Order parameter fluctuations in the holographic superconductor
Plantz, N W M; Vandoren, S
2015-01-01
We investigate the effect of order parameter fluctuations in the holographic superconductor. In particular, the fully backreacted spectral functions of the order parameter in both the normal and the superconducting phase are computed. We also present a vector-like large-$N$ version of the Ginzburg-Landau model that accurately describes our long-wavelength results in both phases. The large-$N$ limit of the latter model explains why the Higgs mode and the second-sound mode are not present in the spectral functions. Our results indicate that the holographic superconductor describes a relativistic multi-component superfluid in the universal regime of the BEC-BCS crossover.
Order parameter fluctuations in the holographic superconductor
Plantz, N. W. M.; Stoof, H. T. C.; Vandoren, S.
2017-03-01
We investigate the effect of order parameter fluctuations in the holographic superconductor. In particular, following an introduction to the concept of intrinsic dynamics and its implementation within holographic models, we compute the intrinsic spectral functions of the order parameter in both the normal and the superconducting phase, using a fully backreacted bulk geometry. We also present a vector-like large-N version of the Ginzburg–Landau model that accurately describes our long-wavelength results in both phases. Our results indicate that the holographic superconductor describes a relativistic multi-component superfluid in the universal regime of the BEC–BCS crossover.
Quantum Fluctuations of a Superconductor Order Parameter.
Arutyunov, K Yu; Lehtinen, J S
2016-12-01
Tunneling I-V characteristics between very narrow titanium nanowires and "massive" superconducting aluminum were measured. The clear trend was observed: the thinner the titanium electrode, the broader the singularity at eV = Δ1(Al) + Δ2(Ti). The phenomenon can be explained by broadening of the gap edge of the quasi-one-dimensional titanium channels due to quantum fluctuations of the order parameter modulus |Δ2|. The range of the nanowire diameters, where the effect is pronounced, correlates with dimensions where the phase fluctuations of the complex superconducting order parameter Δ = |Δ|e(iφ), the quantum phase slips, broadening the R(T) dependencies, have been observed.
Unconventional superconductors experimental investgation of the order-parameter symmetry
Goll, Gernot
2006-01-01
This book offers a comprehensive summary of experiments that are especially suited to reveal the order-parameter symmetry of unconventional superconductors. It briefly introduces readers to the basic theoretical concepts and terms of unconventional superconductivity, followed by a detailed overview of experimental techniques and results investigating the superconducting energy gap and phase, plus the pairing symmetry. This review includes measurements of specific heat, thermal conductivity, penetration depth and nuclearmagnetic resonance and muon-spin rotation experiments. Further, point-contact and tunnelling spectroscopy and Josephson experiments are addressed. Current understanding is reviewed from the experimental point of view. With an appendix offering five tables with almost 200 references that summarize the present results from ambient pressure heavy-fermion and noncopper-oxide superconductors, the monograph provides a valuable resource for further studies in this field.
One-Sign Order Parameter in Iron Based Superconductor
Directory of Open Access Journals (Sweden)
Bernd Büchner
2012-03-01
Full Text Available The onset of superconductivity at the transition temperature is marked by the onset of order, which is characterized by an energy gap. Most models of the iron-based superconductors find a sign-changing (s± order parameter [1–6], with the physical implication that pairing is driven by spin fluctuations. Recent work, however, has indicated that LiFeAs has a simple isotropic order parameter [7–9] and spin fluctuations are not necessary [7,10], contrary to the models [1–6]. The strength of the spin fluctuations has been controversial [11,12], meaning that the mechanism of superconductivity cannot as yet be determined. We report the momentum dependence of the superconducting energy gap, where we find an anisotropy that rules out coupling through spin fluctuations and the sign change. The results instead suggest that orbital fluctuations assisted by phonons [13,14] are the best explanation for superconductivity.
Quasiclassical description of multi-band superconductors with two order parameters
Energy Technology Data Exchange (ETDEWEB)
Moor, Andreas
2014-05-19
This Thesis deals with multi-band superconductors with two order parameters, i.e., the superconductivity and the spin-density wave, also touching on one-band superconductors with a charge-density wave, as well as with only the superconducting order parameter. Quasiclassical description of suchlike structures is developed and applied to investigation of various effects, inter alia, the Josephson and the proximity effects, the Knight shift, the Larkin-Ovchinnikov-Fulde-Ferrell-like state, and the interplay of the order parameters in coexistence regime. The applicability of the developed approach to pnictides is discussed.
Impurity bound states in fully gapped d-wave superconductors with subdominant order parameters
Mashkoori, Mahdi; Björnson, Kristofer; Black-Schaffer, Annica M.
2017-01-01
Impurities in superconductors and their induced bound states are important both for engineering novel states such as Majorana zero-energy modes and for probing bulk properties of the superconducting state. The high-temperature cuprates offer a clear advantage in a much larger superconducting order parameter, but the nodal energy spectrum of a pure d-wave superconductor only allows virtual bound states. Fully gapped d-wave superconducting states have, however, been proposed in several cuprate systems thanks to subdominant order parameters producing d + is- or d + id′-wave superconducting states. Here we study both magnetic and potential impurities in these fully gapped d-wave superconductors. Using analytical T-matrix and complementary numerical tight-binding lattice calculations, we show that magnetic and potential impurities behave fundamentally different in d + is- and d + id′-wave superconductors. In a d + is-wave superconductor, there are no bound states for potential impurities, while a magnetic impurity produces one pair of bound states, with a zero-energy level crossing at a finite scattering strength. On the other hand, a d + id′-wave symmetry always gives rise to two pairs of bound states and only produce a reachable zero-energy level crossing if the normal state has a strong particle-hole asymmetry. PMID:28281570
Impurity bound states in fully gapped d-wave superconductors with subdominant order parameters.
Mashkoori, Mahdi; Björnson, Kristofer; Black-Schaffer, Annica M
2017-03-10
Impurities in superconductors and their induced bound states are important both for engineering novel states such as Majorana zero-energy modes and for probing bulk properties of the superconducting state. The high-temperature cuprates offer a clear advantage in a much larger superconducting order parameter, but the nodal energy spectrum of a pure d-wave superconductor only allows virtual bound states. Fully gapped d-wave superconducting states have, however, been proposed in several cuprate systems thanks to subdominant order parameters producing d + is- or d + id'-wave superconducting states. Here we study both magnetic and potential impurities in these fully gapped d-wave superconductors. Using analytical T-matrix and complementary numerical tight-binding lattice calculations, we show that magnetic and potential impurities behave fundamentally different in d + is- and d + id'-wave superconductors. In a d + is-wave superconductor, there are no bound states for potential impurities, while a magnetic impurity produces one pair of bound states, with a zero-energy level crossing at a finite scattering strength. On the other hand, a d + id'-wave symmetry always gives rise to two pairs of bound states and only produce a reachable zero-energy level crossing if the normal state has a strong particle-hole asymmetry.
Order parameter anisotropy of MgB2 using speciﬁc heat jump of layered superconductors
Indian Academy of Sciences (India)
I N Askerzade
2003-12-01
The recently obtained analytical result [1] for renormalization of the jump of the heat capacity (S-N)/N by anisotropy of the order parameter is applied to the layered superconductors. The graph of (S-N)/N vs. the anisotropy of the order parameter allows a direct determination of the gap anisotropy in MgB2 using available experimental data.
Linscheid, A; Sanna, A; Floris, A; Gross, E K U
2015-08-28
We show that the superconducting order parameter and condensation energy density of phonon-mediated superconductors can be calculated in real space from first principles density functional theory for superconductors. This method highlights the connection between the chemical bonding structure and the superconducting condensation and reveals new and interesting properties of superconducting materials. Understanding this connection is essential to describe nanostructured superconducting systems where the usual reciprocal space analysis hides the basic physical mechanism. In a first application we present results for MgB2, CaC6 and hole-doped graphane.
Venderbos, Jörn W. F.; Kozii, Vladyslav; Fu, Liang
2016-11-01
Motivated by the recent experiment indicating that superconductivity in the doped topological insulator CuxBi2Se3 has an odd-parity pairing symmetry with rotational symmetry breaking, we study the general class of odd-parity superconductors with two-component order parameters in trigonal and hexagonal crystal systems. In the presence of strong spin-orbit interaction, we find two possible superconducting phases below Tc, a time-reversal-breaking (i.e., chiral) phase and an anisotropic (i.e., nematic) phase, and determine their relative energetics from the gap function in momentum space. The nematic superconductor generally has a full quasiparticle gap, whereas the chiral superconductor with a three-dimensional (3D) Fermi surface has point nodes with lifted spin degeneracy, resulting in itinerant Majorana fermions in the bulk and topological Majorana arcs on the surface.
Thomale, Ronny; Platt, Christian; Hanke, Werner; Bernevig, B Andrei
2011-05-01
We put forward a scenario that explains the difference between the order-parameter character in arsenide (As) and phosphorous (P) iron-based superconductors. Using functional renormalization group to analyze it in detail, we find that nodal superconductivity on the electron pockets (hole pocket gaps are always nodeless) can naturally appear when the hole pocket at (π,π) in the unfolded Brillouin zone is absent, as is the case in LaOFeP. There, electron-electron interactions render the gap on the electron pockets softly nodal (of s(±) form). When the pocket of d(xy) orbital character is present, intraorbital interactions with the d(xy) part of the electron Fermi surface drives the superconductivity nodeless.
Charge order in cuprate superconductors
Energy Technology Data Exchange (ETDEWEB)
Bulut, Sinan; Kampf, Arno P. [Theoretical Physics III, Center for Electronic Correlations and Magnetism, Institute of Physics, University of Augsburg (Germany); Atkinson, Bill A. [Department of Physics and Astronomy, Trent University, Peterborough, Ontario (Canada)
2015-07-01
Motivated by widespread experimental evidence of charge orders in underdoped cuprate superconductors, we study a three band model of a cuprate plane. Our calculations start from a pseudogap-like normal system with a reconstructed Fermi surface, and we search for charge instabilities. From the charge susceptibilities, we identify a charge ordering instability with an ordering wavevector, q*, that matches experimental results not only with respect to the doping dependence but more importantly regarding its magnitude and direction. Namely, q* points along the Brillouin zone axes. Thus, our results clarify the discrepancy between many recent theoretical calculations and the experiments. We extend this calculation towards possible loop current instabilities and the charge ordering pattern in bilayer systems.
Guterding, Daniel; Altmeyer, Michaela; Jeschke, Harald O.; Valentí, Roser
2016-07-01
The symmetry of the superconducting order parameter in quasi-two-dimensional bis-ethylenedithio-tetrathiafulvalene (BEDT-TTF) organic superconductors is a subject of ongoing debate. We report ab initio density-functional-theory calculations for a number of organic superconductors containing κ -type layers. Using projective Wannier functions, we derive the parameters of a common low-energy Hamiltonian based on individual BEDT-TTF molecular orbitals. In a random-phase approximation spin-fluctuation approach, we investigate the evolution of the superconducting pairing symmetry within this model, and we point out a phase transition between extended s +dx2-y2 and dx y symmetry. We discuss the origin of the mixed order parameter and the relation between the realistic molecule description and the widely used dimer approximation. Based on our ab initio calculations, we position the investigated materials in the obtained molecule model phase diagram, and we simulate scanning tunneling spectroscopy experiments for selected cases. Our calculations show that many κ -type materials lie close to the phase-transition line between the two pairing symmetry types found in our calculation, possibly explaining the multitude of contradictory experiments in this field.
Taddei, Keith M.
ordering of this phase-separated state will be elucidated and the superconductivity attributed to a pseudo-stable minority phase. Detailed phase diagrams will be constructed for the related BaFe2(As1--xPx) 2 and Sr1--xNaxFe2 As2 compounds leading to a direct comparison of the effects driving of either doping regime. A strong magneto-elastic coupling will be established in both of these materials and a new magnetic phase will be mapped in Sr1--xNaxFe2As2. These observations will lead to a discussion of the role of magnetic fluctuations in the overall behavior of the material. The results of inelastic and elastic diffraction experiments will be combined with the results of the local probe M?ssbauer spectroscopy technique in order to determine magnetic fluctuations as the primary order parameter in the phase evolution of the iron-based superconductors, and therefore their importance in establishment of superconductivity as the ground state of these materials.
Exploring intertwined orders in cuprate superconductors
Tranquada, John M.
2015-03-01
The concept of intertwined orders has been introduced to describe the cooperative relationship between antiferromagnetic spin correlations and electron (or hole) pair correlations that develop in copper-oxide superconductors. This contrasts with systems in which, for example, charge-density-wave (CDW) order competes for Fermi surface area with superconductivity. La2-xBaxCuO4 with x=0.125 provides an example in which the ordering of spin stripes coincides with the onset of two-dimensional superconducting correlations. The apparent frustration of the interlayer Josephson coupling has motivated the concept of the pair-density-wave superconductor, a state that theoretical calculations show to be energetically competitive with the uniform d-wave superconductor. Even at x=0.095, where there is robust superconductivity below 32 K in zero field, the coexistence of strong, low-energy, incommensurate spin excitations implies a spatially modulated and intertwined pair wave function. Recent observations of CDW order in YBa2Cu3O6+x and other cuprate families have raised interesting questions regarding the general role of charge modulations and the relation to superconductivity. While there are differences in the doping dependence of the modulation wave vectors in YBa2Cu3O6+x and La2-xBaxCuO4, the maximum ordering strength is peaked at the hole concentration of 1/8 in both cases. There are also possible connections with the quantum oscillations that have been detected about the same hole concentration but at high magnetic fields. Resolving these relationships remains a research challenge.
Superconducting State Parameters of Binary Superconductors
Directory of Open Access Journals (Sweden)
Aditya M. Vora
2012-05-01
Full Text Available A well known pseudopotential is used to investigate the superconducting state parameters viz. electron-phonon coupling strength , Coulomb pseudopotential *, transition temperature ТС, isotope effect exponent and effective interaction strength N0V for the AgxZn1 – x and AgxAl1 – x binary superconductors 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 the various exchange and correlation functions is concluded from the present study. The comparison with other such experimental values is encouraging, which confirms the applicability of the model potential in explaining the superconducting state parameters of binary mixture.
Entanglement as a quantum order parameter
Brandão, F G S L
2005-01-01
We show that the quantum order parameters (QOP) associated with the transitions between a normal conductor and a superconductor in the BCS and $\\eta$-pairing models and between a Mott-insulator and a superfluid in the Bose-Hubbard model are directly related to the amount of entanglement existent in the ground state of each system. This gives a physical meaningful interpretation to these QOP, which shows the intrinsically quantum nature of the phase transitions considered.
Energy Technology Data Exchange (ETDEWEB)
Kouznetsov, Konstantin Alexander [Univ. of California, Berkeley, CA (US). Dept. of Physics; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
1999-12-01
The cuprate YBa_{2}Cu_{3}O_{7-δ} is the material that drives the majority of the technological applications of high transition temperature (T_{c}) superconductors, particularly in the area of superconducting electronics. Despite the widespread use of high-T_{c} superconducting materials in a variety of applications, the nature of the superconducting state in these materials remains unknown since their discovery more than a decade ago. Many properties of the high-T_{c} superconductors are determined by their order parameter, which is a wavefunction describing the superconducting condensate. The symmetry of the order parameter in cuprates has been the subject of intensive investigation, leading to conflicting sets of results. Some experiments supported conventional, s-wave symmetry of the order parameter, while others indicated an unconventional, d-wave symmetry. The first part of this thesis is an experimental study of the symmetry of the order parameter in YBa_{2}Cu_{3}O_{7-δ}. A new class of phase sensitive experiments is described that involve Josephson tunneling along the c-axis of twinned crystals of YBa_{2}Cu_{3}O_{7-δ}. These experiments showed that an s-wave component must reverse sign across the twin boundary, providing direct evidence for a mixed, s+d symmetry of the order parameter in YBa_{2}Cu_{3}O_{7-δ}, and thereby reconciling two conflicting sets of previous findings and establishing the dominant d-wave pairing symmetry. The second part of the thesis focuses on practical applications of YBa_{2}Cu_{3}O_{7-δ} in superconducting electronics. The authors introduce a novel Superconducting Quantum Interference Device (SQUID) gradiometer. The principle of operation of these long baseline high-T{sub c} SQUID gradiometers is based on the inductive coupling of the input coil of a planar flux transformer to the
Oates, D E; Park, S-H; Koren, G
2004-11-05
We present experimental evidence for the observation of the nonlinear Meissner effect in high-quality epitaxial yttrium barium copper oxide thin films by measuring their intermodulation distortion at microwave frequencies versus temperature. Most of the films measured show a characteristic increase in nonlinearity at low temperatures as predicted by the nonlinear Meissner effect. We could measure the nonlinear Meissner effect because intermodulation distortion measurements are an extremely sensitive method that can detect changes in the penetration depth of the order of 1 part in 10(5).
Holographic entanglement entropy in two-order insulator/superconductor transitions
Peng, Yan
2016-01-01
We study holographic superconductor model with two scalar fields coupled to one single Maxwell field in the AdS soliton background away from the probe limit. We disclose properties of phase transitions mostly from the holographic topological entanglement entropy approach. With different sets of parameters, we observe various types of transitions, especially a new first order phase transition between the condensation of different order parameters in the insulator/superconductor system. Our results show that the entanglement entropy is a good probe to critical phase transition points and the order of phase transitions in the two-order model. We also conclude that the entanglement entropy is useful to some extent in determining the physically supported phases. In addition, we investigate properties of the condensation through the scalar operator and the charge density in the dual theory. As a summary, we draw the complete phase diagram of the effects of the scalar charge on phase transitions. At last, we give so...
Fermi-surface reconstruction by stripe order in cuprate superconductors.
Laliberté, F; Chang, J; Doiron-Leyraud, N; Hassinger, E; Daou, R; Rondeau, M; Ramshaw, B J; Liang, R; Bonn, D A; Hardy, W N; Pyon, S; Takayama, T; Takagi, H; Sheikin, I; Malone, L; Proust, C; Behnia, K; Taillefer, Louis
2011-08-16
The origin of pairing in a superconductor resides in the underlying normal state. In the cuprate high-temperature superconductor YBa(2)Cu(3)O(y) (YBCO), application of a magnetic field to suppress superconductivity reveals a ground state that appears to break the translational symmetry of the lattice, pointing to some density-wave order. Here we use a comparative study of thermoelectric transport in the cuprates YBCO and La(1.8-x)Eu(0.2)Sr(x)CuO(4) (Eu-LSCO) to show that the two materials exhibit the same process of Fermi-surface reconstruction as a function of temperature and doping. The fact that in Eu-LSCO this reconstruction coexists with spin and charge modulations that break translational symmetry shows that stripe order is the generic non-superconducting ground state of hole-doped cuprates.
Striped superconductors: how spin, charge and superconducting orders intertwine in the cuprates
Energy Technology Data Exchange (ETDEWEB)
Berg, Erez; Kivelson, Steven A [Department of Physics, Stanford University, Stanford, CA 94305-4060 (United States); Fradkin, Eduardo [Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801-3080 (United States); Tranquada, John M [Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973-5000 (United States)], E-mail: kivelson@stanford.edu
2009-11-15
Recent transport experiments in the original cuprate high temperature superconductor, La{sub 2-x}Ba{sub x}CuO{sub 4}, have revealed a remarkable sequence of transitions and crossovers that give rise to a form of dynamical dimensional reduction, in which a bulk crystal becomes essentially superconducting in two directions while it remains poorly metallic in the third. We identify these phenomena as arising from a distinct new superconducting state, the 'striped superconductor', in which the superconducting order is spatially modulated, so that its volume average value is zero. Here, in addition to outlining the salient experimental findings, we sketch the order parameter theory of the state, stressing some of the ways in which a striped superconductor differs fundamentally from an ordinary (uniform) superconductor, especially concerning its response to quenched randomness. We also present the results of density matrix renormalization group calculations on a model of interacting electrons in which sign oscillations of the superconducting order are established. Finally, we speculate concerning the relevance of this state to experiments in other cuprates, including recent optical studies of La{sub 2-x}Sr{sub x}CuO{sub 4} in a magnetic field, neutron scattering experiments in underdoped YBa{sub 2}Cu{sub 3}O{sub 6+x} and a host of anomalies seen in STM and ARPES studies of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}}.
Striped superconductors: how spin, charge and superconducting orders intertwine in the cuprates
Berg, Erez; Fradkin, Eduardo; Kivelson, Steven A.; Tranquada, John M.
2009-11-01
Recent transport experiments in the original cuprate high temperature superconductor, La2-xBaxCuO4, have revealed a remarkable sequence of transitions and crossovers that give rise to a form of dynamical dimensional reduction, in which a bulk crystal becomes essentially superconducting in two directions while it remains poorly metallic in the third. We identify these phenomena as arising from a distinct new superconducting state, the 'striped superconductor', in which the superconducting order is spatially modulated, so that its volume average value is zero. Here, in addition to outlining the salient experimental findings, we sketch the order parameter theory of the state, stressing some of the ways in which a striped superconductor differs fundamentally from an ordinary (uniform) superconductor, especially concerning its response to quenched randomness. We also present the results of density matrix renormalization group calculations on a model of interacting electrons in which sign oscillations of the superconducting order are established. Finally, we speculate concerning the relevance of this state to experiments in other cuprates, including recent optical studies of La2-xSrxCuO4 in a magnetic field, neutron scattering experiments in underdoped YBa2Cu3O6+x and a host of anomalies seen in STM and ARPES studies of Bi2Sr2CaCu2O8+δ.
Coulomb interaction and first-order superconductor-insulator transition.
Syzranov, S V; Aleiner, I L; Altshuler, B L; Efetov, K B
2010-09-24
The superconductor-insulator transition (SIT) in regular arrays of Josephson junctions is studied at low temperatures. We derived an imaginary time Ginzburg-Landau-type action properly describing the Coulomb interaction. The renormalization group analysis at zero temperature T=0 in the space dimensionality d=3 shows that the SIT is always of the first order. At finite T, a tricritical point separates the lines of the first- and second-order phase transitions. The same conclusion holds for d=2 if the mutual capacitance is larger than the distance between junctions.
Colloquium: Theory of intertwined orders in high temperature superconductors
Fradkin, Eduardo; Kivelson, Steven A.; Tranquada, John M.
2015-04-01
The electronic phase diagrams of many highly correlated systems, and, in particular, the cuprate high temperature superconductors, are complex, with many different phases appearing with similar (sometimes identical) ordering temperatures even as material properties, such as dopant concentration, are varied over wide ranges. This complexity is sometimes referred to as "competing orders." However, since the relation is intimate, and can even lead to the existence of new phases of matter such as the putative "pair-density wave," the general relation is better thought of in terms of "intertwined orders." Some of the experiments in the cuprates which suggest that essential aspects of the physics are reflected in the intertwining of multiple orders, not just in the nature of each order by itself, are selectively analyzed. Several theoretical ideas concerning the origin and implications of this complexity are also summarized and critiqued.
Zeroth Order Phase Transition in a Holographic Superconductor with Single Impurity
Zeng, Hua Bi
2014-01-01
We studied the single normal impurity effect in superconductor by using the holographic method. When the size of impurity is much smaller compared to the host superconductor, we reproduced the Anderson theorem, which states that a conventional s-wave superconductor is robust to a normal (non-magnetic) impurity with small impurity strength or impurities with small concentration. While by increasing the size of impurity in a fixed host superconductor we also find a decrease $T_c$ of the host superconductor, the phase transition at the critical impurity strength is of zeroth order.
Charge orders, magnetism and pairings in the cuprate superconductors.
Kloss, T; Montiel, X; de Carvalho, V S; Freire, H; Pépin, C
2016-08-01
We review the recent developments in the field of cuprate superconductors with special focus on the recently observed charge order in the underdoped compounds. We introduce new theoretical developments following the study of the antiferromagnetic quantum critical point in two dimensions, in which preemptive orders in both charge and superconducting (SC) sectors emerge, that are in turn related by an SU(2) symmetry. We consider the implications of this proliferation of orders in the underdoped region, and provide a study of the type of fluctuations which characterize the SU(2) symmetry. We identify an intermediate energy scale where the SC fluctuations are dominant and argue that they are unstable towards the formation of a resonant excitonic state at the pseudogap temperature T (*). We discuss the implications of this scenario for a few key experiments.
The order parameter symmetry in CeIrIn5
Directory of Open Access Journals (Sweden)
H Shakeripour
2016-06-01
Full Text Available To understand the mechanism of superconductivity in unconventional super onductors is one of the big challenges in the field of superconductivity. Based on the BCS theory, there is a direct relation between the pairing mechanism and the symmetry of the order parameter. Therefore, identification of the structure of the superconducting gap or the order parameter provides key information on the pairing mechanism. The s-wave conventional superconductors have full point symmetry of the crystal lattice, thus they have full gap symmetry around the Fermi surface. This leads to the exponential temperature dependence of many physical properties in the superconducting state at low temperature. However, the presence of nodes imposed by symmetry in the gap function of unconventional superconductors implies a different order parameter other than conventional s-wave, which may lead to a different pairing mechanism. Here, we show how thermal conductivity measurements in CeIrIn5 at very low temperatures detect the superconducting gap structure.
Disorder-promoted C4-symmetric magnetic order in iron-based superconductors
Hoyer, Mareike; Fernandes, Rafael M.; Levchenko, Alex; Schmalian, Jörg
2016-04-01
In most iron-based superconductors, the transition to the magnetically ordered state is closely linked to a lowering of structural symmetry from tetragonal (C4) to orthorhombic (C2). However, recently, a regime of C4-symmetric magnetic order has been reported in certain hole-doped iron-based superconductors. This novel magnetic ground state can be understood as a double-Q spin density wave characterized by two order parameters M1 and M2 related to each of the two Q vectors. Depending on the relative orientations of the order parameters, either a noncollinear spin-vortex crystal or a nonuniform charge-spin density wave could form. Experimentally, Mössbauer spectroscopy, neutron scattering, and muon spin rotation established the latter as the magnetic configuration of some of these optimally hole-doped iron-based superconductors. Theoretically, low-energy itinerant models do support a transition from single-Q to double-Q magnetic order, but with nearly degenerate spin-vortex crystal and charge-spin density wave states. In fact, extensions of these low-energy models including additional electronic interactions tip the balance in favor of the spin-vortex crystal, in apparent contradiction with the recent experimental findings. In this paper we revisit the phase diagram of magnetic ground states of low-energy multiband models in the presence of weak disorder. We show that impurity scattering not only promotes the transition from C2 to C4-magnetic order, but it also favors the charge-spin density wave over the spin-vortex crystal phase. Additionally, in the single-Q phase, our analysis of the nematic coupling constant in the presence of disorder supports the experimental finding that the splitting between the structural and stripe-magnetic transition is enhanced by disorder.
The competition between s-wave order and d-wave order in holographic superconductors
Li, Li-Fang; Li, Li; Wang, Yong-Qiang
2014-01-01
We study the competition between s-wave order and d-wave order through two holographic superconductor models. We find there are four phases in each model, involving in the normal phase without any condensation, the pure s-wave phase, pure d-wave phase and the s+d coexisting phase. Once the coexisting phase appears, it is thermodynamically favored. The phase diagram is constructed for each model in terms of temperature and the ratio of charges between two orders. We further compare the behaviors of some thermodynamic quantities, and discuss the different aspects and identical ones between two models.
Narlikar, A V
2014-01-01
Superconductors is neither about basic aspects of superconductivity nor about its applications, but its mainstay is superconducting materials. Unusual and unconventional features of a large variety of novel superconductors are presented and their technological potential as practical superconductors assessed. The book begins with an introduction to basic aspects of superconductivity. The presentation is readily accessible to readers from a diverse range of scientific and technical disciplines, such as metallurgy, materials science, materials engineering, electronic and device engineering, and chemistry. The derivation of mathematical formulas and equations has been kept to a minimum and, wherever necessary, short appendices with essential mathematics have been added at the end of the text. The book is not meant to serve as an encyclopaedia, describing each and every superconductor that exists, but focuses on important milestones in their exciting development.
Hidden String Order in a Hole Superconductor with Extended Correlated Hopping.
Chhajlany, Ravindra W; Grzybowski, Przemysław R; Stasińska, Julia; Lewenstein, Maciej; Dutta, Omjyoti
2016-06-01
Ultracold fermions in one-dimensional, spin-dependent nonoverlapping optical lattices are described by a nonstandard Hubbard model with next-nearest-neighbor correlated hopping. In the limit of a kinetically constraining value of the correlated hopping equal to the normal hopping, we map the invariant subspaces of the Hamiltonian exactly to free spinless fermion chains of varying lengths. As a result, the system exactly manifests spin-charge separation and we obtain the system properties for arbitrary filling: ground state collective order characterized by a spin gap, which can be ascribed to an unconventional critical hole superconductor associated with finite long range nonlocal string order. We study the system numerically away from the integrable point and show the persistence of both long range string order and spin gap for appropriate parameters as well as a transition to a ferromagnetic state.
Topological order, symmetry, and Hall response of two-dimensional spin-singlet superconductors
Moroz, Sergej; Prem, Abhinav; Gurarie, Victor; Radzihovsky, Leo
2017-01-01
Fully gapped two-dimensional superconductors coupled to dynamical electromagnetism are known to exhibit topological order. In this work, we develop a unified low-energy description for spin-singlet paired states by deriving topological Chern-Simons field theories for s -wave, d +i d , and chiral higher even-wave superconductors. These theories capture the quantum statistics and fusion rules of Bogoliubov quasiparticles and vortices and incorporate global continuous symmetries—specifically, spin rotation and conservation of magnetic flux—present in all singlet superconductors. For all such systems, we compute the Hall response for these symmetries and investigate the physics at the edge. In particular, the weakly coupled phase of a chiral d +i d chiral state has a spin Hall coefficient νs=2 and a vanishing Hall response for the magnetic flux symmetry. We argue that the latter is a generic result for two-dimensional superconductors with gapped photons, thereby demonstrating the absence of a spontaneous magnetic field in the ground state of chiral superconductors. It is also shown that the Chern-Simons theories of chiral spin-singlet superconductors derived here fall into Kitaev's 16-fold classification of topological superconductors.
Holographic entanglement entropy in two-order insulator/superconductor transitions
Peng, Yan; Liu, Guohua
2017-04-01
We study holographic superconductor model with two orders in the five dimensional AdS soliton background away from the probe limit. We disclose properties of phase transitions mostly from the holographic topological entanglement entropy approach. Our results show that the entanglement entropy is useful in investigating transitions in this general model and in particular, there is a new type of first order phase transition in the insulator/superconductor system. We also give some qualitative understanding and obtain the analytical condition for this first order phase transition to occur. As a summary, we draw the complete phase diagram representing effects of the scalar charge on phase transitions.
Magnetic and orbital ordering in the iron-based superconductors. Role of spin-orbit coupling
Energy Technology Data Exchange (ETDEWEB)
Ahn, Felix; Eremin, Ilya [Institut fuer Theoretische Physik III, Ruhr-Universitaet Bochum (Germany); Knolle, Johannes [Max Planck Institute for the Physics of Complex Systems, Dresden (Germany); Fernandes, Rafael [School of Physics and Astronomy, University of Minnesota, Minneapolis, MN (United States)
2015-07-01
We analyze the magnetic ordering in the iron-based superconductors in presence of spin-orbit coupling. Based on several tight-binding parametrizations of the 3d electron states we show how the spin-orbit coupling introduces the anisotropy of the magnetization of the striped antiferromagnetic state by lifting the degeneracy of all three components of the magnetization m{sub x}, m{sub y} and m{sub z}. The orientation of the magnetic moment is determined by the contribution of the xy, xz, and yz orbitals to the electronic states near the Fermi level of the electron and hole bands and is determined by the electron filling. We find that within an itinerant approach the magnetic ordering is most favorable along the wavevector of the striped AF state. This appears to be a natural consequence of the spin-orbit coupling in the striped AF state where the ferro-orbital order of the xz and yz orbitals is only a consequence of the striped AF order. We further analyze the role of spin-orbit coupling for the C{sub 4} magnetic structure where SDW order parameters with both wavevectors, Q{sub x} = (π,0) and Q{sub y} = (0,π), coexist.
Two magnetic Grüneisen parameters in the ferromagnetic superconductor UGe2
Hardy, F.; Meingast, C.; Taufour, V.; Flouquet, J.; v. Löhneysen, H.; Fisher, R. A.; Phillips, N. E.; Huxley, A.; Lashley, J. C.
2009-11-01
We report ambient-pressure magnetization, heat capacity, and thermal-expansion measurements of the ferromagnetic superconductor UGe2 in high magnetic fields. An analysis of the magnetic heat capacity derived from both magnetization and specific-heat data shows that UGe2 is well described in the framework of the molecular-field theory. Our heat-capacity and thermal-expansion results reveal a clear crossover regime, a feature that illustrates the proximity to the quantum critical end point of a first-order boundary between two different ferromagnetic phases. Furthermore, we show that the ferromagnetic contribution to these thermodynamic quantities can be split into two terms with distinct Grüneisen parameters.
Coexistence of two vector order parameters: a holographic model for ferromagnetic superconductivity
Amoretti, Andrea; Maggiore, Nicola; Magnoli, Nicodemo; Musso, Daniele
2014-01-01
We study a generalization of the standard holographic p-wave superconductor featuring two interacting vector order parameters. Basing our argument on the symmetry and linear response properties of the model, we propose it as a holographic effective theory describing a strongly coupled ferromagnetic superconductor. We show that the two order parameters undergo concomitant condensations as a manifestation of an intrinsically interlaced electric/magnetic dynamics. Such intertwined dynamics is confirmed by the study of the transport properties. We characterize thoroughly the equilibrium and the linear response (i.e. optical conductivity and magnetic susceptibility) of the model at hand by means of a probe approximation analysis. Some insight about the effects of backreaction in the normal phase can be gained by analogy with the s-wave unbalanced holographic superconductor.
A star role for stripes[Charge order in high-temperature superconductors in magnetic fields
Energy Technology Data Exchange (ETDEWEB)
Tranquada, John [Physics Department, Brookhaven National Laboratory (United States)
2002-06-01
New images of magnetic and charge order in copper-oxide compounds are providing important clues about the nature of high-temperature superconductors. Visual images can have a powerful impact on the viewer, and this is certainly the case when the images are atomic-scale pictures of the surface of a high-temperature copper-oxide superconductor. The unusual properties of these materials have vexed condensed-matter theorists for the last 15 years. Now a new flurry of theoretical papers has been stimulated by the latest images of a cuprate superconductor, which reveal that an applied magnetic field can induce 'stripes' of charge. The experimental results provide intriguing and important clues to the nature of these ever-surprising materials - although the theorists have still to agree on their meaning. (U.K.)
Topological order, symmetry, and Hall response of two-dimensional spin-singlet superconductors
Moroz, Sergej; Gurarie, Victor; Radzihovsky, Leo
2016-01-01
Fully gapped two-dimensional superconductors coupled to dynamical electromagnetism are known to exhibit topological order. In this work, we develop a unified low-energy description for spin-singlet paired states by deriving topological Chern-Simons field theories for $s$-wave, $d+id$, and chiral higher even-wave superconductors. These theories capture the quantum statistics and fusion rules of low-energy excitations and incorporate global continuous symmetries - specifically, spin rotation and conservation of magnetic flux - present in all singlet superconductors. We compute the Hall response for these symmetries and investigate the physics at the edge. In particular, the weakly-coupled phase of a chiral state paired in the even $k^{\\text{th}}$ partial wave has a spin Hall coefficient $\
Landau, I. L.; Ott, H. R.
2003-11-01
We show that the scaling procedure, recently proposed for the evaluation of the temperature variation of the normalized upper critical field of type-II superconductors, may easily be modified in order to take into account a possible temperature dependence of the Ginzburg-Landau parameter κ. As an example we consider κ( T) as it follows from the microscopic theory of superconductivity.
Cutoff parameter and vortex core size in d-wave superconductors
Directory of Open Access Journals (Sweden)
Belova P.
2014-07-01
Full Text Available There is some evidence that the electron-phonon mechanism is not strong enough to produce observed high critical temperatures in unconventional superconductors; this is the case in both the cuprates and Fe-based superconductors. The d-wave pairing in strongly correlated systems is consistent with the observation of nodal quasiparticles in the heavily hole doped superconductor KFe2As2 with Tc = 3 K and high-Tc cuprates. In this work the Eilenberger equations are solved for anisotropic dx2−y2-wave superconductors. The cutoﬀ parameter ξh and vortex core size ξ2 (the distance from the vortex center to the radius where the current density reaches its maximum value in the mixed state are investigated numerically. The cutoﬀ parameter determines the ﬁeld distribution in the generalized London equation obtained as a projection of the quasiclassical theory. It can be used for the fitting of the µSR and small-angle neutron scattering (SANS experimental data. Field and temperature dependences of ξh/ξc2 in dx2−y2-wave superconductors are similar to those in s-wave superconductors: ξh/ξc2(B/Bc2dependence has minimum at high temperatures and shows monotonously increasing behavior at low temperatures. Here, ξc2 is determined by the relation Bc2 =Φ0/2πξc22. The ξ2/ξc2(B/Bc2 dependence is monotonously decreasing function at intermediate and high temperatures.
Deductive multiscale simulation using order parameters
Energy Technology Data Exchange (ETDEWEB)
Ortoleva, Peter J.
2017-05-16
Illustrative embodiments of systems and methods for the deductive multiscale simulation of macromolecules are disclosed. In one illustrative embodiment, a deductive multiscale simulation method may include (i) constructing a set of order parameters that model one or more structural characteristics of a macromolecule, (ii) simulating an ensemble of atomistic configurations for the macromolecule using instantaneous values of the set of order parameters, (iii) simulating thermal-average forces and diffusivities for the ensemble of atomistic configurations, and (iv) evolving the set of order parameters via Langevin dynamics using the thermal-average forces and diffusivities.
Nematic spin order and spin-lattice coupling in Fe-based Superconductors
Hu, Jiangping; Fang, Chen; Tsai, Wei-Feng; Yao, Hong; Kivelson, Steve
2009-03-01
We show that the structure transitions observed in Fe-based superconductors are magnetically driven. A quantum Heisenberg model (J1-J2-Jz) exhibits a sequence of two phase transitions: from a high temperature symmetric phase to a narrow region of intermediate ``nematic'' phase, and then to a low temperature spin ordered phase when Jz is small. Identifying phases by their broken symmetries, these phases correspond precisely to the sequence of structural (tetragonal to monoclinic) and magnetic transitions that have been recently revealed in neutron scattering studies of 1111 series of Fe- based superconductors. The structural transition can thus be identified with the existence of incipient (``fluctuating'') magnetic order. We also discuss the effect of spin-lattice coupling on the phase diagram of the model. [3pt] Reference: Chen Fang, Hong Yao, Wei-Feng Tsai, JiangPing Hu and Steven A. Kivelson, Phys. Rev. B 77 224509 (2008).
Inference for ordered parameters in multinomial distributions
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
This paper discusses inference for ordered parameters of multinomial distributions. We first show that the asymptotic distributions of their maximum likelihood estimators (MLEs) are not always normal and the bootstrap distribution estimators of the MLEs can be inconsistent. Then a class of weighted sum estimators (WSEs) of the ordered parameters is proposed. Properties of the WSEs are studied, including their asymptotic normality. Based on those results, large sample inferences for smooth functions of the ordered parameters can be made. Especially, the confidence intervals of the maximum cell probabilities are constructed. Simulation results indicate that this interval estimation performs much better than the bootstrap approaches in the literature. Finally, the above results for ordered parameters of multinomial distributions are extended to more general distribution models.
Fractional Action Cosmology with Variable Order Parameter
El-Nabulsi, Rami Ahmad
2017-04-01
Fractional action cosmology with variable order parameter was constructed in this paper. Starting from a fractional weighted action which generalizes the fractional actionlike variational approach, a large number of cosmological dynamical equations are obtained depending on the mathematical type of the fractional order parameter. Through this paper, we selected two independent types which result on a number of cosmological scenarios and we discussed their dynamical consequences. It was observed that the present fractional cosmological formalism holds a large family of solutions and offers new features not found in the standard formalism and in many fundamental research papers.
Order Parameter Hysteresis on the Complex Network
Institute of Scientific and Technical Information of China (English)
MA Pei-Jie; WANG Bing-Hong
2008-01-01
Collective synchronization is investigated on the small-world network (NW model). The order parameter is introduced to measure the synchronization of phase. It is found that there are differences between the processes of synchronization and desynchronization. The dependence of order parameter on the coupling strength is shown like a hysteresis loop. The size of the 10019 demonstrates the non-monotonicity with the change of adding probability,and is relevant to the construction of the network. The area may be maximum, as the adding probability is equal to 0.4. This phenomenon indicates that the clusters in the network play an important role in the processes of synchronization and desynchronization.
Fractional Action Cosmology with Variable Order Parameter
El-Nabulsi, Rami Ahmad
2017-01-01
Fractional action cosmology with variable order parameter was constructed in this paper. Starting from a fractional weighted action which generalizes the fractional actionlike variational approach, a large number of cosmological dynamical equations are obtained depending on the mathematical type of the fractional order parameter. Through this paper, we selected two independent types which result on a number of cosmological scenarios and we discussed their dynamical consequences. It was observed that the present fractional cosmological formalism holds a large family of solutions and offers new features not found in the standard formalism and in many fundamental research papers.
Topological surface states in nodal superconductors.
Schnyder, Andreas P; Brydon, Philip M R
2015-06-24
Topological superconductors have become a subject of intense research due to their potential use for technical applications in device fabrication and quantum information. Besides fully gapped superconductors, unconventional superconductors with point or line nodes in their order parameter can also exhibit nontrivial topological characteristics. This article reviews recent progress in the theoretical understanding of nodal topological superconductors, with a focus on Weyl and noncentrosymmetric superconductors and their protected surface states. Using selected examples, we review the bulk topological properties of these systems, study different types of topological surface states, and examine their unusual properties. Furthermore, we survey some candidate materials for topological superconductivity and discuss different experimental signatures of topological surface states.
Tan, B S; Harrison, N; Zhu, Z; Balakirev, F; Ramshaw, B J; Srivastava, A; Sabok-Sayr, S A; Sabok, S A; Dabrowski, B; Lonzarich, G G; Sebastian, Suchitra E
2015-08-04
The normal state in the hole underdoped copper oxide superconductors has proven to be a source of mystery for decades. The measurement of a small Fermi surface by quantum oscillations on suppression of superconductivity by high applied magnetic fields, together with complementary spectroscopic measurements in the hole underdoped copper oxide superconductors, point to a nodal electron pocket from charge order in YBa2Cu3(6+δ). Here, we report quantum oscillation measurements in the closely related stoichiometric material YBa2Cu4O8, which reveals similar Fermi surface properties to YBa2Cu3(6+δ), despite the nonobservation of charge order signatures in the same spectroscopic techniques, such as X-ray diffraction, that revealed signatures of charge order in YBa2Cu3(6+δ). Fermi surface reconstruction in YBa2Cu4O8 is suggested to occur from magnetic field enhancement of charge order that is rendered fragile in zero magnetic fields because of its potential unconventional nature and/or its occurrence as a subsidiary to more robust underlying electronic correlations.
Intra-unit-cell nematic charge order in the titanium-oxypnictide family of superconductors
Frandsen, Benjamin A.; Bozin, Emil S.; Hu, Hefei; Zhu, Yimei; Nozaki, Yasumasa; Kageyama, Hiroshi; Uemura, Yasutomo J.; Yin, Wei-Guo; Billinge, Simon J. L.
2014-12-01
Understanding the role played by broken-symmetry states such as charge, spin and orbital orders in the mechanism of emergent properties, such as high-temperature superconductivity, is a major current topic in materials research. That the order may be within one unit cell, such as nematic, was only recently considered theoretically, but its observation in the iron-pnictide and doped cuprate superconductors places it at the forefront of current research. Here, we show that the recently discovered BaTi2Sb2O superconductor and its parent compound BaTi2As2O form a symmetry-breaking nematic ground state that can be naturally explained as an intra-unit-cell nematic charge order with d-wave symmetry, pointing to the ubiquity of the phenomenon. These findings, together with the key structural features in these materials being intermediate between the cuprate and iron-pnictide high-temperature superconducting materials, render the titanium oxypnictides an important new material system to understand the nature of nematic order and its relationship to superconductivity.
Crystal nucleation as the ordering of multiple order parameters
Russo, John; Tanaka, Hajime
2016-12-01
Nucleation is an activated process in which the system has to overcome a free energy barrier in order for a first-order phase transition between the metastable and the stable phases to take place. In the liquid-to-solid transition, the process occurs between phases of different symmetry, and it is thus inherently a multi-dimensional process, in which all symmetries are broken at the transition. In this Focus Article, we consider some recent studies which highlight the multi-dimensional nature of the nucleation process. Even for a single-component system, the formation of solid crystals from the metastable melt involves fluctuations of two (or more) order parameters, often associated with the decoupling of positional and orientational symmetry breaking. In other words, we need at least two order parameters to describe the free-energy of a system including its liquid and crystalline states. This decoupling occurs naturally for asymmetric particles or directional interactions, focusing here on the case of water, but we will show that it also affects spherically symmetric interacting particles, such as the hard-sphere system. We will show how the treatment of nucleation as a multi-dimensional process has shed new light on the process of polymorph selection, on the effect of external fields on the nucleation process and on glass-forming ability.
Competing orders in strongly correlated systems. Dirac materials and iron-based superconductors
Energy Technology Data Exchange (ETDEWEB)
Classen, Laura
2016-11-04
In this work we address the collective phenomena appearing in interacting fermion systems due to the competition of distinct orders at the example of Dirac materials and iron-based superconductors. On the one hand we determine leading ordering tendencies in an unbiased way, when Fermi liquid instabilities are expected simultaneously in the particle-particle and particle-hole channel. In this context we analyze the impact of electron-phonon interactions on the many-body instabilities of electrons on the honeycomb lattice. Furthermore we investigate the interplay between superconductivity, magnetism and orbital order in five-pocket iron-based superconductors including the full orbital composition of low-energy excitations. On the other hand we study how the close proximity of different phases affects the structure of the phase diagram and the nature of transitions, as well as the corresponding quantum multicritical behavior. To this end we consider the semimetal-insulator transitions to an antiferromagnetic and a staggered-density state of low-energy Dirac fermions. To account for the decisive role of interactions and the various degrees of freedom in these models, modern renormalization group techniques are applied.
Order Parameter Theory for Anderson Localization
Dobrosavljevic, Vladimir; Pastor, Andrei
2001-03-01
The Anderson metal-insulator transition is well known to display many similarities to standard critical phenomena, yet an obvious order parameter has remained difficult to find. In this work, we demonstrate that a relevant local order parameter can be defined and self-consistently determined, providing a simple and physically transparent picture of the Anderson transition. Our formulation proceeds in close analogy with the well-known coherent potential approximation (CPA), with a small but crucial difference. Our theory self-consistently calculates not the average but instead the typical local density of states, which serves as the order parameter, and is found to vanish at the Anderson transition. As a result, we show that both the escape rate of an electron from a given site, and the conductivity vanish in the insulating phase, which emerges for disorder strengths comparable to the electronic bandwidth. Due to the local character of our theory, it can easily be combined with standard dynamical mean-field approaches for strong electronic correlations, thus opening an attractive avenue for the study of the interplay (A. A. Pastor and V. Dobrosavljevic, Phys. Rev. Lett. 83), 4642 (1999) ( V. Dobrosavljevic and G. Kotliar, Phys. Rev. Lett. 78), 3943 (1997) of interaction and disorder.
Second-order perturbation theory for the single-impurity Anderson model of a BCS superconductor
Alastalo, Ari T.
2017-09-01
This paper presents a conserving approximation for a single magnetic impurity embedded in a BCS superconductor according to the Anderson model. The calculation generalizes the second-order selfenergy theory of a normal metal host into a superconducting medium. Within the second-order theory, both spin and pairing fluctuations contribute to the selfenergy. The second-order theory removes the unphysical spontaneous symmetry breaking of the Hartree-Fock approximation but results in a doubling of the bound-state spectrum within the energy gap. The HF bound states may be recovered in the small-U limit as the average of the two separate bound states. For increasing U, the novel pronounced low-energy bound states tend towards the center of the gap while the other bound states approach the gap edge and their spectral weights vanish.
Zhang, Zhao; Sahoo, Sharmistha; Teo, Jeffrey
We mimic the massless surface Majorana's of topological superconductors by coupled wire models in two spatial dimensions, and introduce many-body gapping interactions that preserve time reversal symmetry. Coupling with a Z2 gauge theory, the symmetric gapped surface generically carries a non-trivial GN topological order, where N is the number of Majorana species and GN is some SO(r)1 or SO(3)3 -like topological state. These form a 32-fold periodic class GN ≅GN + 32 , and a Z32 relative tensor product structure GN1⊗bGN2 ≅GN1 +N2 by anyon condensation. We present the anyon structures of these topological states, and understand the topological orders through bulk-boundary correspondence and the Wilson structures on a torus geometry.
Aguirre, C. A.; González, J. D.; Barba-Ortega, J.
2016-01-01
The magnetic signature of a nanoscopic superconductor immersed in a magnetic applied field H_e is calculated numerically. The calculated magnetic susceptibility partial M / partial H_e of a superconducting nanoprism shows discontinuities and a quasiperiodic modulation at the vortex transition fields H_T (fields for which one or several vortices enter/leave the sample). In this contribution, we studied the influence of the sample size, the Ginzburg-Landau parameter κ and the deGennes parameter b on the magnetic susceptibility in a type-II isotropic superconductor. We found distinct signatures of the magnetic susceptibility when superconducting samples of two and three dimensions are considered.
What is the symmetry of the high T{sub c} order parameter?
Energy Technology Data Exchange (ETDEWEB)
Klemm, R. A.
1998-04-16
In recent years, there has been a raging controversy regarding the orbital symmetry of the superconducting order parameter (OP) in the high temperature superconductors. Many experiments were interpreted in terms of a d{sub x{sup 2}-y{sup 2}}-wave OP, but many others were interpreted in terms of a more conventional s-wave OP. We review the problems of both intrinsic and extrinsic natures with the phase-sensitive experiments on YBCO. The authors further show that the photoemission experiments of the purported superconducting gap in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub g+{delta}} are entirely consistent with charge- and/or spin-density wave formation in that material. The presence of such density waves greatly complicates the analysis of most experiments. Hence, we conclude that the orbital symmetry of the superconducting OP is still unknown in any of the high temperature superconductors.
Chubukov, A. V.
2009-05-01
We analyze antiferromagnetism and superconductivity in novel Fe-based superconductors within the weak-coupling, itinerant model of electron and hole pockets near (0, 0) and ( π, π) in the folded Brillouin zone. We discuss the interaction Hamiltonian, the nesting, the RG flow of the couplings at energies above and below the Fermi energy, and the interplay between SDW magnetism, superconductivity and charge orbital order. We argue that SDW antiferromagnetism wins at zero doping but looses to superconductivity upon doping. We show that the most likely symmetry of the superconducting gap is A1 g in the folded zone. This gap has no nodes on the Fermi surface but changes sign between hole and electron pockets. We also argue that at weak coupling, this pairing predominantly comes not from spin fluctuation exchange but from a direct pair hopping between hole and electron pockets.
Order parameter for design of proteinlike heteropolymers
Nelson, E D; Onuchic, J N; Nelson, Erik D.; Eyck, Lynn F. Ten; Onuchic, Jose' N.
