to favorable estimates for the Kondo temperature and for the coupling across the junction. Since our results show that all the required theoretical and experimental ingredients are available, this provides the demonstration of an ultracold atom device that may in principle exhibit the TK effect.

  7. Multiterminal Conductance and Decoherence Effect of a Three-Terminal Kondo Dot

    Institute of Scientific and Technical Information of China (English)

    FANG Tie-Feng; WANG Shun-Jin

    2006-01-01

    @@ A three-terminal Kondo dot modelled by the Anderson Hamiltonian is investigated. In the strong correlation limit, we calculate the multiterminal conductance and the voltage-induced characteristic splitting of the nonequilibrium Kondo resonance by using the equation of motion approach from viewpoint of the correlation dynamics.A qualitative and reasonable agreement with a recently reported experiment is obtained. We also simulate phenomenologically the decoherence of the Kondo-coherent state formed in the two-terminal setup in the framework of our three-terminal model.

  8. Color superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Wilczek, F. [Institute for Advanced Study, Princeton, NJ (United States)

    1997-09-22

    The asymptotic freedom of QCD suggests that at high density - where one forms a Fermi surface at very high momenta - weak coupling methods apply. These methods suggest that chiral symmetry is restored and that an instability toward color triplet condensation (color superconductivity) sets in. Here I attempt, using variational methods, to estimate these effects more precisely. Highlights include demonstration of a negative pressure in the uniform density chiral broken phase for any non-zero condensation, which we take as evidence for the philosophy of the MIT bag model; and demonstration that the color gap is substantial - several tens of MeV - even at modest densities. Since the superconductivity is in a pseudoscalar channel, parity is spontaneously broken.

  9. SUPERCONDUCTING PHOTOCATHODES.

    Energy Technology Data Exchange (ETDEWEB)

    SMEDLEY, J.; RAO, T.; WARREN, J.; SEKUTOWICZ, LANGNER, J.; STRZYZEWSKI, P.; LEFFERS, R.; LIPSKI, A.

    2005-10-09

    We present the results of our investigation of lead and niobium as suitable photocathode materials for superconducting RF injectors. Quantum efficiencies (QE) have been measured for a range of incident photon energies and a variety of cathode preparation methods, including various lead plating techniques on a niobium substrate. The effects of operating at ambient and cryogenic temperatures and different vacuum levels on the cathode QE have also been studied.

  10. Summary of the Proceedings of the Super-Conductivity Technical Exchange Meeting

    Science.gov (United States)

    1980-04-01

    Contents: Large Superconductive Magnets; Superconductivity Activities at LASL; Superconductivity Studies at Argonne National Laboratory; CFFF MHD Magnet at Argonne National Laboratory; MHD Superconducting Magnets; Fermilab's Energy Saver; LCP and 12 Tesla Programs at ORNL; Division of Electric Energy System's Superconductivity Program; Development of Standards for Practical Superconductors; Casting of Dendritic Cu-Nb Alloys for Superconducting Wire; Review of Recent Developments of Multifilamentary Nb3Sn by 'in Situ' and Cold Powder Metallurgy Processes; Superconducting Magnet Facility at NRL; Airborne Superconductor Applications; High Pressure Synthesis Program at Benet Weapons Laboratory Watervliet Arsenal; CuCl; Stability and Exciton Population Percursive to Anomalous Diagmagnetism; Navy Superconductive Machinery Development Program; and Superconducting Materials Program at NRL.

  11. Sample of superconducting wiring (Niobium Titanium)

    CERN Multimedia

    About NbTi cable: The cable consists of 36 strands of superconducting wire, each strand has a diameter of 0.825 mm and houses 6300 superconducting filaments of niobium-titanium (Nb-Ti, a superconducting alloy). Each filament has a diameter of about 0.006 mm, i.e. 10 times smaller than a typical human hair. The filaments are embedded in a high-purity copper matrix. Copper is a normal conducting material. The filaments are in the superconductive state when the temperature is below about -263ºC (10.15 K). When the filaments leave the superconductive state, the copper acts as conductor transports the electrical current. Each strand of The NbTi cable (at superconducting state) has a current density of up to above 2000 A/mm2 at 9 T and -271ºC (2.15 K). A cable transport a current of about 13000 A at 10 T and -271ºC (2.15 K). About LHC superconducting wiring: The high magnetic fields needed for the LHC can only be reached using superconductors. At very low temperatures, superconductors have no electrical resista...

  12. Sample of superconducting wiring (Niobium Titanium)

    CERN Multimedia

    About NbTi cable: The cable consists of 36 strands of superconducting wire, each strand has a diameter of 0.825 mm and houses 6300 superconducting filaments of niobium-titanium (Nb-Ti, a superconducting alloy). Each filament has a diameter of about 0.006 mm, i.e. 10 times smaller than a typical human hair. The filaments are embedded in a high-purity copper matrix. Copper is a normal conducting material. The filaments are in the superconductive state when the temperature is below about -263ºC (10.15 K). When the filaments leave the superconductive state, the copper acts as conductor transports the electrical current. Each strand of The NbTi cable (at superconducting state) has a current density of up to above 2000 A/mm2 at 9 T and -271ºC (2.15 K). A cable transport a current of about 13000 A at 10 T and -271ºC (2.15 K). About LHC superconducting wiring: The high magnetic fields needed for the LHC can only be reached using superconductors. At very low temperatures, superconductors have no electrical resistan...

  13. Hybridization and crystal-field effects in Kondo insulators studied by means of core-level spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Strigari, Fabio

    2015-04-13

    This thesis is mainly focused on the class of Kondo insulators, which also comprises Kondo semiconductors and semimetals. When the right conditions are met - i.e. for a certain number of electrons per unit cell and for certain symmetries of the electronic structure - the interaction between the conduction and f electrons opens a narrow hybridization gap close to the Fermi level. Here we investigate the Kondo semiconductor CeNiSn, as well as the CeM{sub 2}Al{sub 10} compound family with M=Ru, Os and Fe. Many explanations for the low-temperature behavior have been suggested, all of which stress the significance of the 4f crystalline-electric-field (CEF) ground state, which is investigated in the framework of this thesis. We determine the CEF wave functions in this compound family and quantify the degree of c-f hybridization in order to address speculations about the impact of hybridization on the magnetic order. In addition, on the search for parameters which correlate with ground-state properties in heavy-fermion compounds, we investigate the CEF ground states of the intermetallic substitution series CeRh{sub 1-x}Ir{sub x}In{sub 5} since its phase diagram covers all phases of interest, from antiferromagnetic to superconducting as well as regions of phase coexistence. To shed light on the issues above, namely the CEF ground state and the hybridization strength, respectively, two new experimental approaches are used: polarization-dependent X-ray absorption spectroscopy (XAS) and hard X-ray photoelectron spectroscopy (HAXPES). Recently, linearly polarized XAS at the Ce M{sub 4,5} edge has been proven to be highly useful when it comes to the determination of the 4f ground-state wave function in tetragonal rare earth systems. In the present thesis the same technique is applied to the above-mentioned materials, demonstrating that linearly polarized XAS can be employed to obtain an unambiguous and reliable picture of the CEF ground state even in Kondo-insulating systems

  14. Gate-controlled Kondo screening in graphene: Quantum criticality and electron-hole asymmetry

    Science.gov (United States)

    Vojta, M.; Fritz, L.; Bulla, R.

    2010-04-01

    Magnetic impurities in neutral graphene provide a realization of the pseudogap Kondo model, which displays a quantum phase transition between phases with screened and unscreened impurity moment. Here, we present a detailed study of the pseudogap Kondo model with finite chemical potential μ. While carrier doping restores conventional Kondo screening at lowest energies, properties of the quantum critical fixed point turn out to influence the behavior over a large parameter range. Most importantly, the Kondo temperature TK shows an extreme asymmetry between electron and hole doping. At criticality, depending on the sign of μ, TK follows either the scaling prediction TK~|μ| with a universal prefactor, or TK~|μ|x with x≈2.6. This asymmetry between electron and hole doping extends well outside the quantum critical regime and also implies a qualitative difference in the shape of the tunneling spectra for both signs of μ.

  15. Observation of Kondo resonance in rare-earth hexaborides using high resolution photoemission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Maiti, Kalobaran; Patil, Swapnil; Adhikary, Ganesh [Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005 (India); Balakrishnan, Geetha, E-mail: kbmaiti@tifr.res.in [Department of Physics, University of Warwick, Coventry, CV4 7AL (United Kingdom)

    2011-01-01

    We studied the electronic structure of rare earth hexaborides, CeB{sub 6}, PrB{sub 6} and NdB{sub 6} using state-of-the-art high resolution photoemission spectroscopy. CeB{sub 6} is a dense Kondo system. PrB{sub 6} and NdB{sub 6} are antiferromagnetic (Neel temperature {approx}7 K), known to be stable moment systems and do not exhibit Kondo effect. Photoemission spectra exhibit distinct signature of surface and bulk electronic structures of these compounds. The energy position of the surface feature is not influenced by the 4f density of states. High resolution spectra of CeB{sub 6} reveal multiple Kondo resonance features in the bulk spectra due to various photoemission final states. Interestingly, high resolution photoemission spectra of antiferromagnetic PrB{sub 6} also exhibit a sharp feature at the Fermi level that shows temperature dependence similar to the Kondo resonance features.

  16. Validity of equation-of-motion approach to kondo problem in the large N limit

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Jian-xin [Los Alamos National Laboratory; Ting, C S [UNIV OF HOUSTON; Qi, Yunong [UNIV OF HOUSTON

    2008-01-01

    The Anderson impurity model for Kondo problem is investigated for arbitrary orbit-spin degeneracy N of the magnetic impurity by the equation of motion method (EOM). By employing a new decoupling scheme, a self-consistent equation for the one-particle Green function is derived and numerically solved in the large-N approximation. For the particle-hole symmetric Anderson model with finite Coulomb interaction U, we show that the Kondo resonance at the impurity site exists for all N {>=} 2. The approach removes the pathology in the standard EOM for N = 2, and has the same level of applicability as non-crossing approximation. For N = 2, an exchange field splits the Kondo resonance into only two peaks, consist with the result from more rigorous numerical renormalization group (NRG) method. The temperature dependence of the Kondo resonance peak is also discussed.

  17. Emergence of a Fermionic Finite-Temperature Critical Point in a Kondo Lattice.

    Science.gov (United States)

    Chou, Po-Hao; Zhai, Liang-Jun; Chung, Chung-Hou; Mou, Chung-Yu; Lee, Ting-Kuo

    2016-04-29

    The underlying Dirac point is central to the profound physics manifested in a wide class of materials. However, it is often difficult to drive a system with Dirac points across the massless fermionic critical point. Here by exploiting screening of local moments under spin-orbit interactions in a Kondo lattice, we show that below the Kondo temperature, the Kondo lattice undergoes a topological transition from a strong topological insulator to a weak topological insulator at a finite temperature T_{D}. At T_{D}, massless Dirac points emerge and the Kondo lattice becomes a Dirac semimetal. Our analysis indicates that the emergent relativistic symmetry dictates nontrivial thermal responses over large parameter and temperature regimes. In particular, it yields critical scaling behaviors both in magnetic and transport responses near T_{D}.

  18. Self-sustained oscillations in nanoelectromechanical systems induced by Kondo resonance

    Science.gov (United States)

    Song, Taegeun; Kiselev, Mikhail N.; Kikoin, Konstantin; Shekhter, Robert I.; Gorelik, Leonid Y.

    2014-03-01

    We investigate the instability and dynamical properties of nanoelectromechanical systems represented by a single-electron device containing movable quantum dots attached to a vibrating cantilever via asymmetric tunnel contacts. The Kondo resonance in electron tunneling between the source and shuttle facilitates self-sustained oscillations originating from the strong coupling of mechanical and electronic/spin degrees of freedom. We analyze a stability diagram for the two-channel Kondo shuttling regime due to limitations given by the electromotive force acting on a moving shuttle, and find that the saturation oscillation amplitude is associated with the retardation effect of the Kondo cloud. The results shed light on possible ways to experimentally realize the Kondo-cloud dynamical probe by using high mechanical dissipation tunability as well as supersensitive detection of mechanical displacement.

  19. Electrostatic tuning of Kondo effect in a rare-earth-doped wide-band-gap oxide

    KAUST Repository

    Li, Yongfeng

    2013-04-29

    As a long-lived theme in solid-state physics, the Kondo effect reflects the many-body physics involving the short-range Coulomb interactions between itinerant electrons and localized spins in metallic materials. Here we show that the Kondo effect is present in ZnO, a prototypical wide-band-gap oxide, doped with a rare-earth element (Gd). The localized 4f electrons of Gd ions do not produce remanent magnetism, but interact strongly with the host electrons, giving rise to a saturating resistance upturn and negative magnetoresistance at low temperatures. Furthermore, the Kondo temperature and resistance can be electrostatically modulated using electric-double-layer gating with liquid ionic electrolyte. Our experiments provide the experimental evidence of tunable Kondo effect in ZnO, underscoring the magnetic interactions between localized and itinerant electrons and the emergent transport behaviors in such doped wide-band-gap oxides.

  20. Blocking transport resonances via Kondo many-body entanglement in quantum dots

    Science.gov (United States)

    Niklas, Michael; Smirnov, Sergey; Mantelli, Davide; Margańska, Magdalena; Nguyen, Ngoc-Viet; Wernsdorfer, Wolfgang; Cleuziou, Jean-Pierre; Grifoni, Milena

    2016-08-01

    Many-body entanglement is at the heart of the Kondo effect, which has its hallmark in quantum dots as a zero-bias conductance peak at low temperatures. It signals the emergence of a conducting singlet state formed by a localized dot degree of freedom and conduction electrons. Carbon nanotubes offer the possibility to study the emergence of the Kondo entanglement by tuning many-body correlations with a gate voltage. Here we show another side of Kondo correlations, which counterintuitively tend to block conduction channels: inelastic co-tunnelling lines in the magnetospectrum of a carbon nanotube strikingly disappear when tuning the gate voltage. Considering the global SU(2) \\xotime SU(2) symmetry of a nanotube coupled to leads, we find that only resonances involving flips of the Kramers pseudospins, associated to this symmetry, are observed at temperatures and voltages below the corresponding Kondo scale. Our results demonstrate the robust formation of entangled many-body states with no net pseudospin.

  1. Superconducting state parameters of AgxZn1-x and AgxAl1-x binary alloys superconductors%AgxZn1-x和AgxAl1-x双相合金超导体的超导态参数

    Institute of Scientific and Technical Information of China (English)

    VORA Aditya Mahabhai

    2008-01-01

    A well-known pseudopotential is used to investigate the superconducting state parameters (SSP), viz., electron-phonon coupling strength, Coulomb pseudopotential, transition temperature, isotope effect exponent and effective interaction strength for AgxZn1-x and AgxAl1-x binary alloys theoretically for the first time. We have incorporated here five different types of the local field correction functions to show the effect of exchange and correlation on the aforesaid properties. Very strong influence of various exchange and correlation functions is concluded from the present study. Comparison with others such experimental values is encouraging, which confirms applicability of the model potential in explaining the superconducting state parameters of binary mixture.

  2. Kondo effect in triple quantum dots: interplay between continuous and discrete symmetries

    Energy Technology Data Exchange (ETDEWEB)

    Kikoin, K. [Department of Physics, Ben-Gurion University, Beer-Sheva, 84105 (Israel)]. E-mail: kikoin@bgumail.bgu.ac.il; Kuzmenko, T. [Department of Physics, Ben-Gurion University, Beer-Sheva, 84105 (Israel); Avishai, Y. [Department of Physics, Ben-Gurion University, Beer-Sheva, 84105 (Israel); Ilse Kats Center for Nano-Technology, Ben-Gurion University, Beer-Sheva, 84105 (Israel)

    2006-05-01

    The physics of Kondo effect and related phenomena in a triangular triple quantum dot (TTQD) is studied. A fascinating property of TTQD is the interplay between continuous SU(2) symmetry in spin space and discrete C{sub 3v} symmetry in real space. We show that this interplay is manifested in strong oscillations of conductance as a function of magnetic flux through TTQD due to interplay between Kondo and Aharonov-Bohm effect.

  3. Photoemission in YbCu sub 2 Si sub 2 : Problems with the Kondo impurity model

    Energy Technology Data Exchange (ETDEWEB)

    Lawrence, J.M. (California Univ., Irvine (United States)); Arko, A.J.; Joyce, J.J.; Canfield, P.C.; Fisk, Z.; Thompson, J.D. (Los Alamos National Lab., NM (United States))

    1991-01-01

    We report valence band photoemission results for YbCu{sub 2}Si{sub 2}. The 4f{sup 13}(J=7/2) final state peak, centered 60meV below the Fermi level {epsilon}{sub F}, lacks the temperature dependence and is broader than predicted for a Kondo resonance. Together with the recent photoemission results for cerium compounds, these results raise serious doubts about the Kondo impurity explanation of heavy fermion photoemission. 7 refs., 3 figs.

  4. Photoemission in YbCu sub 2 Si sub 2 : problem with the Kondo impurity model

    Energy Technology Data Exchange (ETDEWEB)

    Lawrence, J.M.; Arko, A.J.; Joyce, J.J.; Canfield, P.C.; Fisk, Z.; Thompson, J.D.; Bartlett, R.J. (Los Alamos National Lab., NM (United States))

    1992-02-01

    We report valence band photoemission results for YbCu{sub 2}Si{sub 2}. The 4f{sup 13}(J = 7/2) final state peak, centered 60 meV below the Fermi level element of{sub F}, lacks the temperature dependence and is broader than predicted for a Kondo resonance. Together with recent photoemission results for cerium compounds, these results raise serious doubts about the Kondo impurity explanation of heavy fermion photoemission. (orig.).

  5. Processing and characterization of superconducting solenoids made of Bi-2212/Ag-alloy multifilament round wire for high field magnet applications

    Science.gov (United States)

    Chen, Peng

    As the only high temperature superconductor with round wire (RW) geometry, Bi2Sr2CaCu2O8+x (Bi-2212) superconducting wire has the advantages of being multi-filamentary, macroscopically isotropic and twistable. With overpressure (OP) processing techniques recently developed by our group at the National High Magnetic Field Laboratory (NHMFL), the engineering current density (Je) of Bi-2212 RW can be dramatically increased. For example, Je of more than 600 A/mm 2 (4.2 K and 20 T) is achieved after 100 bar OP processing. With these intrinsically beneficial properties and recent processing progress, Bi-2212 RW has become very attractive for high field magnet applications, especially for nuclear magnetic resonance (NMR) magnets and accelerator magnets etc. This thesis summarizes my graduate study on Bi-2212 solenoids for high field and high homogeneity NMR magnet applications, which mainly includes performance study of Bi-2212 RW insulations, 1 bar and OP processing study of Bi-2212 solenoids, and development of superconducting joints between Bi-2212 RW conductors. Electrical insulation is one of the key components of Bi-2212 coils to provide sufficient electrical standoff within coil winding pack. A TiO 2/polymer insulation offered by nGimat LLC was systematically investigated by differential thermal analysis (DTA), thermo-gravimetric analysis (TGA), scanning electron microscopy (SEM), dielectric property measurements, and transport critical current (Ic) property measurements. About 29% of the insulation by weight is polymer. When the Bi-2212 wire is fully heat treated, this decomposes with slow heating to 400 °C in flowing O2. After the full reaction, we found that the TiO2 did not degrade the critical current properties, adhered well to the conductor, and provided a breakdown voltage of more than 100 V. A Bi-2212 RW wound solenoid coil was built using this insulation being offered by nGimat LLC. The coil resistance was constant through coil winding, polymer burn

  6. Phase diagram of the Kondo-Heisenberg model on honeycomb lattice with geometrical frustration

    Science.gov (United States)

    Li, Huan; Song, Hai-Feng; Liu, Yu

    2016-11-01

    We calculated the phase diagram of the Kondo-Heisenberg model on a two-dimensional honeycomb lattice with both nearest-neighbor and next-nearest-neighbor antiferromagnetic spin exchanges, to investigate the interplay between RKKY and Kondo interactions in the presence of magnetic frustration. Within a mean-field decoupling technology in slave-fermion representation, we derived the zero-temperature phase diagram as a function of Kondo coupling J k and frustration strength Q. The geometrical frustration can destroy the magnetic order, driving the original antiferromagnetic (AF) phase to non-magnetic valence bond solids (VBS). In addition, we found two distinct VBS. As J k is increased, a phase transition from AF to Kondo paramagnetic (KP) phase occurs, without the intermediate phase coexisting AF order with Kondo screening found in square lattice systems. In the KP phase, the enhancement of frustration weakens the Kondo screening effect, resulting in a phase transition from KP to VBS. We also found a process to recover the AF order from VBS by increasing J k in a wide range of frustration strength. Our work may provide predictions for future experimental observation of new processes of quantum phase transitions in frustrated heavy-fermion compounds.

  7. Controlling orbital-selective Kondo effects in a single molecule through coordination chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Tsukahara, Noriyuki; Kawai, Maki; Takagi, Noriaki, E-mail: n-takagi@k.u-tokyo.ac.jp [Department of Advanced Materials Science, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan); Minamitani, Emi; Kim, Yousoo [RIKEN, 2-1 Hirosawa, Saitama 351-0198 (Japan)

    2014-08-07

    Iron(II) phthalocyanine (FePc) molecule causes novel Kondo effects derived from the unique electronic structure of multi-spins and multi-orbitals when attached to Au(111). Two unpaired electrons in the d{sub z}{sup 2} and the degenerate dπ orbitals are screened stepwise, resulting in spin and spin+orbital Kondo effects, respectively. We investigated the impact on the Kondo effects of the coordination of CO and NO molecules to the Fe{sup 2+} ion as chemical stimuli by using scanning tunneling microscopy (STM) and density functional theory calculations. The impacts of the two diatomic molecules are different from each other as a result of the different electronic configurations. The coordination of CO converts the spin state from triplet to singlet, and then the Kondo effects completely disappear. In contrast, an unpaired electron survives in the molecular orbital composed of Fe d{sub z}{sup 2} and NO 5σ and 2π* orbitals for the coordination of NO, causing a sharp Kondo resonance. The isotropic magnetic response of the peak indicates the origin is the spin Kondo effect. The diatomic molecules attached to the Fe{sup 2+} ion were easily detached by applying a pulsed voltage at the STM junction. These results demonstrate that the single molecule chemistry enables us to switch and control the spin and the many-body quantum states reversibly.

  8. Enhanced Kondo Effect in an Electron System Dynamically Coupled with Local Optical Phonon

    Science.gov (United States)

    Hotta, Takashi

    2007-08-01

    We discuss Kondo behavior of a conduction electron system coupled with local optical phonon by analyzing the Anderson-Holstein model with the use of a numerical renormalization group (NRG) method. There appear three typical regions due to the balance between Coulomb interaction Uee and phonon-mediated attraction Uph. For Uee>Uph, we observe the standard Kondo effect concerning spin degree of freedom. Since the Coulomb interaction is effectively reduced as Uee-Uph, the Kondo temperature TK is increased when Uph is increased. On the other hand, for UeeUph, there occurs the Kondo effect concerning charge degree of freedom, since vacant and double occupied states play roles of pseudo-spins. Note that in this case, TK is decreased with the increase of Uph. Namely, TK should be maximized for Uee≈ Uph. Then, we analyze in detail the Kondo behavior at Uee=Uph, which is found to be explained by the polaron Anderson model with reduced hybridization of polaron and residual repulsive interaction among polarons. By comparing the NRG results of the polaron Anderson model with those of the original Anderson-Holstein model, we clarify the Kondo behavior in the competing region of Uee≈ Uph.

  9. Kondo effect and spin quenching in high-spin molecules on metal substrates

    Science.gov (United States)

    Jacob, D.; Soriano, M.; Palacios, J. J.

    2013-10-01

    Using a state-of-the art combination of density functional theory and impurity solver techniques, we present a complete and parameter-free picture of the Kondo effect in the high-spin (S=3/2) coordination complex known as manganese phthalocyanine adsorbed on the Pb(111) surface. We calculate the correlated electronic structure and corresponding tunnel spectrum and find an asymmetric Kondo resonance, as recently observed in experiments. Contrary to previous claims, the Kondo resonance stems from only one of three possible Kondo channels with origin in the Mn 3d orbitals, its peculiar asymmetric shape arising from the modulation of the hybridization due to a strong coupling to the organic ligand. The spectral signature of the second Kondo channel is strongly suppressed as the screening occurs via the formation of a many-body singlet with the organic part of the molecule. Finally, a spin-1/2 in the 3d shell remains completely unscreened due to the lack of hybridization of the corresponding orbital with the substrate, hence leading to a spin-3/2 underscreened Kondo effect.

  10. Kondo Breakdown and Quantum Oscillations in SmB_{6}.

    Science.gov (United States)

    Erten, Onur; Ghaemi, Pouyan; Coleman, Piers

    2016-01-29

    Recent quantum oscillation experiments on SmB_{6} pose a paradox, for while the angular dependence of the oscillation frequencies suggest a 3D bulk Fermi surface, SmB_{6} remains robustly insulating to very high magnetic fields. Moreover, a sudden low temperature upturn in the amplitude of the oscillations raises the possibility of quantum criticality. Here we discuss recently proposed mechanisms for this effect, contrasting bulk and surface scenarios. We argue that topological surface states permit us to reconcile the various data with bulk transport and spectroscopy measurements, interpreting the low temperature upturn in the quantum oscillation amplitudes as a result of surface Kondo breakdown and the high frequency oscillations as large topologically protected orbits around the X point. We discuss various predictions that can be used to test this theory.

  11. SU(4) Kondo entanglement in double quantum dot devices

    Science.gov (United States)

    Bonazzola, Rodrigo; Andrade, J. A.; Facio, Jorge I.; García, D. J.; Cornaglia, Pablo S.

    2017-08-01

    We analyze, from a quantum information theory perspective, the possibility of realizing an SU(4) entangled Kondo regime in semiconductor double quantum dot devices. We focus our analysis on the ground-state properties and consider the general experimental situation where the coupling parameters of the two quantum dots differ. We model each quantum dot with an Anderson-type Hamiltonian including an interdot Coulomb repulsion and tunnel couplings for each quantum dot to independent fermionic baths. We find that the spin and pseudospin entanglements can be made equal, and the SU(4) symmetry recovered, if the gate voltages are chosen in such a way that the average charge occupancies of the two quantum dots are equal, and the double occupancy on the double quantum dot is suppressed. We present density matrix renormalization group numerical results for the spin and pseudospin entanglement entropies, and analytical results for a simplified model that captures the main physics of the problem.

  12. Superconductivity in MgB2

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    In January of 2001 the superconductivity of the compound MgB2 with a critical temperature Tc of up to 39 K was discovered. This Tc is the highest in all intermetallic compound and alloy superconductors. MgB2 has a simple structure and its manufacturing capital cost is lower, therefore it could become a practical superconductor in the future. The recent progress is reviewed here which covers the progress in electronic structure, high Tc mechanism, superconducting parameters (Debye temperature, specific heat coefficient of electron, critical fields, coherent length, penetration depth, energy gap, critical current and relaxation rate of flux). Moreover the issue on power transmission is discussed.

  13. Pressure-induced instability of magnetic order in Kondo-lattice system. Neutron diffraction study of the pseudo-binary alloy system Ce(Ru sub 0 sub . sub 9 sub 0 Rh sub 0 sub . sub 1 sub 0) sub 2 (Si sub 1 sub - sub y Ge sub y) sub 2

    CERN Document Server

    Watanabe, K; Kanadani, C; Taniguchi, T; Kawarazaki, S; Uwatoko, Y; Kadowaki, H

    2003-01-01

    Neutron diffraction experiments have been carried out to study the nature of the magnetic order of the pseudo-binary alloy system Ce(Ru sub 0 sub . sub 9 sub 0 Rh sub 0 sub . sub 1 sub 0) sub 2 (Si sub 1 sub - sub y Ge sub y) sub 2. Response of the ordered atomic magnetic moment, mu, the transition temperature, T sub N , and the magnitude of the magnetic modulation vector, q, to the chemical pressure and also to the applied hydrostatic pressure, P, were examined at low temperatures. When y changes, all of mu, T sub N and q show a sudden alteration of the manner of the y-dependence at around y - 0.08. The P-dependence of q shows quite different features for different y's of 0.0, 0.2 and 0.25. On the basis of these observations the possibility of a pressure-induced alternation of the magnetic regime of the order is discussed. (author)

  14. Itinerant Ferromagnetism and Superconductivity

    OpenAIRE

    Karchev, Naoum

    2004-01-01

    Superconductivity has again become a challenge following the discovery of unconventional superconductivity. Resistance-free currents have been observed in heavy-fermion materials, organic conductors and copper oxides. The discovery of superconductivity in a single crystal of $UGe_2$, $ZrZn_2$ and $URhGe$ revived the interest in the coexistence of superconductivity and ferromagnetism. The experiments indicate that: i)The superconductivity is confined to the ferromagnetic phase. ii)The ferromag...

  15. 100 years of superconductivity

    CERN Document Server

    Rogalla, Horst

    2011-01-01

    Even a hundred years after its discovery, superconductivity continues to bring us new surprises, from superconducting magnets used in MRI to quantum detectors in electronics. 100 Years of Superconductivity presents a comprehensive collection of topics on nearly all the subdisciplines of superconductivity. Tracing the historical developments in superconductivity, the book includes contributions from many pioneers who are responsible for important steps forward in the field.The text first discusses interesting stories of the discovery and gradual progress of theory and experimentation. Emphasizi

  16. Strongly correlated superconductivity and pseudogap phase near a multiband Mott insulator.

    Science.gov (United States)

    Capone, Massimo; Fabrizio, Michele; Castellani, Claudio; Tosatti, Erio

    2004-07-23

    Near a Mott transition, strong electron correlations may enhance Cooper pairing. This is demonstrated in the dynamical mean field theory solution of a twofold-orbital degenerate Hubbard model with an inverted on-site Hund rule exchange, favoring local spin-singlet configurations. Close to the Mott insulator (which here is a local version of a valence bond insulator) a pseudogap non-Fermi-liquid metal, a superconductor, and a normal metal appear, in striking similarity with the physics of cuprates. The strongly correlated s-wave superconducting state has a larger Drude weight than the corresponding normal state. The role of the impurity Kondo problem is underscored.

  17. Decoupling between Field-Instabilities of Antiferromagnetism and Pseudo-Metamagnetism in Rh-Doped CeRu2Si2 Kondo Lattice

    Science.gov (United States)

    Aoki, Dai; Paulsen, Carley; Kotegawa, Hisashi; Hardy, Frédéric; Meingast, Christoph; Haen, Pierre; Boukahil, Mounir; Knafo, William; Ressouche, Eric; Raymond, Stephane; Flouquet, Jacques

    2012-03-01

    Doping Kondo lattice system CeRu2Si2 with Rh-8% (Ce(Ru0.92Rh0.08)2Si2) leads to drastic consequences due to the mismatch of the lattice parameters between CeRu2Si2 and CeRh2Si2. A large variety of experiments clarifies the unusual properties of the ground state induced by the magnetic field from longitudinal antiferromagnetic (AF) mode at H=0 to polarized paramagnetic phase in very high magnetic field. The separation between AF phase, paramagnetic phase and polarized paramagnetic phase varying with temperature, magnetic field and pressure is discussed on the basis of the experiments down to very low temperature. Similarities and differences between Rh and La substituted alloys are discussed with emphasis on the competition between transverse and longitudinal AF modes, and ferromagnetic fluctuations.

  18. High field superconducting magnets

    Science.gov (United States)

    Hait, Thomas P. (Inventor); Shirron, Peter J. (Inventor)

    2011-01-01

    A superconducting magnet includes an insulating layer disposed about the surface of a mandrel; a superconducting wire wound in adjacent turns about the mandrel to form the superconducting magnet, wherein the superconducting wire is in thermal communication with the mandrel, and the superconducting magnet has a field-to-current ratio equal to or greater than 1.1 Tesla per Ampere; a thermally conductive potting material configured to fill interstices between the adjacent turns, wherein the thermally conductive potting material and the superconducting wire provide a path for dissipation of heat; and a voltage limiting device disposed across each end of the superconducting wire, wherein the voltage limiting device is configured to prevent a voltage excursion across the superconducting wire during quench of the superconducting magnet.

  19. Ferromagnetism in the Kondo-lattice compound CePd2P2.

    Science.gov (United States)

    Tran, Vinh Hung; Bukowski, Zbigniew

    2014-06-25

    We report physical properties of CePd2P2 crystallizing in the tetragonal ThCr2Si2-type structure (space group I4/mmm). Dc-magnetic susceptibility, magnetization, specific heat, electrical resistivity and magnetoresistance measurements establish a ferromagnetic ordering below the Curie temperature TC = 28.4 ± 0.2 K. Critical analysis of isothermal and isofield magnetization yields critical exponents of β = 0.405 ± 0.005, γ = 1.11 ± 0.05 and δ = 3.74 ± 0.04. The ordered state is characterized by saturation moment Ms ∼ 0.98μB and magnon energy gap Δ/kB ∼25–35 K. The studied properties reflect a competing influence of the Kondo and crystalline electric field (CEF) interactions. The strength of the Kondo effect is assigned by a low-temperature Kondo scale TK ∼19 ± 10 K and a high-temperature Kondo scale TK ~ H 117 } 10 K. A model of the inelastic scattering of the conduction electrons with an exchanged CEF energy ΔCEF was applied to the magnetic resistivity. An average value ΔCEF = 260 ± 30 K is consistent in the relationships with TK and TK H. We argue that the CePd2P2 compound appears to be a new ferromagnetic Kondo-lattice among the Ce-based intermetallics.

  20. Effect of Spin-Orbit Coupling on Kondo Phenomena in f7-Electron Systems

    Science.gov (United States)

    Hotta, Takashi

    2015-11-01

    In order to promote our basic understanding of the Kondo behavior recently observed in europium compounds, we analyze an impurity Anderson model with seven f electrons at an impurity site by employing a numerical renormalization group method. The local part of the model consists of Coulomb interactions among f electrons, spin-orbit coupling λ, and crystalline electric field (CEF) potentials, while we consider the hybridization V between local f electrons and single-band conduction electrons with au symmetry. For λ = 0, we observe underscreening Kondo behavior for appropriate values of V, characterized by an entropy change from ln 8 to ln 7, in which one of the seven f electrons is screened by conduction electrons. When λ is increased, we obtain two types of behavior depending on the value of V. For large V, we find an entropy release of ln 7 at low temperatures, determined by the level splitting energy due to the hybridization. For small V, we also observe an entropy change from ln 8 to ln 2 by the level splitting due to the hybridization, but at low temperatures, ln 2 entropy is found to be released, leading to the Kondo effect. We emphasize that the Kondo behavior for small V is observed for realistic values of λ on the order of 0.1 eV. We also discuss the effect of CEF potentials and the multipole properties in the Kondo behavior reported in this paper.

  1. Transport signatures of Kondo physics and quantum criticality in graphene with magnetic impurities

    Science.gov (United States)

    Ruiz-Tijerina, David A.; Dias da Silva, Luis G. G. V.

    2017-03-01

    Localized magnetic moments have been predicted to develop in graphene samples with vacancies or adsorbates. The interplay between such magnetic impurities and graphene's Dirac quasiparticles leads to remarkable many-body phenomena, which have, so far, proved elusive to experimental efforts. In this article we study the thermodynamic, spectral, and transport signatures of quantum criticality and Kondo physics of a dilute ensemble of atomic impurities in graphene. We consider vacancies and adatoms that either break or preserve graphene's C3 v and inversion symmetries. In a neutral graphene sample, all cases display symmetry-dependent quantum criticality, leading to enhanced impurity scattering for asymmetric impurities, in a manner analogous to bound-state formation by nonmagnetic resonant scatterers. Kondo correlations emerge only in the presence of a back gate, with estimated Kondo temperatures well within the experimentally accessible domain for all impurity types. For symmetry-breaking impurities at charge neutrality, quantum criticality is signaled by T-2 resistivity scaling, leading to full insulating behavior at low temperatures, while low-temperature resistivity plateaus appear both in the noncritical and Kondo regimes. By contrast, the resistivity contribution from symmetric vacancies and hollow-site adsorbates vanishes at charge neutrality and for arbitrary back-gate voltages, respectively. This implies that local probing methods are required for the detection of both Kondo and quantum critical signatures in these symmetry-preserving cases.

  2. Conductance of closed and open long Aharonov-Bohm-Kondo rings

    Science.gov (United States)

    Shi, Zheng; Komijani, Yashar

    2017-02-01

    We calculate the finite temperature linear dc conductance of a generic single-impurity Anderson model containing an arbitrary number of Fermi liquid leads, and apply the formalism to closed and open long Aharonov-Bohm-Kondo (ABK) rings. We show that, as with the short ABK ring, there is a contribution to the conductance from the connected four-point Green's function of the conduction electrons. At sufficiently low temperatures this contribution can be eliminated, and the conductance can be expressed as a linear function of the T matrix of the screening channel. For closed rings we show that at temperatures high compared to the Kondo temperature, the conductance behaves differently for temperatures above and below vF/L , where vF is the Fermi velocity and L is the circumference of the ring. For open rings, when the ring arms have both a small transmission and a small reflection, we show from the microscopic model that the ring behaves like a two-path interferometer, and that the Kondo temperature is unaffected by details of the ring. Our findings confirm that ABK rings are potentially useful in the detection of the size of the Kondo screening cloud, the π /2 scattering phase shift from the Kondo singlet, and the suppression of Aharonov-Bohm oscillations due to inelastic scattering.

  3. Theory of Fano-Kondo effect in quantum dot systems: Temperature dependence of the Fano line shapes

    Energy Technology Data Exchange (ETDEWEB)

    Maruyama, I. [Physikalisches Institut der Universitaet Bonn, Nussallee 12, 53115 Bonn (Germany)]. E-mail: maru@th.physik.uni-bonn.de; Shibata, N. [Department of Basic Science, University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902 (Japan); Ueda, K. [Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwa-no-ha, Kashiwa, Chiba 277-8581 (Japan)

    2006-05-01

    The Fano-Kondo effect in zero-bias conductance is studied based on a theoretical model for the T-shaped quantum dot by the finite temperature density matrix renormalization group method. The modification of the two Fano line shapes at much higher temperatures than the Kondo temperature is also investigated by the effective Fano parameter estimated as a fitting parameter.

  4. Quantum interference and Kondo effects in an Aharonov-Bohm-Casher interferometer containing a laterally coupled double quantum dot

    Science.gov (United States)

    Kubo, T.; Tokura, Y.; Tarucha, S.

    2010-01-01

    We theoretically investigate spin-dependent electron transport through an Aharonov-Bohm-Casher interferometer containing a laterally coupled double quantum dot. In particular, we numerically calculate the Aharonov-Bohm and Aharonov-Casher oscillations of the linear conductance in the Kondo regime. We show that the AC oscillation in the Kondo regime deviates from the sinusoidal form.