1998-01-01
We define the energetics of proteinlike heteropolymers according to an ensemble of copolymer sequence interactions, in which (i) the sequences define a basis of orthogonal vectors belonging to an optimal class of bases, and (ii) the matrix of contact energies for each sequence has the Mattis (diagonal) form, which eliminates all energetic frustration loops along closed circuits of contacts within any configuration of the chain. This makes it possible to derive a set of physical order parameters which partition the configuration space into structually similar statistical ensembles, each having low topological frustration. By applying this description to the statistics of homopolymeric chains (with length N = 16 - 128) we obtain a number of important results, which provide a simple explanation for the observed frequency dependence of hydrophobic domains in proteins, and suggest that the diagonal ensemble is sufficient to represent the energetics of minimally frustrated heteropolymers.
Order Parameters of the Dilute A Models
Warnaar, S O; Seaton, K A; Nienhuis, B
1993-01-01
The free energy and local height probabilities of the dilute A models with broken $\\Integer_2$ symmetry are calculated analytically using inversion and corner transfer matrix methods. These models possess four critical branches. The first two branches provide new realisations of the unitary minimal series and the other two branches give a direct product of this series with an Ising model. We identify the integrable perturbations which move the dilute A models away from the critical limit. Generalised order parameters are defined and their critical exponents extracted. The associated conformal weights are found to occur on the diagonal of the relevant Kac table. In an appropriate regime the dilute A$_3$ model lies in the universality class of the Ising model in a magnetic field. In this case we obtain the magnetic exponent $\\delta=15$ directly, without the use of scaling relations.
Unconventional charge order in a co-doped high-Tc superconductor.
Pelc, D; Vučković, M; Grafe, H-J; Baek, S-H; Požek, M
2016-01-01
Charge-stripe order has recently been established as an important aspect of cuprate high-Tc superconductors. However, owing to the complex interplay between competing phases and the influence of disorder, it is unclear how it emerges from the parent high-temperature state. Here we report on the discovery of an unconventional ordered phase between charge-stripe order and (pseudogapped) metal in the cuprate La1.8-xEu0.2SrxCuO4. We use three complementary experiments-nuclear quadrupole resonance, nonlinear conductivity and specific heat-to demonstrate that the order appears through a sharp phase transition and exists in a dome-shaped region of the phase diagram. Our results imply that the new phase is a state, which preserves translational symmetry: a charge nematic. We thus resolve the process of charge-stripe development in cuprates, show that this nematic phase is distinct from high-temperature pseudogap and establish a link with other strongly correlated electronic materials with prominent nematic order.
Unconventional charge order in a co-doped high-Tc superconductor
Pelc, D.; Vučković, M.; Grafe, H.-J.; Baek, S.-H.; Požek, M.
2016-09-01
Charge-stripe order has recently been established as an important aspect of cuprate high-Tc superconductors. However, owing to the complex interplay between competing phases and the influence of disorder, it is unclear how it emerges from the parent high-temperature state. Here we report on the discovery of an unconventional ordered phase between charge-stripe order and (pseudogapped) metal in the cuprate La1.8-xEu0.2SrxCuO4. We use three complementary experiments--nuclear quadrupole resonance, nonlinear conductivity and specific heat--to demonstrate that the order appears through a sharp phase transition and exists in a dome-shaped region of the phase diagram. Our results imply that the new phase is a state, which preserves translational symmetry: a charge nematic. We thus resolve the process of charge-stripe development in cuprates, show that this nematic phase is distinct from high-temperature pseudogap and establish a link with other strongly correlated electronic materials with prominent nematic order.
Fermion pseudogap from fluctuations of an order parameter
Tchernyshyov, Oleg Vladimirovich
Pseudogap behavior, observed in cuprate superconductors and Peierls chains, is studied using various phenomenological approaches. (1) A work of M. V. Sadovskii on Peierls chains with Gaussian fluctuations of the order parameter is revisited. A more transparent diagrammatic method is given and a serious error is pointed out. The method is applied to a recent work of J. Schmalian, B. Stojkovic and D. Pines on "hot spots". It is shown that, while their model is not affected by Sadovskii's mistake, it predicts no pseudogap in the local density of states. (2) A simple analytical treatment based on the self-consistent t-matrix approach is suggested to describe Cooper pair fluctuations deeply in the pseudogap regime. It is argued that a pronounced depletion of the fermion density of states by the pseudogap suppresses the decay of pairing fluctuations, giving them a propagating, rather than diffusing, nature. In view of an approximate particle-hole symmetry at the Fermi surface, both electron pairs and hole pairs should exist in the pseudogap regime, in addition to gapped fermions. Near 2 dimensions, the condensation temperature of these pairs is linearly proportional to the fermion density (the Uemura scaling). (3) A work of J. R. Schrieffer and A. R. Kampf on the crossover between an antiferromagnetic (AFM) insulator and a Fermi liquid is complemented by an exactly solvable toy model with all essential features intact. Based on that solution, the three bands of Schrieffer and Kampf are reinterpreted as just two AFM bands with a gap slowly varying in time or across the sample.
Directory of Open Access Journals (Sweden)
Andrey V. Chubukov
2016-12-01
Full Text Available Magnetism and nematic order are the two nonsuperconducting orders observed in iron-based superconductors. To elucidate the interplay between them and ultimately unveil the pairing mechanism, several models have been investigated. In models with quenched orbital degrees of freedom, magnetic fluctuations promote stripe magnetism, which induces orbital order. In models with quenched spin degrees of freedom, charge fluctuations promote spontaneous orbital order, which induces stripe magnetism. Here, we develop an unbiased approach, in which we treat magnetic and orbital fluctuations on equal footing. Key to our approach is the inclusion of the orbital character of the low-energy electronic states into renormalization group (RG analysis. We analyze the RG flow of the couplings and argue that the same magnetic fluctuations, which are known to promote s^{+-} superconductivity, also promote an attraction in the orbital channel, even if the bare orbital interaction is repulsive. We next analyze the RG flow of the susceptibilities and show that, if all Fermi pockets are small, the system first develops a spontaneous orbital order, then s^{+-} superconductivity, and magnetic order does not develop down to T=0. We argue that this scenario applies to FeSe. In systems with larger pockets, such as BaFe_{2}As_{2} and LaFeAsO, we find that the leading instability is either towards a spin-density wave or superconductivity. We argue that in this situation nematic order is caused by composite spin fluctuations and is vestigial to stripe magnetism. Our results provide a unifying description of different iron-based materials.
Chubukov, Andrey V.; Khodas, M.; Fernandes, Rafael M.
2016-10-01
Magnetism and nematic order are the two nonsuperconducting orders observed in iron-based superconductors. To elucidate the interplay between them and ultimately unveil the pairing mechanism, several models have been investigated. In models with quenched orbital degrees of freedom, magnetic fluctuations promote stripe magnetism, which induces orbital order. In models with quenched spin degrees of freedom, charge fluctuations promote spontaneous orbital order, which induces stripe magnetism. Here, we develop an unbiased approach, in which we treat magnetic and orbital fluctuations on equal footing. Key to our approach is the inclusion of the orbital character of the low-energy electronic states into renormalization group (RG) analysis. We analyze the RG flow of the couplings and argue that the same magnetic fluctuations, which are known to promote s+- superconductivity, also promote an attraction in the orbital channel, even if the bare orbital interaction is repulsive. We next analyze the RG flow of the susceptibilities and show that, if all Fermi pockets are small, the system first develops a spontaneous orbital order, then s+- superconductivity, and magnetic order does not develop down to T =0 . We argue that this scenario applies to FeSe. In systems with larger pockets, such as BaFe2 As2 and LaFeAsO, we find that the leading instability is either towards a spin-density wave or superconductivity. We argue that in this situation nematic order is caused by composite spin fluctuations and is vestigial to stripe magnetism. Our results provide a unifying description of different iron-based materials.
The influence of oxygen doping on critical parameters of mercury based superconductors
Energy Technology Data Exchange (ETDEWEB)
Çataltepe, Ö. Aslan, E-mail: ozdenaslan@yahoo.com, E-mail: ozden.aslan@gedik.edu.tr [Gedik University, Faculty of Engineering, 34876, İstanbul (Turkey); Özdemir, Z. Güven, E-mail: zguvenozdemir@yahoo.com [Yıldız Technical University, Department of Physics, 34210, İstanbul (Turkey); Onbaşlı, Ü., E-mail: phonon@doruk.net.tr [Marmara University, Department of Physics, Rıdvanpaşa Cad., Gülhane. sok.,4/12, 34730, İstanbul (Turkey)
2016-03-25
In this work, the effect of oxygen doping on the critical parameters of the mercury based superconducting sample such as critical transition temperature, T{sub c}, critical magnetic field, H{sub c}, critical current density, J{sub c}, has been investigated by the magnetic susceptibility versus temperature (χ-T) and magnetization versus applied magnetic field (M-H) measurements and, X-Ray Diffraction (XRD) patterns. It has been observed that regardless of the oxygen doping concentration, the mercury cuprate system possesses two intrinsic superconducting phases together, HgBa{sub 2}Ca{sub 2}Cu{sub 3}O{sub 8+x} and HgBa{sub 2}CaCu{sub 2}O{sub 6+x}. However, the highest T{sub c} has been determined for the optimum oxygen doped sample. Moreover, it has been revealed that superconducting properties, crystal lattice parameters, coherent lengths, ξ{sub ab}, ξ{sub c} and the anisotropy factor γ etc. are very sensitive to oxygen doping procedures. Hence, the results presented this work enables one to obtain the mercury based superconductor with the most desirable criticals and other parameters for theoretical and technological applications by arranging the oxygen doping concentration.
Energy Technology Data Exchange (ETDEWEB)
Shukrinov, Yu.M. [BLTP, JINR, Moscow Region, Dubna 141980 (Russian Federation) and Physical Technical Institute, Dushanbe 734063 (Tajikistan)]. E-mail: shukrinv@theor.jinr.ru; Mahfouzi, F. [Institute for Advanced Studies in Basic Sciences, P.O. Box 45195-1159, Zanjan (Iran, Islamic Republic of)
2006-02-01
We study the current-voltage characteristics of intrinsic Josephson junctions in high-T {sub c} superconductors by numerical calculations and in framework of capacitively coupled Josephson junctions model we obtain the total number of branches. The influence of the coupling parameter {alpha} on the current-voltage characteristics at fixed parameter {beta} ({beta} {sup 2} 1/{beta} {sub c}, where {beta} {sub c} is McCumber parameter) and the influence of {alpha} on {beta}-dependence of the current-voltage characteristics are investigated. We obtain the {alpha}-dependence of the branch's slopes and branch's endpoints. The presented results show new features of the coupling effect on the scheme of hysteresis jumps in current-voltage characteristics of intrinsic Josephson junctions in high-T {sub c} superconductors.
Shukrinov, Yu. M.; Mahfouzi, F.
2006-02-01
We study the current-voltage characteristics of intrinsic Josephson junctions in high-Tc superconductors by numerical calculations and in framework of capacitively coupled Josephson junctions model we obtain the total number of branches. The influence of the coupling parameter α on the current-voltage characteristics at fixed parameter β (β2 = 1/βc, where βc is McCumber parameter) and the influence of α on β-dependence of the current-voltage characteristics are investigated. We obtain the α-dependence of the branch's slopes and branch's endpoints. The presented results show new features of the coupling effect on the scheme of hysteresis jumps in current-voltage characteristics of intrinsic Josephson junctions in high-Tc superconductors.
Institute of Scientific and Technical Information of China (English)
LIN Ming-Xi; QI Sheng-Wen; LIU Yu-Liang
2006-01-01
@@ Based on a two-dimensional electron system with pure gauge field, we demonstrate that the long range order of the electron pairing order parameter can be destroyed by the gauge fluctuation for both s-wave and d-wave symmetric Cooper pair parameters, even if the pure gauge field mediates attractive interaction between the spinup and spin-down electrons, while the signal of the Meissner effect is observable. This model can be used to explain the recent experimental data of the high Tc cuprate superconductors observed.
Andreev Spectra and Subgap Bound States in Multiband Superconductors
Golubov, A. A.; Brinkman, A.; Tanaka, Yukio; Mazin, I.I.; Dolgov, O. V.
2009-01-01
The theory of Andreev conductance is formulated for junctions involving normal metals (N) and multiband superconductors (S) and applied to the case of superconductors with nodeless extended $s_{\\pm}$-wave order parameter symmetry, as possibly realized in the recently discovered ferro pnictides. We find qualitative differences from tunneling into s-wave or d-wave superconductors that may help to identify such a state. First, interband interference leads to a suppression of Andreev reflection i...
Hart, Sean; Ren, Hechen; Kosowsky, Michael; Ben-Shach, Gilad; Leubner, Philipp; Brüne, Christoph; Buhmann, Hartmut; Molenkamp, Laurens W.; Halperin, Bertrand I.; Yacoby, Amir
2017-01-01
Conventional s-wave superconductivity arises from singlet pairing of electrons with opposite Fermi momenta, forming Cooper pairs with zero net momentum. Recent studies have focused on coupling s-wave superconductors to systems with an unusual configuration of electronic spin and momentum at the Fermi surface, where the nature of the paired state can be modified and the system may even undergo a topological phase transition. Here we present measurements and theoretical calculations of HgTe quantum wells coupled to aluminium or niobium superconductors and subject to a magnetic field in the plane of the quantum well. We find that this magnetic field tunes the momentum of Cooper pairs in the quantum well, directly reflecting the response of the spin-dependent Fermi surfaces. In the high electron density regime, the induced superconductivity evolves with electron density in agreement with our model based on the Hamiltonian of Bernevig, Hughes and Zhang. This agreement provides a quantitative value for g ˜/vF, where g ˜ is the effective g-factor and vF is the Fermi velocity. Our new understanding of the interplay between spin physics and superconductivity introduces a way to spatially engineer the order parameter from singlet to triplet pairing, and in general allows investigation of electronic spin texture at the Fermi surface of materials.
Spin and quadrupolar orders in the spin-1 bilinear-biquadratic model for iron-based superconductors
Luo, Cheng; Datta, Trinanjan; Yao, Dao-Xin
2016-06-01
Motivated by the recent experimental and theoretical progress of the magnetic properties in iron-based superconductors, we provide a comprehensive analysis of the extended spin-1 bilinear-biquadratic (BBQ) model on the square lattice. Using a variational approach at the mean-field level, we identify the existence of various magnetic phases, including conventional spin dipolar orders (ferro- and antiferromagnet), novel quadrupolar orders (spin nematic), and mixed dipolar-quadrupolar orders. In contrast to the regular Heisenberg model, the elementary excitations of the spin-1 BBQ model are described by the SU(3) flavor-wave theory. By fitting the experimental spin-wave dispersion, we determine the refined exchange couplings corresponding to the collinear antiferromagnetic iron pnictides. We also present the dynamic structure factors of both spin dipolar and quadrupolar components with connections to the future experiments.
Reduced density matrix and order parameters of a topological insulator
Yu, Wing Chi; Li, Yan Chao; Sacramento, P. D.; Lin, Hai-Qing
2016-12-01
It has been recently proposed that the reduced density matrix may be used to derive the order parameter of a condensed matter system. Here we propose order parameters for the phases of a topological insulator, specifically a spinless Su-Schrieffer-Heeger (SSH) model, and consider the effect of short-range interactions. All the derived order parameters and their possible corresponding quantum phases are verified by the entanglement entropy and electronic configuration analysis results. The order parameter appropriate to the topological regions is further proved by calculating the Berry phase under twisted boundary conditions. It is found that the topological nontrivial phase is robust to the introduction of repulsive intersite interactions and can appear in the topological trivial parameter region when appropriate interactions are added.
Characteristic of wireless power transmission S-Parameter for a superconductor coil
Energy Technology Data Exchange (ETDEWEB)
Jeong, In Sung; Jung, Byung Ik; Choi, Hyo Sang [Chosun University, Gwangju (Korea, Republic of)
2015-03-15
Many studies are being conducted to implement wireless charging, for example, for cellular phones or electronic tooth brushes, via wireless power transmission technique. However, the magnetic induction method had a very short transmission distance. To solve this problem, the team of Professor Marin Soljacic proposed a magnetic resonance system that used two resonance coils with the same resonance frequency. It had an approximately 40% efficiency at a 2m distance. The system improved the low efficiency and short distance problems of the existing systems. So it could also widen the application range of wireless power transmission. Many studies on the subject are underway. In this paper, the superconductor coil was used to improve the efficiency of magnetic resonance wireless power transmission. The resonance wireless power transmission system had a source coil, a load coil, and resonance coils (a transmitter and a receiver). The efficiency and distance depended on the characteristics of the transmitter and receiver coils that had the same resonance frequency. Therefore, two resonance coils were fabricated by superconductors. The current density of the superconductor was higher than that of the normal conductor coil. Accordingly, it had a high quality-factor and improved efficiency.
Second-order sensitivity of eigenpairs in multiple parameter structures
Institute of Scientific and Technical Information of China (English)
Su-huan CHEN; Rui GUO; Guang-wei MENG
2009-01-01
This paper presents methods for computing a second-order sensitivity matrix and the Hessian matrix of eigenvalues and eigenvectors of multiple parameter structures. Second-order perturbations of eigenvalues and eigenvectors are transformed into multiple parameter forms, and the second-order perturbation sensitivity matrices of eigenvalues and eigenvectors are developed. With these formulations, the efficient methods based on the second-order Taylor expansion and second-order perturbation are obtained to estimate changes of eigenvalues and eigenvectors when the design parameters are changed. The presented method avoids direct differential operation, and thus reduces difficulty for computing the second-order sensitivity matrices of eigenpairs. A numerical example is given to demonstrate application and accuracy of the proposed method.
Nontrivial order parameter in Sr2IrO4
Ganguly, Shreemoyee; Grânäs, Oscar; Nordström, Lars
2015-01-01
A thorough analysis of the ground state of the relativistic magnetic insulator Sr2IrO4 is performed. The results are in accordance with the small antiferromagnetic moment and gapped state found in experiment. The solution, obtained using the DFT+SO+U methodology, is thoroughly analyzed in terms of Landau theory. We find that the ordered magnetic moment only forms a secondary order parameter while the primary order parameter is a higher order magnetic multipole of rank five. It is further observed that the electronic structure in the presence of this order parameter is related to the earlier proposed jeff=1 /2 model, but in contrast to that model, the present picture can exactly explain the small magnitude of the ordered magnetic moments.
't Hooft loops and consistent order parameters for confinement
De Forcrand, Philippe; Forcrand, Philippe de; Smekal, Lorenz von
2002-01-01
We study ratios of partition functions in two types of sectors of SU(2), with fixed temporal center flux and with static fundamental charge. Both can be used as bona fide order parameters for the deconfinement transition.
Ariosa, D.; Cancellieri, C.; Lin, P. H.; Pavuna, D.
2007-05-01
We propose a simple model for the nucleation of random intercalates during the growth of high-temperature superconductor (HTSC) films by pulsed laser deposition (PLD). The model predicts a very particular spatial distribution of defects: a Markovian-like sequence of displacements along the growth direction ( c axis), as well as a two-component in-plane correlation function, characteristic of self-organized intercalates. A model for x-ray diffraction (XRD) on such structures is also developed and accounts for both c -axis and in-plane anomalies observed in XRD experiments. The method presented in this work constitutes a useful characterization tool in the optimization of deposition parameters for the growth of HTSC films.
Dynamics of order parameters for globally coupled oscillators
DEFF Research Database (Denmark)
De Monte, Silvia; D'ovidio, Francesco
2002-01-01
The equation of motion for the centroid of globally coupled oscillators with natural frequency mismatch is obtained through a series expansion in order parameters, valid for any population size. In the case of strong coupling and narrow-frequency distribution the first-order expansion (correspond...
Nakano, Kousuke; Hongo, Kenta; Maezono, Ryo
2016-01-01
There has been a puzzle between experiments and theoretical predictions on the charge ordering of layered titanium-oxypnictides superconductors. Unconventional mechanisms to explain this discrepancy have been argued so far, even affecting the understanding of superconductivity on the compound. We provide a new theoretical prediction, by which the discrepancy itself is resolved without any complicated unconventional explanation. Phonon dispersions and changes of nesting vectors in Fermi surfaces are clarified to lead to the variety of superlattice structures even for the common crystal structures when without CDW, including orthorhombic 2 × 2 × 1 one for BaTi2As2O, which has not yet been explained successfully so far, being different from tetragonal for BaTi2Sb2O and BaTi2Bi2O. The electronic structure analysis can naturally explain experimental observations about CDW including most latest ones without any cramped unconventional mechanisms. PMID:27430418
Identification of slow molecular order parameters for Markov model construction
Perez-Hernandez, Guillermo; Giorgino, Toni; de Fabritiis, Gianni; Noé, Frank
2013-01-01
A goal in the kinetic characterization of a macromolecular system is the description of its slow relaxation processes, involving (i) identification of the structural changes involved in these processes, and (ii) estimation of the rates or timescales at which these slow processes occur. Most of the approaches to this task, including Markov models, Master-equation models, and kinetic network models, start by discretizing the high-dimensional state space and then characterize relaxation processes in terms of the eigenvectors and eigenvalues of a discrete transition matrix. The practical success of such an approach depends very much on the ability to finely discretize the slow order parameters. How can this task be achieved in a high-dimensional configuration space without relying on subjective guesses of the slow order parameters? In this paper, we use the variational principle of conformation dynamics to derive an optimal way of identifying the "slow subspace" of a large set of prior order parameters - either g...
Intrinsic ambiguity in second order viscosity parameters in relativistic hydrodynamics
Nakayama, Yu
2012-01-01
We show that relativistic hydrodynamics in Minkowski space-time has intrinsic ambiguity in second order viscosity parameters in the Landau-Lifshitz frame. This stems from the possibility of improvements of energy-momentum tensor. There exist at least two viscosity parameters which can be removed by using this ambiguity in scale invariant hydrodynamics in (1+3) dimension, and seemingly non-conformal hydrodynamic theories can be hiddenly conformal invariant.
DEFF Research Database (Denmark)
Haug, D.; Hinkov, V.; Suchaneck, A.
2009-01-01
We present a neutron-scattering study of the static and dynamic spin correlations in the underdoped high-temperature superconductor YBa2Cu3O6.45 in magnetic fields up to 15 T. The field strongly enhances static incommensurate magnetic order at low temperatures and induces a spectral-weight shift...
Order-parameter model for unstable multilane traffic flow
Lubashevsky; Mahnke
2000-11-01
We discuss a phenomenological approach to the description of unstable vehicle motion on multilane highways that explains in a simple way the observed sequence of the "free flow synchronized mode jam" phase transitions as well as the hysteresis in these transitions. We introduce a variable called an order parameter that accounts for possible correlations in the vehicle motion at different lanes. So, it is principally due to the "many-body" effects in the car interaction in contrast to such variables as the mean car density and velocity being actually the zeroth and first moments of the "one-particle" distribution function. Therefore, we regard the order parameter as an additional independent state variable of traffic flow. We assume that these correlations are due to a small group of "fast" drivers and by taking into account the general properties of the driver behavior we formulate a governing equation for the order parameter. In this context we analyze the instability of homogeneous traffic flow that manifested itself in the above-mentioned phase transitions and gave rise to the hysteresis in both of them. Besides, the jam is characterized by the vehicle flows at different lanes which are independent of one another. We specify a certain simplified model in order to study the general features of the car cluster self-formation under the "free flow synchronized motion" phase transition. In particular, we show that the main local parameters of the developed cluster are determined by the state characteristics of vehicle motion only.
First Measurements of Higher Order Optics Parameters in the LHC
Vanbavinckhove, G; Bartolini, R; Calaga, R; Giovannozzi, M; Maclean, E H; Miyamoto, R; Schmidt, F; Tomas, R
2011-01-01
Higher order effects can play an important role in the performance of the LHC. Lack of knowledge of these pa- rameters can increase the tune footprint and compromise the beam lifetime. First measurements of these parameters at injection and flattop have been conducted. Detailed sim- ulations are compared to the measurements together with discussions on the measurement limitations.
Nature of the superconductor-insulator transition in disordered superconductors.
Dubi, Yonatan; Meir, Yigal; Avishai, Yshai
2007-10-18
The interplay of superconductivity and disorder has intrigued scientists for several decades. Disorder is expected to enhance the electrical resistance of a system, whereas superconductivity is associated with a zero-resistance state. Although superconductivity has been predicted to persist even in the presence of disorder, experiments performed on thin films have demonstrated a transition from a superconducting to an insulating state with increasing disorder or magnetic field. The nature of this transition is still under debate, and the subject has become even more relevant with the realization that high-transition-temperature (high-T(c)) superconductors are intrinsically disordered. Here we present numerical simulations of the superconductor-insulator transition in two-dimensional disordered superconductors, starting from a microscopic description that includes thermal phase fluctuations. We demonstrate explicitly that disorder leads to the formation of islands where the superconducting order is high. For weak disorder, or high electron density, increasing the magnetic field results in the eventual vanishing of the amplitude of the superconducting order parameter, thereby forming an insulating state. On the other hand, at lower electron densities or higher disorder, increasing the magnetic field suppresses the correlations between the phases of the superconducting order parameter in different islands, giving rise to a different type of superconductor-insulator transition. One of the important predictions of this work is that in the regime of high disorder, there are still superconducting islands in the sample, even on the insulating side of the transition. This result, which is consistent with experiments, explains the recently observed huge magneto-resistance peak in disordered thin films and may be relevant to the observation of 'the pseudogap phenomenon' in underdoped high-T(c) superconductors.
On the Cartesian definition of orientational order parameters
Turzi, Stefano S.
2011-05-01
Orientational order parameters can be effectively and economically defined using spherical tensors. However, their definition in terms of Cartesian tensors can sometimes provide a clearer physical intuition. We show that it is possible to build a fully Cartesian theory of the orientational order parameters which is consistent with the traditional spherical tensor approach. The key idea is to build a generalised multi-pole expansion of the orientational probability distribution function in terms of outer products of rotation matrices. Furthermore, we show that the Saupe ordering super-matrix, as found, for example, in the text by de Gennes and Prost [The Physics of Liquid Crystals, 2nd ed. (Oxford University Press, Oxford, UK, 1995)] and which is used to define the Cartesian second-rank orientational order parameters, is not consistent with its spherical tensor counterpart. We then propose a symmetric version of the Saupe super-matrix which is fully consistent with the spherical tensor definition. The proposed definition is important for a correct description of liquid crystal materials composed of low symmetry molecules.
Parameter estimation of stable distribution based on zero - order statistics
Chen, Jian; Chen, Hong; Cai, Xiaoxia; Weng, Pengfei; Nie, Hao
2017-08-01
With the increasing complexity of the channel, there are many impulse noise signals in the real channel. The statistical properties of such processes are significantly deviated from the Gaussian distribution, and the Alpha stable distribution provides a very useful theoretical tool for this process. This paper focuses on the parameter estimation method of the Alpha stable distribution. First, the basic theory of Alpha stable distribution is introduced. Then, the concept of logarithmic moment and geometric power are proposed. Finally, the parameter estimation of Alpha stable distribution is realized based on zero order statistic (ZOS). This method has better toughness and precision.
Nonlocal order parameters for the 1D Hubbard model.
Montorsi, Arianna; Roncaglia, Marco
2012-12-07
We characterize the Mott-insulator and Luther-Emery phases of the 1D Hubbard model through correlators that measure the parity of spin and charge strings along the chain. These nonlocal quantities order in the corresponding gapped phases and vanish at the critical point U(c)=0, thus configuring as hidden order parameters. The Mott insulator consists of bound doublon-holon pairs, which in the Luther-Emery phase turn into electron pairs with opposite spins, both unbinding at U(c). The behavior of the parity correlators is captured by an effective free spinless fermion model.
Orientational order parameter of two cyano nematogens by optical spectroscopy
Vinutha, N.; Pardhasaradhi, P.; Usha, M. K.; Revannasiddaiah, D.
2016-05-01
Refractive index and density measurements of two cyano nematogens, namely p-hexyloxybenzylidene p-aminobenzonitrile and p-octyloxybenzylidene p-aminobenzonitrile have been carried out. From these data, orientational order parameter S has been estimated using different methods. Principal polarizabilities have been calculated using the well-known Vuks isotropic and Neugebauer anisotropic models. Polarizability anisotropy has been estimated using Lippincott δ-function, molecular vibration, Haller's extrapolation and Vuks scaling methods. Using these values, the orientational order parameter S has been estimated at different temperatures in their nematic phases. The values obtained have been compared and discussed. Further, using the experimental refractive index data, the nematic crossover temperatures have also been estimated for these compounds.
Testing for one Generalized Linear Single Order Parameter
DEFF Research Database (Denmark)
Ellegaard, Niels Langager; Christensen, Tage Emil; Dyre, Jeppe
work the order parameter may be chosen to have a non-exponential relaxation. The model predictions contradict the general consensus of the properties of viscous liquids in two ways: (i) The model predicts that following a linear isobaric temperature step, the normalized volume and entalpy relaxation...... functions are identical. This assumption conflicts with some (but not all) reports, utilizing the Tool-Narayanaswamy formalism to extrapolate from non-linear measurements to the linear regime. (ii) The model predicts that the theoretical "linear Prigogine-Defay" ratio is one. This ratio has never been...... responses or extrapolate from measurements of a glassy state away from equilibrium. Starting from a master equation description of inherent dynamics, we calculate the complex thermodynamic response functions. We device a way of testing for the generalized single order parameter model by measuring 3 complex...
Glass-forming liquids: one or more "order" parameters"
DEFF Research Database (Denmark)
Bailey, Nicholas; Christensen, Tage Emil; Jakobsen, Bo
2008-01-01
that a description with a single "order" parameter applies to a good approximation whenever thermal equilibrium fluctuations of fundamental variables like energy and pressure are strongly correlated. Results from computer simulations showing that this is the case for a number of simple glass-forming liquids, as well......We first summarize the classical arguments that the vast majority of glass-forming liquids require more than one ‘order' parameter for their description. Critiques against this conventional wisdom are then presented, and it is argued that the matter deserves to be reconsidered in the light...... as a few exceptions, are briefly presented. Finally, we briefly discuss a new conjecture according to which experiments at varying temperature and pressure follow the density scaling expression for the relaxation time, τ = F(ρ^x/T ) (ρ and T are density and temperature), if and only if the liquid...
Accelerated gravitational wave parameter estimation with reduced order modeling.
Canizares, Priscilla; Field, Scott E; Gair, Jonathan; Raymond, Vivien; Smith, Rory; Tiglio, Manuel
2015-02-20
Inferring the astrophysical parameters of coalescing compact binaries is a key science goal of the upcoming advanced LIGO-Virgo gravitational-wave detector network and, more generally, gravitational-wave astronomy. However, current approaches to parameter estimation for these detectors require computationally expensive algorithms. Therefore, there is a pressing need for new, fast, and accurate Bayesian inference techniques. In this Letter, we demonstrate that a reduced order modeling approach enables rapid parameter estimation to be performed. By implementing a reduced order quadrature scheme within the LIGO Algorithm Library, we show that Bayesian inference on the 9-dimensional parameter space of nonspinning binary neutron star inspirals can be sped up by a factor of ∼30 for the early advanced detectors' configurations (with sensitivities down to around 40 Hz) and ∼70 for sensitivities down to around 20 Hz. This speedup will increase to about 150 as the detectors improve their low-frequency limit to 10 Hz, reducing to hours analyses which could otherwise take months to complete. Although these results focus on interferometric gravitational wave detectors, the techniques are broadly applicable to any experiment where fast Bayesian analysis is desirable.
Simple empirical order parameter for a first-order quantum phase transition in atomic nuclei.
Bonatsos, Dennis; McCutchan, E A; Casten, R F; Casperson, R J
2008-04-11
A simple, empirical, easy-to-measure effective order parameter of a first-order phase transition in atomic nuclei is presented, namely, the ratio of the energies of the first excited 6+ and 0+ states, distinguishing between first- and second-order transitions, and taking on a special value in the critical region, as data in Nd-Dy show. In the large NB limit of the interacting boson approximation model, a repeating degeneracy between alternate yrast and successive 0+ states is found in the critical region around the line of a first-order phase transition, pointing to a possible underlying symmetry.
Dynamical layer decoupling in a stripe-ordered high-T(c) superconductor.
Berg, E; Fradkin, E; Kim, E-A; Kivelson, S A; Oganesyan, V; Tranquada, J M; Zhang, S C
2007-09-21
In the stripe-ordered state of a strongly correlated two-dimensional electronic system, under a set of special circumstances, the superconducting condensate, like the magnetic order, can occur at a nonzero wave vector corresponding to a spatial period double that of the charge order. In this case, the Josephson coupling between near neighbor planes, especially in a crystal with the special structure of La(2-x)Ba(x)CuO(4), vanishes identically. We propose that this is the underlying cause of the dynamical decoupling of the layers recently observed in transport measurements at x = 1/8.
Dynamical Layer Decoupling in a Stripe-Ordered High-Tc Superconductor
Fradkin, Eduardo; Berg, Erez; Kim, Eun-Ah; Kivelson, Steve; Oganesyan, Vadim; Tranquada, John; Zhang, Shoucheng
2008-03-01
In the stripe-ordered state of a strongly correlated two-dimensional electronic system, under a set of special circumstances, the superconducting condensate, like the magnetic order, can occur at a nonzero wave vector corresponding to a spatial period double that of the charge order. In this case, the Josephson coupling between near neighbor planes, especially in a crystal with the special structure of La2-xBaxCuO4, vanishes identically. We propose that this is the underlying cause of the dynamical decoupling of the layers recently observed in transport measurements at x =1/8. [1] E. Berg et al, PRL 99, 127003 (2007)
Dynamical Layer Decoupling in a Stripe-ordered, High T_c Superconductor
Energy Technology Data Exchange (ETDEWEB)
Berg, E.
2010-04-06
In the stripe-ordered state of a strongly-correlated two-dimensional electronic system, under a set of special circumstances, the superconducting condensate, like the magnetic order, can occur at a non-zero wave-vector corresponding to a spatial period double that of the charge order. In this case, the Josephson coupling between near neighbor planes, especially in a crystal with the special structure of La{sub 2-x}Ba{sub x}CuO{sub 4}, vanishes identically. We propose that this is the underlying cause of the dynamical decoupling of the layers recently observed in transport measurements at x = 1/8.
On the Coexistence of Superconductivity and Magnetic Ordering in Unconventional Superconductors
Rodrigues de Campos, Fillipi Klos; Zanella, Fernando; Dartora, C. A.
2017-04-01
It is demonstrated that the coexistence of superconductivity and magnetic ordering, occurring, for instance, in iron-based pnictides and uranium compounds, is not forbidden by classical Maxwell's equations and London-type equations. It predicts simply that internal magnetization is allowed but localized magnetic moments are screened at distances of the order of the London penetration depth. A microscopic theory is considered for the case of ferromagnetic ordering, described in simple terms by electron-magnon coupling. For the sake of simplicity, we assume that itinerant electrons are not responsible for the magnetic ordering, but interact with phonon and magnon excitations, leading to an alternative Cooper pair channel. The temperature dependence and the isotope effect of the superconducting gap is also analysed.
Large-moment antiferromagnetic order in overdoped high-Tc superconductor 154SmFeAsO1-xDx
Iimura, Soshi; Okanishi, Hiroshi; Matsuishi, Satoru; Hiraka, Haruhiro; Honda, Takashi; Ikeda, Kazutaka; Hansen, Thomas C.; Otomo, Toshiya; Hosono, Hideo
2017-05-01
In iron-based superconductors, high critical temperature (Tc) superconductivity over 50 K has only been accomplished in electron-doped hREFeAsO (hRE is heavy rare earth (RE) element). Although hREFeAsO has the highest bulk Tc (58 K), progress in understanding its physical properties has been relatively slow due to difficulties in achieving high-concentration electron doping and carrying out neutron experiments. Here, we present a systematic neutron powder diffraction study of 154SmFeAsO1-xDx, and the discovery of a long-range antiferromagnetic ordering with x ≥ 0.56 (AFM2) accompanying a structural transition from tetragonal to orthorhombic. Surprisingly, the Fe magnetic moment in AFM2 reaches a magnitude of 2.73 μB/Fe, which is the largest in all nondoped iron pnictides and chalcogenides. Theoretical calculations suggest that the AFM2 phase originates in kinetic frustration of the Fe-3dxy orbital, in which the nearest-neighbor hopping parameter becomes zero. The unique phase diagram, i.e., highest-Tc superconducting phase adjacent to the strongly correlated phase in electron-overdoped regime, yields important clues to the unconventional origins of superconductivity.
Classen, Laura; Xing, Rui-Qi; Khodas, Maxim; Chubukov, Andrey V
2017-01-20
We report the results of the parquet renormalization group (RG) analysis of the phase diagram of the most general 5-pocket model for Fe-based superconductors. We use as an input the orbital structure of excitations near the five pockets made out of d_{xz}, d_{yz}, and d_{xy} orbitals and argue that there are 40 different interactions between low-energy fermions in the orbital basis. All interactions flow under the RG, as one progressively integrates out fermions with higher energies. We find that the low-energy behavior is amazingly simple, despite the large number of interactions. Namely, at low energies the full 5-pocket model effectively reduces either to a 3-pocket model made of one d_{xy} hole pocket and two electron pockets or a 4-pocket model made of two d_{xz}/d_{yz} hole pockets and two electron pockets. The leading instability in the effective 4-pocket model is a spontaneous orbital (nematic) order, followed by s^{+-} superconductivity. In the effective 3-pocket model, orbital fluctuations are weaker, and the system develops either s^{+-} superconductivity or a stripe spin-density wave. In the latter case, nematicity is induced by composite spin fluctuations.
Riccati-parameter solutions of nonlinear second-order ODEs
Energy Technology Data Exchange (ETDEWEB)
Reyes, M A [Instituto de Fisica, Universidad de Guanajuato, Leon, Guanajuato (Mexico); Rosu, H C [PotosIInstitute of Science and Technology, Apdo Postal 3-74 Tangamanga, 78231 San Luis PotosI (Mexico)], E-mail: hcr@ipicyt.edu.mx
2008-07-18
It has been proven by Rosu and Cornejo-Perez (Rosu and Cornejo-Perez 2005 Phys. Rev. E 71 046607, Cornejo-Perez and Rosu 2005 Prog. Theor. Phys. 114 533) that for some nonlinear second-order ODEs it is a very simple task to find one particular solution once the nonlinear equation is factorized with the use of two first-order differential operators. Here, it is shown that an interesting class of parametric solutions is easy to obtain if the proposed factorization has a particular form, which happily turns out to be the case in many problems of physical interest. The method that we exemplify with a few explicitly solved cases consists in using the general solution of the Riccati equation, which contributes with one parameter to this class of parametric solutions. For these nonlinear cases, the Riccati parameter serves as a 'growth' parameter from the trivial null solution up to the particular solution found through the factorization procedure.
Strong orientational coordinates and orientational order parameters for symmetric objects
Haji-Akbari, Amir; Glotzer, Sharon C.
2015-12-01
Recent advancements in the synthesis of anisotropic macromolecules and nanoparticles have spurred an immense interest in theoretical and computational studies of self-assembly. The cornerstone of such studies is the role of shape in self-assembly and in inducing complex order. The problem of identifying different types of order that can emerge in such systems can, however, be challenging. Here, we revisit the problem of quantifying orientational order in systems of building blocks with non-trivial rotational symmetries. We first propose a systematic way of constructing orientational coordinates for such symmetric building blocks. We call the arising tensorial coordinates strong orientational coordinates (SOCs) as they fully and exclusively specify the orientation of a symmetric object. We then use SOCs to describe and quantify local and global orientational order, and spatiotemporal orientational correlations in systems of symmetric building blocks. The SOCs and the orientational order parameters developed in this work are not only useful in performing and analyzing computer simulations of symmetric molecules or particles, but can also be utilized for the efficient storage of rotational information in long trajectories of evolving many-body systems.
Three dielectric constants and orientation order parameters in nematic mesophases
Yoon, Hyung Guen; Jeong, Seung Yeon; Kumar, Satyendra; Park, Min Sang; Park, Jung Ok; Srinivasarao, M.; Shin, Sung Tae
2011-03-01
Temperature dependence of the three components ɛ1 , ɛ2 , and ɛ3 of dielectric constant and orientation order parameters in the nematic phase of mesogens with rod, banana, and zero-order dendritic shape were measured using the in-plane and vertical switching geometries, and micro-Raman technique. Results on the well-known uniaxial (Nu) nematogens, E7 and 5CB, revealed two components ɛ1 = ~ɛ| | and ɛ2 = ~ɛ3 = ~ɛ⊥ , as expected. The three dielectric constants were different for two azo substituted (A131 and A103) and an oxadiazole based (ODBP-Ph-C12) bent core mesogens, and a Ge core tetrapode. In some cases, two of the components became the same indicating a loss of biaxiality at temperatures coinciding with the previously reported Nu to biaxial nematic transition. This interpretation is substantiated by micro-Raman measurements of the uniaxial and biaxial nematic order parameters. Supported by the US Department of Energy, Basic Energy Sciences grant ER46572 and by Samsung Electronics Corporation.
Universal behavior of coupled order parameters below three dimensions
Borchardt, Julia
2016-01-01
We explore universal critical behavior in models with two competing order parameters, and an O(N)+O(M) symmetry for dimensions $d \\leq 3$. In d=3, there is always exactly one stable Renormalization Group fixed point, corresponding to bicritical or tetracritical behavior. Employing novel, pseudo-spectral techniques to solve functional Renormalization Group equations in a two-dimensional field space, we uncover a more intricate structure of fixed points in d<3, where two additional bicritical fixed points play a role. Towards d=2, we discover ranges of N=M with several simultaneously stable fixed points, indicating the coexistence of several universality classes.
Order parameter fluctuations at a buried quantum critical point.
Feng, Yejun; Wang, Jiyang; Jaramillo, R; van Wezel, Jasper; Haravifard, S; Srajer, G; Liu, Y; Xu, Z-A; Littlewood, P B; Rosenbaum, T F
2012-05-08
Quantum criticality is a central concept in condensed matter physics, but the direct observation of quantum critical fluctuations has remained elusive. Here we present an X-ray diffraction study of the charge density wave (CDW) in 2H-NbSe(2) at high pressure and low temperature, where we observe a broad regime of order parameter fluctuations that are controlled by proximity to a quantum critical point. X-rays can track the CDW despite the fact that the quantum critical regime is shrouded inside a superconducting phase; and in contrast to transport probes, allow direct measurement of the critical fluctuations of the charge order. Concurrent measurements of the crystal lattice point to a critical transition that is continuous in nature. Our results confirm the long-standing expectations of enhanced quantum fluctuations in low-dimensional systems, and may help to constrain theories of the quantum critical Fermi surface.
Electron-phonon coupling associated with charge-stripe order in cuprate superconductors
Tranquada, John; Reznik, D.; Pintschovius, L.; Ito, M.; Iikubo, S.; Sato, M.; Fujita, M.; Yamada, K.; Gu, G. D.
2006-03-01
We have used inelastic neutron scattering to study the Cu-O bond-stretching phonon in La1.875Ba0.125CuO4 and La1.48Nd0.4Sr0.12CuO4, two cuprate compounds that exhibit charge-stripe order. This is the phonon mode that one expects to be most sensitive to spatial inhomogeneity in the electronic structure of the CuO2 planes. Besides the cosine-like downward dispersion of the mode from zone center to zone boundary, we observe a dip in the dispersion and a very large energy width (> 10 meV) at q = a*/4. The dip and width gradually become smaller with increasing temperature. These evidences of a strong electron-phonon coupling (the dispersion dip and large energy width) have not been predicted by any conventional calculations. The nature of the connection with charge-stripe order will be discussed.
Spin susceptibility of underdoped cuprate superconductors: Insights from a stripe-ordered crystal
Hücker, M.; Gu, G. D.; Tranquada, J. M.
2008-12-01
We report a detailed study of the temperature and magnetic-field dependence of the spin susceptibility for a single crystal of La1.875Ba0.125CuO4 . From a quantitative analysis, we find that the temperature-dependent anisotropy of the susceptibility, observed in both the paramagnetic and stripe-ordered phases, directly indicates that localized Cu moments dominate the magnetic response. A field-induced spin-flop transition provides further corroboration for the role of local moments. Contrary to previous analyses of data from polycrystalline samples, we find that a commonly assumed isotropic and temperature-independent contribution from free carriers, if present, must be quite small. Our conclusion is strengthened by extending the quantitative analysis to include crystals of La2-xBaxCuO4 with x=0.095 and 0.155. On the basis of our results, we present a revised interpretation of the temperature and doping dependence of the spin susceptibility in La2-x(Sr,Ba)xCuO4 .
Shankaraiah, N.; Dubey, Awadhesh K.; Puri, Sanjay; Shenoy, Subodh R.
2016-12-01
In the conceptual framework of phase ordering after temperature quenches below transition, we consider the underdamped Bales-Gooding-type "momentum conserving" dynamics of a 2D martensitic structural transition from a square-to-rectangle unit cell. The one-component or NOP=1 order parameter is one of the physical strains, and the Landau free energy has a triple well, describing a first-order transition. We numerically study the evolution of the strain-strain correlation, and find that it exhibits dynamical scaling, with a coarsening length L (t ) ˜tα . We find at intermediate and long times that the coarsening exponent sequentially takes on respective values close to α =2 /3 and 1 /2 . For deep quenches, the coarsening can be arrested at long times, with α ≃0 . These exponents are also found in 3D. To understand such behavior, we insert a dynamical-scaling ansatz into the correlation function dynamics to give, at a dominant scaled separation, a nonlinear kinetics of the curvature g (t )≡1 /L (t ) . The curvature solutions have time windows of power-law decays g ˜1 /tα , with exponent values α matching simulations, and manifestly independent of spatial dimension. Applying this curvature-kinetics method to mass-conserving Cahn-Hilliard dynamics for a double-well Landau potential in a scalar NOP=1 order parameter yields exponents α =1 /4 and 1 /3 for intermediate and long times. For vector order parameters with NOP≥2 , the exponents are α =1 /4 only, consistent with previous work. The curvature kinetics method could be useful in extracting coarsening exponents for other phase-ordering dynamics.
Limits on the Superconducting Order Parameter in NdFeAsO_{1-x}F_y from Scanning SQUID Microscopy
Energy Technology Data Exchange (ETDEWEB)
Hicks, Clifford W.; Lippman, Thomas M.; /Stanford U., Geballe Lab.; Huber, Martin E.; /Colorado U.; Ren, Zhi-An; Yang, Jie; Zhao, Zhong-Xian; /Beijing, Inst. Phys.; Moler, Kathryn A.; /Stanford U., Geballe Lab.
2009-01-08
Identifying the symmetry of the superconducting order parameter in the recently-discovered ferrooxypnictide family of superconductors, RFeAsO{sub 1-x}F{sub y}, where R is a rare earth, is a high priority. Many of the proposed order parameters have internal {pi} phase shifts, like the d-wave order found in the cuprates, which would result in direction-dependent phase shifts in tunneling. In dense polycrystalline samples, these phase shifts in turn would result in spontaneous orbital currents and magnetization in the superconducting state. We perform scanning SQUID microscopy on a dense polycrystalline sample of NdFeAsO{sub 0.94}F{sub 0.06} with T{sub c} = 48K and find no such spontaneous currents, ruling out many of the proposed order parameters.
Order Parameter Equations for Front Transitions Planar and Circular Fronts
Hagberg, A; Rubinstein, I; Zaltzman, B; Hagberg, Aric; Meron, Ehud
1997-01-01
Near a parity breaking front bifurcation, small perturbations may reverse the propagation direction of fronts. Often this results in nonsteady asymptotic motion such as breathing and domain breakup. Exploiting the time scale differences of an activator-inhibitor model and the proximity to the front bifurcation, we derive equations of motion for planar and circular fronts. The equations involve a translational degree of freedom and an order parameter describing transitions between left and right propagating fronts. Perturbations, such as a space dependent advective field or uniform curvature (axisymmetric spots), couple these two degrees of freedom. In both cases this leads to a transition from stationary to oscillating fronts as the parity breaking bifurcation is approached. For axisymmetric spots, two additional dynamic behaviors are found: rebound and collapse.
Boulter, C. J.; Parry, A. O.
1995-04-01
We consider a model of the complete wetting transition in three dimensions with short-ranged forces which allows for coupling between fluctuations in the order parameter near a substrate and the depinning interface. A renormalization group analysis shows that the effective value of our capillary parameter determining nonuniversal critical amplitudes is renormalized due to this coupling. Our results are in excellent quantitative agreement with the latest Ising model simulation studies of Binder, Landau, and Ferrenberg, which are inexplicable using a standard effective interfacial Hamiltonian model.
Ryan, D. H.; Cadogan, J. M.; Ritter, C.; Canepa, F.; Palenzona, A.; Putti, M.
2009-12-01
Powder neutron-diffraction measurements on both SmFeAsO and the fluorine-doped superconductor, SmFeAsO0.85F0.15 , show that the Sm sublattice orders magnetically. In both cases we observe a simple layered antiferromagnetic arrangement of the ˜0.5μB Sm moments. This provides direct evidence that long-ranged magnetic order of the samarium moments coexists with superconductivity in the SmFeAsO1-xFx system.
Iron-Based Superconductors as Odd-Parity Superconductors
Directory of Open Access Journals (Sweden)
Jiangping Hu
2013-07-01
Full Text Available Parity is a fundamental quantum number used to classify a state of matter. Materials rarely possess ground states with odd parity. We show that the superconducting state in iron-based superconductors is classified as an odd-parity s-wave spin-singlet pairing state in a single trilayer FeAs/Se, the building block of the materials. In a low-energy effective model constructed on the Fe square bipartite lattice, the superconducting order parameter in this state is a combination of an s-wave normal pairing between two sublattices and an s-wave η pairing within the sublattices. The state has a fingerprint with a real-space sign inversion between the top and bottom As/Se layers. The results suggest that iron-based superconductors are a new quantum state of matter, and the measurement of the odd parity can help to establish high-temperature superconducting mechanisms.
Shielding superconductors with thin films
Posen, Sam; Catelani, Gianluigi; Liepe, Matthias U; Sethna, James P
2015-01-01
Determining the optimal arrangement of superconducting layers to withstand large amplitude AC magnetic fields is important for certain applications such as superconducting radiofrequency cavities. In this paper, we evaluate the shielding potential of the superconducting film/insulating film/superconductor (SIS') structure, a configuration that could provide benefits in screening large AC magnetic fields. After establishing that for high frequency magnetic fields, flux penetration must be avoided, the superheating field of the structure is calculated in the London limit both numerically and, for thin films, analytically. For intermediate film thicknesses and realistic material parameters we also solve numerically the Ginzburg-Landau equations. It is shown that a small enhancement of the superheating field is possible, on the order of a few percent, for the SIS' structure relative to a bulk superconductor of the film material, if the materials and thicknesses are chosen appropriately.
Layer-multiplicity as a community order-parameter
Fraundorf, P
2013-01-01
A small number of (perhaps only 6) broken-symmetries, marked by the edges of a hierarchical series of physical {\\em subsystem-types}, underlie the delicate correlation-based complexity of life on our planet's surface. Order-parameters associated with these broken symmetries might in the future help us broaden our definitions of community health. For instance we show that a model of metazoan attention-focus, on correlation-layers that look in/out from the 3 boundaries of skin, family & culture, predicts that behaviorally-diverse communities require a characteristic task layer-multiplicity {\\em per individual} of only about $4 \\frac14$ of the six correlation layers that comprise that community. The model may facilitate explorations of task-layer diversity, go beyond GDP & body count in quantifying the impact of policy-changes & disasters, and help manage electronic idea-streams in ways that strengthen community networks. Empirical methods for acquiring task-layer multiplicity data are in their infan...