  5. Superconducting fluctuations in organic molecular metals enhanced by Mott criticality.

    Science.gov (United States)

    Nam, Moon-Sun; Mézière, Cécile; Batail, Patrick; Zorina, Leokadiya; Simonov, Sergey; Ardavan, Arzhang

    2013-12-02

    Unconventional superconductivity typically occurs in materials in which a small change of a parameter such as bandwidth or doping leads to antiferromagnetic or Mott insulating phases. As such competing phases are approached, the properties of the superconductor often become increasingly exotic. For example, in organic superconductors and underdoped high-T(c) cuprate superconductors a fluctuating superconducting state persists to temperatures significantly above T(c). By studying alloys of quasi-two-dimensional organic molecular metals in the κ-(BEDT-TTF)₂X family, we reveal how the Nernst effect, a sensitive probe of superconducting phase fluctuations, evolves in the regime of extreme Mott criticality. We find strong evidence that, as the phase diagram is traversed through superconductivity towards the Mott state, the temperature scale for superconducting fluctuations increases dramatically, eventually approaching the temperature at which quasiparticles become identifiable at all.

  6. Finite-size effect and Kondo screening effect in an A-B ring with a quantum dot

    Institute of Scientific and Technical Information of China (English)

    Wu Shao-Quan; Wang Shun-Jin; Sun Wei-Li; Yu Wan-Lun

    2004-01-01

    The properties of the ground state of a closed dot-ring system with a magnetic flux in the Kondo regime are studied theoretically by means of a one-impurity Anderson Hamiltonian. The Hamiltonian is solved by means of the slave-boson mean-field theory. It is shown that at T=0, a suppressed Kondo effect exists in this system even when the mean level spacing of electrons in the ring is larger than the bulk Kondo temperature. The physical quantities depend sensitively on both the parity of the system and the size of the ring; the rich physical behaviour can be attributed to the coexistence of both the finite-size effect and the Kondo screening effect. It is also possible to detect the Kondo screening cloud by measuring the persistent current or the zero field impurity susceptibility Ximp directly in future experiments.

  7. Superconducting cables: Long distance energy transmission. (Latest citations from the NTIS bibliographic database). Published Search

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1997-06-01

    The bibliography contains citations concerning the design, development, and evaluation of superconducting cables and power transmission lines for long distance energy transmission. Topics include methods of cryogenic refrigeration and electrical insulation, fabrication and development of niobium alloy conductors, energy loss analysis, and dielectric design of superconducting power transmission systems. Government research reports on superconducting technology for electric power transmission and distribution are also reviewed.(Contains 50-250 citations and includes a subject term index and title list.) (Copyright NERAC, Inc. 1995)

  8. The possibility of nanostructure character in approaching Kondo effect

    Energy Technology Data Exchange (ETDEWEB)

    Kamali, N; Yazdani, A; Shahsavari, L [Tarbiat Modares University, Jalal al Ahmad, P. O. Box 14115-175, Tehran (Iran, Islamic Republic of)

    2007-12-15

    Based on instability of magnetic structure, a new class of heavy fermions is constructed with a stable local magnetic ion 'Gd'. The lattice constants, D.C magnetic susceptibility and the electrical resistivity measurements in the magnetic unstable intermetallic compounds show; (1) the Instability of crystal structure, as well as high transition temperature 'T{sub c}', strongly depends on the conduction electrons concentration. The reduced size effect and the reduction in correlation length, is expected to be the cause of this behaviour as it could be due to the nanostructure character as well as the competition of inter and intra-cluster also (2) the coexistence of Kondo lattice behaviour and magnetic ordering 'reentrant antiferromagnet' for the temperature range of 30 < T{sub k} < 90K with T{sub N} = T{sub max} = 30K and finally (3) the metal-insulator-like behaviour with complete quench of magnetic ordering occur antiferromagnetically named 'super paramagnet' at a certain conduction electron concentration.

  9. Spin dynamics of the Kondo insulator CeNiSn approaching the metallic phase

    DEFF Research Database (Denmark)

    Schröder, A.; Aeppli, G.; Mason, T.E.

    1997-01-01

    The spin dynamics of Kondo insulators has been studied by high-resolution magnetic neutron spectroscopy at a triple-axes spectrometer on CeNi1-xCuxSn single crystals using a vertical 9 T magnet. While upon doping (x = 0.13) the spin gap of the Kondo insulator CeNiSn collapses at the transition...... to an antiferromagnetic ordered metallic Kondo compound, no such instability is observed in CeNiSn in magnetic fields up to 9 T. Both the sharp magnetic excitations (at 2 and 4 meV) appear significantly broader for energy and momentum transfer at high fields, while the ground-state correlations (probed by chi'(0)) remain...

  10. Quantum phase transitions and thermodynamics of the power-law Kondo model

    Science.gov (United States)

    Mitchell, Andrew K.; Vojta, Matthias; Bulla, Ralf; Fritz, Lars

    2013-11-01

    We revisit the physics of a Kondo impurity coupled to a fermionic host with a diverging power-law density of states near the Fermi level, ρ(ω)˜|ω|r, with exponent -1Kondo coupling leads to strong screening with a negative zero-temperature impurity entropy, while ferromagnetic Kondo coupling can induce a stable fractional spin moment. We formulate the quantum field theories for all critical fixed points of the problem, which are fermionic in nature and allow for a perturbative renormalization-group treatment.

  11. Kondo decoherence : finding the right spin model for iron impurities in gold and silver.

    Energy Technology Data Exchange (ETDEWEB)

    Costi, T. A.; Bergqvist, L.; Weichselbaum, A.; von Delft, J.; Micklitz, T.; Rosch, A.; Mavropoulos, P.; Dederichs, P. H.; Mallet, F.; Saminadayar, L.; Bauerle, C. (Materials Science Division); (Forschungszentrum Julich); (Ludwig-Maximilians-Univ. Munchen); (Univ. of Cologne); (CNRS); (Univ. Joseph Fourier); (Inst. Univ. de France)

    2009-02-01

    We exploit the decoherence of electrons due to magnetic impurities, studied via weak localization, to resolve a long-standing question concerning the classic Kondo systems of Fe impurities in the noble metals gold and silver: which Kondo-type model yields a realistic description of the relevant multiple bands, spin, and orbital degrees of freedom? Previous studies suggest a fully screened spin S Kondo model, but the value of S remained ambiguous. We perform density functional theory calculations that suggest S=3/2. We also compare previous and new measurements of both the resistivity and decoherence rate in quasi-one-dimensional wires to numerical renormalization group predictions for S=1/2, 1, and 3/2, finding excellent agreement for S=3/2.

  12. Spin relaxation and the Kondo effect in transition metal dichalcogenide monolayers

    Science.gov (United States)

    Rostami, Habib; Moghaddam, Ali G.; Asgari, Reza

    2016-12-01

    We investigate the spin relaxation and Kondo resistivity caused by magnetic impurities in doped transition metal dichalcogenide monolayers. We show that momentum and spin relaxation times, due to the exchange interaction by magnetic impurities, are much longer when the Fermi level is inside the spin-split region of the valence band. In contrast to the spin relaxation, we find that the dependence of Kondo temperature T K on the doping is not strongly affected by the spin-orbit induced splitting, although only one of the spin species are present at each valley. This result, which is obtained using both perturbation theory and the poor man’s scaling methods, originates from the intervalley spin-flip scattering in the spin-split region. We further demonstrate the decline in the conductivity with temperatures close to T K, which can vary with the doping. Our findings reveal the qualitative difference with the Kondo physics in conventional metallic systems and other Dirac materials.

  13. Quantum dots with even number of electrons: kondo effect in a finite magnetic field

    Science.gov (United States)

    Pustilnik; Avishai; Kikoin

    2000-02-21

    We show that the Kondo effect can be induced by an external magnetic field in quantum dots with an even number of electrons. If the Zeeman energy B is close to the single-particle level spacing Delta in the dot, the scattering of the conduction electrons from the dot is dominated by an anisotropic exchange interaction. A Kondo resonance then occurs despite the fact that B exceeds by far the Kondo temperature T(K). As a result, at low temperatures T

  14. Kondo effects in a triangular triple quantum dot II: ground-state properties for deformed configurations

    Science.gov (United States)

    Oguri, Akira; Amaha, Shinichi; Nisikawa, Yunori; Hewson, A. C.; Tarucha, Seigo; Numata, Takahide

    2010-03-01

    We study transport through a triangular triple quantum dot (TTQD) connected to two noninteracting leads, using the numerical renormalization group. The system has been theoretically revealed to show a variety of Kondo effects depending on the electron filling of the triangle [1]. For instance, the SU(4) Kondo effect takes place at three-electron filling, and a two-stage Kondo screening of a high-spin S=1 Nagaoka state takes place at four-electron filling. Because of the enhanced freedom in the configurations, however, the large parameter space of the TTQD still has not been fully explored, especially for large deformations. We report the effects of the inhomogeneity in the inter-dot couplings and the level positions in a wide region of the filling. [1] T. Numata, Y. Nisikawa, A. Oguri, and A. C. Hewson: PRB 80, 155330 (2009).

  15. Instability of Non-Fermi Liquid Behavior in the Two-Channel Kondo Model

    Institute of Scientific and Technical Information of China (English)

    YUAN Qing-Shan; CHEN Hong; ZHANG Yu-Mei

    2001-01-01

    The effects of interchannel scattering of conduction electrons by the impu rity and repulsion of conduction electrons at the impurity site on the two-channel Kondo model are simultaneously considered in this paper.It is shown that these two perturbations will substantially modify the usual local non-Fermi liquid behavior of the two-channel Kondo model.With bosonization and unitary transformations we find that the system can be transformed into a single channel Kondo model with anisotropy between longitudinal and transverse exchange couplings.Whatever for originally antiferromagnetic or ferromagnetic isotropic coupling,the system always flows to strong-coupling limit,which exhibits local Fermi liquid behavior at low temperatures.

  16. Prediction of femtosecond oscillations in the transient current of a quantum dot in the Kondo regime

    KAUST Repository

    Goker, A.

    2010-10-11

    We invoke the time-dependent noncrossing approximation in order to study the effects of the density of states of gold contacts on the instantaneous conductance of a single electron transistor which is abruptly moved into the Kondo regime by means of a gate voltage. For an asymmetrically coupled system, we observe that the instantaneous conductance in the Kondo time scale exhibits beating with distinct frequencies, which are proportional to the separation between the Fermi level and the sharp features in the density of states of gold. Increasing the ambient temperature or bias quenches the amplitude of the oscillations. We attribute the oscillations to interference between the emerging Kondo resonance and van-Hove singularities in the density of state. In addition, we propose an experimental realization of this model.

  17. Zero-temperature magnetic transition in an easy-axis Kondo lattice model.

    Science.gov (United States)

    Zhu, Jian-Xin; Kirchner, Stefan; Bulla, Ralf; Si, Qimiao

    2007-11-30

    We address the quantum transition of a spin-1/2 antiferromagnetic Kondo lattice model with an easy-axis anisotropy using the extended dynamical mean field theory. We derive results in real frequency by using the bosonic numerical renormalization group (BNRG) method and compare them with quantum Monte Carlo results in Matsubara frequency. The BNRG results show a logarithmic divergence in the critical local spin susceptibility, signaling a destruction of Kondo screening. The T=0 transition is consistent with being second order. The BNRG results also display some subtle features; we identify their origin and suggest means for further microscopic studies.

  18. Nonequilibrium Transport through a Kondo-dot in a Magnetic Field

    DEFF Research Database (Denmark)

    Wölfle, Peter; Rosch, Achim; Paaske, Jens

    2002-01-01

    Electron transport through a quantum-dot in the Coulomb blockade regime is modeled by a Kondo-type hamiltonian describing spin-dependent tunneling and exchange interaction with the local spin. We consider the regime of large transport voltage V and magnetic field B with max(V, B) » Tk, the Kondo ...... to be generalized to allow for frequency dependent coupling functions. We simplify the full RG equations in the spirit of poor man’s scaling and calculate M and G in leading order of 1/ln[(V, B)/T k]....

  19. Zero-Temperature Magnetic Transition in an Easy-Axis Kondo Lattice Model

    Science.gov (United States)

    Zhu, Jian-Xin; Kirchner, Stefan; Bulla, Ralf; Si, Qimiao

    2007-11-01

    We address the quantum transition of a spin-1/2 antiferromagnetic Kondo lattice model with an easy-axis anisotropy using the extended dynamical mean field theory. We derive results in real frequency by using the bosonic numerical renormalization group (BNRG) method and compare them with quantum Monte Carlo results in Matsubara frequency. The BNRG results show a logarithmic divergence in the critical local spin susceptibility, signaling a destruction of Kondo screening. The T=0 transition is consistent with being second order. The BNRG results also display some subtle features; we identify their origin and suggest means for further microscopic studies.

  20. Temperature-invariant photoelectron spectra in cerium heavy-fermion compounds: Inconsistencies with the Kondo model

    Energy Technology Data Exchange (ETDEWEB)

    Joyce, J.J.; Arko, A.J.; Lawrence, J.; Canfield, P.C.; Fisk, Z.; Bartlett, R.J.; Thompson, J.D. (Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States))

    1992-01-13

    4{ital f} levels in Ce heavy-fermion compounds are examined using resonant photoemission. We find the following inconsistencies with the predictions of the Kondo model: (a) All temperature dependence can be accounted for simply by phonon broadening and the Fermi function; (b) the spectral weights of the features near {ital E}{sub {ital F}} do not scale with {ital T}{sub {ital K}}; and (c) the line shape of the feature previously identified as the Kondo resonance is Lorentzian and about an order of magnitude broader than predictions. Instrument resolution is not a limiting factor.

  1. Nonequilibrium Transport through a Kondo-dot in a Magnetic Field

    DEFF Research Database (Denmark)

    Wölfle, Peter; Rosch, Achim; Paaske, Jens;

    2002-01-01

    Electron transport through a quantum-dot in the Coulomb blockade regime is modeled by a Kondo-type hamiltonian describing spin-dependent tunneling and exchange interaction with the local spin. We consider the regime of large transport voltage V and magnetic field B with max(V, B) » Tk, the Kondo...... temperature, and show that a renormalized perturbation theory can be formulated describing the local magnetization M and the differential conductance G quantitatively. Based on the structure of leading logarithmic corrections in bare perturbation theory we argue that the perturbative renormalization group has...

  2. Kondo effect in transport through Aharonov-Bohm and Aharonov-Casher interferometers

    Science.gov (United States)

    Lobos, A. M.; Aligia, A. A.

    2009-10-01

    We derive the extension of the Hubbard model to include Rashba spin-orbit coupling that correctly describes Aharonov-Bohm and Aharonov-Casher phases in a ring under applied magnetic and electric fields. When the ring is connected to conducting leads, we develop a formalism that is able to describe both, Kondo and interference effects. We find that in the Kondo regime, the spin-orbit coupling reduces strongly the conductance from the unitary limit. This effect in combination with the magnetic flux, can be used to produce spin polarized carriers.

  3. Kondo effect in transport through Aharonov-Bohm and Aharonov-Casher interferometers

    Energy Technology Data Exchange (ETDEWEB)

    Lobos, A.M. [DPMC-MaNEP, University of Geneva, 24 Quai Ernest Ansermet, CH-1211 Geneva 4 (Switzerland); Aligia, A.A., E-mail: aligia@cab.cnea.gov.a [Centro Atomico Bariloche and Instituto Balseiro, Comision Nacional de Energia Atomica, 8400 Bariloche (Argentina)

    2009-10-15

    We derive the extension of the Hubbard model to include Rashba spin-orbit coupling that correctly describes Aharonov-Bohm and Aharonov-Casher phases in a ring under applied magnetic and electric fields. When the ring is connected to conducting leads, we develop a formalism that is able to describe both, Kondo and interference effects. We find that in the Kondo regime, the spin-orbit coupling reduces strongly the conductance from the unitary limit. This effect in combination with the magnetic flux, can be used to produce spin polarized carriers.

  4. Exact results for the Kondo screening cloud of two helical liquids.

    Science.gov (United States)

    Posske, Thore; Liu, Chao-Xing; Budich, Jan Carl; Trauzettel, Björn

    2013-01-04

    We analyze the screening of a magnetic quantum dot with spin 1/2 coupled to two helical liquids. Interestingly, we find two qualitatively different sets of Toulouse points, i.e., nontrivial parameters for which we can solve the two channel Kondo model exactly. This enables us to calculate the temperature and voltage dependent Kondo screening cloud, which develops oscillations for an applied spin voltage μ(s). Such a spin voltage can be conveniently applied by a charge bias in a four-terminal helical liquid setup.

  5. A Theoretic Approach to SU(4) Kondo Effect in Carbon Nanotube Quantum Dots

    Institute of Scientific and Technical Information of China (English)

    ZHU Rui

    2006-01-01

    We propose a mean Geld approach to the transport properties of carbon nanotube quantum dots. Quantum interaction between spin and orbital pseudo-spin degrees of freedom results in an SU(4) Kondo effect at low temperatures. By calculating the chemical potentials and the tunnelling strengths, and hence the spectral functions for different coupling constants and applied magnetic fields, we find that this exotic Kondo effect manifests as a four-peak splitting in the non-linear conductance when an axial magnetic field is applied.

  6. Mapping spin distributions in electron acceptor molecules adsorbed on nanostructured graphene by the Kondo effect

    Science.gov (United States)

    Garnica, Manuela; Calleja, Fabián; Vázquez de Parga, Amadeo L.; Miranda, Rodolfo

    2014-12-01

    Electron acceptor molecules adsorbed on nanostructured graphene grown on Ru(0001) were investigated by low temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS). Our experiments reveal a considerable charge transfer from the substrate to the single molecules leading to the partial occupation of the LUMO of the neutral molecules. The nanostructured graphene modulates the hybridization between the transferred unpaired electron and the ruthenium conduction electrons leading to the appearance of a Kondo effect. Spatially resolved LT-STS allows the high resolution mapping of the spin distribution of the charge transferred and a characteristic inelastic Kondo features associated to specific vibrational modes.

  7. Simple Superconducting "Permanent" Electromagnet

    Science.gov (United States)

    Israelson, Ulf E.; Strayer, Donald M.

    1992-01-01

    Proposed short tube of high-temperature-superconducting material like YBa2Cu3O7 acts as strong electromagnet that flows as long as magnetic field remains below critical value and temperature of cylinder maintained sufficiently below superconducting-transition temperature. Design exploits maximally anisotropy of high-temperature-superconducting material.

  8. Basic principle of superconductivity

    OpenAIRE

    De Cao, Tian

    2007-01-01

    The basic principle of superconductivity is suggested in this paper. There have been two vital wrong suggestions on the basic principle, one is the relation between superconductivity and the Bose-Einstein condensation (BEC), and another is the relation between superconductivity and pseudogap.

  9. Spin-sensitive interference due to Majorana state on the interface between normal and superconducting leads

    Science.gov (United States)

    Barański, J.; Kobiałka, A.; Domański, T.

    2017-02-01

    We investigate the subgap spectrum and transport properties of the quantum dot on the interface between the metallic and superconducting leads and additionally side-coupled to the edge of the topological superconducting (TS) chain, hosting the Majorana quasiparticle. Due to the chiral nature of the Majorana states only one spin component of the quantum dot electrons (say \\uparrow ) is directly affected, however the proximity induced on-dot pairing transmits its influence on the opposite spin as well. We investigate the unique interferometric patterns driven by the Majorana quasiparticle that are different for each spin component. We also address the spin-sensitive interplay with the Kondo effect manifested at the same zero-energy and we come to the conclusion that quantum interferometry can unambiguously identify the Majorana quasiparticle.

  10. Superconductivity in Medicine

    Science.gov (United States)

    Alonso, Jose R.; Antaya, Timothy A.

    2012-01-01

    Superconductivity is playing an increasingly important role in advanced medical technologies. Compact superconducting cyclotrons are emerging as powerful tools for external beam therapy with protons and carbon ions, and offer advantages of cost and size reduction in isotope production as well. Superconducting magnets in isocentric gantries reduce their size and weight to practical proportions. In diagnostic imaging, superconducting magnets have been crucial for the successful clinical implementation of magnetic resonance imaging. This article introduces each of those areas and describes the role which superconductivity is playing in them.

  11. Enhanced superconductivity of fullerenes

    Energy Technology Data Exchange (ETDEWEB)

    Washington, II, Aaron L.; Teprovich, Joseph A.; Zidan, Ragaiy

    2017-06-20

    Methods for enhancing characteristics of superconductive fullerenes and devices incorporating the fullerenes are disclosed. Enhancements can include increase in the critical transition temperature at a constant magnetic field; the existence of a superconducting hysteresis over a changing magnetic field; a decrease in the stabilizing magnetic field required for the onset of superconductivity; and/or an increase in the stability of superconductivity over a large magnetic field. The enhancements can be brought about by transmitting electromagnetic radiation to the superconductive fullerene such that the electromagnetic radiation impinges on the fullerene with an energy that is greater than the band gap of the fullerene.

  12. Superconducting microfabricated ion traps

    CERN Document Server

    Wang, Shannon X; Labaziewicz, Jaroslaw; Dauler, Eric; Berggren, Karl; Chuang, Isaac L

    2010-01-01

    We fabricate superconducting ion traps with niobium and niobium nitride and trap single 88Sr ions at cryogenic temperatures. The superconducting transition is verified and characterized by measuring the resistance and critical current using a 4-wire measurement on the trap structure, and observing change in the rf reflection. The lowest observed heating rate is 2.1(3) quanta/sec at 800 kHz at 6 K and shows no significant change across the superconducting transition, suggesting that anomalous heating is primarily caused by noise sources on the surface. This demonstration of superconducting ion traps opens up possibilities for integrating trapped ions and molecular ions with superconducting devices.

  13. Superconducting material development

    Science.gov (United States)

    1987-09-01

    A superconducting compound was developed that showed a transition to a zero-resistance state at 65 C, or 338 K. The superconducting material, which is an oxide based on strontium, barium, yttrium, and copper, continued in the zero-resistance state similar to superconductivity for 10 days at room temperature in the air. It was also noted that measurements of the material allowed it to observe a nonlinear characteristic curve between current and voltage at 65 C, which is another indication of superconductivity. The research results of the laboratory experiment with the superconducting material will be published in the August edition of the Japanese Journal of Applied Physics.

  14. Protective link for superconducting coil

    Science.gov (United States)

    Umans, Stephen D.

    2009-12-08

    A superconducting coil system includes a superconducting coil and a protective link of superconducting material coupled to the superconducting coil. A rotating machine includes first and second coils and a protective link of superconducting material. The second coil is operable to rotate with respect to the first coil. One of the first and second coils is a superconducting coil. The protective link is coupled to the superconducting coil.

  15. Supercoducting property of Zr-Cu-Al-Ni-Nb alloys

    Science.gov (United States)

    Okai, D.; Motoyama, G.; Kimura, H.; Inoue, A.

    The superconducting property of Zr55Cu(30-X)Al10Ni5NbX alloys prepared by arc melting and liquid quenching methods was investigated by magnetic susceptibility measurements. The crystalline alloys with X = 0∼25 at.% prepared by arc melting method exhibited superconductivity with maximum Tc,on of 10.1 K. The alloys (X = 10∼23 at.%) with crystalline particles embedded in an amorphous structure, which were fabricated by melt spinning method, showed superconductivity with Tc,on of less than 4.0 K. The superconducting property of the Zr-Cu-Al-Ni-Nb alloys was attributed to superconducting phases of Zr2Cu, Zr2Ni, Zr65Al10Nb25 and Zr-Nb contained in the Zr-Cu-Al-Ni-Nb alloys. The melt-spun Zr55Cu(30-X)Al10Ni5NbX (X = 10∼20 at.%) alloys exhibited glass transition at 718∼743 K and were found to be superconducting metallic glasses.

  16. Superconductivity in transition metals.

    Science.gov (United States)

    Slocombe, Daniel R; Kuznetsov, Vladimir L; Grochala, Wojciech; Williams, Robert J P; Edwards, Peter P

    2015-03-13

    A qualitative account of the occurrence and magnitude of superconductivity in the transition metals is presented, with a primary emphasis on elements of the first row. Correlations of the important parameters of the Bardeen-Cooper-Schrieffer theory of superconductivity are highlighted with respect to the number of d-shell electrons per atom of the transition elements. The relation between the systematics of superconductivity in the transition metals and the periodic table high-lights the importance of short-range or chemical bonding on the remarkable natural phenomenon of superconductivity in the chemical elements. A relationship between superconductivity and lattice instability appears naturally as a balance and competition between localized covalent bonding and so-called broken covalency, which favours d-electron delocalization and superconductivity. In this manner, the systematics of superconductivity and various other physical properties of the transition elements are related and unified.

  17. Prototype Superconducting Quadrupole for the ISR low-beta insertion

    CERN Multimedia

    CERN PhotoLab

    1977-01-01

    The picture shows the cold mass of the Quadrupole with its outer aluminium alloy rings pre-compressing the superconducting coils via the magnetic yoke split in 4 parts.The end of the inner vacuum chamber,supporting the 6-pole correction windings, can also be seen as well as the electrical connections. See also photos 7702690X, 7702307.

  18. A 3D printed superconducting aluminium microwave cavity

    Science.gov (United States)

    Creedon, Daniel L.; Goryachev, Maxim; Kostylev, Nikita; Sercombe, Timothy B.; Tobar, Michael E.

    2016-07-01

    3D printing of plastics, ceramics, and metals has existed for several decades and has revolutionized many areas of manufacturing and science. Printing of metals, in particular, has found a number of applications in fields as diverse as customized medical implants, jet engine bearings, and rapid prototyping in the automotive industry. Although many techniques are used for 3D printing metals, they commonly rely on computer controlled melting or sintering of a metal alloy powder using a laser or electron beam. The mechanical properties of parts produced in such a way have been well studied, but little attention has been paid to their electrical properties. Here we show that a microwave cavity (resonant frequencies 9.9 and 11.2 GHz) 3D printed using an Al-12Si alloy exhibits superconductivity when cooled below the critical temperature of aluminium (1.2 K), with a performance comparable with the common 6061 alloy of aluminium. Superconducting cavities find application in numerous areas of physics, from particle accelerators to cavity quantum electrodynamics experiments. The result is achieved even with a very large concentration of non-superconducting silicon in the alloy of 12.18%, compared with Al-6061, which has between 0.4% and 0.8%. Our results may pave the way for the possibility of 3D printing superconducting cavity configurations that are otherwise impossible to machine.

  19. Spin-orbit interaction and asymmetry effects on Kondo ridges at finite magnetic field

    DEFF Research Database (Denmark)

    Grap, Stephan; Andergassen, Sabine; Paaske, Jens

    2011-01-01

    ridges, which are robust against SOI as time-reversal symmetry is preserved. As a result of the crossing of a spin-up and a spin-down level at vanishing SOI, two additional Kondo plateaus appear at finite B. They are not protected by symmetry and rapidly vanish if the SOI is turned on. Left...

  20. Environment-modulated Kondo phenomena in FePc/Au(111) adsorption systems

    Science.gov (United States)

    Wang, Yu; Zheng, Xiao; Yang, Jinlong

    2016-03-01

    Recent scanning tunneling microscopy experiments on electron transport through iron(II) phthalocyanine (FePc) molecules adsorbed on the Au(111) surface have revealed that the measured Kondo conductance signature depends strongly on the specific adsorption site. To understand the physical origin of experimental observations, particularly the variation of Kondo features with the molecular adsorption site, we employ a combined density functional theory (DFT) and hierarchical equations of motion (HEOM) approach to investigate the electronic structure and Kondo correlation in FePc/Au(111) composite systems. The calculation results indicate that, for the on-top adsorption configuration, the two degenerate spin-unpaired dπ orbitals on the Fe center are coupled indirectly through substrate band states, leading to the Fano-like antiresonance line shape in the d I /d V spectra, while for the bridge adsorption configuration, the environment-induced couplings are largely suppressed because of the two different spin-unpaired d orbitals. Therefore, our work suggests that the environment-induced coupling as an essential physical factor could greatly influence the Fano-Kondo features in magnetic molecule/metal composites, and the crucial role of local orbital degeneracy and symmetry is discovered. These findings provide important insights into the electron correlation effects in complex solid-state systems. The usefulness and practicality of the combined DFT+HEOM method is also highlighted.

  1. Spin relaxation through Kondo scattering in Cu/Py lateral spin valves

    Science.gov (United States)

    Batley, J. T.; Rosaond, M. C.; Ali, M.; Linfield, E. H.; Burnell, G.; Hickey, B. J.

    Within non-magnetic metals it is reasonable to expect the Elliot-Yafet mechanism to govern spin-relaxation and thus the temperature dependence of the spin diffusion length might be inversely proportional to resistivity. However, in lateral spin valves, measurements have found that at low temperatures the spin diffusion length unexpectedly decreases. We have fabricated lateral spin valves from Cu with different concentrations of magnetic impurities. Through temperature dependent charge and spin transport measurements we present clear evidence linking the presence of the Kondo effect within Cu to the suppression of the spin diffusion length below 30 K. We have calculated the spin-relaxation rate and isolated the contribution from magnetic impurities. At very low temperatures electron-electron interactions play a more prominent role in the Kondo effect. Well below the Kondo temperature a strong-coupling regime exists, where the moments become screened and the magnetic dephasing rate is reduced. We also investigate the effect of this low temperature regime (>1 K) on a pure spin current. This work shows the dominant role of Kondo scattering, even in low concentrations of order 1 ppm, within pure spin transport.

  2. Strong spin Seebeck effect in Kondo T-shaped double quantum dots

    Science.gov (United States)

    Wójcik, K. P.; Weymann, I.

    2017-02-01

    We investigate, taking a theoretical approach, the thermoelectric and spin thermoelectric properties of a T-shaped double quantum dot strongly coupled to two ferromagnetic leads, focusing on the transport regime in which the system exhibits the two-stage Kondo effect. We study the dependence of the (spin) Seebeck coefficient, the corresponding power factor and the figure of merit on temperature, leads’ spin polarization and dot level position. We show that the thermal conductance fulfills a modified Wiedemann-Franz law, also in the regime of suppression of subsequent stages of the Kondo effect by the exchange field resulting from the presence of ferromagnets. Moreover, we demonstrate that the spin thermopower is enhanced at temperatures corresponding to the second stage of Kondo screening. Very interestingly, the spin-thermoelectric response of the system is found to be highly sensitive to the spin polarization of the leads. In some cases spin polarization of the order of 1% is sufficient for a strong spin Seebeck effect to occur. This is explained as a consequence of the interplay between the two-stage Kondo effect and the exchange field induced in the double quantum dot. Due to the possibility of tuning the exchange field by the choice of gate voltage, the spin thermopower may also be tuned to be maximal for desired spin polarization of the leads. All calculations are performed with the aid of the numerical renormalization group technique.

  3. Spin-flux phase in the Kondo lattice model with classical localized spins

    NARCIS (Netherlands)

    Agterberg, DF; Yunoki, S

    2000-01-01

    We provide numerical evidence that a spin-flux phase exists as a ground state of the Kondo lattice model with classical local spins on a square lattice. This state manifests itself as a double-e magnetic order in the classical spins with spin density at both (0, pi) and (pi ,0) and further exhibits

  4. Kondo quantum dot coupled to ferromagnetic leads: Numerical renormalization group study

    Science.gov (United States)

    Sindel, M.; Borda, L.; Martinek, J.; Bulla, R.; König, J.; Schön, G.; Maekawa, S.; von Delft, J.

    2007-07-01

    We systematically study the influence of ferromagnetic leads on the Kondo resonance in a quantum dot tuned to the local moment regime. We employ Wilson’s numerical renormalization group method, extended to handle leads with a spin asymmetric density of states, to identify the effects of (i) a finite spin polarization in the leads (at the Fermi surface), (ii) a Stoner splitting in the bands (governed by the band edges), and (iii) an arbitrary shape of the lead density of states. For a generic lead density of states, the quantum dot favors being occupied by a particular spin species due to exchange interaction with ferromagnetic leads, leading to suppression and splitting of the Kondo resonance. The application of a magnetic field can compensate this asymmetry, restoring the Kondo effect. We study both the gate voltage dependence (for a fixed band structure in the leads) and the spin polarization dependence (for fixed gate voltage) of this compensation field for various types of bands. Interestingly, we find that the full recovery of the Kondo resonance of a quantum dot in the presence of leads with an energy-dependent density of states is possible not only by an appropriately tuned external magnetic field but also via an appropriately tuned gate voltage. For flat bands, simple formulas for the splitting of the local level as a function of the spin polarization and gate voltage are given.

  5. Universality and scaling in a charge two-channel Kondo device

    NARCIS (Netherlands)

    Mitchell, Andrew K.; Landau, L. A.; Fritz, L.; Sela, E.

    2016-01-01

    We study a charge two-channel Kondo model, demonstrating that recent experiments [Iftikhar et al, Nature 526, 233 (2015)] realize an essentially perfect quantum simulation -- not just of its universal physics, but also nonuniversal effects away from the scaling limit. Numerical renormalization group

  6. Kondo effect and impurity band conduction in Co:TiO2 magnetic semiconductor

    NARCIS (Netherlands)

    Ramaneti, R.; Lodder, J.C.; Jansen, R.

    2007-01-01

    The nature of charge carriers and their interaction with local magnetic moments in an oxide magnetic semiconductor is established. For cobalt-doped anatase TiO2 films, we demonstrate conduction in a metallic donor-impurity band. Moreover, we observe a clear signature of the Kondo effect in electrica

  7. Numerical renormalization group studies of the partially brogen SU(3) Kondo model

    Energy Technology Data Exchange (ETDEWEB)

    Fuh Chuo, Evaristus

    2013-04-15

    The two-channel Kondo (2CK) effect with its exotic ground state properties has remained difficult to realize in physical systems. At low energies, a quantum impurity with orbital degree of freedom, like a proton bound in an interstitial lattice space, comprises a 3-level system with a unique ground state and (at least) doubly degenerate rotational excitations with excitation energy {Delta}{sub 0}. When immersed in a metal, electronic angular momentum scattering induces transitions between any two of these levels (couplings J), while the electron spin is conserved. We show by extensive numerical renormalization group (NRG) calculations that without fi ne-tuning of parameters this system exhibits a 2CK fixed point, due to Kondo correlations in the excited-state doublet whose degeneracy is stabilized by the host lattice parity, while the channel symmetry (electron spin) is guaranteed by time reversal symmetry. We find a pronounced plateau in the entropy at S(T{sub K}>{Delta}{sub 0})=k{sub B} ln 3, and the 2CK ground state value, S(0)=k{sub B} ln {radical}(2). This indicates a downward renormalization of the doublet below the non-interacting ground state, thus realizing the 2CK fixed point, in agreement with earlier conjectures. We mapped out the phase diagram of the model in the J-{Delta}{sub 0} plane. The Kondo temperature T{sub K} shows non-monotonic J-dependence, characteristic for 2CK systems. Beside the two-channel Kondo effect of the model, we also study the single-channel version, which is realized by applying a strong magnetic fi eld to the conduction band electrons so that their degeneracy is lifted and consequently having only one kind of electrons scattering off the impurity. This single-channel case is easier to analyze since the Hilbert space is not as large as that of the 2CK. We equally find a downward renormalization of the excited state energy by the Kondo correlations in the SU(2) doublet

  8. Search for pressure-induced superconductivity in CeFeAsO and CeFePO iron pnictides

    Energy Technology Data Exchange (ETDEWEB)

    Zocco, D. A. [University of California, San Diego; Baumbach, R. E. [University of California, San Diego; Hamlin, J. J. [University of California, San Diego; Janoschek, M. [University of California, San Diego; Lum, I. K. [University of California, San Diego; McGuire, Michael A [ORNL; Safa-Sefat, Athena [ORNL; Sales, Brian C [ORNL; Jin, Rongying [ORNL; Mandrus, David [ORNL; Jeffries, J. R. [Lawrence Livermore National Laboratory (LLNL); Weir, S. T. [Lawrence Livermore National Laboratory (LLNL); Vohra, Y. K. [University of Alabama, Birmingham; Maple, M. B. [University of California, San Diego

    2011-01-01

    The CeFeAsO and CeFePO iron pnictide compounds were studied via electrical transport measurements under high pressure. In CeFeAsO polycrystals, the magnetic phases involving the Fe and Ce ions coexist for hydrostatically applied pressures up to 15 GPa, and with no signs of pressure-induced superconductivity up to 50 GPa for the less hydrostatic pressure techniques. For the CeFePO single crystals, pressure further stabilizes the Kondo screening of the Ce 4f-electron magnetic moments.

  9. Genome sequence of Frateuria aurantia type strain (Kondo 67(T)), a xanthomonade isolated from Lilium auratium Lindl.

    Energy Technology Data Exchange (ETDEWEB)

    Anderson, Iain [U.S. Department of Energy, Joint Genome Institute; Teshima, Hazuki [Los Alamos National Laboratory (LANL); Nolan, Matt [U.S. Department of Energy, Joint Genome Institute; Lapidus, Alla L. [U.S. Department of Energy, Joint Genome Institute; Tice, Hope [U.S. Department of Energy, Joint Genome Institute; Glavina Del Rio, Tijana [U.S. Department of Energy, Joint Genome Institute; Cheng, Jan-Fang [U.S. Department of Energy, Joint Genome Institute; Han, Cliff [Los Alamos National Laboratory (LANL); Tapia, Roxanne [Los Alamos National Laboratory (LANL); Goodwin, Lynne A. [Los Alamos National Laboratory (LANL); Pitluck, Sam [U.S. Department of Energy, Joint Genome Institute; Liolios, Konstantinos [U.S. Department of Energy, Joint Genome Institute; Mavromatis, K [U.S. Department of Energy, Joint Genome Institute; Pagani, Ioanna [U.S. Department of Energy, Joint Genome Institute; Ivanova, N [U.S. Department of Energy, Joint Genome Institute; Mikhailova, Natalia [U.S. Department of Energy, Joint Genome Institute; Pati, Amrita [U.S. Department of Energy, Joint Genome Institute; Chen, Amy [U.S. Department of Energy, Joint Genome Institute; Palaniappan, Krishna [U.S. Department of Energy, Joint Genome Institute; Land, Miriam L [ORNL; Rohde, Manfred [HZI - Helmholtz Centre for Infection Research, Braunschweig, Germany; Lang, Elke [DSMZ - German Collection of Microorganisms and Cell Cultures GmbH, Braunschweig, Germany; Detter, J. Chris [U.S. Department of Energy, Joint Genome Institute; Goker, Markus [DSMZ - German Collection of Microorganisms and Cell Cultures GmbH, Braunschweig, Germany; Woyke, Tanja [U.S. Department of Energy, Joint Genome Institute; Bristow, James [U.S. Department of Energy, Joint Genome Institute; Eisen, Jonathan [U.S. Department of Energy, Joint Genome Institute; Markowitz, Victor [U.S. Department of Energy, Joint Genome Institute; Hugenholtz, Philip [U.S. Department of Energy, Joint Genome Institute; Kyrpides, Nikos C [U.S. Department of Energy, Joint Genome Institute; Klenk, Hans-Peter [DSMZ - German Collection of Microorganisms and Cell Cultures GmbH, Braunschweig, Germany

    2013-01-01

    rateuria aurantia (ex Kondo and Ameyama 1958) Swings et al. 1980 is a member of the bispecific genus Frateuria in the family Xanthomonadaceae, which is already heavily targeted for non-type strain genome sequencing. Strain Kondo 67(T) was initially (1958) identified as a member of 'Acetobacter aurantius', a name that was not considered for the approved list. Kondo 67(T) was therefore later designated as the type strain of the newly proposed acetogenic species Frateuria aurantia. The strain is of interest because of its triterpenoids (hopane family). F. aurantia Kondo 67(T) is the first member of the genus Frateura whose genome sequence has been deciphered, and here we describe the features of this organism, together with the complete genome sequence and annotation. The 3,603,458-bp long chromosome with its 3,200 protein-coding and 88 RNA genes is a part of the Genomic Encyclopedia of Bacteria and Archaea project.