Order parameter fluctuation and ordering competition in Ba1 -xKxFe2As2
Wang, Jing; Liu, Guo-Zhu; Efremov, Dmitry V.; van den Brink, Jeroen
2017-01-01
The competition among superconductivity, stripe-type magnetic order, and a new type of C4 symmetric magnetic order in Ba1-xKxFe2As2 is theoretically studied, focusing on its impact on the global phase diagram. By carrying out a renormalization group analysis of an effective field theory, we obtain the energy-scale dependent flows of all the model parameters, and then apply the results to understand the observed phase diagram. On the basis of the renormalization group analysis, we show that the critical line of nematic order has a negative slope in the superconducting dome and superconductivity is suppressed near the magnetic quantum critical point, which are both consistent with recent experiments. Moreover, we find that, although the observed C4 symmetric magnetic state could be a charge-spin density wave or a spin-vortex crystal at high temperatures, charge-spin density wave is the only stable C4 magnetic state in the low-temperature regime. Therefore, ordering competition provides a method to distinguish these two candidate C4 magnetic states.
On n-quantum vortices in superconductors
Marchenko, V I
2002-01-01
The conditions of the n-quantum vortices observation in the superconductors are discussed. It is established in the course of calculating the coefficient by the |psi| sup 6 (psi - the order parameter) in the Ginzburg-Landau theory for the BCS standard model that the sign of this coefficient is negative. This favours the possibility of observing the n-quantum vortices in the superconductors, wherein the vortex lattice with gravitation is formed. The existence of gravitation is manifested in the magnetization finite jump in the H sub 0 = H sub c sub sup 1 field. When by the temperature change the superconductor behavior changes in such a way, that its magnetization in the H sub 0 = H sub c field reduces to the zero, than the observation of the n-quantum vortices near this transition is possible
Two-dimensional orbital-like magnetic order in the high-temperature La(2-x)Sr(x)CuO4 superconductor.
Balédent, V; Fauqué, B; Sidis, Y; Christensen, N B; Pailhès, S; Conder, K; Pomjakushina, E; Mesot, J; Bourges, P
2010-07-09
In high-temperature copper oxide superconductors, a novel magnetic order associated with the pseudogap phase has been identified in two different cuprate families over a wide region of temperature and doping. We report here the observation below 120 K of a similar magnetic ordering in the archetypal cuprate La(2-x)Sr(x)CuO4 (LSCO) system for x=0.085. In contrast with the previous reports, the magnetic ordering in LSCO is only short range with an in-plane correlation length of ∼10 A and is bidimensional (2D). Such a less pronounced order suggests an interaction with other electronic instabilities. In particular, LSCO also exhibits a strong tendency towards stripes ordering at the expense of the superconducting state.
Energy Technology Data Exchange (ETDEWEB)
RodrIguez-Nunez, J J [Departamento de FIsica-FACYT, Universidad de Carabobo, Valencia 2001, Edo. Carabobo (Venezuela); Schmidt, A A [Departamento de Matematica, CCNE, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS (Brazil); Beck, H [Institut de Physique, Universite de Neuchatel, Ch-2000 Neuchatel (Switzerland)
2005-01-19
We study numerically the superconductivity in a system whose normal state is characterized by the presence of a phenomenological pseudogap, E{sub g}/t, in the energy spectrum, for 0 {<=} T {<=} T*. T* is called the crossover temperature and it is defined in the high-temperature superconductors (HTSC) where the static spin susceptibility, {chi}(T), is a maximum. At T* one also observes the formation of a pseudogap in the density of states around the chemical potential (Maier et al 2002 Preprint cond-mat/0208419). In order to fix ideas, we have chosen the pseudogap and the superconducting gap to have the same symmetry. We have adopted the scenario where the pseudogap and the superconducting gap are independent of each other (Tallon and Loram 2001 Physica C 349 53), for which the pseudogap enters in the superconducting phase going down to zero at zero temperature. We have found that for all E{sub g}/t {ne}0 we require a critical value of the superconducting interaction, V/t, to produce a finite superconducting critical temperature, T{sub c}/t, and the superconductor order parameter at T/t = 0, {delta}{sub 0}/t. These results have been obtained for both {mu}/t = 0 and {mu}/t {ne} 0. We have obtained a phase diagram, namely, V/t versus E{sub g}/t, at half-filling. We have compared our results with the analytical calculations of Tifrea et al (2002 Physica C 371 104), the recent work of Tifrea and Moca (2003 Preprint cond-mat/0307362 (2004 Europhys. J. B, at press)) and other relevant theoretical results.
Klassen, Joel; Wen, Xiao-Gang
2015-10-14
We study a chain of ferromagnetic sites, ie nano-particles, molecules or atoms, on a substrate of fully gapped superconductors. We find that under quite realistic conditions, the fermion-number-parity symmetry Z₂(f) can spontaneously break. In other words, such a chain can realize a 1 + 1D fermionic topologically ordered state and the corresponding two-fold topological degeneracy on an open chain. Such a topological degeneracy becomes the so called Majorana zero mode in the non-interacting limit.
Quantum interference in an interfacial superconductor
Goswami, Srijit; Mulazimoglu, Emre; Monteiro, Ana M. R. V. L.; Wölbing, Roman; Koelle, Dieter; Kleiner, Reinhold; Blanter, Ya. M.; Vandersypen, Lieven M. K.; Caviglia, Andrea D.
2016-10-01
The two-dimensional superconductor that forms at the interface between the complex oxides lanthanum aluminate (LAO) and strontium titanate (STO) has several intriguing properties that set it apart from conventional superconductors. Most notably, an electric field can be used to tune its critical temperature (Tc; ref. 7), revealing a dome-shaped phase diagram reminiscent of high-Tc superconductors. So far, experiments with oxide interfaces have measured quantities that probe only the magnitude of the superconducting order parameter and are not sensitive to its phase. Here, we perform phase-sensitive measurements by realizing the first superconducting quantum interference devices (SQUIDs) at the LAO/STO interface. Furthermore, we develop a new paradigm for the creation of superconducting circuit elements, where local gates enable the in situ creation and control of Josephson junctions. These gate-defined SQUIDs are unique in that the entire device is made from a single superconductor with purely electrostatic interfaces between the superconducting reservoir and the weak link. We complement our experiments with numerical simulations and show that the low superfluid density of this interfacial superconductor results in a large, gate-controllable kinetic inductance of the SQUID. Our observation of robust quantum interference opens up a new pathway to understanding the nature of superconductivity at oxide interfaces.
Gabovich, Alexander M.; Voitenko, Alexander I.
2016-10-01
The state of the art concerning tunnel measurements of energy gaps in cuprate oxides has been analyzed. A detailed review of the relevant literature is made, and original results calculated for the quasiparticle tunnel current J(V) between a metallic tip and a disordered d-wave superconductor partially gapped by charge density waves (CDWs) are reported, because it is this model of high-temperature superconductors that becomes popular owing to recent experiments in which CDWs were observed directly. The current was calculated suggesting the scatter of both the superconducting and CDW order parameters due to the samples' intrinsic inhomogeneity. It was shown that peculiarities in the current-voltage characteristics inherent to the case of homogeneous superconducting material are severely smeared, and the CDW-related features transform into experimentally observed peak-dip-hump structures. Theoretical results were used to fit data measured for YBa2Cu3O7-δ and Bi2Sr2CaCu2O8+δ. The fitting demonstrated a good qualitative agreement between the experiment and model calculations. The analysis of the energy gaps in high-Tc superconductors is important both per se and as a tool to uncover the nature of superconductivity in cuprates not elucidated so far despite of much theoretical effort and experimental progress.
Introduction to Holographic Superconductor Models
Cai, Rong-Gen; Li, Li-Fang; Yang, Run-Qiu
2015-01-01
In the last years it has been shown that some properties of strongly coupled superconductors can be potentially described by classical general relativity living in one higher dimension, which is known as holographic superconductors. This paper gives a quick and introductory overview of some holographic superconductor models with s-wave, p-wave and d-wave orders in the literature from point of view of bottom-up, and summarizes some basic properties of these holographic models in various regimes. The competition and coexistence of these superconductivity orders are also studied in these superconductor models.
Theoretical studies of unconventional superconductors
Energy Technology Data Exchange (ETDEWEB)
Groensleth, Martin Sigurd
2008-07-01
This thesis presents four research papers. In the first three papers we have derived analytical results for the transport properties in unconventional superconductors and ferromagnetic systems with multiple broken symmetries. In Paper I and parts of Paper II we have studied tunneling transport between two non-unitary ferromagnetic spin-triplet superconductors, and found a novel interplay between ferromagnetism and superconductivity manifested in the Josephson effect as a spin- and charge-current in the absence of an applied voltage across the junction. The critical amplitudes of these currents can be adjusted by the relative magnetization direction on each side of the junction. Furthermore, in Paper II, we have found a way of controlling a spin-current between two ferromagnets with spin-orbit coupling. Paper III considers a junction consisting of a ferromagnet and a non-unitary ferromagnetic superconductor, and we show that the conductance spectra contains detailed information about the superconducting gaps and pairing symmetry of the Cooper-pairs. In the last paper we present a Monte Carlo study of an effective Hamiltonian describing orbital currents in the CuO2 layers of high-temperature superconductive cuprates. The model features two intrinsically anisotropic Ising models, coupled through an anisotropic next-nearest neighbor interaction, and an Ashkin-Teller nearest neighbor fourth order coupling. We have studied the specific heat anomaly, as well as the anomaly in the staggered magnetization associated with the orbital currents and its susceptibility. We have found that in a limited parameter regime, the specific heat anomaly is substantially suppressed, while the susceptibility has a non-analytical peak across the order-disorder transition. The model is therefore a candidate for describing the breakup of hidden order when crossing the pseudo-gap line on the under-doped side in the phase diagram of high-temperature superconductors. (Author) 64 refs., figs
Nonadiabatic dynamics and coherent control of nonequilibrium superconductors
Energy Technology Data Exchange (ETDEWEB)
Schnyder, Andreas; Manske, Dirk [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, D-70569 Stuttgart (Germany); Krull, Holger; Uhrig, Goetz [Lehrstuhl fuer Theoretische Physik I, Technische Univeritaet Dortmund, Otto-Hahn Strasse 4, 44221 Dortmund (Germany)
2015-07-01
Inspired by recent THz pump-THz probe experiments on NbN films, we theoretically study the pump-probe response of nonequilibrium superconductors coupled to optical phonons. For ultrashort pump pulses a nonadiabatic regime emerges, which is characterized by amplitude oscillations of the superconducting gap and by the generation of coherent phonons. Using density-matrix theory as well as analytical methods, we compute the pump-probe response of the superconductor in the nonadiabatic regime and determine the signatures of the order parameter and of the phonon oscillations in the pump-probe conductivity. We find that the nonadiabatic dynamics of the superconductor reflects itself in oscillations of the pump-probe response as a function of delay time between pump and probe pulses. We also consider two-band superconductors and study the interplay of the two amplitude oscillations of the two gaps.
Copper-tuned magnetic order and excitations in iron-based superconductors Fe1+yTe1-xSex
Wen, Jinsheng; Xu, Zhijun; Xu, Guangyong; Lumsden, Mark; Matsuda, Masaaki; Valdivia, Patrick; Bourret, Edith; Lee, Dunghai; Gu, Genda; Tranquada, John; Birgeneau, Robert
2012-02-01
We report neutron scattering results on the Cu-substitution effects in the iron-based superconductors, Fe1+yTe1-xSex. In the parent compound, it is found that Cu drives the low-temperature magnetic ground state from long-range commensurate antiferromagnetic order in Fe1.06TeCu0.04 to short-range incommensurate order in FeTeCu0.1. In the former sample, the structural and magnetic ordering temperature is 40 K; in FeTeCu0.1, the structural phase transition is not obvious and a transition to the spin-glass state is found at 22 K. Cu suppresses superconductivity in FeTe0.5Se0.5---Tc is reduced to 7 K with a 2% Cu doping, and no superconductivity is found in the 10% Cu-doped sample. In the meantime, the intensity and energy of the resonance mode are suppressed in the 2% Cu-doped sample, while there is no resonance in the non-superconducting sample. Besides, the low-temperature magnetic excitation spectra are distinct for these two samples, with the superconducting one having an ``hour-glass" shape and the other one having a ``waterfall" shape. Our results provide further insights on the interplay between magnetism and superconductivity in the iron-based superconductors.
Electrodynamics of Metallic Superconductors
Directory of Open Access Journals (Sweden)
M. Dressel
2013-01-01
Full Text Available The theoretical and experimental aspects of the microwave, terahertz, and infrared properties of superconductors are discussed. Electrodynamics can provide information about the superconducting condensate as well as about the quasiparticles. The aim is to understand the frequency dependence of the complex conductivity, the change with temperature and time, and its dependence on material parameters. We confine ourselves to conventional metallic superconductors, in particular, Nb and related nitrides and review the seminal papers but also highlight latest developments and recent experimental achievements. The possibility to produce well-defined thin films of metallic superconductors that can be tuned in their properties allows the exploration of fundamental issues, such as the superconductor-insulator transition; furthermore it provides the basis for the development of novel and advanced applications, for instance, superconducting single-photon detectors.
Current fluctuations in unconventional superconductor junctions with impurity scattering
Burset, Pablo; Lu, Bo; Tamura, Shun; Tanaka, Yukio
2017-06-01
The order parameter of bulk two-dimensional superconductors is classified as nodal if it vanishes for a direction in momentum space, or gapful if it does not. Each class can be topologically nontrivial if Andreev bound states are formed at the edges of the superconductor. Nonmagnetic impurities in the superconductor affect the formation of Andreev bound states and can drastically change the tunneling spectra for small voltages. Here, we investigate the mean current and its fluctuations for two-dimensional tunnel junctions between normal-metal and unconventional superconductors by solving the quasiclassical Eilenberger equation self-consistently, including the presence of nonmagnetic impurities in the superconductor. As the impurity strength increases, we find that superconductivity is suppressed for almost all order parameters since (i) at zero applied bias, the effective transferred charge calculated from the noise-current ratio tends to the electron charge e , and (ii) for finite bias, the current-voltage characteristics follows that of a normal-state junction. There are notable exceptions to this trend. First, gapful nontrivial (chiral) superconductors are very robust against impurity scattering due to the linear dispersion relation of their surface Andreev bound states. Second, for nodal nontrivial superconductors, only px-wave pairing is almost immune to the presence of impurities due to the emergence of odd-frequency s -wave Cooper pairs near the interface. Due to their anisotropic dependence on the wave vector, impurity scattering is an effective pair-breaking mechanism for the remaining nodal superconductors. All these behaviors are neatly captured by the noise-current ratio, providing a useful guide to find experimental signatures for unconventional superconductivity.
Kontani, H.; Inoue, Y.; Saito, T.; Yamakawa, Y.; Onari, S.
2012-01-01
The main features in iron-based superconductors would be (i) the orthorhombic transition accompanied by remarkable softening of shear modulus, (ii) high-Tc superconductivity close to the orthorhombic phase, and (iii) nematic transition in the tetragonal phase. In this paper, we present a unified explanation for them, based on the orbital fluctuation theory, considering both the e-ph and the Coulomb interaction. It is found that a small e-ph coupling constant ($\\lambda ~ 0.2$) is enough to pro...
Holographic entanglement entropy in general holographic superconductor models
Peng, Yan
2014-01-01
We study the entanglement entropy of general holographic dual models both in AdS soliton and AdS black hole backgrounds with full backreaction. We find that the entanglement entropy is a good probe to explore the properties of the holographic superconductors and provides richer physics in the phase transition. We obtain the effects of the scalar mass, model parameter and backreaction on the entropy, and argue that the jump of the entanglement entropy may be a quite general feature for the first order phase transition. In strong contrast to the insulator/superconductor system, we note that the backreaction coupled with the scalar mass can not be used to trigger the first order phase transition if the model parameter is below its bottom bound in the metal/superconductor system.
Subgap states in disordered superconductors
Energy Technology Data Exchange (ETDEWEB)
Skvortsov, M. A., E-mail: skvor@itp.ac.ru; Feigel' man, M. V., E-mail: feigel@landau.ac.ru [Russian Academy of Sciences, Landau Institute for Theoretical Physics (Russian Federation)
2013-09-15
We revise the problem of the density of states in disordered superconductors. Randomness of local sample characteristics translates to the quenched spatial inhomogeneity of the spectral gap, smearing the BCS coherence peak. We show that various microscopic models of potential and magnetic disorder can be reduced to a universal phenomenological random order parameter model, whereas the details of the microscopic description are encoded in the correlation function of the order parameter fluctuations. The resulting form of the density of states is generally described by two parameters: the width {Gamma} measuring the broadening of the BCS peak and the energy scale {Gamma}{sub tail} that controls the exponential decay of the density of subgap states. We refine the existing instanton approaches for determination of {Gamma}{sub tail} and show that they appear as limiting cases of a unified theory of optimal fluctuations in a nonlinear system. The application to various types of disorder is discussed.
Energy Technology Data Exchange (ETDEWEB)
Trastoy, J. [Unité Mixte de Physique CNRS/Thales, 1 avenue A. Fresnel, 91767 Palaiseau (France); Université Paris Sud, 91405 Orsay (France); Rouco, V. [Unité Mixte de Physique CNRS/Thales, 1 avenue A. Fresnel, 91767 Palaiseau (France); Université Paris Sud, 91405 Orsay (France); Institut de Ciència de Materials de Barcelona, ICMAB-CSIC, Campus de la UAB, E-08193 Bellaterra (Spain); Ulysse, C. [CNRS, Phynano Team, Laboratoire de Photonique et de Nanostructures, route de Nozay, 91460 Marcoussis (France); Bernard, R. [Unité Mixte de Physique CNRS/Thales, 1 avenue A. Fresnel, 91767 Palaiseau (France); Université Paris Sud, 91405 Orsay (France); Faini, G. [CNRS, Phynano Team, Laboratoire de Photonique et de Nanostructures, route de Nozay, 91460 Marcoussis (France); Lesueur, J. [LPEM, CNRS-ESPCI, 10 rue Vauquelin, 75231 Paris (France); Briatico, J. [Unité Mixte de Physique CNRS/Thales, 1 avenue A. Fresnel, 91767 Palaiseau (France); Université Paris Sud, 91405 Orsay (France); Villegas, J.E., E-mail: javier.villegas@thalesgroup.com [Unité Mixte de Physique CNRS/Thales, 1 avenue A. Fresnel, 91767 Palaiseau (France); Université Paris Sud, 91405 Orsay (France)
2014-11-15
Highlights: • Study of magneto-transport in YBCO films with a periodic pinning array. • Commensurability effects investigated as a function of vortex velocity. • At low temperatures, the periodic pinning is more efficient for low vortex velocities. • At high temperatures, the periodic pinning becomes stronger with increasing vortex velocity. - Abstract: We studied vortex dynamics in a YBa{sub 2}Cu{sub 3}O{sub 7−δ} thin film with two different sources of pinning: intrinsic random defects and an artificial square array of defects created by masked ion irradiation. We study commensurability effects between the vortex lattice and the pinning array as a function of the vortex velocity v and the temperature. We find that at low temperatures the commensurability effects (magneto-resistance drop at the matching fields) are stronger at low velocities, in contrast with the behavior previously observed in low-critical-temperature superconductors.
Superconducting order parameter fluctuations above Tc in polycrystalline Ho 1Ba 2Cu 3O 7-δ compounds
Vidal, Félix; Veira, J. A.; Maza, J.; Ponte, J. J.; Amador, J.; Cascales, C.; Casais, M. T.; Rasines, I.
1988-08-01
We report measurements of the excess electrical conductivity, Δσ, above Tc in polycrystalline HoBa 2Cu 3O 7-δ single-phase 0 (within 4%) compounds. The relative temperature resolution is of the order of 10 -2 K which, in spite of the broadening of the transition by nonintrinsic effects, should probably make accessible the whole mean-field regime for Δσ and also to penetrate inside the full critical dynamic region. The general behavior of Δσ(ɛ) in these Ho-based samples is very similar to that previously observed in our laboratory for Y-based high-temperature superconductors. In particular, when analyzed in terms of the Aslamazov-Larkin theory and by using some dynamic scaling ideas, the Δσ(ɛ) data are compatible with a superconducting order parameter of two components fluctuating in three dimensions. No influence of the magnetic Ho ions on Δσ is observed in the whole reduced-temperature range studied.
Beyer, A. D.; Grinolds, M. S.; Teague, M. L.; Yeh, N.-C.; Lee, S.-I.
2008-03-01
Our cryogenic scanning tunneling spectroscopic studies of spatially resolved QP density of states (DOS) in hole-type YBa2Cu3Ox and electron-type La0.1Sr0.9CuO2 cuprate superconductors (SC) reveal that the existence of COs in the cuprates can account for many seeming non-universal phenomena. Namely, we analyze the low-energy QP excitation spectra by using a microscopic model of coexisting SC/CO, with density-wave type COs, and find that various spectral characteristics are uniquely determined by the parameters δSC, VCO, Q, η, and γ (δSC: SC gap, VCO: CO gap, Q: CO wave-vector, η: strength of quantum fluctuations, γ: line-width of QP spectral peak). For instance, VCO>δSC (VCOVCO values derived by our analysis.
Photoemission study of iron-based superconductor
Institute of Scientific and Technical Information of China (English)
Liu Zhong-Hao; Cai Yi-Peng; Zhao Yan-Ge; Jia Lei-Lei; Wang Shan-Cai
2013-01-01
The iron-based superconductivity (IBSC) is a great challenge in correlated system.Angle-resolved photoemission spectroscopy (ARPES) provides electronic structure of the IBSCs,the pairing strength,and the order parameter symmetry.Here,we briefly review the recent progress in IBSCs and focus on the results from ARPES.The ARPES study shows the electronic structure of “122”,“111”,“11”,and “122*” families of IBSCs.It has been agreed that the IBSCs are unconventional superconductors in strong coupling region.The order parameter symmetry basically follows s± form with considerable out-of-plane contribution.
An Adaptive Tracking Control of Fractional-Order Chaotic Systems with Uncertain System Parameter
Ping Zhou; Rui Ding
2011-01-01
An adaptive tracking control scheme is presented for fractional-order chaotic systems with uncertain parameter. It is theoretically proved that this approach can make the uncertain parameter fractional-order chaotic system track any given reference signal and the uncertain system parameter is estimated through the adaptive tracking control process. Furthermore, the reference signal may belong to other integer-orders chaotic system or belong to different fractional-order chaotic system with di...
Liping Chen; Shanbi Wei; Yi Chai; Ranchao Wu
2012-01-01
Projective synchronization between two different fractional-order chaotic systems with fully unknown parameters for drive and response systems is investigated. On the basis of the stability theory of fractional-order differential equations, a suitable and effective adaptive control law and a parameter update rule for unknown parameters are designed, such that projective synchronization between the fractional-order chaotic Chen system and the fractional-order chaotic Lü system with unknown par...
Theoretical study of pair density wave superconductors
Zheng, Zhichao
In conventional superconductors, the Cooper pairs are formed from quasiparticles. We explore another type of superconducting state, a pair density wave (PDW) order, which spontaneously breaks some of the translational and point group symmetries. In a PDW superconductor, the order parameter is a periodic function of the center-of-mass coordinate, and the spatial average value of the superconducting order parameter vanishes. In the early 1960s, following the success of the BCS theory of superconductivity, Fulde and Ferrell and Larkin and Ovchinnikov (FFLO) developed theories of inhomogeneous superconducting states. Because of this Zeeman splitting in a magnetic field, the Cooper pairs having a nonzero center-of-mass momentum are more stable than the normal pairing, leading to the FFLO state. Experiments suggest possible occurrence of the FFLO state in the heavy-fermion compound CeCoIn5, and in quasi-low-dimensional organic superconductors. FFLO phases have also been argued to be of importance in understanding ultracold atomic Fermi gases and in the formation of color superconductivity in high density quark matter. In all Fermi superfluids known at the present time, Cooper pairs are composed of particles with spin 1/2. The spin component of a pair wave function can be characterized by its total spin S = 0 (singlet) and S = 1 (triplet). In the discovered broken inversion superconductors CePt3Si, Li2Pt3B, and Li2Pd3B, the magnetic field leads to novel inhomogeneous superconducting states, namely the helical phase and the multiple-q phase. Its order parameter exhibits periodicity similar to FFLO phase, and the consequences of both phases are same: the enhancement of transition temperature as a function of magnetic field. We have studied the PDW phases in broken parity superconductors with vortices included. By studying PDW vortex states, we find the usual Abrikosov vortex solution is unstable against a new solution with fractional vortex pairs. We have also studied the
Ordering dynamics of microscopic models with nonconserved order parameter of continuous symmetry
DEFF Research Database (Denmark)
Zhang, Z.; Mouritsen, Ole G.; Zuckermann, Martin J.
1993-01-01
Numerical Monte Carlo temperature-quenching experiments have been performed on two three-dimensional classical lattice models with continuous ordering symmetry: the Lebwohl-Lasher model [Phys. Rev. A 6, 426 (1972)] and the ferromagnetic isotropic Heisenberg model. Both models describe a transition...... from a disordered phase to an orientationally ordered phase of continuous symmetry. The Lebwohl-Lasher model accounts for the orientational ordering properties of the nematic-isotropic transition in liquid crystals and the Heisenberg model for the ferromagnetic-paramagnetic transition in magnetic...
含参Schur型排序不等式%Schur Formal Ordering Inequalities Involving Parameter
Institute of Scientific and Technical Information of China (English)
陈胜利; 姚勇; 徐嘉
2008-01-01
In this paper,to make an analogy to the classical Schur inequalities,we establish several ordering inequalities of Schur type with a parameter.As applications.some generalizations of Schur type with parameter axe obtained.
A universal order parameter for synchrony in networks of limit cycle oscillators
Schröder, Malte; Timme, Marc; Witthaut, Dirk
2017-07-01
We analyze the properties of order parameters measuring synchronization and phase locking in complex oscillator networks. First, we review network order parameters previously introduced and reveal several shortcomings: none of the introduced order parameters capture all transitions from incoherence over phase locking to full synchrony for arbitrary, finite networks. We then introduce an alternative, universal order parameter that accurately tracks the degree of partial phase locking and synchronization, adapting the traditional definition to account for the network topology and its influence on the phase coherence of the oscillators. We rigorously prove that this order parameter is strictly monotonously increasing with the coupling strength in the phase locked state, directly reflecting the dynamic stability of the network. Furthermore, it indicates the onset of full phase locking by a diverging slope at the critical coupling strength. The order parameter may find applications across systems where different types of synchrony are possible, including biological networks and power grids.
Dorris, Stephen E.; Burlone, Dominick A.; Morgan; Carol W.
1999-02-02
A superconducting conductor fabricated from a plurality of wires, e.g., fine silver wires, coated with a superconducting powder. A process of applying superconducting powders to such wires, to the resulting coated wires and superconductors produced therefrom.
Synchronization-based parameter estimation of fractional-order neural networks
Gu, Yajuan; Yu, Yongguang; Wang, Hu
2017-10-01
This paper focuses on the parameter estimation problem of fractional-order neural network. By combining the adaptive control and parameter update law, we generalize the synchronization-based identification method that has been reported in several literatures on identifying unknown parameters of integer-order systems. With this method, parameter identification and synchronization can be achieved simultaneously. Finally, a numerical example is given to illustrate the effectiveness of the theoretical results.
An Adaptive Tracking Control of Fractional-Order Chaotic Systems with Uncertain System Parameter
Directory of Open Access Journals (Sweden)
Ping Zhou
2011-01-01
Full Text Available An adaptive tracking control scheme is presented for fractional-order chaotic systems with uncertain parameter. It is theoretically proved that this approach can make the uncertain parameter fractional-order chaotic system track any given reference signal and the uncertain system parameter is estimated through the adaptive tracking control process. Furthermore, the reference signal may belong to other integer-orders chaotic system or belong to different fractional-order chaotic system with different fractional orders. Two examples are presented to demonstrate the effectiveness of the proposed method.
Current status of iron-based superconductors
Energy Technology Data Exchange (ETDEWEB)
Kamihara, Yoichi, E-mail: kamihara_yoichi@appi.keio.ac.jp [Keio University, Department of Applied Physics and Physico-Informatics, Faculty of Science and Technology (Japan)
2012-03-15
Current status of iron-based superconductors is summarized. Although short range magnetic ordering and magnetic phase separation of Fe are controversial, (long range) magnetic and electronic phase diagrams of iron based superconductors can be classified into two-type. Antiferromagnetic ordering of itinerant Fe does not coexist with superconducting phase of SmFeAsO{sub 1 - x}F{sub x}. The very large H{sub c2} of iron-based superconductors attract us to attempts at applications.
Current status of iron-based superconductors
Kamihara, Yoichi
2012-03-01
Current status of iron-based superconductors is summarized. Although short range magnetic ordering and magnetic phase separation of Fe are controversial, (long range) magnetic and electronic phase diagrams of iron based superconductors can be classified into two-type. Antiferromagnetic ordering of itinerant Fe does not coexist with superconducting phase of SmFeAsO1 - xFx. The very large H c2 of iron-based superconductors attract us to attempts at applications.
A novel approach to topological defects in a vector order parameter system
Institute of Scientific and Technical Information of China (English)
Ren Ji-Rong; Rong Shu-Jun; Zhu Tao
2009-01-01
Based on Duan's topological current theory, we propose a novel approach to study the topological properties of topological defects in a two-dimensional complex vector order parameter system. This method shows explicitly the fine topological structure of defects. The branch processes of defects in the vector order parameter system have also been investigated with this method.
Wetting, prewetting and surface transitions in type-I superconductors
Indekeu, J. O.; van Leeuwen, J. M. J.
1995-02-01
Within the Ginzburg-Landau theory, which is quantitatively correct for classical superconductors, it is shown that a type-I superconductor can display an interface delocalization or “wetting” transition, in which a macroscopically thick superconducting layer intrudes from the surface into the bulk normal phase. The condition for this transition to occur is that the superconducting order parameter | ψ| 2 is enhanced at the surface. This corresponds to a negative surface extrapolation length b. The wetting transition takes place at bulk two-phase coexistence of normal and superconducting phases, at a temperature TD below the critical temperature Tc, and at magnetic field HD = Hc( TD). The field is applied parallel to the surface. Surprisingly, the order of the wetting transition is controlled by a bulk material constant, the Ginzburg-Landau parameter κ. This is very unusual, since in other systems (fluids, Ising magnets,…) the order of the wetting transition depends on surface parameters that are difficult to determine or control. For superconductors, first-order wetting is predicted for 0 ≤ κ wetting for 0.374 wetting, the prewetting extension is also found. Unlike in standard wetting problems, the prewetting line does not terminate at a critical point but changes from first to second order at a tricritical point. Twinning-plane superconductivity (TPS) is reinterpreted as a prewetting phenomenon. The possibility of critical wetting in superconductors is especially interesting because this phenomenon has largely eluded experimental verification in any system until now. Furthermore, superconductors provide a realization of wetting in systems with short-range (exponentially decaying) interactions. This is very different from the usual long-range (algebraically decaying) interactions, such as van der Waals forces, and has important consequences for the wetting characteristics.
Scattering from Incipient Stripe Order in the High-temperature Superconductor Bi2Sr2CaCu2O8
Energy Technology Data Exchange (ETDEWEB)
da Silva Neto E. H.; Wen J.; Parker, C.V.; Aynajian, P.; Pushp, A.; Yazdani, A.; Xu, Z.; Gu, G.
2012-03-01
Recently, we have used spectroscopic mapping with a scanning tunneling microscope to probe modulations of the electronic density of states in single crystals of the high-temperature superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} (Bi-2212) as a function of temperature [C.V. Parker et al. Nature (London) 468 677 (2010)]. These measurements showed Cu-O bond-oriented modulations that form below the pseudogap temperature with a temperature-dependent energy dispersion displaying different behaviors in the superconducting and pseudogap states. Here we demonstrate that quasiparticle scattering from impurities does not capture the experimentally observed energy and temperature dependence of these modulations. Instead, a model of scattering of quasiparticles from short-range stripe order, with periodicity near four lattice constants (4a), reproduces the experimentally observed energy dispersion of the bond-oriented modulations and its temperature dependence across the superconducting critical temperature T{sub c}. The present study confirms the existence of short-range stripe order in Bi-2212.
Magnetic-field-induced charge-stripe order in the high-temperature superconductor YBa2Cu3Oy.
Wu, Tao; Mayaffre, Hadrien; Krämer, Steffen; Horvatić, Mladen; Berthier, Claude; Hardy, W N; Liang, Ruixing; Bonn, D A; Julien, Marc-Henri
2011-09-07
Electronic charges introduced in copper-oxide (CuO(2)) planes generate high-transition-temperature (T(c)) superconductivity but, under special circumstances, they can also order into filaments called stripes. Whether an underlying tendency towards charge order is present in all copper oxides and whether this has any relationship with superconductivity are, however, two highly controversial issues. To uncover underlying electronic order, magnetic fields strong enough to destabilize superconductivity can be used. Such experiments, including quantum oscillations in YBa(2)Cu(3)O(y) (an extremely clean copper oxide in which charge order has not until now been observed) have suggested that superconductivity competes with spin, rather than charge, order. Here we report nuclear magnetic resonance measurements showing that high magnetic fields actually induce charge order, without spin order, in the CuO(2) planes of YBa(2)Cu(3)O(y). The observed static, unidirectional, modulation of the charge density breaks translational symmetry, thus explaining quantum oscillation results, and we argue that it is most probably the same 4a-periodic modulation as in stripe-ordered copper oxides. That it develops only when superconductivity fades away and near the same 1/8 hole doping as in La(2-x)Ba(x)CuO(4) (ref. 1) suggests that charge order, although visibly pinned by CuO chains in YBa(2)Cu(3)O(y), is an intrinsic propensity of the superconducting planes of high-T(c) copper oxides.
Shot Noise in Ferromagnetic Superconductor Tunnel Junctions
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
In this paper, the superconducting order parameter and the energy spectrum of the Bogoliubov excitations are obtained from the Bogoliubov-de Gennes (BdG) equation for a ferromagnetic superconductor (FS). Taking into account the rough interface scattering effect, we calculate the shot noise and the differential conductance of the normal- metal insulator ferromagnetic superconductor junction. It is shown that the exchange energy Eh in FS can lead to splitting of the differential shot noise peaks and the conductance peaks. The energy difference between the two splitting peaks is equal to 2Eh. The rough interface scattering strength results in descent of conductance peaks and the shot noise-to-current ratio but increases the shot noise.
Order parameter and its critical exponent for some binary mixtures showing induced nematic phase
Sarkar, Sudipta Kumar; Das, Malay Kumar
2016-09-01
Refractive index measurements as a function of temperature have been performed for an induced nematic binary system by means of thin prism technique. The temperature dependence of the birefringence (Δn) has been assessed from the measured refractive index data. A direct extrapolation method has been employed to determine the orientational order parameter for the investigated mixtures and the order parameter so obtained has also been compared with the mean field values. The Haller type fitting expression results in a relatively lower value of the order parameter critical exponent (β) compared to the theoretically predicted values. Therefore, a four-parameter power law expression, consistent with the mean field theory as well as the first-order character of the nematic-isotropic (N-I) phase transition have been used to explore the critical behavior of the order parameter near the N-I transition.
Directory of Open Access Journals (Sweden)
T.A. Nelyubina
2009-09-01
Full Text Available In this article, author considers a class of technologies aggregates, which can be present as complex socio-economic systems. The order parameters are chosen as instrument of reflect the system integrity of this technologies aggregates. The analysis of aggregates through order parameters permit: to diagnose the state of the system and its life phase, understand the compatibility extent between the current state of system and the assumed modifications in it, understand the nature of attendant risks. It also allows to compare the systems, track the dynamics of order parameters and forecast the trends of the future changes. Author formulates number and definitions of order parameters for this class of technologies aggregates; proposes the assessment method of condition of order parameters for technologies aggregate of region; makes express-assessment of preparedness level of technologies aggregates of some regions to innovation changes.
Conditions for stimulated emission in anomalous gravity-superconductors interactions
Modanese, G
2009-01-01
Several authors have studied the generation of gravitational fields by condensed-matter systems in non-extreme density conditions. General Relativity and lowest-order perturbative Quantum Gravity predict in this case an extremely small emission rate, so these phenomena can become relevant only if some strong quantum effect occurs. Quantum aspects of gravity are still poorly understood. It is believed that they could play a role in systems which exhibit macroscopic quantum coherence, like superconductors and superfluids, leading to an "anomalous" coupling between matter and field. We mention here recent work in this field by Woods, Chiao, Becker, Agop et al., Ummarino, Kiefer and Weber. New results are presented concerning anomalous stimulated gravitational emission in a layered superconductor like YBCO. We model the superconductor as an array of intrinsic Josephson junctions. The superconducting parameters are defined by our preliminary measurements with melt-textured samples. We write explicitly and solve nu...
Variances as order parameter and complexity measure for random Boolean networks
Energy Technology Data Exchange (ETDEWEB)
Luque, Bartolo [Departamento de Matematica Aplicada y EstadIstica, Escuela Superior de Ingenieros Aeronauticos, Universidad Politecnica de Madrid, Plaza Cardenal Cisneros 3, Madrid 28040 (Spain); Ballesteros, Fernando J [Observatori Astronomic, Universitat de Valencia, Ed. Instituts d' Investigacio, Pol. La Coma s/n, E-46980 Paterna, Valencia (Spain); Fernandez, Manuel [Departamento de Matematica Aplicada y EstadIstica, Escuela Superior de Ingenieros Aeronauticos, Universidad Politecnica de Madrid, Plaza Cardenal Cisneros 3, Madrid 28040 (Spain)
2005-02-04
Several order parameters have been considered to predict and characterize the transition between ordered and disordered phases in random Boolean networks, such as the Hamming distance between replicas or the stable core, which have been successfully used. In this work, we propose a natural and clear new order parameter: the temporal variance. We compute its value analytically and compare it with the results of numerical experiments. Finally, we propose a complexity measure based on the compromise between temporal and spatial variances. This new order parameter and its related complexity measure can be easily applied to other complex systems.
Spin manipulation in nanoscale superconductors.
Beckmann, D
2016-04-27
The interplay of superconductivity and magnetism in nanoscale structures has attracted considerable attention in recent years due to the exciting new physics created by the competition of these antagonistic ordering phenomena, and the prospect of exploiting this competition for superconducting spintronics devices. While much of the attention is focused on spin-polarized supercurrents created by the triplet proximity effect, the recent discovery of long range quasiparticle spin transport in high-field superconductors has rekindled interest in spin-dependent nonequilibrium properties of superconductors. In this review, the experimental situation on nonequilibrium spin injection into superconductors is discussed, and open questions and possible future directions of the field are outlined.
EAM Analysis of the Lattice Parameter Effect in Order-Disorder Transformation
Institute of Scientific and Technical Information of China (English)
Timothée Nsongoa; Guoliang CHEN; Xiaodong NI
2001-01-01
The embedded atom method was used to theoretically analyze the effect of the lattice parameter variation on the order-disorder transformation in binary alloys. The simple model was considered in which the configuration energy E as function of the lattice parameter a and the long-range order parameter σ was given by Taylor expansion at σ=0. The following results were found for AB alloy, at T=0 K, the stable state exists in the completely ordered phase which was also found in the case of A3B or AB3 compounds .The order-disorder was found to be a secondorder transition. Only one kind of order-disorder was found for AB alloy. Three groups of order-disorder transformation can be observed for the A3B or AB3 compound. For the group Ⅰ when the temperature is below the critical temperature, the order-disorder is a first order transformation. For the group Ⅱ, the order-disorder transformation is a first order transition.For the group Ⅲ, the order-disorder transformation is found to be a second order transition.The lattice parameter variations have a significant effect on E2 coefficient, which is related to the ordering energy. These results are in a good agreement with those obtained by using EAM (embedded atom method) and CVM (cluster variation method) calculations.
Thermodynamic parameters of the first order in low-concentration binary alloys
Bol'shov, L. A.; Korneichuk, S. K.
2015-12-01
Thermodynamic parameters of the first order (Wagner interaction parameter ɛ 2 (2) , enthalpy, and entropy parameter σ 2 (2) ) in low-concentration liquid binary alloys are considered. The values of these parameters for 32 binary systems are estimated from experimental data. A system of classification is proposed for the obtained data. These data are compared to similar data for aqueous solutions of nonelectrolytes. A qualitative explanation of the obtained differences is given.
Belkhatir, Zehor
2017-05-31
This paper proposes a two-stage estimation algorithm to solve the problem of joint estimation of the parameters and the fractional differentiation orders of a linear continuous-time fractional system with non-commensurate orders. The proposed algorithm combines the modulating functions and the first-order Newton methods. Sufficient conditions ensuring the convergence of the method are provided. An error analysis in the discrete case is performed. Moreover, the method is extended to the joint estimation of smooth unknown input and fractional differentiation orders. The performance of the proposed approach is illustrated with different numerical examples. Furthermore, a potential application of the algorithm is proposed which consists in the estimation of the differentiation orders of a fractional neurovascular model along with the neural activity considered as input for this model.
Bulk superconductivity in Type II superconductors near the second critical field
DEFF Research Database (Denmark)
Fournais, Søren; Helffer, Bernard
2010-01-01
We consider superconductors of Type II near the transition from the ‘bulk superconducting’ to the ‘surface superconducting’ state. We prove a new L∞ estimate on the order parameter in the bulk, i.e. away from the boundary. This solves an open problem posed by Aftalion and Serfaty [AS].......We consider superconductors of Type II near the transition from the ‘bulk superconducting’ to the ‘surface superconducting’ state. We prove a new L∞ estimate on the order parameter in the bulk, i.e. away from the boundary. This solves an open problem posed by Aftalion and Serfaty [AS]....
Energy Technology Data Exchange (ETDEWEB)
Aksu, E. [Ankara Nuclear Research and Training Center, TAEA, 06100 Besevler-Ankara (Turkey)]. E-mail: eaksu@taek.gov.tr; Gencer, A. [Ankara University, Department of Physics, Faculty of Science, 06100 Besevler-Ankara (Turkey); Calinli, N. [Ankara Nuclear Research and Training Center, TAEA, 06100 Besevler-Ankara (Turkey); Koralay, H. [Ankara Nuclear Research and Training Center, TAEA, 06100 Besevler-Ankara (Turkey); Cavdar, S. [Ankara Nuclear Research and Training Center, TAEA, 06100 Besevler-Ankara (Turkey)
2005-06-15
The fundamental and high-order harmonic susceptibility, {chi}{sub n}={chi}{sub n}{sup '}+i{chi}{sub n}{sup '}' (n=1,3,5 and 7) were measured as a function of temperature (50-130K), frequencies (11 and 140Hz) and AC magnetic field amplitude (80-1280A/m) on a bulk Tl{sub 2}Ba{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} high-T{sub c} superconductor prepared by the solid-state reaction method. They exhibit dependence on the amplitude of the AC field. The observed dependences were analyzed by using the Bean Model. We have obtained an empirical function for the penetration field H{sub p}=H{sub {alpha}}(1-t){sup {beta}}, with t=T/T{sub cb}. Best fitting to data was obtained with parameters H{sub {alpha}}{approx}2.6x10{sup 4}A/m and {beta}=1.74. The experimental values agree well with the theoretical findings. The XRD pattern, resistivity measurement and SEM analysis were also carried out to characterize the sample.
Fast recovery of the stripe magnetic order by Mn/Fe substitution in F-doped LaFeAsO superconductors
Moroni, M.; Carretta, P.; Allodi, G.; De Renzi, R.; Gastiasoro, M. N.; Andersen, B. M.; Materne, P.; Klauss, H.-H.; Kobayashi, Y.; Sato, M.; Sanna, S.
2017-05-01
75As nuclear magnetic (NMR) and quadrupolar (NQR) resonance were used, together with Mössbauer spectroscopy, to investigate the magnetic state induced by Mn for Fe substitutions in F-doped LaFe1 -xMnxAsO superconductors. The results show that 0.5% of Mn doping is enough to suppress the superconducting transition temperature Tc from 27 K to zero and to recover the magnetic structure observed in the parent undoped LaFeAsO. Also the tetragonal to orthorhombic transition of the parent compound is recovered by introducing Mn, as evidenced by a sharp drop of the NQR frequency. The NQR spectra also show that a charge localization process is at play in the system. Theoretical calculations using a realistic five-band model show that correlation-enhanced RKKY exchange interactions between nearby Mn ions stabilize the observed stripe magnetic order. These results give compelling evidence that F-doped LaFeAsO is a strongly correlated electron system at the verge of an electronic instability.
Gate-tuned Superconductor-Insulator transition in (Li,Fe)OHFeSe
Lei, B; Xiang, Z. J.; Lu, X. F.; Wang, N. Z.; Chang, J. R.; Shang, C.; Luo, X. G.; Wu, T.; Z. Sun; Chen, X. H.
2015-01-01
The antiferromagnetic(AFM) insulator-superconductor transition has been always a center of interest in the underlying physics of unconventional superconductors. The quantum phase transition between Mott insulator with AFM and superconductor can be induced by doping charge carriers in high-Tc cuprate superconductors. For the best characterized organic superconductors of k-(BEDT-TTF)2X (X=anion), a first order transition between AFM insulator and superconductor can be tuned by applied external ...
Electronic transport in unconventional superconductors
Energy Technology Data Exchange (ETDEWEB)
Graf, M.J.
1998-12-31
The author investigates the electron transport coefficients in unconventional superconductors at low temperatures, where charge and heat transport are dominated by electron scattering from random lattice defects. He discusses the features of the pairing symmetry, Fermi surface, and excitation spectrum which are reflected in the low temperature heat transport. For temperatures {kappa}{sub B}T {approx_lt} {gamma} {much_lt} {Delta}{sub 0}, where {gamma} is the bandwidth of impurity induced Andreev states, certain eigenvalues become universal, i.e., independent of the impurity concentration and phase shift. Deep in the superconducting phase ({kappa}{sub B}T {approx_lt} {gamma}) the Wiedemann-Franz law, with Sommerfeld`s value of the Lorenz number, is recovered. He compares the results for theoretical models of unconventional superconductivity in high-{Tc} and heavy fermion superconductors with experiment. The findings show that impurities are a sensitive probe of the low-energy excitation spectrum, and that the zero-temperature limit of the transport coefficients provides an important test of the order parameter symmetry.
Parameter identification of fractional order linear system based on Haar wavelet operational matrix.
Li, Yuanlu; Meng, Xiao; Zheng, Bochao; Ding, Yaqing
2015-11-01
Fractional order systems can be more adequate for the description of dynamical systems than integer order models, however, how to obtain fractional order models are still actively exploring. In this paper, an identification method for fractional order linear system was proposed. This is a method based on input-output data in time domain. The input and output signals are represented by Haar wavelet, and then fractional order systems described by fractional order differential equations are transformed into fractional order integral equations. Taking use of the Haar wavelet operational matrix of the fractional order integration, the fractional order linear system can easily be converted into a system of algebraic equation. Finally, the parameters of the fractional order system are determined by minimizing the errors between the output of the real system and that of the identified system. Numerical simulations, involving integral and fractional order systems, confirm the efficiency of the above methodology.
A Local Order Parameter-Based Method for Simulation of Free Energy Barriers in Crystal Nucleation.
Eslami, Hossein; Khanjari, Neda; Müller-Plathe, Florian
2017-03-14
While global order parameters have been widely used as reaction coordinates in nucleation and crystallization studies, their use in nucleation studies is claimed to have a serious drawback. In this work, a local order parameter is introduced as a local reaction coordinate to drive the simulation from the liquid phase to the solid phase and vice versa. This local order parameter holds information regarding the order in the first- and second-shell neighbors of a particle and has different well-defined values for local crystallites and disordered neighborhoods but is insensitive to the type of the crystal structure. The order parameter is employed in metadynamics simulations to calculate the solid-liquid phase equilibria and free energy barrier to nucleation. Our results for repulsive soft spheres and the Lennard-Jones potential, LJ(12-6), reveal better-resolved solid and liquid basins compared with the case in which a global order parameter is used. It is also shown that the configuration space is sampled more efficiently in the present method, allowing a more accurate calculation of the free energy barrier and the solid-liquid interfacial free energy. Another feature of the present local order parameter-based method is that it is possible to apply the bias potential to regions of interest in the order parameter space, for example, on the largest nucleus in the case of nucleation studies. In the present scheme for metadynamics simulation of the nucleation in supercooled LJ(12-6) particles, unlike the cases in which global order parameters are employed, there is no need to have an estimate of the size of the critical nucleus and to refine the results with the results of umbrella sampling simulations. The barrier heights and the nucleation pathway obtained from this method agree very well with the results of former umbrella sampling simulations.
Tilt order parameters, polarity, and inversion phenomena in smectic liquid crystals.
Karahaliou, P K; Vanakaras, A G; Photinos, D J
2002-03-01
The order parameters for the phenomenological description of the smectic-A to smectic-C phase transition are formulated on the basis of molecular symmetry and structure. It is shown that, unless the long molecular axis is an axis of twofold or higher rotational symmetry, the ordering of the molecules in the smectic-C phase gives rise to more than one tilt order parameter and to one or more polar order parameters. The latter describe the indigenous polarity of the smectic-C phase, which is not related to molecular chirality but underlies the appearance of spontaneous polarization in chiral smectics. A phenomenological theory of the phase transition is formulated by means of a Landau expansion in two tilt order parameters (primary and secondary) and an indigenous polarity order parameter. The coupling among these order parameters determines the possibility of sign inversions in the temperature dependence of the spontaneous polarization and of the helical pitch observed experimentally for some chiral smectic-C* materials. The molecular interpretation of the inversion phenomena is examined in the light of this formulation.
Alff, L; Krockenberger, Y; Welter, B; Schonecke, M; Gross, R; Manske, D; Naito, M
2003-04-17
The ground state of superconductors is characterized by the long-range order of condensed Cooper pairs: this is the only order present in conventional superconductors. The high-transition-temperature (high-T(c)) superconductors, in contrast, exhibit more complex phase behaviour, which might indicate the presence of other competing ground states. For example, the pseudogap--a suppression of the accessible electronic states at the Fermi level in the normal state of high-T(c) superconductors-has been interpreted as either a precursor to superconductivity or as tracer of a nearby ground state that can be separated from the superconducting state by a quantum critical point. Here we report the existence of a second order parameter hidden within the superconducting phase of the underdoped (electron-doped) high-T(c) superconductor Pr2-xCe(x)CuO4-y and the newly synthesized electron-doped material La2-xCe(x)CuO4-y (ref. 8). The existence of a pseudogap when superconductivity is suppressed excludes precursor superconductivity as its origin. Our observation is consistent with the presence of a (quantum) phase transition at T = 0, which may be a key to understanding high-T(c) superconductivity. This supports the picture that the physics of high-T(c) superconductors is determined by the interplay between competing and coexisting ground states.
Allais, Arnaud; Schmidt, Frank; Marzahn, Erik
2010-05-04
A superconductor cable is described, having a superconductive flexible cable core (1) , which is laid in a cryostat (2, 3, 4), in which the cable core (1) runs in the cryostat (2, 3, 4) in the form of a wave or helix at room temperature.
Self-assembled fluids with order-parameter- dependent mobility: The large- limit
Indian Academy of Sciences (India)
N P Rapapa; N B Maliehe
2006-08-01
The effect of the order-parameter-dependent mobility, $ (\\vec{}) ∝ \\left( 1 - g \\dfrac{\\vec{}^{2}}{N} \\right)^{}$, on phase-ordering dynamics of self-assembled fluids is studied analytically within the large- limit. The study is for quenching from an uncorrelated high temperature state into the Lifshitz line within the microemulsion phase. In the later stage of the ordering process, the structure factor exhibits multiscaling behavior with characteristic length scale (/ ln )1/2(2+3). The order-parameter-dependent mobility is found to slow down the rate of coarsening.
Energy Technology Data Exchange (ETDEWEB)
Xu Longdao; Gao Yuliang
1985-09-01
Two variational parameters are included in the most probable constrained effective wave function with the accurate Hamiltonian remained. The third critical field which coincides with the result in paper (1) has been easily obtained through the variational principle.
Ordering of two small parameters in the shallow water wave problem
Burde, Georgy I
2013-01-01
The classical problem of irrotational long waves on the surface of a shallow layer of an ideal fluid moving under the influence of gravity as well as surface tension is considered. A systematic procedure for deriving an equation for surface elevation for a prescribed relation between the orders of the two expansion parameters, the amplitude parameter $\\alpha$ and the long wavelength (or shallowness) parameter $\\beta$, is developed. Unlike the heuristic approaches found in the literature, when modifications are made in the equation for surface elevation itself, the procedure starts from the consistently truncated asymptotic expansions for unidirectional waves, a counterpart of the Boussinesq system of equations for the surface elevation and the bottom velocity, from which the leading order and higher order equations for the surface elevation can be obtained by iterations. The relations between the orders of the two small parameters are taken in the form $\\beta=O(\\alpha^n)$ and $\\alpha=O(\\beta^m)$ with $n$ and ...
Chromonic nematic phase and scalar order parameter of indanthrone derivative with ionic additives
Boiko O.P.; Vasyuta R.M.; Semenyshyn O.M.; Nastishin Yu.A.; Nazarenko V.G.
2008-01-01
We investigate influence of different ionic additives on the phase behaviour and scalar order parameter of lyotropic chromonic nematic liquid crystals formed by the molecules representing derivatives of indanthrone. KI, (NH4)2SO4 and NaCl salts increase biphasic nematic region on the temperature-concentration phase diagram, whereas the scalar orientational order parameter is hardly sensitive to their presence. We suggest that these changes are attributed to increase in the ag-gregate length a...
Order parameters of liquid crystal on the rubbing surfaces of alignment layers
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
Liquid crystal (LC) alignment is most important in LC devices. In this paper, we quantitatively analyze the LC scalar order parameters on the rubbed surface of an alignment layer. Careful measurement of dichroic infrared absorbance is performed. The result gives the evidence that the order parameter of LC just on the rubbed alignment film is only 1/3-1/2 that in the LC bulk.
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
Based on pair potential, the Bragg Williams (B-W) model is modified to take into account the effect of the lattice parameter on theoretical order-disorder transformation analysis. The main purpose of this work is to understand the basic aspects of this effect and related reasonable model on order-disorder transformation. In the present approach, the configuration free energy is chosen as function of the lattice parameter and the long-range order. This energy is calculated through Taylor's expansion, starting from the disordered state. It was found that the configuration free energy has been strongly modified when the lattice parameter is taken into account. It was also found only one type of order-disorder transformation exists in AB alloy and three kinds of order-disorder transformations for non-equiatomic alloy system such as A3B alloy. This result is in agreement with experiments.
Energy Technology Data Exchange (ETDEWEB)
Blackburn, E
2005-12-15
In this thesis, multiple order parameters originating in the same electronic system are studied. The multi-k magnetic structures, where more than one propagation wavevector, k, is observed in the same volume, are considered as prototypical models. The effect of this structure on the elastic and inelastic response is studied. In cubic 3-k uranium rock-salts, unexpected elastic diffraction events were observed at positions in reciprocal space where the structure factor should have been zero. These diffraction peaks are identified with correlations between the (orthogonal) magnetic order parameters. The 3-k structure also affects the observed dynamics; the spin-wave fluctuations in uranium dioxide as observed by inelastic neutron polarization analysis can only be explained on the basis of a 3-k structure. In the antiferromagnetic superconductor UPd{sub 2}Al{sub 3} the magnetic order and the super-conducting state coexist, and are apparently generated by the same heavy fermions. The effect of an external magnetic field on both the normal and superconducting states is examined. In the normal state, the compound displays Fermi-liquid-like behaviour. The inelastic neutron response is strongly renormalized on entering the superconducting state, and high-precision measurements of the low-energy transfer part of this response confirm that the superconducting energy gap has the same symmetry as the antiferromagnetic lattice. (author)
Ekin, Jack W.; Cheggour, Najib; Goodrich, Loren; Splett, Jolene; Bordini, Bernardo; Richter, David
2016-12-01
A scaling study of several thousand Nb3Sn critical-current (I c) measurements is used to derive the Extrapolative Scaling Expression (ESE), a relation that can quickly and accurately extrapolate limited datasets to obtain full three-dimensional dependences of I c on magnetic field (B), temperature (T), and mechanical strain (ɛ). The relation has the advantage of being easy to implement, and offers significant savings in sample characterization time and a useful tool for magnet design. Thorough data-based analysis of the general parameterization of the Unified Scaling Law (USL) shows the existence of three universal scaling constants for practical Nb3Sn conductors. The study also identifies the scaling parameters that are conductor specific and need to be fitted to each conductor. This investigation includes two new, rare, and very large I c(B,T,ɛ) datasets (each with nearly a thousand I c measurements spanning magnetic fields from 1 to 16 T, temperatures from ˜2.26 to 14 K, and intrinsic strains from -1.1% to +0.3%). The results are summarized in terms of the general USL parameters given in table 3 of Part 1 (Ekin J W 2010 Supercond. Sci. Technol. 23 083001) of this series of articles. The scaling constants determined for practical Nb3Sn conductors are: the upper-critical-field temperature parameter v = 1.50 ± 0.04 the cross-link parameter w = 3.0 ± 0.3 and the strain curvature parameter u = 1.7 ± 0.1 (from equation (29) for b c2(ɛ) in Part 1). These constants and required fitting parameters result in the ESE relation, given by I c ( B , T , ɛ ) B = C [ b c 2 ( ɛ ) ] s ( 1 - t 1.5 ) η - μ ( 1 - t 2 ) μ b p ( 1 - b ) q with reduced magnetic field b ≡ B/B c2*(T,ɛ) and reduced temperature t ≡ T/T c*(ɛ), where: B c 2 * ( T , ɛ ) = B c 2 * ( 0 , 0 ) ( 1 - t 1.5 ) b c 2 ( ɛ ) T c * ( ɛ ) = T c * ( 0 ) [ b c 2 ( ɛ ) ] 1/3 and fitting parameters: C, B c2*(0,0), T c*(0), s, either η or μ (but not both), plus the parameters in the strain function b c2
Muon spin relaxation and Moessbauer studies of iron pnictide superconductors
Energy Technology Data Exchange (ETDEWEB)
Klauss, Hans-Henning; Maeter, H.; Dellmann, T. [Technische Universitaet, Dresden (Germany); Luetkens, H.; Khasanov, R.; Amato, A. [PSI, Villigen (Switzerland); Pashkevich, Y. [Donetsk Phystech, NASU (Ukraine); Hess, C.; Klingeler, R.; Buechner, B. [IFW, Dresden (Germany); Leithe-Jasper, A.; Rosner, H.; Geibel, C.; Schnelle, W. [MPI-CPfS, Dresden (Germany); Braden, M. [Universitaet Koeln (Germany); Litterst, J. [Technische Universitaet, Braunschweig (Germany)
2010-07-01
We have determined the electronic phase diagrams and order parameters of ReO{sub 1-x}F{sub x}FeAs and (Sr,Eu)Fe{sub 2-x}Co{sub x}As{sub 2} superconductors. The results prove an important role of the structural distortion for the SDW magnetism and reveal two gap multiband superconductivity. We examined the interplay of iron and rare earth magnetic order in ReO{sub 1-x}F{sub x}FeAs. The undoped compounds show different magnetic coupling strength of the rare earth ion to the antiferromagnetic iron layers ranging from independent order to strong polarization of the rare earth moments by the ordered iron. Finally, we present recent studies on (Ca,Sr,Ba,Eu)Fe{sub 2}As{sub 2} and (Fe{sub 2}As{sub 2})(Sr{sub 4}T{sub 2}O{sub 6})based pnictide superconductors.
BAYESIAN PARAMETER ESTIMATION IN A MIXED-ORDER MODEL OF BOD DECAY. (U915590)
We describe a generalized version of the BOD decay model in which the reaction is allowed to assume an order other than one. This is accomplished by making the exponent on BOD concentration a free parameter to be determined by the data. This "mixed-order" model may be ...
A first-order Lyapunov robustness method for linear systems with uncertain parameters
Leal, M. A.; Gibson, J. S.
1990-01-01
A method for stability-robustness analysis based on a quadratic Liapunov function that varies linearly with uncertainty parameters is derived. Linear time-invariant systems with structured uncertainties are discussed. The Liapunov function is optimized numerically to maximize the robustness region in parameter space. Numerical results are given for four examples in which the first-order method is compared to previous Liapunov methods. While the zero-order method is slightly better than the first-order method for one example, the first-order method is clearly superior in the other three (more realistic) examples. The first-order method is especially superior for the active control of flexible structures, where robustness with respect to (1) unmodeled coupling between modeled modes and (2) unmodeled modes is important. For such applications, the first-order method is much better at detecting the increased robustness associated with increased separation between frequencies.
A first-order Lyapunov robustness method for linear systems with uncertain parameters
Leal, M. A.; Gibson, J. S.
1990-01-01
A method for stability-robustness analysis based on a quadratic Liapunov function that varies linearly with uncertainty parameters is derived. Linear time-invariant systems with structured uncertainties are discussed. The Liapunov function is optimized numerically to maximize the robustness region in parameter space. Numerical results are given for four examples in which the first-order method is compared to previous Liapunov methods. While the zero-order method is slightly better than the first-order method for one example, the first-order method is clearly superior in the other three (more realistic) examples. The first-order method is especially superior for the active control of flexible structures, where robustness with respect to (1) unmodeled coupling between modeled modes and (2) unmodeled modes is important. For such applications, the first-order method is much better at detecting the increased robustness associated with increased separation between frequencies.
Two kinds of magnetic gauge potentials due to coherent effect in two-gap superconductor
Shi, Xuguang
2016-10-01
Two-component Ginzburg-Landau model with one magnetic gauge potential can be used to describe the physical properties of two-gap superconductor. When the order parameters in two-gap superconductor have different phases, the gauge invariance will be destroyed. In order to preserve gauge invariance, two kinds of gauge potentials must be introduced. For seeking the origins of two kinds of gauge potentials, one suggests two kinds of order parameters are in the coherent state. Therefore, two different gauge potentials and masses of the order parameters arise through deducing the super-current of the coherent state. As a result, two different gauge potentials lead to different magnetic fields at the zero points of the order parameters. In other places, the gauge potentials have no contributions to the magnetic field. Moreover, the topological properties of two different gauge potentials are discussed in detail.
Xing, Rui-Qi; Classen, Laura; Khodas, Maxim; Chubukov, Andrey V.
2017-02-01
We report the results of a parquet renormalization group (RG) study of competing instabilities in the full 2D four-pocket, three-orbital low-energy model for iron-based superconductors. We derive and analyze the RG flow of the couplings, which describes all symmetry-allowed interactions between low-energy fermions. Despite that the number of the couplings is large, we argue that there are only two stable fixed trajectories of the RG flow and one weakly unstable fixed trajectory with a single unstable direction. Each fixed trajectory has a finite basin of attraction in the space of initial system parameters. On the stable trajectories, either interactions involving only dx z and dy z or only dx y orbital components on electron pockets dominate, while on the weakly unstable trajectory interactions involving dx z (dy z) and dx y orbital states on electron pockets remain comparable. The behavior along the two stable fixed trajectories has been analyzed earlier [Chubukov, Khodas, and Fernandes, Phys. Rev. X 6, 041045 (2016), 10.1103/PhysRevX.6.041045]. Here we focus on the system behavior along the weakly unstable trajectory and apply the results to FeSe. We find, based on the analysis of susceptibilities along this trajectory, that the leading instability upon lowering the temperature is towards a three-component d -wave orbital nematic order. Two components are the differences between fermionic densities on dx z and dy z orbitals on hole pockets and on electron pockets, and the third one is the difference between the densities of dx y orbitals on the two electron pockets. We argue that this order is consistent with the splitting of band degeneracies, observed in recent photoemission data on FeSe by Fedorov et al. [Sci. Rep. 6, 36834 (2016), 10.1038/srep36834].
Indian Academy of Sciences (India)
A D Thakur; S S Banerjee; M J Higgins; S Ramakrishnan; A K Grover
2006-01-01
We explore the effect of varying drive on metastability features exhibited by the vortex matter in single crystals of 2H-NbSe2 and CeRu2 with varying degree of random pinning. The metastable nature of vortex matter is reflected in the path dependence of the critical current density, which in turn is probed in a contact-less way via AC-susceptibility measurements. The sinusoidal AC magnetic field applied during AC susceptibility measurements appears to generate a driving force on the vortex matter. In a nascent pinned single crystal of 2H-NbSe2, where the peak effect (PE) pertaining to the order-disorder phenomenon is a sharp first-order-like transition, the supercooling feature below the peak temperature is easily wiped out by the reorganization caused by the AC driving force. In this paper, we elucidate the interplay between the drive and the pinning which can conspire to make the path-dependent AC-susceptibility response of different metastable vortex states appear identical. An optimal balance between the pinning and driving force is needed to view the metastability effects in typically weakly pinned specimen of low temperature superconductors. As one uses samples with larger pinning in order to differentiate the response of different metastable vortex states, one encounters a new phenomenon, viz., the second magnetization peak (SMP) anomaly prior to the PE. Supercooling/superheating can occur across both the PE and the SMP anomalies and both of these are known to display non-linear characteristics as well. Interplay between the path dependence in the critical current density and the non-linearity in the electromagnetic response determine the metastability effects seen in the first and the third harmonic response of the AC susceptibility across the temperature regions of the SMP and the PE. The limiting temperature above which metastability effects cease can be conveniently located in the third harmonic data, and the observed behavior can be rationalized within
Free energy of a Lovelock holographic superconductor
Aranguiz, Ligeia
2014-01-01
We study black hole solutions in Lanczos-Lovelock AdS gravity in d+1 dimensions coupled to nonlinear electrodynamics and a Stueckelberg scalar field. This class of theories with [d/2] gravitational coupling constants and two arbitrary functions that govern the matter interaction is used in the context of gauge/gravity duality to describe a high-temperature superconductor in d dimensions. We regularize the gravitational action and find the finite conserved quantities for a planar black hole with scalar hair. Then we derive the quantum statistical relation in the Euclidean sector of the theory, and obtain the exact formula for the free energy of the superconductor in the holographic quantum field theory. Our result is exact, analytic and it includes the effects of back reaction of the gravitational field. We further discuss on how this formula could be used to analyze second order phase transitions through the discontinuities of the free energy, and classify holographic superconductors in terms of the parameter...
Charge of a quasiparticle in a superconductor.
Ronen, Yuval; Cohen, Yonatan; Kang, Jung-Hyun; Haim, Arbel; Rieder, Maria-Theresa; Heiblum, Moty; Mahalu, Diana; Shtrikman, Hadas
2016-02-16
Nonlinear charge transport in superconductor-insulator-superconductor (SIS) Josephson junctions has a unique signature in the shuttled charge quantum between the two superconductors. In the zero-bias limit Cooper pairs, each with twice the electron charge, carry the Josephson current. An applied bias VSD leads to multiple Andreev reflections (MAR), which in the limit of weak tunneling probability should lead to integer multiples of the electron charge ne traversing the junction, with n integer larger than 2Δ/eVSD and Δ the superconducting order parameter. Exceptionally, just above the gap eVSD ≥ 2Δ, with Andreev reflections suppressed, one would expect the current to be carried by partitioned quasiparticles, each with energy-dependent charge, being a superposition of an electron and a hole. Using shot-noise measurements in an SIS junction induced in an InAs nanowire (with noise proportional to the partitioned charge), we first observed quantization of the partitioned charge q = e*/e = n, with n = 1-4, thus reaffirming the validity of our charge interpretation. Concentrating next on the bias region eVSD ~ 2Δ, we found a reproducible and clear dip in the extracted charge to q ~ 0.6, which, after excluding other possibilities, we attribute to the partitioned quasiparticle charge. Such dip is supported by numerical simulations of our SIS structure.
Gömöry, F
2014-01-01
Superconductors used in magnet technology could carry extreme currents because of their ability to keep the magnetic flux motionless. The dynamics of the magnetic flux interaction with superconductors is controlled by this property. The cases of electrical transport in a round wire and the magnetization of wires of various shapes (circular, elliptical, plate) in an external magnetic field are analysed. Resistance to the magnetic field penetration means that the field produced by the superconducting magnet is no longer proportional to the supplied current. It also leads to a dissipation of electromagnetic energy. In conductors with unequal transverse dimensions, such as flat cables, the orientation with respect to the magnetic field plays an essential role. A reduction of magnetization currents can be achieved by splitting the core of a superconducting wire into fine filaments; however, new kinds of electrical currents that couple the filaments consequently appear. Basic formulas allowing qualitative analyses ...
Kallin, Catherine; Berlinsky, John
2016-05-01
Chiral superconductivity is a striking quantum phenomenon in which an unconventional superconductor spontaneously develops an angular momentum and lowers its free energy by eliminating nodes in the gap. It is a topologically non-trivial state and, as such, exhibits distinctive topological modes at surfaces and defects. In this paper we discuss the current theory and experimental results on chiral superconductors, focusing on two of the best-studied systems, Sr2RuO4, which is thought to be a chiral triplet p-wave superconductor, and UPt3, which has two low-temperature superconducting phases (in zero magnetic field), the lower of which is believed to be chiral triplet f-wave. Other systems that may exhibit chiral superconductivity are also discussed. Key signatures of chiral superconductivity are surface currents and chiral Majorana modes, Majorana states in vortex cores, and the possibility of half-flux quantum vortices in the case of triplet pairing. Experimental evidence for chiral superconductivity from μSR, NMR, strain, polar Kerr effect and Josephson tunneling experiments are discussed.
Studies on Magnetization Technique of High Temperature Superconductors
大橋, 忠巌; 荻原, 宏康
1999-01-01
It is known that permanent magnets produce magnetic fields up to 1T. On the other hand, magnetized high temperature superconductors can be used as "super"-permanent magnets which produce magnetic fields higher than 1T, because superconductors can trap higher magnetic fluxes than usual permanent magnets. In order to magnetize a YBCO bulk superconductor, there are two ways; a field cooling (FC) method and a zero field cooling (ZFC) method. FC is the way of magnetizing the superconductor by appl...
Ginzburg-Landau theory of a holographic superconductor
Yin, Lei; Hou, Defu; Ren, Hai-cang
2015-01-01
The general Ginzburg-Landau (GL) formulation of a holographic superconductor is developed near the transition temperature in the probe limit for two kinds of conformal dimension. elow the transition temperature, T grand canonical ensemble and the canonical ensemble are derived and the gradient term is studied. Furthermore this scaling coefficient of the order parameter takes different values in the grand canonical ensemble and the canonical ensemble, suggesting the strong coupling nature of the boundary field theory of the superconductivity.
HQET at order 1/m. Pt. 1. Non-perturbative parameters in the quenched approximation
Energy Technology Data Exchange (ETDEWEB)
Blossier, Benoit [Paris XI Univ., 91 - Orsay (France). Lab. de Physique Theorique; Della Morte, Michele [Mainz Univ. (Germany). Inst. fuer Kernphysik; Garron, Nicolas [Universidad Autonoma de Madrid (Spain). Dept. Fisica Teorica y Inst. de Fisica Teorica UAM/CSIC; Edinburgh Univ. (United Kingdom). School of Physics and Astronomy - SUPA; Sommer, Rainer [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC
2010-01-15
We determine non-perturbatively the parameters of the lattice HQET Lagrangian and those of heavy-light axial-vector and vector currents in the quenched approximation. The HQET expansion includes terms of order 1/m{sub b}. Our results allow to compute, for example, the heavy-light spectrum and B-meson decay constants in the static approximation and to order 1/m{sub b} in HQET. The determination of the parameters is separated into universal and non-universal parts. The universal results can be used to determine the parameters for various discretizations. The computation reported in this paper uses the plaquette gauge action and the ''HYP1/2'' action for the b-quark described by HQET. The parameters of the currents also depend on the light-quark action, for which we choose non-perturbatively O(a)-improved Wilson fermions. (orig.)
Berezovska, Ganna; Mostarda, Stefano; Rao, Francesco
2012-01-01
Molecular simulations as well as single molecule experiments have been widely analyzed in terms order parameters, the latter representing candidate probes for the relevant degrees of freedom. Notwithstanding this approach is very intuitive, mounting evidence showed that such description is not accurate, leading to ambiguous definitions of states and wrong kinetics. To overcome these limitations a framework making use of order parameter fluctuations in conjunction with complex network analysis is investigated. Derived from recent advances in the analysis of single molecule time traces, this approach takes into account of the fluctuations around each time point to distinguish between states that have similar values of the order parameter but different dynamics. Snapshots with similar fluctuations are used as nodes of a transition network, the clusterization of which into states provides accurate Markov-State-Models of the system under study. Application of the methodology to theoretical models with a noisy orde...
Comparison between the continuum threshold and the Polyakov loop as deconfinement order parameters
Carlomagno, J P
2016-01-01
We study the relation between the continuum threshold as function of the temperature $s_0(T)$ within finite energy sum rules and the trace of the Polyakov loop $\\Phi$ in the framework of a nonlocal SU(2) chiral quark model, establishing a contact between both deconfinement order parameters at finite temperature $T$ and chemical potential $\\mu$. In our analysis, we also include the order parameter for the chiral symmetry restoration, the chiral quark condensate. We found that $s_0$ and $\\Phi$ providing us the same information for the deconfinement transition, both for the zero and finite chemical potential cases. At zero density, the critical temperatures for both quantities coincide exactly and, at finite $\\mu$ both order parameters provide evidence for the appearance of a quarkyonic phase.
Formulation of the third-order Grueneisen parameter at extreme compression
Energy Technology Data Exchange (ETDEWEB)
Shanker, J. [Department of Physics, Institute of Basic Sciences, Dr. B.R. Ambedkar University, Khandari Campus, Agra 282 002 (India); Sunil, K., E-mail: k.sunil.ibs@gmail.com [Department of Physics, Institute of Basic Sciences, Dr. B.R. Ambedkar University, Khandari Campus, Agra 282 002 (India); Sharma, B.S. [Department of Physics, Institute of Basic Sciences, Dr. B.R. Ambedkar University, Khandari Campus, Agra 282 002 (India)
2012-06-15
We present a direct method using the basic principles of calculus to derive the expression for the third-order Grueneisen parameter in terms of the pressure derivatives of bulk modulus at extreme compression. The derivation presented here does not depend on the assumptions regarding the values of free-volume parameter and its variation with pressure. The identities used in the present analysis are valid at extreme compression for all physically acceptable equations of state.
A SINGULARLY PERTURBED PROBLEM OF THIRD ORDER EQUATION WITH TWO PARAMETERS
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
A singularly perturbed problem of third order equation with two parameters is studied. Using singular perturbation method, the structure of asymptotic solutions to the problem is discussed under three possible cases of two related small parameters. The results obtained reveal the different structures and limit behaviors of the solutions in three different cases. And in comparison with the exact solutions of the autonomous equation they are relatively perfect.
Nearly best linear estimates of logistic parameters based on complete ordered statistics
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
Deals with the determination of the nearly best linear estimates of location and scale parameters of a logistic population, when both parameters are unknown, by introducing Bloms semi-empirical α, β-correction′into the asymptotic mean and covariance formulae with complete and ordered samples taken into consideration and various nearly best linear estimates established and points out the high efficiency of these estimators relative to the best linear unbiased estimators (BLUEs) and other linear estimators makes them useful in practice.
Shape phase transitions in nuclei:Effective order parameters and trajectories
Institute of Scientific and Technical Information of China (English)
无
2011-01-01
We analyze systematically the effective order parameters in nuclear shape phase transition both in experiments and in the interacting boson model. We find that energy ratios and B(E2) ratios can distinguish the first from the second-order phase transition in theory above a certain boson number N (about 50), but in experiments, only those quantities, such as E(L1+)/E(02+) and B(E2; (L+2)1 → L1)/B(E2; 21 → 01), etc., of which the monotonous transitional behavior in the second-order phase transition is broken in the first order phase transition independent of N, are qualified as the effective order parameters. By implementing the originally proposed effective order parameters and the new ones, we find that the isotones with neutron number Nn = 62 are a trajectory of the second order phase transition. In addition, we predict that the transitional behavior of isomer shifts of Xe, Ba isotopes and Nn = 62 isotones is approximately monotonous due to the finiteness of nuclear system.
Yang, Qingxia; Xu, Jun; Cao, Binggang; Li, Xiuqing
2017-01-01
Identification of internal parameters of lithium-ion batteries is a useful tool to evaluate battery performance, and requires an effective model and algorithm. Based on the least square genetic algorithm, a simplified fractional order impedance model for lithium-ion batteries and the corresponding parameter identification method were developed. The simplified model was derived from the analysis of the electrochemical impedance spectroscopy data and the transient response of lithium-ion batteries with different states of charge. In order to identify the parameters of the model, an equivalent tracking system was established, and the method of least square genetic algorithm was applied using the time-domain test data. Experiments and computer simulations were carried out to verify the effectiveness and accuracy of the proposed model and parameter identification method. Compared with a second-order resistance-capacitance (2-RC) model and recursive least squares method, small tracing voltage fluctuations were observed. The maximum battery voltage tracing error for the proposed model and parameter identification method is within 0.5%; this demonstrates the good performance of the model and the efficiency of the least square genetic algorithm to estimate the internal parameters of lithium-ion batteries. PMID:28212405
Yang, Qingxia; Xu, Jun; Cao, Binggang; Li, Xiuqing
2017-01-01
Identification of internal parameters of lithium-ion batteries is a useful tool to evaluate battery performance, and requires an effective model and algorithm. Based on the least square genetic algorithm, a simplified fractional order impedance model for lithium-ion batteries and the corresponding parameter identification method were developed. The simplified model was derived from the analysis of the electrochemical impedance spectroscopy data and the transient response of lithium-ion batteries with different states of charge. In order to identify the parameters of the model, an equivalent tracking system was established, and the method of least square genetic algorithm was applied using the time-domain test data. Experiments and computer simulations were carried out to verify the effectiveness and accuracy of the proposed model and parameter identification method. Compared with a second-order resistance-capacitance (2-RC) model and recursive least squares method, small tracing voltage fluctuations were observed. The maximum battery voltage tracing error for the proposed model and parameter identification method is within 0.5%; this demonstrates the good performance of the model and the efficiency of the least square genetic algorithm to estimate the internal parameters of lithium-ion batteries.
Bulk superconductivity in Type II superconductors near the second critical field
Fournais, S
2008-01-01
We consider superconductors of Type II near the transition from the 'bulk superconducting' to the 'surface superconducting' state. We prove a new $L^{\\infty}$ estimate on the order parameter in the bulk, i.e. away from the boundary. This solves an open problem posed by Aftalion and Serfaty.
Snyman, I.; Nazarov, Y.V.
2009-01-01
As a generic example of a voltage-driven superconducting structure, we study a short superconductor connected to normal leads by means of low transparency tunnel junctions with a voltage bias V between the leads. The superconducting order parameter Δ is to be determined self-consistently. We study t
On Mean-Field Theory of Quantum Phase Transition in Granular Superconductors
Simkin, M V
1996-01-01
In previous work on quantum phase transition in granular superconductors, where mean-field theory was used, an assumption was made that the order parameter as a function of the mean field is a convex up function. Though this is not always the case in phase transitions, this assumption must be verified, what is done in this article.
Diffusionless phase transition with two order parameters in spin-crossover solids
Energy Technology Data Exchange (ETDEWEB)
Gudyma, Iurii, E-mail: yugudyma@gmail.com; Ivashko, Victor [Department of General Physics, Chernivtsi National University, 58012 Chernivtsi (Ukraine); Linares, Jorge [Groupe d' Etude de la Matière Condensée (GEMAC), UMR 8635, CNRS, Université de Versailles Saint Quentin, 45 avenue des Etats-Unis, 78035 Versailles (France)
2014-11-07
The quantitative analysis of the interface boundary motion between high-spin and low-spin phases is presented. The nonlinear effect of the switching front rate on the temperature is shown. A compressible model of spin-crossover solid is studied in the framework of the Ising-like model with two-order parameters under statistical approach, where the effect of elastic strain on interaction integral is considered. These considerations led to examination of the relation between the order parameters during temperature changes. Starting from the phenomenological Hamiltonian, entropy has been derived using the mean field approach. Finally, the phase diagram, which characterizes the system, is numerically analyzed.
Diffusionless phase transition with two order parameters in spin-crossover solids
Gudyma, Iurii; Ivashko, Victor; Linares, Jorge
2014-11-01
The quantitative analysis of the interface boundary motion between high-spin and low-spin phases is presented. The nonlinear effect of the switching front rate on the temperature is shown. A compressible model of spin-crossover solid is studied in the framework of the Ising-like model with two-order parameters under statistical approach, where the effect of elastic strain on interaction integral is considered. These considerations led to examination of the relation between the order parameters during temperature changes. Starting from the phenomenological Hamiltonian, entropy has been derived using the mean field approach. Finally, the phase diagram, which characterizes the system, is numerically analyzed.
Interlocking order parameter fluctuations in structural transitions between adsorbed polymer phases.
Martins, Paulo H L; Bachmann, Michael
2016-01-21
By means of contact-density chain-growth simulations of a simple coarse-grained lattice model for a polymer grafted at a solid homogeneous substrate, we investigate the complementary behavior of the numbers of surface-monomer and monomer-monomer contacts under various solvent and thermal conditions. This pair of contact numbers represents an appropriate set of order parameters that enables the distinct discrimination of significantly different compact phases of polymer adsorption. Depending on the transition scenario, these order parameters can interlock in perfect cooperation. The analysis helps understand the transitions from compact filmlike adsorbed polymer conformations into layered morphologies and dissolved adsorbed structures, respectively, in more detail.
Ekin, Jack W; Goodrich, Loren; Splett, Jolene; Bordini, Bernardo; Richter, David
2016-01-01
A scaling study of several thousand Nb3Sn critical-current $(I_c)$ measurements is used to derive the Extrapolative Scaling Expression (ESE), a relation that can quickly and accurately extrapolate limited datasets to obtain full three-dimensional dependences of I c on magnetic field (B), temperature (T), and mechanical strain (ε). The relation has the advantage of being easy to implement, and offers significant savings in sample characterization time and a useful tool for magnet design. Thorough data-based analysis of the general parameterization of the Unified Scaling Law (USL) shows the existence of three universal scaling constants for practical Nb3Sn conductors. The study also identifies the scaling parameters that are conductor specific and need to be fitted to each conductor. This investigation includes two new, rare, and very large I c(B,T,ε) datasets (each with nearly a thousand I c measurements spanning magnetic fields from 1 to 16 T, temperatures from ~2.26 to 14 K, and intrinsic strains from –...
Orientational order parameter studies in two symmetric dimeric liquid crystals - an optical study
Pardhasaradhi, P.; Datta Prasad, P. V.; Madhavi Latha, D.; Pisipati, V. G. K. M.; Padmaja Rani, G.
2012-12-01
The optical technique developed by [W. Kuczynski, B. Zywucki, and J. Malecki, Determination of orientational order parameter in various liquid-crystalline phases, Mol. Cryst. Liq. Cryst. 381 (2002), pp. 1-19; B.J. Zywucki and W. Kuczynski, IEEE transactions on optical phenomena - The orientational order in nematic liquid crystals from birefringence measurements, Dielectr. Electr. Insul. 8 (2001), pp. 512-515] is fabricated and used to determine the orientational order parameter in two dimeric liquid crystalline compounds nematic and SmA phases of α,ω-bis(4-alkylanilinebenzylidene-4‧-oxy)alkane (m.OnO.m) homologous series. The compounds studied are 5.O8O.5 and 5.O10O.5 which exhibit nematic and SmA, and nematic phases, respectively. The orientational order parameter in both the phases of nematic and SmA phases of the compound one and the nematic phase of the compound two are obtained using the principle of Newton's rings which gives directly the birefringence, δn of the liquid crystal dimer. The merits of the technique used are presented over the conventional techniques for the determination of orientational order parameter. The results for the two compounds are compared with those values estimated from n e, n o and density using the two internal field models due to Vuks and Neugebauer applicable to nematic phase.
Parameter-invariant second-order variational problems in one variable
Muñoz Masqué, J.; Pozo Coronado, L. M.
1998-07-01
A projection is defined such that a second-order Lagrangian density factors through this projection modulo contact forms if and only if it is parameter invariant. In this way, a geometric interpretation of the parameter invariance conditions is obtained. The above projection is then used to prove the strict factorization of the Poincaré-Cartan form attached to a parameter-invariant variational problem thus leading us to state the Hamilton-Cartan formalism, the complete description of symmetries and regularity for such problems. The case of the squared curvature Lagrangian in the plane is analysed especially.
Huang, Yu; Guo, Feng; Li, Yongling; Liu, Yufeng
2015-01-01
Parameter estimation for fractional-order chaotic systems is an important issue in fractional-order chaotic control and synchronization and could be essentially formulated as a multidimensional optimization problem. A novel algorithm called quantum parallel particle swarm optimization (QPPSO) is proposed to solve the parameter estimation for fractional-order chaotic systems. The parallel characteristic of quantum computing is used in QPPSO. This characteristic increases the calculation of each generation exponentially. The behavior of particles in quantum space is restrained by the quantum evolution equation, which consists of the current rotation angle, individual optimal quantum rotation angle, and global optimal quantum rotation angle. Numerical simulation based on several typical fractional-order systems and comparisons with some typical existing algorithms show the effectiveness and efficiency of the proposed algorithm.
Directory of Open Access Journals (Sweden)
Yu Huang
Full Text Available Parameter estimation for fractional-order chaotic systems is an important issue in fractional-order chaotic control and synchronization and could be essentially formulated as a multidimensional optimization problem. A novel algorithm called quantum parallel particle swarm optimization (QPPSO is proposed to solve the parameter estimation for fractional-order chaotic systems. The parallel characteristic of quantum computing is used in QPPSO. This characteristic increases the calculation of each generation exponentially. The behavior of particles in quantum space is restrained by the quantum evolution equation, which consists of the current rotation angle, individual optimal quantum rotation angle, and global optimal quantum rotation angle. Numerical simulation based on several typical fractional-order systems and comparisons with some typical existing algorithms show the effectiveness and efficiency of the proposed algorithm.
Reduced-order modeling for cardiac electrophysiology. Application to parameter identification
Boulakia, Muriel; Gerbeau, Jean-Frédéric
2011-01-01
A reduced-order model based on Proper Orthogonal Decomposition (POD) is proposed for the bidomain equations of cardiac electrophysiology. Its accuracy is assessed through electrocardiograms in various configurations, including myocardium infarctions and long-time simulations. We show in particular that a restitution curve can efficiently be approximated by this approach. The reduced-order model is then used in an inverse problem solved by an evolutionary algorithm. Some attempts are presented to identify ionic parameters and infarction locations from synthetic ECGs.
Surface energy from order parameter profile: At the QCD phase transition
Frei, Z.; Patkos, A.
1989-01-01
The order parameter profile between coexisting confined and plasma regions at the quantum chromodynamic (QCD) phase transition is constructed. The dimensionless combination of the surface energy (Sigma) and the correlation length (Zeta) is estimated to be Sigma Zeta 3 approximately equals 0.8.
Minima of the fluctuations of the order parameter of global seismicity
Energy Technology Data Exchange (ETDEWEB)
Sarlis, N. V., E-mail: nsarlis@phys.uoa.gr; Christopoulos, S.-R. G.; Skordas, E. S. [Department of Solid State Physics and Solid Earth Physics Institute, Faculty of Physics, School of Science, National and Kapodistrian University of Athens, Panepistimiopolis, Zografos 157 84, Athens (Greece)
2015-06-15
It has been recently shown [N. V. Sarlis, Phys. Rev. E 84, 022101 (2011) and N. V. Sarlis and S.-R. G. Christopoulos, Chaos 22, 023123 (2012)] that earthquakes of magnitude M greater or equal to 7 are globally correlated. Such correlations were identified by studying the variance κ{sub 1} of natural time which has been proposed as an order parameter for seismicity. Here, we study the fluctuations of this order parameter using the Global Centroid Moment Tensor catalog for a magnitude threshold M{sub thres} = 5.0 and focus on its behavior before major earthquakes. Natural time analysis reveals that distinct minima of the fluctuations of the order parameter of seismicity appear within almost five and a half months on average before all major earthquakes of magnitude larger than 8.4. This phenomenon corroborates the recent finding [N. V. Sarlis et al., Proc. Natl. Acad. Sci. U.S.A. 110, 13734 (2013)] that similar minima of the seismicity order parameter fluctuations had preceded all major shallow earthquakes in Japan. Moreover, on the basis of these minima a statistically significant binary prediction method for earthquakes of magnitude larger than 8.4 with hit rate 100% and false alarm rate 6.67% is suggested.
SINGULARLY PERTURBED SOLUTION FOR THIRD ORDER NONLINEAR EQUATIONS WITH TWO PARAMETERS
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
A class of singularly perturbed boundary value problems for nonlinear equation of the third order with two parameters is considered. Under suitable conditions, using the theory of differential inequalities the existence and asymptotic behavior of the solution for boundary value problem are studied.
Solution of Seventh Order Boundary Value Problems by Variation of Parameters Method
Directory of Open Access Journals (Sweden)
Muzammal Iftikhar
2013-01-01
Full Text Available The induction motor behavior is represented by a fifth order differential equation model. Addition of a torque correction factor to this model accurately reproduces the transient torques and instantaneous real and reactive power flows of the full seventh order differential equation model. The aim of this study is to solve the seventh order boundary value problems and the variation of parameters method is used for this purpose. The approximate solutions of the problems are obtained in terms of rapidly convergent series. Two numerical examples have been given to illustrate the efficiency and implementation of the method.
Energy Technology Data Exchange (ETDEWEB)
Mazumdar, Chandan, E-mail: chandan.mazumdar@saha.ac.in [Saha Institute of Nuclear Physics, Kolkata 700064 (India); Nagarajan, R., E-mail: nagarajan@cbs.ac.in [University of Mumbai-Department of Atomic Energy Centre for Excellence in Basic Sciences, Santacruz (East), Mumbai 400 098 (India)
2015-07-15
Discovery of superconductivity in Y–Ni–B–C (T{sub c} ∼ 13 K) gave rise to the class of quaternary rare earth transition metal borocarbide superconductors. Before the discovery of Fe-based arsenide superconductors, this was the only class of materials containing a magnetic element, viz., Ni, yet exhibiting T{sub c}s > 5 K. Many members of this class have high T{sub c} (>10 K). T{sub c} of ∼23 K in Y–Pd–B–C system equaled the record T{sub c} known then, for intermetallics. Another feature that sets this class apart, is the occurrence of the exotic phenomenon of coexistence of superconductivity and magnetism at temperatures >5 K. Availability of large and electronically ‘clean’ single crystals and large Ginzburg-Landau (G–L) parameter, κ, have enabled detailed investigation of nonlocal effects of superconductivity. Intermediate value of upper critical field H{sub c2}, has enabled detailed investigation of superconductivity in this class, over the complete H–T plane. This has revealed details of anisotropy of superconductivity (e.g., a fourfold symmetry in the square a–b plane is found) and raised questions on the symmetry of order parameter. After a brief outline of the discovery, this article gives a summary of the materials and highlights of superconducting properties of this class of materials. Interesting results from studies, using various techniques, on YNi{sub 2}B{sub 2}C (T{sub c} ∼ 15 K) and LuNi{sub 2}B{sub 2}C (T{sub c} ∼ 16 K) are presented, including observation of unusual square vortex lattice and its structural transformation with H and T. With conduction electrons involved in the magnetic order of this class of superconductors, the interplay of superconductivity and magnetism is intimate in these magnetic superconductors. With T{sub c} (∼11 K) > T{sub N} (∼6 K) in ErNi{sub 2}B{sub 2}C, T{sub c} (∼8 K) = T{sub N} (∼8 K) in HoNi{sub 2}B{sub 2}C and T{sub c} (∼6 K) < T{sub N} (∼11 K) in DyNi{sub 2}B{sub 2}C, and
An alternative order-parameter for non-equilibrium generalized spin models on honeycomb lattices
Sastre, Francisco; Henkel, Malte
2016-04-01
An alternative definition for the order-parameter is proposed, for a family of non-equilibrium spin models with up-down symmetry on honeycomb lattices, and which depends on two parameters. In contrast to the usual definition, our proposal takes into account that each site of the lattice can be associated with a local temperature which depends on the local environment of each site. Using the generalised voter motel as a test case, we analyse the phase diagram and the critical exponents in the stationary state and compare the results of the standard order-parameter with the ones following from our new proposal, on the honeycomb lattice. The stationary phase transition is in the Ising universality class. Finite-size corrections are also studied and the Wegner exponent is estimated as ω =1.06(9).
Order parameters in the Landau–de Gennes theory – the static and dynamic scenarios
Majumdar, Apala
2011-02-17
We obtain quantitative estimates for the scalar order parameters of liquid crystal configurations in three-dimensional geometries, within the Landau-de Gennes framework. We consider both static equilibria and non-equilibrium dynamics and we include external fields and surface anchoring energies in our formulation. Using maximum principle-type arguments, we obtain explicit bounds for the corresponding scalar order parameters in both static and dynamic situations; these bounds are given in terms of the material-dependent thermotropic coefficients, electric field strength and surface anchoring coefficients. These bounds provide estimates for the degree of orientational ordering, quantify the competing effects of the different energetic contributions and can be used to test the accuracy of numerical simulations. © 2011 Taylor & Francis.
Generalized Holographic Superconductors with Higher Derivative Couplings
Dey, Anshuman; Sarkar, Tapobrata
2014-01-01
We introduce and study generalized holographic superconductors with higher derivative couplings between the field strength tensor and a complex scalar field, in four dimensional AdS black hole backgrounds. We study this theory in the probe limit, as well as with backreaction. There are multiple tuning parameters in the theory, and with two non-zero parameters, we show that the theory has a rich phase structure, and in particular, the transition from the normal to the superconducting phase can be tuned to be of first order or of second order within a window of one of these. This is established numerically as well as by computing the free energy of the boundary theory. We further present analytical results for the critical temperature of the model, and compare these with numerical analysis. Optical properties of this system are also studied numerically in the probe limit, and our results show evidence for negative refraction at low frequencies.
Eilenberger and Ginzburg-Landau models of the vortex core in high κ-superconductors
Belova, P.; Traito, K. B.; Lähderanta, E.
2011-08-01
Eilenberger approach to the cutoff parameter, ξh, of the field distribution in the mixed state of high κ-superconductors is developed. It is found that normalized value of ξh/ξc2 decreases both with temperature (due to Kramer-Pesch effect) and with impurity scattering rate Γ. Our theory explains μSR experiments in some low-field superconductors and different ξh values from the Ginzburg-Landau theory predictions in isotropic s-wave superconductors. A comparison with another characteristic length ξ1, describing the gradient of the order parameter in the vortex center, is done. They have very different Γ-dependences: monotonous suppression of ξh(B) values and crossing behavior of the ξ1(B) curves at various Γ. This is explained by the nonlocal effects in the Eilenberger theory.
Ngo, An T; Jakubek, Zygmunt J; Lu, Zhengfang; Joós, Béla; Morris, Catherine E; Johnston, Linda J
2014-11-01
Incorporating ethanol in lipid membranes leads to changes in bilayer structure, including the formation of an interdigitated phase. We have used polarized total-internal-reflection fluorescence microscopy (pTIRFM) to measure the order parameter for Texas Red DHPE incorporated in the ethanol-induced interdigitated phase (LβI) formed from ternary lipid mixtures comprising dioleoylphosphatidylcholine, cholesterol and egg sphingomyelin or dipalmitoylphosphatidylcholine. These lipid mixtures have 3 co-existing phases in the presence of ethanol: liquid-ordered, liquid-disordered and LβI. pTIRFM using Texas Red DHPE shows a reversal in fluorescence contrast between the LβI phase and the surrounding disordered phase with changes in the polarization angle. The contrast reversal is due to changes in the orientation of the dye, and provides a rapid method to identify the LβI phase. The measured order parameters for the LβI phase are consistent with a highly ordered membrane environment, similar to a gel phase. An acyl-chain labeled BODIPY-FL-PC was also tested for pTIRFM studies of ethanol-treated bilayers; however, this probe is less useful since the order parameters of the interdigitated phase are consistent with orientations that are close to random, either due to local membrane disorder or to a mixture of extended and looping conformations in which the fluorophore is localized in the polar headgroup region of the bilayer. In summary, we demonstrate that order parameter measurements via pTIRFM using Texas Red-DHPE can rapidly identify the interdigitated phase in supported bilayers. We anticipate that this technique will aid further research in the effects of alcohols and other additives on membranes.
Energy Technology Data Exchange (ETDEWEB)
Huxley, Andrew D.
2015-07-15
Highlights: • Review of ferromagnetic superconductors. • Covers UGe{sub 2}, URhGe and UCoGe and briefly other materials. • The focus is on experimental data and the pairing mechanism. - Abstract: The co-existence of superconductivity and ferromagnetism is of potential interest for spintronics and high magnetic field applications as well as a fascinating fundamental state of matter. The recent focus of research is on a family of ferromagnetic superconductors that are superconducting well below their Curie temperature, the first example of which was discovered in 2000. Although there is a ‘standard’ theoretical model for how magnetic pairing might bring about such a state, why it has only been seen in a few materials that at first sight appear to be very closely related has yet to be fully explained. This review covers the current state of knowledge of the magnetic and superconducting properties of these materials with emphasis on how they conform and differ from the behaviour expected from the ‘standard’ model and from each other.
Directory of Open Access Journals (Sweden)
Thresiamma Phlip
2005-01-01
Full Text Available The second- and third-order elastic constants of trigonal calcite have been obtained using the deformation theory. The strain energy density derived using the deformation theory is compared with the strain dependent lattice energy obtained from the elastic continuum model approximation to get the expressions for the second- and third-order elastic constants. Higher order elastic constants are a measure of the anharmonicity of a crystal lattice. The seven second-order elastic constants and the fourteen non-vanishing third-order elastic constants of trigonal calcite are obtained. The second-order elastic constants C11, which corresponds to the elastic stiffness along the basal plane of the crystal is greater than C33, which corresponds to the elastic stiffness tensor component along the c-axis of the crystal. First order pressure derivatives of the second-order elastic constants of calcite are evaluated. The higher order elastic constants are used to find the generalized Gruneisen parameters of the elastic waves propagating in different directions in calcite. The Brugger gammas are evaluated and the low temperature limit of the Gruneisen gamma is obtained. The results are compared with available reported values.
Holographic Multi-Band Superconductor
Huang, Ching-Yu; Maity, Debaprasad
2011-01-01
We propose a gravity dual for the holographic superconductor with multi-band carriers. Moreover, the currents of these carriers are unified under a global non-Abelian symmetry, which is dual to the bulk non-Abelian gauge symmetry. We study the phase diagram of our model, and find it qualitatively agrees with the one for the realistic 2-band superconductor, such as MgB2. We also evaluate the holographic conductivities and find the expected mean-field like behaviors in some cases. However, for a wide range of the parameter space, we also find the non-mean-field like behavior with negative conductivities.
Symmetry-Enforced Line Nodes in Unconventional Superconductors
Micklitz, T.; Norman, M. R.
2017-05-01
We classify line nodes in superconductors with strong spin-orbit interactions and time-reversal symmetry, where the latter may include nonprimitive translations in the magnetic Brillouin zone to account for coexistence with antiferromagnetic order. We find four possible combinations of irreducible representations of the order parameter on high-symmetry planes, two of which allow for line nodes in pseudospin-triplet pairs and two that exclude conventional fully gapped pseudospin-singlet pairs. We show that the former can only be realized in the presence of band-sticking degeneracies, and we verify their topological stability using arguments based on Clifford algebra extensions. Our classification exhausts all possible symmetry protected line nodes in the presence of spin-orbit coupling and a (generalized) time-reversal symmetry. Implications for existing nonsymmorphic and antiferromagnetic superconductors are discussed.
Polyakov-Nambu-Jona-Lasinio phase diagrams and quarkyonic phase from order parameters
Dutra, M; Delfino, A; Frederico, T; Malheiro, M
2013-01-01
We show that the magnitude of the order parameters in Polyakov-Nambu-Jona-Lasinio (PNJL) model, given by the quark condensate and the Polyakov loop, can be used as a criterium to clearly identify, without ambiguities, phases and boundaries of the strongly interacting matter, namely, the broken/restored chiral symmetry, and confinement/deconfinement regions. This structure is represented by the projection of the order parameters in the temperature-chemical potential plane, which allows a clear identification of pattern changes in the phase diagram. Such a criterium also enables the emergence of a quarkyonic phase even in the two-flavor system. We still show that this new phase diminishes due to the influence of an additional vector-type interaction in the PNJL phase diagrams, and is quite sensitive to the effect of the change of the $T_0$ parameter in the Polyakov potential. Finally, we show that the phases and boundaries constructed by our method indicate that the order parameters should be more strongly corr...
Energy Technology Data Exchange (ETDEWEB)
Materne, Philipp; Kamusella, Sirko; Sarkar, Rajib; Klauss, Hans-Henning [IFP, TU Dresden, 01062 Dresden (Germany); Harnagea, Luminita [IFW Dresden, Postfach 270016, 01171 Dresden (Germany); Wurmehl, Sabine; Buechner, Bernd [IFP, TU Dresden, 01062 Dresden (Germany); IFW Dresden, Postfach 270016, 01171 Dresden (Germany); Luetkens, Hubertus [PSI, 5232 Villigen (Switzerland); Timm, Carsten [ITP, TU Dresden, 01062 Dresden (Germany)
2016-07-01
We examined Ca{sub 1-x}Na{sub x}Fe{sub 2}As{sub 2} single crystals with x=0.00, 0.35, 0.50, and 0.67 by means of muon spin relaxation and Moessbauer spectroscopy to investigate the electronic and structural properties of these compounds. CaFe{sub 2}As{sub 2} is a semimetal, which shows spin density wave order below 167 K. By hole doping via Ca→Na substitution, the magnetic order is suppressed and superconductivity emerges with T{sub c}∼34K at optimal doping including a substitution level region where both phases coexist. We have studied the interplay of order parameters in this coexistence region and found nanoscopic coexistence of both order parameters. This is proven by a reduction of the magnetic order parameter by 7% below the superconducting transition temperature. We present a systematic correlation between the reduction of the magnetic order parameter and the ratio of the transition temperatures, T{sub c}/T{sub N}, for the 122 family of the iron-based superconductors.