  10. Frontiers in Superconducting Materials

    CERN Document Server

    Narlikar, Anant V

    2005-01-01

    Frontiers in Superconducting Materials gives a state-of-the-art report of the most important topics of the current research in superconductive materials and related phenomena. It comprises 30 chapters written by renowned international experts in the field. It is of central interest to researchers and specialists in Physics and Materials Science, both in academic and industrial research, as well as advanced students. It also addresses electronic and electrical engineers. Even non-specialists interested in superconductivity might find some useful answers.

  11. Superconducting energy recovery linacs

    Science.gov (United States)

    Ben-Zvi, Ilan

    2016-10-01

    High-average-power and high-brightness electron beams from a combination of laser photocathode electron guns and a superconducting energy recovery linac (ERL) is an emerging accelerator science with applications in ERL light sources, high repetition rate free electron lasers , electron cooling, electron ion colliders and more. This paper reviews the accelerator physics issues of superconducting ERLs, discusses major subsystems and provides a few examples of superconducting ERLs.

  12. High-Temperature Superconductivity

    Science.gov (United States)

    Tanaka, Shoji

    2006-12-01

    A general review on high-temperature superconductivity was made. After prehistoric view and the process of discovery were stated, the special features of high-temperature superconductors were explained from the materials side and the physical properties side. The present status on applications of high-temperature superconductors were explained on superconducting tapes, electric power cables, magnets for maglev trains, electric motors, superconducting quantum interference device (SQUID) and single flux quantum (SFQ) devices and circuits.

  13. Theoretical study of Kondo effect and related transport properties in topological insulator systems

    Science.gov (United States)

    Xin, Xianhao

    This thesis presents theoretical studies of the Kondo effect and related transport properties in topological insulator systems. The thesis mainly covers two topics: the Kondo effect on the surface of a bulk topological insulator material and the Kondo effect in a topological insulator quantum dot. Other relevant background knowledge and theoretical techniques for the transport calculations are also discussed in the thesis. For the first topic, we investigate the role of magnetic impurities in the transport properties of a three-dimensional topological insulator's surface states. First, we combine the second-order perturbation theory and the Boltzmann transport equation to calculate the magnetically induced resistivity in a topological insulator. Our result shows a non-perturbative behavior when conduction electrons and magnetic impurities' spins are antiferromagnetically coupled. The surface resistivity is found to display an oscillatory rather than isotropic behavior compared to the conventional Kondo effect. Both the variational method and renormalization group (RG) analysis are employed to compute the Kondo temperature, through which the non-perturbative behavior is confirmed. We further study the RG flows and demonstrate that the RG trajectories eventually flow into a strong coupling regime if the coupling is antiferromagnetic. This work is motivated by the recent transport experiments, in which surface currents were detected in topological insulators. The calculation is shown to be qualitatively consistent with the low temperature dip observed in the experimental R - T curve, and it might be one of the possible origins of the dip. For the second main topic, we investigate theoretically the nonequilibrium transport properties of a topological insulator quantum dot (TIQD) in the Coulomb blockade and Kondo regime. An Anderson impurity model is applied to a TIQD system coupled to two external leads, and we show that the model realizes the spin-orbital Kondo effect

  14. Fundamentals of Superconducting Nanoelectronics

    CERN Document Server

    Sidorenko, Anatolie

    2011-01-01

    This book demonstrates how the new phenomena in superconductivity on the nanometer scale (FFLO state, triplet superconductivity, Crossed Andreev Reflection, synchronized generation etc.) serve as the basis for the invention and development of novel nanoelectronic devices and systems. It demonstrates how rather complex ideas and theoretical models, like odd-pairing, non-uniform superconducting state, pi-shift etc., adequately describe the processes in real superconducting nanostructues and novel devices based on them. The book is useful for a broad audience of readers, researchers, engineers, P

  15. Superconductive imaging surface magnetometer

    Science.gov (United States)

    Overton, Jr., William C.; van Hulsteyn, David B.; Flynn, Edward R.

    1991-01-01

    An improved pick-up coil system for use with Superconducting Quantum Interference Device gradiometers and magnetometers involving the use of superconducting plates near conventional pick-up coil arrangements to provide imaging of nearby dipole sources and to deflect environmental magnetic noise away from the pick-up coils. This allows the practice of gradiometry and magnetometry in magnetically unshielded environments. One embodiment uses a hemispherically shaped superconducting plate with interior pick-up coils, allowing brain wave measurements to be made on human patients. another embodiment using flat superconducting plates could be used in non-destructive evaluation of materials.

  16. Superconducting optical modulator

    Science.gov (United States)

    Bunt, Patricia S.; Ference, Thomas G.; Puzey, Kenneth A.; Tanner, David B.; Tache, Nacira; Varhue, Walter J.

    2000-12-01

    An optical modulator based on the physical properties of high temperature superconductors has been fabricated and tested. The modulator was constructed form a film of Yttrium Barium Copper Oxide (YBCO) grown on undoped silicon with a buffer layer of Yttria Stabilized Zirconia. Standard lithographic procedures were used to pattern the superconducting film into a micro bridge. Optical modulation was achieved by passing IR light through the composite structure normal to the micro bridge and switching the superconducting film in the bridge region between the superconducting and non-superconducting states. In the superconducting state, IR light reflects from the superconducting film surface. When a critical current is passed through the micro bridge, it causes the film in this region to switch to the non-superconducting state allowing IR light to pass through it. Superconducting materials have the potential to switch between these two states at speeds up to 1 picosecond using electrical current. Presently, fiber optic transmission capacity is limited by the rate at which optical data can be modulated. The superconducting modulator, when combined with other components, may have the potential to increase the transmission capacity of fiber optic lines.

  17. Basic Study of Superconductive Actuator

    OpenAIRE

    涌井, 和也; 荻原, 宏康

    2000-01-01

    There are two kinds of electromagnetic propulsion ships : a superconductive electromagnetic propulsion ship and a superconductive electricity propulsion ship. A superconductive electromagnetic propulsion ship uses the electromagnetic force (Lorenz force) by the interaction between a magnetic field and a electric current. On the other hand, a superconductive electricity propulsion ship uses screws driven by a superconductive motor. A superconductive propulsion ship technique has the merits of ...

  18. Sample of superconducting wiring  (Niobium Titanium)

    CERN Multimedia

    About NbTi cable: The cable consists of 36 strands of superconducting wire, each strand has a diameter of 0.825 mm and houses 6300 superconducting filaments of niobium-titanium (Nb-Ti, a superconducting alloy). Each filament has a diameter of about 0.006 mm, i.e. 10 times smaller than a typical human hair. The filaments are embedded in a high-purity copper matrix.  Copper is a normal conducting material. The filaments are in the superconductive state when the temperature is below about -263ºC (10.15 K). When the filaments leave the superconductive state, the copper acts as conductor transports the electrical current. Each strand of The NbTi cable (at superconducting state) has a current density of up to above 2000 A/mm2 at 9 T and -271ºC (2.15 K). A cable transport a current of about 13000 A at 10 T and -271ºC (2.15 K). About LHC superconducting wiring: The high magnetic fields needed for the LHC can only be reached using superconductors. At very low temperatures, superconductors have no electrical resis...

  19. Pressure-tuned quantum criticality in the antiferromagnetic Kondo semimetal CeNi2-δAs2.

    Science.gov (United States)

    Luo, Yongkang; Ronning, F; Wakeham, N; Lu, Xin; Park, Tuson; Xu, Z-A; Thompson, J D

    2015-11-03

    The easily tuned balance among competing interactions in Kondo-lattice metals allows access to a zero-temperature, continuous transition between magnetically ordered and disordered phases, a quantum-critical point (QCP). Indeed, these highly correlated electron materials are prototypes for discovering and exploring quantum-critical states. Theoretical models proposed to account for the strange thermodynamic and electrical transport properties that emerge around the QCP of a Kondo lattice assume the presence of an indefinitely large number of itinerant charge carriers. Here, we report a systematic transport and thermodynamic investigation of the Kondo-lattice system CeNi2-δAs2 (δ ≈ 0.28) as its antiferromagnetic order is tuned by pressure and magnetic field to zero-temperature boundaries. These experiments show that the very small but finite carrier density of ~0.032 E-/formular unit in CeNi2-δAs2 leads to unexpected transport signatures of quantum criticality and the delayed development of a fully coherent Kondo-lattice state with decreasing temperature. The small carrier density and associated semimetallicity of this Kondo-lattice material favor an unconventional, local-moment type of quantum criticality and raises the specter of the Nozières exhaustion idea that an insufficient number of conduction-electron spins to separately screen local moments requires collective Kondo screening.

  20. Pressure-tuned quantum criticality in the antiferromagnetic Kondo semimetal CeNi2−δAs2

    Science.gov (United States)

    Luo, Yongkang; Ronning, F.; Wakeham, N.; Lu, Xin; Park, Tuson; Xu, Z.-A.; Thompson, J. D.

    2015-01-01

    The easily tuned balance among competing interactions in Kondo-lattice metals allows access to a zero-temperature, continuous transition between magnetically ordered and disordered phases, a quantum-critical point (QCP). Indeed, these highly correlated electron materials are prototypes for discovering and exploring quantum-critical states. Theoretical models proposed to account for the strange thermodynamic and electrical transport properties that emerge around the QCP of a Kondo lattice assume the presence of an indefinitely large number of itinerant charge carriers. Here, we report a systematic transport and thermodynamic investigation of the Kondo-lattice system CeNi2−δAs2 (δ ≈ 0.28) as its antiferromagnetic order is tuned by pressure and magnetic field to zero-temperature boundaries. These experiments show that the very small but finite carrier density of ∼0.032 e−/formular unit in CeNi2−δAs2 leads to unexpected transport signatures of quantum criticality and the delayed development of a fully coherent Kondo-lattice state with decreasing temperature. The small carrier density and associated semimetallicity of this Kondo-lattice material favor an unconventional, local-moment type of quantum criticality and raises the specter of the Nozières exhaustion idea that an insufficient number of conduction-electron spins to separately screen local moments requires collective Kondo screening. PMID:26483465

  1. Superconducting state parameters of ternary metallic glasses

    Indian Academy of Sciences (India)

    Aditya M Vora

    2011-12-01

    The well-known empty core (EMC) model potential of Ashcroft was used to study the theoretical investigation of the superconducting state parameters (SSP) viz. electron–phonon coupling strength , Coulomb pseudopotential $\\mu^{\\ast}$, transition temperature $T_{C}$, isotope effect exponent and effective interaction strength $N_{O}V$ of some ternary metallic glasses. Most recent local field correction function due to Sarkar et al is used to study the screening influence on the aforesaid properties. Quadratic $T_{C}$ equations have been proposed and found successful. Also, the present findings are found to be in qualitative agreement with other such earlier reported data, which confirms the superconducting phase in the ternary superconductors. The pseudo-alloy-atom (PAA) model was applied for the first time instead of Vegard’s law.

  2. Two-Channel Kondo Physics due to As Vacancies in the Layered Compound ZrAs1.58 Se0.39

    Science.gov (United States)

    Cichorek, T.; Bochenek, L.; Schmidt, M.; Czulucki, A.; Auffermann, G.; Kniep, R.; Niewa, R.; Steglich, F.; Kirchner, S.

    2016-09-01

    We address the origin of the magnetic-field-independent -|A |T1 /2 term observed in the low-temperature resistivity of several As-based metallic systems of the PbFCl structure type. For the layered compound ZrAs1.58 Se0.39 , we show that vacancies in the square nets of As give rise to the low-temperature transport anomaly over a wide temperature regime of almost two decades in temperature. This low-temperature behavior is in line with the nonmagnetic version of the two-channel Kondo effect, whose origin we ascribe to a dynamic Jahn-Teller effect operating at the vacancy-carrying As layer with a C4 symmetry. The pair-breaking nature of the dynamical defects in the square nets of As explains the low superconducting transition temperature Tc≈0.14 K of ZrAs1.58 Se0.39 compared to the free-of-vacancies homologue ZrP1.54 S0.46 (Tc≈3.7 K ). Our findings should be relevant to a wide class of metals with disordered pnictogen layers.

  3. Magnetic Characteristics of Two Metglas Alloys

    Science.gov (United States)

    Blatnik, Marie; SNS nEDM Collaboration

    2016-09-01

    Magnetic shielding is gaining greater significance as precision experiments become more sensitive, such as for the Spallation Neutron Source nEDM [neutron electric dipole moment] measurement. Targeting a sensitivity of 10-28 e-cm, the SNS nEDM collaboration minimizes magnetic shield gradients and magnetic noise with a superconducting lead shield and several shield layers that include using a Metglas layer as a primary component. Metglas is a thin ribbon of proprietary engineered alloy that comes in many varieties. One alloy with high (as cast) permeability is Metglas alloy 2705M, which is primarily composed of Cobalt. However, this alloy will activate under neutron radiation and is therefore unsuitable. However, another high-performance Metglas alloy, 2826 MB, contains only trace amounts of Cobalt. A study of the shielding characteristics of the two alloys was performed, paying close attention to field oscillation frequency and magnitude.

  4. Graphene: Carbon's superconducting footprint

    Science.gov (United States)

    Vafek, Oskar

    2012-02-01

    Graphene exhibits many extraordinary properties, but superconductivity isn't one of them. Two theoretical studies suggest that by decorating the surface of graphene with the right species of dopant atoms, or by using ionic liquid gating, superconductivity could yet be induced.

  5. Superconducting cavities for LEP

    CERN Multimedia

    1983-01-01

    Above: a 350 MHz superconducting accelerating cavity in niobium of the type envisaged for accelerating electrons and positrons in later phases of LEP. Below: a small 1 GHz cavity used for investigating the surface problems of superconducting niobium. Albert Insomby stays on the right. See Annual Report 1983 p. 51.

  6. Academic training: Applied superconductivity

    CERN Multimedia

    2007-01-01

    LECTURE SERIES 17, 18, 19 January from 11.00 to 12.00 hrs Council Room, Bldg 503 Applied Superconductivity : Theory, superconducting Materials and applications E. PALMIERI/INFN, Padova, Italy When hearing about persistent currents recirculating for several years in a superconducting loop without any appreciable decay, one realizes that we are dealing with a phenomenon which in nature is the closest known to the perpetual motion. Zero resistivity and perfect diamagnetism in Mercury at 4.2 K, the breakthrough during 75 years of several hundreds of superconducting materials, the revolution of the "liquid Nitrogen superconductivity"; the discovery of still a binary compound becoming superconducting at 40 K and the subsequent re-exploration of the already known superconducting materials: Nature discloses drop by drop its intimate secrets and nobody can exclude that the last final surprise must still come. After an overview of phenomenology and basic theory of superconductivity, the lectures for this a...

  7. Magnetic ordering and non-Fermi-liquid behavior in the multichannel Kondo-lattice model

    Science.gov (United States)

    Irkhin, Valentin Yu.

    2016-05-01

    Scaling equations for the Kondo lattice in the paramagnetic and magnetically ordered phases are derived to next-leading order with account of spin dynamics. The results are applied to describe various mechanisms of the non-Fermi-liquid (NFL) behavior in the multichannel Kondo-lattice model where a fixed point occurs in the weak-coupling region. The corresponding temperature dependences of electronic and magnetic properties are discussed. The model describes naturally formation of a magnetic state with soft boson mode and small moment value. An important role of Van Hove singularities in the magnon spectral function is demonstrated. The results are rather sensitive to the type of magnetic ordering and space dimensionality, the conditions for NFL behavior being more favorable in the antiferromagnetic and 2D cases.

  8. Magnetic Quantum Phase Transitions of a Kondo Lattice Model with Ising Anisotropy

    Science.gov (United States)

    Zhu, Jian-Xin; Kirchner, Stefan; Si, Qimiao; Grempel, Daniel R.; Bulla, Ralf

    2006-03-01

    We study the Kondo Lattice model with Ising anisotropy, within an extended dynamical mean field theory (EDMFT) in the presence or absence of antiferromagnetic ordering. The EDMFT equations are studied using both the Quantum Monte Carlo (QMC) and Numerical Renormalization Group (NRG) methods. We discuss the overall magnetic phase diagram by studying the evolution, as a function of the ratio of the RKKY interaction and bare Kondo scale, of the local spin susceptibility, magnetic order parameter, and the effective Curie constant of a nominally paramagnetic solution with a finite moment. We show that, within the numerical accuracy, the quantum magnetic transition is second order. The local quantum critical aspect of the transition is also discussed.

  9. Excitons in topological Kondo insulators: Theory of thermodynamic and transport anomalies in SmB_{6}.

    Science.gov (United States)

    Knolle, Johannes; Cooper, Nigel R

    2017-03-03

    Kondo insulating materials lie outside the usual dichotomy of weakly versus correlated-band versus Mott-insulators. They are metallic at high temperatures but resemble band insulators at low temperatures because of the opening of an interaction-induced band gap. The first discovered Kondo insulator (KI) SmB_{6} has been predicted to form a topological KI (TKI). However, since its discovery thermodynamic and transport anomalies have been observed that have defied a theoretical explanation. Enigmatic signatures of collective modes inside the charge gap are seen in specific heat, thermal transport, and quantum oscillation experiments in strong magnetic fields. Here, we show that TKIs are susceptible to the formation of excitons and magnetoexcitons. These charge neutral composite particles can account for long-standing anomalies in SmB_{6}.

  10. Magnetic field effects on the DOS of a Kondo quantum dot coupled to LL leads

    Science.gov (United States)

    Yang, Kai-Hua; Qin, Chang-Dong; Wang, Huai-Yu; Wang, Xu

    2017-01-01

    We investigate the joint effects of a magnetic field and electron-electron interaction on the tunneling density of states (DOS) of a quantum dot coupled to the Luttinger liquid leads in the Kondo regime. We find that for intralead electron interaction, the DOS develops two peaks deviated from the origin by the Zeeman energy. With the increase of the intralead interaction, a phase transition occurs. For moderately strong interaction, the Zeeman splitting peaks develop into two dips. The splitting of the Kondo peak and dip is not symmetric with respect to up and down spins. In the limit of strong interaction the Zeeman splitting behavior disappears and there appears a power-law scaling behavior.

  11. Jahn-Teller / Kondo Interplay in a Three-Terminal Quantum Dot

    Science.gov (United States)

    Toonen, R. C.; Qin, H.; Huettel, A. K.; Goswami, S.; van der Weide, D. W.; Eberl, K.; Blick, R. H.

    2006-03-01

    The Jahn-Teller effect is the spontaneous geometric distortion of a nonlinear molecular entity. The Kondo effect, an expression of asymptotic freedom, arises from the hybridization between localized states of a magnetic impurity and the itinerant states of its environment. The interplay of these two phenomena has attracted the attention of theorists studying the growth and interactions of heavy-fermion systems. Because of the technical difficulties associated with probing isolated impurities in bulk materials, this composite effect has remained experimentally unexplored. We have investigated co-tunneling transport phenomena in a three-terminal quantum dot with triangular symmetry. Our measurements of anomalous spectral signatures reveal interplay between the Jahn-Teller and Kondo effects. This discovery suggests a means of controlling the correlation of spatially separated pairs of entangled electrons (EPR pairs)---a necessary condition for the physical realization of a quantum computer (DiVincenzo's 7th requirement).

  12. Temperature dependence of the Kondo resonance and its satellites in CeCu2Si2.

    Science.gov (United States)

    Reinert, F; Ehm, D; Schmidt, S; Nicolay, G; Hüfner, S; Kroha, J; Trovarelli, O; Geibel, C

    2001-09-03

    We present high-resolution photoemission spectroscopy studies on the Kondo resonance of the strongly correlated Ce system CeCu2Si2. By exploiting the thermal broadening of the Fermi edge we analyze position, spectral weight, and temperature dependence of the low-energy 4f spectral features, whose major weight lies above the Fermi level E(F). We also present theoretical predictions based on the single-impurity Anderson model using an extended noncrossing approximation, including all spin-orbit and crystal field splittings of the 4f states. The excellent agreement between theory and experiment provides strong evidence that the spectral properties of CeCu2Si2 can be described by single-impurity Kondo physics down to T approximately 5 K.

  13. Spin-spin correlations between two Kondo impurities coupled to an open Hubbard chain

    Science.gov (United States)

    Tiegel, A. C.; Dargel, P. E.; Hallberg, K. A.; Frahm, H.; Pruschke, T.

    2013-02-01

    In order to study the interplay between Kondo and Ruderman-Kittel-Kasuya-Yosida interaction, we calculate the spin-spin correlation functions between two Kondo impurities coupled to different sites of a half-filled open Hubbard chain. Using the density-matrix renormalization group (DMRG), we reexamine the exponents for the power-law decay of the correlation function between the two impurity spins as a function of the antiferromagnetic coupling J, the Hubbard interaction U, and the distance R between the impurities. The exponents for finite systems obtained in this work deviate from previously published DMRG calculations. We furthermore show that the long-distance behavior of the exponents is the same for impurities coupled to the bulk or to both ends of the chain. We note that a universal exponent for the asymptotic behavior can not be extracted from these finite-size systems with open boundary conditions.

  14. 4f heavy femion photoelectron spectra do not exhibit the Kondo scale

    Energy Technology Data Exchange (ETDEWEB)

    Arko, A.J.; Joyce, J.J.; Andrews, A.B.; Blyth, I.R.; Barlett, R.J.; Fisk, Z. [Los Alamos National Laboratory, NM (United States); Canfield, P.C.; Olson, C.G.; Benning, P.J. [Iowa Sate Univ., Ames, IA (United States); Poirier, D.M.; Weaver, J.H. [Univ. of Minnesota, Minneapolis, MN (United States); Riseborough, P.S. [Polytechnic Univ., Brookyln, NY (United States)

    1994-12-31

    It has been the authors contention for some time that the Single Impurity Anderson Model (SIAM), as extended by Gunnarsson and Schonhammer (GS), or the non-crossing approximation (NCA), does not correctly describe the 4f photoelectron spectra of heavy fermions. Recently they have concentrated on Yb heavy fermions since in these materials the Kondo resonance (KR) is fully occupied and thus accessible via photoemission. In particular, they have repeatedly pointed out that the width, position, spectral weight, lineshape, and temperature dependence of the features assumed to be the KR and its sidebands, are nearly independent of the Kondo temperature, T{sub K}, while at the same time bearing a striking resemblance to the simple 4f core level spectra of pure Yb metal, or of Lu isostructural Lu compounds. It is important to resolve these issues in view of the fundamental nature of the problem.

  15. Spiral magnetic phases on the Kondo Lattice Model: A Hartree-Fock approach

    Science.gov (United States)

    Costa, N. C.; Lima, J. P.; dos Santos, Raimundo R.

    2017-02-01

    We study the Kondo Lattice Model (KLM) on a square lattice through a Hartree-Fock approximation in which the local spins are treated semi-classically, in the sense that their average values are modulated by a magnetic wavevector Q while they couple with the conduction electrons through fermion operators. In this way, we obtain a ground state phase diagram in which spiral magnetic phases (in which the wavevector depends on the coupling constants and on the density) interpolate between the low-density ferromagnetic phase and the antiferromagnetic phase at half filling; within small regions of the phase diagram commensurate magnetic phases can coexist with Kondo screening. We have also obtained 'Doniach-like' diagrams, showing the effect of temperature on the ground state phases, and established that for some ranges of the model parameters (the exchange coupling and conduction electron density) the magnetic wavevector changes with temperature, either continuously or abruptly (e.g., from spiral to ferromagnetic).

  16. Interplay between the Kondo effect and the Ruderman-Kittel-Kasuya-Yosida interaction.

    Science.gov (United States)

    Prüser, Henning; Dargel, Piet E; Bouhassoune, Mohammed; Ulbrich, Rainer G; Pruschke, Thomas; Lounis, Samir; Wenderoth, Martin

    2014-11-11

    The interplay between the Ruderman-Kittel-Kasuya-Yosida interaction and the Kondo effect is expected to provide the driving force for the emergence of many phenomena in strongly correlated electron materials. Two magnetic impurities in a metal are the smallest possible system containing all these ingredients and define a bottom-up approach towards a long-term understanding of concentrated/dense systems. Here we report on the experimental and theoretical investigation of iron dimers buried below a Cu(100) surface by means of low-temperature scanning tunnelling spectroscopy combined with density functional theory and numerical renormalization group calculations. The Kondo effect, in particular the width of the Abrikosov-Suhl resonance, is strongly altered or even suppressed due to magnetic coupling between the impurities. It oscillates as a function of dimer separation revealing that it is related to indirect exchange interactions mediated by the conduction electrons.

  17. Unusual phonon softening in the Kondo lattice CeCu 2

    Science.gov (United States)

    Loewenhaupt, Michael; Witte, Ulrike; Kramp, Sirko; Braden, Markus; Svoboda, Pavel

    2002-03-01

    CeCu2 is a Kondo lattice with antiferromagnetic order below 3.5 K and a Kondo temperature of about 6 K. Earlier neutron scattering experiments lead to the assumption of a coupling between a crystal field transition and some phonons with energies around 14 meV. With the results from our newly performed inelastic neutron measurements on a single crystal we found these assumptions confirmed. We observed an unusual softening of certain phonons with increasing temperature. This softening of up to 15% is much stronger than the normal thermal behavior of phonons. Additionally, the line width of these phonons is increasing. At the same time the magnetic response is strongly broadened by the coupling to the phonons. The findings for CeCu2 are discussed in relation with similar observation of a coupling between electronic and lattice degrees of freedom in CeAl2 and YbPO4.

  18. Ionic Hamiltonians for transition metal atoms: effective exchange coupling and Kondo temperature

    Science.gov (United States)

    Flores, F.; Goldberg, E. C.

    2017-02-01

    An ionic Hamiltonian for describing the interaction between a metal and a d-shell transition metal atom having an orbital singlet state is introduced and its properties analyzed using the Schrieffer-Wolf transformation (exchange coupling) and the poor man’s scaling method (Kondo temperature). We find that the effective exchange coupling between the metal and the atom has an antiferromagnetic or a ferromagnetic interaction depending on the kind of atomic fluctuations, either S\\to S-1/2 or S\\to S+1/2 , associated with the metal-atom coupling. We present a general scheme for all those processes and calculate, for the antiferromagnetic interaction, the corresponding Kondo-temperature.

  19. Superconductivity in carbon nanomaterials

    Science.gov (United States)

    Dlugon, Katarzyna

    The purpose of this thesis is to explain the phenomenon of superconductivity in carbon nanomaterials such as graphene, fullerenes and carbon nanotubes. In the introductory chapter, there is a description of superconductivity and how it occurs at critical temperature (Tc) that is characteristic and different to every superconducting material. The discovery of superconductivity in mercury in 1911 by Dutch physicist Heike Kamerlingh Onnes is also mentioned. Different types of superconductors, type I and type II, low and high temperatures superconductors, as well as the BCS theory that was developed in 1957 by Bardeen, Cooper, and Schrieffer, are also described in detail. The BCS theory explains how Cooper's pairs are formed and how they are responsible for the superconducting properties of many materials. The following chapters explain superconductivity in doped fullerenes, graphene and carbon nanotubes, respectively. There is a thorough explanation followed by many examples of different types of carbon nanomaterials in which small changes in chemical structure cause significant changes in superconducting properties. The goal of this research was not only to take into consideration well known carbon based superconductors but also to search for the newest available materials such as the fullerene nanowhiskers discovered quite recently. There is also a presentation of fairly new ideas about inducing superconductivity in a monolayer of graphene which is more challenging than inducing superconductivity in graphite by simply intercalating metal atoms between its graphene sheets. An effort has been taken to look for any available information about carbon nanomaterials that have the potential to superconduct at room temperature, mainly because discovery of such materials would be a real revolution in the modern world, although no such materials have been discovered yet.

  20. Two Types of Pressure Dependence of Residual Resistivity in Doped Kondo Insulators

    Institute of Scientific and Technical Information of China (English)

    YUAN Yi-Zhe; LI Zheng-Zhong; XIAO Ming-Wen; XU Wang; XU Xiao-Hua

    2004-01-01

    The pressure dependence of the residual resistivity of the doped electron-type and hole-type Kondo insulators (KIs) are calculated within the framework of the slave-boson mean-field theory and the coherent potential approximation. It is shown that as the pressure increases, the resistivity increases and decreases for the dilute doping electron-type and hole-type KIs, respectively. These results are qualitatively in agreement with the experiments.

  1. Ground-state phase diagram of the Kondo lattice model on triangular-to-kagome lattices

    OpenAIRE

    Akagi, Yutaka; Motome, Yukitoshi

    2012-01-01

    We investigate the ground-state phase diagram of the Kondo lattice model with classical localized spins on triangular-to-kagome lattices by using a variational calculation. We identify the parameter regions where a four-sublattice noncoplanar order is stable with a finite spin scalar chirality while changing the lattice structure from triangular to kagome continuously. Although the noncoplanar spin states appear in a wide range of parameters, the spin configurations on the kagome network beco...

  2. Enhancement of Superconductivity of Lanthanum and Yttrium Sesquicarbide

    Science.gov (United States)

    Krupka, M. C.; Giorgi, A. L.; Krikorian, N. H.; Szklarz, E. G.

    1972-06-22

    A method of enhancing the superconductivity of body-centered cubic lanthanum and yttrium sesquicarbide through formation of the sesquicarbides from ternary alloys of novel composition (N/sub x/M/sub 1-x/)C/sub z/, where N is yttrium or lanthanum, M is thorium, any of the Group IV and VI transition metals, or gold, germanium or silicon, and z is approximately 1.2 to 1.6. These ternary sesquicarbides have superconducting transition temperatures as high as 17.0/sup 0/K.

  3. Spin fluctuations in the anisotropic Kondo insulator CeRu4 Sn6

    Science.gov (United States)

    Fuhrman, Wesley T.; Haenel, J.; Rodriguez, J.; Paschen, S.; Broholm, C. L.

    We report and model anisotropic quasi-elastic magnetic neutron scattering from single crystalline CeRu4Sn6. For T ~ 2 K the magnetic neutron scattering is broad in momentum (Q) with a persistent 1 / ℏω spectrum throughout the Brillouin zone. This indicates a lack of spatial coherence and no characteristic energy scale beyond the 0.2 meV resolution of the measurement. We find the Q-dependence of the scattering can be modeled by a Kondo-Heisenberg Hamiltonian that describes residual carriers and incompletely compensated localized electrons. These findings support the interpretation of tetragonal CeRu4Sn6 as an anisotropic or nodal Kondo insulator, markedly different from typical cubic Kondo insulators. We further discuss potential topological implications. Work at IQM was supported by the U.S. Department of Energy, office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-FG02-08ER4654. W.T.F. thanks the ARCS foundation and Lockheed Martin for additional support.

  4. Anisotropy induced Kondo splitting in a mechanically stretched molecular junction: A first-principles based study

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Xiaoli; Hou, Dong, E-mail: houdong@ustc.edu.cn [Hefei National Laboratory for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Zheng, Xiao, E-mail: xz58@ustc.edu.cn [Hefei National Laboratory for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Guizhou Provincial Key Laboratory of Computational Nano-Material Science, Institute of Applied Physics, Guizhou Normal College, Guiyang, Guizhou 550018 (China); Yan, YiJing [Hefei National Laboratory for Physical Sciences at the Microscale, iChEM (Collaborative Innovation Center of Chemistry for Energy Materials), University of Science and Technology of China, Hefei, Anhui 230026 (China); Department of Chemistry, Hong Kong University of Science and Technology, Hong Kong (China)

    2016-01-21

    The magnetic anisotropy and Kondo phenomena in a mechanically stretched magnetic molecular junction are investigated by combining the density functional theory (DFT) and hierarchical equations of motion (HEOM) approach. The system is comprised of a magnetic complex Co(tpy–SH){sub 2} sandwiched between adjacent gold electrodes, which is mechanically stretched in experiments done by Parks et al. [Science 328, 1370 (2010)]. The electronic structure and mechanical property of the stretched system are investigated via the DFT calculations. The HEOM approach is then employed to characterize the Kondo resonance features, based on the Anderson impurity model parameterized from the DFT results. It is confirmed that the ground state prefers the S = 1 local spin state. The structural properties, the magnetic anisotropy, and corresponding Kondo peak splitting in the axial stretching process are systematically evaluated. The results reveal that the strong electron correlations and the local magnetic properties of the molecule magnet are very sensitive to structural distortion. This work demonstrates that the combined DFT+HEOM approach could be useful in understanding and designing mechanically controlled molecular junctions.

  5. Kondo physics of the Anderson impurity model by distributional exact diagonalization

    Science.gov (United States)

    Motahari, S.; Requist, R.; Jacob, D.

    2016-12-01

    The distributional exact diagonalization (DED) scheme is applied to the description of Kondo physics in the Anderson impurity model. DED maps Anderson's problem of an interacting impurity level coupled to an infinite bath onto an ensemble of finite Anderson models, each of which can be solved by exact diagonalization. An approximation to the self-energy of the original infinite model is then obtained from the ensemble-averaged self-energy. Using Friedel's sum rule, we show that the particle number constraint, a central ingredient of the DED scheme, ultimately imposes Fermi liquid behavior on the ensemble-averaged self-energy, and thus is essential for the description of Kondo physics within DED. Using the numerical renormalization group (NRG) method as a benchmark, we show that DED yields excellent spectra, both inside and outside the Kondo regime for a moderate number of bath sites. Only for very strong correlations (U /Γ ≫10 ) does the number of bath sites needed to achieve good quantitative agreement become too large to be computationally feasible.

  6. Magnetic-field-induced mixed-level Kondo effect in two-level systems

    Energy Technology Data Exchange (ETDEWEB)

    Wong, Arturo; Ngo, Anh T.; Ulloa, Sergio E.

    2016-10-17

    We consider a two-orbital impurity system with intra-and interlevel Coulomb repulsion that is coupled to a single conduction channel. This situation can generically occur in multilevel quantum dots or in systems of coupled quantum dots. For finite energy spacing between spin-degenerate orbitals, an in-plane magnetic field drives the system from a local-singlet ground state to a "mixed-level" Kondo regime, where the Zeeman-split levels are degenerate for opposite-spin states. We use the numerical renormalization group approach to fully characterize this mixed-level Kondo state and discuss its properties in terms of the applied Zeeman field, temperature, and system parameters. Under suitable conditions, the total spectral function is shown to develop a Fermi-level resonance, so that the linear conductance of the system peaks at a finite Zeeman field while it decreases as a function of temperature. These features, as well as the local moment and entropy contribution of the impurity system, are commensurate with Kondo physics, which can be studied in suitably tuned quantum dot systems.

  7. Photoemission and the electronic properties of heavy fermions -- limitations of the Kondo model

    Energy Technology Data Exchange (ETDEWEB)

    Joyce, J.J.; Arko, A.J.; Andrews, A.B. [and others

    1993-09-01

    The electronic properties of Yb-based heavy fermions have been investigated by means of high resolution synchrotron radiation photoemission and compared with predictions of the Kondo model. The Yb heavy fermion photoemission spectra show massive disagreement with the Kondo model predictions (as calculated within the Gunnarsson-Schonhammer computational method). Moreover, the Yb heavy fermion photoemission spectra give very strong indications of core-like characteristics and compare favorable to purely divalent Yb metal and core-like Lu 4f levels. The heavy fermions YbCu{sub 2}Si{sub 2}, YbAgCu{sub 4} and YbAl{sub 3} were measured and shown to have lineshapes much broader and deeper in binding energy than predicted by the Kondo model. The lineshape of the bulk component of the 4f emission for these three heavy fermion materials was compared with that from Yb metal and the Lu 4f levels in LuAl{sub 3}, the heavy fermion materials show no substantive spectroscopic differences from simple 4f levels observed in Yb metal and LuAl{sub 3}. Also, the variation with temperature of the 4f fineshape was measured for Yb metal and clearly demonstrates that phonon broadening plays a major role in 4f level lineshape analysis and must be accounted for before considerations of correlated electron resonance effects are presumed to be at work.

  8. Photoemission and the electronic properties of heavy fermions - limitations of the Kondo model

    Energy Technology Data Exchange (ETDEWEB)

    Joyce, J.J. [Los Alamos Nat. Lab., NM (United States); Arko, A.J. [Los Alamos Nat. Lab., NM (United States); Andrews, A.B. [Los Alamos Nat. Lab., NM (United States); Blyth, R.I.R. [Los Alamos Nat. Lab., NM (United States); Bartlett, R.J. [Los Alamos Nat. Lab., NM (United States); Thompson, J.D. [Los Alamos Nat. Lab., NM (United States); Fisk, Z. [Los Alamos Nat. Lab., NM (United States); Riseborough, P.S. [Polytechnic Institute of New York, Department of Physics, Brooklyn, NY 11201 (United States); Canfield, P.C. [Ames Laboratory USDOE, Ames, IA 50011 (United States); Olson, C.G. [Ames Laboratory USDOE, Ames, IA 50011 (United States); Benning, P.J. [Ames Laboratory USDOE, Ames, IA 50011 (United States)

    1995-03-01

    The electronic properties of Yb-based heavy fermions have been investigated by means of high resolution synchrotron radiation photoemission and compared with predictions of the Kondo model. The Yb heavy fermion photoemission spectra show significant disagreement with the Kondo model predictions (as calculated within the Gunnarsson-Schonhammer computational method). Moreover, the Yb heavy fermion photoemission spectra give strong indications of core-like characteristics and compare favorably to purely divalent Yb metal and core-like Lu 4f levels. The heavy fermions YbCu{sub 2}Si{sub 2}, YbAgCu{sub 4} and YbAl{sub 3} were measured and shown to have lineshapes much broader and deeper in binding energy than predicted by the Kondo model. The lineshape of the bulk component of the 4f emission for these three heavy fermion materials was compared with that from Yb metal and the Lu 4f levels in LuAl{sub 3}. The heavy fermion materials show no substantive spectroscopic differences from 4f levels observed in Yb metal and LuAl{sub 3}. Also, the variation with temperature of the 4f lineshape was measured for Yb metal and clearly demonstrates that phonon broadening plays a major role in 4f level lineshape analysis and must be accounted for before considerations of correlated electron resonance effects are presumed to be at work. ((orig.)).

  9. Kondo screening in two-dimensional p -type transition-metal dichalcogenides

    Science.gov (United States)

    Phillips, Michael; Aji, Vivek

    2017-02-01

    Systems with strong spin-orbit coupling support a number of new phases of matter and novel phenomena. This work focuses on the interplay of spin-orbit coupling and interactions in yielding correlated phenomena in two-dimensional transition-metal dichalcogenides. In particular we explore the physics of Kondo screening resulting from the lack of centrosymmetry, large spin splitting, and spin valley locking in hole-doped systems. The key ingredients are (i) valley-dependent spin-momentum locking perpendicular to the two-dimensional crystal, (ii) a single nondegenerate Fermi surface per valley, and (iii) nontrivial Berry curvature associated with the low-energy bands. The resulting Kondo resonance has a finite-triplet component and nontrivial momentum space structure which facilitates new approaches to both probing and manipulating the correlated state. Using a variational wave function and the numerical renormalization group approaches we study the nature of the Kondo resonance both in the absence and presence of circularly polarized light. The latter induces an imbalance in the population of the two valleys leading to novel magnetic phenomena in the correlated state.

  10. Superconductivity in aromatic hydrocarbons

    Energy Technology Data Exchange (ETDEWEB)

    Kubozono, Yoshihiro, E-mail: kubozono@cc.okayama-u.ac.jp [Research Laboratory for Surface Science, Okayama University, Okayama 700-8530 (Japan); Research Center of New Functional Materials for Energy Production, Storage and Transport, Okayama University, Okayama 700-8530 (Japan); Japan Science and Technology Agency, ACT-C, Kawaguchi 332-0012 (Japan); Goto, Hidenori; Jabuchi, Taihei [Research Laboratory for Surface Science, Okayama University, Okayama 700-8530 (Japan); Yokoya, Takayoshi [Research Laboratory for Surface Science, Okayama University, Okayama 700-8530 (Japan); Research Center of New Functional Materials for Energy Production, Storage and Transport, Okayama University, Okayama 700-8530 (Japan); Kambe, Takashi [Department of Physics, Okayama University, Okayama 700-8530 (Japan); Sakai, Yusuke; Izumi, Masanari; Zheng, Lu; Hamao, Shino; Nguyen, Huyen L.T. [Research Laboratory for Surface Science, Okayama University, Okayama 700-8530 (Japan); Sakata, Masafumi; Kagayama, Tomoko; Shimizu, Katsuya [Center of Science and Technology under Extreme Conditions, Osaka University, Osaka 560-8531 (Japan)

    2015-07-15

    Highlights: • Aromatic superconductor is one of core research subjects in superconductivity. Superconductivity is observed in certain metal-doped aromatic hydrocarbons. Some serious problems to be solved exist for future advancement of the research. This article shows the present status of aromatic superconductors. - Abstract: ‘Aromatic hydrocarbon’ implies an organic molecule that satisfies the (4n + 2) π-electron rule and consists of benzene rings. Doping solid aromatic hydrocarbons with metals provides the superconductivity. The first discovery of such superconductivity was made for K-doped picene (K{sub x}picene, five benzene rings). Its superconducting transition temperatures (T{sub c}’s) were 7 and 18 K. Recently, we found a new superconducting K{sub x}picene phase with a T{sub c} as high as 14 K, so we now know that K{sub x}picene possesses multiple superconducting phases. Besides K{sub x}picene, we discovered new superconductors such as Rb{sub x}picene and Ca{sub x}picene. A most serious problem is that the shielding fraction is ⩽15% for K{sub x}picene and Rb{sub x}picene, and it is often ∼1% for other superconductors. Such low shielding fractions have made it difficult to determine the crystal structures of superconducting phases. Nevertheless, many research groups have expended a great deal of effort to make high quality hydrocarbon superconductors in the five years since the discovery of hydrocarbon superconductivity. At the present stage, superconductivity is observed in certain metal-doped aromatic hydrocarbons (picene, phenanthrene and dibenzopentacene), but the shielding fraction remains stubbornly low. The highest priority research area is to prepare aromatic superconductors with a high superconducting volume-fraction. Despite these difficulties, aromatic superconductivity is still a core research target and presents interesting and potentially breakthrough challenges, such as the positive pressure dependence of T{sub c} that is clearly

  11. Signature of coexistence of superconductivity and ferromagnetism in two-dimensional NbSe2 triggered by surface molecular adsorption

    Science.gov (United States)

    Zhu, Xiaojiao; Guo, Yuqiao; Cheng, Hao; Dai, Jun; An, Xingda; Zhao, Jiyin; Tian, Kangzhen; Wei, Shiqiang; Cheng Zeng, Xiao; Wu, Changzheng; Xie, Yi

    2016-04-01

    Ferromagnetism is usually deemed incompatible with superconductivity. Consequently, the coexistence of superconductivity and ferromagnetism is usually observed only in elegantly designed multi-ingredient structures in which the two competing electronic states originate from separate structural components. Here we report the use of surface molecular adsorption to induce ferromagnetism in two-dimensional superconducting NbSe2, representing the freestanding case of the coexistence of superconductivity and ferromagnetism in one two-dimensional nanomaterial. Surface-structural modulation of the ultrathin superconducting NbSe2 by polar reductive hydrazine molecules triggers a slight elongation of the covalent Nb-Se bond, which weakens the covalent interaction and enhances the ionicity of the tetravalent Nb with unpaired electrons, yielding ferromagnetic ordering. The induced ferromagnetic momentum couples with conduction electrons generating unique correlated effects of intrinsic negative magnetoresistance and the Kondo effect. We anticipate that the surface molecular adsorption will be a powerful tool to regulate spin ordering in the two-dimensional paradigm.

  12. Signature of coexistence of superconductivity and ferromagnetism in two-dimensional NbSe2 triggered by surface molecular adsorption.

    Science.gov (United States)

    Zhu, Xiaojiao; Guo, Yuqiao; Cheng, Hao; Dai, Jun; An, Xingda; Zhao, Jiyin; Tian, Kangzhen; Wei, Shiqiang; Cheng Zeng, Xiao; Wu, Changzheng; Xie, Yi

    2016-04-04

    Ferromagnetism is usually deemed incompatible with superconductivity. Consequently, the coexistence of superconductivity and ferromagnetism is usually observed only in elegantly designed multi-ingredient structures in which the two competing electronic states originate from separate structural components. Here we report the use of surface molecular adsorption to induce ferromagnetism in two-dimensional superconducting NbSe2, representing the freestanding case of the coexistence of superconductivity and ferromagnetism in one two-dimensional nanomaterial. Surface-structural modulation of the ultrathin superconducting NbSe2 by polar reductive hydrazine molecules triggers a slight elongation of the covalent Nb-Se bond, which weakens the covalent interaction and enhances the ionicity of the tetravalent Nb with unpaired electrons, yielding ferromagnetic ordering. The induced ferromagnetic momentum couples with conduction electrons generating unique correlated effects of intrinsic negative magnetoresistance and the Kondo effect. We anticipate that the surface molecular adsorption will be a powerful tool to regulate spin ordering in the two-dimensional paradigm.

  13. The superconducting spin valve and triplet superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Garifullin, I.A., E-mail: ilgiz_garifullin@yahoo.com [Zavoisky Physical-Technical Institute, Kazan Scientific Center of Russian Academy of Sciences, 420029 Kazan (Russian Federation); Leksin, P.V.; Garif' yanov, N.N.; Kamashev, A.A. [Zavoisky Physical-Technical Institute, Kazan Scientific Center of Russian Academy of Sciences, 420029 Kazan (Russian Federation); Fominov, Ya.V. [L. D. Landau Institute for Theoretical Physics RAS, 119334 Moscow (Russian Federation); Moscow Institute of Physics and Technology, 141700 Dolgoprudny (Russian Federation); Schumann, J.; Krupskaya, Y.; Kataev, V.; Schmidt, O.G. [Leibniz Institute for Solid State and Materials Research IFW Dresden, D-01171 Dresden (Germany); Büchner, B. [Leibniz Institute for Solid State and Materials Research IFW Dresden, D-01171 Dresden (Germany); Institut für Festkörperphysik, Technische Universität Dresden, D-01062 Dresden (Germany)

    2015-01-01

    A review of our recent results on the spin valve effect is presented. We have used a theoretically proposed spin switch design F1/F2/S comprising a ferromagnetic bilayer (F1/F2) as a ferromagnetic component, and an ordinary superconductor (S) as the second interface component. Based on it we have prepared and studied in detail a set of multilayers CoO{sub x}/Fe1/Cu/Fe2/S (S=In or Pb). In these heterostructures we have realized for the first time a full spin switch effect for the superconducting current, have observed its sign-changing oscillating behavior as a function of the Fe2-layer thickness and finally have obtained direct evidence for the long-range triplet superconductivity arising due to noncollinearity of the magnetizations of the Fe1 and Fe2 layers. - Highlights: • We studied a spin switch design F1/F2/S. • We prepared a set of multilayers CoOx/Fe1/Cu/Fe2/S (S=In or Pb). • The full spin switch effect for the superconducting current was realized. • We observed its oscillating behavior as a function of the Fe2-layer thickness. • We obtained direct evidence for the long-range triplet superconductivity.

  14. Tunneling in superconducting structures

    Science.gov (United States)

    Shukrinov, Yu. M.

    2010-12-01

    Here we review our results on the breakpoint features in the coupled system of IJJ obtained in the framework of the capacitively coupled Josephson junction model with diffusion current. A correspondence between the features in the current voltage characteristics (CVC) and the character of the charge oscillations in superconducting layers is demonstrated. Investigation of the correlations of superconducting currents in neighboring Josephson junctions and the charge correlations in neighboring superconducting layers reproduces the features in the CVC and gives a powerful method for the analysis of the CVC of coupled Josephson junctions. A new method for determination of the dissipation parameter is suggested.

  15. Superconductivity in doped insulators

    Energy Technology Data Exchange (ETDEWEB)

    Emery, V.J. [Brookhaven National Lab., Upton, NY (United States); Kivelson, S.A. [California Univ., Los Angeles, CA (United States). Dept. of Physics

    1995-12-31

    It is shown that many synthetic metals, including high temperature superconductors are ``bad metals``, with such a poor conductivity that the usual meanfield theory of superconductivity breaks down because of anomalously large classical and quantum fluctuations of the phase of the superconducting order parameter. It is argued that the supression of a first order phase transition (phase separation) by the long-range Coulomb interaction leads to high temperature superconductivity accompanied by static or dynamical charge inhomogeneIty. Evidence in support of this picture for high temperature superconductors is described.

  16. Site dependence of the Kondo scale in CePd{sub 1-x}Rh{sub x} evidenced by thermopower

    Energy Technology Data Exchange (ETDEWEB)

    Stockert, Ulrike; Hartmann, Stefanie; Deppe, Micha; Caroca-Canales, Nubia; Geibel, Christoph; Steglich, Frank [Max Planck Institute for Chemical Physics of Solids, Dresden (Germany); Sereni, Julian [Division Bajas Temperaturas, Centro Atomico Bariloche (Argentina)

    2015-07-01

    CePd{sub 1-x}Rh{sub x} undergoes a continuous evolution from ferromagnetic order in CePd to an intermediate-valence (IV) ground state for CeRh. Close to the disappearance of magnetic order at x{sub cr} ∼ 0.87 unusual behavior of the ac susceptibility and the specific heat was observed. It was explained with a broad distribution of local Kondo temperatures T{sub K} from below 2 K to above 50 K due to the disorder introduced by Pd-Rh exchange. The thermopower S is very sensitive to Kondo scattering even for diluted 4f systems. In Ce compounds a large positive maximum in S(T) is usually observed around T{sub K}. We studied S(T) in CePd{sub 1-x}Rh{sub x} in order to evaluate the presence of Kondo scattering and the involved energy scales. Pure CeRh shows typical IV behavior with a large maximum at 220 K and small values at low T. Already 5 % Pd substitution leads to a strong enhancement of the low-T thermopower. Even larger values are found around x{sub cr}, while the high-T maximum shifts only moderately. Our results are in line with the existence of low (local) Kondo scales in the presence of IV behavior at high Rh content x > x{sub cr}. For lower Rh content a decreasing (average) Kondo scale is found.

  17. On the zero-bias anomaly and Kondo physics in quantum point contacts near pinch-off.

    Science.gov (United States)

    Xiang, S; Xiao, S; Fuji, K; Shibuya, K; Endo, T; Yumoto, N; Morimoto, T; Aoki, N; Bird, J P; Ochiai, Y

    2014-03-26

    We investigate the linear and non-linear conductance of quantum point contacts (QPCs), in the region near pinch-off where Kondo physics has previously been connected to the appearance of the 0.7 feature. In studies of seven different QPCs, fabricated in the same high-mobility GaAs/AlGaAs heterojunction, the linear conductance is widely found to show the presence of the 0.7 feature. The differential conductance, on the other hand, does not generally exhibit the zero-bias anomaly (ZBA) that has been proposed to indicate the Kondo effect. Indeed, even in the small subset of QPCs found to exhibit such an anomaly, the linear conductance does not always follow the universal temperature-dependent scaling behavior expected for the Kondo effect. Taken collectively, our observations demonstrate that, unlike the 0.7 feature, the ZBA is not a generic feature of low-temperature QPC conduction. We furthermore conclude that the mere observation of the ZBA alone is insufficient evidence for concluding that Kondo physics is active. While we do not rule out the possibility that the Kondo effect may occur in QPCs, our results appear to indicate that its observation requires a very strict set of conditions to be satisfied. This should be contrasted with the case of the 0.7 feature, which has been apparent since the earliest experimental investigations of QPC transport.

  18. Real-space renormalization group flow in quantum impurity systems: Local moment formation and the Kondo screening cloud

    Science.gov (United States)

    Mitchell, Andrew K.; Becker, Michael; Bulla, Ralf

    2011-09-01

    The existence of a length scale ξK˜1/TK (with TK the Kondo temperature) has long been predicted in quantum impurity systems. At low temperatures T≪TK, the standard interpretation is that a spin-(1)/(2) impurity is screened by a surrounding “Kondo cloud” of spatial extent ξK. We argue that renormalization group (RG) flow between any two fixed points (FPs) results in a characteristic length scale, observed in real space as a crossover between physical behavior typical of each FP. In the simplest example of the Anderson impurity model, three FPs arise, and we show that “free orbital,” “local moment,” and “strong coupling” regions of space can be identified at zero temperature. These regions are separated by two crossover length scales ξLM and ξK, with the latter diverging as the Kondo effect is destroyed on increasing temperature through TK. One implication is that moment formation occurs inside the “Kondo cloud”, while the screening process itself occurs on flowing to the strong coupling FP at distances ˜ξK. Generic aspects of the real-space physics are exemplified by the two-channel Kondo model, where ξK now separates local moment and overscreening clouds.

  19. Prototype Superconducting Quadrupole for the ISR high-luminosity (low beta)insertion:end view.

    CERN Multimedia

    1977-01-01

    In this picture, taken before the insertion of the inner vacuum chamber with inbedded 6-pole superconducting windings, one can see the main components of the magnet structure: (from inside outwards) the superconducting quadrupole coils surronded by glass epoxy bandage rings and stainless steel spacers, the low-carbon steel yoke quadrants and the aluminium alloy shrinking rings. See also photos 7702307, 7702688X, 7702690X.

  20. Superconducting wind turbine generators

    DEFF Research Database (Denmark)

    Abrahamsen, Asger Bech; Mijatovic, Nenad; Seiler, Eugen

    2010-01-01

    , the main challenge of the superconducting direct drive technology is to prove that the reliability is superior to the alternative drive trains based on gearboxes or permanent magnets. A strategy of successive testing of superconducting direct drive trains in real wind turbines of 10 kW, 100 kW, 1 MW and 10...... offshore turbines of 8 and 10 MW have been determined from an up-scaling of an existing 5 MW turbine and the necessary properties of the superconducting drive train are discussed. We have found that the absence of the gear box is the main benefit and the reduced weight and size is secondary. However...... MW generator and it is concluded that the present production capacity of coated conductors must be increased by a factor of 36 by 2020, resulting in a ten times lower price of the tape in order to reach a realistic price level for the superconducting drive train....

  1. Magnetic and superconducting nanowires

    DEFF Research Database (Denmark)

    Piraux, L.; Encinas, A.; Vila, L.

    2005-01-01

    magnetic and superconducting nanowires. Using different approaches entailing measurements on both single wires and arrays, numerous interesting physical properties have been identified in relation to the nanoscopic dimensions of these materials. Finally, various novel applications of the nanowires are also...

  2. Effect of electron count and chemical complexity in the Ta-Nb-Hf-Zr-Ti high-entropy alloy superconductor

    Science.gov (United States)

    von Rohr, Fabian; Winiarski, Michał J.; Tao, Jing; Klimczuk, Tomasz; Cava, Robert Joseph

    2016-11-01

    High-entropy alloys are made from random mixtures of principal elements on simple lattices, stabilized by a high mixing entropy. The recently discovered body-centered cubic (BCC) Ta-Nb-Hf-Zr-Ti high-entropy alloy superconductor appears to display properties of both simple crystalline intermetallics and amorphous materials; e.g., it has a well-defined superconducting transition along with an exceptional robustness against disorder. Here we show that the valence electron count dependence of the superconducting transition temperature in the high-entropy alloy falls between those of analogous simple solid solutions and amorphous materials and test the effect of alloy complexity on the superconductivity. We propose high-entropy alloys as excellent intermediate systems for studying superconductivity as it evolves between crystalline and amorphous materials.

  3. Superconductivity and symmetry breaking

    Energy Technology Data Exchange (ETDEWEB)

    Sarasua, L.G., E-mail: sarasua@fisica.edu.uy [Instituto de Fisica, Facultad de Ciencias, Universidad de la Republica, Montevideo (Uruguay)

    2012-02-15

    In the present work we consider the relation between superconductivity and spontaneous gauge symmetry breaking (SGBS). We show that ODLRO does not require in principle SBGS, even in the presence of particle number fluctuations, by examining exact solutions of a fermionic pairing model. The criteria become equivalent if a symmetry breaking field is allowed, which can be attributed to the interaction with the environment. However, superconducting states without SBGS are not forbidden.

  4. Photoemission, Correlation and Superconductivity:

    Science.gov (United States)

    Abrecht, M.; Ariosa, D.; Cloëtta, D.; Pavuna, D.; Perfetti, L.; Grioni, M.; Margaritondo, G.

    We review some of the problems still affecting photoemission as a probe of high-temperature superconductivity, as well as important recent results concerning their solution. We show, in particular, some of the first important results on thin epitaxial films grown by laser ablation, which break the monopoly of cleaved BCSCO in this type of experiments. Such results, obtained on thin LSCO, may have general implications on the theory of high-temperature superconductivity.

  5. Emergent Higgsless Superconductivity

    Directory of Open Access Journals (Sweden)

    Cristina Diamantini M.

    2017-01-01

    Full Text Available We present a new Higgsless model of superconductivity, inspired from anyon superconductivity but P- and T-invariant and generalizable to any dimension. While the original anyon superconductivity mechanism was based on incompressible quantum Hall fluids as average field states, our mechanism involves topological insulators as average field states. In D space dimensions it involves a (D-1-form fictitious pseudovector gauge field which originates from the condensation of topological defects in compact lowenergy effective BF theories. There is no massive Higgs scalar as there is no local order parameter. When electromagnetism is switched on, the photon acquires mass by the topological BF mechanism. Although the charge of the gapless mode (2 and the topological order (4 are the same as those of the standard Higgs model, the two models of superconductivity are clearly different since the origins of the gap, reflected in the high-energy sectors are totally different. In 2D thi! s type of superconductivity is explicitly realized as global superconductivity in Josephson junction arrays. In 3D this model predicts a possible phase transition from topological insulators to Higgsless superconductors.

  6. Superconducting Fullerene Nanowhiskers

    Directory of Open Access Journals (Sweden)

    Yoshihiko Takano

    2012-04-01

    Full Text Available We synthesized superconducting fullerene nanowhiskers (C60NWs by potassium (K intercalation. They showed large superconducting volume fractions, as high as 80%. The superconducting transition temperature at 17 K was independent of the K content (x in the range between 1.6 and 6.0 in K-doped C60 nanowhiskers (KxC60NWs, while the superconducting volume fractions changed with x. The highest shielding fraction of a full shielding volume was observed in the material of K3.3C60NW by heating at 200 °C. On the other hand, that of a K-doped fullerene (K-C60 crystal was less than 1%. We report the superconducting behaviors of our newly synthesized KxC60NWs in comparison to those of KxC60 crystals, which show superconductivity at 19 K in K3C60. The lattice structures are also discussed, based on the x-ray diffraction (XRD analyses.

  7. High temperature interfacial superconductivity

    Science.gov (United States)

    Bozovic, Ivan [Mount Sinai, NY; Logvenov, Gennady [Port Jefferson Station, NY; Gozar, Adrian Mihai [Port Jefferson, NY

    2012-06-19

    High-temperature superconductivity confined to nanometer-scale interfaces has been a long standing goal because of potential applications in electronic devices. The spontaneous formation of a superconducting interface in bilayers consisting of an insulator (La.sub.2CuO.sub.4) and a metal (La.sub.1-xSr.sub.xCuO.sub.4), neither of which is superconducting per se, is described. Depending upon the layering sequence of the bilayers, T.sub.c may be either .about.15 K or .about.30 K. This highly robust phenomenon is confined to within 2-3 nm around the interface. After exposing the bilayer to ozone, T.sub.c exceeds 50 K and this enhanced superconductivity is also shown to originate from a 1 to 2 unit cell thick interfacial layer. The results demonstrate that engineering artificial heterostructures provides a novel, unconventional way to fabricate stable, quasi two-dimensional high T.sub.c phases and to significantly enhance superconducting properties in other superconductors. The superconducting interface may be implemented, for example, in SIS tunnel junctions or a SuFET.

  8. The superconducting spin valve and triplet superconductivity

    Science.gov (United States)

    Garifullin, I. A.; Leksin, P. V.; Garif`yanov, N. N.; Kamashev, A. A.; Fominov, Ya. V.; Schumann, J.; Krupskaya, Y.; Kataev, V.; Schmidt, O. G.; Büchner, B.

    2015-01-01

    A review of our recent results on the spin valve effect is presented. We have used a theoretically proposed spin switch design F1/F2/S comprising a ferromagnetic bilayer (F1/F2) as a ferromagnetic component, and an ordinary superconductor (S) as the second interface component. Based on it we have prepared and studied in detail a set of multilayers CoOx/Fe1/Cu/Fe2/S (S=In or Pb). In these heterostructures we have realized for the first time a full spin switch effect for the superconducting current, have observed its sign-changing oscillating behavior as a function of the Fe2-layer thickness and finally have obtained direct evidence for the long-range triplet superconductivity arising due to noncollinearity of the magnetizations of the Fe1 and Fe2 layers.

  9. Kondo Impurities in the Kitaev Spin Liquid: Numerical Renormalization Group Solution and Gauge-Flux-Driven Screening.

    Science.gov (United States)

    Vojta, Matthias; Mitchell, Andrew K; Zschocke, Fabian

    2016-07-15

    Kitaev's honeycomb-lattice compass model describes a spin liquid with emergent fractionalized excitations. Here, we study the physics of isolated magnetic impurities coupled to the Kitaev spin-liquid host. We reformulate this Kondo-type problem in terms of a many-state quantum impurity coupled to a multichannel bath of Majorana fermions and present the numerically exact solution using Wilson's numerical renormalization group technique. Quantum phase transitions occur as a function of Kondo coupling and locally applied field. At zero field, the impurity moment is partially screened only when it binds an emergent gauge flux, while otherwise it becomes free at low temperatures. We show how Majorana degrees of freedom determine the fixed-point properties, make contact with Kondo screening in pseudogap Fermi systems, and discuss effects away from the dilute limit.

  10. Structural materials for large superconducting magnets for tokamaks

    Energy Technology Data Exchange (ETDEWEB)

    Long, C.J.

    1976-12-01

    The selection of structural materials for large superconducting magnets for tokamak-type fusion reactors is considered. The important criteria are working stress, radiation resistance, electromagnetic interaction, and general feasibility. The most advantageous materials appear to be face-centered-cubic alloys in the Fe-Ni-Cr system, but high-modulus composites may be necessary where severe pulsed magnetic fields are present. Special-purpose structural materials are considered briefly.

  11. Kondo Hybridization and the Origin of Metallic States at the (001 Surface of SmB_{6}

    Directory of Open Access Journals (Sweden)

    E. Frantzeskakis

    2013-12-01

    Full Text Available SmB_{6}, a well-known Kondo insulator, has been proposed to be an ideal topological insulator with states of topological character located in a clean, bulk electronic gap, namely, the Kondo-hybridization gap. Since the Kondo gap arises from many-body electronic correlations, SmB_{6} would be placed at the head of a new material class: topological Kondo insulators. Here, for the first time, we show that the k-space characteristics of the Kondo-hybridization process is the key to unraveling the origin of the two types of metallic states experimentally observed by angle-resolved photoelectron spectroscopy (ARPES in the electronic band structure of SmB_{6}(001. One group of these states is essentially of bulk origin and cuts the Fermi level due to the position of the chemical potential 20 meV above the lowest-lying 5d-4f hybridization zone. The other metallic state is more enigmatic, being weak in intensity, but represents a good candidate for a topological surface state. However, before this claim can be substantiated by an unequivocal measurement of its massless dispersion relation, our data raise the bar in terms of the ARPES resolution required, as we show there to be a strong renormalization of the hybridization gaps by a factor 2–3 compared to theory, following from the knowledge of the true position of the chemical potential and a careful comparison with the predictions from recent local-density-approximation (LDA+Gutzwiller calculations. All in all, these key pieces of evidence act as triangulation markers, providing a detailed description of the electronic landscape in SmB_{6} and pointing the way for future, ultrahigh-resolution ARPES experiments to achieve a direct measurement of the Dirac cones in the first topological Kondo insulator.

  12. Single crystal study on a novel Kondo compound Ce{sub 6}Pt{sub 11}In{sub 14}

    Energy Technology Data Exchange (ETDEWEB)

    Pikul, A.P. E-mail: a.pikul@int.pan.wroc.pl; Bukowski, Z.; Stepien-Damm, J.; Kaczorowski, D

    2004-05-01

    Ce{sub 6}Pt{sub 11}In{sub 14} crystallizes with a monoclinic unit cell (space group C2/m; lattice parameters: a=22.729(5) A, b=4.3960(10) A, c=14.780(3) A, {beta}=118.35(3) deg.; Z=2). It is paramagnetic down to 1.9 K, and strongly anisotropic in the entire temperature range studied. The electrical resistivity along the b-axis shows Kondo features with a maximum located at 7 K. The transverse magnetoresistivity isotherms, measured in the incoherent region, follow a single-ion Kondo scaling with the characteristic temperature T*=4 K.

  13. Modulated Spin Liquid and Magnetic Order from a Kondo-Heisenberg model applied to $URu_{2}Si_{2}$

    OpenAIRE

    Montiel, Xavier; Burdin, Sébastien; Pépin, Catherine; Ferraz, Alvaro

    2013-01-01

    International audience; Using the Kondo-Heisenberg model framework, we analyze the effect of charge fluctuations in the modulated spin liquid (MSL) and in the antiferromagnetic (AF) ordering which were introduced by Pépin et al. [Phys. Rev. Lett. 106, 106601 (2011)] and Thomas et al. [Phys. Rev. B 87, 014422 (2013)]. Coupling the spin liquid to the charge sector enables us to discuss the formation of the Kondo effect in this system. As a result, we are able to observe the emergence of two pha...

  14. Kondo Resonance in a Mesoscopic Ring Coupled to a Quantum Dot: Exact Results for the Aharonov-Bohm/Casher Effects

    OpenAIRE

    Eckle, H. -P.; Johannesson, H.; Stafford, C. A.

    2000-01-01

    We study the persistent currents induced by both the Aharonov-Bohm and Aharonov-Casher effects in a one-dimensional mesoscopic ring coupled to a side-branch quantum dot at Kondo resonance. For privileged values of the Aharonov-Bohm-Casher fluxes, the problem can be mapped onto an integrable model, exactly solvable by a Bethe ansatz. In the case of a pure magnetic Aharonov-Bohm flux, we find that the presence of the quantum dot has no effect on the persistent current. In contrast, the Kondo re...

  15. Superconductivity versus quantum criticality: what can we learn from heavy fermions?

    Science.gov (United States)

    Steglich, F; Arndt, J; Friedemann, S; Krellner, C; Tokiwa, Y; Westerkamp, T; Brando, M; Gegenwart, P; Geibel, C; Wirth, S; Stockert, O

    2010-04-28

    Two quantum critical point (QCP) scenarios are being discussed for different classes of antiferromagnetic (AF) heavy-fermion (HF) systems. In the itinerant one, where AF order is of the spin-density wave (SDW) type, the heavy 'composite' charge carriers keep their integrity at the QCP. The second one implies a breakdown of the Kondo effect and a disintegration of the composite fermions at the AF QCP. We discuss two isostructural compounds as exemplary materials for these two different scenarios: CeCu(2)Si(2) exhibits a three-dimensional (3D) SDW QCP and superconductivity, presumably mediated by SDW fluctuations, as strongly suggested by recent inelastic neutron scattering experiments. In Y bRh(2)Si(2), the AF QCP is found to coincide with a Kondo-destroying one. However, in the latter compound these two QCPs can be detached by varying the average unit-cell volume, e.g. through the application of chemical pressure, as realized by partial substitution of either Ir or Co for Rh. A comparison of CeCu(2)Si(2) and Y bRh(2)Si(2) indicates that the apparent differences in quantum critical behaviour go along with disparate behaviour concerning the (non-) existence of superconductivity (SC). No sign of SC could be detected in Y bRh(2)Si(2) down to mK temperatures. A potential correlation between the specific nature of the QCP and the occurrence of SC, however, requires detailed studies on further quantum critical HF superconductors, e.g. on β-Y bAlB(4), UBe(13), CeCoIn(5) and CeRhIn(5).

  16. Two-channel Kondo effect and the low-temperature crossover

    Science.gov (United States)

    Keller, Andrew; Peeters, Lucas; Weymann, Ireneusz; Moca, Cătălin Paşcu; Mahalu, Diana; Umansky, Vladimir; Zaránd, Gergely; Goldhaber-Gordon, David

    2015-03-01

    The two-channel Kondo (2CK) state, where a spin-1/2 impurity is equally exchange-coupled to two independent reservoirs, is a canonical non-Fermi liquid state. Experimental observations are rare because of its sensitivity to common and hard-to-control perturbations. We implement experimentally a 2CK state in a coupled dot-grain system (Potok, et al., doi:10.1038/nature05556), and explore the physics of the low-temperature crossover: how magnetic field and gate voltage drive the system towards a Fermi liquid ground state. Our experimental findings are corroborated by detailed numerical renormalization group modeling of our device.

  17. Fano versus Kondo Resonances in a Closed Aharonov-Bohm Interferometer Coupled to Ferromagnetic Electrodes

    Institute of Scientific and Technical Information of China (English)

    WU Shao-Quan; SUN Wei-Li

    2007-01-01

    Using the Keldysh Nonequilibrium Green function and equation-of-motion technique,we investigate Fano versus Kondo resonances in closed Aharonov-Bohm interferometer coupled to ferromagnetic leads and study their effects on the conductance of this system.The conductance with both parallel and antiparallel lead-polarization alignments is analysed for various values of the magnetic flux.Our results show that this system can provide an excellent spin filtering property,and a large tunnelling magnetoresistance can arise by adjusting the system parameters,which indicates that this system is a possible candidate for spin valve transistors and has important applications in spintronics.

  18. Pressure-Resistant Intermediate Valence in the Kondo Insulator SmB_{6}.

    Science.gov (United States)

    Butch, Nicholas P; Paglione, Johnpierre; Chow, Paul; Xiao, Yuming; Marianetti, Chris A; Booth, Corwin H; Jeffries, Jason R

    2016-04-15

    Resonant x-ray emission spectroscopy was used to determine the pressure dependence of the f-electron occupancy in the Kondo insulator SmB_{6}. Applied pressure reduces the f occupancy, but surprisingly, the material maintains a significant divalent character up to a pressure of at least 35 GPa. Thus, the closure of the resistive activation energy gap and onset of magnetic order are not driven by stabilization of an integer valent state. Over the entire pressure range, the material maintains a remarkably stable intermediate valence that can in principle support a nontrivial band structure.

  19. Temperature dependence of the Kondo resonance and its satellites in CeCu_2Si_2

    OpenAIRE

    Reinert, F.; Ehm, D.; Schmidt, S; Nicolay, G.; H"ufner, S.; Kroha, J.; Trovarelli, O.; Geibel, C.

    2001-01-01

    We present high-resolution photoemission spectroscopy studies on the Kondo resonance of the strongly-correlated Ce system CeCu$_2$Si$_2$. Exploiting the thermal broadening of the Fermi edge we analyze position, spectral weight, and temperature dependence of the low-energy 4f spectral features, whose major weight lies above the Fermi level $E_F$. We also present theoretical predictions based on the single-impurity Anderson model using an extended non-crossing approximation (NCA), including all...

  20. Spontaneous Polarization of Kondo problem associated with Higher-spin analog of the 6-vertex model

    CERN Document Server

    Fukushima, N

    1999-01-01

    We study Kondo-type model associated with an integrable Higher-spin analog of the 6-vertex mode, which is constructed by inserting a spin 1/2 to spin 1 lines: $... C^3 \\otimes C^3 \\otimes C^2 \\otimes C^3 \\otimes C^3 ... .$ We formulate the problem in terms of representation theory of quantum affine algebra $U_q(\\hat{sl_2})$. We derive an exact formula of the spontaneous staggered polarization for our model, which corresponds to Baxter's formula for the 6-vertex model.

  1. Scanning Gate Microscopy of Kondo Dots: Fabry-P\\'erot Interferences and Thermally Induced Rings

    OpenAIRE

    Kleshchonok, Andrii; Fleury, Geneviève; Pichard, Jean-Louis

    2013-01-01

    We study the conductance of an electron interferometer formed in a two dimensional electron gas between a nanostructured quantum contact and the charged tip of a scanning gate microscope. Measuring the conductance as a function of the tip position, thermally induced rings may be observed in addition to Fabry-P\\'erot interference fringes spaced by half the Fermi wavelength. If the contact is made of a quantum dot opened in the middle of a Kondo valley, we show how the location of the rings all...

  2. Scanning Gate Microscopy of Kondo Dots: Fabry-Pérot Interferences and Thermally Induced Rings

    OpenAIRE

    Kleshchonok, Andrii; Fleury, Geneviève; Pichard, Jean-Louis

    2013-01-01

    5 pages, 4 figures; We study the conductance of an electron interferometer formed in a two dimensional electron gas between a nanostructured quantum contact and the charged tip of a scanning gate microscope. Measuring the conductance as a function of the tip position, thermally induced rings may be observed in addition to Fabry-Pérot interference fringes spaced by half the Fermi wavelength. If the contact is made of a quantum dot opened in the middle of a Kondo valley, we show how the locatio...

  3. Fermi/non-Fermi mixing in SU($N$) Kondo effect

    CERN Document Server

    Kimura, Taro

    2016-01-01

    We apply conformal field theory analysis to the $k$-channel SU($N$) Kondo system, and find a peculiar behavior in the cases $N > k > 1$, which we call Fermi/non-Fermi mixing: The low temperature scaling is described as the Fermi liquid, while the zero temperature IR fixed point exhibits the non-Fermi liquid signature. We also show that the Wilson ratio is no longer universal for the cases $N > k > 1$. The deviation from the universal value of the Wilson ratio could be used as an experimental signal of the Fermi/non-Fermi mixing.

  4. Magnetically tunable Kondo-Aharonov-Bohm effect in a triangular quantum dot.

    Science.gov (United States)

    Kuzmenko, T; Kikoin, K; Avishai, Y

    2006-02-03

    The role of discrete orbital symmetry in mesoscopic physics is manifested in a system consisting of three identical quantum dots forming an equilateral triangle. Under a perpendicular magnetic field, this system demonstrates a unique combination of Kondo and Aharonov-Bohm features due to an interplay between continuous [spin-rotation SU(2)] and discrete (permutation C3v) symmetries, as well as U(1) gauge invariance. The conductance as a function of magnetic flux displays sharp enhancement or complete suppression depending on contact setups.

  5. Vibration-induced Kondo tunneling through metal-organic complexes with even electron occupation number.

    Science.gov (United States)

    Kikoin, K; Kiselev, M N; Wegewijs, M R

    2006-05-05

    We investigate transport through a mononuclear transition-metal complex with strong tunnel coupling to two electrodes. The ground state of this molecule is a singlet, while the first excited state is a triplet. We show that a modulation of the tunnel-barrier due to a molecular distortion which couples to the tunneling induces a Kondo-effect, provided the discrete vibrational energy compensates the singlet-triplet gap. We discuss the single-phonon and two-phonon-assisted cotunneling and possible experimental realization of the theory.

  6. A low-temperature derivation of spin-spin exchange in Kondo lattice model

    Energy Technology Data Exchange (ETDEWEB)

    Feng Szeshiang [Physics Department, Florida A and M University, Tallahassee, FL 32307 (United States)]. E-mail: shixiang.feng@famu.edu; Mochena, Mogus [Physics Department, Florida A and M University, Tallahassee, FL 32307 (United States)

    2005-11-01

    Using Hubbard-Stratonovich transformation and drone-fermion representations for spin-12 and for spin-32, which is presented for the first time, we make a path-integral formulation of the Kondo lattice model. In the case of weak coupling and low temperature, the functional integral over conduction fermions can be approximated to the quadratic order and this gives the well-known RKKY interaction. In the case of strong coupling, the same quadratic approximation leads to an effective local spin-spin interaction linear in hopping energy t.

  7. Quantum size effects in Pb layers with absorbed Kondo adatoms: Determination of the exchange coupling constant

    KAUST Repository

    Schwingenschlögl, Udo

    2009-07-01

    We consider the magnetic interaction of manganese phtalocyanine (MnPc) absorbed on Pb layers that were grown on a Si substrate. We perform an ab initio calculation of the density of states and Kondo temperature as a function of the number of Pb monolayers. Comparison to experimental data [Y.-S. Fu et al., Phys. Rev. Lett. 99, 256601 (2007)] then allows us to determine the exchange coupling constant J between the spins of the adsorbed molecules and those of the Pb host. This approach gives rise to a general and reliable method for obtaining J by combining experimental and numerical results.

  8. Nanoscience and Engineering in Superconductivity

    CERN Document Server

    Moshchalkov, Victor; Lang, Wolfgang

    2010-01-01

    For emerging energy saving technologies, superconducting materials with superior performance are needed. Such materials can be developed by manipulating the 'elementary building blocks' through nanostructuring. For superconductivity the 'elementary blocks' are Cooper pair and fluxon (vortex). This book presents new ways how to modify superconductivity and vortex matter through nanostructuring and the use of nanoscale magnetic templates. The basic nano-effects, vortex and vortex-antivortex patterns, vortex dynamics, Josephson phenomena, critical currents, and interplay between superconductivity

  9. Interface high-temperature superconductivity

    Science.gov (United States)

    Wang, Lili; Ma, Xucun; Xue, Qi-Kun

    2016-12-01

    Cuprate high-temperature superconductors consist of two quasi-two-dimensional (2D) substructures: CuO2 superconducting layers and charge reservoir layers. The superconductivity is realized by charge transfer from the charge reservoir layers into the superconducting layers without chemical dopants and defects being introduced into the latter, similar to modulation-doping in the semiconductor superlattices of AlGaAs/GaAs. Inspired by this scheme, we have been searching for high-temperature superconductivity in ultra-thin films of superconductors epitaxially grown on semiconductor/oxide substrates since 2008. We have observed interface-enhanced superconductivity in both conventional and unconventional superconducting films, including single atomic layer films of Pb and In on Si substrates and single unit cell (UC) films of FeSe on SrTiO3 (STO) substrates. The discovery of high-temperature superconductivity with a superconducting gap of ∼20 meV in 1UC-FeSe/STO has stimulated tremendous interest in the superconductivity community, for it opens a new avenue for both raising superconducting transition temperature and understanding the pairing mechanism of unconventional high-temperature superconductivity. Here, we review mainly the experimental progress on interface-enhanced superconductivity in the three systems mentioned above with emphasis on 1UC-FeSe/STO, studied by scanning tunneling microscopy/spectroscopy, angle-resolved photoemission spectroscopy and transport experiments. We discuss the roles of interfaces and a possible pairing mechanism inferred from these studies.