Klassen, Joel; Wen, Xiao-Gang
2015-10-01
We study a chain of ferromagnetic sites, ie nano-particles, molecules or atoms, on a substrate of fully gapped superconductors. We find that under quite realistic conditions, the fermion-number-parity symmetry Z2f can spontaneously break. In other words, such a chain can realize a 1 + 1D fermionic topologically ordered state and the corresponding two-fold topological degeneracy on an open chain. Such a topological degeneracy becomes the so called Majorana zero mode in the non-interacting limit.
An Non-parametrical Approach to Estimate Location Parameters under Simple Order
Institute of Scientific and Technical Information of China (English)
孙旭
2005-01-01
This paper deals with estimating parameters under simple order when samples come from location models. Based on the idea of Hodges and Lehmann estimator (H-L estimator), a new approach to estimate parameters is proposed, which is difference with the classical L1 isotoaic regression and L2 isotonic regression. An algorithm to corupute estimators is given. Simulations by the Monte-Carlo method is applied to compare the likelihood functions with respect to L1 estimators and weighted isotonic H-L estimators.
NMR observation of quadrupolar order parameter in NpO{sub 2}
Energy Technology Data Exchange (ETDEWEB)
Tokunaga, Y. [ASRC, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan)]. E-mail: tokunaga.yo@jaea.go.jp; Aoki, D. [IMR Tohoku University, 2145-2 Narita Oarai Higashiibaraki Ibaraki 311-1313 (Japan); Homma, Y. [IMR Tohoku University, 2145-2 Narita Oarai Higashiibaraki Ibaraki 311-1313 (Japan); Kambe, S. [ASRC, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Sakai, H. [ASRC, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Ikeda, S. [ASRC, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Fujimoto, T. [ASRC, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Walstedt, R.E. [ASRC, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Yasuoka, H. [ASRC, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Shiokawa, Y. [IMR Tohoku University, 2145-2 Narita Oarai Higashiibaraki Ibaraki 311-1313 (Japan); Yamamoto, E. [ASRC, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Nakamura, A. [ASRC, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan)
2007-03-15
We report O17 NMR measurements in a single crystal of NpO{sub 2}. We have observed oscillatory spin-echo decay for certain O sites below T{sub 0}=26K. These spin-echo oscillations are well understood in terms of an axially symmetric electric field gradient created by a longitudinal triple-q antiferro-quadrupolar ordering. In the present work, we show that direct observation of the quadrupolar order parameters is possible by means of NMR.
Strain/order parameter coupling in the ferroelastic transition in dense SiO 2
Hemley, R. J.; Shu, J.; Carpenter, M. A.; Hu, J.; Mao, H. K.; Kingma, K. J.
2000-05-01
New high-pressure measurements reveal the coupling of strain and order parameter in the pressure-induced ferroelastic transition in dense SiO 2. Single-crystal X-ray diffraction measurements in quasi-hydrostatic media reversibly probe the spontaneous strain in the vicinity of the P4 2/ mnm→ Pnnm transition near 50 GPa, and indicate weak first-order character. A Landau model is developed that quantitatively relates all of the spectroscopic, elastic, structural, and thermodynamic data for the system. The elastic instability at the transition gives rise to anomalies in the Raman spectrum, which are expected to be a general feature of such pressure-induced transitions.
Modulating functions method for parameters estimation in the fifth order KdV equation
Asiri, Sharefa M.
2017-07-25
In this work, the modulating functions method is proposed for estimating coefficients in higher-order nonlinear partial differential equation which is the fifth order Kortewegde Vries (KdV) equation. The proposed method transforms the problem into a system of linear algebraic equations of the unknowns. The statistical properties of the modulating functions solution are described in this paper. In addition, guidelines for choosing the number of modulating functions, which is an important design parameter, are provided. The effectiveness and robustness of the proposed method are shown through numerical simulations in both noise-free and noisy cases.
Tuning non-equilibrium superconductors with lasers
Energy Technology Data Exchange (ETDEWEB)
Sentef, Michael A.; Kollath, Corinna [HISKP, University of Bonn, Nussallee 14-16, D-53115 Bonn (Germany); Kemper, Alexander F. [LBL Berkeley (United States); Georges, Antoine [Ecole Polytechnique and College de France, Paris (France)
2015-07-01
The study of the real-time dynamics dynamics of solids perturbed by short laser pulses is an intriguing opportunity of ultrafast materials science. Previous theoretical work on pump-probe photoemission spectroscopy revealed spectroscopic signatures of electron-boson coupling, which are reminiscent of features observed in recent pump-probe photoemission experiments on cuprate superconductors. Here we investigate the ordered state of electron-boson mediated superconductors subject to laser driving using Migdal-Eliashberg theory on the Kadanoff-Baym-Keldysh contour. We extract the characteristic time scales on which the non-equilibrium superconductor reacts to the perturbation, and their relation to the coupling boson and the underlying order.
Fallarino, Lorenzo; Berger, Andreas; Binek, Christian
2015-02-01
A Landau-theoretical approach is utilized to model the magnetic field induced reversal of the antiferromagnetic order parameter in thin films of magnetoelectric antiferromagnets. A key ingredient of this peculiar switching phenomenon is the presence of a robust spin polarized state at the surface of the antiferromagnetic films. Surface or boundary magnetization is symmetry allowed in magnetoelectric antiferromagnets and experimentally established for chromia thin films. It couples rigidly to the antiferromagnetic order parameter and its Zeeman energy creates a pathway to switch the antiferromagnet via magnetic field application. In the framework of a minimalist Landau free energy expansion, the temperature dependence of the switching field and the field dependence of the transition width are derived. Least-squares fits to magnetometry data of (0001 ) textured chromia thin films strongly support this model of the magnetic reversal mechanism.
Universal order parameters and quantum phase transitions: a finite-size approach.
Shi, Qian-Qian; Zhou, Huan-Qiang; Batchelor, Murray T
2015-01-08
We propose a method to construct universal order parameters for quantum phase transitions in many-body lattice systems. The method exploits the H-orthogonality of a few near-degenerate lowest states of the Hamiltonian describing a given finite-size system, which makes it possible to perform finite-size scaling and take full advantage of currently available numerical algorithms. An explicit connection is established between the fidelity per site between two H-orthogonal states and the energy gap between the ground state and low-lying excited states in the finite-size system. The physical information encoded in this gap arising from finite-size fluctuations clarifies the origin of the universal order parameter. We demonstrate the procedure for the one-dimensional quantum formulation of the q-state Potts model, for q = 2, 3, 4 and 5, as prototypical examples, using finite-size data obtained from the density matrix renormalization group algorithm.
Interacting N-vector order parameters with O(N) symmetry
Pelissetto, A; Pelissetto, Andrea; Vicari, Ettore
2004-01-01
We consider the critical behavior of the most general system of two N-vector order parameters that is O(N) invariant. We show that it may a have a multicritical transition with enlarged symmetry controlled by the chiral O(2)xO(N) fixed point. For N=2, 3, 4, if the system is also invariant under the exchange of the two order parameters and under independent parity transformations, one may observe a critical transition controlled by a fixed point belonging to the mn model. Also in this case there is a symmetry enlargement at the transition, the symmetry being [SO(N)+SO(N)]xC_2, where C_2 is the symmetry group of the square.
Dieleman, P; Klapwijk, T.M; Kovtonyuk, S.; van de Stadt, H.
1996-01-01
DC heating effects in superconductor-insulator-superconductor (SIS) tunnel junctions are studied by comparing junctions sandwiched between niobium or aluminum layers. With niobium a temperature rise of several Kelvin is observed, which is reduced by an order of magnitude by using aluminum. A simple
Dual Symmetry in Bent-Core Liquid Crystals and Unconventional Superconductors
Directory of Open Access Journals (Sweden)
Vladimir Lorman
2010-01-01
Full Text Available We extend the Landau theory of bent-core mesophases and d-wave high-Tc superconductors by considering additional secondary pseudo-proper order parameters. These systems exhibit a remarkable analogy relating their symmetry groups, lists of phases, and an infinite set of physical tensors. This analogy lies upon an internal dual structure shared by the two theories. We study the dual operator transforming rotations into translations in liquid crystals, and gauge symmetries into rotations in superconductors. It is used to classify the bent-core line defects, and to analyze the electronic gap structure of lamellar d-wave superfluids.
On the estimation of the structure parameter of a normal distribution of order p
Directory of Open Access Journals (Sweden)
Angelo M. Mineo
2007-10-01
Full Text Available In this paper we compare four different approaches to estimate the structure parameter of a normal distribution of order p (often called exponential power distribution. In particular, we have considered the maximization of the log-likelihood, of the profile log-likelihood, of the conditional profile log-likelihood and a method based on an index of kurtosis. The results of a simulation study seem to indicate the latter approach as the best.
Order parameter and barrier height in LaSrMnO cluster glasses
Energy Technology Data Exchange (ETDEWEB)
Okunev, V.D., E-mail: okunev@mail.fti.ac.donetsk.u [Donetsk Physico-Technical Institute, Ukrainian National Academy of Sciences, 83114 Donetsk (Ukraine); Samoilenko, Z.A. [Donetsk Physico-Technical Institute, Ukrainian National Academy of Sciences, 83114 Donetsk (Ukraine); Szymczak, H.; Lewandowski, S.J.; Szymczak, R. [Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw (Poland)
2009-10-19
Using the results of magnetization measurements of LaSrMnO cluster glasses, it is shown that the concentration of frozen magnetic moments exponentially decreases with the increase of temperature. We find that temperature dependence of the order parameter q, of the form q-q(T)approxT{sup -5/2}, is universal characteristic of the investigated cluster glasses and that the barrier height DELTA closely follows the quadratic relation to the temperature, DELTAapproxBT{sup 2}.
Higher Order Statistsics of Stokes Parameters in a Random Birefringent Medium
Said, Salem; Bihan, Nicolas le
2007-01-01
We present a new model for the propagation of polarized light in a random birefringent medium. This model is based on a decomposition of the higher order statistics of the reduced Stokes parameters along the irreducible representations of the rotation group. We show how this model allows a detailed description of the propagation, giving analytical expressions for the probability densities of the Mueller matrix and the Stokes vector throughout the propagation. It also allows an exact descripti...
Directory of Open Access Journals (Sweden)
Thresiamma Philip
2006-01-01
Full Text Available The second and third-order elastic constants and pressure derivatives of second- order elastic constants of trigonal LiNbO3 (lithium niobate have been obtained using the deformation theory. The strain energy density estimated using finite strain elasticity is compared with the strain dependent lattice energy density obtained from the elastic continuum model approximation. The second-order elastic constants and the non-vanishing third-order elastic constants along with the pressure derivatives of trigonal LiNbO3 are obtained in the present work. The second and third-order elastic constants are compared with available experimental values. The second-order elastic constant C11 which corresponds to the elastic stiffness along the basal plane of the crystal is less than C33 which corresponds to the elastic stiffness tensor component along the c-axis of the crystal. The pressure derivatives, dC'ij/dp obtained in the present work, indicate that trigonal LiNbO3 is compressible. The higher order elastic constants are used to find the generalized Gruneisen parameters of the elastic waves propagating in different directions in LiNbO3. The Brugger gammas are evaluated and the low temperature limit of the Gruneisen gamma is obtained. The results are compared with available reported values.
Huxley, Andrew D.
2015-07-01
The co-existence of superconductivity and ferromagnetism is of potential interest for spintronics and high magnetic field applications as well as a fascinating fundamental state of matter. The recent focus of research is on a family of ferromagnetic superconductors that are superconducting well below their Curie temperature, the first example of which was discovered in 2000. Although there is a 'standard' theoretical model for how magnetic pairing might bring about such a state, why it has only been seen in a few materials that at first sight appear to be very closely related has yet to be fully explained. This review covers the current state of knowledge of the magnetic and superconducting properties of these materials with emphasis on how they conform and differ from the behaviour expected from the 'standard' model and from each other.
Allais, Arnaud; Schmidt, Frank (Langenhagen, DE
2009-12-15
A superconductor cable includes a superconductive cable core (1) and a cryostat (2) enclosing the same. The cable core (1) has a superconductive conductor (3), an insulation (4) surrounding the same and a shielding (5) surrounding the insulation (4). A layer (3b) of a dielectric or semiconducting material is applied to a central element (3a) formed from a normally conducting material as a strand or tube and a layer (3c) of at least one wire or strip of superconductive material is placed helically on top. The central element (3a) and the layer (3c) are connected to each other in an electrically conducting manner at the ends of the cable core (1).
The structure and thermal parameters of ordered Cu65Fe10Pd25 ternary alloy
Ahmad, N.; Ziya, A. B.; Ibrahim, A.; Atiq, S.; Ahmad, S.; Bashir, F.
2015-03-01
Structural and thermal parameters have been studied in Cu65Fe10Pd25 alloy during order-disorder (O-D) transformation using differential scanning calorimetry (DSC) and high temperature X-ray diffraction (HTXRD). The results reveal that the Cu65Fe10Pd25 alloy undergoes an O-D transformation at Tc=797 K. The alloy shows L12 type ordering below Tc and has disordered face centered cubic (fcc) structure above Tc. The lattice parameter shows a positive deviation from Vegard's rule which may be related to the weakening of interatomic forces by the addition of Fe. The integrated intensity data obtained from the diffraction experiments was utilized to determine the coefficient of thermal expansion (α(T)), mean square amplitude of vibration (u2 bar (T)) and Debye temperatures (ΘD) during the O-D transformation. The abrupt change in the value of lattice parameter and coefficient of thermal expansion at Tc shows that the nature of O-D transition is first order. These results have been discussed by comparing them to those for Cu3Pd alloy.
The asymptotic behavior of the order parameter for the infinite-N Kuramoto model
Mirollo, Renato E.
2012-12-01
The Kuramoto model, first proposed in 1975, consists of a population of sinusoidally coupled oscillators with random natural frequencies. It has served as an idealized model for coupled oscillator systems in physics, chemistry, and biology. This paper addresses a long-standing problem about the infinite-N Kuramoto model, which is to describe the asymptotic behavior of the order parameter for this system. For coupling below a critical level, Kuramoto predicted that the order parameter would decay to 0. We use Fourier transform methods to prove that for general initial conditions, this decay is not exponential; in fact, exponential decay to 0 can only occur if the initial condition satisfies a fairly strong regularity condition that we describe. Our theorem is a partial converse to the recent results of Ott and Antonsen, who proved that for a special class of initial conditions, the order parameter does converge exponentially to its limiting value. Consequently, our result shows that the Ott-Antonsen ansatz does not completely capture all the possible asymptotic behavior in the full Kuramoto system.
Energy Technology Data Exchange (ETDEWEB)
Farkas, Balázs; Romano, Ilaria; Ceseracciu, Luca; Diaspro, Alberto [Department of Nanophysics, Istituto Italiano di Tecnologia (IIT), Via Morego 30, 16163 Genova (Italy); Brandi, Fernando [Department of Nanophysics, Istituto Italiano di Tecnologia (IIT), Via Morego 30, 16163 Genova (Italy); Istituto Nazionale di Ottica, Via Moruzzi 1, 56124 Pisa (Italy); Beke, Szabolcs, E-mail: szabolcs.beke@iit.it [Department of Nanophysics, Istituto Italiano di Tecnologia (IIT), Via Morego 30, 16163 Genova (Italy)
2015-10-01
The effects of various fabrication parameters of our Mask Projection Excimer Laser StereoLithography (MPExSL) system were investigated. We demonstrate that laser parameters directly change the physical properties (stiffness, thermal degradation, and height/thickness) of the poly(propylene fumarate) (PFF) scaffold structures. The tested parameters were the number of pulses, fluence per pulse and laser repetition rate. We present a four-order tuning capability of MPExSL-fabricated structures' stiffness without altering the resin composition or using cumbersome post-treatment procedures. Thermogravimetric analysis and differential scanning calorimetry confirmed this tuning capability. Prototype-segmented scaffold designs are presented and analyzed to further expand the concept and exploit this in situ stiffness tuning capability of the scaffolds for tissue engineering and regenerative medicine applications. - Highlights: • Facile stiffness control of scaffolds is beneficial in tissue engineering. • Four-order tuning capability of structures' stiffness is presented. • Scaffold's stiffness can be tuned in four orders (4 MPa–4 GPa). • All scaffolds have been fabricated from the same polymer resin in a broad stiffness range.
Unconventional Andreev reflection on the quasi-one-dimensional superconductor Nb2PdxSe5
Directory of Open Access Journals (Sweden)
Yeping Jiang
2016-04-01
Full Text Available We have carried out Andreev reflection measurements on point contact junctions between normal metal and single crystals of the quasi-one-dimensional (Q1D superconductor Nb2PdxSe5 (Tc ∼ 5.5 K. The contacts of the junctions were made on either self-cleaved surfaces or crystal edges so that the current flow directions in the two types of junctions are different, and the measurements provide a directional probe for the order parameter of the superconductor. Junctions made in both configurations show typical resistances of ∼20-30 Ohms, and a clear double-gap Andreev reflection feature was consistently observed at low temperatures. Quantitative analysis of the conductance spectrum based on a modified Blonder-Tinkham-Klapwijk (BTK model suggests that the amplitudes of two order parameters may have angular dependence in the a-c plane. Moreover, the gap to transition temperature ratio (Δ/TC for the larger gap is substantially higher than the BCS ratio expected for phonon-mediated s-wave superconductors. We argue that the anisotropic superconducting order parameter and the extremely large gap to transition temperature ratio may be associated with an unconventional pairing mechanism in the inorganic Q1D superconductor.
Evaluation of third order nonlinear optical parameters of CdS/PVA nanocomposite
Energy Technology Data Exchange (ETDEWEB)
Sharma, Mamta [Department of Physics, Center of Advanced Study in Physics, Panjab University, Chandigarh-160014 (India); Department of Applied Sciences (Physics), UIET, Panjab University, Chandigarh-160014 (India); Tripathi, S. K., E-mail: surya@pu.ac.in, E-mail: surya-tr@yahoo.com [Department of Physics, Center of Advanced Study in Physics, Panjab University, Chandigarh-160014 (India)
2015-06-24
CdS nanoparticles dispersed in PVA are prepared by Chemical method at room temperature. The nonlinear optical parameters such as nonlinear absorption (β), nonlinear refractive index (n{sub 2}) and nonlinear susceptibility (χ{sup 3}) are calculated for this sample by using Z-scan technique. CdS/PVA samples show the two photon absorption mechanism. The third order nonlinear susceptibility is calculated from n{sub 2} and β and is found to be of the order of 10{sup −7} – 10{sup −8} m{sup 2}/V{sup 2}. The larger value of third order nonlinear susceptibility is due to dielectric and quantum confinement effect.
Translating landfill methane generation parameters among first-order decay models.
Krause, Max J; Chickering, Giles W; Townsend, Timothy G
2016-11-01
Landfill gas (LFG) generation is predicted by a first-order decay (FOD) equation that incorporates two parameters: a methane generation potential (L0) and a methane generation rate (k). Because non-hazardous waste landfills may accept many types of waste streams, multiphase models have been developed in an attempt to more accurately predict methane generation from heterogeneous waste streams. The ability of a single-phase FOD model to predict methane generation using weighted-average methane generation parameters and tonnages translated from multiphase models was assessed in two exercises. In the first exercise, waste composition from four Danish landfills represented by low-biodegradable waste streams was modeled in the Afvalzorg Multiphase Model and methane generation was compared to the single-phase Intergovernmental Panel on Climate Change (IPCC) Waste Model and LandGEM. In the second exercise, waste composition represented by IPCC waste components was modeled in the multiphase IPCC and compared to single-phase LandGEM and Australia's Solid Waste Calculator (SWC). In both cases, weight-averaging of methane generation parameters from waste composition data in single-phase models was effective in predicting cumulative methane generation from -7% to +6% of the multiphase models. The results underscore the understanding that multiphase models will not necessarily improve LFG generation prediction because the uncertainty of the method rests largely within the input parameters. A unique method of calculating the methane generation rate constant by mass of anaerobically degradable carbon was presented (kc) and compared to existing methods, providing a better fit in 3 of 8 scenarios. Generally, single phase models with weighted-average inputs can accurately predict methane generation from multiple waste streams with varied characteristics; weighted averages should therefore be used instead of regional default values when comparing models. Translating multiphase first-order
2013-01-01
Identification of the unknown parameters and orders of fractional chaotic systems is of vital significance in controlling and synchronization of fractional-order chaotic systems. In this paper, a non-Lyapunov novel approach is proposed to estimate the unknown parameters and orders together for non-commensurate and hyper fractional chaotic systems based on cuckoo search oriented statistically the differential evolution (CSODE). Firstly, a novel Gao's mathematical model is put and analysed in t...
High-order harmonic generation from Rydberg states at fixed Keldysh parameter
Bleda, E A; Altun, Z; Topcu, T
2013-01-01
Because the commonly adopted viewpoint that the Keldysh parameter $\\gamma $ determines the dynamical regime in strong field physics has long been demonstrated to be misleading, one can ask what happens as relevant physical parameters, such as laser intensity and frequency, are varied while $\\gamma$ is kept fixed. We present results from our one- and fully three-dimensional quantum simulations of high-order harmonic generation (HHG) from various bound states of hydrogen with $n$ up to 40, where the laser intensities and the frequencies are scaled from those for $n=1$ in order to maintain a fixed Keldysh parameter $\\gamma$$< 1$ for all $n$. We find that as we increase $n$ while keeping $\\gamma $ fixed, the position of the cut-off scales in well defined manner. Moreover, a secondary plateau forms with a new cut-off, splitting the HHG plateau into two regions. First of these sub-plateaus is composed of lower harmonics, and has a higher yield than the second one. The latter extends up to the semiclassical $I_p+...
Order parameter symmetry in the superconducting ferromagnets UGe{sub 2} and URhGe
Energy Technology Data Exchange (ETDEWEB)
Huxley, A.; Mineev, V.; Grenier, B.; Ressouche, E.; Aoki, D.; Brison, J.P.; Flouquet, J
2004-03-15
In UGe{sub 2}, ZrZn{sub 2} and URhGe the co-existence of superconductivity and ferromagnetism appears to arise as a co-operative phenomena rather than as the overlap of two mutually competing orders. In all three compounds the magnetism is in intimate contact with the electronic degrees of freedom while the Curie temperatures are more than an order of magnitude higher than their critical temperatures for superconductivity. The most direct indication that the two orders are conjugate however is that the superconductivity and ferromagnetism are suppressed at the same critical pressure in both UGe{sub 2} and ZrZn{sub 2}. This has motivated the recent theoretical classification of the permitted superconducting order parameter symmetries for such states. In the following we will review the experimental evidence relevant to the identification of the actual symmetries. This is followed by a discussion of the possible states allowed theoretically. Finally we discuss briefly whether the magnetic order can indeed lead to an enhancement of the superconductivity.
Order parameter symmetry in the superconducting ferromagnets UGe 2 and URhGe
Huxley, A.; Mineev, V.; Grenier, B.; Ressouche, E.; Aoki, D.; Brison, J. P.; Flouquet, J.
2004-03-01
In UGe 2, ZrZn 2 and URhGe the co-existence of superconductivity and ferromagnetism appears to arise as a co-operative phenomena rather than as the overlap of two mutually competing orders. In all three compounds the magnetism is in intimate contact with the electronic degrees of freedom while the Curie temperatures are more than an order of magnitude higher than their critical temperatures for superconductivity. The most direct indication that the two orders are conjugate however is that the superconductivity and ferromagnetism are suppressed at the same critical pressure in both UGe 2 and ZrZn 2. This has motivated the recent theoretical classification of the permitted superconducting order parameter symmetries for such states. In the following we will review the experimental evidence relevant to the identification of the actual symmetries. This is followed by a discussion of the possible states allowed theoretically. Finally we discuss briefly whether the magnetic order can indeed lead to an enhancement of the superconductivity.
Critical behavior in the presence of an order-parameter pinning field
Parisen Toldin, Francesco; Assaad, Fakher F.; Wessel, Stefan
2017-01-01
We apply a recently advocated simulation scheme that employs a local order-parameter pinning field to study quantum critical phenomena in the two-dimensional square-lattice bilayer quantum Heisenberg model. Using a world-line quantum Monte Carlo approach, we show that for this model, the pinning-field approach allows to locate the quantum critical point over a wide range of pinning-field strengths. However, the identification of the quantum critical scaling behavior is found to be hard since the pinning field introduces strong corrections to scaling. In order to further elucidate the scaling behavior in this situation, we also study an improved classical lattice model in the three-dimensional Ising universality class by means of Monte Carlo simulations on large lattice sizes, which allow us to employ refined finite-size scaling considerations. A renormalization group analysis exhibits the presence of an important crossover effect from the zero pinning-field to a critical adsorption fixed point. In line with field-theoretical results, we find that at the critical adsorption fixed point the short-distance expansion of the order-parameter profile exhibits a new universal critical exponent. This result also implies the presence of slowly decaying scaling corrections, which we analyze in detail.
The dual quark condensate in local and nonlocal NJL models: An order parameter for deconfinement?
Directory of Open Access Journals (Sweden)
Federico Marquez
2015-07-01
Full Text Available We study the behavior of the dual quark condensate Σ1 in the Nambu–Jona-Lasinio (NJL model and its nonlocal variant. In quantum chromodynamics Σ1 can be related to the breaking of the center symmetry and is therefore an (approximate order parameter of confinement. The deconfinement transition is then signaled by a strong rise of Σ1 as a function of temperature. However, a similar behavior is also seen in the NJL model, which is known to have no confinement. Indeed, it was shown that in this model the rise of Σ1 is triggered by the chiral phase transition. In order to shed more light on this issue, we calculate Σ1 for several variants of the NJL model, some of which have been suggested to be confining. Switching between “confining” and “non-confining” models and parametrizations we find no qualitative difference in the behavior of Σ1, namely, it always rises in the region of the chiral phase transition. We conclude that without having established a relation to the center symmetry in a given model, Σ1 should not blindly be regarded as an order parameter of confinement.
Archer, Adam; Foxhall, Henry R; Allan, Neil L; Gunn, David S D; Harding, John H; Todorov, Ilian T; Travis, Karl P; Purton, John A
2014-12-01
We apply bond order and topological methods to the problem of analysing the results of radiation damage cascade simulations in ceramics. Both modified Steinhardt local order and connectivity topology analysis techniques provide results that are both translationally and rotationally invariant and which do not rely on a particular choice of a reference structure. We illustrate the methods with new analyses of molecular dynamics simulations of single cascades in the pyrochlores Gd(2)Ti(2)O(7) and Gd(2)Zr(2)O(7) similar to those reported previously (Todorov et al 2006 J. Phys.: Condens. Matter 18 2217). Results from the Steinhardt and topology analyses are consistent, while often providing complementary information, since the Steinhardt parameters are sensitive to changes in angular arrangement even when the overall topological connectivity is fixed. During the highly non-equilibrium conditions at the start of the cascade, both techniques reveal significant localized transient structural changes and variation in the cation connectivity. After a few picoseconds, the connectivity is largely fixed, while the order parameters continue to change. In the zirconate there is a shift to the anion disordered system while in the titanate there is substantial reversion and healing back to the parent pyrochlore structure.
Archer, Adam; Foxhall, Henry R.; Allan, Neil L.; Gunn, David S. D.; Harding, John H.; Todorov, Ilian T.; Travis, Karl P.; Purton, John A.
2014-12-01
We apply bond order and topological methods to the problem of analysing the results of radiation damage cascade simulations in ceramics. Both modified Steinhardt local order and connectivity topology analysis techniques provide results that are both translationally and rotationally invariant and which do not rely on a particular choice of a reference structure. We illustrate the methods with new analyses of molecular dynamics simulations of single cascades in the pyrochlores Gd2Ti2O7 and Gd2Zr2O7 similar to those reported previously (Todorov et al 2006 J. Phys.: Condens. Matter 18 2217). Results from the Steinhardt and topology analyses are consistent, while often providing complementary information, since the Steinhardt parameters are sensitive to changes in angular arrangement even when the overall topological connectivity is fixed. During the highly non-equilibrium conditions at the start of the cascade, both techniques reveal significant localized transient structural changes and variation in the cation connectivity. After a few picoseconds, the connectivity is largely fixed, while the order parameters continue to change. In the zirconate there is a shift to the anion disordered system while in the titanate there is substantial reversion and healing back to the parent pyrochlore structure.
Theoretical study of magnetoelectric effects in noncentrosymmetric and cuprate superconductors
Kashyap, Manoj K.
analytical and numerical solutions of the Ginzburg-Landau equations that reveal the spatial structure of this current as well as the associated component of the magnetic field for both a single vortex and in the vortex lattice phase near the upper critical field. The discovery of superconductivity in lanthanum barium copper oxide (LBCO) in 1986, was followed by yttrium barium copper oxide (YBCO) in 1987, commencing the era of high temperature superconductivity. The astonishingly rich phase diagram of cuprates includes the pseudogap phase which was earlier thought to be a precursor to superconductivity. Now signatures of broken symmetries have been seen, indicating a true phase transition. Pair density wave (PDW) order has earlier been proposed to account for superconducting correlations and charge density wave (CDW) order in pseudogap phase. There is evidence that the pseudogap phase in the cuprates also breaks time-reversal symmetry. Here we show that pair density wave (PDW) states give rise to a translational invariant nonsuperconducting order parameter that breaks time-reversal and parity symmetries, but preserves their product. This secondary order parameter has a different origin, but shares the same symmetry properties as a magnetoelectric loop current order that has been proposed earlier in the context of the cuprates to explain the appearance of intracell magnetic order. We further show that, due to fluctuations, this secondary loop current order, which breaks only discrete symmetries, can preempt PDW order, which breaks both continuous and discrete symmetries. In such a phase, the emergent loop current order coexists with spatial short-range superconducting order and possibly short-range charge density wave (CDW) order. Finally, we propose a PDW phase that accounts for intracell magnetic order and the polar Kerr effect, has CDW order consistent with x-ray scattering and nuclear magnetic resonance observations, and quasiparticle (QP) properties consistent with angle
Directory of Open Access Journals (Sweden)
P. A. Ermolaev
2014-03-01
Full Text Available Data processing in the interferometer systems requires high-resolution and high-speed algorithms. Recurrence algorithms based on parametric representation of signals execute consequent processing of signal samples. In some cases recurrence algorithms make it possible to increase speed and quality of data processing as compared with classic processing methods. Dependence of the measured interferometer signal on parameters of its model and stochastic nature of noise formation in the system is, in general, nonlinear. The usage of nonlinear stochastic filtering algorithms is expedient for such signals processing. Extended Kalman filter with linearization of state and output equations by the first vector parameters derivatives is an example of these algorithms. To decrease approximation error of this method the second order extended Kalman filtering is suggested with additionally usage of the second vector parameters derivatives of model equations. Examples of algorithm implementation with the different sets of estimated parameters are described. The proposed algorithm gives the possibility to increase the quality of data processing in interferometer systems in which signals are forming according to considered models. Obtained standard deviation of estimated amplitude envelope does not exceed 4% of the maximum. It is shown that signal-to-noise ratio of reconstructed signal is increased by 60%.
Superconductors in plasmonics and metamaterials: some experimental data
Gombos, M.; Romano, S.; Rendina, I.; Ciancio, R.; Carapella, G.; Mocella, V.
2013-05-01
High frequencies (visible and near infrared) applications of metamaterials and plasmonic structures are strongly limited by dissipative losses in structures, due to poor conductivity of most used metals in this frequency range. The use of high temperature superconductors (HTSC) is a possible approach to this problem, being HTSC plasmonic materials at nonzero temperature. Negative dielectic constant and variety of charge carriers (electrons or holes) are further very attractive features for plasmonic applications. Characterization of the high frequency response of these materials is then necessary in order to correctly understand the optical parameters of HTSC. We report on FTIR and ellipsometry measurements on NdBa2Cu3O7-δ (Nd123) and the ruthenocuprate superconductor GdSr2RuCu2O8-δ (Gd1212) in optical and near infrared regime. Among YBCO-like cuprate superconductors, Nd123 presents the highest Tc (96K), and the most interesting magnetic response properties. Even more interesting, in view of use for metamaterial, is Gd1212, whose main characteristic is the coexistence, in the same cell, of superconductivity and magnetic order below Tc: Ru ions intrinsic magnetic moments order themselves below 135K, whereas superconductivity onset is at about 40K, depending on fabrication details. We performed measurements on Melt-Textured bulk samples, which present the best superconducting properties. Results confirm the promising feature of the considered materials; further analyses, also on powders and films, are in progress.
Institute of Scientific and Technical Information of China (English)
YING Na; ZHAO Xiao-hui; DONG Jing
2007-01-01
Unvoiced/voiced classification of speech is a challenging problem especially under conditions of low signal-to-noise ratio or the non-white-stationary noise environment. To solve this problem, an algorithm for speech classification, and a technique for the estimation of pairwise magnitude frequency in voiced speech are proposed. By using third order spectrum of speech signal to remove noise, in this algorithm the least spectrum difference to get refined pitch and the max harmonic number is given. And this algorithm utilizes spectral envelope to estimate signal-to-noise ratio of speech harmonics. Speech classification, voicing probability, and harmonic parameters of the voiced frame can be obtained.Simulation results indicate that the proposed algorithm, under complicated background noise, especially Gaussian noise, can effectively classify speech in high accuracy for voicing probability and the voiced parameters.
Extension VIKOR for Priority Orders Based on Three Parameters Interval Fuzzy Number
Directory of Open Access Journals (Sweden)
Qian Zhang
2013-05-01
Full Text Available In this study, an improved VIKOR method was presented to deal with multi-attribute decision-making based on three parameters interval fuzzy number. The attribute weights were unknown but alternative priority of object preference was given. A new non-linear rewards and punishment method in positive interval was proposed to make the attributes normal, information covered reliability and relative superiority degree two methods were used to compare and sort the Three Parameters Interval Fuzzy Number (TPIFN and a quadratic programming based on contribution was constructed to get attribute weights, then defined the information entropy distance between TPIFN and the optimum object orders was obtained by VIKOR. The numerical example was provided to demonstrate the feasibility and validity.
Parameter estimation for the Pearson type 3 distribution using order statistics
Rocky Durrans, S.
1992-05-01
The Pearson type 3 distribution and its relatives, the log Pearson type 3 and gamma family of distributions, are among the most widely applied in the field of hydrology. Parameter estimation for these distributions has been accomplished using the method of moments, the methods of mixed moments and generalized moments, and the methods of maximum likelihood and maximum entropy. This study evaluates yet another estimation approach, which is based on the use of the properties of an extreme-order statistic. Based on the hypothesis that the population is distributed as Pearson type 3, this estimation approach yields both parameter and 100-year quantile estimators that have lower biases and variances than those of the method of moments approach as recommended by the US Water Resources Council.
Behaviour of the order parameter of the simple magnet in an external field
Directory of Open Access Journals (Sweden)
M.P.Kozlovskii
2005-01-01
Full Text Available The effect of a homogeneous external field on the three-dimensional uniaxial magnet behaviour near the critical point is investigated within the framework of the nonperturbative collective variables method using the ρ4 model. The research is carried out for the low-temperature region. The analytic explicit expressions for the free energy, average spin moment and susceptibility are obtained for weak and strong fields in comparison with the field value belonging to the pseudocritical line. The calculations are performed on the microscopic level without any adjusting parameters. It is established that the long-wave fluctuations of the order parameter play a crucial role in forming a crossover between the temperature-dependence and field-dependence critical behaviour of the system.
Unconventional superconductors under a rotating magnetic field. II. Thermal transport
Vorontsov, A. B.; Vekhter, I.
2007-06-01
We present a microscopic approach to the calculations of thermal conductivity in unconventional superconductors for a wide range of temperatures and magnetic fields. Our work employs the nonequilibrium Keldysh formulation of the quasiclassical theory. We solve the transport equations using a variation of the Brandt-Pesch-Tewordt method that accounts for the quasiparticle scattering on vortices. We focus on the dependence of the thermal conductivity on the direction of the field with the respect to the nodes of the order parameter, and discuss it in the context of experiments aiming to determine the shape of the gap from such anisotropy measurements. We consider quasi-two-dimensional Fermi surfaces with vertical line nodes and use our analysis to establish the location of gap nodes in heavy-fermion CeCoIn5 and the organic superconductor κ-(BEDT-TTF)2Cu(NCS)2 .
High-temperature superconductors
Saxena, Ajay Kumar
2010-01-01
The present book aims at describing the phenomenon of superconductivity and high-temperature superconductors discovered by Bednorz and Muller in 1986. The book covers the superconductivity phenomenon, structure of high-Tc superconductors, critical currents, synthesis routes for high Tc materials, superconductivity in cuprates, the proximity effect and SQUIDs, theories of superconductivity and applications of superconductors.
Effects of backreaction and exponential nonlinear electrodynamics on the holographic superconductors
Sheykhi, Ahmad
2016-01-01
We analytically study the properties of a $(2+1)$-dimensional $s$-wave holographic superconductor in the presence of exponential nonlinear electrodynamics. We consider the case in which the scalar and gauge fields back react on the background metric. Employing the analytical Sturm-Liouville method, we find that in the black hole background, the nonlinear electrodynamics correction will affect the properties of the holographic superconductors. We find that with increasing both backreaction and nonlinear parameters, the scalar hair condensation on the boundary will develop more difficult. We obtain the relation connecting the critical temperature with the charge density. Our analytical results support that, even in the presence of the nonlinear electrodynamics and backreaction, the phase transition for the holographic superconductor still belongs to the second order and the critical exponent of the system always takes the mean-field value $1/2$.
Nagai, Yuki; Kato, Yusuke
2010-11-01
We investigate the impurity scattering rates for quasiparticles in vortex cores of sign-reversing s -wave superconductors as a probe to detect the internal phase difference of the order parameters among different Fermi surfaces. The impurity scattering rates and coherence factors are related to quasiparticle interference effect by the scanning tunneling microscopy and spectroscopy technique. With use of the Born and Kramer-Pesch approximations for the Andreev bound states, we show that the sign-reversed forward scatterings are dominant in vortex cores. Owing to the coherence factor in vortex cores of ±s -wave superconductors, the impurity scattering rate of the Andreev bound states has a characteristic distribution on the Fermi surfaces. For comparison, the impurity scattering rates in vortex cores of s -wave and d -wave superconductors are also discussed.
Nonperturbative quantum dynamics of the order parameter in the BCS pairing model
Galitski, Victor
2010-08-01
We consider quantum dynamics of the order parameter in the discrete pairing model (Richardson model) in thermodynamic equilibrium. The integrable Richardson Hamiltonian is represented as a direct sum of Hamiltonians acting in different Hilbert spaces of single-particle and paired/empty states. This allows us to factorize the full thermodynamic partition function into a combination of simple terms associated with real spins on singly occupied states and the partition function of the quantum XY model for Anderson pseudospins associated with the paired/empty states. Using coherent-state path integral, we calculate the effects of superconducting phase fluctuations exactly. The contribution of superconducting amplitude fluctuations to the partition function in the broken-symmetry phase is shown to follow from the Bogoliubov-de Gennes equations in imaginary time. These equations in turn allow several interesting mappings, e.g., they are shown to be in a one-to-one correspondence with the one-dimensional Schrödinger equation in supersymmetric quantum mechanics. However, the most practically useful approach to calculate functional determinants is found to be via an analytical continuation of the quantum order parameter to real time, Δ(τ→it) , such that the problem maps onto that of a driven two-level system. The contribution of a particular dynamic order parameter, Δ(τ) , to the partition function is shown to correspond to the sum of the Berry phase and dynamic phase accumulated by the pseudospin. We also examine a family of exact solutions for two-level-system dynamics on a class of elliptic functions and suggest a compact expression to estimate the functional determinants on such trajectories. The possibility of having quantum soliton solutions coexisting with classical BCS mean field is discussed.
Clamping of ferroelectric and antiferromagnetic order parameters of YMnO{sub 3}
Energy Technology Data Exchange (ETDEWEB)
Hanamura, Eiichi [Chitose Institute of Science and Technology, 758-65 Bibi, Chitose, Hokkaido (Japan); Hagita, Katsumi [Japan Science and Technology Corporation (CREST), 758-65 Bibi, Chitose, Hokkaido (Japan); Tanabe, Yukito [Department of Applied Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo (Japan)
2003-01-29
It was observed that a ferroelectric domain boundary (DB) is always accompanied by an antiferromagnetic DB in hexagonal YMnO{sub 3}, by means of interference effects of the second-harmonic signal. The clamping of these two order parameters at the ferroelectric DB is shown theoretically to originate from Dzyaloshinski-Moriya interaction. This interaction favouring a right angle between the neighbouring spins is found to be operative within the DB and to reverse the direction of the spins across the ferroelectric DB. (letter to the editor)
Topology of the Order Parameter in the Little-Parks Experiment
Berger, Jorge; Rubinstein, Jacob
1995-07-01
Under appropriate geometry, magnetic field, and temperature, numerical minimization of the free energy predicts a stable superconducting phase where part of the sample is normal, so that the magnetic flux is not enclosed by the superconducting part. This phase mediates between the normal phase and the superconducting phase which has been usually considered. For one point in the filed-temperature plane, it has been proven analytically that this intermediate phase minimizes the free energy. Near the transition, even when the doubly connected phase is stable, the order parameter tries to mimic that of a simply connected phase.
Classical Order Parameter Dynamics and the Decay of a Metastable Vacuum State
Szép, Z
2000-01-01
Transition of the ground state of a classical $\\Phi^4$ theory in 2+1 dimensions is studied from a metastable state into the stable equilibrium. The transition occurs in the broken $Z_2$ symmetry phase and is triggered by a vanishingly small amplitude homogeneous external field $h$. A phenomenological theory is proposed in form of an effective equation of the quantitatively accounts for the decay of the false vacuum. The large amplitude transition of the order parameter between the two minima displays characteristics reflecting dynamical aspects of the Maxwell construction.
The adaptive synchronization of fractional-order Liu chaotic system with unknown parameters
Indian Academy of Sciences (India)
NOURIAN ADELEH; BALOCHIAN SAEED
2016-06-01
In this paper, the chaos control and the synchronization of two fractional-order Liu chaotic systems with unknown parameters are studied. According to the Lyapunov stabilization theory and the adaptive control theorem, the adaptive control rule is obtained for the described error dynamic stabilization. Using the adaptive rule and a proper Lyapunov candidate function, the unknown coefficients of the system are estimated and the stabilization of the synchronizer system is demonstrated. Finally, the numerical simulation illustrates the efficiency of the proposed method in synchronizing two chaotic systems.
Institute of Scientific and Technical Information of China (English)
Ma Heng; Sun Rui-Zhi; Li Zhen-Xin; Liu Yu-Fang
2008-01-01
Temperature dependence of ratio between dielectric anisotropy and order parameter of fluorinated nematic liquid crystal is investigated by using a semi-empirical molecular orbital package that can accurately calculate an angle between molecular dipole moment and long axis.We optimize the molecular conformations with three semi-empirical Hamiltonians AM1,PM3 and PM5,and then make a comparison between computational results and experimental measurements.It is shown that the results obtained from AM1 method are in good agreement with the measurements.The present study offers an applicable method to predict the dielectric properties of liquid crystal material.
National Aeronautics and Space Administration — The overall goal of the project is to develop reliable reduced order modeling technologies to automatically generate nonlinear, parameter-varying (PV),...
Simulation of Higher-Order Electrical Circuits with Stochastic Parameters via SDEs
Directory of Open Access Journals (Sweden)
BRANCIK, L.
2013-02-01
Full Text Available The paper deals with a technique for the simulation of higher-order electrical circuits with parameters varying randomly. The principle consists in the utilization of the theory of stochastic differential equations (SDE, namely the vector form of the ordinary SDEs. Random changes of both excitation voltage and some parameters of passive circuit elements are considered, and circuit responses are analyzed. The voltage and/or current responses are computed and represented in the form of the sample means accompanied by their confidence intervals to provide reliable estimates. The method is applied to analyze responses of the circuit models of optional orders, specially those consisting of a cascade connection of the RLGC networks. To develop the model equations the state-variable method is used, afterwards a corresponding vector SDE is formulated and a stochastic Euler numerical method applied. To verify the results the deterministic responses are also computed by the help of the PSpice simulator or the numerical inverse Laplace transforms (NILT procedure in MATLAB, while removing random terms from the circuit model.
Minimum of the order parameter fluctuations of seismicity before major earthquakes in Japan.
Sarlis, Nicholas V; Skordas, Efthimios S; Varotsos, Panayiotis A; Nagao, Toshiyasu; Kamogawa, Masashi; Tanaka, Haruo; Uyeda, Seiya
2013-08-20
It has been shown that some dynamic features hidden in the time series of complex systems can be uncovered if we analyze them in a time domain called natural time χ. The order parameter of seismicity introduced in this time domain is the variance of χ weighted for normalized energy of each earthquake. Here, we analyze the Japan seismic catalog in natural time from January 1, 1984 to March 11, 2011, the day of the M9 Tohoku earthquake, by considering a sliding natural time window of fixed length comprised of the number of events that would occur in a few months. We find that the fluctuations of the order parameter of seismicity exhibit distinct minima a few months before all of the shallow earthquakes of magnitude 7.6 or larger that occurred during this 27-y period in the Japanese area. Among the minima, the minimum before the M9 Tohoku earthquake was the deepest. It appears that there are two kinds of minima, namely precursory and nonprecursory, to large earthquakes.
Health Parameter Estimation with Second-Order Sliding Mode Observer for a Turbofan Engine
Directory of Open Access Journals (Sweden)
Xiaodong Chang
2017-07-01
Full Text Available In this paper the problem of health parameter estimation in an aero-engine is investigated by using an unknown input observer-based methodology, implemented by a second-order sliding mode observer (SOSMO. Unlike the conventional state estimator-based schemes, such as Kalman filters (KF and sliding mode observers (SMO, the proposed scheme uses a “reconstruction signal” to estimate health parameters modeled as artificial inputs, and is not only applicable to long-time health degradation, but reacts much quicker in handling abrupt fault cases. In view of the inevitable uncertainties in engine dynamics and modeling, a weighting matrix is created to minimize such effect on estimation by using the linear matrix inequalities (LMI. A big step toward uncertainty modeling is taken compared with our previous SMO-based work, in that uncertainties are considered in a more practical form. Moreover, to avoid chattering in sliding modes, the super-twisting algorithm (STA is employed in observer design. Various simulations are carried out, based on the comparisons between the KF-based scheme, the SMO-based scheme in our earlier research, and the proposed method. The results consistently demonstrate the capabilities and advantages of the proposed approach in health parameter estimation.
Energy Technology Data Exchange (ETDEWEB)
Tegel, Marcus Christian
2011-03-22
The scope of this dissertation therefore has not only been the synthesis of various new superconducting and non-superconducting iron pnictides of several structural families but also their in-depth crystallographic and physical characterisation. In Chapters 3 - 6, the family of the ZrCuSiAs-type (1111) compounds is subject of discussion. The solid solution series La(Co{sub x}Fe{sub 1-x})PO is analysed regarding magnetic and superconducting properties and the new compounds EuMnPF and REZnPO, as well as the new superconductor parent compound SrFeAsF are presented. Chapters 7 - 9 are dedicated to the new iron arsenide superconductors of the ThCr{sub 2}Si{sub 2}-type (122 family). Therein, also the discovery of the first superconductor in this structural family, Ba{sub 0.6}K{sub 0.4}Fe{sub 2}As{sub 2}, is unveiled. A detailed examination of the complete solid solution series (Ba{sub 1-x}K{sub x})Fe{sub 2}As{sub 2} is presented. Moreover, the crystallographic phase transitions of the closely related compounds SrFe{sub 2}As{sub 2} and EuFe{sub 2}As{sub 2} are characterised and the superconductors Sr{sub 1-x}K{sub x}Fe{sub 2}As{sub 2} and Ca{sub 1-x}Na{sub x}Fe{sub 2}As{sub 2} are examined for magnetic and phononic excitations. In Chapter 10, the redetermined crystal structure of the superconductor Fe(Se{sub 1-x}Te{sub x}) (11-type) is presented from a chemist's point of view. Chapters 11 - 14 look into the superconducting and non-superconducting iron arsenides of more complex structural families (32522-type and 21311-type). Therein, crystallographic and magnetic details of Sr{sub 3}Sc{sub 2}O{sub 5}Fe{sub 2}As{sub 2} are presented and Ba{sub 2}ScO{sub 3}FeAs and Sr{sub 2}CrO{sub 3}FeAs, the first two members of the new 21311-type are portrayed. Sr{sub 2}CrO{sub 3}FeAs is looked at in close detail with various methods, so e.g. the spin structure of the magnetically ordered compound is solved and a possible reason for the absence of superconductivity in this compound
Josephson junction between two high Tc superconductors with arbitrary transparency of interface
Directory of Open Access Journals (Sweden)
GhR Rashedi
2010-03-01
Full Text Available In this paper, a dc Josephson junction between two singlet superconductors (d-wave and s-wave with arbitrary reflection coefficient has been investigated theoretically. For the case of high Tc superconductors, the c-axes are parallel to an interface with finite transparency and their ab-planes have a mis-orientation. The physics of potential barrier will be demonstrated by a transparency coefficient via which the tunneling will occur. We have solved the nonlocal Eilenberger equations and obtained the corresponding and suitable Green functions analytically. Then, using the obtained Green functions, the current-phase diagrams have been calculated. The effect of the potential barrier and mis-orientation on the currents is studied analytically and numerically. It is observed that, the current phase relations are totally different from the case of ideal transparent Josephson junctions between d-wave superconductors and two s-wave superconductors. This apparatus can be used to demonstrate d-wave order parameter in high Tc superconductors.
Theory of quantum metal to superconductor transitions in highly conducting systems
Energy Technology Data Exchange (ETDEWEB)
Spivak, B.
2010-04-06
We derive the theory of the quantum (zero temperature) superconductor to metal transition in disordered materials when the resistance of the normal metal near criticality is small compared to the quantum of resistivity. This can occur most readily in situations in which 'Anderson's theorem' does not apply. We explicitly study the transition in superconductor-metal composites, in an swave superconducting film in the presence of a magnetic field, and in a low temperature disordered d-wave superconductor. Near the point of the transition, the distribution of the superconducting order parameter is highly inhomogeneous. To describe this situation we employ a procedure which is similar to that introduced by Mott for description of the temperature dependence of the variable range hopping conduction. As the system approaches the point of the transition from the metal to the superconductor, the conductivity of the system diverges, and the Wiedemann-Franz law is violated. In the case of d-wave (or other exotic) superconductors we predict the existence of (at least) two sequential transitions as a function of increasing disorder: a d-wave to s-wave, and then an s-wave to metal transition.
Charge of a quasiparticle in a superconductor
Ronen, Yuval; Cohen, Yonatan; Kang, Jung-Hyun; Haim, Arbel; Rieder, Maria-Theresa; Heiblum, Moty; Mahalu, Diana; Shtrikman, Hadas
2016-01-01
Nonlinear charge transport in superconductor–insulator–superconductor (SIS) Josephson junctions has a unique signature in the shuttled charge quantum between the two superconductors. In the zero-bias limit Cooper pairs, each with twice the electron charge, carry the Josephson current. An applied bias VSD leads to multiple Andreev reflections (MAR), which in the limit of weak tunneling probability should lead to integer multiples of the electron charge ne traversing the junction, with n integer larger than 2Δ/eVSD and Δ the superconducting order parameter. Exceptionally, just above the gap eVSD ≥ 2Δ, with Andreev reflections suppressed, one would expect the current to be carried by partitioned quasiparticles, each with energy-dependent charge, being a superposition of an electron and a hole. Using shot-noise measurements in an SIS junction induced in an InAs nanowire (with noise proportional to the partitioned charge), we first observed quantization of the partitioned charge q = e*/e=n, with n = 1–4, thus reaffirming the validity of our charge interpretation. Concentrating next on the bias region eVSD∼2Δ, we found a reproducible and clear dip in the extracted charge to q ∼0.6, which, after excluding other possibilities, we attribute to the partitioned quasiparticle charge. Such dip is supported by numerical simulations of our SIS structure. PMID:26831071
Li, Wenchao; Yang, Jianyu; Huang, Yulin; Kong, Lingjiang
For Doppler parameter estimation of forward-looking SAR, the third-order Doppler parameter can not be neglected. In this paper, the azimuth signal of the transmitter fixed bistatic forward-looking SAR is modeled as a cubic polynomial phase signal (CPPS) and multiple time-overlapped CPPSs, and the modified cubic phase function is presented to estimate the third-order Doppler parameter. By combining the cubic phase function (CPF) with Radon transform, the method can give an accurate estimation of the third-order Doppler parameter. Simulations validate the effectiveness of the algorithm.
Directory of Open Access Journals (Sweden)
Fei Gao
2013-01-01
Full Text Available In this paper, a non-Lyapunov novel approach is proposed to estimate the unknown parameters and orders together for noncommensurate and hyper fractional chaotic systems based on cuckoo search oriented statistically by the differential evolution (CSODE. Firstly, a novel Gaos’ mathematical model is proposed and analyzed in three submodels, not only for the unknown orders and parameters’ identification but also for systems’ reconstruction of fractional chaos systems with time delays or not. Then the problems of fractional-order chaos’ identification are converted into a multiple modal nonnegative functions’ minimization through a proper translation, which takes fractional-orders and parameters as its particular independent variables. And the objective is to find the best combinations of fractional-orders and systematic parameters of fractional order chaotic systems as special independent variables such that the objective function is minimized. Simulations are done to estimate a series of noncommensurate and hyper fractional chaotic systems with the new approaches based on CSODE, the cuckoo search, and Genetic Algorithm, respectively. The experiments’ results show that the proposed identification mechanism based on CSODE for fractional orders and parameters is a successful method for fractional-order chaotic systems, with the advantages of high precision and robustness.
Atomic ordering of the fluorine dopant in the $HgBa_{2}CuO_{4+\\delta}high-T_{c}$ superconductor
Correia, João Guilherme; Araújo, João Pedro; Bordet, P; Haas, Heinz; Le Floc'h, S; Lopes, A M L; Rita, E; Carvalho-Soares, João
2005-01-01
Lattice sites and collective ordering of fluorine atoms in oxygen- reduced samples of HgBa/sub 2/CuO/sub 4/ were investigated with the perturbed angular correlation technique by measuring the electric field gradients induced at /sup 199m/Hg nuclei. The experimental data were interpreted with the help of ab initio calculations of charge distributions for different fluorine configurations in Hg/sub m/Ba /sub 2m/Cu/sub m/O/sub 4m/F/sub n/, supercells. Internal parameters were allowed to relax, to cancel residual atomic forces due to the dopant. The experimental results show clearly that fluorine occupies only the center of the mercury mesh. For a fluorine content delta F>~0.35 the best agreement with theoretical data is obtained under the assumption that fluorine shows a tendency toward ordering along interstitial rows parallel to a, b. In conformity with experimental data from diffraction techniques the calculations show elongations of the O(2)-Hg-O(2) dumbbell and barium shifts towards the fluorine atoms as ef...
Generalized Superconductors and Holographic Optics
Mahapatra, Subhash; Sarkar, Tapobrata
2013-01-01
We study generalized holographic s-wave superconductors in four dimensional R-charged black hole backgrounds, in the probe limit. We first establish the superconducting nature of the boundary theory, and then study its optical properties. Numerical analysis indicates that a negative index of refraction appears at low frequencies in the theory, for certain temperature ranges, for specific values of the charge parameter. The corresponding cut-off values for these are numerically established in several cases.
Rinaldi, Antonio
2011-04-01
Traditional fiber bundles models (FBMs) have been an effective tool to understand brittle heterogeneous systems. However, fiber bundles in modern nano- and bioapplications demand a new generation of FBM capturing more complex deformation processes in addition to damage. In the context of loose bundle systems and with reference to time-independent plasticity and soft biomaterials, we formulate a generalized statistical model for ductile fracture and nonlinear elastic problems capable of handling more simultaneous deformation mechanisms by means of two order parameters (as opposed to one). As the first rational FBM for coupled damage problems, it may be the cornerstone for advanced statistical models of heterogeneous systems in nanoscience and materials design, especially to explore hierarchical and bio-inspired concepts in the arena of nanobiotechnology. Applicative examples are provided for illustrative purposes at last, discussing issues in inverse analysis (i.e., nonlinear elastic polymer fiber and ductile Cu submicron bars arrays) and direct design (i.e., strength prediction).
Order Parameters and Phase Diagram of Multiferroic RMn2O5
Harris, A. Brooks
2009-03-01
ρ τ λ σ ξ χ 1 2 1 3 1 4 3 4 Recently there has been great interest in systems which display phase transitions at which incommensurate magnetic order and a spontaneous polarization develop simultaneously. Perhaps the most puzzling and seemingly complicated behavior occurs in the series of compounds RMn2O5, where R=Y, Ho, Er, Tb, Tm, and Dy. (For references to experimental data, see [1].) The sequence of magnetoelectric phases of the type I systems R=Tb, Ho, and Dy is slightly different from that of the type II systems R= Y, Tm, and Er. At about 45K both types develop essentially collinear modulated magnetic order into a ``high-temperature ordered" (HTO) phase with a wave vector q = (1/2-δ, 0, 1/4 + ɛ) where δ and |ɛ| are of order 0.01 and the spontaneous polarization is zero. There is a lower-temperature phase transition to a ferroelectric phase in which transverse magnetic order appears and produces a magnetic spiral with δ=ɛ=0. In type I systems, this transition occurs directly from the HTO phase, whereas for type II systems, there is an intervening ferroelectric phase in which ɛ=0, but δ remains nonzero. %At low (<10K) temperature the classification into types I and II %breaks down and each system requires its own specific description. I will discuss a Landau free energy[1] which allows both type I and type II sequences of phase transitions. This theory is couched in terms of the uniform polarization vector P and two complex-valued magnetic order parameters σ1(q) and σ2(q) whose symmetry follows from the magnetic structure analyses.[2] The magnetoelectric coupling and the competition between commensurate and incommensurate phases are analyzed. [4pt] [1] A. B. Harris, A. Aharony, and O. Entin-Wohlman, Phys. Rev. Lett. 100, 217202 (2008) and J. Phys. Condens. Mat. 20, 434202 (2008). [0pt] [2] A. B. Harris, Phys. Rev. 76, 054447 (2007); A. B. Harris, M. Kenzelmann, A. Aharony, and O. Entin-Wohlman, Phys. Rev. B 78, 014407 (2008).
Nastishin, Yu A; Liu, H; Schneider, T; Nazarenko, V; Vasyuta, R; Shiyanovskii, S V; Lavrentovich, O D
2005-10-01
We report on the optical properties of the nematic (N) phase formed by lyotropic chromonic liquid crystals (LCLCs) in well aligned planar samples. LCLCs belong to a broad class of materials formed by one-dimensional molecular self-assembly and are similar to other systems such as "living polymers" and "wormlike micelles." We study three water soluble LCLC forming materials: disodium chromoglycate, a derivative of indanthrone called Blue 27, and a derivative of perylene called Violet 20. The individual molecules have a planklike shape and assemble into rodlike aggregates that form the phase once the concentration exceeds about 0.1 M. The uniform surface alignment of the N phase is achieved by buffed polyimide layers. According to the light absorption anisotropy data, the molecular planes are on average perpendicular to the aggregate axes and thus to the nematic director. We determined the birefringence of these materials in the N and biphasic N-isotropic (I) regions and found it to be negative and significantly lower in the absolute value as compared to the birefringence of typical thermotropic low-molecular-weight nematic materials. In the absorbing materials Blue 27 and Violet 20, the wavelength dependence of birefringence is nonmonotonic because of the effect of anomalous dispersion near the absorption bands. We describe positive and negative tactoids formed as the nuclei of the new phase in the biphasic N-I region (which is wide in all three materials studied). Finally, we determined the scalar order parameter of the phase of Blue 27 and found it to be relatively high, in the range 0.72-0.79, which puts the finding into the domain of general validity of the Onsager model. However, the observed temperature dependence of the scalar order parameter points to the importance of factors not accounted for in the athermal Onsager model, such as interaggregate interactions and the temperature dependence of the aggregate length.
Parameter Sensitivity of High–Order Equivalent Circuit Models Of Turbine Generator
Directory of Open Access Journals (Sweden)
T. Niewierowicz–Swiecicka
2010-01-01
Full Text Available This work shows the results of a parametric sensitivity analysis applied to a state–space representation of high–order two–axis equivalent circuits (ECs of a turbo generator (150 MVA, 120 MW, 13.8 kV y 50 Hz. The main purpose of this study is to evaluate each parameter impact on the transient response of the analyzed two–axis models –d–axis ECs with one to five damper branches and q–axis ECs from one to four damper branches–. The parametric sensitivity concept is formulated in a general context and the sensibility function is established from the generator response to a short circuit condition. Results ponder the importance played by each parameter in the model behavior. The algorithms were design within MATLAB® environment. The study gives way to conclusions on electromagnetic aspects of solid rotor synchronous generators that have not been previously studied. The methodology presented here can be applied to any other physical system.
Manufacturing of Superconductors
DEFF Research Database (Denmark)
Bech, Jakob Ilsted; Bay, Niels
Superconducting tapes based on the ceramic high temperature superconductor (HTS) is a new promising product for high current applications such as electro-magnets and current transmission cables. The tapes are made by the oxide powder in tube (OPIT) method implying drawing and rolling of silver...... on the mechanical and thermal processes applied. One of the most crucial processes is probably the flat rolling process, where the round or square wire is rolled to form a thin tape (about 3 mm x 0.2 mm), while the density of the powder fibres increase and the fibres obtain their final geometry. For instance...... rolling a tape to a thickness of 250 µm may give a very high Je, whereas further reduction to 200 µm may be fatal. In the present work the flat rolling process is analysed systematically from a mechanical forming point of view. This work implies · Mechanical characterisation of the plastic parameters...
METABOLIC AND BEHAVIORAL PARAMETERS IN NEWBORN PIGLETS IN RELATION TO BIRTH ORDER
Directory of Open Access Journals (Sweden)
H. SĂRĂNDAN
2013-12-01
Full Text Available The experiment had 2 phases:During the first phase 19 sows were monitored during farrowing; the piglets were numbered according to birth order, they were weighed and there were recorded the time each piglet was born and when it first suckled. There was calculated the time from the beginning of the farrowing until the time each piglet was born (TNPP and the time from birth until the first suckle (TPS. A statistical correlation was established between these parameters.During the second experimental phase, for 49 piglets from 5 sows were determined: birth weight, TPS, glycemia at birth (G0 and after the first suckle (G1, rectal temperature at birth (T0 and after the first suckles (T1. This data was statistically analyzed using the Mann-Whitney U test.Respecting the birth order, TPS is shorter for piglets born last (p<0.05. Average TPS was 23.04±2.49 minutes; during this time glycemia rises from 58.35 mg% to 64.35 mg% and rectal temperature drops from 38.58°C to 37.35°C. T0 is positively correlated with G0 (p<0.01 with G1 (p<0.01 and T1 (p<0.01. G0 is highly correlated to G1 (r=0.8855; p=0.
Holographic p-wave Superconductor with Disorder
Arean, Daniel; Zayas, Leopoldo A Pando; Landea, Ignacio Salazar; Scardicchio, Antonello
2014-01-01
We implement the effects of disorder on a holographic p-wave superconductor by introducing a random chemical potential which defines the local energy of the charge carriers. Since there are various possibilities for the orientation of the vector order parameter, we explore the behavior of the condensate in the parallel and perpendicular directions to the introduced disorder. We clarify the nature of various branches representing competing solutions and construct the disordered phase diagram. We find that moderate disorder enhances superconductivity as determined by the value of the condensate. The disorder we introduce is characterized by its spectral properties, and we also study its influence on the spectral properties of the condensate and charge density. We find fairly universal responses of the resulting power spectra characterized by linear functions of the disorder power spectrum.
Order Parameter Profile in AN Adsorbed Binary Liquid Mixture Near Criticality.
Schlossman, Mark Loren
Adsorption of a binary liquid mixture near criticality onto a solid glass substrate can be studied using light reflected off the glass/liquid boundary. In Part 1, reflectivity data analyzed with a modified Landau-Ginzburg theory using a contact wall interaction are shown to be consistent with an exponential decay of the order parameter into the bulk. This analysis provides a measure of h_{1 }, the effective glass/liquid interaction strength. The reflectivity can also be expressed as an expansion in the moments of the order parameter profile. For the data presented and an exponential profile the expansion can be truncated at the first order moment, M_{1} . We assume an exponential form of the profile to express the zeroth moment as a function of M _{1}. The first moment is fitted as a power law in t, the reduced temperature. Analysis of these data yields an exponent p = 0.88 +/- 0.10 that is consistent with the prediction p = 2nu - beta from the scaling law of Fisher and de Gennes. To further explore the profile an AC ellipsometer which used a photoelastic modulator was constructed. An unusual thermostat without traditional windows allowed the angle of incidence at the glass/liquid boundary to be varied over a large range. This allowed a large region in k -space to be explored, where k is twice the transmitted momentum wave vector perpendicular to the glass/liquid boundary. Excellent temperature control (0.1 mK/several hours) allowed the quantity kxi to be as large as kxi cong 15, where xi is the bulk correlation length. This should have allowed us to explore the power law region of the profile. During the investigation of the adsorption, certain anomalous data far above T _{c} (the critical temperature) were discovered. Temperature dependent hysteresis and very long equilibration times characterize the data. Until resolved, these features restrict progress in understanding the data closer to T_{c}. The data remain unexplained and are discussed, along with the
The electronic phase diagram of the LaO(1-x)F(x)FeAs superconductor.
Luetkens, H; Klauss, H-H; Kraken, M; Litterst, F J; Dellmann, T; Klingeler, R; Hess, C; Khasanov, R; Amato, A; Baines, C; Kosmala, M; Schumann, O J; Braden, M; Hamann-Borrero, J; Leps, N; Kondrat, A; Behr, G; Werner, J; Büchner, B
2009-04-01
The competition of magnetic order and superconductivity is a key element in the physics of all unconventional superconductors, for example in high-transition-temperature cuprates, heavy fermions and organic superconductors. Here superconductivity is often found close to a quantum critical point where long-range antiferromagnetic order is gradually suppressed as a function of a control parameter, for example charge-carrier doping or pressure. It is believed that dynamic spin fluctuations associated with this quantum critical behaviour are crucial for the mechanism of superconductivity. Recently, high-temperature superconductivity has been discovered in iron pnictides, providing a new class of unconventional superconductors. Similar to other unconventional superconductors, the parent compounds of the pnictides show a magnetic ground state and superconductivity is induced on charge-carrier doping. In this Letter the structural and electronic phase diagram is investigated by means of X-ray scattering, muon spin relaxation and Mössbauer spectroscopy on the series LaO(1-x)F(x)FeAs. We find a discontinuous first-order-like change of the Néel temperature, the superconducting transition temperature and the respective order parameters. Our results strongly question the relevance of quantum critical behaviour in iron pnictides and prove a strong coupling of the structural orthorhombic distortion and the magnetic order both disappearing at the phase boundary to the superconducting state.
Fine uniform filament superconductors
Riley, Jr., Gilbert N.; Li, Qi; Roberts, Peter R.; Antaya, Peter D.; Seuntjens, Jeffrey M.; Hancock, Steven; DeMoranville, Kenneth L.; Christopherson, Craig J.; Garrant, Jennifer H.; Craven, Christopher A.
2002-01-01
A multifilamentary superconductor composite having a high fill factor is formed from a plurality of stacked monofilament precursor elements, each of which includes a low density superconductor precursor monofilament. The precursor elements all have substantially the same dimensions and characteristics, and are stacked in a rectilinear configuration and consolidated to provide a multifilamentary precursor composite. The composite is thereafter thermomechanically processed to provide a superconductor composite in which each monofilament is less than about 50 microns thick.
The Ginzburg-Landau Theory of a Holographic Superconductor
Yin, Lei; Ren, Hai-cang
2013-01-01
The Ginzburg-Landau formulation of a holographic superconductor is derived near the transition temperature in the probe limit. Below the transition temperature, $T
Higgs mode excitation in superconductors by intense terahertz pulse
Matsunaga, Ryusuke; Shimano, Ryo
2016-05-01
Recent development of intense terahertz (THz) pulse generation technique has offered novel opportunities to reveal ultrafast phenomena in a variety of materials on tabletop experiments and provided a new pathway toward ultrafast control of quantum phases. Here we present our recent study of nonequilibrium dynamics in metallic superconductors NbN excited by intense THz pulse. Since the superconducting gap energy is located in the THz frequency range, the intense THz pulse excitation makes it possible to instantaneously excite high-density quasiparticles at the gap edge without injecting excess energies. It has also become possible to coherently drive the superconducting ground state without exciting incoherent quasiparticles by tuning the pump frequency below the gap energy. The ultrafast dynamics of the order parameter induced by such an intense low energy excitation is directly probed, and the nature of a collective excitation, namely the Higgs amplitude mode, is revealed. Efficient THz higher-harmonic generation from a superconductor is discovered, manifesting the nonlinear coupling between the THz wave and the Higgs mode. We also report the experimental results in a multi-gap superconductor MgB2.
Superconductor rotor cooling system
Gamble, Bruce B.; Sidi-Yekhlef, Ahmed; Schwall, Robert E.; Driscoll, David I.; Shoykhet, Boris A.
2002-01-01
A system for cooling a superconductor device includes a cryocooler located in a stationary reference frame and a closed circulation system external to the cryocooler. The closed circulation system interfaces the stationary reference frame with a rotating reference frame in which the superconductor device is located. A method of cooling a superconductor device includes locating a cryocooler in a stationary reference frame, and transferring heat from a superconductor device located in a rotating reference frame to the cryocooler through a closed circulation system external to the cryocooler. The closed circulation system interfaces the stationary reference frame with the rotating reference frame.
Photothermal measurements of superconductors
Energy Technology Data Exchange (ETDEWEB)
Kino, G.S.; Studenmund, W.R.; Fishman, I.M. [Stanford Univ., Stanford, CA (United States)
1996-12-31
A photothermal technique has been used to measure diffusion and critical temperature in high temperature superconductors. The technique is particularly suitable for determining material quality and inhomogeneity.
Energy Technology Data Exchange (ETDEWEB)
Nogueira, Flavio; Eremin, Ilya [Theoretische Physik III, Ruhr-Universitaet Bochum (Germany)
2015-07-01
We discuss the peculiar nature of Higgs mechanism in an effective field theory for three-dimensional topological superconductors. The effective theory features two order parameters associated to the two chiral fermion species in the system. The resulting electrodynamics of such a topological superconductor exhibits a topological magnetoelectric effect with an axion field given by the phase difference of the order parameters. As consequence, the London regime is highly non-linear and anomalous Hall effect in the absence of an external magnetic field occurs. In this anomalous Hall effect the generated current transverse to an applied electric field changes sign with the temperature. We also discuss the scaling behavior of the penetration depth near the transition temperature, which is also shown to exhibit a scaling exponent that is crucially influenced by the axion term, varying continuously as function of the average phase difference.
Nonlinear terahertz spectroscopy of Higgs mode in s-wave superconductors
Matsunaga, Ryusuke; Shimano, Ryo
2017-02-01
We review our recent experiments of ultrafast dynamics in s-wave superconductors Nb1-x Ti x N by using nonlinear terahertz (THz) spectroscopy. The free oscillation of the Higgs mode, i.e. the amplitude mode of the superconducting order parameter, is observed after instantaneous injection of quasiparticles at the superconducting gap edge by an intense monocycle THz pulse. The ultrafast nonequilibrium dynamics of the order parameter under the strong AC driving field with the photon energy tuned below the superconducting gap is also investigated. A resonant nonlinear interaction between the Higgs mode and the electromagnetic field is revealed, as manifested by an efficient THz third-harmonic generation from the superconductor.
Misra, Avijit; Biswas, Anindya; Pati, Arun K; Sen De, Aditi; Sen, Ujjwal
2015-05-01
Quantum discord is a measure of quantum correlations beyond the entanglement-separability paradigm. It is conceptualized by using the von Neumann entropy as a measure of disorder. We introduce a class of quantum correlation measures as differences between total and classical correlations, in a shared quantum state, in terms of the sandwiched relative Rényi and Tsallis entropies. We compare our results with those obtained by using the traditional relative entropies. We find that the measures satisfy all the plausible axioms for quantum correlations. We evaluate the measures for shared pure as well as paradigmatic classes of mixed states. We show that the measures can faithfully detect the quantum critical point in the transverse quantum Ising model and find that they can be used to remove an unquieting feature of nearest-neighbor quantum discord in this respect. Furthermore, the measures provide better finite-size scaling exponents of the quantum critical point than the ones for other known order parameters, including entanglement and information-theoretic measures of quantum correlations.
Energy Technology Data Exchange (ETDEWEB)
Vanderbemden, P; Laurent, P [SUPRATECS and Department of Electrical Engineering and Computer Science B28, Sart-Tilman, B-4000 Liege (Belgium); Fagnard, J-F [SUPRATECS, Royal Military Academy of Belgium, Avenue de la Renaissance, B-1000 Brussels (Belgium); Ausloos, M [SUPRATECS and Department of Physics B5, Sart-Tilman, B-4000 Liege (Belgium); Hari Babu, N [Brunel Centre for Advanced Solidification Technology (BCAST), Brunel University, West London UB8 3PH (United Kingdom); Cardwell, D A, E-mail: Philippe.Vanderbemden@ulg.ac.b [Bulk Superconductivity Group, Engineering Department, University of Cambridge, Cambridge CB2 1PZ (United Kingdom)
2010-07-15
In the present work we study, both theoretically and experimentally, the temperature increase in a bulk high temperature superconductor subjected to applied AC magnetic fields of large amplitude. We calculate analytically the equilibrium temperatures of the bulk sample as a function of the experimental parameters using a simple critical state model for an infinitely long type-II superconducting slab or cylinder. The results show the existence of a limit heat transfer coefficient (AU{sub lim}) separating two thermal regimes with different characteristics. The theoretical analysis predicts a 'forbidden' temperature window within which the temperature of the superconductor can never stabilize when the heat transfer coefficient is small. In addition, we determine analytical expressions for two threshold fields H{sub tr1} and H{sub tr2} characterizing the importance of magneto-thermal effects and show that a thermal runaway always occurs when the field amplitude is larger than H{sub tr2}. The theoretical predictions of the temperature evolution of the bulk sample during a self-heating process agree well with the experimental data. The simple analytical study presented in this paper enables order of magnitude thermal effects to be estimated for simple superconductor geometries under applied AC magnetic fields and can be used to predict the influence of experimental parameters on the self-heating characteristics of bulk type-II superconductors.
Phonon spectrum of the ferromagnetic superconductor UGe2 and consequences for its specific heat
Raymond, S.; Huxley, A.
2006-03-01
We report inelastic neutron scattering measurements of the phonon spectrum of the pressure-induced ferromagnetic superconductor UGe2 . The phonon contribution to the specific heat was estimated from a fit to our data. The excess specific heat previously noted at around Tx≈30K is not due to phonons but is well described by the temperature dependence of the magnetic order parameter at the molecular field level.
Nonlinear Sum Operator Equations with a Parameter and Application to Second-Order Three-Point BVPs
Directory of Open Access Journals (Sweden)
Wen-Xia Wang
2014-01-01
Full Text Available A class of nonlinear sum operator equations with a parameter on order Banach spaces were considered. The existence and uniqueness of positive solutions for this kind of operator equations and the dependence of solutions on the parameter have been obtained by using the properties of cone and nonlinear analysis methods. The critical value of the parameter was estimated. Further, the application to some nonlinear three-point boundary value problems was given to show the significance of the discussion.
Polar Kerr effect studies of time reversal symmetry breaking states in heavy fermion superconductors
Energy Technology Data Exchange (ETDEWEB)
Schemm, E.R., E-mail: eschemm@alumni.stanford.edu [Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA 94305 (United States); Levenson-Falk, E.M. [Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA 94305 (United States); Department of Physics, Stanford University, Stanford, CA 94305 (United States); Kapitulnik, A. [Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA 94305 (United States); Department of Physics, Stanford University, Stanford, CA 94305 (United States); Department of Applied Physics, Stanford University, Stanford, CA 94305 (United States); Stanford Institute of Energy and Materials Science, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025 (United States)
2017-04-15
Highlights: • Polar Kerr effect (PKE) probes broken time-reversal symmetry (TRS) in superconductors. • Absence of PKE below Tc in CeCoIn{sub 5} is consistent with dx2-y2 order parameter symmetry. • PKE in the B phase of the multiphase superconductor UPt3 agrees with an E2u model. • Data on URu2Si2 show broken TRS and additional structure in the superconducting state. - Abstract: The connection between chiral superconductivity and topological order has emerged as an active direction in research as more instances of both have been identified in condensed matter systems. With the notable exception of {sup 3}He-B, all of the known or suspected chiral – that is to say time-reversal symmetry-breaking (TRSB) – superfluids arise in heavy fermion superconductors, although the vast majority of heavy fermion superconductors preserve time-reversal symmetry. Here we review recent experimental efforts to identify TRSB states in heavy fermion systems via measurement of polar Kerr effect, which is a direct consequence of TRSB.
Energy Technology Data Exchange (ETDEWEB)
Jayachandran, K.P.; Menon, C.S. [School of Pure and Applied Physics, Mahatma Gandhi University, Kottayam, Kerala (India)
2002-01-14
The anisotropy of low temperature thermal expansion of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} (Bi 2212) is analysed theoretically using quasiharmonic theory of thermal expansion. Vibrational anharmonicity as determined by the generalized Grueneisen parameters (GPs){gamma}'{sub j} and {gamma}''{sub j} of the various normal mode frequencies of the lattice has been studied. {gamma}'{sub j} refers to change in frequencies due to a uniform areal strain perpendicular to the c-axis and {gamma}''{sub j} to the change in frequencies due to a uniform areal strain along the c-axis of the Bi 2212 crystal. The generalized GPs are calculated using the second-order elastic constants (SOECs) and third-order elastic constants (TOECs). The SOECs and TOECs are calculated using deformation theory. The strain energy density {phi} is estimated by taking into account the interactions of nine nearest neighbours of each atom in the unit cell of Bi 2212. The energy density thus obtained is compared with the strain-dependent lattice energy from the continuum model approximation to obtain the complete set of non-vanishing SOECs and TOECs of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}. Generally, {gamma}''{sub j} exhibits higher values than {gamma}'{sub j}. Thus the crystal is more anharmonic along the c-axis than in the ab-plane. The longitudinal acoustic mode 3'' is the most anisotropic of all the mode gammas. The transverse acoustic mode {gamma}{sub 1}' attains negative values from {theta}=25 deg. to 55 deg., where {theta} is the angle made by the direction of wave propagation with the c-axis of the crystal Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}. The low temperature limit of the effective Grueneisen functions {gamma}-bar{sub parall}(0), which is parallel to the c-axis of Bi 2212, is almost double the value of {gamma}-bar {sub perpendicular} (0). Hence the discrepancy in the vibrational anharmonicity along the c-axis and along the CuO{sub 2
Optimization of accelerator parameters using normal form methods on high-order transfer maps
Energy Technology Data Exchange (ETDEWEB)
Snopok, Pavel [Michigan State Univ., East Lansing, MI (United States)
2007-05-01
in a way that is easy to understand, such important characteristics as the strengths of the resonances and the tune shifts with amplitude and various parameters of the system are calculated. Each major section is supplied with the results of applying various numerical optimization methods to the problems stated. The emphasis is made on the efficiency comparison of various approaches and methods. The main simulation tool is the arbitrary order code COSY INFINITY written by M. Berz, K. Makino, et al. at Michigan State University. Also, the code MAD is utilized to design the 750 x 750 GeV Muon Collider storage ring baseline lattice.
Energy Technology Data Exchange (ETDEWEB)
Green, M.A.
1988-04-01
This report presents a method for calculating the J/sub C/, H/sub C/, T/sub C/ surface for Type II Superconductors. The method requires that one knows T/sub C/ at zero current and field, H/sub c2/ at zero current and temperature, and J/sub c/ at at least one temperature and field. The theory presented in this report agrees with the measured data quite well over virtually the entire J/sub c/, H/sub c/, T/sub c/ surface given the value of J/sub c/ versus H at one or two temperatures. This report presents calculated and measured values of J/sub c/ versus T and B for niobium titanium, niobium zirconium, niobium tin, niobium titanium tin, niobium tantalum tin, vanadium zirconium hafnium, and vanadium gallium. Good agreement of theory with measured data was obtained for commercial niobium titanium and niobium tin. 76 refs., 26 figs., 6 tabs.
Giant supercurrent states in a superconductor-InAs/GaSb-superconductor junction
Energy Technology Data Exchange (ETDEWEB)
Shi, Xiaoyan, E-mail: xshi@sandia.gov; Pan, W.; Hawkins, S. D.; Klem, J. F. [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Yu, Wenlong; Jiang, Zhigang [School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States); Andrei Bernevig, B. [Department of Physics, Princeton University, Princeton, New Jersey 08544 (United States)
2015-10-07
Superconductivity in topological materials has attracted a great deal of interest in both electron physics and material sciences since the theoretical predictions that Majorana fermions can be realized in topological superconductors. Topological superconductivity could be realized in a type II, band-inverted, InAs/GaSb quantum well if it is in proximity to a conventional superconductor. Here, we report observations of the proximity effect induced giant supercurrent states in an InAs/GaSb bilayer system that is sandwiched between two superconducting tantalum electrodes to form a superconductor-InAs/GaSb-superconductor junction. Electron transport results show that the supercurrent states can be preserved in a surprisingly large temperature-magnetic field (T – H) parameter space. In addition, the evolution of differential resistance in T and H reveals an interesting superconducting gap structure.
Ni, R.; Smallenburg, F.; Filion, L.C.; Dijkstra, M.
2011-01-01
We study crystal nucleation in a binary mixture of hard spheres and investigate the composition and size of the (non)critical clusters using Monte Carlo simulations. In order to study nucleation of a crystal phase in computer simulations, a one-dimensional order parameter is usually defined to ident
Directory of Open Access Journals (Sweden)
I.V. Pylyuk
2013-06-01
Full Text Available The application of the collective variables method to the study of the behaviour of nonuniversal characteristics of the system in the critical region is illustrated by an example of the order parameter. Explicit expressions for the order parameter (the average spin moment of a three-dimensional uniaxial magnet are obtained in approximations of quartic and sextic non-Gaussian fluctuation distributions (the ρ4 and ρ6 models, respectively, taking into account confluent corrections. Some distinctive features appearing in the process of calculating the order parameter on the basis of two successive non-Gaussian approximations are indicated. The dependence of the average spin moment of an Ising-like system on the temperature and microscopic parameters is studied.
Is a color superconductor topological?
Nishida, Yusuke
2010-01-01
A fully gapped state of matter, whether insulator or superconductor, can be asked if it is topologically trivial or nontrivial. Here we investigate topological properties of superconducting Dirac fermions in 3D having a color superconductor as an application. In the chiral limit, when the pairing gap is parity even, the right-handed and left-handed sectors of the free space Hamiltonian have nontrivial topological charges with opposite signs. Accordingly, a vortex line in the superconductor supports localized gapless right-handed and left-handed fermions with the dispersion relations E=+/-vp_z (v is a parameter dependent velocity) and thus propagating in opposite directions along the vortex line. However, the presence of the fermion mass immediately opens up a mass gap for such localized fermions and the dispersion relations become E=+/-v(m^2+p_z^2)^(1/2). When the pairing gap is parity odd, the situation is qualitatively different. The right-handed and left-handed sectors of the free space Hamiltonian in the ...
Thresiamma Philip; Menon, C S; Indulekha, K.
2006-01-01
The second and third-order elastic constants and pressure derivatives of second- order elastic constants of trigonal LiNbO3 (lithium niobate) have been obtained using the deformation theory. The strain energy density estimated using finite strain elasticity is compared with the strain dependent lattice energy density obtained from the elastic continuum model approximation. The second-order elastic constants and the non-vanishing third-order elastic constants along with the pressure derivative...
Thresiamma Phlip; Menon, C S; Indulekha, K.
2005-01-01
The second- and third-order elastic constants of trigonal calcite have been obtained using the deformation theory. The strain energy density derived using the deformation theory is compared with the strain dependent lattice energy obtained from the elastic continuum model approximation to get the expressions for the second- and third-order elastic constants. Higher order elastic constants are a measure of the anharmonicity of a crystal lattice. The seven second-order elastic constants and the...
Fabrication of high temperature superconductors
Balachandran, Uthamalingam; Dorris, Stephen E.; Ma, Beihai; Li, Meiya
2003-06-17
A method of forming a biaxially aligned superconductor on a non-biaxially aligned substrate substantially chemically inert to the biaxially aligned superconductor comprising is disclosed. A non-biaxially aligned substrate chemically inert to the superconductor is provided and a biaxially aligned superconductor material is deposited directly on the non-biaxially aligned substrate. A method forming a plume of superconductor material and contacting the plume and the non-biaxially aligned substrate at an angle greater than 0.degree. and less than 90.degree. to deposit a biaxially aligned superconductor on the non-biaxially aligned substrate is also disclosed. Various superconductors and substrates are illustrated.
Aslam, Mohammad; Paul, Arpita; Thakur, Gohil S.; Gayen, Sirshendu; Kumar, Ritesh; Singh, Avtar; Das, Shekhar; Ganguli, Ashok K.; Waghmare, Umesh V.; Sheet, Goutam
2016-05-01
From temperature and magnetic field dependent point-contact spectroscopy on the ferromagnetic superconductor Sr0.5Ce0.5FBiS2 (bulk superconducting {{T}\\text{c}}=2.5 K) we observe (a) a pseudogap in the normal state that sustains to a remarkably high temperature of 40 K and (b) two-fold enhancement of T c upto 5 K in the point-contact geometry. In addition, Andreev reflection spectroscopy reveals a superconducting gap of 6 meV for certain point-contacts suggesting that the mean field T c of this system could be approximately 40 K, the onset temperature of pseudo-gap. Our results suggest that quantum fluctuations originating from other competing orders in Sr0.5Ce0.5FBiS2 forbid a global phase coherence at high temperatures thereby suppressing T c. Apart from the known ordering to a ferromagnetic state, our first-principles calculations reveal nesting of a multi-band Fermi surface and a significant electron-phonon coupling that could result in charge density wave-like instabilities.
Aslam, Mohammad; Paul, Arpita; Thakur, Gohil S; Gayen, Sirshendu; Kumar, Ritesh; Singh, Avtar; Das, Shekhar; Ganguli, Ashok K; Waghmare, Umesh V; Sheet, Goutam
2016-05-18
From temperature and magnetic field dependent point-contact spectroscopy on the ferromagnetic superconductor Sr0.5Ce0.5FBiS2 (bulk superconducting [Formula: see text] K) we observe (a) a pseudogap in the normal state that sustains to a remarkably high temperature of 40 K and (b) two-fold enhancement of T c upto 5 K in the point-contact geometry. In addition, Andreev reflection spectroscopy reveals a superconducting gap of 6 meV for certain point-contacts suggesting that the mean field T c of this system could be approximately 40 K, the onset temperature of pseudo-gap. Our results suggest that quantum fluctuations originating from other competing orders in Sr0.5Ce0.5FBiS2 forbid a global phase coherence at high temperatures thereby suppressing T c. Apart from the known ordering to a ferromagnetic state, our first-principles calculations reveal nesting of a multi-band Fermi surface and a significant electron-phonon coupling that could result in charge density wave-like instabilities.
Evaluation of second-order texture parameters for sea ice classification from radar images
Shokr, Mohammed E.
1991-06-01
With the advent of airborne and spaceborne synthetic aperture radar (SAR) systems, sea ice classification from SAR images has become an important research subject. Since gray tone alone has proven to be of limited capability in differentiating ice types, texture has naturally become an attractive avenue to explore. Accordingly, performance of texture quantification parameters as related to their ability to discriminate ice types has to be examined. SAR image appearance depends on radar parameters involved in the image construction procedures from the doppler history record. Therefore the feasibility of using universal texture/ice type relationships that hold for all combinations of radar parameters also has to be investigated. To that end, imagery data from three different SAR systems were used in this study. Five conventional texture parameters, derived from the gray level co-occurrence matrix (GLCM), were examined. Two of them were modified to ensure their invariant character under linear gray tone transformations. Results indicated that all parameters were highly correlated. The parameters did not, in general, vary with the computational variables used in generating co-occurrence matrices. Ice types can be identified uniquely by the mean value of any texture parameter. The relatively high variability of texture parameters, however, confuses ice discrimination, particularly of smoother ice types. Ice classification was conducted using a per-pixel maximum likelihood supervised scheme. When texture was combined with gray tone, the overall average classification accuracy was improved. Texture was successful in improving the classification accuracy of multiyear ice but was less promising in discriminating first-season ice types. The best two GLCM texture parameters, according to the computed overall average classification accuracies, were the inverse difference moment and the entropy. A brief description of GLCM texture parameters as related to ice's physical
Holographic superconductor models in the non-minimal derivative coupling theory
Institute of Scientific and Technical Information of China (English)
Chen Song-Bai; Pan Qi-Yuan; Jing Ji-Liang
2012-01-01
We study a general class of holographic superconductor models via the Stückelberg mechanism in the non-minimal derivative coupling theory in which the charged scalar field is kinetically coupling to Einstein's tensor.We explore the effects of the coupling parameter on the critical temperature,the order of phase transitions and the critical exponents near the second-order phase transition point.Moreover,we compute the electrical conductivity using the probe approximation and check the ratios ωg/Tc for the different coupling parameters.
Ground state of an antiferromagnetic superconductor in the presence of a homogeneous magnetic field
Energy Technology Data Exchange (ETDEWEB)
Suzumura, Y.; Naji, A.D.S. (Waterloo Univ., Ontario (Canada). Dept. of Physics)
1981-11-01
The effect of a homogeneous magnetic field, H/sub 0/. on the ground state of an antiferromagnetic superconductor has been investigated. Assuming a one-dimensional like half-filled band, a new state has been found having gapless superconductivity and H/sub 0/-dependent order parameter. This state exists for Hsub(Q)/..delta../sub 0/ > 0.22 and when ..delta.. - Hsub(Q) <= H/sub 0/ < ..delta.. + Hsub(Q) Hsub(Q) is the staggered magnetic field, ..delta.. is the superconducting order parameter and ..delta../sub 0/ is ..delta.. in the absence of Hsub(Q) and H/sub 0/.
Pairing state with a time-reversal symmetry breaking in FeAs-based superconductors.
Lee, Wei-Cheng; Zhang, Shou-Cheng; Wu, Congjun
2009-05-29
We investigate the competition between the extended s+/--wave and dx2-y2-wave pairing order parameters in the iron-based superconductors. Because of the frustrating pairing interactions among the electron and the hole Fermi pockets, a time-reversal symmetry breaking s+id pairing state could be favored. We analyze this pairing state within the Ginzburg-Landau theory and explore the experimental consequences. In such a state, spatial inhomogeneity induces a supercurrent near a nonmagnetic impurity and the corners of a square sample. The resonance mode between the s+/-- and dx2-y2-wave order parameters can be detected through the B1g Raman spectroscopy.
Edge instabilities of topological superconductors
Hofmann, Johannes S.; Assaad, Fakher F.; Schnyder, Andreas P.
2016-05-01
Nodal topological superconductors display zero-energy Majorana flat bands at generic edges. The flatness of these edge bands, which is protected by time-reversal and translation symmetry, gives rise to an extensive ground-state degeneracy. Therefore, even arbitrarily weak interactions lead to an instability of the flat-band edge states towards time-reversal and translation-symmetry-broken phases, which lift the ground-state degeneracy. We examine the instabilities of the flat-band edge states of dx y-wave superconductors by performing a mean-field analysis in the Majorana basis of the edge states. The leading instabilities are Majorana mass terms, which correspond to coherent superpositions of particle-particle and particle-hole channels in the fermionic language. We find that attractive interactions induce three different mass terms. One is a coherent superposition of imaginary s -wave pairing and current order, and another combines a charge-density-wave and finite-momentum singlet pairing. Repulsive interactions, on the other hand, lead to ferromagnetism together with spin-triplet pairing at the edge. Our quantum Monte Carlo simulations confirm these findings and demonstrate that these instabilities occur even in the presence of strong quantum fluctuations. We discuss the implications of our results for experiments on cuprate high-temperature superconductors.
Entanglement Entropy for time dependent two dimensional holographic superconductor
Mazhari, N S; Myrzakulov, Kairat; Myrzakulov, R
2016-01-01
We studied entanglement entropy for a time dependent two dimensional holographic superconductor. We showed that the conserved charge of the system plays the role of the critical parameter to have condensation.
Trani, F.; Campagnano, G.; Tagliacozzo, A.; Lucignano, P.
2016-10-01
We study possible applications of high critical temperature nodal superconductors for the search for Majorana bound states in the DIII class. We propose a microscopic analysis of the proximity effect induced by d -wave superconductors on a semiconductor wire with strong spin-orbit coupling. We characterize the induced superconductivity on the wire employing a numerical self-consistent tight-binding Bogoliubov-de Gennes approach, and analytical considerations on the Green's function. The order parameter induced on the wire, the pair correlation function, and the renormalization of the Fermi points are analyzed in detail, as well as the topological phase diagram in the case of weak coupling. We highlight optimal Hamiltonian parameters to access the nontrivial topological phase which could display time-reversal invariant Majorana doublets at the boundaries of the wire.
First-order method of zoom lens design by means of generalized parameters.
Khorokhorov, Alexei M; Piskunov, Dmitry E; Shirankov, Alexander F
2016-08-01
A method of paraxial zoom lens design is proposed that makes it possible to determine the optical powers and component movements of a zoom lens with the required zoom ratio. The method is based on the theory of generalized parameters, which can be used to analyze a zoom system by varying only one parameter. All possible zoom lenses with two movable components are considered for an object at infinity.
Magnetic ordering of Fe atoms in the YBa2(Cu/0. 95/Fe/0. 05/)3O(7. 01) superconductor
Energy Technology Data Exchange (ETDEWEB)
Liubutin, I.S.; Terziev, V.G.; Morozov, O.N. (Institut Kristallografii, Moscow (USSR))
1990-11-01
Moessbauer spectroscopy detected the magnetic ordering of Fe atoms in YBa2(Cu/0.95/Fe/0.05/)3O(y) in both the superconducting and the nonsuperconducting states. It is shown that, in the superconducting sample, the superconductivity coexists with magnetic ordering of the Fe atoms in Cu1 nodes. In the nonsuperconducting sample, the Fe atoms in the Cu1 nodes have a magnetic-ordering point (20 K) which is reduced by 10 K upon transition to the superconducting state. 15 refs.
Extended Ginzburg-Landau formalism for two-band superconductors.
Shanenko, A A; Milošević, M V; Peeters, F M; Vagov, A V
2011-01-28
Recent observation of unusual vortex patterns in MgB(2) single crystals raised speculations about possible "type-1.5" superconductivity in two-band materials, mixing the properties of both type-I and type-II superconductors. However, the strict application of the standard two-band Ginzburg-Landau (GL) theory results in simply proportional order parameters of the two bands-and does not support the "type-1.5" behavior. Here we derive the extended GL formalism (accounting all terms of the next order over the small τ=1-T/T(c) parameter) for a two-band clean s-wave superconductor and show that the two condensates generally have different spatial scales, with the difference disappearing only in the limit T→T(c). The extended version of the two-band GL formalism improves the validity of GL theory below T(c) and suggests revisiting the earlier calculations based on the standard model.
Energy Technology Data Exchange (ETDEWEB)
Silva Neto, Eduardo H. da; Aynajian, Pegor; Parker, Colin V. [Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ 08544 (United States); Yazdani, Ali, E-mail: yazdani@princeton.edu [Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ 08544 (United States)
2012-11-01
We review recent spectroscopic mapping measurements on Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x} that establish experimental signatures of incipient stripe order. Model calculations show how to disentangle the effects of band structure and incipient order and allow us to model details of the energy-dependence of the observed modulations associated with incipient stripe order. Comprehensive doping and temperature studies reveal the correlation between the onset of the pseudogap and incipient stripe order in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x}, yet they also show that stripes are most likely the consequence of the pseudogap rather than its cause.
Li, Xinbi; Ponomarev, Sergei Y; Sa, Qina; Sigalovsky, Daniel L; Kaminski, George A
2013-05-30
A previously introduced polarizable simulations with second-order interaction model (POSSIM) force field has been extended to include parameters for small molecules serving as models for peptide and protein side-chains. Parameters have been fitted to permit reproducing many-body energies, gas-phase dimerization energies, and geometries and liquid-phase heats of vaporization and densities. Quantum mechanical and experimental data have been used as the target for the fitting. The POSSIM framework combines accuracy of a polarizable force field and computational efficiency of the second-order approximation of the full-scale induced point dipole polarization formalism. The resulting parameters can be used for simulations of the parameterized molecules themselves or their analogues. In addition to this, these force field parameters are currently being used in further development of the POSSIM fast polarizable force field for proteins.
Superconducting gap and order parameter in Bi2Sr2CaCu2O8+x
Kelley, R. J.; Ma, Jian; Quitmann, C.; Margaritondo, G.; Onellion, M.
1994-07-01
Using angle-resolved photoemission, we observed a nonzero superconducting gap and the presence of a superconducting condensate along all three major symmetry directions. We find that the gap is highly anisotropic, with a gap as small as 1-2 meV along Γ-Y, 4-8 meV along Γ-X, and 14-20 meV along Γ-M. We argue that our data imply either an anisotropic s-wave order parameter or an unconventional, two-component order parameter, and that measuring the size of the gap does not by itself distinguish between the two possibilities. We propose a phenomenological unconventional order parameter, and note the quantitative agreement between theory and experiment.
Proximity effect of iron-based superconductor in conventional s-wave superconducting thin films
Groll, Nick; Proslier, Thomas; Koshelev, Alex; Stantev, Valentin; Chung, Duck-Young
2012-02-01
The proximity effect has been proposed as a mechanism to unambiguously identify the possible s±-state in iron-based superconductors.ootnotetextA. E. Koshelev, V. Stanev, Europhysics Letters, Vol. 96, 27014 (2011) With a thin s-wave superconductor atop a s±-superconductor it is suggested that the s-wave order parameter will couple to the s±-gaps differently, inducing a correction to the s-wave density of states that can be probed using electron tunneling spectroscopy. In this talk, we will present recent results of the superconducting proximity effect in s-wave MoGe thin films sputtered on top of bulk superconducting Ba0.6K0.4Fe2As2 (Tc=35K) pnictide. Electron tunneling spectroscopy measurements were performed for several MoGe film thicknesses using a homemade point contact setup. Finally, results will also be presented for similar measurements using two conventional s-wave superconductors.
Large area bulk superconductors
Miller, Dean J.; Field, Michael B.
2002-01-01
A bulk superconductor having a thickness of not less than about 100 microns is carried by a polycrystalline textured substrate having misorientation angles at the surface thereof not greater than about 15.degree.; the bulk superconductor may have a thickness of not less than about 100 microns and a surface area of not less than about 50 cm.sup.2. The textured substrate may have a thickness not less than about 10 microns and misorientation angles at the surface thereof not greater than about 15.degree.. Also disclosed is a process of manufacturing the bulk superconductor and the polycrystalline biaxially textured substrate material.
Superconductor terahertz metamaterial
Gu, Jianqiang; Tian, Zhen; Cao, Wei; Xing, Qirong; Han, Jiaguang; Zhang, Weili
2010-01-01
We characterize the behaviour of split ring resonators made up of high-transition temperature YBCO superconductor using terahertz time domain spectroscopy. The superconductor metamaterial shows sharp change in the transmission spectrum at the fundamental inductive-capacitive resonance and the dipole resonance as the temperature dips below the transition temperature. Our results reveal that the high performance of such a metamaterial is limited by material imperfections and defects such as cracks, voids and secondary phases which play dominant role in partially impeding the flow of current causing dissipation of energy and electrical resistance to appear in the superconductor film.
Theoretical approach to direct resonant inelastic X-ray scattering on magnets and superconductors
Energy Technology Data Exchange (ETDEWEB)
Marra, Pasquale
2015-10-26
The capability to probe the dispersion of elementary spin, charge, orbital, and lattice excitations has positioned resonant inelastic X-ray scattering (RIXS) at the forefront of photon science. In this work, we will investigate how RIXS can contribute to a deeper understanding of the orbital properties and of the pairing mechanism in unconventional high-temperature superconductors. In particular, we show how direct RIXS spectra of magnetic excitations can reveal long-range orbital correlations in transition metal compounds, by discriminating different kind of orbital order in magnetic and antiferromagnetic systems. Moreover, we show how RIXS spectra of quasiparticle excitations in superconductors can measure the superconducting gap magnitude, and reveal the presence of nodal points and phase differences of the superconducting order parameter on the Fermi surface. This can reveal the properties of the underlying pairing mechanism in unconventional superconductors, in particular cuprates and iron pnictides, discriminating between different superconducting order parameter symmetries, such as s,d (singlet pairing) and p wave (triplet pairing).
Performance of ceramic superconductors in magnetic bearings
Kirtley, James L., Jr.; Downer, James R.
1993-01-01
Magnetic bearings are large-scale applications of magnet technology, quite similar in certain ways to synchronous machinery. They require substantial flux density over relatively large volumes of space. Large flux density is required to have satisfactory force density. Satisfactory dynamic response requires that magnetic circuit permeances not be too large, implying large air gaps. Superconductors, which offer large magnetomotive forces and high flux density in low permeance circuits, appear to be desirable in these situations. Flux densities substantially in excess of those possible with iron can be produced, and no ferromagnetic material is required. Thus the inductance of active coils can be made low, indicating good dynamic response of the bearing system. The principal difficulty in using superconductors is, of course, the deep cryogenic temperatures at which they must operate. Because of the difficulties in working with liquid helium, the possibility of superconductors which can be operated in liquid nitrogen is thought to extend the number and range of applications of superconductivity. Critical temperatures of about 98 degrees Kelvin were demonstrated in a class of materials which are, in fact, ceramics. Quite a bit of public attention was attracted to these new materials. There is a difficulty with the ceramic superconducting materials which were developed to date. Current densities sufficient for use in large-scale applications have not been demonstrated. In order to be useful, superconductors must be capable of carrying substantial currents in the presence of large magnetic fields. The possible use of ceramic superconductors in magnetic bearings is investigated and discussed and requirements that must be achieved by superconductors operating at liquid nitrogen temperatures to make their use comparable with niobium-titanium superconductors operating at liquid helium temperatures are identified.