  10. Connectivity and superconductivity

    CERN Document Server

    Rubinstein, Jacob

    2000-01-01

    The motto of connectivity and superconductivity is that the solutions of the Ginzburg--Landau equations are qualitatively influenced by the topology of the boundaries, as in multiply-connected samples. Special attention is paid to the "zero set", the set of the positions (also known as "quantum vortices") where the order parameter vanishes. The effects considered here usually become important in the regime where the coherence length is of the order of the dimensions of the sample. It takes the intuition of physicists and the awareness of mathematicians to find these new effects. In connectivity and superconductivity, theoretical and experimental physicists are brought together with pure and applied mathematicians to review these surprising results. This volume is intended to serve as a reference book for graduate students and researchers in physics or mathematics interested in superconductivity, or in the Schrödinger equation as a limiting case of the Ginzburg--Landau equations.

  11. Large Superconducting Magnet Systems

    CERN Document Server

    Védrine, P.

    2014-07-17

    The increase of energy in accelerators over the past decades has led to the design of superconducting magnets for both accelerators and the associated detectors. The use of Nb−Ti superconducting materials allows an increase in the dipole field by up to 10 T compared with the maximum field of 2 T in a conventional magnet. The field bending of the particles in the detectors and generated by the magnets can also be increased. New materials, such as Nb3Sn and high temperature superconductor (HTS) conductors, can open the way to higher fields, in the range 13–20 T. The latest generations of fusion machines producing hot plasma also use large superconducting magnet systems.

  12. Failed theories of superconductivity

    CERN Document Server

    Schmalian, Joerg

    2010-01-01

    Almost half a century passed between the discovery of superconductivity by Kammerlingh Onnes and the theoretical explanation of the phenomenon by Bardeen, Cooper and Schrieffer. During the intervening years the brightest minds in theoretical physics tried and failed to develop a microscopic understanding of the effect. A summary of some of those unsuccessful attempts to understand superconductivity not only demonstrates the extraordinary achievement made by formulating the BCS theory, but also illustrates that mistakes are a natural and healthy part of the scientific discourse, and that inapplicable, even incorrect theories can turn out to be interesting and inspiring.

  13. Superconducting magnetic quadrupole

    Energy Technology Data Exchange (ETDEWEB)

    Kim, J.W.; Shepard, K.W.; Nolen, J.A.

    1995-08-01

    A design was developed for a 350 T/m, 2.6-cm clear aperture superconducting quadrupole focussing element for use in a very low q/m superconducting linac as discussed below. The quadrupole incorporates holmium pole tips, and a rectangular-section winding using standard commercially-available Nb-Ti wire. The magnet was modeled numerically using both 2D and 3D codes, as a basis for numerical ray tracing using the quadrupole as a linac element. Components for a prototype singlet are being procured during FY 1995.

  14. Fingerprints of Mott Superconductivity

    Institute of Scientific and Technical Information of China (English)

    王强华

    2003-01-01

    We improve a previous theory of doped Mott insulators with duality between pairing and magnetism by a further duality transform. As the result we obtained a quantum Ginzburg-Landau theory describing the Cooper pair condensate and the dual of spin condensate. We address the superconductivity by doping a Mott insulator,which we call the Mott superconductivity. Some fingerprints of such novelty in cuprates are the scaling between neutron resonance energy and superfluid density, and the induced quantized spin moment by vortices or Zn impurity (together with circulating charge super-current to be checked by experiments).

  15. Phase diagram of the one-dimensional anisotropic Kondo-necklace model

    Science.gov (United States)

    Mahmoudian, S.; Langari, A.

    2008-01-01

    The one-dimensional anisotropic Kondo-necklace model has been studied by several methods. It is shown that a mean field approach fails to gain the correct phase diagram for the Ising-type anisotropy. We then applied the spin wave theory which is justified for the anisotropic case. We have derived the phase diagram between the antiferromagnetic long range order and the Kondo singlet phases. We have found that the exchange interaction (J) between the itinerant spins and local ones enhances the quantum fluctuations around the classical long range antiferromagnetic order and finally destroy the ordered phase at the critical value Jc . Moreover, our results show that the onset of anisotropy in the XY term of the itinerant interactions develops the antiferromagnetic order for J

  16. Thermoelectric response of a correlated impurity in the nonequilibrium Kondo regime

    Science.gov (United States)

    Dorda, Antonius; Ganahl, Martin; Andergassen, Sabine; von der Linden, Wolfgang; Arrigoni, Enrico

    2016-12-01

    We study nonequilibrium thermoelectric transport properties of a correlated impurity connected to two leads for temperatures below the Kondo scale. At finite bias, for which a current flows across the leads, we investigate the differential response of the current to a temperature gradient. In particular, we compare the influence of a bias voltage and of a finite temperature on this thermoelectric response. This is of interest from a fundamental point of view to better understand the two different decoherence mechanisms produced by a bias voltage and by temperature. Our results show that in this respect the thermoelectric response behaves differently from the electric conductance. In particular, while the latter displays a similar qualitative behavior as a function of voltage and temperature, both in theoretical and experimental investigations, qualitative differences occur in the case of the thermoelectric response. In order to understand this effect, we analyze the different contributions in connection to the behavior of the impurity spectral function versus temperature. Especially in the regime of strong interactions and large enough bias voltages, we obtain a simple picture based on the asymmetric suppression or enhancement of the split Kondo peaks as a function of the temperature gradient. Besides the academic interest, these studies could additionally provide valuable information to assess the applicability of quantum dot devices as responsive nanoscale temperature sensors.

  17. Zero-Temperature Magnetic Transition in an Easy-Axis Kondo Lattice Model --- An NRG Study

    Science.gov (United States)

    Zhu, Jian-Xin; Kirchner, Stefan; Bulla, Ralf; Si, Qimiao

    2007-03-01

    Antiferromagnetic heavy fermion metals close to their quantum critical points display a richness in their physical properties unanticipated by the traditional approach to quantum criticality. Here we address the quantum transition of a spin-12 antiferromagnetic Kondo lattice model with an easy-axis anisotropy within the extended dynamical mean field theory. We derive results [1] in real frequency using the bosonic numerical renormalization group (bNRG) method and compare them with Quantum Monte Carlo results in Matsubara frequency. The bNRG results show a logarithmic divergence in the critical local spin susceptibility, signaling a destruction of Kondo screening. The T=0 transition is nearly second order, with any jump in the magnetic order parameter not exceeding a few percents of the full moment. The bNRG results also display some subtle features; we discuss their possible origins and suggest means for further microscopic studies. [1] J.-X. Zhu, S. Kirchner, R. Bulla, and Q. Si, cond-mat/0607567.

  18. Possible undercompensation effect in the Kondo insulator (Yb,Tm)B12

    Science.gov (United States)

    Alekseev, P. A.; Nemkovski, K. S.; Mignot, J.-M.; Clementyev, E. S.; Ivanov, A. S.; Rols, S.; Bewley, R. I.; Filipov, V. B.; Shitsevalova, N. Yu.

    2014-03-01

    The effects of Tm substitution on the dynamical magnetic response of Yb1-xTmxB12 (x=0, 0.08, 0.15, and 0.75) and Lu0.92Tm0.08B12 compounds have been studied using time-of-flight inelastic neutron scattering. Major changes were observed in the spectral structure and temperature evolution of the Yb contribution to the inelastic response for a rather low content of magnetic Tm ions. A sizable influence of the RB12 host (YbB12, as compared to LuB12 or pure TmB12) on the crystal-field splitting of the Tm3+ ion is also reported. The results point to a specific effect of impurities carrying a magnetic moment (Tm, as compared to Lu or Zr) in a Kondo insulator, which is thought to reflect the "undercompensation" of Yb magnetic moments, originally Kondo screened in pure YbB12. A parallel is made with the strong effect of Tm substitution on the temperature dependence of the Seebeck coefficient in Yb1-xTmxB12, which was reported previously.

  19. Kondo behavior and conductance through 3d impurities in gold chains doped with oxygen

    Science.gov (United States)

    Barral, M. A.; Di Napoli, S.; Blesio, G.; Roura-Bas, P.; Camjayi, A.; Manuel, L. O.; Aligia, A. A.

    2017-03-01

    Combining ab initio calculations and effective models derived from them, we discuss the electronic structure of oxygen doped gold chains when one Au atom is replaced by any transition-metal atom of the 3d series. The effect of O doping is to bring extended Au 5dxz and 5dyz states to the Fermi level, which together with the Au states of zero angular momentum projection leads to three possible channels for the screening of the magnetism of the impurity. For most 3d impurities the expected physics is similar to that of the underscreened Kondo model, with singular Fermi liquid behavior. For Fe and Co under a tetragonal crystal field introduced by leads, the system might display a non-Fermi liquid behavior. Ni and Cu impurities are described by a S = 1 two channel Kondo model and an SU(4) impurity Anderson model in the intermediate valence regime, respectively. In both cases, the system is a Fermi liquid, but the conductance shows some observable differences with the ordinary SU(2) Anderson model.

  20. Keldysh effective action theory for universal physics in spin-(1)/(2) Kondo dots

    Science.gov (United States)

    Smirnov, Sergey; Grifoni, Milena

    2013-03-01

    We present a theory for the Kondo spin-(1)/(2) effect in strongly correlated quantum dots. The theory is applicable at any temperature and voltage. It is based on a quadratic Keldysh effective action parametrized by a universal function. We provide a general analytical form for the tunneling density of states through this universal function for which we propose a simple microscopic model. We apply our theory to the highly asymmetric Anderson model with U=∞ and describe its strong-coupling limit, weak-coupling limit, and crossover region within a single analytical expression. We compare our results with a numerical renormalization group in equilibrium and with a real-time renormalization group out of equilibrium and show that the universal shapes of the linear and differential conductance obtained in our theory and in these theories are very close to each other in a wide range of temperatures and voltages. In particular, as in the real-time renormalization group, we predict that at the Kondo voltage the differential conductance is equal to 2/3 of its maximum.

  1. Long-range ferrimagnetic order in a two-dimensional supramolecular Kondo lattice

    Science.gov (United States)

    Girovsky, Jan; Nowakowski, Jan; Ali, Md. Ehesan; Baljozovic, Milos; Rossmann, Harald R.; Nijs, Thomas; Aeby, Elise A.; Nowakowska, Sylwia; Siewert, Dorota; Srivastava, Gitika; Wäckerlin, Christian; Dreiser, Jan; Decurtins, Silvio; Liu, Shi-Xia; Oppeneer, Peter M.; Jung, Thomas A.; Ballav, Nirmalya

    2017-05-01

    Realization of long-range magnetic order in surface-supported two-dimensional systems has been challenging, mainly due to the competition between fundamental magnetic interactions as the short-range Kondo effect and spin-stabilizing magnetic exchange interactions. Spin-bearing molecules on conducting substrates represent a rich platform to investigate the interplay of these fundamental magnetic interactions. Here we demonstrate the direct observation of long-range ferrimagnetic order emerging in a two-dimensional supramolecular Kondo lattice. The lattice consists of paramagnetic hexadeca-fluorinated iron phthalocyanine (FeFPc) and manganese phthalocyanine (MnPc) molecules co-assembled into a checkerboard pattern on single-crystalline Au(111) substrates. Remarkably, the remanent magnetic moments are oriented in the out-of-plane direction with significant contribution from orbital moments. First-principles calculations reveal that the FeFPc-MnPc antiferromagnetic nearest-neighbour coupling is mediated by the Ruderman-Kittel-Kasuya-Yosida exchange interaction via the Au substrate electronic states. Our findings suggest the use of molecular frameworks to engineer novel low-dimensional magnetically ordered materials and their application in molecular quantum devices.

  2. Transport through artificial single-molecule magnets:Spin-pair state sequential tunneling and Kondo effects

    Institute of Scientific and Technical Information of China (English)

    Niu Peng-Bin; Wang Qiang; Nie Yi-Hang

    2013-01-01

    The transport properties of an artificial single-molecule magnet based on a CdTe quantum dot doped with a single Mn+2 ion (S =5/2) are investigated by the non-equilibrium Green function method.We consider a minimal model where the Mn-hole exchange coupling is strongly anisotropic so that spin-flip is suppressed and the impurity spin S and a hole spin s entering the quantum dot are coupled into spin pair states with (2S+ 1) sublevels.In the sequential tunneling regime,the differential conductance exhibits (2S + 1) possible peaks,corresponding to resonance tunneling via (2S + 1) sublevels.At low temperature,Kondo physics dominates transport and (2S + 1) Kondo peaks occur in the local density of states and conductance.These peaks originate from the spin-singlet state formed by the holes in the leads and on the dot via higher-order processes and are related to the parallel and antiparallel spin pair states.

  3. Long-range ferrimagnetic order in a two-dimensional supramolecular Kondo lattice.

    Science.gov (United States)

    Girovsky, Jan; Nowakowski, Jan; Ali, Md Ehesan; Baljozovic, Milos; Rossmann, Harald R; Nijs, Thomas; Aeby, Elise A; Nowakowska, Sylwia; Siewert, Dorota; Srivastava, Gitika; Wäckerlin, Christian; Dreiser, Jan; Decurtins, Silvio; Liu, Shi-Xia; Oppeneer, Peter M; Jung, Thomas A; Ballav, Nirmalya

    2017-05-22

    Realization of long-range magnetic order in surface-supported two-dimensional systems has been challenging, mainly due to the competition between fundamental magnetic interactions as the short-range Kondo effect and spin-stabilizing magnetic exchange interactions. Spin-bearing molecules on conducting substrates represent a rich platform to investigate the interplay of these fundamental magnetic interactions. Here we demonstrate the direct observation of long-range ferrimagnetic order emerging in a two-dimensional supramolecular Kondo lattice. The lattice consists of paramagnetic hexadeca-fluorinated iron phthalocyanine (FeFPc) and manganese phthalocyanine (MnPc) molecules co-assembled into a checkerboard pattern on single-crystalline Au(111) substrates. Remarkably, the remanent magnetic moments are oriented in the out-of-plane direction with significant contribution from orbital moments. First-principles calculations reveal that the FeFPc-MnPc antiferromagnetic nearest-neighbour coupling is mediated by the Ruderman-Kittel-Kasuya-Yosida exchange interaction via the Au substrate electronic states. Our findings suggest the use of molecular frameworks to engineer novel low-dimensional magnetically ordered materials and their application in molecular quantum devices.

  4. 4 f excitations in Ce Kondo lattices studied by resonant inelastic x-ray scattering

    Science.gov (United States)

    Amorese, A.; Dellea, G.; Fanciulli, M.; Seiro, S.; Geibel, C.; Krellner, C.; Makarova, I. P.; Braicovich, L.; Ghiringhelli, G.; Vyalikh, D. V.; Brookes, N. B.; Kummer, K.

    2016-04-01

    The potential of resonant inelastic soft x-ray scattering to measure 4 f crystal electric-field excitation spectra in Ce Kondo lattices has been examined. Spectra have been obtained for several Ce systems and show a well-defined structure determined by crystal-field, spin-orbit, and charge-transfer excitations only. The spectral shapes of the excitation spectra can be well understood in the framework of atomic multiplet calculations. For CeCu2Si2 we found notable disagreement between the inelastic x-ray-scattering spectra and theoretical calculations when using the crystal-field scheme proposed from inelastic neutron scattering. Modified sets of crystal-field parameters yield better agreement. Our results also show that, with the very recent improvements of soft x-ray spectrometers in resolution to below 30 meV at the Ce M4 ,5 edges, resonant inelastic x-ray scattering could be an ideal tool to determine the crystal-field scheme in Ce Kondo lattices and other rare-earth compounds.

  5. Importance of conduction electron correlation in a Kondo lattice, Ce{sub 2}CoSi{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Patil, Swapnil; Pandey, Sudhir K; Medicherla, V R R; Singh, R S; Bindu, R; Sampathkumaran, E V; Maiti, Kalobaran, E-mail: kbmaiti@tifr.res.i [Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai-400 005 (India)

    2010-06-30

    Kondo systems are usually described by the interaction of the correlation induced local moments with the highly itinerant conduction electrons. Here, we study the role of electron correlations among conduction electrons in the electronic structure of a Kondo lattice compound, Ce{sub 2}CoSi{sub 3}, using high resolution photoemission spectroscopy and ab initio band structure calculations, where Co 3d electrons contribute in the conduction band. High energy resolution employed in the measurements helped to reveal the signatures of Ce 4f states derived Kondo resonance features at the Fermi level and the dominance of Co 3d contributions at higher binding energies in the conduction band. The lineshape of the experimental Co 3d band is found to be significantly different from that obtained from the band structure calculations within the local density approximations, LDA. Consideration of electron-electron Coulomb repulsion, U, among Co 3d electrons within the LDA + U method leads to a better representation of experimental results. The signature of an electron correlation induced satellite feature is also observed in the Co 2p core level spectrum. These results clearly demonstrate the importance of the electron correlation among conduction electrons in deriving the microscopic description of such Kondo systems.

  6. Antiferroquadrupolar Ordering in Quadrupolar Kondo Lattice of Non-Kramers System PrTa2Al20

    Science.gov (United States)

    Higashinaka, Ryuji; Nakama, Akihiro; Miyazaki, Ryoichi; Yamaura, Jun-ichi; Sato, Hideyuki; Aoki, Yuji

    2017-10-01

    Single crystals of PrTa2Al20 have been investigated by means of single-crystal structural analysis and measurements of magnetization, specific heat, and electrical resistivity. The crystalline-electric-field level scheme of the Pr ions has a nonmagnetic Γ3 doublet ground state and a Γ5 magnetic excited state with an energy separation of 53 K. The 4f-electron contribution to the electrical resistivity shows -log T magnetic Kondo scattering above 50 K and a downward curvature characteristic of a quadrupolar Kondo lattice formation below 20 K. A phase transition appears at 0.65 K in zero field and shifts to higher temperatures in applied fields, indicating that this transition is antiferroquadrupolar (AFQ) in nature. The largely enhanced Sommerfeld coefficient ˜1.5 J/(mol K2) in the AFQ state may indicate the formation of heavy quasiparticles. The hierarchically arranged sequence of the magnetic Kondo regime, quadrupolar Kondo lattice regime, and AFQ ordered state in the wide temperature range 0.2-300 K demonstrates that PrTa2Al20 is a good playground to investigate quadrupole physics with strong electron correlations.

  7. Kondo Effect in CeXc (Xc = S, Se, Te) Studied by Electrical Resistivity Measurements under High Pressure

    Science.gov (United States)

    Hayashi, Yuya; Takai, Shun; Matsumura, Takeshi; Tanida, Hiroshi; Sera, Masafumi; Matsubayashi, Kazuyuki; Uwatoko, Yoshiya; Ochiai, Akira

    2016-03-01

    We have measured the electrical resistivity of cerium monochalcogenides, CeS, CeSe, and CeTe, under high pressures of up to 8 GPa. The pressure dependences of the antiferromagnetic ordering temperature TN, crystal field splitting, and the ln T anomaly of the Kondo effect have been studied to cover the entire region from the magnetic ordering regime at low pressure to the Fermi liquid regime at high pressure. TN initially increases with increasing pressure, and starts to decrease at high pressure as expected from Doniach’s diagram. Simultaneously, the ln T behavior in the resistivity is enhanced, indicating the enhancement of the Kondo effect by pressure. It is also characteristic of CeXc that the crystal field splitting rapidly decreases at a common rate of -12.2 K/GPa. This leads to the increase in the degeneracy of the f state and the further enhancement of the Kondo effect. It is shown that the pressure-dependent degeneracy of the f state is a key factor for understanding the pressure dependence of TN, the Kondo effect, magnetoresistance, and the peak structure in the temperature dependence of resistivity.

  8. Superconducting Magnets for Particle Accelerators

    CERN Document Server

    Rossi, L

    2012-01-01

    Superconductivity has been the most influential technology in the field of accelerators in the last 30 years. Since the commissioning of the Tevatron, which demonstrated the use and operability of superconductivity on a large scale, superconducting magnets and rf cavities have been at the heart of all new large accelerators. Superconducting magnets have been the invariable choice for large colliders, as well as cyclotrons and large synchrotrons. In spite of the long history of success, superconductivity remains a difficult technology, requires adequate R&D and suitable preparation, and has a relatively high cost. Hence, it is not surprising that the development has also been marked by a few setbacks. This article is a review of the main superconducting accelerator magnet projects; it highlights the main characteristics and main achievements, and gives a perspective on the development of superconducting magnets for the future generation of very high energy colliders.

  9. Spin-orbit-coupled superconductivity.

    Science.gov (United States)

    Lo, Shun-Tsung; Lin, Shih-Wei; Wang, Yi-Ting; Lin, Sheng-Di; Liang, C-T

    2014-06-25

    Superconductivity and spin-orbit (SO) interaction have been two separate emerging fields until very recently that the correlation between them seemed to be observed. However, previous experiments concerning SO coupling are performed far beyond the superconducting state and thus a direct demonstration of how SO coupling affects superconductivity remains elusive. Here we investigate the SO coupling in the critical region of superconducting transition on Al nanofilms, in which the strength of disorder and spin relaxation by SO coupling are changed by varying the film thickness. At temperatures T sufficiently above the superconducting critical temperature T(c), clear signature of SO coupling reveals itself in showing a magneto-resistivity peak. When T superconductivity. By studying such magneto-resistivity peaks under different strength of spin relaxation, we highlight the important effects of SO interaction on superconductivity.

  10. AC/RF Superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Ciovati, Gianluigi [JLAB

    2015-02-01

    This contribution provides a brief introduction to AC/RF superconductivity, with an emphasis on application to accelerators. The topics covered include the surface impedance of normal conductors and superconductors, the residual resistance, the field dependence of the surface resistance, and the superheating field.

  11. Superconducting Technology Assessment

    Science.gov (United States)

    2005-08-01

    of Nb/Al- Nx /NbTiN junctions for SIS mixer applications,” IEEE Trans. Appl. Superconduct., vol. 11, pp. 76–79, Mar. 2001. [48] M. Gurvitch, W. A...Another connector developed by IBM for commercial applications using a dendritic interposer technology. A “beam-on-pad” approach developed by Siemens

  12. Hybrid superconducting neutron detectors

    Energy Technology Data Exchange (ETDEWEB)

    Merlo, V.; Lucci, M.; Ottaviani, I. [Dipartimento di Fisica, Università Tor Vergata, Via della Ricerca Scientifica, I-00133 Roma (Italy); Salvato, M.; Cirillo, M. [Dipartimento di Fisica, Università Tor Vergata, Via della Ricerca Scientifica, I-00133 Roma (Italy); CNR SPIN Salerno, Università di Salerno, Via Giovanni Paolo II, n.132, 84084 Fisciano (Italy); Scherillo, A. [Science and Technology Facility Council, ISIS Facility Chilton, Didcot, Oxfordshire OX11 0QX (United Kingdom); Celentano, G. [ENEA Frascati Research Centre, Via. E. Fermi 45, 00044 Frascati (Italy); Pietropaolo, A., E-mail: antonino.pietropaolo@enea.it [ENEA Frascati Research Centre, Via. E. Fermi 45, 00044 Frascati (Italy); Mediterranean Institute of Fundamental Physics, Via Appia Nuova 31, 00040 Marino, Roma (Italy)

    2015-03-16

    A neutron detection concept is presented that is based on superconductive niobium (Nb) strips coated by a boron (B) layer. The working principle of the detector relies on the nuclear reaction, {sup 10}B + n → α + {sup 7}Li, with α and Li ions generating a hot spot on the current-biased Nb strip which in turn induces a superconducting-normal state transition. The latter is recognized as a voltage signal which is the evidence of the incident neutron. The above described detection principle has been experimentally assessed and verified by irradiating the samples with a pulsed neutron beam at the ISIS spallation neutron source (UK). It is found that the boron coated superconducting strips, kept at a temperature T = 8 K and current-biased below the critical current I{sub c}, are driven into the normal state upon thermal neutron irradiation. As a result of the transition, voltage pulses in excess of 40 mV are measured while the bias current can be properly modulated to bring the strip back to the superconducting state, thus resetting the detector. Measurements on the counting rate of the device are presented and the basic physical features of the detector are discussed.

  13. Levitation Kits Demonstrate Superconductivity.

    Science.gov (United States)

    Worthy, Ward

    1987-01-01

    Describes the "Project 1-2-3" levitation kit used to demonstrate superconductivity. Summarizes the materials included in the kit. Discusses the effect demonstrated and gives details on how to obtain kits. Gives an overview of the documentation that is included. (CW)

  14. LEP superconducting cavity

    CERN Multimedia

    1995-01-01

    Engineers work in a clean room on one of the superconducting cavities for the upgrade to the LEP accelerator, known as LEP-2. The use of superconductors allow higher electric fields to be produced so that higher beam energies can be reached.

  15. Niobium superconducting cavity

    CERN Multimedia

    CERN PhotoLab

    1980-01-01

    This 5-cell superconducting cavity, made from bulk-Nb, stems from the period of general studies, not all directed towards direct use at LEP. This one is dimensioned for 1.5 GHz, the frequency used at CEBAF and also studied at Saclay (LEP RF was 352.2 MHz). See also 7908227, 8007354, 8209255, 8210054, 8312339.

  16. LHC Superconducting Magnets

    CERN Document Server

    Jean Leyder

    2000-01-01

    The LHC is the next step in CERN's quest to unravel the mysteries of the Universe. It will accelerate protons to energies never before achieved in laboratories, and to hold them on course it will use powerful superconducting magnets on an unprecedented scale.

  17. Coupled superconducting flux qubits

    NARCIS (Netherlands)

    Plantenberg, J.H.

    2007-01-01

    This thesis presents results of theoretical and experimental work on superconducting persistent-current quantum bits. These qubits offer an attractive route towards scalable solid-state quantum computing. The focus of this work is on the gradiometer flux qubit which has a special geometric design, t

  18. Superconducting Quantum Circuits

    NARCIS (Netherlands)

    Majer, J.B.

    2002-01-01

    This thesis describes a number of experiments with superconducting cir- cuits containing small Josephson junctions. The circuits are made out of aluminum islands which are interconnected with a very thin insulating alu- minum oxide layer. The connections form a Josephson junction. The current trough

  19. Checking BEBC superconducting magnet

    CERN Multimedia

    1974-01-01

    The superconducting coils of the magnet for the 3.7 m Big European Bubble Chamber (BEBC) had to be checked, see Annual Report 1974, p. 60. The photo shows a dismantled pancake. By December 1974 the magnet reached again the field design value of 3.5 T.

  20. Nonequilibrium superconducting detectors

    Science.gov (United States)

    Cristiano, R.; Ejrnaes, M.; Esposito, E.; Lisitskyi, M. P.; Nappi, C.; Pagano, S.; Perez de Lara, D.

    2006-03-01

    Nonequilibrium superconducting detectors exploit the early stages of the energy down cascade which occur after the absorption of radiation. They operate on a short temporal scale ranging from few microseconds down to tens of picoseconds. In such a way they provide fast counting capability, high time discrimination and also, for some devices, energy sensitivity. Nonequilibrium superconducting detectors are developed for their use both in basic science and in practical applications for detection of single photons or single ionized macromolecules. In this paper we consider two devices: distributed readout imaging detectors (DROIDs) based on superconducting tunnel junctions (STJs), which are typically used for high-speed energy spectroscopy applications, and hot-electron superconductive detectors (HESDs), which are typically used as fast counters and time discriminators. Implementation of the DROID geometry to use a single superconductor is discussed. Progress in the fabrication technology of NbN nanostructured HESDs is presented. The two detectors share the high sensitivity that makes them able to efficiently detect even single photons down to infrared energy.

  1. Nonequilibrium superconducting detectors

    Energy Technology Data Exchange (ETDEWEB)

    Cristiano, R [CNR-Istituto di Cibernetica E. Caianiello, 80078 Pozzuoli (Namibia) (Italy); Ejrnaes, M [CNR-Istituto di Cibernetica E. Caianiello, 80078 Pozzuoli (Namibia) (Italy); INFN Sezione di Napoli, 80126 Naples (Italy); Esposito, E [CNR-Istituto di Cibernetica E. Caianiello, 80078 Pozzuoli (Namibia) (Italy); Lisitskyi, M P [CNR-Istituto di Cibernetica E. Caianiello, 80078 Pozzuoli (Namibia) (Italy); Nappi, C [CNR-Istituto di Cibernetica E. Caianiello, 80078 Pozzuoli (Namibia) (Italy); Pagano, S [CNR-Istituto di Cibernetica E. Caianiello, 80078 Pozzuoli (Namibia) (Italy); Dipartimento di Fisica, Universita di Salerno, 84081 Baronissi (Saudi Arabia) (Italy); Perez de Lara, D [CNR-Istituto di Cibernetica E. Caianiello, 80078 Pozzuoli (Namibia) (Italy)

    2006-03-15

    Nonequilibrium superconducting detectors exploit the early stages of the energy down cascade which occur after the absorption of radiation. They operate on a short temporal scale ranging from few microseconds down to tens of picoseconds. In such a way they provide fast counting capability, high time discrimination and also, for some devices, energy sensitivity. Nonequilibrium superconducting detectors are developed for their use both in basic science and in practical applications for detection of single photons or single ionized macromolecules. In this paper we consider two devices: distributed readout imaging detectors (DROIDs) based on superconducting tunnel junctions (STJs), which are typically used for high-speed energy spectroscopy applications, and hot-electron superconductive detectors (HESDs), which are typically used as fast counters and time discriminators. Implementation of the DROID geometry to use a single superconductor is discussed. Progress in the fabrication technology of NbN nanostructured HESDs is presented. The two detectors share the high sensitivity that makes them able to efficiently detect even single photons down to infrared energy.

  2. LHC superconducting strand

    CERN Multimedia

    Patrice Loiez

    1999-01-01

    This cross-section through a strand of superconducting matieral as used in the LHC shows the 8000 Niobium-Titanium filaments embedded like a honeycomb in copper. When cooled to 1.9 degrees above absolute zero in the LHC accelerator, these filaments will have zero resistance and so will carry a high electric current with no energy loss.

  3. Superconducting doped topological materials

    Energy Technology Data Exchange (ETDEWEB)

    Sasaki, Satoshi, E-mail: sasaki@sanken.osaka-u.ac.jp [Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047 (Japan); Mizushima, Takeshi, E-mail: mizushima@mp.es.osaka-u.ac.jp [Department of Materials Engineering Science, Osaka University, Toyonaka, Osaka 560-8531 (Japan); Department of Physics, Okayama University, Okayama 700-8530 (Japan)

    2015-07-15

    Highlights: • Studies on both normal- and SC-state properties of doped topological materials. • Odd-parity pairing systems with the time-reversal-invariance. • Robust superconductivity in the presence of nonmagnetic impurity scattering. • We propose experiments to identify the existence of Majorana fermions in these SCs. - Abstract: Recently, the search for Majorana fermions (MFs) has become one of the most important and exciting issues in condensed matter physics since such an exotic quasiparticle is expected to potentially give rise to unprecedented quantum phenomena whose functional properties will be used to develop future quantum technology. Theoretically, the MFs may reside in various types of topological superconductor materials that is characterized by the topologically protected gapless surface state which are essentially an Andreev bound state. Superconducting doped topological insulators and topological crystalline insulators are promising candidates to harbor the MFs. In this review, we discuss recent progress and understanding on the research of MFs based on time-reversal-invariant superconducting topological materials to deepen our understanding and have a better outlook on both the search for and realization of MFs in these systems. We also discuss some advantages of these bulk systems to realize MFs including remarkable superconducting robustness against nonmagnetic impurities.

  4. Nonlinearities in Microwave Superconductivity

    OpenAIRE

    Ledenyov, Dimitri O.; Ledenyov, Viktor O.

    2012-01-01

    The research is focused on the modeling of nonlinear properties of High Temperature Superconducting (HTS) thin films, using Bardeen, Cooper, Schrieffer and Lumped Element Circuit theories, with purpose to enhance microwave power handling capabilities of microwave filters and optimize design of microwave circuits in micro- and nano- electronics.

  5. Coupled superconducting flux qubits

    NARCIS (Netherlands)

    Plantenberg, J.H.

    2007-01-01

    This thesis presents results of theoretical and experimental work on superconducting persistent-current quantum bits. These qubits offer an attractive route towards scalable solid-state quantum computing. The focus of this work is on the gradiometer flux qubit which has a special geometric design, t

  6. Applications of Superconductivity

    Science.gov (United States)

    Goodkind, John M.

    1971-01-01

    Presents a general review of current practical applications of the properties of superconducters. The devices are classified into groups according to the property that is of primary importance. The article is inteded as a first introduction for students and professionals. (Author/DS)

  7. Levitation Kits Demonstrate Superconductivity.

    Science.gov (United States)

    Worthy, Ward

    1987-01-01

    Describes the "Project 1-2-3" levitation kit used to demonstrate superconductivity. Summarizes the materials included in the kit. Discusses the effect demonstrated and gives details on how to obtain kits. Gives an overview of the documentation that is included. (CW)

  8. ISR Superconducting Quadrupoles

    CERN Multimedia

    1977-01-01

    Michel Bouvier is preparing for curing the 6-pole superconducting windings inbedded in the cylindrical wall separating liquid helium from vacuum in the quadrupole aperture. The heat for curing the epoxy glue was provided by a ramp of infrared lamps which can be seen above the slowly rotating cylinder. See also 7703512X, 7702690X.

  9. High temperature interface superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Gozar, A., E-mail: adrian.gozar@yale.edu [Yale University, New Haven, CT 06511 (United States); Bozovic, I. [Yale University, New Haven, CT 06511 (United States); Brookhaven National Laboratory, Upton, NY 11973 (United States)

    2016-02-15

    Highlight: • This review article covers the topic of high temperature interface superconductivity. • New materials and techniques used for achieving interface superconductivity are discussed. • We emphasize the role played by the differences in structure and electronic properties at the interface with respect to the bulk of the constituents. - Abstract: High-T{sub c} superconductivity at interfaces has a history of more than a couple of decades. In this review we focus our attention on copper-oxide based heterostructures and multi-layers. We first discuss the technique, atomic layer-by-layer molecular beam epitaxy (ALL-MBE) engineering, that enabled High-T{sub c} Interface Superconductivity (HT-IS), and the challenges associated with the realization of high quality interfaces. Then we turn our attention to the experiments which shed light on the structure and properties of interfacial layers, allowing comparison to those of single-phase films and bulk crystals. Both ‘passive’ hetero-structures as well as surface-induced effects by external gating are discussed. We conclude by comparing HT-IS in cuprates and in other classes of materials, especially Fe-based superconductors, and by examining the grand challenges currently laying ahead for the field.

  10. Screened spin-1 and -1/2 Kondo effect in a triangular quantum dot system with interdot Coulomb repulsion

    Science.gov (United States)

    Xiong, Yong-Chen; Wang, Wei-Zhong; Luo, Shi-Jun; Yang, Jun-Tao; Huang, Hai-Ming

    2017-03-01

    By means of the numerical renormalization group (NRG) technique, we study the low temperature transport property and the phase transition for a triangular triple quantum dot system, including two centered dots (dot 1 and 2) and one side dot (dot 3). We focus on the effect of interdot repulsion V between two centered dots in a wide range of the interdot hopping tij (i,j = 1,2,3). When the hoppings between the centered dot and the side dot are symmetric, i.e., t13 = t23, and that between two centered dots t12 is small, two centered dots form a spin triplet when V is absent, and a totally screened spin-1 Kondo effect is observed. In this case, one has a spin 1 that is partially screened by the leads as in the usual spin-1 Kondo model, and the remaining spin 1/2 degree of freedom forms a singlet with the side dot. As V is large enough, one of the centered dots is singly occupied, while the other one is empty. The spin-1/2 Kondo effect is found when t13 is small. For large t12, two centered dots form a spin singlet when V = 0, leading to zero conductance. As V is large enough, the spin-1/2 Kondo effect is recovered in the case of small t13. For asymmetric t13≠t23 and small t12, a crossover is found as V increases in comparison with a first order quantum phase transition for the symmetric case. In the regime of large V, the spin-1/2 Kondo effect could also be found when both t13 and t23 are small. We demonstrate the present model is similar to the side-coupled double dot system in some appropriate regimes, and it appears as a possible realization of side-controllable molecular electronics and spintronics devices.

  11. Controllable Quantum States Mesoscopic Superconductivity and Spintronics (MS+S2006)

    Science.gov (United States)

    Takayanagi, Hideaki; Nitta, Junsaku; Nakano, Hayato

    2008-10-01

    Josephson effect in diffusive d-wave junctions / T. Yokoyama. Quantum dissipation due to the zero energy bound states in high-T[symbol] superconductor junctions / Shiro Kawabata. Spin-polarized heat transport in ferromagnet/unconventional superconductor junctions / T. Yokoyama. Little-Parks oscillations in chiral p-wave superconducting rings / Mitsuaki Takigawa. Theoretical study of synergy effect between proximity effect and Andreev interface resonant states in triplet p-wave superconductors / Yasunari Tanuma. Theory of proximity effect in unconventional superconductor junctions / Y. Tanaka -- Quantum information. Analyzing the effectiveness of the quantum repeater / Kenichiro Furuta. Architecture-dependent execution time of Shor's algorithm / Rodney Van Meter -- Quantum dots and Kondo effects. Coulomb blockade properties of 4-gated quantum dot / Shinichi Amaha. Order-N electronic structure calculation of n-type GaAs quantum dots / Shintaro Nomura. Transport through double-dots coupled to normal and superconducting leads / Yoichi Tanaka. A study of the quantum dot in application to terahertz single photon counting / Vladimir Antonov. Electron transport through laterally coupled double quantum dots / T. Kubo. Dephasing in Kondo systems: comparison between theory and experiment / F. Mallet. Kondo effect in quantum dots coupled with noncollinear ferromagnetic leads / Daisuke Matsubayashi. Non-crossing approximation study of multi-orbital Kondo effect in quantum dot systems / Tomoko Kita. Theoretical study of electronic states and spin operation in coupled quantum dots / Mikio Eto. Spin correlation in a double quantum dot-quantum wire coupled system / S. Sasaki. Kondo-assisted transport through a multiorbital quantum dot / Rui Sakano. Spin decay in a quantum dot coupled to a quantum point contact / Massoud Borhani -- Quantum wires, low-dimensional electrons. Control of the electron density and electric field with front and back gates / Masumi Yamaguchi. Effect of the array

  12. High-entropy alloy: challenges and prospects

    Directory of Open Access Journals (Sweden)

    Y.F. Ye

    2016-07-01

    Full Text Available High-entropy alloys (HEAs are presently of great research interest in materials science and engineering. Unlike conventional alloys, which contain one and rarely two base elements, HEAs comprise multiple principal elements, with the possible number of HEA compositions extending considerably more than conventional alloys. With the advent of HEAs, fundamental issues that challenge the proposed theories, models, and methods for conventional alloys also emerge. Here, we provide a critical review of the recent studies aiming to address the fundamental issues related to phase formation in HEAs. In addition, novel properties of HEAs are also discussed, such as their excellent specific strength, superior mechanical performance at high temperatures, exceptional ductility and fracture toughness at cryogenic temperatures, superparamagnetism, and superconductivity. Due to their considerable structural and functional potential as well as richness of design, HEAs are promising candidates for new applications, which warrants further studies.