Development of superconductor bulk for superconductor bearing
Energy Technology Data Exchange (ETDEWEB)
Kim, Chan Joong; Jun, Byung Hyuk; Park, Soon Dong (and others)
2008-08-15
Current carrying capacity is one of the most important issues in the consideration of superconductor bulk materials for engineering applications. There are numerous applications of Y-Ba-Cu-O (YBCO) bulk superconductors e.g. magnetic levitation train, flywheel energy storage system, levitation transportation, lunar telescope, centrifugal device, magnetic shielding materials, bulk magnets etc. Accordingly, to obtain YBCO materials in the form of large, single crystals without weak-link problem is necessary. A top seeded melt growth (TSMG) process was used to fabricate single crystal YBCO bulk superconductors. The seeded and infiltration growth (IG) technique was also very promising method for the synthesis of large, single-grain YBCO bulk superconductors with good superconducting properties. 5 wt.% Ag doped Y211 green compacts were sintered at 900 .deg. C {approx} 1200 .deg.C and then a single crystal YBCO was fabricated by an infiltration method. A refinement and uniform distribution of the Y211 particles in the Y123 matrix were achieved by sintering the Ag-doped samples. This enhancement of the critical current density was ascribable to a fine dispersion of the Y211 particles, a low porosity and the presence of Ag particles. In addition, we have designed and manufactured large YBCO single domain with levitation force of 10-13 kg/cm{sup 2} using TSMG processing technique.
Generalized superconductors and holographic optics
Energy Technology Data Exchange (ETDEWEB)
Mahapatra, Subhash; Phukon, Prabwal; Sarkar, Tapobrata [Department of Physics, Indian Institute of Technology,Kanpur 208016 (India)
2014-01-24
We study generalized holographic s-wave superconductors in four dimensional R-charged black hole and Lifshitz black hole backgrounds, in the probe limit. We first establish the superconducting nature of the boundary theories, and then study their optical properties. Numerical analysis indicates that a negative Depine-Lakhtakia index may appear at low frequencies in the theory dual to the R-charged black hole, for certain temperature ranges, for specific values of the charge parameter. The corresponding cut-off values for these are numerically established in several cases. Such effects are seen to be absent in the Lifshitz background where this index is always positive.
Amirkhanov, I V; Sarker, N R; Sarhadov, I
2004-01-01
In this work the solutions of different boundary-value problems are retrieved analytically and numerically for the equation of high order with small parameter at a higher derivative. The analysis of these solutions is given. It is found that for some variants of symmetric boundary conditions the solutions of a boundary-value problem for the equations of the 4th, 6th, $\\ldots$ orders transfer into the solution of a Schrödinger equation at $\\varepsilon \\to 0$ ($\\varepsilon $ is small parameter). The retrieved solutions with different knots are orthogonal among themselves. The results of numerical calculations are given.
DEFF Research Database (Denmark)
Maragakis, Paul; Lindorff-Larsen, Kresten; Eastwood, Michael P
2008-01-01
methods. However, apparent systematic discrepancies between order parameters extracted from simulations and experiments are common, particularly for elements of noncanonical secondary structure. In this paper, results from a 1.2 micros explicit solvent MD simulation of the protein ubiquitin are compared...... with previously determined backbone order parameters derived from NMR relaxation experiments [Tjandra, N.; Feller, S. E.; Pastor, R. W.; Bax, A. J. Am. Chem. Soc. 1995, 117, 12562-12566]. The simulation reveals fluctuations in three loop regions that occur on time scales comparable to or longer than...
AC susceptibilities of grain-textured superconductors
Sakamoto, N.; Fukuda, Y.; Koga, M.; Akune, T.; Khan, H. R.; Lüders, K.
2008-09-01
In-phase χ n‧ and out-phase χ n″ components of nth harmonics of AC susceptibility with measuring parameters of a DC magnetic field Bdc, an amplitude Ba and a frequency f of the superimposed AC magnetic fields give substantial information of the superconducting properties. In low- Tc metallic superconductors, χ1‧ shows smooth transition and χ1″ does single peak. High- Tc oxide superconductors with anisotropic and grain-textured structures show deformed complex characteristics. Double peaks in χ1″ and shoulders in χ1‧ appear in AC susceptibility of Hg-1223 superconductors. Instead of simple Bean model, a grained model, where the superconducting grains are immersed in weak superconducting matrix, are proposed. The susceptibilities numerically analyzed using the model show varied and deformed curves and are successfully compared with the measured results.
Crack problem in a long cylindrical superconductor
Yong, Hua-Dong; Zhou, You-He; Zeng, Jun
2008-12-01
In this work, the general problem of a center crack in a long cylindrical superconductor is studied. The dependence of the stress intensity factor on the parameters, including the crack length and the applied field, is investigated. We presented a simple model in which the effect of the crack on the critical current is taken into account. It is assumed that the crack forms a perfect barrier to the flow of current. The Bean model and the Kim model are considered for the critical state. Based on the complex potential and boundary collocation methods, the stress intensity factor under the magnetic field is obtained for a long cylindrical superconductor containing a central crack. The results show that the crack length and the applied field have significant effects on the fracture behavior of the superconductor.
Directory of Open Access Journals (Sweden)
S. Badoux
2016-04-01
Full Text Available The Seebeck coefficient S of the cuprate superconductor La_{2-x}Sr_{x}CuO_{4} (LSCO was measured in magnetic fields large enough to access the normal state at low temperatures, for a range of Sr concentrations from x=0.07 to x=0.15. For x=0.11, 0.12, 0.125, and 0.13, S/T decreases upon cooling to become negative at low temperatures. The same behavior is observed in the Hall coefficient R_{H}(T. In analogy with other hole-doped cuprates at similar hole concentrations p, the negative S and R_{H} show that the Fermi surface of LSCO undergoes a reconstruction caused by the onset of charge-density-wave modulations. Such modulations have indeed been detected in LSCO by x-ray diffraction in precisely the same doping range. Our data show that in LSCO this Fermi-surface reconstruction is confined to 0.085
order ends at a critical doping p_{CDW}=0.15±0.005, well below the pseudogap critical doping p^{⋆}≃0.19.
Institute of Scientific and Technical Information of China (English)
ShenYike; FeiHeliang
1999-01-01
In this article, Bayes estimation of location parameters under restriction is broughtforth. Since Bayes estimator is closely connected with the first value of order statistics that canbe observed, it is possible to consider “complete data” method, through which the pseudo-value of first order statistics and pseudo-right censored samples can he obtained. Thus the results under Type- Ⅱ right censoring can be used directly to get more accurate estimators by Bayes method.
A Holographic P-wave Superconductor Model
Cai, Rong-Gen; Li, Li-Fang
2014-01-01
We study a holographic p-wave superconductor model in a four dimensional Einstein-Maxwell-complex vector field theory with a negative cosmological constant. The complex vector field is charged under the Maxwell field. We solve the full coupled equations of motion of the system and find black hole solutions with the vector hair. The vector hairy black hole solutions are dual to a thermal state with the U(1) symmetry as well as the spatial rotational symmetry breaking spontaneously. Depending on two parameters, the mass and charge of the vector field, we find a rich phase structure: zeroth order, first order and second order phase transitions can happen in this model. We also find "retrograde condensation" in which the hairy black hole solution exists only for the temperatures above a critical value with the free energy much larger than the black hole without hair. We construct the phase diagram for this system in terms of the temperature and charge of the vector field.
Topological superconductors: a review.
Sato, Masatoshi; Ando, Yoichi
2017-04-03
This review elaborates pedagogically on the fundamental concept, basic theory, expected properties, and materials realizations of topological superconductors. The relation between topological superconductivity and Majorana fermions are explained, and the difference between dispersive Majorana fermions and a localized Majorana zero mode is emphasized. A variety of routes to topological superconductivity are explained with an emphasis on the roles of spin-orbit coupling. Present experimental situations and possible signatures of topological superconductivity are summarized with an emphasis on intrinsic topological superconductors.
Layered nickel based superconductors
Energy Technology Data Exchange (ETDEWEB)
Ronning, Filip [Los Alamos National Laboratory; Bauer, Eric D [Los Alamos National Laboratory; Park, Tuson [Los Alamos National Laboratory; Kurita, Nobuyuki [Los Alamos National Laboratory; Klimczuk, T [Los Alamos National Laboratory; Movshovich, R [Los Alamos National Laboratory; Thompson, J D [Los Alamos National Laboratory; Sefat, A S [ORNL; Mandrus, D [ORNL
2009-01-01
We review the properties of Ni-based superconductors which contain Ni{sub 2}X{sub 2} (X=As, P, Bi, Si, Ge, B) planes, a common structural element to the recently discovered FeAs superconductors. We also compare the properties ofthe Ni-and Fe-based systems from a perspective ofelectronic structure as well as structure-property relations.
Continuous lengths of oxide superconductors
Kroeger, Donald M.; List, III, Frederick A.
2000-01-01
A layered oxide superconductor prepared by depositing a superconductor precursor powder on a continuous length of a first substrate ribbon. A continuous length of a second substrate ribbon is overlaid on the first substrate ribbon. Sufficient pressure is applied to form a bound layered superconductor precursor powder between the first substrate ribbon and the second substrate ribbon. The layered superconductor precursor is then heat treated to establish the oxide superconducting phase. The layered oxide superconductor has a smooth interface between the substrate and the oxide superconductor.
A Generalized Information Criterion for Parameters under an Umbrella Order Restriction
Institute of Scientific and Technical Information of China (English)
宋海燕; 陶剑; 史宁中
2005-01-01
The detection of the configuration of parameters is one of the most important problems im statistical studies. It is well known that the Akaike's information criterion (AIC) is a key tool for this problem (see [1]). Usually, the AIC is defined as: AIC(μ) := l(μ) -p, where l(μ) is the log-likelihood with the maximum likelihood estimator (MLE) μ for μ,
Controller Designing and Parameter Tuning in the First Order plus Large Delay Time System
Directory of Open Access Journals (Sweden)
DAXIAO Wang
2011-10-01
Full Text Available Based on the traditional PID controllerstructure, we proposed a new controller which can behandle the large time delay systems magnificently. Inthe meantime, we provide an easy to understand andpragmatic strategy to tuning the parameters of thecontroller. To inspect and verify our idea, we apply thismethod in the large dead-time system and the commonemployed systems, and compared it with the ideal PIDstructure and the relative PID tuning methods.
Fermi Surface and Order Parameter Driven Vortex Lattice Structure Transitions in Twin-Free YBa2Cu3O7
DEFF Research Database (Denmark)
White, J.S.; Hinkov, V.; Heslop, R.W.;
2009-01-01
fields. It is separated from a low-field hexagonal phase of different orientation and distortion by a first-order transition at 2.0(2) T that is probably driven by Fermi surface effects. We argue that another first-order transition at 6.7(2) T, into a rhombic structure with a distortion of opposite sign......, marks a crossover from a regime where Fermi surface anisotropy is dominant, to one where the VL structure and distortion is controlled by the order-parameter anisotropy....
Lugo-Frías, Rodrigo; Klapp, Sabine H L
2016-06-22
This paper is concerned with the dynamics of a binary mixture of rod-like, repulsive colloidal particles driven out of equilibrium by means of a steady shear flow (Couette geometry). To this end we first derive, starting from a microscopic density functional in Parsons-Lee approximation, a mesoscopic free energy functional whose main variables are the orientational order parameter tensors. Based on this mesoscopic functional we then explore the stability of isotropic and nematic equilibrium phases in terms of composition and rod lengths. Second, by combining the equilibrium theory with the Doi-Hess approach for the order parameter dynamics under shear, we investigate the orientational dynamics of binary mixtures for a range of shear rates and coupling parameters. We find a variety of dynamical states, including synchronized oscillatory states of the two components, but also symmetry breaking behavior where the components display different in-plane oscillatory states.
Higher order corrections to Higgs boson decays in the MSSM with complex parameters
Energy Technology Data Exchange (ETDEWEB)
Williams, Karina E. [Bonn Univ. (Germany). Bethe Center for Theoretical Physics; Rzehak, Heidi [Freiburg Univ. (Germany). Physikalisches Inst.; Weiglein, Georg [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)
2011-03-15
We discuss Higgs boson decays in the CP-violating MSSM, and examine their phe- nomenological impact using cross section limits from the LEP Higgs searches. This includes a discussion of the full 1-loop results for the partial decay widths of neutral Higgs bosons into lighter neutral Higgs bosons (h{sub a}{yields}h{sub b}h{sub c}) and of neutral Higgs bosons into fermions (h{sub a}{yields}f anti f). In calculating the genuine vertex corrections, we take into account the full spectrum of supersymmetric particles and all complex phases of the supersymmetric parameters. These genuine vertex corrections are supplemented with Higgs propagator corrections incorporating the full one-loop and the dominant two-loop contributions, and we illustrate a method of consistently treating diagrams involving mixing with Goldstone and Z bosons. In particular, the genuine vertex corrections to the process h{sub a}{yields}h{sub b}h{sub c} are found to be very large and, where this process is kinematically allowed, can have a significant effect on the regions of the CPX bench- mark scenario which can be excluded by the results of the Higgs searches at LEP. However, there remains an unexcluded region of CPX parameter space at a lightest neutral Higgs boson mass of {proportional_to}45 GeV. In the analysis, we pay particular attention to the conversion between parameters defined in different renormalisation schemes and are therefore able to make a comparison to the results found using renormalisation group improved/effective potential calculations. (orig.)
Wolf, Elizabeth Skubak; Anderson, David F
2012-12-14
We present an efficient finite difference method for the approximation of second derivatives, with respect to system parameters, of expectations for a class of discrete stochastic chemical reaction networks. The method uses a coupling of the perturbed processes that yields a much lower variance than existing methods, thereby drastically lowering the computational complexity required to solve a given problem. Further, the method is simple to implement and will also prove useful in any setting in which continuous time Markov chains are used to model dynamics, such as population processes. We expect the new method to be useful in the context of optimization algorithms that require knowledge of the Hessian.
Mendonca, Tania Melo; Haas, Heinz; Odier, Philippe; Tavares, Pedro; Silva, Manuel Ribeiro; Lopes, Armandina; Pereira, Andre; Goncalves, Joao Nuno; Amaral, Joao; Darie, Celine; Araujo, Joao Pedro
2011-01-01
Lattice sites and collective ordering of oxygen atoms in HgBa$_2$CaCu$_2$O$_{6+\\delta}$ were studied using the perturbed angular correlation (PAC) technique at ISOLDE/CERN. The electric field gradients (EFG) at $^{199m}$Hg nuclei have been measured as functions of oxygen doping on the Hg planes, above and below T$_c$. In comparison with the results obtained for oxygen and fluorine doping in Hg-1201, the analysis shows a different oxygen ordering exhibited by Hg-1212. Moreover, for all studied cases, the experimental results show that at a local scale there is non-uniform oxygen distribution. A series of ab initio EFG calculations allowed to infer that at low concentrations, regions without oxygen coexist with regions where O$_{2\\delta}$ dumbbell molecules are located at the center of the Hg mesh. On the other side, at high concentrations, O$_{2\\delta}$ dumbbell molecules coexist with single O$_\\delta$ atoms occupying the center of the Hg mesh. The present results suggest that oxygen sits on the Hg planes in t...
Heidari, Ali; Forouzan, Mohammad R
2013-01-01
Chatter has been recognized as major restriction for the increase in productivity of cold rolling processes, limiting the rolling speed for thin steel strips. It is shown that chatter has close relation with rolling conditions. So the main aim of this paper is to attain the optimum set points of rolling to achieve maximum rolling speed, preventing chatter to occur. Two combination methods were used for optimization. First method is done in four steps: providing a simulation program for chatter analysis, preparing data from simulation program based on central composite design of experiment, developing a statistical model to relate system tendency to chatter and rolling parameters by response surface methodology, and finally optimizing the process by genetic algorithm. Second method has analogous stages. But central composite design of experiment is replaced by Taguchi method and response surface methodology is replaced by neural network method. Also a study on the influence of the rolling parameters on system stability has been carried out. By using these combination methods, new set points were determined and significant improvement achieved in rolling speed.
Design features of internal tin superconductors for ITER magnetic system
Energy Technology Data Exchange (ETDEWEB)
Pantsyrnyi, V.I.; Shikov, A.K.; Nikulin, A.D.; Silaev, A.G.; Bel`akov, N.A.; Vdovin, V.F.; Semin, M.J. [Bochvar All-Russia Inst. of Inorganic Materials, Moscow (Russian Federation)
1996-07-01
The influence of parameters of internal tin superconductor design on the main working characteristics such as critical current density and hysteresis losses were analyzed. It was shown that having the value of hysteresis losses at the acceptable level of 400--600 mJ/cm{sup 3} the critical current density 20--30% higher than the value typical for bronze route processed superconductors was attainable in principle. The results of experimental work on the design of new types of internal tin superconductors for ITER magnetic system are given.
Hashimoto, Ichihiko; Matsubara, Takahiko; Namikawa, Toshiya; Yokoyama, Shuichiro
2015-01-01
We investigate the statistical power of higher-order statistics and cross-correlation statistics to constrain the primordial non-Gaussianity from the imaging surveys. In particular, we consider the local-type primordial non- Gaussianity and discuss how well one can tightly constrain the higher-order non-Gaussian parameters ($g_{\\rm NL}$ and $\\tau_{\\rm NL}$) as well as the leading order parameter $f_{\\rm NL}$ from the halo/galaxy clustering and weak gravitational lensing measurements. Making use of a strong scale-dependent behavior in the galaxy/halo clustering, Fisher matrix analysis reveals that the bispectra can break the degeneracy between non-Gaussian parameters ($f_{\\rm NL}$, $g_{\\rm NL}$ and $\\tau_{\\rm NL}$) and this will give simultaneous constraints on those three parameters. The combination of cross-correlation statistics further improves the constraints by factor of 2. As a result, upcoming imaging surveys like the Large Synoptic Survey Telescope have the potential to improve the constraints on the ...
Worms, Julien
2010-01-01
Let $X_1, \\ldots, X_n$ be some i.i.d. observations from a heavy tailed distribution $F$, i.e. such that the common distribution of the excesses over a high threshold $u_n$ can be approximated by a Generalized Pareto Distribution $G_{\\gamma,\\sigma_n}$ with $\\gamma >0$. This work is devoted to the problem of finding confidence regions for the couple $(\\gamma,\\sigma_n)$ : combining the empirical likelihood methodology with estimation equations (close but not identical to the likelihood equations) introduced by J. Zhang (Australian and New Zealand J. Stat n.49(1), 2007), asymptotically valid confidence regions for $(\\gamma,\\sigma_n)$ are obtained and proved to perform better than Wald-type confidence regions (especially those derived from the asymptotic normality of the maximum likelihood estimators). By profiling out the scale parameter, confidence intervals for the tail index are also derived.
High temperature superconductor accelerator magnets
van Nugteren, J.
2016-01-01
For future particle accelerators bending dipoles are considered with magnetic fields exceeding 20T. This can only be achieved using high temperature superconductors (HTS). These exhibit different properties from classical low temperature superconductors and still require significant research and dev
Institute of Scientific and Technical Information of China (English)
赵佳; 张威; 方进; 杨中平; 郑琼林; 刘友梅
2011-01-01
A new type high temperature superconductor linear induction motor (HTS LIM) is designed. The primary windings are made of Bi-2223/Ag. And the motor is the single-layer concentrated structure. The critical current of the motor is determined mainly by the primary slot leakage flux.The electromagnetic force is decided mainly by the air magnetic flux and the eddy current of the secondary plate. The structural parameters of the motor have a great impact on the distribution of the magnetic field. Under constant currents the steady and transient properties of the motor were analyzed with different slot width, slot height and winding tums. The properties of the motor, such as the maximum slot leakage flux,the motor thrust and the motor vertical force, were analyzed with different structural parameters.%设计了一种新型高温超导直线感应电机,初级线圈为Bi-2223/Ag高温超导线圈,采用单层整距集中绕组结构排列.高温超导直线感应电机临界电流的大小主要由电机初级槽漏磁通密度决定,电磁力的人小主要由空气主磁通和次级感应板涡流决定.电机结构参数对电机磁场的分布影响很大.使用有限元法比较分析了恒流条件下电机槽宽、槽高和绕组匝数对电机稳态和瞬态电磁性能的影响,研究了电机结构参数对电机最大槽漏磁通密度、电机推力和电机垂向力的影响.
Zermeño, Víctor M. R.; Habelok, Krzysztof; Stępień, Mariusz; Grilli, Francesco
2017-03-01
The estimation of the critical current (I c) and AC losses of high-temperature superconductor devices through modeling and simulation requires the knowledge of the critical current density (J c) of the superconducting material. This J c is in general not constant and depends both on the magnitude (B loc) and the direction (θ, relative to the tape) of the local magnetic flux density. In principle, J c(B loc,θ) can be obtained from the experimentally measured critical current I c(B a,θ), where B a is the magnitude of the applied magnetic field. However, for applications where the superconducting materials experience a local field that is close to the self-field of an isolated conductor, obtaining J c(B loc,θ) from I c(B a,θ) is not a trivial task. It is necessary to solve an inverse problem to correct for the contribution derived from the self-field. The methods presented in the literature comprise a series of approaches dealing with different degrees of mathematical regularization to fit the parameters of preconceived nonlinear formulas by means of brute force or optimization methods. In this contribution, we present a parameter-free method that provides excellent reproduction of experimental data and requires no human interaction or preconception of the J c dependence with respect to the magnetic field. In particular, it allows going from the experimental data to a ready-to-run J c(B loc,θ) model in a few minutes.
Institute of Scientific and Technical Information of China (English)
Huijuan Tian; Ying Liu; Lijun Wang; Xiaojuan Zhang; Zonghui Gao
2006-01-01
@@ Influences of the scattering phase functions on spatially resolved diffuse reflectance from a homogenous semi-infinite medium close to source are studied with Monte Carlo simulation. It is shown that the influences of optical parameters higher than the second order on the diffuse reflectance are quite weak in the region from 0.3 to several transport mean free pathes when Henyey-Greenstein phase function or a combined phase function of two parameters are used. But this influence may be substantial if the double Henyey-Greenstein function is used to describe the scattering property of tissue.
Pair correlation functions of FeAs-based superconductors: Quantum Monte Carlo study
Kashurnikov, V. A.; Krasavin, A. V.
2015-01-01
The new generalized quantum continuous time world line Monte Carlo algorithm was developed to calculate pair correlation functions for two-dimensional FeAs-clusters modeling of iron-based superconductors within the framework of the two-orbital model. The analysis of pair correlations depending on the cluster size, temperature, interaction, and the type of symmetry of the order parameter is carried out. The data obtained for clusters with sizes up to 1 0x1 0 FeAs-cells favor the possibility of an effective charge carrier's attraction that is corresponding the A1g-symmetry, at some parameters of interaction.
Directory of Open Access Journals (Sweden)
O. Cyr-Choinière
2017-09-01
Full Text Available The Seebeck coefficient S of the cuprate YBa_{2}Cu_{3}O_{y} is measured in magnetic fields large enough to suppress superconductivity, at hole dopings p=0.11 and p=0.12, for heat currents along the a and b directions of the orthorhombic crystal structure. For both directions, S/T decreases and becomes negative at low temperature, a signature that the Fermi surface undergoes a reconstruction due to broken translational symmetry. Above a clear threshold field, a strong new feature appears in S_{b}, for conduction along the b axis only. We attribute this feature to the onset of 3D-coherent unidirectional charge-density-wave modulations seen by x-ray diffraction, also along the b axis only. Because these modulations have a sharp onset temperature well below the temperature where S/T starts to drop towards negative values, we infer that they are not the cause of Fermi-surface reconstruction. Instead, the reconstruction must be caused by the quasi-2D bidirectional modulations that develop at significantly higher temperature. The unidirectional order only confers an additional anisotropy to the already reconstructed Fermi surface, also manifest as an in-plane anisotropy of the resistivity.
Cyr-Choinière, O.; Badoux, S.; Grissonnanche, G.; Michon, B.; Afshar, S. A. A.; Fortier, S.; LeBoeuf, D.; Graf, D.; Day, J.; Bonn, D. A.; Hardy, W. N.; Liang, R.; Doiron-Leyraud, N.; Taillefer, Louis
2017-07-01
The Seebeck coefficient S of the cuprate YBa2 Cu3 Oy is measured in magnetic fields large enough to suppress superconductivity, at hole dopings p =0.11 and p =0.12 , for heat currents along the a and b directions of the orthorhombic crystal structure. For both directions, S /T decreases and becomes negative at low temperature, a signature that the Fermi surface undergoes a reconstruction due to broken translational symmetry. Above a clear threshold field, a strong new feature appears in Sb, for conduction along the b axis only. We attribute this feature to the onset of 3D-coherent unidirectional charge-density-wave modulations seen by x-ray diffraction, also along the b axis only. Because these modulations have a sharp onset temperature well below the temperature where S /T starts to drop towards negative values, we infer that they are not the cause of Fermi-surface reconstruction. Instead, the reconstruction must be caused by the quasi-2D bidirectional modulations that develop at significantly higher temperature. The unidirectional order only confers an additional anisotropy to the already reconstructed Fermi surface, also manifest as an in-plane anisotropy of the resistivity.
Factors affecting characterization of bulk high-temperature superconductors
Energy Technology Data Exchange (ETDEWEB)
Hull, J.R. [Argonne National Lab., IL (United States). Energy Technology Div.
1997-11-01
Three major factors affect the characterization of bulk high-temperature superconductors in terms of their levitation properties during interaction with permanent magnets. First, the appropriate parameter for the permanent magnet is internal magnetization, not the value of the magnetic field measured at the magnet`s surface. Second, although levitation force grows with superconductor thickness and surface area, for a given permanent magnet size, comparison of levitation force between samples is meaningful when minimum values are assigned to the superconductor size parameters. Finally, the effect of force creep must be considered when time-averaging the force measurements. In addition to levitational force, the coefficient of friction of a levitated rotating permanent magnet may be used to characterize the superconductor.
Moor, Andreas; Volkov, Anatoly F.; Efetov, Konstantin B.
2016-03-01
On the basis of the Usadel equation we study a multiterminal Josephson junction. This junction is composed by "magnetic" superconductors Sm, which have singlet pairing and are separated from the normal n wire by spin filters so that the Josephson coupling is caused only by fully polarized triplet components. We show that there is no interaction between triplet Cooper pairs with antiparallel total spin orientations. The presence of an additional singlet superconductor S attached to the n wire leads to a finite Josephson current IQ with an unusual current-phase relation. The density of states in the n wire for different orientations of spins of Cooper pairs is calculated. We derive a general formula for the current IQ in a multiterminal Josephson contact and apply this formula for analysis of two four-terminal Josephson junctions of different structures. It is shown in particular that both the "nematic" and the "magnetic" cases can be realized in these junctions. In a two-terminal structure with parallel filter orientations and in a three-terminal structure with antiparallel filter orientations of the "magnetic" superconductors with attached additional singlet superconductor, we find a nonmonotonic temperature dependence of the critical current. Also, in these structures, the critical current shows a Riedel peak like dependence on the exchange field in the "magnetic" superconductors. Although there is no current through the S/n interface due to orthogonality of the singlet and triplet components, the phase of the order parameter in the superconuctor S is shown to affect the Josephson current in a multiterminal structure.
Indian Academy of Sciences (India)
Kumar Vishal; Saurabh K Agrawal; Subir Das
2016-01-01
In this paper, we have discussed the local stability of the Mathieu–van der Pol hyperchaotic system with the fractional-order derivative. The fractional Routh–Hurwitz stability conditions were provided and were used to discuss the stability. Feedback control method was used to control chaos in the Mathieu–van der Pol system with fractional-order derivative and after controlling the chaotic behaviour of the system the synchronization between the fractional-order hyperchaotic Mathieu–van der Pol system and controlled system was introduced. In this study, modified adaptive control methods with uncertain parameters at various equilibrium points were used. Also the analysis of control time with respect to different fractional-order derivatives is the key feature of this paper. Numerical simulation results achieved using Adams–Boshforth–Moulton method show that the method is effective and reliable.
Vortexlike excitations in the heavy-fermion superconductor CeIrIn5
Luo, Yongkang; Rosa, P. F. S.; Bauer, E. D.; Thompson, J. D.
2016-05-01
We report a systematic study of temperature- and field-dependent charge (ρ ) and entropy (S ) transport in the heavy-fermion superconductor CeIrIn5. Its large positive thermopower Sx x is typical of Ce-based Kondo lattice systems, and strong electronic correlations play an important role in enhancing the Nernst signal Sx y. By separating the off-diagonal Peltier coefficient αx y from Sx y, we find that αx y becomes positive and greatly enhanced at temperatures well above the bulk Tc. Compared with the nonmagnetic analog LaIrIn5, these results suggest vortexlike excitations in a precursor state to unconventional superconductivity in CeIrIn5. This study sheds light on the similarity of heavy-fermion and cuprate superconductors and on the possibility of states not characterized by the amplitude of an order parameter.
Guo, Hanqi; Phillips, Carolyn L; Peterka, Tom; Karpeyev, Dmitry; Glatz, Andreas
2016-01-01
We propose a method for the vortex extraction and tracking of superconducting magnetic flux vortices for both structured and unstructured mesh data. In the Ginzburg-Landau theory, magnetic flux vortices are well-defined features in a complex-valued order parameter field, and their dynamics determine electromagnetic properties in type-II superconductors. Our method represents each vortex line (a 1D curve embedded in 3D space) as a connected graph extracted from the discretized field in both space and time. For a time-varying discrete dataset, our vortex extraction and tracking method is as accurate as the data discretization. We then apply 3D visualization and 2D event diagrams to the extraction and tracking results to help scientists understand vortex dynamics and macroscale superconductor behavior in greater detail than previously possible.
Coupling of Higgs and Leggett modes in non-equilibrium superconductors
Krull, H.; Bittner, N.; Uhrig, G. S.; Manske, D.; Schnyder, A. P.
2016-01-01
In equilibrium systems amplitude and phase collective modes are decoupled, as they are mutually orthogonal excitations. The direct detection of these Higgs and Leggett collective modes by linear-response measurements is not possible, because they do not couple directly to the electromagnetic field. In this work, using numerical exact simulations we show for the case of two-gap superconductors, that optical pump–probe experiments excite both Higgs and Leggett modes out of equilibrium. We find that this non-adiabatic excitation process introduces a strong interaction between the collective modes, which is absent in equilibrium. Moreover, we propose a type of pump–probe experiment, which allows to probe and coherently control the Higgs and Leggett modes, and thus the order parameter directly. These findings go beyond two-band superconductors and apply to general collective modes in quantum materials. PMID:27323887
Morisaki, Tsubasa; Wakaura, Hikaru; Koizumi, Hiroyasu
2017-10-01
Rashba type spin-orbit interaction is included in the model Hamiltonian for the spin-vortex-induced loop current (SVILC) mechanism of superconductivity for hole doped cuprate superconductors and its effects are investigated. We assume that a Rashba interaction appears around the small polarons formed by the doped holes in the bulk; its internal electric field is assumed to be in the direction perpendicular to the CuO2 plane and stabilizes the spin polarization lying in the CuO2 plane. We examine 4 × 4, 4 × 6, and 4 × 8 spin-vortex-quartet (SVQ) and perform Monte Carlo simulations to estimate the superconducting transition temperature Tc, where each SVQ is a n × m two dimensional region (in the units of the lattice constant) containing four holes, four spin-vortices, and four SVILCs. We find that the 4 × 6 SVQ is the most stable one among them with the highest Tc; in this case, the hole concentration per Cu atom is x = 0.167, which is close to the optimal doping value x = 0.170, suggesting that the optimal doping may be related to the stabilization of the superconducting state by the Rashba interaction. We also find that the 4 × 8 SVQ becomes more stable than the 4 × 6 SVQ in a current flowing situation; this indicates that the conversion from the 4 × 6 SVQs to 4 × 8 SVQs may occur upon the emergence of a macroscopic current by the application of a magnetic field. This conversion may explain the enhancement of the charge order around x = 0.125 and the Fermi surface reconstruction upon an application of a magnetic field.
Pan, M.-Ch.; Chu, W.-Ch.; Le, Duc-Do
2016-12-01
The paper presents an alternative Vold-Kalman filter order tracking (VKF_OT) method, i.e. adaptive angular-velocity VKF_OT technique, to extract and characterize order components in an adaptive manner for the condition monitoring and fault diagnosis of rotary machinery. The order/spectral waveforms to be tracked can be recursively solved by using Kalman filter based on the one-step state prediction. The paper comprises theoretical derivation of computation scheme, numerical implementation, and parameter investigation. Comparisons of the adaptive VKF_OT scheme with two other ones are performed through processing synthetic signals of designated order components. Processing parameters such as the weighting factor and the correlation matrix of process noise, and data conditions like the sampling frequency, which influence tracking behavior, are explored. The merits such as adaptive processing nature and computation efficiency brought by the proposed scheme are addressed although the computation was performed in off-line conditions. The proposed scheme can simultaneously extract multiple spectral components, and effectively decouple close and crossing orders associated with multi-axial reference rotating speeds.
Zhuravlev, Vladimir; Duan, Wenye; Maniv, Tsofar
2017-01-01
A self-consistent Bogoliubov-de Gennes theory of the vortex lattice state in a 2D strong type-II superconductor at high magnetic fields reveals a novel quantum mixed state around the semiclassical Hc 2, characterized by a well-defined Landau-Bloch band structure in the quasiparticle spectrum and suppressed order-parameter amplitude, which sharply crossover into the well-known semiclassical (Helfand-Werthamer) results upon decreasing magnetic field. Application to the 2D superconducting state observed recently on the surface of the topological insulator Sb2Te3 accounts well for the experimental data, revealing a strong type-II superconductor, with unusually low carrier density and very small cyclotron mass, which can be realized only in the strong coupling superconductor limit.
Stability of magnetic tip/superconductor levitation systems
Institute of Scientific and Technical Information of China (English)
M. K. Alqadi
2015-01-01
The vertical stability of a magnetic tip over a superconducting material is investigated by using the critical state and the frozen image models. The analytical expressions of the stiffness and the vibration frequency about the equilibrium position are derived in term of the geometrical parameters of the magnet/superconductor system. It is found that the stability of the system depends on the shape of the superconductor as well as its thickness.
Weyl holographic superconductor in the Lifshitz black hole background
Mansoori, S A Hosseini; Mokhtari, A; Dezaki, F Lalehgani; Sherkatghanad, Z
2016-01-01
We investigate analytically the properties of the Weyl holographic superconductor in the Lifshitz black hole background. We find that the critical temperature of the Weyl superconductor decreases with increasing Lifshitz dynamical exponent, $z$, indicating that condensation becomes difficult. In addition, it is found that the critical temperature and condensation operator could be affected by applying the Weyl coupling, $\\gamma$. Finally, we compute the critical magnetic field and investigate its dependence on the parameters $\\gamma$ and $z$.
Granular Superconductors and Gravity
Noever, David; Koczor, Ron
1999-01-01
As a Bose condensate, superconductors provide novel conditions for revisiting previously proposed couplings between electromagnetism and gravity. Strong variations in Cooper pair density, large conductivity and low magnetic permeability define superconductive and degenerate condensates without the traditional density limits imposed by the Fermi energy (approx. 10(exp -6) g cu cm). Recent experiments have reported anomalous weight loss for a test mass suspended above a rotating Type II, YBCO superconductor, with a relatively high percentage change (0.05-2.1%) independent of the test mass' chemical composition and diamagnetic properties. A variation of 5 parts per 104 was reported above a stationary (non-rotating) superconductor. In experiments using a sensitive gravimeter, bulk YBCO superconductors were stably levitated in a DC magnetic field and exposed without levitation to low-field strength AC magnetic fields. Changes in observed gravity signals were measured to be less than 2 parts in 108 of the normal gravitational acceleration. Given the high sensitivity of the test, future work will examine variants on the basic magnetic behavior of granular superconductors, with particular focus on quantifying their proposed importance to gravity.
Zhang, BiTao; Pi, YouGuo; Luo, Ying
2012-09-01
A fractional order sliding mode control (FROSMC) scheme based on parameters auto-tuning for the velocity control of permanent magnet synchronous motor (PMSM) is proposed in this paper. The control law of the proposed F(R)OSMC scheme is designed according to Lyapunov stability theorem. Based on the property of transferring energy with adjustable type in F(R)OSMC, this paper analyzes the chattering phenomenon in classic sliding mode control (SMC) is attenuated with F(R)OSMC system. A fuzzy logic inference scheme (FLIS) is utilized to obtain the gain of switching control. Simulations and experiments demonstrate that the proposed FROSMC not only achieve better control performance with smaller chatting than that with integer order sliding mode control, but also is robust to external load disturbance and parameter variations.
Local order parameters for use in driving homogeneous ice nucleation with all-atom models of water.
Reinhardt, Aleks; Doye, Jonathan P K; Noya, Eva G; Vega, Carlos
2012-11-21
We present a local order parameter based on the standard Steinhardt-Ten Wolde approach that is capable both of tracking and of driving homogeneous ice nucleation in simulations of all-atom models of water. We demonstrate that it is capable of forcing the growth of ice nuclei in supercooled liquid water simulated using the TIP4P/2005 model using over-biassed umbrella sampling Monte Carlo simulations. However, even with such an order parameter, the dynamics of ice growth in deeply supercooled liquid water in all-atom models of water are shown to be very slow, and so the computation of free energy landscapes and nucleation rates remains extremely challenging.
Crystal structure and order parameters in the phase transition of antiferroelectric PbZrO sub 3
Fujishita, H; Tanaka, S; Ogawaguchi, A; Katano, S
2003-01-01
X-ray and neutron diffraction and dielectric measurements were performed for the antiferroelectric phase of PbZrO sub 3. The antiferroelectric SIGMA sub 3 (TO) and the R sub 2 sub 5 superlattice-reflection intensities, and the pseudo-tetragonal lattice distortion of the perovskite sublattice showed the same temperature dependence below room temperature, showing a saturation below about 60 K. Above room temperature, however, they showed rather different temperature dependences. These temperature dependences can be well described by the free energy based on a group theoretical method, which includes a quantum effect. The atomic shifts do not necessarily conform to a simple concept of order parameter in soft mode condensation. However the antiferroelectric phase transition can be understood by the phenomenological theory for coupled order parameters if applied over the whole temperature region. (author)
Fermionic spectral functions in backreacting p-wave superconductors at finite temperature
Giordano, G L; Lugo, A R
2016-01-01
We investigate the spectral function of fermions in a $p$-wave superconducting state, at finite both temperature and gravitational coupling, using the $AdS/CFT$ correspondence and extending previous research. We found that, for any coupling below a critical value, the system behaves as its zero temperature limit. By increasing the coupling, the "peak-dip-hump" structure that characterizes the spectral function at fixed momenta disappears. In the region where the normal/superconductor phase transition is first order, the presence of a non-zero order parameter is reflected in the absence of rotational symmetry in the fermionic spectral function at the critical temperature.
Indian Academy of Sciences (India)
Smarajit Das; Jayprokas Chakrabarti; Zhumur Ghosh; Satyabrata Sahoo; Bibekanand Mallick
2005-12-01
We analyse forty-seven chloroplast genes of the large subunit of RuBisCO, from the algal order Ectocarpales, sourced from GenBank. Codon-usage weighted by the nucleotide base-bias defines our score called the codon-impact-parameter. This score is used to obtain phylogenetic relations amongst the 47 Ectocarpales. We compare our classification with the ones done earlier.
Shojaei, M
2010-01-01
The asymptotic behavior (such as convergence to an equilibrium, convergence to a 2-cycle, and divergence to infinity) of solutions of the following multi-parameter, rational, second order difference equation x_{n+1} =(ax_{n}^3+ bx_{n}^2x_{n-1}+cx_{n}x_{n-1}^2+dx_{n-1}^3)/x_{n}^2, x_{-1},x_{0}\\in R, is studied in this paper.
Directory of Open Access Journals (Sweden)
Igor B. Krasnyuk
2009-01-01
Full Text Available The asymptotical behavior of order parameter in confined binary mixture is considered in one-dimensional geometry. The interaction between bulk and surface forces in the mixture is investigated. Its established conditions are when the bulk spinodal decomposition may be ignored and when the main role in the process of formation of the oscillating asymptotic periodic spatiotemporal structures plays the surface-directed spinodal decomposition which is modelled by nonlinear dynamical boundary conditions.
Bonetti, Marco; Tancredi, Lorenzo
2016-01-01
We compute the two-loop electroweak correction to the production of the Higgs boson in gluon fusion to higher orders in the dimensional-regularization parameter $\\epsilon = (d-4)/2$. We employ the method of differential equations to compute the relevant integrals and express them in terms of Goncharov polylogarithms. Our result provides one of the necessary inputs for the computation of mixed three-loop QCD-electroweak corrections to $gg \\to H$.
Directory of Open Access Journals (Sweden)
Zhang Peiguo
2011-01-01
Full Text Available Abstract By obtaining intervals of the parameter λ, this article investigates the existence of a positive solution for a class of nonlinear boundary value problems of second-order differential equations with integral boundary conditions in abstract spaces. The arguments are based upon a specially constructed cone and the fixed point theory in cone for a strict set contraction operator. MSC: 34B15; 34B16.
Energy Technology Data Exchange (ETDEWEB)
Kalmykov, M.Yu.; Kniehl, B.A. [Hamburg Univ. (Germany). 2. Inst. fuer Theoretische Physik
2008-07-15
We prove the following theorems: 1) The Laurent expansions in {epsilon} of the Gauss hypergeometric functions {sub 2}F{sub 1}(I{sub 1}+a{epsilon},I{sub 2}+b{epsilon};I{sub 3}+(p)/(q)+c{epsilon};z), {sub 2}F{sub 1}(I{sub 1}+(p)/(q)+a{epsilon},I{sub 2}+(p/q)+b{epsilon};I{sub 3}+(p)/(q)+c{epsilon};z) and {sub 2}F{sub 1}(I{sub 1}+(p)/(q)+ a{epsilon},I{sub 2}+b{epsilon};I{sub 3}+(p)/(q)+c{epsilon};z), where I{sub 1},I{sub 2},I{sub 3},p,q are arbitrary integers, a,b,c are arbitrary numbers and {epsilon} is an infinitesimal parameter, are expressible in terms of multiple polylogarithms of q-roots of unity with coefficients that are ratios of polynomials; 2) The Laurent expansion of the Gauss hypergeometric function {sub 2}F{sub 1}(I{sub 1}+(p)/(q)+a{epsilon},I{sub 2}+b{epsilon};I{sub 3}+c{epsilon};z) is expressible in terms of multiple polylogarithms of q-roots of unity times powers of logarithm with coefficients that are ratios of polynomials; 3) The multiple inverse rational sums {sigma}{sup {infinity}}{sub j=1}({gamma}(j))/({gamma}(1+j-(p)/(q))) (z{sup j})/(j{sup c}) S{sub a{sub 1}}(j-1).. S{sub a{sub p}}(j-1) and the multiple rational sums {sigma}{sup {infinity}}{sub j=1} ({gamma}(j+(p)/(q)))/({gamma}(1+j)) (z{sup j})/(j{sup c}) S{sub a{sub 1}}(j-1).. S{sub a{sub p}}(j-1), where S{sub a}(j)={sigma}{sup j}{sub k=1}(1)/(k{sup a}) is a harmonic series and c is an arbitrary integer, are expressible in terms of multiple polylogarithms; 4) The generalized hypergeometric functions {sub p}F{sub p.1}((vector)A+(vector)a{epsilon};(vector)B+(vector)b{epsilon},(p)/(q)+B{sub p-1};z) and {sub p}F{sub p-1}((vector)A+(vector)a{epsilon},(p)/(q)+A{sub p};(vector)B+(vector)b{epsilon};z) are expressible in terms of multiple polylogarithms with coefficients that are ratios of polynomials. (orig.)
Wang, Junlei; Echtenkamp, Will; Street, Mike; Binek, Christian
2015-03-01
Magnetoelectric oxides are of great interest for ultra-low power spintronics with memory and logic function. A key property for the realization of electrically switchable state variables is the voltage-controlled boundary magnetization in magnetoelectric antiferromagnets. It allows electric switching of an adjacent exchange coupled ferromagnetic layer in the absence of dissipative currents. Previous surface sensitive measurements of boundary magnetization in thin films of the archetypical magnetoelectric antiferromagnet chromia lacked explicit demonstration of the predicted rigid coupling between the bulk antiferromagnetic order parameter and the boundary magnetization. We designed a magneto-optical setup allowing simultaneous measurement of Kerr and Faraday rotation. Our experiments correlate electric field induced bulk magneto-optical effects (non-reciprocal rotation), including the response on switching of the antiferromagnetic order parameter, with the boundary magnetization. Our results suggest that switching of a ferromagnetic film strongly exchange coupled to a magnetoelectric antiferromagnetic ultra-thin film allows switching of the antiferromagnetic order parameter. We investigate the possibility that this switching phenomenon might induce a voltage pulse via a generalized variation of the inverse linear magnetoelectric effect. This project was supported by SRC through CNFD, an SRC-NRI Center, by C-SPIN, part of STARnet, and by the NSF through MRSEC.
Kumar, R V Sudheer; Ramanathan, Krishna V
2015-07-20
NMR spectroscopy is a powerful means of studying liquid-crystalline systems at atomic resolutions. Of the many parameters that can provide information on the dynamics and order of the systems, (1) H-(13) C dipolar couplings are an important means of obtaining such information. Depending on the details of the molecular structure and the magnitude of the order parameters, the dipolar couplings can vary over a wide range of values. Thus the method employed to estimate the dipolar couplings should be capable of estimating both large and small dipolar couplings at the same time. For this purpose, we consider here a two-dimensional NMR experiment that works similar to the insensitive nuclei enhanced by polarization transfer (INEPT) experiment in solution. With the incorporation of a modification proposed earlier for experiments with low radio frequency power, the scheme is observed to enable a wide range of dipolar couplings to be estimated at the same time. We utilized this approach to obtain dipolar couplings in a liquid crystal with phenyl rings attached to either end of the molecule, and estimated its local order parameters.
Topologically stable gapped state in a layered superconductor
Doria, Mauro; Cariglia, Marco; Vargas-Paredes, Alfredo A.
2014-03-01
We show that a layered charged superconductor, described by a spinorial (two-component) order parameter, has a gapped state above the ground state, topologically protected from decay. This state is made of skyrmions, breaks the time reversal symmetry and produces a weak local magnetic field. This excited but stable state contains spontaneous circulating supercurrents, with flow and counter flow in the layers, even without the presence of an external magnetic field. We derive the order parameter and the local magnetic field of this skyrmion state from the Abrikosov-Bogomolny (first order) equations, instead of the second order variational equations. We find a gap density of the order of 0 . 1hmaxmeV.nm-3 , where hmax is the maximum local magnetic field between layers expressed in Gauss. The present threshold of detection, set by μSR and NMR/NQR, hmax ~ 0 . 01G , gives a gap density of the order 10-3meV.nm-3 for the single-layer cuprates (inter-layer distance d ~ 1 . 0 nm). We suggest that the pseudogap is a skyrmion state, and so, estimate that the density of carriers that condense in the pseudogap is of the order of 10-4nm-3 , or 0 . 01 % of the Cooper pair density in the cuprates. Acknowledge support from CNPq-Brazil.
Kostadinov, Ivan Zahariev
2016-01-01
Experimental evidence of superconductors with critical temperatures above $373\\:K$ is presented. In a family of different compounds we demonstrate the superconductor state, the transition to normal state above $387\\:K$, an intermediate $242\\:K$ superconductor, susceptibility up to $350\\:K$, $I-V$ curves at $4.2\\:K$ in magnetic field of $12\\:T$ and current up to $60\\:A$, $300\\:K$ Josephson Junctions and Shapiro steps with radiation of $5\\:GHz$ to $21\\:THz$, $300\\:K$ tapes tests with high currents up to $3000\\:A$ and many $THz$ images of coins and washers. Due to a pending patent, the exact chemical characterization and technological processes for these materials are temporarily withheld and will be presented elsewhere.
Vestgården, J I; Shantsev, D V; Galperin, Y M; Johansen, T H
2012-01-01
Crucially important for application of type-II superconductor films is the stability of the vortex matter--magnetic flux lines penetrating the material. If some vortices get detached from pinning centres, the energy dissipated by their motion will facilitate further depinning, and may trigger a massive electromagnetic breakdown. Up to now, the time-resolved behaviour of these ultra-fast events was essentially unknown. We report numerical simulation results revealing the detailed dynamics during breakdown as within nanoseconds it develops branching structures in the electromagnetic fields and temperature, with striking resemblance of atmospheric lightning. During a dendritic avalanche the superconductor is locally heated above its critical temperature, while electrical fields rise to several kV/m as the front propagates at instant speeds near up to 100 km/s. The numerical approach provides an efficient framework for understanding the ultra-fast coupled non-local dynamics of electromagnetic fields and dissipation in superconductor films.
Schabinger, Robert M
2011-01-01
In this paper we discuss in detail computational methods and new results for one-loop virtual corrections to N = 4 super Yang-Mills scattering amplitudes calculated to all orders in epsilon, the dimensional regularization parameter. It is often the case that one-loop gauge theory computations are carried out to order epsilon^0, since higher order in epsilon contributions vanish in the small epsilon limit. We will show, however, that the higher order contributions are actually quite useful. In the context of maximally supersymmetric Yang-Mills, we consider two examples in detail to illustrate our point. First we will concentrate on computations with gluonic external states and argue that N = 4 supersymmetry implies a simple relation between all-orders-in-epsilon one-loop N = 4 super Yang-Mills amplitudes and the first and second stringy corrections to analogous tree-level superstring amplitudes. For our second example we will derive a new result for the all-orders-in-epsilon one-loop superamplitude for planar ...
Directory of Open Access Journals (Sweden)
S E Mousavi
2009-08-01
Full Text Available In this paper, Bi-Sr-Ca-Cu-O (BCSCCO system superconductor is made by the solid state reaction method. The effect of doping Pb, Cd, Sb, Cu and annealing time on the critical temperature and critical current density have been investigated. The microstructure and morphology of the samples have been studied by X-ray diffraction, scanning electron microscope and energy dispersive X-ray. The results show that the fraction of Bi-2223 phase in the Bi- based superconductor, critical temperature and critical current density depend on the annealing temperature, annealing time and the kind and amount of doping .
Physical Vacuum in Superconductors
de Matos, Clovis Jacinto
2009-01-01
Although experiments carried out by Jain et al. showed that the Cooper pairs obey the strong equivalence principle, The measurement of the Cooper pairs inertial mass by Tate et al. revealed an anomalous excess of mass. In the present paper we interpret these experimental results in the framework of an electromagnetic model of dark energy for the superconductors' vacuum. We argue that this physical vacuum is associated with a preferred frame. Ultimately from the conservation of energy for Cooper pairs we derive a model for a variable vacuum speed of light in the superconductors physical vacuum in relation with a possible breaking of the weak equivalence principle for Cooper pairs.