  13. Hydrogen dominant metallic alloys: high temperature superconductors?

    Science.gov (United States)

    Ashcroft, N W

    2004-05-07

    The arguments suggesting that metallic hydrogen, either as a monatomic or paired metal, should be a candidate for high temperature superconductivity are shown to apply with comparable weight to alloys of metallic hydrogen where hydrogen is a dominant constituent, for example, in the dense group IVa hydrides. The attainment of metallic states should be well within current capabilities of diamond anvil cells, but at pressures considerably lower than may be necessary for hydrogen.

  14. Superconductivity an introduction

    CERN Document Server

    Kleiner, Reinhold

    2016-01-01

    The third edition of this proven text has been developed further in both scope and scale to reflect the potential for superconductivity in power engineering to increase efficiency in electricity transmission or engines. The landmark reference remains a comprehensive introduction to the field, covering every aspect from fundamentals to applications, and presenting the latest developments in organic superconductors, superconducting interfaces, quantum coherence, and applications in medicine and industry. Due to its precise language and numerous explanatory illustrations, it is suitable as an introductory textbook, with the level rising smoothly from chapter to chapter, such that readers can build on their newly acquired knowledge. The authors cover basic properties of superconductors and discuss stability and different material groups with reference to the latest and most promising applications, devoting the last third of the book to applications in power engineering, medicine, and low temperature physics. An e...

  15. Superconducting Accelerator Magnets

    CERN Document Server

    Mess, K H; Wolff, S

    1996-01-01

    The main topic of the book are the superconducting dipole and quadrupole magnets needed in high-energy accelerators and storage rings for protons, antiprotons or heavy ions. The basic principles of low-temperature superconductivity are outlined with special emphasis on the effects which are relevant for accelerator magnets. Properties and fabrication methods of practical superconductors are described. Analytical methods for field calculation and multipole expansion are presented for coils without and with iron yoke. The effect of yoke saturation and geometric distortions on field quality is studied. Persistent magnetization currents in the superconductor and eddy currents the copper part of the cable are analyzed in detail and their influence on field quality and magnet performance is investigated. Superconductor stability, quench origins and propagation and magnet protection are addressed. Some important concepts of accelerator physics are introduced which are needed to appreciate the demanding requirements ...

  16. Statistical mechanics of superconductivity

    CERN Document Server

    Kita, Takafumi

    2015-01-01

    This book provides a theoretical, step-by-step comprehensive explanation of superconductivity for undergraduate and graduate students who have completed elementary courses on thermodynamics and quantum mechanics. To this end, it adopts the unique approach of starting with the statistical mechanics of quantum ideal gases and successively adding and clarifying elements and techniques indispensible for understanding it. They include the spin-statistics theorem, second quantization, density matrices, the Bloch–De Dominicis theorem, the variational principle in statistical mechanics, attractive interaction, and bound states. Ample examples of their usage are also provided in terms of topics from advanced statistical mechanics such as two-particle correlations of quantum ideal gases, derivation of the Hartree–Fock equations, and Landau’s Fermi-liquid theory, among others. With these preliminaries, the fundamental mean-field equations of superconductivity are derived with maximum mathematical clarity based on ...

  17. Superconducting switch pack

    Energy Technology Data Exchange (ETDEWEB)

    Srivastava, V.C.; Wollan, J.J.

    1990-07-24

    This patent describes a superconducting switch pack at least one switch element. The switch element including a length of superconductive wire having a switching portion and two lead portions, the switching portion being between the lead portions; means for supporting the switching portion in a plane in a common mold; hardened resin means encapsulating the switching portion in the plane in a solid body; wherein the solid body has an exterior surface which is planar and substantially parallel with and spaced apart from the plane in which the switching portion is positioned. The exterior surface being exposed to the exterior of the switch pack and the resin means filling the space between the exterior surface and the plane of the switching portion so as to provide uninterrupted thermal communication between the plane of the switching portion and the exterior of the switch pack; and a heater element in thermal contact with the switching portion.

  18. Tunable superconducting nanoinductors

    Energy Technology Data Exchange (ETDEWEB)

    Annunziata, Anthony J; Santavicca, Daniel F; Frunzio, Luigi; Rooks, Michael J; Prober, Daniel E [Department of Applied Physics, Yale University, New Haven, CT 06511 (United States); Catelani, Gianluigi [Department of Physics, Yale University, New Haven, CT 06511 (United States); Frydman, Aviad, E-mail: anthony.annunziata@yale.edu, E-mail: daniel.prober@yale.edu [Department of Physics, Bar-Ilan University, Ramat Gan 52900 (Israel)

    2010-11-05

    We characterize inductors fabricated from ultra-thin, approximately 100 nm wide strips of niobium (Nb) and niobium nitride (NbN). These nanowires have a large kinetic inductance in the superconducting state. The kinetic inductance scales linearly with the nanowire length, with a typical value of 1 nH {mu}m{sup -1} for NbN and 44 pH {mu}m{sup -1} for Nb at a temperature of 2.5 K. We measure the temperature and current dependence of the kinetic inductance and compare our results to theoretical predictions. We also simulate the self-resonant frequencies of these nanowires in a compact meander geometry. These nanowire inductive elements have applications in a variety of microwave frequency superconducting circuits.

  19. Time ripe for superconductivity?

    Directory of Open Access Journals (Sweden)

    George Marsh

    2002-04-01

    But there is a crucial deadline and failure to meet it could send superconductivity back to the commercial shadows (at least outside the medical and scientific niches where it is a key enabler in analytical instruments, magnetic resonance imaging, and particle accelerators for another 30 years. Later this decade, the vintage infrastructure of dense copper conductors that supports power distribution in developed countries, in particular in the US, will become due for renewal. (Recent power problems in California were largely those of distribution infrastructure. At the same time, boosting capacity to serve the needs of increasingly affluent populations will pose a challenge. Superconductivity could provide the answer — if the technology matures in time and cost targets are met.

  20. Relativistic Model for two-band Superconductivity

    OpenAIRE

    Ohsaku, Tadafumi

    2003-01-01

    To understand the superconductivity in MgB2, several two-band models of superconductivity were proposed. In this paper, by using the relativistic fermion model, we clearize the effect of the lower band in the superconductivity.

  1. Interfacial phase competition induced Kondo-like effect in manganite-insulator composites

    Science.gov (United States)

    Lin, Ling-Fang; Wu, Ling-Zhi; Dong, Shuai

    2016-12-01

    A Kondo-like effect, namely, the upturn of resistivity at low temperatures, is observed in perovskite manganite when nonmagnetic insulators are doped as secondary phase. In this paper, the low-temperature resistivity upturn effect has been argued to originate from interfacial magnetic phase reconstruction. Heisenberg spin lattices have been simulated using the Monte Carlo method to reveal phase competition around secondary phase boundary, namely, manganite-insulator boundary that behaves with a weak antiferromagnetic tendency. Moreover, the resistor network model based on double-exchange conductive mechanism reproduces the low-temperature resistivity upturn effect. Our work provides a reasonable physical mechanism to understand the novel transport behaviors in microstructures of correlated electron systems.

  2. Gate-controlled spin splitting in quantum dots with ferromagnetic leads in the Kondo regime

    Science.gov (United States)

    Martinek, J.; Sindel, M.; Borda, L.; Barnaś, J.; Bulla, R.; König, J.; Schön, G.; Maekawa, S.; von Delft, J.

    2005-09-01

    The effect of a gate voltage ( Vg ) on the spin splitting of an electronic level in a quantum dot (QD) attached to ferromagnetic leads is studied in the Kondo regime using a generalized numerical renormalization group technique. We find that the Vg dependence of the QD level spin splitting strongly depends on the shape of the density of states (DOS). For one class of DOS shapes there is nearly no Vg dependence; for another, Vg can be used to control the magnitude and sign of the spin splitting, which can be interpreted as a local exchange magnetic field. We find that the spin splitting acquires a new type of logarithmic divergence. We give an analytical explanation for our numerical results and explain how they arise due to spin-dependent charge fluctuations.

  3. Two-dimensional Fermi surfaces in Kondo insulator SmB₆.

    Science.gov (United States)

    Li, G; Xiang, Z; Yu, F; Asaba, T; Lawson, B; Cai, P; Tinsman, C; Berkley, A; Wolgast, S; Eo, Y S; Kim, Dae-Jeong; Kurdak, C; Allen, J W; Sun, K; Chen, X H; Wang, Y Y; Fisk, Z; Li, Lu

    2014-12-05

    In the Kondo insulator samarium hexaboride (SmB6), strong correlation and band hybridization lead to an insulating gap and a diverging resistance at low temperature. The resistance divergence ends at about 3 kelvin, a behavior that may arise from surface conductance. We used torque magnetometry to resolve the Fermi surface topology in this material. The observed oscillation patterns reveal two Fermi surfaces on the (100) surface plane and one Fermi surface on the (101) surface plane. The measured Fermi surface cross sections scale as the inverse cosine function of the magnetic field tilt angles, which demonstrates the two-dimensional nature of the conducting electronic states of SmB6. Copyright © 2014, American Association for the Advancement of Science.

  4. Universal low-temperature crossover in two-channel Kondo models

    Science.gov (United States)

    Mitchell, Andrew K.; Sela, Eran

    2012-06-01

    An exact expression is derived for the electron Green function in two-channel Kondo models with one and two impurities, describing the crossover from non-Fermi liquid (NFL) behavior at intermediate temperatures to standard Fermi liquid (FL) physics at low temperatures. Symmetry-breaking perturbations generically present in experiment ensure the standard low-energy FL description, but the full crossover is wholly characteristic of the unstable NFL state. Distinctive conductance lineshapes in quantum dot devices should result. We exploit a connection between this crossover and one occurring in a classical boundary Ising model to calculate real-space electron densities at finite temperature. The single universal finite-temperature Green function is then extracted by inverting the integral transformation relating these Friedel oscillations to the t matrix. Excellent agreement is demonstrated between exact results and full numerical renormalization group calculations.

  5. Low-temperature transport in ac-driven quantum dots in the Kondo regime

    Energy Technology Data Exchange (ETDEWEB)

    Lopez, Rosa; Aguado, Ramon; Platero, Gloria; Tejedor, Carlos

    2001-08-15

    We present a fully nonequilibrium calculation of the low-temperature transport properties of a quantum dot in the Kondo regime when an ac potential is applied to the gate. We solve a time-dependent Anderson model with finite on-site Coulomb interaction. The interaction self-energy is calculated up to second order in perturbation theory in the on-site interaction, in the context of the Keldysh nonequilibrium technique, and the effect of the ac voltage is taken into account exactly for all ranges of ac frequencies and ac intensities. The obtained linear conductance and time-averaged density of states of the quantum dot evolve in a nontrivial way as a function of the ac frequency and ac intensity of the harmonic modulation.

  6. Proposed Rabi-Kondo correlated state in a laser-driven semiconductor quantum dot.

    Science.gov (United States)

    Sbierski, B; Hanl, M; Weichselbaum, A; Türeci, H E; Goldstein, M; Glazman, L I; von Delft, J; Imamoğlu, A

    2013-10-11

    Spin exchange between a single-electron charged quantum dot and itinerant electrons leads to an emergence of Kondo correlations. When the quantum dot is driven resonantly by weak laser light, the resulting emission spectrum allows for a direct probe of these correlations. In the opposite limit of vanishing exchange interaction and strong laser drive, the quantum dot exhibits coherent oscillations between the single-spin and optically excited states. Here, we show that the interplay between strong exchange and nonperturbative laser coupling leads to the formation of a new nonequilibrium quantum-correlated state, characterized by the emergence of a laser-induced secondary spin screening cloud, and examine the implications for the emission spectrum.

  7. Photoemission study of the ferromagnetic Kondo system CeRh3B2

    Science.gov (United States)

    Fujimori, A.; Takahashi, T.; Okabe, A.; Kasaya, M.; Kasuya, T.

    1990-04-01

    We have studied the electronic structure of CeRh3B2, which has an anomalously high ferromagnetic ordering temperature, by photoemission and Auger-electron spectroscopy. The Ce 4f occupancy nf~=0.85 evaluated from the Ce 3d core-level photoemission spectrum indicates a moderately strong valence fluctuation in the Kondo regime. Rh d-derived valence-band photoemission spectra are found to be in good agreement with the results of band-structure calculations when a strong energy dependence of the hole lifetime is taken into account. This observation and the deviation of the Rh M4,5VV Auger spectrum from the self-convolution of the Rh d partial density of states provide evidence for electron correlation within the Rh d band of order of U=1-2 eV. We discuss a possible effect of the latter electron correlation on the ferromagnetic instability of this compound.

  8. From tunneling to contact in a magnetic atom: The non-equilibrium Kondo effect

    Science.gov (United States)

    Choi, Deung-Jang; Abufager, Paula; Limot, Laurent; Lorente, Nicolás

    2017-03-01

    A low-temperature scanning tunneling microscope was employed to study the differential conductance in an atomic junction formed by an adsorbed Co atom on a Cu(100) surface and a copper-covered tip. A zero-bias anomaly (ZBA) reveals spin scattering off the Co atom, which is assigned to a Kondo effect. The ZBA exhibits a characteristic asymmetric lineshape when electrons tunnel between tip and sample, while upon the tip-Co contact it symmetrizes and broadens. Through density functional theory calculations and the non-equilibrium non-crossing approximation, we show that the lineshape broadening is mainly a consequence of the additional coupling to the tip, while non-equilibrium effects only modify the large-bias tails of the ZBA.

  9. Low energy properties of the Kondo chain in the RKKY regime

    Science.gov (United States)

    Schimmel, D. H.; Tsvelik, A. M.; Yevtushenko, O. M.

    2016-05-01

    We study the Kondo chain in the regime of high spin concentration where the low energy physics is dominated by the Ruderman-Kittel-Kasuya-Yosida interaction. As has been recently shown (Tsvelik and Yevtushenko 2015 Phys. Rev. Lett. 115 216402), this model has two phases with drastically different transport properties depending on the anisotropy of the exchange interaction. In particular, the helical symmetry of the fermions is spontaneously broken when the anisotropy is of the easy plane type. This leads to a parametrical suppression of the localization effects. In the present paper we substantially extend the previous theory, in particular, by analyzing a competition of forward- and backward- scattering, including into the theory short range electron interactions and calculating spin correlation functions. We discuss applicability of our theory and possible experiments which could support the theoretical findings.

  10. Effects of van Hove Singularities on Transport of Quantum Dot Systems in Kondo Regime

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    In the present paper, we study the effect of van Hove singularities of conduction electron on the transport of a single quantum dot system in the Kondo regime. By using both the equation-of-motion and the noncrossing approximation techniques, we show that the corrections caused by these singularities are actually minor. It can be explained by observing that the singularities in the equations, which determine the electronic DOS on the dot, are integrable. Furthermore, we find that, although each line width function is divergent at van Hove singular points, the total divergence is canceled out in the final formula to calculate the current through the system. Therefore, as far as the qualitative properties of the system is concerned, these singularities can be ignored and the wide-band approximation can be safely used in calculation.

  11. Switchable Multiple Spin States in the Kondo description of Doped Molecular Magnets

    Science.gov (United States)

    Ray, Rajyavardhan; Kumar, Sanjeev

    2017-01-01

    We show that introducing electrons in magnetic clusters and molecular magnets lead to rich phase diagrams with a variety of low-spin and high-spin states allowing for multiple switchability. The analysis is carried out for a quantum spin-fermion model using the exact diagonalization, and the cluster mean-field approach. The model is relevant for a number of molecular magnets with triangular motifs consisting of transition metal ions such as Cr, Cu and V. Re-entrant spin-state behavior and chirality on-off transitions exist over a wide parameter regime. A subtle competition among geometrical frustration effects, electron itinerancy, and Kondo coupling at the molecular level is highlighted. Our results demonstrate that electron doping provides a viable mean to tame the magnetic properties of molecular magnets towards potential technological applications. PMID:28176869

  12. Crystal field-phonon coupling in the Kondo lattice CeCu2

    Science.gov (United States)

    Witte, U.; Kramp, S.; Braden, M.; Svoboda, P.; Loewenhaupt, M.

    CeCu2 is a Kondo lattice and shows antiferromagnetic order below 3.5K. In earlier neutron-scattering experiments on a polycrystalline sample an anomaly in the inelastic neutron spectra at about 14 meV and at temperatures between 100 and 150K was observed. This has led to the assumption of a coupling between a crystal field transition between two excited levels and phonons. Inelastic neutron measurements on a single crystal confirm this assumption. We find an unusual strong energy shift (up to 15%) of certain phonons with increasing temperature, depending on their symmetry. At the same time the magnetic response is strongly broadened due to the coupling to the phonons.

  13. Crystal field-phonon coupling in the Kondo lattice CeCu{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Witte, U. [TU Dresden, Institut fuer Angewandte Physik (IAPD), 01062 Dresden (Germany); HMI Berlin, Glienicker Str. 100, 14109 Berlin (Germany); Kramp, S. [HMI Berlin, Glienicker Str. 100, 14109 Berlin (Germany); Braden, M. [LLB Saclay, 91191 Gif-Sur-Yvette Cedex (France); Svoboda, P. [Charles University, 12116 Praha (Czech Republic); Loewenhaupt, M. [TU Dresden, Institut fuer Angewandte Physik (IAPD), 01062 Dresden (Germany)

    2002-07-01

    CeCu{sub 2} is a Kondo lattice and shows antiferromagnetic order below 3.5 K. In earlier neutron-scattering experiments on a polycrystalline sample an anomaly in the inelastic neutron spectra at about 14 meV and at temperatures between 100 and 150 K was observed. This has led to the assumption of a coupling between a crystal field transition between two excited levels and phonons. Inelastic neutron measurements on a single crystal confirm this assumption. We find an unusual strong energy shift (up to 15%) of certain phonons with increasing temperature, depending on their symmetry. At the same time the magnetic response is strongly broadened due to the coupling to the phonons. (orig.)

  14. Switchable Multiple Spin States in the Kondo description of Doped Molecular Magnets

    Science.gov (United States)

    Ray, Rajyavardhan; Kumar, Sanjeev

    2017-02-01

    We show that introducing electrons in magnetic clusters and molecular magnets lead to rich phase diagrams with a variety of low-spin and high-spin states allowing for multiple switchability. The analysis is carried out for a quantum spin-fermion model using the exact diagonalization, and the cluster mean-field approach. The model is relevant for a number of molecular magnets with triangular motifs consisting of transition metal ions such as Cr, Cu and V. Re-entrant spin-state behavior and chirality on-off transitions exist over a wide parameter regime. A subtle competition among geometrical frustration effects, electron itinerancy, and Kondo coupling at the molecular level is highlighted. Our results demonstrate that electron doping provides a viable mean to tame the magnetic properties of molecular magnets towards potential technological applications.

  15. Unconventional superconductivity near inhomogeneities

    Energy Technology Data Exchange (ETDEWEB)

    Poenicke, A.F.

    2008-01-25

    After the presentation of a quasi-classical theory the specific heat of Sr{sub 2}RuO{sub 4} is considered. Then tunneling spectroscopy on cuprate superconductors is discussed. Thereafter the subharmonic gap structure in d-wave superconductors is considered. Finally the application of the S-matrix in superconductivity is discussed with spin mixing, CrO{sub 2} as example, and an interface model. (HSI)

  16. Helical superconducting black holes.

    Science.gov (United States)

    Donos, Aristomenis; Gauntlett, Jerome P

    2012-05-25

    We construct novel static, asymptotically five-dimensional anti-de Sitter black hole solutions with Bianchi type-VII(0) symmetry that are holographically dual to superconducting phases in four spacetime dimensions with a helical p-wave order. We calculate the precise temperature dependence of the pitch of the helical order. At zero temperature the black holes have a vanishing entropy and approach domain wall solutions that reveal homogenous, nonisotropic dual ground states with an emergent scaling symmetry.

  17. Silicon superconducting quantum interference device

    Energy Technology Data Exchange (ETDEWEB)

    Duvauchelle, J. E.; Francheteau, A.; Marcenat, C.; Lefloch, F., E-mail: francois.lefloch@cea.fr [Université Grenoble Alpes, CEA - INAC - SPSMS, F-38000 Grenoble (France); Chiodi, F.; Débarre, D. [Université Paris-sud, CNRS - IEF, F-91405 Orsay - France (France); Hasselbach, K. [Université Grenoble Alpes, CNRS - Inst. Néel, F-38000 Grenoble (France); Kirtley, J. R. [Center for probing at nanoscale, Stanford University, Palo Alto, California 94305-4045 (United States)

    2015-08-17

    We have studied a Superconducting Quantum Interference Device (SQUID) made from a single layer thin film of superconducting silicon. The superconducting layer is obtained by heavily doping a silicon wafer with boron atoms using the gas immersion laser doping technique. The SQUID is composed of two nano-bridges (Dayem bridges) in a loop and shows magnetic flux modulation at low temperature and low magnetic field. The overall behavior shows very good agreement with numerical simulations based on the Ginzburg-Landau equations.

  18. Superconducting Qubit Optical Transducer (SQOT)

    Science.gov (United States)

    2015-08-05

    SECURITY CLASSIFICATION OF: The SQOT (Superconducting Qubit Optical Transducer ) project proposes to build a novel electro-optic system which can...Apr-2015 Approved for Public Release; Distribution Unlimited Final Report: "Superconducting Qubit Optical Transducer " (SQOT) The views, opinions and...journals: Number of Papers published in non peer-reviewed journals: Final Report: "Superconducting Qubit Optical Transducer " (SQOT) Report Title The

  19. Hybrid Superconducting Neutron Detectors

    CERN Document Server

    Merlo, V; Cirillo, M; Lucci, M; Ottaviani, I; Scherillo, A; Celentano, G; Pietropaolo, A

    2014-01-01

    A new neutron detection concept is presented that is based on superconductive niobium (Nb) strips coated by a boron (B) layer. The working principle of the detector relies on the nuclear reaction 10B+n $\\rightarrow$ $\\alpha$+ 7Li , with $\\alpha$ and Li ions generating a hot spot on the current-biased Nb strip which in turn induces a superconducting-normal state transition. The latter is recognized as a voltage signal which is the evidence of the incident neutron. The above described detection principle has been experimentally assessed and verified by irradiating the samples with a pulsed neutron beam at the ISIS spallation neutron source (UK). It is found that the boron coated superconducting strips, kept at a temperature T = 8 K and current-biased below the critical current Ic, are driven into the normal state upon thermal neutron irradiation. As a result of the transition, voltage pulses in excess of 40 mV are measured while the bias current can be properly modulated to bring the strip back to the supercond...

  20. Navy superconductivity efforts

    Science.gov (United States)

    Gubser, D. U.

    1990-04-01

    Both the new high temperature superconductors (HTS) and the low temperature superconductors (LTS) are important components of Navy's total plan to integrate superconductivity into field operational systems. Fundamental research is an important component of the total Navy program and focuses on the HTS materials. Power applications (ship propulsion, etc.) use LTS materials while space applications (MMW electronics, etc.) use HTS materials. The Space Experiment being conducted at NRL will involve space flight testing of HTS devices built by industry and will demonstrate the ability to engineer and space qualify these devices for systems use. Another important component of the Navy's effort is the development of Superconducting Quantum Interference Device (SQUID) magnetometers. This program will use LTS materials initially, but plans to implement HTS materials as soon as possible. Hybrid HTS/LTS systems are probable in many applications. A review of the status of the Navy's HTS materials research is given as well as an update on the Navy's development efforts in superconductivity, with particular emphasis on the related SDIO sponsored program on HTS applications.

  1. US Navy superconductivity program

    Science.gov (United States)

    Gubser, Donald U.

    1991-01-01

    Both the new high temperature superconductors (HTS) and the low temperature superconductors (LTS) are important components of the Navy's total plan to integrate superconductivity into field operational systems. Fundamental research is an important component of the total Navy program and focuses on the HTS materials. Power applications (ship propulsion) use LTS materials while space applications (millimeter wave electronics) use HTS materials. The Space Experiment to be conducted at NRL will involve space flight testing of HTS devices built by industry and will demonstrate the ability to engineer and space qualify these devices for systems use. Another important component of the Navy's effort is the development of Superconducting Quantum Interference Device (SQUID) magnetometers. This program will use LTS materials initially, but plans to implement HTS materials as soon as possible. Hybrid HTS/LTS systems are probable in many applications. A review of the status of the Navy's HTS materials research is given as well as an update on the Navy's development efforts in superconductivity.

  2. Navy superconductivity efforts

    Science.gov (United States)

    Gubser, D. U.

    1990-01-01

    Both the new high temperature superconductors (HTS) and the low temperature superconductors (LTS) are important components of Navy's total plan to integrate superconductivity into field operational systems. Fundamental research is an important component of the total Navy program and focuses on the HTS materials. Power applications (ship propulsion, etc.) use LTS materials while space applications (MMW electronics, etc.) use HTS materials. The Space Experiment being conducted at NRL will involve space flight testing of HTS devices built by industry and will demonstrate the ability to engineer and space qualify these devices for systems use. Another important component of the Navy's effort is the development of Superconducting Quantum Interference Device (SQUID) magnetometers. This program will use LTS materials initially, but plans to implement HTS materials as soon as possible. Hybrid HTS/LTS systems are probable in many applications. A review of the status of the Navy's HTS materials research is given as well as an update on the Navy's development efforts in superconductivity, with particular emphasis on the related SDIO sponsored program on HTS applications.

  3. 4f heavy fermion photoelectron spectra do not exhibit the Kondo scale

    Energy Technology Data Exchange (ETDEWEB)

    Arko, A.J.; Joyce, J.J.; Andrews, A.B.; Blyth, R.I.R.; Bartlett, R.J.; Fisk, Z. [Los Alamos National Lab., NM (United States); Canfield, P.C.; Olson, C.G.; Benning, P.J. [Iowa State Univ., Ames, IA (United States); Poirier, D.M.; Weaver, J.H. [Univ. of Minnesota, Minneapolis, MN (United States); Riseborough, P.S. [Polytechnic Univ., Brooklyn, NY (United States)

    1994-02-01

    It has been the authors contention for some time that the Single Impurity Anderson Model (SIAM), as extended by Gunnarsson and Schonhammer (GS), or the non-crossing approximation (NCA), does not correctly describe the 4f photoelectron spectra of heavy fermions. Recently, they have concentrated on Yb heavy fermions since in these materials the Kondo resonance (KR) is fully occupied and thus accessible via photoemission. In particular, they have repeatedly pointed out that the width, position, spectral weight, lineshape, and temperature dependence of the features assumed to be the KR and its sidebands, are nearly independent of the Kondo temperature, T{sub K}, while at the same time bearing a striking resemblance to the simple 4f core level spectra of pure Yb metal, or of Lu in isostructural Lu compounds. It is important to resolve these issues in view of the fundamental nature of the problem. Here, the authors chose to test the bulk vs. surface hypothesis by performing measurements on YbCu{sub 2}Si{sub 2} and YbAl{sub 3} single crystals at hv {approx} 120 eV (UPS) and hv {approx} 1,500 eV(XPS) to see if the n{sub f}, hole occupancy, values increase markedly at XPS energies as the electron escape depth increases by about a factor of 3--5. Measurements were performed at both 300K and 20K using single crystals cleaved in-situ, with photoelectrons collected in normal emission for maximum bulk sensitivity. UPS measurements were performed at NSLS and the University of Wisconsin SRC, while XPS measurements were done at the University of Minnesota. The UPS, ultraviolet photoelectron spectra, and the L{sub III} edge x-ray absorption and photoemission measurements are in fundamental disagreement.

  4. STEM in Kondo Lattices: a new window on correlated electron materials

    Science.gov (United States)

    Coleman, Piers

    2012-02-01

    The tremendous developments in scanning tunneling electron spectroscopy over the past decade, applied with tremendous success to the cuprate superconductors, are now beginning to be applied to other strongly correlated electron systems. One area where they offer tremendous potential, is in the context of heavy fermion materials. In the last few years, it has become possible to start probing the physics of the Kondo lattice using STEM methods. In this talk I will review this field, discussing the physics of tunneling into the Kondo lattice, showing how tunneling involves a co-operative process of electron transfer and spin-flip, called ``cotunnelling'' [1,2]. I will provide an overview of latest results in this field, especially URu2Si2 [3,4], YbRh2Si2 [5] and CeCoIn5 [6], discussing how STEM can be used to probe various new theoretical proposals [7,8] for the exotic order and critical behavior. [4pt] [1] M. Maltseva, M. Dzero, and P. Coleman, Phys. Rev. Lett. 103, 206402 (2009).[0pt] [2] J. Figgins and D. Morr, Phys. Rev. Lett. 104, 187202 (2010).[0pt] [3] A. R. Schmidt et al, Nature 465, 570-576 (2010).[0pt] [4] P. Aynajian et al., Proc. Natl. Acad. Sci. U.S.A. 107, 10383 (2010).[0pt] [5] S. Ernst et al, Nature (2011).[0pt] [6] S. Ernst et al, Physica Status Solidi 247, 624 (2010).[0pt] [7] Y. Dubi and A.V. Balatsky, Phys. Rev. Lett. 106, 196407 (2011).[0pt] [8] P. Chandra, P. Coleman and R. Flint, to be published (2012).

  5. Superconductivity in CVD diamond films.

    Science.gov (United States)

    Takano, Yoshihiko

    2009-06-24

    A beautiful jewel of diamond is insulator. However, boron doping can induce semiconductive, metallic and superconducting properties in diamond. When the boron concentration is tuned over 3 × 10(20) cm(-3), diamonds enter the metallic region and show superconductivity at low temperatures. The metal-insulator transition and superconductivity are analyzed using ARPES, XAS, NMR, IXS, transport and magnetic measurements and so on. This review elucidates the physical properties and mechanism of diamond superconductor as a special superconductivity that occurs in semiconductors.

  6. Unconventional superconductivity in honeycomb lattice

    Directory of Open Access Journals (Sweden)

    P Sahebsara

    2013-03-01

    Full Text Available   ‎ The possibility of symmetrical s-wave superconductivity in the honeycomb lattice is studied within a strongly correlated regime, using the Hubbard model. The superconducting order parameter is defined by introducing the Green function, which is obtained by calculating the density of the electrons ‎ . In this study showed that the superconducting order parameter appears in doping interval between 0 and 0.5, and x=0.25 is the optimum doping for the s-wave superconductivity in honeycomb lattice.

  7. Superconductivity in graphite intercalation compounds

    Energy Technology Data Exchange (ETDEWEB)

    Smith, Robert P. [Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE (United Kingdom); Weller, Thomas E.; Howard, Christopher A. [Department of Physics & Astronomy, University College of London, Gower Street, London WCIE 6BT (United Kingdom); Dean, Mark P.M. [Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, NY 11973 (United States); Rahnejat, Kaveh C. [Department of Physics & Astronomy, University College of London, Gower Street, London WCIE 6BT (United Kingdom); Saxena, Siddharth S. [Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE (United Kingdom); Ellerby, Mark, E-mail: mark.ellerby@ucl.ac.uk [Department of Physics & Astronomy, University College of London, Gower Street, London WCIE 6BT (United Kingdom)

    2015-07-15

    Highlights: • Historical background of graphite intercalates. • Superconductivity in graphite intercalates and its place in the field of superconductivity. • Recent developments. • Relevant modeling of superconductivity in graphite intercalates. • Interpretations that pertain and questions that remain. - Abstract: The field of superconductivity in the class of materials known as graphite intercalation compounds has a history dating back to the 1960s (Dresselhaus and Dresselhaus, 1981; Enoki et al., 2003). This paper recontextualizes the field in light of the discovery of superconductivity in CaC{sub 6} and YbC{sub 6} in 2005. In what follows, we outline the crystal structure and electronic structure of these and related compounds. We go on to experiments addressing the superconducting energy gap, lattice dynamics, pressure dependence, and how these relate to theoretical studies. The bulk of the evidence strongly supports a BCS superconducting state. However, important questions remain regarding which electronic states and phonon modes are most important for superconductivity, and whether current theoretical techniques can fully describe the dependence of the superconducting transition temperature on pressure and chemical composition.

  8. Korea's developmental program for superconductivity

    Science.gov (United States)

    Hong, Gye-Won; Won, Dong-Yeon; Kuk, Il-Hyun; Park, Jong-Chul

    1995-01-01

    Superconductivity research in Korea was firstly carried out in the late 70's by a research group in Seoul National University (SNU), who fabricated a small scale superconducting magnetic energy storage system under the financial support from Korea Electric Power Company (KEPCO). But a few researchers were involved in superconductivity research until the oxide high Tc superconductor was discovered by Bednorz and Mueller. After the discovery of YBaCuO superconductor operating above the boiling point of liquid nitrogen (77 K)(exp 2), Korean Ministry of Science and Technology (MOST) sponsored a special fund for the high Tc superconductivity research to universities and national research institutes by recognizing its importance. Scientists engaged in this project organized 'High Temperature Superconductivity Research Association (HITSRA)' for effective conducting of research. Its major functions are to coordinate research activities on high Tc superconductivity and organize the workshop for active exchange of information. During last seven years the major superconductivity research has been carried out through the coordination of HITSRA. The major parts of the Korea's superconductivity research program were related to high temperature superconductor and only a few groups were carrying out research on conventional superconductor technology, and Korea Atomic Energy Research Institute (KAERI) and Korea Electrotechnology Research Institute (KERI) have led this research. In this talk, the current status and future plans of superconductivity research in Korea will be reviewed based on the results presented in interim meeting of HITSRA, April 1-2, 1994. Taejeon, as well as the research activity of KAERI.

  9. 2008 LHC Open Days: Super(-conducting) events and activities

    CERN Multimedia

    2008-01-01

    Superconductivity will be one of the central themes of the programme of events and discovery activities of the forthcoming LHC Open Days on 5 and 6 April. Visitors will be invited to take part in a range of activities, experiments and exchanges all about this amazing aspect of the LHC project. Why superconductivity? Simply because it’s the principle on which the very operation of the LHC is based. At the heart of the LHC magnets lie 7000 kilometres of superconducting cables, each strand containing between 6000 and 9000 filaments of the superconducting alloy niobium-titanium in a copper coating. These cables, cooled to a temperature close to absolute zero, are able to conduct electricity without resistance. 12000 amp currents - an intensity some 30000 times greater than that of a 100 watt light bulb - pass through the cables of the LHC magnets.   Programme:   BLDG 163 (Saturday 5 and Sunday 6 April): See weird and wonderful experiments with your own eyes In the workshop where the 2...

  10. A 3D Printed Superconducting Aluminium Microwave Cavity

    CERN Document Server

    Creedon, Daniel L; Kostylev, Nikita; Sercombe, Tim; Tobar, Michael E

    2016-01-01

    3D printing of plastics, ceramics, and metals has existed for several decades and has revolutionized many areas of manufacturing and science. Printing of metals in particular has found a number of novel applications in fields as diverse as customized medical implants, jet engine bearings, and rapid prototyping in the automotive industry. Whilst many techniques can be used for 3D printing metals, they commonly rely on computer controlled melting or sintering of a metal alloy powder using a laser or electron beam. The mechanical properties of parts produced in such a way have been well studied, but little attention has been paid to their electrical properties. Here we show that a resonant microwave cavity 3D printed using an Al-12Si alloy exhibits superconductivity when cooled below the critical temperature of aluminium (1.2 K), with a performance comparable to the common 6061 alloy of aluminium. Superconducting cavities find application in numerous areas of physics, from particle accelerators to cavity quantum...

  11. Optimization of superconducting tiling pattern for superconducting bearings

    Energy Technology Data Exchange (ETDEWEB)

    Hull, John R. (Hinsdale, IL)

    1996-01-01

    An apparatus and method for reducing magnetic field inhomogeneities which produce rotational loss mechanisms in high temperature superconducting magnetic bearings. Magnetic field inhomogeneities are reduced by dividing high temperature superconducting structures into smaller structures, and arranging the smaller structures into tiers which stagger the magnetic field maximum locations of the smaller structures.

  12. State-of-the-art of superconducting magnets

    Energy Technology Data Exchange (ETDEWEB)

    Lubell, M. S.

    1972-09-01

    A survey of the most recent developments in superconducting magnet materials is presented, and complete data on the upper critical field and transition temperature for the NbTi alloy system are given. The overall critical current density of compound conductors is shown for both low and high field commercial superconductors. A tabulation is given of high field and large bore solenoids, comparing design and test data. Comparative data are also given for some nonsolenoidal coils, and details are listed for the systems under construction or design. A criterion is derived for the stable current density attainable in extremely large magnet systems such as those envisioned for fusion reactors: j ∝ (stored energy)-1/6 . The review concludes with summaries concerning the structural materials useful in large magnets and the effects of radiation on superconducting magnets.

  13. Field Measurement for Superconducting Magnets of ADS Injector I

    CERN Document Server

    Yang, Xiangchen

    2013-01-01

    The superconducting solenoid magnet prototype for ADS injection-I had been fabricated in Beijing Qihuan Mechanical and Electric Engineer Company and tested in Haerbin Institute of Technology (HIT) in Nov, 2012. Batch magnet production was processed after some major revision from the magnet prototype, they include: removing off the perm-alloy shield, extending the iron yoke, using thin superconducting cable, etc. The first one of the batch magnets was tested in the vertical Dewar in HIT in Sept. 2013. Field measurement was carried out at the same time by the measurement platform that seated on the top of the vertical Dewar. This paper will present the field measurement system design, measurement results and discussion on the residual field from the persistent current effect.

  14. Temperature Dependence of the Kondo Resonance and Its Satellites in CeCu{sub 2}Si{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Reinert, F.; Ehm, D.; Schmidt, S.; Nicolay, G.; Huefner, S.; Kroha, J.; Trovarelli, O.; Geibel, C.

    2001-09-03

    We present high-resolution photoemission spectroscopy studies on the Kondo resonance of the strongly correlated Ce system CeCu{sub 2}Si {sub 2} . By exploiting the thermal broadening of the Fermi edge we analyze position, spectral weight, and temperature dependence of the low-energy 4f spectral features, whose major weight lies above the Fermi level E{sub F} . We also present theoretical predictions based on the single-impurity Anderson model using an extended noncrossing approximation, including all spin-orbit and crystal field splittings of the 4f states. The excellent agreement between theory and experiment provides strong evidence that the spectral properties of CeCu{sub 2}Si {sub 2} can be described by single-impurity Kondo physics down to T{approx}5 K .

  15. Kondo Resonance in a Mesoscopic Ring Coupled to a Quantum Dot: Exact Results for the Aharonov-Bohm-Casher Effects

    Energy Technology Data Exchange (ETDEWEB)

    Eckle, H.-P.; Johannesson, H.; Stafford, C. A.

    2001-07-02

    We study the persistent currents induced by both the Aharonov-Bohm and Aharonov-Casher effects in a one-dimensional mesoscopic ring coupled to a sidebranch quantum dot at Kondo resonance. For privileged values of the Aharonov-Bohm-Casher fluxes, the problem can be mapped onto an integrable model, exactly solvable by a Bethe ansatz. In the case of a pure magnetic Aharonov-Bohm flux, we find that the presence of the quantum dot has no effect on the persistent current. In contrast, the Kondo resonance interferes with the spin-dependent Aharonov-Casher effect to induce a current which, in the strong-coupling limit, is independent of the number of electrons in the ring.

  16. Kondo resonance in a mesoscopic ring coupled to a quantum dot: exact results for the Aharonov-Bohm-Casher effects.

    Science.gov (United States)

    Eckle, H P; Johannesson, H; Stafford, C A

    2001-07-02

    We study the persistent currents induced by both the Aharonov-Bohm and Aharonov-Casher effects in a one-dimensional mesoscopic ring coupled to a sidebranch quantum dot at Kondo resonance. For privileged values of the Aharonov-Bohm-Casher fluxes, the problem can be mapped onto an integrable model, exactly solvable by a Bethe ansatz. In the case of a pure magnetic Aharonov-Bohm flux, we find that the presence of the quantum dot has no effect on the persistent current. In contrast, the Kondo resonance interferes with the spin-dependent Aharonov-Casher effect to induce a current which, in the strong-coupling limit, is independent of the number of electrons in the ring.

  17. GW approach to electron-electron interactions within the Anderson impurity model: Kondo correlated quantum transport through two coupled molecules

    Science.gov (United States)

    Aksu, H.; Goker, A.

    2017-03-01

    We invoke the nonequilibrium self-consistent GW method within the Anderson impurity model to investigate the dynamical effects occurring in a nanojunction comprised of two coupled molecules. Contrary to the previous single impurity model calculations based on the GW approximation, we observe that the density of states manages to capture both the Kondo resonance and the Breit-Wigner resonances associated with the HOMO and LUMO levels of the molecule. Moreover, the prominence of the Kondo resonance grows dramatically upon switching from the intermediate to the weak coupling regime involving large U / Γ values. The conductance is calculated as a function of the HOMO level and the applied bias across the molecular nanojunction. Calculated conductance curves deviate from the monotonic decay behaviour as a function of the bias when the half-filling condition is not met. The importance of the effect of the molecule-molecule coupling for the electron transport phenomena is also investigated.

  18. Giant Kondo Resonance of Parallel-Coupled Double Quantum Dots Embedded in an A-B Ring

    Institute of Scientific and Technical Information of China (English)

    CHEN Xiong-Wen; HE Da-Jiang; SONG Ke-Hui; WU Shao-Quan

    2006-01-01

    We theoretically study the properties of the ground state of the parallel-coupled double quantum dots embedded in a mesoscopic ring in the Kondo regime by means of the two-impurity Anderson Hamiltonian. The Hamiltonian is solved by means of the slave-boson mean-field theory. We find that in this system, the persistent current depends sensitively on both the parity of this system and the size of the ring. In the strong coupling regime, the giant sharp current peak appears, at the same time, the parity dependence of the persistent current disappears. These imply that in the strong coupling regime, there exists giant Kondo resonance and the two dots can be coupled coherently. Thus this system might be a candidate for future device applications.

  19. Spin-Orbit-Coupled Correlated Metal Phase in Kondo Lattices: An Implementation with Alkaline-Earth Atoms

    Science.gov (United States)

    Isaev, L.; Schachenmayer, J.; Rey, A. M.

    2016-09-01

    We show that an interplay between quantum effects, strong on-site ferromagnetic exchange interaction, and antiferromagnetic correlations in Kondo lattices can give rise to an exotic spin-orbit coupled metallic state in regimes where classical treatments predict a trivial insulating behavior. This phenomenon can be simulated with ultracold alkaline-earth fermionic atoms subject to a laser-induced magnetic field by observing dynamics of spin-charge excitations in quench experiments.

  20. Spin-Orbit-Coupled Correlated Metal Phase in Kondo Lattices: An Implementation with Alkaline-Earth Atoms.

    Science.gov (United States)

    Isaev, L; Schachenmayer, J; Rey, A M

    2016-09-23

    We show that an interplay between quantum effects, strong on-site ferromagnetic exchange interaction, and antiferromagnetic correlations in Kondo lattices can give rise to an exotic spin-orbit coupled metallic state in regimes where classical treatments predict a trivial insulating behavior. This phenomenon can be simulated with ultracold alkaline-earth fermionic atoms subject to a laser-induced magnetic field by observing dynamics of spin-charge excitations in quench experiments.

  1. The Danish Superconducting Cable Project

    DEFF Research Database (Denmark)

    Tønnesen, Ole

    1997-01-01

    The design and construction of a superconducting cable is described. The cable has a room temperature dielectric design with the cryostat placed inside the electrical insulation.BSCCO 2223 superconducting tapes wound in helix form around a former are used as the cable conductor. Results from...

  2. Superconducting bearings for flywheel applications

    DEFF Research Database (Denmark)

    Abrahamsen, A.B.

    2001-01-01

    A literature study on the application of superconducting bearings in energy storage flywheel systems. The physics of magnetic levitation and superconductors are presented in the first part of the report, followed by a discussion of the literature found onthe applications of superconducting bearings...

  3. Anomalous electrical resistivity of the Kondo system Ce(Rh1-xCox)3B2

    Science.gov (United States)

    Ku, H. C.; Yu, H.

    1986-08-01

    Electrical resistivity measurements have been carried out on the high-Curie-temperature ferromagnetic compound CeRh3B2 (TC=110-115 K). The temperature dependence of the electrical resistivity ρ(T) during the initial cooldown above TC gives the first solid indication of the Kondo-like behavior in this system. However, the resisitivity is irreversible above TC when warming up from low temperature and ρ(T) approaches the previous reported form. This irreversibility is closely related to microscopic cracks created by the strong internal magnetic field of the ferromagnetic state and was not observed in the nonmagnetic compound CeCo3B2 with the same hexagonal structure. Further proof of this Kondo state can be obtained in the study of the pseudoternary system Ce(Rh1-xCox)3B2 where the resistivity increases with decreasing temperature during the initial cooldown and a local minimum Kondo anomaly was observed. The magnetic state is rapidly broken up with the replacement of Rh by Co and the resistivity anomaly disappears after the disappearance of ferromagnetic order.

  4. Kondo Resonance versus Fano Interference in Double Quantum Dots Coupled to a Two-Lead One-Ring System

    Institute of Scientific and Technical Information of China (English)

    CHEN Xiong-Wen; SHI Zhen-Gang; CHEN Bao-Ju; SONG Ke-Hui

    2007-01-01

    We analyse the transport properties of a coupled double quantum dot (DQD) device with one of the dots (QD1) coupled to metallic leads and the other (QD2) embedded in an Aharonov-Bhom (A-B) ring by means of the slave-boson mean-Geld theory. It is found that in this system, the Kondo resonance and the Fano interference exist simultaneously, the enhancing Kondo effect and the increasing hopping of the QD2-Ring destroy the localized electron state in the QD2 for the QD1-leads, and accordingly, the Fano interference between the DQD-leads and the QD1-leads are suppressed. Under some conditions, the Fano interference can be quenched fully and the single Kondo resonance of the QD1-leads comes into being. Moreover, when the magnetic flux of the A-B ring is zero, the influence of the parity of the A-B ring on the transport properties is very weak, but this inSuence becomes more obvious with non-zero magnetic flux. Thus this model may be a candidate for future device applications.

  5. A superconducting magnetic gear

    Science.gov (United States)

    Campbell, A. M.

    2016-05-01

    A comparison is made between a magnetic gear using permanent magnets and superconductors. The objective is to see if there are any fundamental reasons why superconducting magnets should not provide higher power densities than permanent magnets. The gear is based on the variable permeability design of Attilah and Howe (2001 IEEE Trans. Magn. 37 2844-46) in which a ring of permanent magnets surrounding a ring of permeable pole pieces with a different spacing gives an internal field component at the beat frequency. Superconductors can provide much larger fields and forces but will saturate the pole pieces. However the gear mechanism still operates, but in a different way. The magnetisation of the pole pieces is now constant but rotates with angle at the beat frequency. The result is a cylindrical Halbach array which produces an internal field with the same symmetry as in the linear regime, but has an analytic solution. In this paper a typical gear system is analysed with finite elements using FlexPDE. It is shown that the gear can work well into the saturation regime and that the Halbach array gives a good approximation to the results. Replacing the permanent magnets with superconducting tapes can give large increases in torque density, and for something like a wind turbine a combined gear and generator is possible. However there are major practical problems. Perhaps the most fundamental is the large high frequency field which is inevitably present and which will cause AC losses. Also large magnetic fields are required, with all the practical problems of high field superconducting magnets in rotating machines. Nevertheless there are ways of mitigating these difficulties and it seems worthwhile to explore the possibilities of this technology further.

  6. Superconductivity in a chiral nanotube

    Science.gov (United States)

    Qin, F.; Shi, W.; Ideue, T.; Yoshida, M.; Zak, A.; Tenne, R.; Kikitsu, T.; Inoue, D.; Hashizume, D.; Iwasa, Y.

    2017-02-01

    Chirality of materials are known to affect optical, magnetic and electric properties, causing a variety of nontrivial phenomena such as circular dichiroism for chiral molecules, magnetic Skyrmions in chiral magnets and nonreciprocal carrier transport in chiral conductors. On the other hand, effect of chirality on superconducting transport has not been known. Here we report the nonreciprocity of superconductivity--unambiguous evidence of superconductivity reflecting chiral structure in which the forward and backward supercurrent flows are not equivalent because of inversion symmetry breaking. Such superconductivity is realized via ionic gating in individual chiral nanotubes of tungsten disulfide. The nonreciprocal signal is significantly enhanced in the superconducting state, being associated with unprecedented quantum Little-Parks oscillations originating from the interference of supercurrent along the circumference of the nanotube. The present results indicate that the nonreciprocity is a viable approach toward the superconductors with chiral or noncentrosymmetric structures.

  7. Japan. Superconductivity for Smart Grids

    Energy Technology Data Exchange (ETDEWEB)

    Hayakawa, K.

    2012-11-15

    Currently, many smart grid projects are running or planned worldwide. These aim at controlling the electricity supply more efficiently and more stably in a new power network system. In Japan, especially superconductivity technology development projects are carried out to contribute to the future smart grid. Japanese cable makers such as Sumitomo Electric and Furukawa Electric are leading in the production of high-temperature superconducting (HTS) power cables. The world's largest electric current and highest voltage superconductivity proving tests have been started this year. Big cities such as Tokyo will be expected to introduce the HTS power cables to reduce transport losses and to meet the increased electricity demand in the near future. Superconducting devices, HTS power cables, Superconducting Magnetic Energy Storage (SMES) and flywheels are the focus of new developments in cooperations between companies, universities and research institutes, funded by the Japanese research and development funding organization New Energy and Industrial Technology Development Organization (NEDO)

  8. Structural transformation studies on the rare earth containing Heusler alloys Pd 2RESn

    Science.gov (United States)

    Umarji, A. M.; Malik, S. K.; Shenoy, G. K.

    1985-03-01

    The Heusler alloys Pd 2RESn form for rare-earths (RE) from Tb to Lu and for Sc and Y. Of these, the alloys containing Yb, Tm, Lu, Sc and Y are superconducting. We have carried out structural studies on all these alloys by studying the temperature dependence of the X-ray patterns in the temperature range 5 to 300 K. Some nonstoichiometric compositions were also investigated. Structural transformation is observed only in Tb and Dy containing alloys while none of the superconducting alloys show a transformation. The transformation temperature is lowered by about 50 K in going from stoichiometric Pd 2TbSn to nonstoichiometric Pd 2Tb 0.95Sn while it is completely suppressed in Pd 2Dy 0.95Sn. Magnetic and Mössbauer studies on Dy compound are also reported.

  9. Aluminum alloy

    Science.gov (United States)

    Blackburn, Linda B. (Inventor); Starke, Edgar A., Jr. (Inventor)

    1989-01-01

    This invention relates to aluminum alloys, particularly to aluminum-copper-lithium alloys containing at least about 0.1 percent by weight of indium as an essential component, which are suitable for applications in aircraft and aerospace vehicles. At least about 0.1 percent by weight of indium is added as an essential component to an alloy which precipitates a T1 phase (Al2CuLi). This addition enhances the nucleation of the precipitate T1 phase, producing a microstructure which provides excellent strength as indicated by Rockwell hardness values and confirmed by standard tensile tests.

  10. Superconducting dipole electromagnet

    Science.gov (United States)

    Purcell, John R.

    1977-07-26

    A dipole electromagnet of especial use for bending beams in particle accelerators is wound to have high uniformity of magnetic field across a cross section and to decrease evenly to zero as the ends of the electromagnet are approached by disposing the superconducting filaments of the coil in the crescent-shaped nonoverlapping portions of two intersecting circles. Uniform decrease at the ends is achieved by causing the circles to overlap increasingly in the direction of the ends of the coil until the overlap is complete and the coil is terminated.

  11. 100 years of superconductivity

    CERN Multimedia

    Globe Info

    2011-01-01

    Public lecture by Philippe Lebrun, who works at CERN on applications of superconductivity and cryogenics for particle accelerators. He was head of CERN’s Accelerator Technology Department during the LHC construction period. Centre culturel Jean Monnet, route de Gex Tuesday 11 October from 8.30 p.m. to 10.00 p.m. » Suitable for all – Admission free - Lecture in French » Number of places limited For further information: +33 (0)4 50 42 29 37

  12. TOPICAL REVIEW: Superconducting bearings

    Science.gov (United States)

    Hull, John R.

    2000-02-01

    The physics and technology of superconducting bearings is reviewed. Particular attention is given to the use of high-temperature superconductors (HTSs) in rotating bearings. The basic phenomenology of levitational forces is presented, followed by a brief discussion of the theoretical models that can be used for conceptual understanding and calculations. The merits of various HTS bearing designs are presented, and the behaviour of HTS bearings in typical situations is discussed. The article concludes with a brief survey of various proposed applications for HTS bearings.

  13. Conventional and unconventional superconductivity

    Science.gov (United States)

    Fernandes, R. M.

    2012-02-01

    Superconductivity has been one of the most fruitful areas of research in condensed matter physics, bringing together researchers with distinct interests in a collaborative effort to understand from its microscopic basis to its potential for unprecedented technological applications. The concepts, techniques, and methods developed along its centennial history have gone beyond the realm of condensed matter physics and influenced the development of other fascinating areas, such as particle physics and atomic physics. These notes, based on a set of lectures given at the 2011 Advanced Summer School of Cinvestav, aim to motivate the young undergraduate student in getting involved in the exciting world of conventional and unconventional superconductors.

  14. Superconductivity from correlated hopping

    CERN Document Server

    Batista, C D; Aligia, A A

    1995-01-01

    We consider a chain described by a next-nearest-neighbor hopping combined with a nearest-neighbor spin flip. In two dimensions this three-body term arises from a mapping of the three-band Hubbard model for CuO$_2$ planes to a generalized $t-J$ model and for large O-O hopping favors resonance-valence-bond superconductivity of predominantly $d$-wave symmetry. Solving the ground state and low-energy excitations by analytical and numerical methods we find that the chain is a Luther-Emery liquid with correlation exponent $K_{\\rho} = (2-n)^2/2$, where $n$ is the particle density.

  15. Superconductivity in nanowires

    CERN Document Server

    Bezryadin, Alexey

    2012-01-01

    The importance and actuality of nanotechnology is unabated and will be for years to come. A main challenge is to understand the various properties of certain nanostructures, and how to generate structures with specific properties for use in actual applications in Electrical Engineering and Medicine.One of the most important structures are nanowires, in particular superconducting ones. They are highly promising for future electronics, transporting current without resistance and at scales of a few nanometers. To fabricate wires to certain defined standards however, is a major challenge, and so i

  16. Introduction to superconductivity

    CERN Document Server

    Rose-Innes, AC

    1978-01-01

    Introduction to Superconductivity differs from the first edition chiefly in Chapter 11, which has been almost completely rewritten to give a more physically-based picture of the effects arising from the long-range coherence of the electron-waves in superconductors and the operation of quantum interference devices. In this revised second edition, some further modifications have been made to the text and an extra chapter dealing with """"high-temperature"""" superconductors has been added. A vast amount of research has been carried out on these since their discovery in 1986 but the results, both

  17. Superconducting Electronic Film Structures

    Science.gov (United States)

    1991-02-14

    cubic, yttria stabilized, zirconia (YSZ) single crystals with (100) orientation and ao = 0.512 to 0.516 nm. Films were magnetron-sputtered... Crown by Solid-State and Vapor-Phase Epitaxy," IEEE Trans. Uagn. 25(2), 2538 (1989). 6. J. H. Kang, R. T. Kampwirth, and K. E. Gray, "Superconductivity...summarized in Fig. 1, are too high for SrTiO3 or yttria- stabilized zirconia (YSZ) to be used in rf applications. MgO, LaAIO 3 , and LaGaO3 have a tan 6

  18. Heavy fermion superconductivity

    Science.gov (United States)

    Brison, Jean-Pascal; Glémot, Loı̈c; Suderow, Hermann; Huxley, Andrew; Kambe, Shinsaku; Flouquet, Jacques

    2000-05-01

    The quest for a precise identification of the symmetry of the order parameter in heavy fermion systems has really started with the discovery of the complex superconducting phase diagram in UPt 3. About 10 years latter, despite numerous experiments and theoretical efforts, this is still not achieved, and we will quickly review the present status of knowledge and the main open question. Actually, the more forsaken issue of the nature of the pairing mechanism has been recently tackled by different groups with macroscopic or microscopic measurement, and significant progress have been obtained. We will discuss the results emerging from these recent studies which all support non-phonon-mediated mechanisms.

  19. Electrical and thermal transport properties of the alloy system (Ce1-xLax)Cu4In

    Science.gov (United States)

    Bashir, Aiman K.; Tchoula Tchokonté, Moise B.; Britz, Douglas; Sondezi, B. M.; Strydom, André M.; Kaczorowski, Dariusz

    2015-03-01

    The studies of electrical resistivity, ρ(T), magnetoresistivity, MR, thermoelectric power, S(T) and thermal conductivity, λ(T), of the alloy system (Ce1-xLax)Cu4In (0 Pnnm (No. 58) for all investigated compositions across the series. ρ(T) results indicate an evolution from coherent Kondo scattering to incoherent single - ion Kondo scattering, with increased La content x. ρ(T) for each composition at high temperature is described by a -ln(T) behaviour. MR measurements on Ce dilute alloys are interpreted within the single - ion Bethe ansatz description of the Coqblin - Schrieffer model. S(T) results are described by the phenomenological resonance model. λ(T) data increase linearly with temperature from low T and shows a tendency toward saturation above 300 K for dilute Ce alloys. The Lorentz number, L/L0 and the dimensionless figure of merit, ZT = S2T/λρ increase upon cooling and exhibit maxima at low temperatures.

  20. A Novel superconducting toroidal field magnet concept using advanced materials

    Science.gov (United States)

    Schwartz, J.

    1992-03-01

    The plasma physics database indicates that two distinct approaches to tokamak design may lead to commercial fusion reactors: low Aspect ratio, high plasma current, relatively low magnetic field devices, and high Aspect ratio, high field devices. The former requires significant enhancements in plasma performance, while the latter depends primarily upon technology development. The key technology for the commercialization of the high-field approach is large, high magnetic field superconducting magnets. In this paper, the physics motivation for the high field approach and key superconducting magnet (SCM) development issues are reviewed. Improved SCM performance may be obtained from improved materials and/or improved engineering. Superconducting materials ranging from NbTi to high- T c oxides are reviewed, demonstrating the broad range of potential superconducting materials. Structural material options are discussed, including cryogenic steel alloys and fiber-reinforced composite materials. Again, the breadth of options is highlighted. The potential for improved magnet engineering is quantified in terms of the Virial Theorem Limit, and two examples of approaches to highly optimized magnet configurations are discussed. The force-reduced concept, which is a finite application of the force-free solutions to Ampere's Law, appear promising for large SCMs but may be limited by the electromagnetics of a fusion plasma. The Solid Superconducting Cylinder (SSC) concept is proposed. This concept combines the unique properties of high- T c superconductors within a low- T c SCM to obtain (1) significant reductions in the structural material volume, (2) a decoupling of the tri-axial (compressive and tensile) stress state, and (3) a demountable TF magnet system. The advantages of this approach are quantified in terms of a 24 T commercial reactor TF magnet system. Significant reductions in the mechanical stress and the TF radial build are demonstrated.

  1. Overview on superconducting photoinjectors

    CERN Document Server

    Arnold, A

    2011-01-01

    The success of most of the proposed energy recovery linac (ERL) based electron accelerator projects for future storage ring replacements (SRR) and high power IR–free-electron lasers (FELs) largely depends on the development of an appropriate source. For example, to meet the FEL specifications [J.W. Lewellen, Proc. SPIE Int. Soc. Opt. Eng. 5534, 22 (2004)] electron beams with an unprecedented combination of high brightness, low emittance (0.1 µmrad), and high average current (hundreds of mA) are required. An elegant way to create a beam of such quality is to combine the high beam quality of a normal conducting rf photoinjector with the superconducting technology, i.e., to build a superconducting rf photoinjector (SRF gun). SRF gun R&D programs based on different approaches have been launched at a growing number of institutes and companies (AES, Beijing University, BESSY, BNL, DESY, FZD, TJNAF, Niowave, NPS, Wisconsin University). Substantial progress was achieved in recent years and the first long term ...

  2. Overview of Superconducting Photoinjectors

    CERN Document Server

    Arnold, A

    2009-01-01

    The success of most of the proposed ERL based electron accelerator projects for future storage ring replacements (SRR) and high power IR-FELs is contingent upon the development of an appropriate source. Electron beams with an unprecedented combination of high brightness, low emittance (0.1 µm rad) and high average current (hundreds of mA) are required to meet the FEL specification [1]. An elegant way to create such an unique beam is to combine the high beam quality of a normal conducting RF photo injector with the superconducting technology to get a superconducting RF photo injector (SRF gun). SRF gun R&D programs based on different approaches are under investigation at a growing number of institutes and companies (AES, Beijing University, BESSY, BNL, DESY, FZD, JLab, Niowave, NPS, Wisconsin University). Lot of progress could be achieved during the last years and first long term operation was demonstrated at the FZD [2]. In the near future, this effort will lead to SRF guns, which are indispensab...

  3. Superconducting magnets for MRI

    Energy Technology Data Exchange (ETDEWEB)

    Williams, J.E.

    1984-08-01

    Three types of magnets are currently used to provide the background field required for magnet resonance imaging (MRI). (i) Permanent magnets produce fields of up to 0.3 T in volumes sufficient for imaging the head or up to 0.15 T for whole body imaging. Cost and simplicity of operation are advantages, but relatively low field, weight (up to 100 tonnes) and, to a small extent, instability are limitations. (ii) Water-cooled magnets provide fields of up to 0.25 T in volumes suitable for whole body imaging, but at the expense of power (up to 150 kW for 0.25 T) and water-cooling. Thermal stability of the field requires the maintenance of constant temperature through periods both of use and of quiescence. (iii) Because of the limitations imposed by permanent and resistive magnets, particularly on field strength, the superconducting magnet is now most widely used to provide background fields of up to 2 T for whole body MRI. It requires very low operating power and that only for refrigeration. Because of the constant low temperature, 4.2 K, at which its stressed structure operates, its field is stable. The following review deals principally with superconducting magnets for MRI. However, the sections on field analysis apply to all types of magnet and the description of the source terms of circular coils and of the principals of design of solenoids apply equally to resistive solenoidal magnets.

  4. Kondo Physics at Interfaces in Metallic Non-Local Spin Transport Devices

    Science.gov (United States)

    Leighton, Chris

    2015-03-01

    Despite the maturity of metallic spintronics there remain large gaps in our understanding of spin transport in metals, particularly with injection of spins across ferromagnetic/non-magnetic (FM/NM) interfaces, and their subsequent diffusion and relaxation. Unresolved issues include the limits of applicability of Elliott-Yafet spin relaxation, quantification of the influence of defects, surfaces, and interfaces on spin relaxation at nanoscopic dimensions, and the importance of magnetic and spin-orbit scattering. The non-local spin-valve is an enabling device in this context as, in addition to offering potentially disruptive applications, it allows for the separation of charge and spin currents. One particularly perplexing issue in metallic non-local spin valves is the widely observed non-monotonicity in the T-dependent spin accumulation, where the spin signal actually decreases at low T, in contrast to simple expectations. In this work, by studying an expanded range of FM/NM combinations (encompassing Ni80Fe20, Ni, Fe, Co, Cu, and Al), we demonstrate that this effect is not a property of a given FM or NM, but rather of the FM/NM pair. The non-monotonicity is in fact strongly correlated with the ability of the FM to form a dilute local magnetic moment in the NM. We show that local moments, resulting in this case from the ppm-level tail of the FM/NM interdiffusion profile, suppress the injected spin polarization and diffusion length via a novel manifestation of the Kondo effect, explaining all observations associated with the low T downturn in spin accumulation. We further show: (a) that this effect can be promoted by thermal annealing, at which point the conventional charge transport Kondo effect is simultaneously detected in the NM, and (b) that this suppression in spin accumulation can be quenched, even at interfaces that are highly susceptible to the effect, by insertion of a thin non-moment-supporting interlayer. Important implications for room temperature

  5. Superconductivity in doped Dirac semimetals

    Science.gov (United States)

    Hashimoto, Tatsuki; Kobayashi, Shingo; Tanaka, Yukio; Sato, Masatoshi

    2016-07-01

    We theoretically study intrinsic superconductivity in doped Dirac semimetals. Dirac semimetals host bulk Dirac points, which are formed by doubly degenerate bands, so the Hamiltonian is described by a 4 ×4 matrix and six types of k -independent pair potentials are allowed by the Fermi-Dirac statistics. We show that the unique spin-orbit coupling leads to characteristic superconducting gap structures and d vectors on the Fermi surface and the electron-electron interaction between intra and interorbitals gives a novel phase diagram of superconductivity. It is found that when the interorbital attraction is dominant, an unconventional superconducting state with point nodes appears. To verify the experimental signature of possible superconducting states, we calculate the temperature dependence of bulk physical properties such as electronic specific heat and spin susceptibility and surface state. In the unconventional superconducting phase, either dispersive or flat Andreev bound states appear between point nodes, which leads to double peaks or a single peak in the surface density of states, respectively. As a result, possible superconducting states can be distinguished by combining bulk and surface measurements.

  6. Meissner effect in superconducting microtraps

    Energy Technology Data Exchange (ETDEWEB)

    Cano, Daniel

    2009-04-30

    This thesis investigates the impact of the Meissner effect on magnetic microtraps for ultracold atoms near superconducting microstructures. This task has been accomplished both theoretically and experimentally. The Meissner effect distorts the magnetic fields near superconducting surfaces, thus altering the parameters of magnetic microtraps. Both computer simulations and experimental measurements demonstrate that the Meissner effect shortens the distance between the magnetic microtrap and the superconducting surface, reduces the magnetic-field gradients and dramatically lowers the trap depth. A novel numerical method for calculating magnetic fields in atom chips with superconducting microstructures has been developed. This numerical method overcomes the geometrical limitations of other calculation techniques and can solve superconducting microstructures of arbitrary geometry. The numerical method has been used to calculate the parameters of magnetic microtraps in computer-simulated chips containing thin-film wires. Simulations were carried out for both the superconducting and the normal-conducting state, and the differences between the two cases were analyzed. Computer simulations have been contrasted with experimental measurements. The experimental apparatus generates a magnetic microtrap for ultracold Rubidium atoms near a superconducting Niobium wire of circular cross section. The design and construction of the apparatus has met the challenge of integrating the techniques for producing atomic quantum gases with the techniques for cooling solid bodies to cryogenic temperatures. By monitoring the position of the atom cloud, one can observe how the Meissner effect influences the magnetic microtrap. (orig.)

  7. Operational Merits of Maritime Superconductivity

    Science.gov (United States)

    Ross, R.; Bosklopper, J. J.; van der Meij, K. H.

    The perspective of superconductivity to transfer currents without loss is very appealing in high power applications. In the maritime sector many machines and systems exist in the roughly 1-100 MW range and the losses are well over 50%, which calls for dramatic efficiency improvements. This paper reports on three studies that aimed at the perspectives of superconductivity in the maritime sector. It is important to realize that the introduction of superconductivity comprises two technology transitions namely firstly electrification i.e. the transition from mechanical drives to electric drives and secondly the transition from normal to superconductive electrical machinery. It is concluded that superconductivity does reduce losses, but its impact on the total energy chain is of little significance compared to the investments and the risk of introducing a very promising but as yet not proven technology in the harsh maritime environment. The main reason of the little impact is that the largest losses are imposed on the system by the fossil fueled generators as prime movers that generate the electricity through mechanical torque. Unless electric power is supplied by an efficient and reliable technology that does not involve mechanical torque with the present losses both normal as well as superconductive electrification of the propulsion will hardly improve energy efficiency or may even reduce it. One exception may be the application of degaussing coils. Still appealing merits of superconductivity do exist, but they are rather related to the behavior of superconductive machines and strong magnetic fields and consequently reduction in volume and mass of machinery or (sometimes radically) better performance. The merits are rather convenience, design flexibility as well as novel applications and capabilities which together yield more adequate systems. These may yield lower operational costs in the long run, but at present the added value of superconductivity rather seems more

  8. Semiannual report for the period April 1 to September 30, 1978 of work on: (1) superconducting power transmission system development; (2) cable insulation development. Power Transmission Project technical note No. 83

    Energy Technology Data Exchange (ETDEWEB)

    1978-11-07

    Progress in the development, fabrication and testing of superconductors for HVAC power transmission systems is reported. Information is included on the materials evaluation of superconducting alloys, production of tapes from these alloys, principally Nb/sub 3/Sn cable insulation requirements and development, and the cryogenic equipment used in this research program. (LCL)

  9. Spinon Superconductivity and Superconductivities Mediated by Spin-Waves and Phonons in Cuprates

    OpenAIRE

    Mourachkine, A.

    1998-01-01

    The disclosure of spinon superconductivity and superconductivity mediated by spin-waves in hole-doped Bi2212 cuprate raises the question about the origin of the superconductivity in other cuprates and specially in an electron-doped NCCO cuprate.

  10. Superconducting interfaces between insulating oxides.

    Science.gov (United States)

    Reyren, N; Thiel, S; Caviglia, A D; Kourkoutis, L Fitting; Hammerl, G; Richter, C; Schneider, C W; Kopp, T; Rüetschi, A-S; Jaccard, D; Gabay, M; Muller, D A; Triscone, J-M; Mannhart, J

    2007-08-31

    At interfaces between complex oxides, electronic systems with unusual electronic properties can be generated. We report on superconductivity in the electron gas formed at the interface between two insulating dielectric perovskite oxides, LaAlO3 and SrTiO3. The behavior of the electron gas is that of a two-dimensional superconductor, confined to a thin sheet at the interface. The superconducting transition temperature of congruent with 200 millikelvin provides a strict upper limit to the thickness of the superconducting layer of congruent with 10 nanometers.

  11. Antiferromagnetic hedgehogs with superconducting cores

    Energy Technology Data Exchange (ETDEWEB)

    Goldbart, P.M.; Sheehy, D.E. [Department of Physics and Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)

    1998-09-01

    Excitations of the antiferromagnetic state that resemble antiferromagnetic hedgehogs at large distances but are predominantly superconducting inside a core region are discussed within the context of Zhang{close_quote}s SO(5)-symmetry-based approach to the physics of high-temperature superconducting materials. Nonsingular, in contrast with their hedgehog cousins in pure antiferromagnetism, these texture excitations are what hedgehogs become when the antiferromagnetic order parameter is permitted to {open_quotes}escape{close_quotes} into superconducting directions. The structure of such excitations is determined in a simple setting, and a number of their experimental implications are examined. {copyright} {ital 1998} {ital The American Physical Society}

  12. Superconducting cable connections and methods

    Energy Technology Data Exchange (ETDEWEB)

    van der Laan, Daniel Cornelis

    2017-09-05

    Superconducting cable connector structures include a terminal body (or other structure) onto which the tapes from the superconducting cable extend. The terminal body (or other structure) has a diameter that is sufficiently larger than the diameter of the former of the superconducting cable, so that the tapes spread out over the outer surface of the terminal body. As a result, gaps are formed between tapes on the terminal body (or other structure). Those gaps are filled with solder (or other suitable flowable conductive material), to provide a current path of relatively high conductivity in the radial direction. Other connector structures omit the terminal body.

  13. Domain wall description of superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Brito, F.A. [Departamento de Física, Universidade Federal de Campina Grande, Caixa Postal 10071, 58109-970 Campina Grande, Paraíba (Brazil); Freire, M.L.F. [Departamento de Física, Universidade Estadual da Paraíba, 58109-753 Campina Grande, Paraíba (Brazil); Mota-Silva, J.C. [Departamento de Física, Universidade Federal de Campina Grande, Caixa Postal 10071, 58109-970 Campina Grande, Paraíba (Brazil); Departamento de Física, Universidade Federal da Paraíba, Caixa Postal 5008, 58051-970 João Pessoa, Paraíba (Brazil)

    2014-01-20

    In the present work we shall address the issue of electrical conductivity in superconductors in the perspective of superconducting domain wall solutions in the realm of field theory. We take our set up made out of a dynamical complex scalar field coupled to gauge field to be responsible for superconductivity and an extra scalar real field that plays the role of superconducting domain walls. The temperature of the system is interpreted through the fact that the soliton following accelerating orbits is a Rindler observer experiencing a thermal bath.

  14. Methodology and search for superconductivity in the La-Si-C system

    Energy Technology Data Exchange (ETDEWEB)

    De la Venta, J; Basaran, Ali C; Schuller, Ivan K [Department of Physics, University of California San Diego, La Jolla, CA 92093 (United States); Grant, T; Machado, A J S; Fisk, Z [Department of Physics and Astronomy, University of California Irvine, Irvine, CA 92697 (United States); Suchomel, M R [Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439 (United States); Weber, R T, E-mail: jdelaventa@physics.ucsd.edu [EPR Division Bruker BioSpin Corporation, Billerica, MA 01821-3931 (United States)

    2011-07-15

    In this paper we describe a methodology for the search for new superconducting materials. This consists of a parallel synthesis of a highly inhomogeneous alloy which covers large areas of the metallurgical phase diagram combined with a fast, microwave-based method which allows non-superconducting portions of the sample to be discarded. Once an inhomogeneous sample containing a minority phase superconductor is identified, we revert to well-known thorough identification methods which include standard physical and structural methods. We show how a systematic structural study helps in avoiding misidentification of new superconducting materials when there are indications from other methods of new discoveries. These ideas are applied to the La-Si-C system which exhibits promising normal state properties which are sometimes correlated with superconductivity. Although this system shows indications for the presence of a new superconducting compound, the careful analysis described here shows that the superconductivity in this system can be attributed to intermediate binary and single phases of the system.

  15. Methodology and search for superconductivity in the La-Si-C system.

    Energy Technology Data Exchange (ETDEWEB)

    de la Venta, J. de la; Basaran, A. C.; Grant, T.; Machado, A. J. S.; Suchomel, M. R.; Weber, R. T.; Fisk, Z.; Schuller, I. K. (X-Ray Science Division); (Univ. of California at San Diego); (Univ. of Sao Paulo); (Bruker BioSpin Corp.)

    2011-01-01

    In this paper we describe a methodology for the search for new superconducting materials. This consists of a parallel synthesis of a highly inhomogeneous alloy which covers large areas of the metallurgical phase diagram combined with a fast, microwave-based method which allows non-superconducting portions of the sample to be discarded. Once an inhomogeneous sample containing a minority phase superconductor is identified, we revert to well-known thorough identification methods which include standard physical and structural methods. We show how a systematic structural study helps in avoiding misidentification of new superconducting materials when there are indications from other methods of new discoveries. These ideas are applied to the La-Si-C system which exhibits promising normal state properties which are sometimes correlated with superconductivity. Although this system shows indications for the presence of a new superconducting compound, the careful analysis described here shows that the superconductivity in this system can be attributed to intermediate binary and single phases of the system.

  16. Electrical Resistance Alloys and Low-Expansion Alloys

    DEFF Research Database (Denmark)

    Kjer, Torben

    1996-01-01

    The article gives an overview of electrical resistance alloys and alloys with low thermal expansion. The electrical resistance alloys comprise resistance alloys, heating alloys and thermostat alloys. The low expansion alloys comprise alloys with very low expansion coefficients, alloys with very low...

  17. Tuning bulk and surface conduction in the proposed topological Kondo insulator SmB(6).

    Science.gov (United States)

    Syers, Paul; Kim, Dohun; Fuhrer, Michael S; Paglione, Johnpierre

    2015-03-06

    Bulk and surface state contributions to the electrical resistance of single-crystal samples of the topological Kondo-insulator compound SmB_{6} are investigated as a function of crystal thickness and surface charge density, the latter tuned by ionic liquid gating with electrodes patterned in a Corbino disk geometry on a single (100) surface. By separately tuning bulk and surface conduction channels, we show conclusive evidence for a model with an insulating bulk and metallic surface states, with a crossover temperature that depends solely on the relative contributions of each conduction channel. The surface conductance, on the order of 100  e^{2}/h, exhibits a field-effect mobility of 133  cm^{2}/Vs and a large carrier density of ∼2×10^{14}  cm^{-2}, in good agreement with recent photoemission results. With the ability to gate modulate surface conduction by more than 25%, this approach provides promise for both fundamental and applied studies of gate-tuned devices structured on bulk crystal samples.

  18. Finite-size effects in a metallic multichannel ring with Kondo impurity: Persistent currents and magnetoresistance

    Energy Technology Data Exchange (ETDEWEB)

    Zvyagin, A.A. [B. I. Verkin Institute for Low Temperature Physics and Engineering of the National Ukrainian Academy of Sciences, 47, Lenin Avenue, 310164, Kharkov (Ukraine); Schlottmann, P. [Department of Physics, Florida State University, Tallahassee, Florida 32306 (United States)

    1996-12-01

    We consider a spin-1/2 impurity interacting with conduction electrons in two different orbital channels via an isotropic spin exchange. The exchange is the same for both channels, but a crystalline field breaks the symmetry between the orbital channels. This corresponds to a splitting of the conduction electron {Gamma}{sub 8} into two doublets in the quadrupolar Kondo effect, or to the electron-assisted tunneling of an atom in a double-well potential in an external magnetic field. Another possible realization could be a quantum dot coupled to two equal rings of the same length subject to an electrostatic potential difference. We consider the Bethe ansatz equations for this model and derive the tower structure of the finite-size corrections to the ground-state energy. These results are used to discuss the Aharonov-Bohm-Casher interference pattern in the persistent charge and spin currents, and the magnetoresistivity due to the scattering of electrons off the impurity. {copyright} {ital 1996 The American Physical Society.}

  19. Kondo effect and quantum critical point in Mn(1-x)CoxSi

    Science.gov (United States)

    Teyssier, J.; Viennois, R.; Guritanu, V.; Giannini, E.; van der Marel, D.

    2010-01-01

    We report magnetic, transport and neutron diffraction studies of the solid solution Mn1-xCoxSi. For the Mn rich compounds, a sharp decrease of the Curie temperature is observed upon cobalt doping and neutron elastic scattering shows that the helimagnetic order of MnSi persists up to x = 0.06 with a shortening of the helix period. For higher Co concentrations (0.06 Weiss temperature changes sign and the system enters an antiferromagnetic state upon cooling (TN=9K for x = 0.50). In this doping range, the antiferromagnetic coupling leads to a Kondo effect marked by a minimum in the resistivity. This scenario is supported by the scaling of the magnetoresistance with a TK approx 6.5 K, close to the change in curvature of the resistivity and in agreement with the Weiss temperature from magnetic susceptibility. The sign change of the Weiss temperature and the transition from a helimagnetic to an antiferromagnetic ground state, with increasing the Co doping, point toward the existence of a quantum critical point at the composition Mn0.94Co0.06Si.

  20. Nonequilibrium spatiotemporal formation of the Kondo screening cloud on a lattice

    Science.gov (United States)

    Nuss, Martin; Ganahl, Martin; Arrigoni, Enrico; von der Linden, Wolfgang; Evertz, Hans Gerd

    2015-02-01

    We study the nonequilibrium formation of a spin screening cloud that accompanies the quenching of a local magnetic moment immersed in a Fermi sea at zero temperature. Based on high-precision density matrix renormalization-group results for the interacting single-impurity Anderson model, we discuss the real-time evolution after a quantum quench in the impurity-reservoir hybridization using time-evolving block decimation. We report emergent length and time scales in the spatiotemporal structure of nonlocal correlation functions in the spin and the charge density channel. At equilibrium, our data for the correlation functions and the extracted length scales show good agreement with existing results, as do local time-dependent observables at the impurity. In the time-dependent data, we identify a major signal which defines a "light cone" moving at the Fermi velocity and a ferromagnetic component in its wake. Inside the light cone we find that the structure of the nonequilibrium correlation functions emerges on two time scales. Initially, the qualitative structure of the correlation functions develops rapidly at the lattice Fermi velocity. Subsequently the spin correlations converge to the equilibrium results on a much larger time scale. This process sets a dynamic energy scale, which we identify to be proportional to the Kondo temperature. Outside the light cone we observe two different power-law decays of the correlation functions in space, with time- and interaction-strength-independent exponents.

  1. Magnetic Doping and Kondo Effect in Bi 2 Se 3 Nanoribbons

    KAUST Repository

    Cha, Judy J.

    2010-03-10

    A simple surface band structure and a large bulk band gap have allowed Bi2Se3 to become a reference material for the newly discovered three-dimensional topological insulators, which exhibit topologically protected conducting surface states that reside inside the bulk band gap. Studying topological insulators such as Bi2Se3 in nanostructures is advantageous because of the high surfaceto-volume ratio, which enhances effects from the surface states; recently reported Aharonov-Bohm oscillation in topological insulator nanoribbons by some of us is a good example. Theoretically, introducing magnetic impurities in topological insulators is predicted to open a small gap in the surface states by breaking time-reversal symmetry. Here, we present synthesis of magnetically doped Bi 2Se3 nanoribbons by vapor-liquid-solid growth using magnetic metal thin films as catalysts. Although the doping concentration is less than ∼2 %. low-temperature transport measurements of the Fe-doped Bi2Se3 nanoribbon devices show a clear Kondo effect at temperatures below 30 K, confirming the presence of magnetic impurities in the Bi2Se3 nanoribbons. The capability to dope topological insulator nanostructures magnetically opens up exciting opportunities for spintronics. © 2010 American Chemical Society.

  2. Transport properties of the topological Kondo insulator SmB6 under the irradiation of light

    Science.gov (United States)

    Zhu, Guo-Bao; Yang, Hui-Min

    2016-10-01

    In this paper, we study transport properties of the X point in the Brillouin zone of the topological Kondo insulator SmB6 under the application of a circularly polarized light. The transport properties at high-frequency regime and low-frequency regime as a function of the ratio (κ) of the Dresselhaus-like and Rashba-like spin-orbit parameter are studied based on the Floquet theory and Boltzmann equation respectively. The sign of Hall conductivity at high-frequency regime can be reversed by the ratio κ and the amplitude of the light. The amplitude of the current can be enhanced by the ratio κ. Our findings provide a way to control the transport properties of the Dirac materials at low-frequency regime. Project supported by the National Natural Science Foundation of China (Grant Nos. 11504095 and 11447145), the Foundation of Heze University (Grant Nos. XY14B002 and XYPY01), and the Project funded by the Higher Educational Science and Technology Program of Shandong Province, China (Grant No. J15LJ55).

  3. Fano resonance and hybridization gap in the Kondo lattice URu2Si2^*

    Science.gov (United States)

    Park, Wan Kyu; Tobash, P. H.; Ronning, F.; Bauer, E. D.; Sarrao, J. L.; Thompson, J. D.; Greene, L. H.

    2012-02-01

    The nature of the `hidden' order transition in URu2Si2 remains puzzling despite intensive research over the past two and half decades. A key question under debate is whether a hybridization gap between the renormalized bands can be identified as the long-sought hidden order parameter. We report on the measurement of a hybridization gap in URu2Si2 employing a spectroscopic technique based on quasiparticle scattering across a ballistic metallic junction [1]. The differential conductance data exhibit an asymmetric double-peak structure, a signature for a Fano resonance in a Kondo lattice [2]. The extracted hybridization gap opens well above the hidden order transition temperature, indicating that it is not the order parameter for the hidden order phase. Our results place constraints on the origin of the hidden order transition in URu2Si2.[4pt] [1] W. K. Park et al., arXiv:1110.5541.[0pt] [2] M. Maltseva, M. Dzero, P. Coleman, PRL 103, 206402 (2009).

  4. Phase boundaries of power-law Anderson and Kondo models: A poor man's scaling study

    Science.gov (United States)

    Cheng, Mengxing; Chowdhury, Tathagata; Mohammed, Aaron; Ingersent, Kevin

    2017-07-01

    We use the poor man's scaling approach to study the phase boundaries of a pair of quantum impurity models featuring a power-law density of states ρ (ɛ ) ∝|ɛ| r , either vanishing (for r >0 ) or diverging (for r 0 ), we find the phase boundary for (a) 0 1 , where the phases are separated by first-order quantum phase transitions that are accessible only for broken p-h symmetry. For the p-h-symmetric Kondo model with easy-axis or easy-plane anisotropy of the impurity-band spin exchange, the phase boundary and scaling trajectories are obtained for both r >0 and r <0 . Throughout the regime of weak-to-moderate impurity-band coupling in which poor man's scaling is expected to be valid, the approach predicts phase boundaries in excellent qualitative and good quantitative agreement with the nonperturbative numerical renormalization group, while also establishing the functional relations between model parameters along these boundaries.

  5. Aspects of Color Superconductivity

    CERN Document Server

    Hong, D K

    2001-01-01

    I discuss some aspects of recent developments in color superconductivity in high density quark matter. I calculate the Cooper pair gap and the critical points at high density, where magnetic gluons are not screened. The ground state of high density QCD with three light flavors is shown to be a color-flavor locking state, which can be mapped into the low-density hadronic phase. The meson mass at the CFL superconductor is also calculated. The CFL color superconductor is bosonized, where the Fermi sea is identified as a $Q$-matter and the gapped quarks as topological excitations, called superqualitons, of mesons. Finally, as an application of color supercoductivity, I discuss the neutrino interactions in the CFL color superconductor.

  6. Superconducting Hadron Linacs

    CERN Document Server

    Ostroumov, Peter

    2013-01-01

    This article discusses the main building blocks of a superconducting (SC) linac, the choice of SC resonators, their frequencies, accelerating gradients and apertures, focusing structures, practical aspects of cryomodule design, and concepts to minimize the heat load into the cryogenic system. It starts with an overview of design concepts for all types of hadron linacs differentiated by duty cycle (pulsed or continuous wave) or by the type of ion species (protons, H-, and ions) being accelerated. Design concepts are detailed for SC linacs in application to both light ion (proton, deuteron) and heavy ion linacs. The physics design of SC linacs, including transverse and longitudinal lattice designs, matching between different accelerating–focusing lattices, and transition from NC to SC sections, is detailed. Design of high-intensity SC linacs for light ions, methods for the reduction of beam losses, preventing beam halo formation, and the effect of HOMs and errors on beam quality are discussed. Examples are ta...

  7. Superconducting energy storage

    Energy Technology Data Exchange (ETDEWEB)

    Giese, R.F.

    1993-10-01

    This report describes the status of energy storage involving superconductors and assesses what impact the recently discovered ceramic superconductors may have on the design of these devices. Our description is intended for R&D managers in government, electric utilities, firms, and national laboratories who wish an overview of what has been done and what remains to be done. It is assumed that the reader is acquainted with superconductivity, but not an expert on the topics discussed here. Indeed, it is the author`s aim to enable the reader to better understand the experts who may ask for the reader`s attention, support, or funding. This report may also inform scientists and engineers who, though expert in related areas, wish to have an introduction to our topic.

  8. Anyon Superconductivity of Sb

    Science.gov (United States)

    Maksoed, Wh-; Parengkuan, August

    2016-10-01

    In any permutatives to Pedro P. Kuczhynski from Peru, for anyon superconductivity sought EZ Kuchinskii et al.: ``Anion height dependence of Tc & d.o.s of Fe-based Superconductors'', 2010 as well as ``on the basis of electron microscopy & AFM measurements, these phenomena are quantified with focus on fractal dimension, particle perimeter & size of the side branch(tip width) in bert Stegemann et al.:Crystallization of Sb nanoparticles-Pattern Formation & Fractal Growth'', J.PhysChem B., 2004. For dendritic & dendrimer fractal characters shown further: ``antimony denrites were found to be composed of well-crystallized nanoflakes with size 20-4 nm''- Bou Zhau, et al., MaterialLetters, 59 (2005). The alkyl triisopropyl attached in TIPSb those includes in DNA, haemoglobin membrane/fixed-bed reactor for instance quotes in Dragony Fu, Nature Review Cancer, 12 (Feb 2012). Heartfelt Gratitudes to HE. Mr. Prof. Ir. Handojo.

  9. Superconductivity of columbium

    Energy Technology Data Exchange (ETDEWEB)

    Cook, D.B.; Zemansky, M.W.; Boorse, H.A.

    1950-11-15

    Isothermal critical magnetic field curves and zero field transitions for several annealed specimens of columbium have been measured by an a.c. mutual inductance method at temperatures from 5.1 deg K to the zero field transition temperature. The H-T curve was found to fit the usual parabolic relationship H = H{sub 0}(1-T(2)/T(2){sub 0}) with H{sub 0} = 8250 oersteds and T{sub 0} = 8.65 deg K. The initial slope of the curve was 1910 oersteds/deg. The electronic specific heat in the normal state calculated from the thermodynamic equations is 0.0375T and the approximate Debye characteristic temperature in the superconducting state, 67 deg K. Results on a different grade of columbium with a tantalum impurity of 0.4 percent, according to neutron scattering measurements, were in agreement, with the data obtained from columbium of 0.2 percent maximum tantalum impurity.

  10. Superconducting pulsed magnets

    CERN Document Server

    CERN. Geneva

    2006-01-01

    Lecture 1. Introduction to Superconducting Materials Type 1,2 and high temperature superconductors; their critical temperature, field & current density. Persistent screening currents and the critical state model. Lecture 2. Magnetization and AC Loss How screening currents cause irreversible magnetization and hysteresis loops. Field errors caused by screening currents. Flux jumping. The general formulation of ac loss in terms of magnetization. AC losses caused by screening currents. Lecture 3. Twisted Wires and Cables Filamentary composite wires and the losses caused by coupling currents between filaments, the need for twisting. Why we need cables and how the coupling currents in cables contribute more ac loss. Field errors caused by coupling currents. Lecture 4. AC Losses in Magnets, Cooling and Measurement Summary of all loss mechanisms and calculation of total losses in the magnet. The need for cooling to minimize temperature rise in a magnet. Measuring ac losses in wires and in magnets. Lecture 5. Stab...

  11. Overview on superconducting photoinjectors

    Directory of Open Access Journals (Sweden)

    A. Arnold

    2011-02-01

    Full Text Available The success of most of the proposed energy recovery linac (ERL based electron accelerator projects for future storage ring replacements (SRR and high power IR–free-electron lasers (FELs largely depends on the development of an appropriate source. For example, to meet the FEL specifications [J. W. Lewellen, Proc. SPIE Int. Soc. Opt. Eng. 5534, 22 (2004PSISDG0277-786X10.1117/12.557378] electron beams with an unprecedented combination of high brightness, low emittance (0.1  μmrad, and high average current (hundreds of mA are required. An elegant way to create a beam of such quality is to combine the high beam quality of a normal conducting rf photoinjector with the superconducting technology, i.e., to build a superconducting rf photoinjector (SRF gun. SRF gun R&D programs based on different approaches have been launched at a growing number of institutes and companies (AES, Beijing University, BESSY, BNL, DESY, FZD, TJNAF, Niowave, NPS, Wisconsin University. Substantial progress was achieved in recent years and the first long term operation was demonstrated at FZD [R. Xiang et al., in Proceedings of the 31st International Free Electron Laser Conference (FEL 09, Liverpool, UK (STFC Daresbury Laboratory, Warrington, 2009, p. 488]. In the near future SRF guns are expected to play an important role for linac-driven FEL facilities. In this paper we will review the concepts, the design parameters, and the status of the major SRF gun projects.

  12. Superconducting Aero Propulsion Motor Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Superconducting electric propulsion systems will yield improvements in total ownership costs due to the simplicity of electric drive when compared with gas turbine...

  13. Mixed-mu superconducting bearings

    Energy Technology Data Exchange (ETDEWEB)

    Hull, John R. (Hinsdale, IL); Mulcahy, Thomas M. (Western Springs, IL)

    1998-01-01

    A mixed-mu superconducting bearing including a ferrite structure disposed for rotation adjacent a stationary superconductor material structure and a stationary permanent magnet structure. The ferrite structure is levitated by said stationary permanent magnet structure.

  14. Superconductivity in all its states

    CERN Multimedia

    Globe Info

    2011-01-01

    Temporary exhibition at the Saint-Genis-Pouilly Tourist Office. For the 100th anniversary of its discovery, take a plunge into the amazing world of superconductivity. Some materials, when cooled down to extreme temperatures, acquire a remarkable property -  they become superconducting. Superconductivity is a rare example of a quantum effect that can be witnessed on the macroscopic scale and is today at the heart of much research. In laboratories, researchers try to gain a better understanding of its origins, study new superconducting materials, explore the phenomenon at the nanometric scale and pursue their indefatigable search for new applications. Monday to Friday: 09:00 a.m. to 12:00 and 2:30 p.m. to 6:30 p.m. Saturday: 10:00 a.m. to 12:00 noon » Open to all – Admission free For further information: +33 (0)4 50 42 29 37

  15. Search for superconductivity in micrometeorites.

    Science.gov (United States)

    Guénon, S; Ramírez, J G; Basaran, Ali C; Wampler, J; Thiemens, M; Taylor, S; Schuller, Ivan K

    2014-12-05

    We have developed a very sensitive, highly selective, non-destructive technique for screening inhomogeneous materials for the presence of superconductivity. This technique, based on phase sensitive detection of microwave absorption is capable of detecting 10(-12) cc of a superconductor embedded in a non-superconducting, non-magnetic matrix. For the first time, we apply this technique to the search for superconductivity in extraterrestrial samples. We tested approximately 65 micrometeorites collected from the water well at the Amundsen-Scott South pole station and compared their spectra with those of eight reference materials. None of these micrometeorites contained superconducting compounds, but we saw the Verwey transition of magnetite in our microwave system. This demonstrates that we are able to detect electro-magnetic phase transitions in extraterrestrial materials at cryogenic temperatures.

  16. Advanced Superconducting Test Accelerator (ASTA)

    Data.gov (United States)

    Federal Laboratory Consortium — The Advanced Superconducting Test Accelerator (ASTA) facility will be based on upgrades to the existing NML pulsed SRF facility. ASTA is envisioned to contain 3 to 6...

  17. Superconductivity in Layered Organic Metals

    Directory of Open Access Journals (Sweden)

    Jochen Wosnitza

    2012-04-01

    Full Text Available In this short review, I will give an overview on the current understanding of the superconductivity in quasi-two-dimensional organic metals. Thereby, I will focus on charge-transfer salts based on bis(ethylenedithiotetrathiafulvalene (BEDT-TTF or ET for short. In these materials, strong electronic correlations are clearly evident, resulting in unique phase diagrams. The layered crystallographic structure leads to highly anisotropic electronic as well as superconducting properties. The corresponding very high orbital critical field for in-plane magnetic-field alignment allows for the occurrence of the Fulde–Ferrell– Larkin–Ovchinnikov state as evidenced by thermodynamic measurements. The experimental picture on the nature of the superconducting state is still controversial with evidence both for unconventional as well as for BCS-like superconductivity.

  18. Advanced Superconducting Test Accelerator (ASTA)

    Data.gov (United States)

    Federal Laboratory Consortium — The Advanced Superconducting Test Accelerator (ASTA) facility will be based on upgrades to the existing NML pulsed SRF facility. ASTA is envisioned to contain 3 to...

  19. Cryogenic Systems and Superconductive Power

    Science.gov (United States)

    The report defines, investigates, and experimentally evaluates the key elements of a representative crogenic turborefrigerator subsystem suitable for providing reliable long-lived cryogenic refrigeration for a superconductive ship propulsion system.

  20. Recent advances in fullerene superconductivity

    CERN Document Server

    Margadonna, S

    2002-01-01

    Superconducting transition temperatures in bulk chemically intercalated fulleride salts reach 33 K at ambient pressure and in hole-doped C sub 6 sub 0 derivatives in field-effect-transistor (FET) configurations, they reach 117 K. These advances pose important challenges for our understanding of high-temperature superconductivity in these highly correlated organic metals. Here we review the structures and properties of intercalated fullerides, paying particular attention to the correlation between superconductivity and interfullerene separation, orientational order/disorder, valence state, orbital degeneracy, low-symmetry distortions, and metal-C sub 6 sub 0 interactions. The metal-insulator transition at large interfullerene separations is discussed in detail. An overview is also given of the exploding field of gate-induced superconductivity of fullerenes in FET electronic devices.

  1. The superconducting bending magnets 'CESAR'

    CERN Document Server

    Pérot, J

    1978-01-01

    In 1975, CERN decided to build two high precision superconducting dipoles for a beam line in the SPS north experimental area. The aim was to determine whether superconducting magnets of the required accuracy and reliability can be built and what their economies and performances in operation will be. Collaboration between CERN and CAE /SACLAY was established in order to make use of the knowledge and experience already acquired in the two laboratories. (0 refs).

  2. Y-Ba Superconducting Ceramics

    Science.gov (United States)

    Shunbao, Tian; Xiaofei, Li; Tinglian, Wen; Zuxiang, Lin; Shichun, Li; Huijun, Yu

    Polycrystalline Y-Ba-Cu-O superconducting materials have been studied. It was found that chemical composition and processing condition may play an important role in the final structure and superconducting properties. The density has been determined and compared with the calculated value according to the structure model reported by Bell Labs. The grain size and the morphology of the materials were observed by SEM.

  3. Entanglement witnessing in superconducting beamsplitters

    Science.gov (United States)

    Soller, H.; Hofstetter, L.; Reeb, D.

    2013-06-01

    We analyse a large class of superconducting beamsplitters for which the Bell parameter (CHSH violation) is a simple function of the spin detector efficiency. For these superconducting beamsplitters all necessary information to compute the Bell parameter can be obtained in Y-junction setups for the beamsplitter. Using the Bell parameter as an entanglement witness, we propose an experiment which allows to verify the presence of entanglement in Cooper pair splitters.

  4. Superconductivity in domains with corners

    DEFF Research Database (Denmark)

    Bonnaillie-Noel, Virginie; Fournais, Søren

    2007-01-01

    We study the two-dimensional Ginzburg-Landau functional in a domain with corners for exterior magnetic field strengths near the critical field where the transition from the superconducting to the normal state occurs. We discuss and clarify the definition of this field and obtain a complete...... asymptotic expansion for it in the large $\\kappa$ regime. Furthermore, we discuss nucleation of superconductivity at the boundary....

  5. Electronic structure and superconductivity of hcp-bcc binary systems based on titanium and rhenium

    Energy Technology Data Exchange (ETDEWEB)

    Prekul, A.F.; Volkenshtein, N.V.

    1978-12-01

    The similarity of hcp--bcc binary systems of transition metals of groups IV--V and VI--VII is shown on the basis of a joint analysis of the kinetic, superconducting, and structural properties. Under the assumption that there is a singularity (a pseudo-gap) in the electronic structure of hardened alloys, a model is proposed for the change in the critical temperature of superconductivity with alloy concentration. According to the model, the two peaks in the functions T/sub c/(x) are due to the partial dielectrization of the electron spectrum and do not belong to the equilibrium solid solutions based on the initial metals, as had earlier been assumed.

  6. First-order superconducting transition in the inter-band model

    Energy Technology Data Exchange (ETDEWEB)

    Gomes da Silva, M. [Universidade Federal do Amazonas, Departamento de Física, 3000, Japiim, 69077-00 Manaus, AM (Brazil); Instituto Federal de Educação Ciência e Tecnologia do Amazonas, Av. 7 de Setembro, 1975 - Centro, Manaus, AM 69020-120 (Brazil); Dinóla Neto, F., E-mail: dinola@ufam.edu.br [Universidade Federal do Amazonas, Departamento de Física, 3000, Japiim, 69077-00 Manaus, AM (Brazil); Padilha, I.T. [Universidade Federal do Amazonas, Departamento de Física, 3000, Japiim, 69077-00 Manaus, AM (Brazil); Ricardo de Sousa, J. [Universidade Federal do Amazonas, Departamento de Física, 3000, Japiim, 69077-00 Manaus, AM (Brazil); National Institute of Science and Technology for Complex Systems, Universidade Federal do Amazonas, 3000, Japiim, 69077-000 Manaus, AM (Brazil); Continentino, M.A. [Centro Brasileiro de Pesquisas Físicas, 22290-180 Rio de Janeiro, RJ (Brazil)

    2014-04-01

    The comprehension about the theoretical features of superconductivity is an interesting and fundamental topic in condensed matter physics. Several theoretical proposals were considered to describe the new classes of superconducting compounds and alloys. In this work we propose to study a non-conventional superconducting system where the Cooper pairs are formed by fermions from different bands described via two band model with hybridization. In this inter-band scenario we find a first-order phase transition at low temperatures and we observe a tricritical point in the phase diagram. In our description, the control parameter is the hybridization that can be tuned by external pressure. This fact indicates the possibility to observe discontinuities in the SC gap amplitude through applying pressure on the system.

  7. Status Of The Work On The Base Directions Of The "rf Superconductivity For Accelerators" Program At The Federate Problem Lab At Ihep

    CERN Document Server

    Sevryukova, L

    2004-01-01

    In this report result of the study of electrophysical phenomena on the superconducting cavity surface, including plasma, bifurcation, hysteresis, emission and diffusion phenomena are considered. Science intensive recourse -saving technologies of superconducting cavities are being studied on the base of these phenomena. The superconducting cavities are made of Nb and Nb film, alloy film or HTC ceramics, which cover the working surface of the weldless copper shells using ion-plasma technologies (axial and planar magnetron sputtering). Quality monitoring (optical, emission, electrochemical and high frequency) of the working surface condition of superconducting cavities is developed under the realization of new technologies. The brief review of the experimental equipment is used as training base for individual students, post-graduate students and research staff in the field of technologies that use superconductivity phenomenon and ionic-plasma, electrochemical and high-vacuum technologies as well. For realizat...

  8. Superconducting Quadrupole for the ISR High Luminosity insertion:end view

    CERN Multimedia

    1977-01-01

    Connection end view of the prototype quadrupole before insertion of the inner vacuum chamber with inbedded 6-pole windings. The main components of the structure can be seen: (from inside outwards) the superconducting quadrupole coils surrounded by glass epoxy bandage rings and stainless steel spacers, the low-carbon steel yoke quadrants and the aluminium alloy shrinking rings. See also photos 7702690X, 7702307, 7702308, 7812604X.

  9. Universal out-of-equilibrium transport in Kondo-correlated quantum dots: renormalized dual fermions on the Keldysh contour.

    Science.gov (United States)

    Muñoz, Enrique; Bolech, C J; Kirchner, Stefan

    2013-01-04

    The nonlinear conductance of semiconductor heterostructures and single molecule devices exhibiting Kondo physics has recently attracted attention. We address the observed sample dependence of the measured steady state transport coefficients by considering additional electronic contributions in the effective low-energy model underlying these experiments that are absent in particle-hole symmetric setups. A novel version of the superperturbation theory of Hafermann et al. in terms of dual fermions is developed, which correctly captures the low-temperature behavior. We compare our results with the measured transport coefficients.

  10. Defects in higher-dimensional quantum field theory. Relations to AdS/CFT-correspondence and Kondo lattices

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt, R.

    2007-03-15

    The present work is addressed to defects and boundaries in quantum field theory considering the application to AdS/CFT correspondence. We examine interactions of fermions with spins localised on these boundaries. Therefore, an algebra method is emphasised adding reflection and transmission terms to the canonical quantisation prescription. This method has already been applied to bosons in two space-time dimensions before. We show the possibilities of such reflection-transmission algebras in two, three, and four dimensions. We compare with models of solid state physics as well as with the conformal field theory approach to the Kondo effect. Furthermore, we discuss ansatzes of extensions to lattice structures. (orig.)

  11. Kondo effect at low electron density and high particle-hole asymmetry in 1D, 2D, and 3D

    Science.gov (United States)

    Žitko, Rok; Horvat, Alen

    2016-09-01

    Using the perturbative scaling equations and the numerical renormalization group, we study the characteristic energy scales in the Kondo impurity problem as a function of the exchange coupling constant J and the conduction-band electron density. We discuss the relation between the energy gain (impurity binding energy) Δ E and the Kondo temperature TK. We find that the two are proportional only for large values of J , whereas in the weak-coupling limit the energy gain is quadratic in J , while the Kondo temperature is exponentially small. The exact relation between the two quantities depends on the detailed form of the density of states of the band. In the limit of low electron density the Kondo screening is affected by the strong particle-hole asymmetry due to the presence of the band-edge van Hove singularities. We consider the cases of one- (1D), two- (2D), and three-dimensional (3D) tight-binding lattices (linear chain, square lattice, cubic lattice) with inverse-square-root, step-function, and square-root onsets of the density of states that are characteristic of the respective dimensionalities. We always find two different regimes depending on whether TK is higher or lower than μ , the chemical potential measured from the bottom of the band. For 2D and 3D, we find a sigmoidal crossover between the large-J and small-J asymptotics in Δ E and a clear separation between Δ E and TK for TKband edge. Furthermore, we find that in 1D the particle-hole asymmetry leads to a large decrease of TK compared to the standard result obtained by approximating the density of states to be constant (flat-band approximation), while in 3D the opposite is the case; this is due to the nontrivial interplay of the exchange and potential scattering renormalization in the presence of particle-hole asymmetry. The 2D square-lattice density of states behaves to a very good approximation as a band with constant density of states.

  12. The Kondo lattice state in the presence of Van Hove singularities: Next-to-leading order scaling

    Science.gov (United States)

    Irkhin, V. Yu.

    2017-07-01

    Renormalization group analysis of the Kondo model with a logarithmic Van Hove singularity in the electron density of states has been carried out in the next-to-leading scaling approximation in different magnetic phases. The effective coupling constant remains small, while the renormalized magnetic moment and the frequency of spin fluctuations decrease by several orders of magnitude. In this way, broad regions of non-Fermi-liquid behavior are found from scaling trajectories in a large interval of the bare coupling constant. Applications to the physics of itinerant magnetism are considered.

  13. High critical current density and enhanced irreversibility field in superconducting MgB2 thin films.

    Science.gov (United States)

    Eom, C B; Lee, M K; Choi, J H; Belenky, L J; Song, X; Cooley, L D; Naus, M T; Patnaik, S; Jiang, J; Rikel, M; Polyanskii, A; Gurevich, A; Cai, X Y; Bu, S D; Babcock, S E; Hellstrom, E E; Larbalestier, D C; Rogado, N; Regan, K A; Hayward, M A; He, T; Slusky, J S; Inumaru, K; Haas, M K; Cava, R J

    2001-05-31

    The discovery of superconductivity at 39 K in magnesium diboride offers the possibility of a new class of low-cost, high-performance superconducting materials for magnets and electronic applications. This compound has twice the transition temperature of Nb3Sn and four times that of Nb-Ti alloy, and the vital prerequisite of strongly linked current flow has already been demonstrated. One possible drawback, however, is that the magnetic field at which superconductivity is destroyed is modest. Furthermore, the field which limits the range of practical applications-the irreversibility field H*(T)-is approximately 7 T at liquid helium temperature (4.2 K), significantly lower than about 10 T for Nb-Ti (ref. 6) and approximately 20 T for Nb3Sn (ref. 7). Here we show that MgB2 thin films that are alloyed with oxygen can exhibit a much steeper temperature dependence of H*(T) than is observed in bulk materials, yielding an H* value at 4.2 K greater than 14 T. In addition, very high critical current densities at 4.2 K are achieved: 1 MA cm-2 at 1 T and 105 A cm-2 at 10 T. These results demonstrate that MgB2 has potential for high-field superconducting applications.

  14. The road to superconducting spintronics

    Science.gov (United States)

    Eschrig, Matthias

    Energy efficient computing has become a major challenge, with the increasing importance of large data centres across the world, which already today have a power consumption comparable to that of Spain, with steeply increasing trend. Superconducting computing is progressively becoming an alternative for large-scale applications, with the costs for cooling being largely outweighed by the gain in energy efficiency. The combination of superconductivity and spintronics - ``superspintronics'' - has the potential and flexibility to develop into such a green technology. This young field is based on the observation that new phenomena emerge at interfaces between superconducting and other, competing, phases. The past 15 years have seen a series of pivotal predictions and experimental discoveries relating to the interplay between superconductivity and ferromagnetism. The building blocks of superspintronics are equal-spin Cooper pairs, which are generated at the interface between superconducting and a ferromagnetic materials in the presence of non-collinear magnetism. Such novel, spin-polarised Cooper pairs carry spin-supercurrents in ferromagnets and thus contribute to spin-transport and spin-control. Geometric Berry phases appear during the singlet-triplet conversion process in structures with non-coplanar magnetisation, enhancing functionality of devices, and non-locality introduced by superconducting order leads to long-range effects. With the successful generation and control of equal-spin Cooper pairs the hitherto notorious incompatibility of superconductivity and ferromagnetism has been not only overcome, but turned synergistic. I will discuss these developments and their extraordinary potential. I also will present open questions posed by recent experiments and point out implications for theory. This work is supported by the Engineering and Physical Science Research Council (EPSRC Grant No. EP/J010618/1).

  15. Research in Materials Science: Superconducting Transition Metal Alloys

    Science.gov (United States)

    1975-07-31

    Myron Hale Frommer , Ph.D. Thesis, MIT (Metallurgy and Materials Science, 1973) unpublished. t-1.■>-’-■ ^mm^m^^^m^^ßm^^^^f*rm**^^1**^^^*mi^^~*^^^^^m...77- 12. J. Bostock, Kofi Agyeman, M.H. Frommer , and M.L.A. MacVicar, J. Appl. Phys. 44 (1973j 5567. 13. W. N. Cheung (unpublished

  16. Buffer layers on metal alloy substrates for superconducting tapes

    Science.gov (United States)

    Jia, Quanxi; Foltyn, Stephen R.; Arendt, Paul N.; Groves, James R.

    2004-06-29

    An article including a substrate, a layer of an inert oxide material upon the surface of the substrate, a layer of an amorphous oxide or oxynitride material upon the inert oxide material layer, a layer of an oriented cubic oxide material having a rock-salt-like structure upon the amorphous oxide material layer, and a layer of a SrRuO.sub.3 buffer material upon the oriented cubic oxide material layer is provided together with additional layers such as a HTS top-layer of YBCO directly upon the layer of a SrRuO.sub.3 buffer material layer. With a HTS top-layer of YBCO upon at least one layer of the SrRuO.sub.3 buffer material in such an article, J.sub.c 's of up to 1.3.times.10.sup.6 A/cm.sup.2 have been demonstrated with projected IC's of over 200 Amperes across a sample 1 cm wide.

  17. Numerical simulations of heavy fermion systems. From He-3 bilayers to topological Kondo insulators

    Energy Technology Data Exchange (ETDEWEB)

    Werner, Jan

    2015-03-27

    In this thesis the results of model calculations based on an extended Periodic Anderson Model are presented. The three particle ring exchange, which is the dominant magnetic exchange process in layered He-3, is included in the model. In addition, the model incorporates the constraint of no double occupancy by taking the limit of large local Coulomb repulsion. By means of Cellular DMFT, the model is investigated for a range of values of the chemical potential μ and inverse temperature β=1/T. The method is a cluster extension to the Dynamical Mean-Field Theory (DMFT), and allows to systematically include non-local correlations beyond the DMFT. The auxiliary cluster model is solved by a hybridization expansion CTQMC cluster solver, which provides unbiased, numerically exact results for the Green's function and other observables of interest. As a first step, the onset of Fermi liquid coherence is studied. At low enough temperature, the self-energy is found to exhibit a linear dependence on Matsubara frequency. Meanwhile, the spin susceptibility crossed over from a Curie-Weiss law to a Pauli law. The heavy fermion state appears at a characteristic coherence scale T{sub coh}. While the density is rather high for small filling, for larger filling T{sub coh} is increasingly suppressed. This involves a decreasing quasiparticle residue Z∝T{sub coh} and an enhanced mass renormalization m{sup *}/m∝T{sub coh}{sup -1}. Extrapolation leads to a critical filling, where the coherence scale is expected to vanish at a quantum critical point. At the same time, the effective mass diverges. This corresponds to a breakdown of the Kondo effect, which is responsible for the formation of quasiparticles, due to a vanishing of the effective hybridization between the layers. Cellular DMFT simulations are conducted for small clusters of size N{sub c}=2 and 3. Furthermore a simple two-band model for two-dimensional topological Kondo insulators is devised, which is based on a single

  18. Superconductivity of lead

    Energy Technology Data Exchange (ETDEWEB)

    Boorse, H.A.; Cook, D.B.; Zemansky, W.M.

    1950-06-01

    Numerous determinations of the zero-field transition temperature of lead have been made. All of these observations except that of Daunt were made by the direct measurement of electrical resistance. Daunt`s method involved the shielding effect of persistent currents in a hollow cylinder. In the authors work on columbium to be described in a forthcoming paper an a.c. induction method was used for the measurement of superconducting transitions. The superconductor was mounted as a cylindrical core of a coil which functioned as the secondary of a mutual inductance. The primary coil was actuated by an oscillator which provided a maximum a.c. field within the secondary of 1.5 oersteds at a frequency of 1000 cycles per second. The secondary e.m.f. which was dependent for its magnitude on the permeability of the core was amplified, rectifie, and observed on a recording potentiometer. During the application of this method to the study of columbium it appeared that a further check on the zero-field transition temperature of lead would be worth while especially if agreement between results for very pure samples could be obtained using this method. Such result would help in establishing the lead transition temperature as a reasonably reproducible reference point in the region between 4 deg and 10 deg K.

  19. High temperature superconducting compounds

    Science.gov (United States)

    Goldman, Allen M.

    1992-11-01

    The major accomplishment of this grant has been to develop techniques for the in situ preparation of high-Tc superconducting films involving the use of ozone-assisted molecular beam epitaxy. The techniques are generalizable to the growth of trilayer and multilayer structures. Films of both the DyBa2Cu3O(7-x) and YBa2Cu3O(7-x) compounds as well as the La(2-x)Sr(x)CuO4 compound have been grown on the usual substrates, SrTiO3, YSZ, MgO, and LaAlO3, as well as on Si substrates without any buffer layer. A bolometer has been fabricated on a thermally isolated SiN substrate coated with YSZ, an effort carried out in collaboration with Honeywell Inc. The deposition process facilitates the fabrication of very thin and transparent films creating new opportunities for the study of superconductor-insulator transitions and the investigation of photo-doping with carriers of high temperature superconductors. In addition to a thin film technology, a patterning technology has been developed. Trilayer structures have been developed for FET devices and tunneling junctions. Other work includes the measurement of the magnetic properties of bulk single crystal high temperature superconductors, and in collaboration with Argonne National Laboratory, measurement of electric transport properties of T1-based high-Tc films.

  20. The Superconducting TESLA Cavities

    CERN Document Server

    Aune, B.; Bloess, D.; Bonin, B.; Bosotti, A.; Champion, M.; Crawford, C.; Deppe, G.; Dwersteg, B.; Edwards, D.A.; Edwards, H.T.; Ferrario, M.; Fouaidy, M.; Gall, P-D.; Gamp, A.; Gössel, A.; Graber, J.; Hubert, D.; Hüning, M.; Juillard, M.; Junquera, T.; Kaiser, H.; Kreps, G.; Kuchnir, M.; Lange, R.; Leenen, M.; Liepe, M.; Lilje, L.; Matheisen, A.; Möller, W-D.; Mosnier, A.; Padamsee, H.; Pagani, C.; Pekeler, M.; Peters, H-B.; Peters, O.; Proch, D.; Rehlich, K.; Reschke, D.; Safa, H.; Schilcher, T.; Schmüser, P.; Sekutowicz, J.; Simrock, S.; Singer, W.; Tigner, M.; Trines, D.; Twarowski, K.; Weichert, G.; Weisend, J.; Wojtkiewicz, J.; Wolff, S.; Zapfe, K.

    2000-01-01

    The conceptional design of the proposed linear electron-positron colliderTESLA is based on 9-cell 1.3 GHz superconducting niobium cavities with anaccelerating gradient of Eacc >= 25 MV/m at a quality factor Q0 > 5E+9. Thedesign goal for the cavities of the TESLA Test Facility (TTF) linac was set tothe more moderate value of Eacc >= 15 MV/m. In a first series of 27industrially produced TTF cavities the average gradient at Q0 = 5E+9 wasmeasured to be 20.1 +- 6.2 MV/m, excluding a few cavities suffering fromserious fabrication or material defects. In the second production of 24 TTFcavities additional quality control measures were introduced, in particular aneddy-current scan to eliminate niobium sheets with foreign material inclusionsand stringent prescriptions for carrying out the electron-beam welds. Theaverage gradient of these cavities at Q0 = 5E+9 amounts to 25.0 +- 3.2 MV/mwith the exception of one cavity suffering from a weld defect. Hence only amoderate improvement in production and preparation technique...