Energy Technology Data Exchange (ETDEWEB)
Yu, Tang-Qing, E-mail: tangqing.yu@nyu.edu; Vanden-Eijnden, Eric, E-mail: eve2@cims.nyu.edu [Courant Institute of Mathematical Sciences, New York University, New York, New York 10012 (United States); Chen, Pei-Yang; Chen, Ming [Department of Chemistry, New York University, New York, New York 10003 (United States); Samanta, Amit [Program in Applied and Computational Mathematics, Princeton University, Princeton, New Jersey 08544, USA and Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Tuckerman, Mark, E-mail: mark.tuckerman@nyu.edu [Courant Institute of Mathematical Sciences, New York University, New York, New York 10012 (United States); Department of Chemistry, New York University, New York, New York 10003 (United States); NYU-ECNU Center for Computational Chemistry at NYU Shanghai, Shanghai 200062 (China)
2014-06-07
The problem of predicting polymorphism in atomic and molecular crystals constitutes a significant challenge both experimentally and theoretically. From the theoretical viewpoint, polymorphism prediction falls into the general class of problems characterized by an underlying rough energy landscape, and consequently, free energy based enhanced sampling approaches can be brought to bear on the problem. In this paper, we build on a scheme previously introduced by two of the authors in which the lengths and angles of the supercell are targeted for enhanced sampling via temperature accelerated adiabatic free energy dynamics [T. Q. Yu and M. E. Tuckerman, Phys. Rev. Lett. 107, 015701 (2011)]. Here, that framework is expanded to include general order parameters that distinguish different crystalline arrangements as target collective variables for enhanced sampling. The resulting free energy surface, being of quite high dimension, is nontrivial to reconstruct, and we discuss one particular strategy for performing the free energy analysis. The method is applied to the study of polymorphism in xenon crystals at high pressure and temperature using the Steinhardt order parameters without and with the supercell included in the set of collective variables. The expected fcc and bcc structures are obtained, and when the supercell parameters are included as collective variables, we also find several new structures, including fcc states with hcp stacking faults. We also apply the new method to the solid-liquid phase transition in copper at 1300 K using the same Steinhardt order parameters. Our method is able to melt and refreeze the system repeatedly, and the free energy profile can be obtained with high efficiency.
Energy Technology Data Exchange (ETDEWEB)
Liu, Qing; Shi, Chaowei [Hefei National Laboratory for Physical Sciences at The Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, 230026 (China); Yu, Lu [Hefei National Laboratory for Physical Sciences at The Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, 230026 (China); High Magnetic Field Laboratory, Chinese Academy of Science, Hefei, Anhui, 230031 (China); Zhang, Longhua [Hefei National Laboratory for Physical Sciences at The Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, 230026 (China); Xiong, Ying, E-mail: yxiong73@ustc.edu.cn [Hefei National Laboratory for Physical Sciences at The Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, 230026 (China); Tian, Changlin, E-mail: cltian@ustc.edu.cn [Hefei National Laboratory for Physical Sciences at The Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, 230026 (China); High Magnetic Field Laboratory, Chinese Academy of Science, Hefei, Anhui, 230031 (China)
2015-02-13
Internal backbone dynamic motions are essential for different protein functions and occur on a wide range of time scales, from femtoseconds to seconds. Molecular dynamic (MD) simulations and nuclear magnetic resonance (NMR) spin relaxation measurements are valuable tools to gain access to fast (nanosecond) internal motions. However, there exist few reports on correlation analysis between MD and NMR relaxation data. Here, backbone relaxation measurements of {sup 15}N-labeled SH3 (Src homology 3) domain proteins in aqueous buffer were used to generate general order parameters (S{sup 2}) using a model-free approach. Simultaneously, 80 ns MD simulations of SH3 domain proteins in a defined hydrated box at neutral pH were conducted and the general order parameters (S{sup 2}) were derived from the MD trajectory. Correlation analysis using the Gromos force field indicated that S{sup 2} values from NMR relaxation measurements and MD simulations were significantly different. MD simulations were performed on models with different charge states for three histidine residues, and with different water models, which were SPC (simple point charge) water model and SPC/E (extended simple point charge) water model. S{sup 2} parameters from MD simulations with charges for all three histidines and with the SPC/E water model correlated well with S{sup 2} calculated from the experimental NMR relaxation measurements, in a site-specific manner. - Highlights: • Correlation analysis between NMR relaxation measurements and MD simulations. • General order parameter (S{sup 2}) as common reference between the two methods. • Different protein dynamics with different Histidine charge states in neutral pH. • Different protein dynamics with different water models.
Ekin, Jack W.; Cheggour, Najib; Goodrich, Loren; Splett, Jolene
2017-03-01
of the USL in several new areas: (l) A five-fold reduction in the measurement space for unified temperature-strain apparatuses through extrapolation of minimum datasets; (2) Combination of data from separate temperature and strain apparatuses, which provides flexibility and productive use of more limited data; and (3) Full conductor characterization from as little as a single I c(B) curve when a few core parameters have been measured in a similar conductor. Default core scaling parameter values are also given, based on analysis of a wide range of practical Nb3Sn conductors.
Experimental demonstration of vortex pancake in high temperature superconductor
Institute of Scientific and Technical Information of China (English)
WANG Wei-xian; ZHANG Yu-heng
2006-01-01
In order to demonstrate the existence of the vortex pancake in high temperature superconductor experimentally,a configuration in which the current and voltage electrodes lies separately on the top and bottom surface is used.The E-j relation obtained with this electrodes spatial configuration is different from the expected E-j behavior of the stiff vortex line model.Thus,the current results support the existence of the vortex pancake in high temperature superconductor.
Theory of vortices in hybridized ballistic/diffusive-band superconductors
Tanaka, K.; Eschrig, M.; Agterberg, D. F.
2007-06-01
We study the electronic structure in the vicinity of a vortex in a two-band superconductor in which the quasiparticle motion is ballistic in one band and diffusive in the other. This study is based on a model appropriate for such a case, that we have introduced recently [Tanaka , Phys. Rev. B 73, 220501(R) (2006)]. We argue that in the two-band superconductor MgB2 , such a case is realized. Motivated by the experimental findings on MgB2 , we assume that superconductivity in the diffusive band is “weak,” i.e., mostly induced. We examine intriguing features of the order parameter, the current density, and the vortex core spectrum in the “strong” ballistic band under the influence of hybridization with the “weak” diffusive band. Although the order parameter in the diffusive band is induced, the characteristic length scales in the two bands differ due to Coulomb interactions. The current density in the vortex core is dominated by the contribution from the ballistic band, while outside the core the contribution from the diffusive band can be substantial, or even dominating. The current density in the diffusive band has strong temperature dependence, exhibiting the Kramer-Pesch effect when hybridization is strong. A particularly interesting feature of our model is the possibility of additional bound states near the gap edge in the ballistic band, that are prominent in the vortex center spectra. This contrasts with the single band case, where there is no gap-edge bound state in the vortex center. We find the above-mentioned unique features for parameter values relevant for MgB2 .
Joseph, Boby; Marini, Carlo; Demitri, Nicola; Capitani, Francesco; Bernasconi, Andrea; Zhou, Wei; Xing, Xiangzhuo; Shi, Zhixiang
2015-09-01
Temperature dependent synchrotron x-ray powder diffraction data on {{Ca}}0.82{{La}}0.18FeAs2 pnictide superconductor demonstrate anisotropic thermal expansion along the out-of-plane and in-plane lattice parameters. Thermal expansion along the c-axis shows a distinct change from 2.9 × 10-4 Å K-1 at ˜300 K to 1.0 × 10-4 Å K-1 at ˜110 K, whereas the in-plane axes, a and b, in the temperature range 300 to 100 K, show a constant thermal expansion that is an order of magnitude smaller (˜0.3×10-4 Å K-1). The temperature dependence of the out-of-plane lattice parameter is found to have a good correlation with the behavior of the resistivity indicating the importance of the interlayer interaction in governing the transport properties of 112 pnictide superconductors.
High Temperature Superconductor Accelerator Magnets
AUTHOR|(CDS)2079328; de Rijk, Gijs; Dhalle, Marc
2016-11-10
For future particle accelerators bending dipoles are considered with magnetic fields exceeding $20T$. This can only be achieved using high temperature superconductors (HTS). These exhibit different properties from classical low temperature superconductors and still require significant research and development before they can be applied in a practical accelerator magnet. In order to study HTS in detail, a five tesla demonstrator magnet named Feather-M2 is designed and constructed. The magnet is based on ReBCO coated conductor, which is assembled into a $10kA$ class Roebel cable. A new and optimized Aligned Block layout is used, which takes advantage of the anisotropy of the conductor. This is achieved by providing local alignment of the Roebel cable in the coil windings with the magnetic field lines. A new Network Model capable of analyzing transient electro-magnetic and thermal phenomena in coated conductor cables and coils is developed. This model is necessary to solve critical issues in coated conductor ac...
Analytical Computation of Critical Exponents in Several Holographic Superconductors
Zeng, Hua-Bi; Jiang, Yu; Zong, Hong-Shi
2010-01-01
It is very interesting that all holographic superconductors like $s$-wave, $p$-wave and $d$-wave holographic superconductors shows the universal mean-field critical exponent $1/2$ at the critical temperature just like Gindzburg-Landau (G-L) theory for second order phase transitions. Now it is believed that the universal critical exponents appear since the dual gravity theory is classic in the large $N$ limit. However, there is an exception called "non-mean-field theory" even in the large $N$ limit: An extension of the $s$-wave model with a cubic term of the charged scalar field provides a different critical exponent $1$. In this paper, we try to use analytical calculation to get the critical exponents for these models to see how these properties of the gravity action decides the appearance of the mean-field or "non-mean-field" behaviors. It will be seen that like the G-L theory, it is the fundamental symmetries rather than the detail parameters of the bulk theory result in the universal properties of the holo...
On the parameters identification of the Duffing's system by means of a reduced order observer
Energy Technology Data Exchange (ETDEWEB)
Mendoza-Camargo, Juan [CINVESTAV-IPN, Departamento de Control Automatico, Av. IPN 2508, A.P. 14740, Mexico, D.F. 07360 (Mexico); Aguilar-Iban-tilde ez, Carlos [CIC-IPN, Av. Juan de Dios Batiz s/n Esq. Manuel Othon de M., Unidad Profesional Adolfo Lopez Mateos, Col. San Pedro Zacatenco, A.P. 75476, Mexico, D.F. 07700 (Mexico)]. E-mail: caguilar@cic.ipn.mx; Martinez-Guerra, Rafael [CINVESTAV-IPN, Departamento de Control Automatico, Av. IPN 2508, A.P. 14740, Mexico, D.F. 07360 (Mexico)]. E-mail: rguerra@ctrl.cinvestav.mx; Garrido-Moctezuma, Ruben [CINVESTAV-IPN, Departamento de Control Automatico, Av. IPN 2508, A.P. 14740, Mexico, D.F. 07360 (Mexico)
2004-10-25
An on-line procedure for recovering the unknown parameters set of the Duffing's oscillator by means of a reduced order proportional integral observer is presented in this Letter. First, it is shown that the oscillator has the properties of being algebraically observable and algebraically identifiable with respect to a well-chosen output (which turns out to be the oscillator's position). Therefore, an extended differential parametrization of the output and its time derivatives can be obtained. This extended differential parametrization has the necessary information to estimate the output time derivatives and to recover the unknown parameters. The numerical implementation of this method is easily accomplished in a digital computer.
Manufacturing of Superconductors
DEFF Research Database (Denmark)
Bech, Jakob Ilsted; Bay, Niels
Superconducting tapes based on the ceramic high temperature superconductor (HTS) is a new promising product for high current applications such as electro-magnets and current transmission cables. The tapes are made by the oxide powder in tube (OPIT) method implying drawing and rolling of silver tu...
High temperature superconductors applications in telecommunications
Kumar, A. Anil; Li, Jiang; Zhang, Ming Fang
1995-01-01
The purpose of this paper is twofold: (1) to discuss high temperature superconductors with specific reference to their employment in telecommunications applications; and (2) to discuss a few of the limitations of the normally employed two-fluid model. While the debate on the actual usage of high temperature superconductors in the design of electronic and telecommunications devices - obvious advantages versus practical difficulties - needs to be settled in the near future, it is of great interest to investigate the parameters and the assumptions that will be employed in such designs. This paper deals with the issue of providing the microwave design engineer with performance data for such superconducting waveguides. The values of conductivity and surface resistance, which are the primary determining factors of a waveguide performance, are computed based on the two-fluid model. A comparison between two models - a theoretical one in terms of microscopic parameters (termed Model A) and an experimental fit in terms of macroscopic parameters (termed Model B) - shows the limitations and the resulting ambiguities of the two-fluid model at high frequencies and at temperatures close to the transition temperature. The validity of the two-fluid model is then discussed. Our preliminary results show that the electrical transport description in the normal and superconducting phases as they are formulated in the two-fluid model needs to be modified to incorporate the new and special features of high temperature superconductors. Parameters describing the waveguide performance - conductivity, surface resistance and attenuation constant - will be computed. Potential applications in communications networks and large scale integrated circuits will be discussed. Some of the ongoing work will be reported. In particular, a brief proposal is made to investigate of the effects of electromagnetic interference and the concomitant notion of electromagnetic compatibility (EMI/EMC) of high T
High temperature superconductors applications in telecommunications
Energy Technology Data Exchange (ETDEWEB)
Kumar, A.A.; Li, J.; Zhang, M.F. [Prairie View A& M Univ., Texas (United States)
1994-12-31
The purpose of this paper is twofold: to discuss high temperature superconductors with specific reference to their employment in telecommunications applications; and to discuss a few of the limitations of the normally employed two-fluid model. While the debate on the actual usage of high temperature superconductors in the design of electronic and telecommunications devices-obvious advantages versus practical difficulties-needs to be settled in the near future, it is of great interest to investigate the parameters and the assumptions that will be employed in such designs. This paper deals with the issue of providing the microwave design engineer with performance data for such superconducting waveguides. The values of conductivity and surface resistance, which are the primary determining factors of a waveguide performance, are computed based on the two-fluid model. A comparison between two models-a theoretical one in terms of microscopic parameters (termed Model A) and an experimental fit in terms of macroscopic parameters (termed Model B)-shows the limitations and the resulting ambiguities of the two-fluid model at high frequencies and at temperatures close to the transition temperature. The validity of the two-fluid model is then discussed. Our preliminary results show that the electrical transport description in the normal and superconducting phases as they are formulated in the two-fluid model needs to be modified to incorporate the new and special features of high temperature superconductors. Parameters describing the waveguide performance-conductivity, surface resistance and attenuation constant-will be computed. Potential applications in communications networks and large scale integrated circuits will be discussed. Some of the ongoing work will be reported. In particular, a brief proposal is made to investigate of the effects of electromagnetic interference and the concomitant notion of electromagnetic compatibility (EMI/EMC) of high T{sub c} superconductors.
Directory of Open Access Journals (Sweden)
Yasushi Narushima
2013-01-01
Full Text Available We deal with complementarity problems over second-order cones. The complementarity problem is an important class of problems in the real world and involves many optimization problems. The complementarity problem can be reformulated as a nonsmooth system of equations. Based on the smoothed Fischer-Burmeister function, we construct a smoothing Newton method for solving such a nonsmooth system. The proposed method controls a smoothing parameter appropriately. We show the global and quadratic convergence of the method. Finally, some numerical results are given.
Emulating “Chaos + Chaos = Order” in Chen’s Circuit of Fractional Order by Parameter Switching
Tang, Wallace K. S.; Danca, Marius-F.
2016-06-01
In this paper, the effect of the parameter switching (PS) algorithm in a fractional order chaotic circuit is investigated both in simulation and experiment. The Chen system of fractional order is focused and realized in an electronic circuit. By designing a switching circuit, the PS algorithm is implemented and it is the first time, the paradoxical “Chaos + Chaos = Order” is presented in an electronic circuit. Both the simulation and experimental results confirm that the obtained attractor under switching approximates the attractor of the time-averaged model. Some important design issues for the circuitry realization of the PS scheme are pointed out. Finally, our work confirms the practical usage of PS algorithm in potential applications such as attractor synthesis and chaos control.
Interaction effects along the edge of a topological superconductor
Energy Technology Data Exchange (ETDEWEB)
Hofmann, Johannes S. [Institut fuer Theoretische Physik und Astrophysik, Wuerzburg (Germany); Max-Planck-Institut fuer Festkoerperforschung, Stuttgart (Germany); Schnyder, Andreas P. [Max-Planck-Institut fuer Festkoerperforschung, Stuttgart (Germany); Assaad, Fakher [Institut fuer Theoretische Physik und Astrophysik, Wuerzburg (Germany)
2015-07-01
Topological nodal superconductors, such as d{sub xy}-wave and nodal non-centrosymmetric superconductors, exhibit protected zero-energy flat-band edge states. These zero-energy edge modes are protected by time-reversal and translation symmetry and their stability is guaranteed by the conservation of a quantized topological invariant. Here, we study the fate of these flat-band edge states in the presence of interactions. We find that Hubbard interactions lead to spontaneous breaking of time-reversal or translation symmetry at the edge of the system. For the d{sub xy}-wave superconductor in the presence of attractive Hubbard interactions we find that the flat-band states become unstable towards the formation of a charge-density wave state or a state with s-wave type pairing correlations. Repulsive Hubbard interactions, on the other hand, induce ferromagnetic order at the edge of the d{sub xy}-wave superconductor.
Antiferromagnetic topological superconductor and electrically controllable Majorana fermions.
Ezawa, Motohiko
2015-02-01
We investigate the realization of a topological superconductor in a generic bucked honeycomb system equipped with four types of mass-generating terms, where the superconductor gap is introduced by attaching the honeycomb system to an s-wave superconductor. Constructing the topological phase diagram, we show that Majorana modes are formed in the phase boundary. In particular, we analyze the honeycomb system with antiferromagnetic order in the presence of perpendicular electric field E(z). It becomes topological for |E(z)|>E(z)(cr) and trivial for |E(z)|superconductor by controlling applied electric field. One Majorana zero-energy bound state appears at the phase boundary. We can arbitrarily control the position of the Majorana fermion by moving the spot of applied electric field, which will be made possible by a scanning tunneling microscope probe.
Imaging the anisotropic nonlinear Meissner effect in unconventional superconductors
Energy Technology Data Exchange (ETDEWEB)
Zhuravel, Alexander P. [B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine, Kharkov (Ukraine); Ghamsari, Behnood G.; Kurter, Cihan; Abrahams, John [CNAM, Physics Department, University of Maryland, College Park, MD (United States); Jung, Philipp; Lukashenko, Alexander; Ustinov, Alexey V. [Physikalisches Institut and DFG-Center for Functional Nanostructures (CFN), Karlsruhe Institute of Technology, Karlsruhe (Germany); Remillard, Stephen [Physics Department, Hope College, Holland, MI (United States); Anlage, Steven M. [CNAM, Physics Department, University of Maryland, College Park, MD (United States); Physikalisches Institut and DFG-Center for Functional Nanostructures (CFN), Karlsruhe Institute of Technology, Karlsruhe (Germany)
2013-07-01
We present measurements on the anisotropic nonlinear Meissner effect (aNLME). Using a laser scanning microscope we have directly imaged this effect in a self-resonant spiral patterned from a thin film of the d{sub x{sup 2}-y{sup 2}} superconductor YBa{sub 2}Cu{sub 3}O{sub 7-δ}. The spiral is excited at one of its resonant frequencies while a focused laser spot is scanned across its surface. The local illumination by the laser gives rise to a detectable change in the resonant properties. At low temperatures, the aNLME causes a direction dependent contribution to the critical current density. This makes it possible to image the directions of nodes and anti-nodes of the superconducting order parameter and the contribution of Andreev bound states associated with them. These two contributions to the photoresponse can be distinguished by their temperature dependence, which is consistent with theoretical predictions.
The Origin of Tc Enhancement in Heterostructure Cuprate Superconductors
Directory of Open Access Journals (Sweden)
Doron L. Bergman
2011-10-01
Full Text Available Recent experiments on heterostructures composed of two or more films of cuprate superconductors of different oxygen doping levels have shown a remarkable Tc enhancement (up to 50% relative to single compound films. We provide a simple explanation of the enhancement which arises naturally from a collection of experimental works. We show that the enhancement could be caused by a structural change in the lattice, namely an increase in the distance of the apical oxygen from the copper-oxygen plane. This increase modifies the effective off-site interaction in the plane which in turn enhances the d-wave superconductivity order parameter. To illustrate this point we study the extended Hubbard model using the fluctuation exchange approximation.
Topology of nonsymmorphic crystalline insulators and superconductors
Shiozaki, Ken; Sato, Masatoshi; Gomi, Kiyonori
2016-05-01
Topological classification in our previous paper [K. Shiozaki and M. Sato, Phys. Rev. B 90, 165114 (2014), 10.1103/PhysRevB.90.165114] is extended to nonsymmorphic crystalline insulators and superconductors. Using the twisted equivariant K theory, we complete the classification of topological crystalline insulators and superconductors in the presence of additional order-two nonsymmorphic space-group symmetries. The order-two nonsymmorphic space groups include half-lattice translation with Z2 flip, glide, twofold screw, and their magnetic space groups. We find that the topological periodic table shows modulo-2 periodicity in the number of flipped coordinates under the order-two nonsymmorphic space group. It is pointed out that the nonsymmorphic space groups allow Z2 topological phases even in the absence of time-reversal and/or particle-hole symmetries. Furthermore, the coexistence of the nonsymmorphic space group with time-reversal and/or particle-hole symmetries provides novel Z4 topological phases, which have not been realized in ordinary topological insulators and superconductors. We present model Hamiltonians of these new topological phases and analytic expressions of the Z2 and Z4 topological invariants. The half-lattice translation with Z2 spin flip and glide symmetry are compatible with the existence of boundaries, leading to topological surface gapless modes protected by the order-two nonsymmorphic symmetries. We also discuss unique features of these gapless surface modes.
Rice, T. Maurice; Sigrist, Manfred; Maeno, Yoshiteru
2009-05-01
here and a consistent theoretical description of all aspects of their superconductivity remains a formidable challenge. While the discovery of the BCS theory led, in only a few years, to the complete and consistent theoretical description of all aspects of conventional superconductivity, we are far from this goal for the exotic superconductors. Hence these superconductors continue to be the focus of most research activity in the field of superconductivity today. The papers in this special issue represent a cross section of current activity in both experiment and theory on these fascinating materials. Focus on Superconductors with Exotic Symmetries Contents Phase-sensitive-measurement determination of odd-parity, spin-triplet superconductivity in Sr2RuO4 Ying Liu Striped superconductors: how spin, charge and superconducting orders intertwine in the cuprates Erez Berg, Eduardo Fradkin, Steven A Kivelson and John M Tranquada A twisted ladder: relating the Fe superconductors to the high-Tc cuprates E Berg, S A Kivelson and D J Scalapino Fractional vortex lattice structures in spin-triplet superconductors Suk Bum Chung, Daniel F Agterberg and Eun-A Kim Momentum dependence of pseudo-gap and superconducting gap in variation theory T Watanabe, H Yokoyama, K Shigeta and M Ogata Variational ground states of the two-dimensional Hubbard model D Baeriswyl, D Eichenberger and M Menteshashvili Charge dynamics of vortex cores in layered chiral triplet superconductors M Eschrig and J A Sauls Vortices in chiral, spin-triplet superconductors and superfluids J A Sauls and M Eschrig Flux periodicities in loops of nodal superconductors Florian Loder, Arno P Kampf, Thilo Kopp and Jochen Mannhart Evidence of magnetic mechanism for cuprate superconductivity Amit Keren Wave function for odd-frequency superconductors Hari P Dahal, E Abrahams, D Mozyrsky, Y Tanaka and A V Balatsky Nernst effect as a probe of superconducting fluctuations in disordered thin films A Pourret, P Spathis, H Aubin and K
Keefe, Peter D.
2012-11-01
J Bardeen proposed that the adiabatic phase transition of mesoscopic-size type I superconductors must be accompanied by magnetic hysteresis in the critical magnetic field of sufficient magnitude to satisfy the second law of thermodynamics, herein referred to as ‘Bardeen Hysteresis’. Bardeen Hysteresis remains speculative in that it has not been reported in the literature. This paper investigates Bardeen Hysteresis as a possible accompaniment to the adiabatic phase transition of isolated mesoscopic-size type I superconductors and its implications with respect to the second law of thermodynamics. A causal mechanism for Bardeen Hysteresis is discussed which contrasts with the long accepted causal mechanism of magnetic hysteresis, as first summarized by Pippard, herein referred to as ‘Pippard Hysteresis’. The paper offers guidance for an experimental verification and comments on how the existence of Bardeen Hysteresis has relation to a quantum mechanical basis for the second law of thermodynamics.
Caiazzo, A; Caforio, Federica; Montecinos, Gino; Muller, Lucas O; Blanco, Pablo J; Toro, Eluterio F
2016-10-25
This work presents a detailed investigation of a parameter estimation approach on the basis of the reduced-order unscented Kalman filter (ROUKF) in the context of 1-dimensional blood flow models. In particular, the main aims of this study are (1) to investigate the effects of using real measurements versus synthetic data for the estimation procedure (i.e., numerical results of the same in silico model, perturbed with noise) and (2) to identify potential difficulties and limitations of the approach in clinically realistic applications to assess the applicability of the filter to such setups. For these purposes, the present numerical study is based on a recently published in vitro model of the arterial network, for which experimental flow and pressure measurements are available at few selected locations. To mimic clinically relevant situations, we focus on the estimation of terminal resistances and arterial wall parameters related to vessel mechanics (Young's modulus and wall thickness) using few experimental observations (at most a single pressure or flow measurement per vessel). In all cases, we first perform a theoretical identifiability analysis on the basis of the generalized sensitivity function, comparing then the results owith the ROUKF, using either synthetic or experimental data, to results obtained using reference parameters and to available measurements.
Moessbauer studies of ternary superconductors
Energy Technology Data Exchange (ETDEWEB)
Kimball, C.W.; Van Landuyt, G.L.; Barnet, C.D.; Shenoy, G.K.; Dunlap, B.D.; Fradin, F.Y.
1978-01-01
Moessbauer studies of the ternary Chevrel phase and rare earth rhodium boride superconductors have been made. Anomalous phonon properties at the Sn site in SnMo/sub 6/S/sub 8/, SnMo/sub 6/Se/sub 8/, and La/sub 0/ /sub 98/Sn/sub 0/ /sub 02/Mo/sub 6/Se/sub 8/ have been investigated. Studies of polarization of conduction electrons at the site of the magnetic ion have been made by means of the /sup 151/Eu Moessbauer effect in Eu/sub x/Sn/sub 1-x/Mo/sub 6/S/sub 8/ and the effects of such polarization on superconducting properties discussed. The Moessbauer effect in /sup 166/Er has been used to investigate the electronic ground state in the ternary compound ErRh/sub 4/B/sub 4/ both in the superconducting and magnetically ordered states.
Ambient-pressure organic superconductor
Williams, Jack M.; Wang, Hsien-Hau; Beno, Mark A.
1986-01-01
A new class of organic superconductors having the formula (ET).sub.2 MX.sub.2 wherein ET represents bis(ethylenedithio)-tetrathiafulvalene, M is a metal such as Au, Ag, In, Tl, Rb, Pd and the like and X is a halide. The superconductor (ET).sub.2 AuI.sub.2 exhibits a transition temperature of 5 K which is high for organic superconductors.
Unconventional properties of non-centrosymmetric superconductors
Energy Technology Data Exchange (ETDEWEB)
Klam, Ludwig
2010-10-28
A kinetic theory for non-centrosymmetric superconductors (NCS) is formulated for low temperatures and in the clean limit. The transport equations are solved quite generally for any kind of antisymmetric spin-orbit coupling (ASOC) in an extended momentum and frequency range. The result is a particle-hole symmetric, gauge-invariant and charge conserving description, which is used to calculate the current response, the specific heat capacity, and the Raman response function. A detailed analysis of the gauge invariance and the associated phase fluctuations of the superconducting order parameter revealed two gauge modes: the Anderson-Bogoliubov mode on the one side and a new gauge mode on the other side, which strongly depends on the symmetry of the ASOC. As application of the kinetic theory, the polarization-dependence of the T = 0 electronic Raman response in NCS is studied for two important classes of ASOC with the representative systems CePt{sub 3}Si and Li{sub 2}Pd{sub x}Pt{sub 3-x}B. Analytical expressions for the Raman vertices are derived, and the frequency power laws and pair-breaking peaks are calculated. A characteristic two- peak structure is predicted for NCS and might serve as an indicator for the unknown relative magnitude of the singlet and triplet contributions to the superconducting order parameter. An efficient numerical method is introduced in order to calculate the dynamical spin and charge response of CePt{sub 3}Si, using an itinerant description for the electrons. With a realistic parameterization of the band structure, the nesting function, inelastic neutron scattering cross sections, and Kohn anomalies are calculated for a selected band in the normal non-magnetic state. From the spin and charge susceptibility, a superconducting pairing interaction is constructed for the weak-coupling gap equation. A sign analysis of the decoupled gap equation supports the experimental evidence of a strong triplet contribution to the order parameter in CePt{sub 3
Unconventional properties of non-centrosymmetric superconductors
Energy Technology Data Exchange (ETDEWEB)
Klam, Ludwig
2010-10-28
A kinetic theory for non-centrosymmetric superconductors (NCS) is formulated for low temperatures and in the clean limit. The transport equations are solved quite generally for any kind of antisymmetric spin-orbit coupling (ASOC) in an extended momentum and frequency range. The result is a particle-hole symmetric, gauge-invariant and charge conserving description, which is used to calculate the current response, the specific heat capacity, and the Raman response function. A detailed analysis of the gauge invariance and the associated phase fluctuations of the superconducting order parameter revealed two gauge modes: the Anderson-Bogoliubov mode on the one side and a new gauge mode on the other side, which strongly depends on the symmetry of the ASOC. As application of the kinetic theory, the polarization-dependence of the T = 0 electronic Raman response in NCS is studied for two important classes of ASOC with the representative systems CePt{sub 3}Si and Li{sub 2}Pd{sub x}Pt{sub 3-x}B. Analytical expressions for the Raman vertices are derived, and the frequency power laws and pair-breaking peaks are calculated. A characteristic two- peak structure is predicted for NCS and might serve as an indicator for the unknown relative magnitude of the singlet and triplet contributions to the superconducting order parameter. An efficient numerical method is introduced in order to calculate the dynamical spin and charge response of CePt{sub 3}Si, using an itinerant description for the electrons. With a realistic parameterization of the band structure, the nesting function, inelastic neutron scattering cross sections, and Kohn anomalies are calculated for a selected band in the normal non-magnetic state. From the spin and charge susceptibility, a superconducting pairing interaction is constructed for the weak-coupling gap equation. A sign analysis of the decoupled gap equation supports the experimental evidence of a strong triplet contribution to the order parameter in CePt{sub 3
Directory of Open Access Journals (Sweden)
Shukrinov Yu. M.
2016-01-01
Full Text Available The current-voltage (IV characteristics of the intrinsic Josephson junctions in high temperature superconductors under external electromagnetic radiation are calculated numerically in the parametric resonance region. We discuss a numerical method for calculation of the Shapiro step width on the amplitude of radiation. In order to accelerate computations we used parallelization by task parameter via Simple Linux Utility for Resource Management (SLURM arrays and tested it in the case of a single junction. An analysis of the junction transitions between rotating and oscillating states in the branching region of IV-characteristics is presented.
Theory of thermal conductivity in a multi-band superconductor : Application to pnictides
Mishra, Vivek; Vorontsov, A. B.; Hirschfeld, P. J.; Vekhter, I.
2010-03-01
We calculate low temperature thermal conductivity within a two band model for newly discovered ferro-pnictide superconductors. We consider three different cases, sign changing s-wave state, highly anisotropic s-wave state and a state with order parameter nodes on one band. To include the effect of disorder, we have performed fully self-consistent T-matrix approximation including both intraband and interband impurity scatterings. We also study the behavior of the low temperature thermal conductivity under applied magnetic field using a recently developed variant of the Brandt-Pesch-Tewordt approximation, and compare our results with latest experimental data.
Shukrinov, Yu. M.; Rahmonov, I. R.; Plecenik, A.; Streltsova, O. I.; Zuev, M. I.; Ososkov, G. A.
2016-02-01
The current-voltage (IV) characteristics of the intrinsic Josephson junctions in high temperature superconductors under external electromagnetic radiation are calculated numerically in the parametric resonance region. We discuss a numerical method for calculation of the Shapiro step width on the amplitude of radiation. In order to accelerate computations we used parallelization by task parameter via Simple Linux Utility for Resource Management (SLURM) arrays and tested it in the case of a single junction. An analysis of the junction transitions between rotating and oscillating states in the branching region of IV-characteristics is presented.
Spectral density of Cooper pairs in two level quantum dot-superconductors Josephson junction
Dhyani, A.; Rawat, P. S.; Tewari, B. S.
2016-09-01
In the present paper, we report the role of quantum dot energy levels on the electronic spectral density for a two level quantum dot coupled to s-wave superconducting leads. The theoretical arguments in this work are based on the Anderson model so that it necessarily includes dot energies, single particle tunneling and superconducting order parameter for BCS superconductors. The expression for single particle spectral function is obtained by using the Green's function equation of motion technique. On the basis of numerical computation of spectral function of superconducting leads, it has been found that the charge transfer across such junctions can be controlled by the positions and availability of the dot levels.
Spectral density of Cooper pairs in two level quantum dot–superconductors Josephson junction
Energy Technology Data Exchange (ETDEWEB)
Dhyani, A., E-mail: archana.d2003@gmail.com [Department of Physics, University of Petroleum and Energy Studies, Dehradun 248007, Uttarakhand (India); Rawat, P.S. [Department of Nuclear Science and Technology, University of Petroleum and Energy Studies, Dehradun 248007, Uttarakhand (India); Tewari, B.S., E-mail: bstewari@ddn.upes.ac.in [Department of Physics, University of Petroleum and Energy Studies, Dehradun 248007, Uttarakhand (India)
2016-09-15
Highlights: • The present work deals with the study of the electronic spectral density of electron pairs and its effect in charge transport in superconductor-quantum dot-superconductor junctions. • The charge transfer across such junctions can be controlled by changing the positions of the dot level. • The Josephson supercurrent can also be tuned by controlling the position of quantum dot energy levels. - Abstract: In the present paper, we report the role of quantum dot energy levels on the electronic spectral density for a two level quantum dot coupled to s-wave superconducting leads. The theoretical arguments in this work are based on the Anderson model so that it necessarily includes dot energies, single particle tunneling and superconducting order parameter for BCS superconductors. The expression for single particle spectral function is obtained by using the Green's function equation of motion technique. On the basis of numerical computation of spectral function of superconducting leads, it has been found that the charge transfer across such junctions can be controlled by the positions and availability of the dot levels.
Application of High Temperature Superconductors to Accelerators
Ballarino, A
2000-01-01
Since the discovery of high temperature superconductivity, a large effort has been made by the scientific community to investigate this field towards a possible application of the new oxide superconductors to different devices like SMES, magnetic bearings, flywheels energy storage, magnetic shielding, transmission cables, fault current limiters, etc. However, all present day large scale applications using superconductivity in accelerator technology are based on conventional materials operating at liquid helium temperatures. Poor mechanical properties, low critical current density and sensitivity to the magnetic field at high temperature are the key parameters whose improvement is essential for a large scale application of high temperature superconductors to such devices. Current leads, used for transferring currents from the power converters, working at room temperature, into the liquid helium environment, where the magnets are operating, represent an immediate application of the emerging technology of high t...
Very General Holographic Superconductors and Entanglement Thermodynamics
Dey, Anshuman; Sarkar, Tapobrata
2014-01-01
We construct and analyze holographic superconductors with generalized higher derivative couplings, in single R-charged black hole backgrounds in four and five dimensions. These systems, which we call very general holographic superconductors, have multiple tuning parameters and are shown to exhibit a rich phase structure. We establish the phase diagram numerically as well as by computing the free energy, and then validated the results by calculating the entanglement entropy for these systems. The entanglement entropy is shown to be a perfect indicator of the phase diagram. The differences in the nature of the entanglement entropy in R-charged backgrounds compared to the AdS-Schwarzschild cases are pointed out. We also compute the analogue of the entangling temperature for a subclass of these systems and compare the results with non-hairy backgrounds.
Vortices and nanostructured superconductors
2017-01-01
This book provides expert coverage of modern and novel aspects of the study of vortex matter, dynamics, and pinning in nanostructured and multi-component superconductors. Vortex matter in superconducting materials is a field of enormous beauty and intellectual challenge, which began with the theoretical prediction of vortices by A. Abrikosov (Nobel Laureate). Vortices, vortex dynamics, and pinning are key features in many of today’s human endeavors: from the huge superconducting accelerating magnets and detectors at the Large Hadron Collider at CERN, which opened new windows of knowledge on the universe, to the tiny superconducting transceivers using Rapid Single Flux Quanta, which have opened a revolutionary means of communication. In recent years, two new features have added to the intrinsic beauty and complexity of the subject: nanostructured/nanoengineered superconductors, and the discovery of a range of new materials showing multi-component (multi-gap) superconductivity. In this book, leading researche...
Vortex cutting in superconductors
Glatz, A.; Vlasko-Vlasov, V. K.; Kwok, W. K.; Crabtree, G. W.
2016-08-01
Vortex cutting and reconnection is an intriguing and still-unsolved problem central to many areas of classical and quantum physics, including hydrodynamics, astrophysics, and superconductivity. Here, we describe a comprehensive investigation of the crossing of magnetic vortices in superconductors using time dependent Ginsburg-Landau modeling. Within a macroscopic volume, we simulate initial magnetization of an anisotropic high temperature superconductor followed by subsequent remagnetization with perpendicular magnetic fields, creating the crossing of the initial and newly generated vortices. The time resolved evolution of vortex lines as they approach each other, contort, locally conjoin, and detach, elucidates the fine details of the vortex-crossing scenario under practical situations with many interacting vortices in the presence of weak pinning. Our simulations also reveal left-handed helical vortex instabilities that accompany the remagnetization process and participate in the vortex crossing events.
Directory of Open Access Journals (Sweden)
Alexander I. Voitenko
2011-10-01
Full Text Available A review of the theory describing the coexistence between d-wave superconductivity and s-wave charge-density-waves (CDWs is presented. The CDW gapping is identified with pseudogapping observed in high-Tc oxides. According to the cuprate specificity, the analysis is carried out for the two-dimensional geometry of the Fermi surface (FS. Phase diagrams on the σ0 − α plane—here, σ0 is the ratio between the energy gaps in the parent pure CDW and superconducting states, and the quantity 2α is connected with the degree of dielectric (CDW FS gapping—were obtained for various possible configurations of the order parameters in the momentum space. Relevant tunnel and photoemission experimental data for high-Tc oxides are compared with theoretical predictions. A brief review of the results obtained earlier for the coexistence between s-wave superconductivity and CDWs is also given.
Izmailov, Alexander; Myerson, Allan S.
1993-01-01
A new mathematical ansatz for a solution of the time-dependent Ginzburg-Landau non-linear partial differential equation is developed for non-critical systems such as non-critical binary solutions (solute + solvent) described by the non-conserved scalar order parameter. It is demonstrated that in such systems metastability initiates heterogeneous solute redistribution which results in formation of the non-equilibrium singly-periodic spatial solute structure. It is found how the time-dependent period of this structure evolves in time. In addition, the critical radius r(sub c) for solute embryo of the new solute rich phase together with the metastable state lifetime t(sub c) are determined analytically and analyzed.
Brünger, C; Assaad, F F; Capponi, S; Alet, F; Aristov, D N; Kiselev, M N
2008-01-11
We consider a spin-1/2 ladder with a ferromagnetic rung coupling J perpendicular and inequivalent chains. This model is obtained by a twist (theta) deformation of the ladder and interpolates between the isotropic ladder (theta=0) and the SU(2) ferromagnetic Kondo necklace model (theta = pi). We show that the ground state in the (theta, J perpendicular) plane has a finite string order parameter characterizing the Haldane phase. Twisting the chain introduces a new energy scale, which we interpret in terms of a Suhl-Nakamura interaction. As a consequence we observe a crossover in the scaling of the spin gap at weak coupling from delta/J parallel proportional, variant J perpendicular/J parallel for theta theta c. Those results are obtained on the basis of large scale quantum Monte Carlo calculations.
Ruta, Sergiu; Hovorka, Ondrej; Huang, Pin-Wei; Wang, Kangkang; Ju, Ganping; Chantrell, Roy
2017-03-01
The generic problem of extracting information on intrinsic particle properties from the whole class of interacting magnetic fine particle systems is a long standing and difficult inverse problem. As an example, the Switching Field Distribution (SFD) is an important quantity in the characterization of magnetic systems, and its determination in many technological applications, such as recording media, is especially challenging. Techniques such as the first order reversal curve (FORC) methods, were developed to extract the SFD from macroscopic measurements. However, all methods rely on separating the contributions to the measurements of the intrinsic SFD and the extrinsic effects of magnetostatic and exchange interactions. We investigate the underlying physics of the FORC method by applying it to the output predictions of a kinetic Monte-Carlo model with known input parameters. We show that the FORC method is valid only in cases of weak spatial correlation of the magnetisation and suggest a more general approach.
Roy, Prasanta; Roy, Binoy Krishna
2016-07-01
The Quadruple Tank Process (QTP) is a well-known benchmark of a nonlinear coupled complex MIMO process having both minimum and nonminimum phase characteristics. This paper presents a novel self tuning type Dual Mode Adaptive Fractional Order PI controller along with an Adaptive Feedforward controller for the QTP. The controllers are designed based on a novel Variable Parameter Transfer Function model. The effectiveness of the proposed model and controllers is tested through numerical simulation and experimentation. Results reveal that the proposed controllers work successfully to track the reference signals in all ranges of output. A brief comparison with some of the earlier reported similar works is presented to show that the proposed control scheme has some advantages and better performances than several other similar works.
Ruta, Sergiu; Hovorka, Ondrej; Huang, Pin-Wei; Wang, Kangkang; Ju, Ganping; Chantrell, Roy
2017-01-01
The generic problem of extracting information on intrinsic particle properties from the whole class of interacting magnetic fine particle systems is a long standing and difficult inverse problem. As an example, the Switching Field Distribution (SFD) is an important quantity in the characterization of magnetic systems, and its determination in many technological applications, such as recording media, is especially challenging. Techniques such as the first order reversal curve (FORC) methods, were developed to extract the SFD from macroscopic measurements. However, all methods rely on separating the contributions to the measurements of the intrinsic SFD and the extrinsic effects of magnetostatic and exchange interactions. We investigate the underlying physics of the FORC method by applying it to the output predictions of a kinetic Monte-Carlo model with known input parameters. We show that the FORC method is valid only in cases of weak spatial correlation of the magnetisation and suggest a more general approach. PMID:28338056
Golia, E E; Dimirkou, A; Mitsios, I K
2008-07-01
The main purpose of this research was to determine the levels of heavy metals in tomato, potato and lettuce, grown in agricultural soils of different soil orders (Alfisols, Endisols and Vertisols), located at Central Greece. Soil samples were analysed for available forms (after extraction with DTPA) and for total concentrations (after digestion with Aqua Regia) of metals. Zn, Cu, Cr and Ni were the common metals detected in the vegetables studied. Pb and Cd concentrations were low and in some cases not detectable. Significant correlations among metals concentrations and soil physicochemical parameters were obtained and discussed. The pH value and the percentage of clay content were found to determine the solubility of metals in the soil and their availability for uptake by plants.
Antonov, N. V.; Kompaniets, M. V.; Lebedev, N. M.
2017-02-01
We consider the critical behavior of the O( n)-symmetric model of the ϕ 4 type with an antisymmetric tensor order parameter. According to a previous study of the one-loop approximation in the quantum field theory renormalization group, there is an IR-attractive fixed point in the model, and IR scaling with universal indices hence applies. Using a more specific analysis based on three-loop calculations of the renormalization-group functions and Borel conformal summation, we show that the IR behavior is in fact governed by another fixed point of the renormalization-group equations and the model therefore belongs to a different universality class than the one suggested by the simplest one-loop approximation. Nevertheless, the validity of the obtained results remains a subject for discussion.
DEFF Research Database (Denmark)
Ade, P. A. R.; Aghanim, N.; Armitage-Caplan, C.
2014-01-01
We have constructed the first all-sky map of the thermal Sunyaev-Zeldovich (tSZ) effect by applying specifically tailored component separation algorithms to the 100 to 857 GHz frequency channel maps from the Planck survey. This map shows an obvious galaxy cluster tSZ signal that is well matched...... with blindly detected clusters in the Planck SZ catalogue. To characterize the signal in the tSZ map we have computed its angular power spectrum. At large angular scales (l thermal dust emission. At small angular scales (l > 500) the clustered cosmic......-Gaussianity of the Compton parameter map is further characterized by computing its 1D probability distribution function and its bispectrum. The measured tSZ power spectrum and high order statistics are used to place constraints on sigma(8)....
Amiri, Manouchehr
2014-01-01
We introduce a type of symmetry breaking and associated order parameter in connection with Laplace-Runge-Lenz vector of Kepler orbit through an extended spatial dimension and Ensemble view. By implementation of a small extra spatial dimension and embedded infinitesimal toral manifold, it has been shown that emerging of LRL vector under SO(4)symmetry is in analogy with a variety of explicit and spontaneous symmetry breaking situations and related Goldstone bosons such as phonons and spin waves. A theorem introduced to generalize this concept of breaking symmetry. The diffeomorphism of circular orbit(geodesic)to elliptic one proved to be equivalent with a covariant derivative and related parallel displacement in this extended four dimensional spatial space.Respect to ensemble definition this diffeomorphism breaks the O(2) symmetry of initial orbit and Hamiltonian to Z2 resulting in broken generators in quotient space and associated Goldstone boson as perturbing Hamiltonian term leading to a perpetual circular m...
Christopoulos, Stavros-Richard G.; Sarlis, Nicholas V.; Skordas, Efthimios S.
2016-04-01
It has been recently shown [1,2] that earthquakes of magnitude M greater or equal to 7 are globally correlated. The identification of this correlation became possible when studying the variance κ1 of natural time which has been proposed as an order parameter for seismicity[3,4]. In the present study, we focus on the behaviour of the fluctuations of κ1 before major earthquakes using the Global Centroid Moment Tensor catalogue for a magnitude threshold Mthres=5.0 as in Ref.[5]. Natural time analysis reveals that distinct minima of the fluctuations κ1of seismicity appear within almost five and a half months on average before all major earthquakes of magnitude larger than M8.4. This phenomenon corroborates the recent finding [6] that similar minima of seismicity order parameter fluctuations had been observed before all major shallow earthquakes in Japan. Finally, we examine the statistical significance of the results by using ROC graphs [7,8] and the proposed prediction method has a p-value to occur by chance well below 0.1%. The hit rate is 100% with a false alarm rate only 6.67%. An attempt to lower the target earthquake magnitude threshold will be also presented. REFERENCES [1] N. V. Sarlis, Phys. Rev. E 84, 022101 (2011). [2] N. V. Sarlis and S.-R. G. Christopoulos, Chaos 22, 023123 (2012) [3] P. A. Varotsos, N. V. Sarlis, and E. S. Skordas, Practica of Athens Acad. 76, 294 (2001). [4] P. A. Varotsos, N. V. Sarlis, and E. S. Skordas, Phys. Rev. E 66, 011902 (2002). [5] N.V. Sarlis, S.-R. G. Christopoulos, and E. S. Skordas, Chaos 25, 063110 (2015) [6] N. V. Sarlis et al., Proc. Natl. Acad. Sci. U.S.A. 110, 13734 (2013) [7] T. Fawcett, Pattern Recognit. Lett. 27, 861 (2006). [8] N. V. Sarlis and S.-R. G. Christopoulos, Comput. Phys. Commun. 185, 1172 (2014).
Ponomarev, Sergei Y.; Kaminski, George A.
2011-01-01
A previously introduced POSSIM (POlarizable Simulations with Second order Interaction Model) force field has been extended to include parameters for alanine peptides and protein backbones. New features were introduced into the fitting protocol, as compared to the previous generation of the polarizable force field for proteins. A reduced amount of quantum mechanical data was employed in fitting the electrostatic parameters. Transferability of the electrostatics between our recently developed NMA model and the protein backbone was confirmed. Binding energy and geometry for complexes of alanine dipeptide with a water molecule were estimated and found in a good agreement with high-level quantum mechanical results (for example, the intermolecular distances agreeing within ca. 0.06Å). Following the previously devised procedure, we calculated average errors in alanine di- and tetra-peptide conformational energies and backbone angles and found the agreement to be adequate (for example, the alanine tetrapeptide extended-globular conformational energy gap was calculated to be 3.09 kcal/mol quantim mechanically and 3.14 kcal/mol with the POSSIM force field). However, we have now also included simulation of a simple alpha-helix in both gas-phase and water as the ultimate test of the backbone conformational behavior. The resulting alanine and protein backbone force field is currently being employed in further development of the POSSIM fast polarizable force field for proteins. PMID:21743799
Simulating atomic-scale phenomena on surfaces of unconventional superconductors
Energy Technology Data Exchange (ETDEWEB)
Kreisel, Andreas; Andersen, Brian [Niels Bohr Institute (Denmark); Choubey, Peayush; Hirschfeld, Peter [Univ. of Florida (United States); Berlijn, Tom [CNMS and CSMD, Oak Ridge National Laboratory (United States)
2016-07-01
Interest in atomic scale effects in superconductors has increased because of two general developments: First, the discovery of new materials as the cuprate superconductors, heavy fermion and Fe-based superconductors where the coherence length of the cooper pairs is as small to be comparable to the lattice constant, rendering small scale effects important. Second, the experimental ability to image sub-atomic features using scanning-tunneling microscopy which allows to unravel numerous physical properties of the homogeneous system such as the quasi particle excitation spectra or various types of competing order as well as properties of local disorder. On the theoretical side, the available methods are based on lattice models restricting the spatial resolution of such calculations. In the present project we combine lattice calculations using the Bogoliubov-de Gennes equations describing the superconductor with wave function information containing sub-atomic resolution obtained from ab initio approaches. This allows us to calculate phenomena on surfaces of superconductors as directly measured in scanning tunneling experiments and therefore opens the possibility to identify underlying properties of these materials and explain observed features of disorder. It will be shown how this method applies to the cuprate material Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} and a Fe based superconductor.
Processing of Superconductor-Normal-Superconductor Josephson Edge Junctions
Kleinsasser, A. W.; Barner, J. B.
1997-01-01
The electrical behavior of epitaxial superconductor-normal-superconductor (SNS) Josephson edge junctions is strongly affected by processing conditions. Ex-situ processes, utilizing photoresist and polyimide/photoresist mask layers, are employed for ion milling edges for junctions with Yttrium-Barium-Copper-Oxide (YBCO) electrodes and primarily Co-doped YBCO interlayers.
Holographic Phase Transitions of P-wave Superconductors in Gauss-Bonnet Gravity with Back-reaction
Cai, Rong-Gen; Zhang, Hai-Qing
2010-01-01
We investigate the phase transitions of holographic p-wave superconductors in (4+1)-dimensional Einstein-Yang-Mills-Gauss-Bonnet theories, in a grand canonical ensemble. Turning on the back-reaction of the Yang-Mills field, it is found that the condensations of vector order parameter become harder if the Gauss-Bonnet coefficient grows up or the back-reaction becomes stronger. In particular, the vector order parameter exhibits the features of first order and second order phase transitions, while only the second order phase transition is observed in the probe limit. We discuss the roles that the Gauss-Bonnet term and the back-reaction play in changing the order of phase transition.
Directory of Open Access Journals (Sweden)
Jia Lin Wu
2013-06-01
Full Text Available In macromolecular self-avoiding random walk, movement of each chain-particle accompanies an instantaneous spin system with de Gennes n = 0 that provides extra energy, extra vacancy volume and relaxation time needed for chain-particles co-movement. Using these additional and instantaneous spin systems not only directly yields the same Brownian motion mode in glass transition (GT and reptation-tube model, but also proves that the entangled chain length corresponding to the Reynolds number in hydrodynamics and the inherent diffusion - delocalization mode of entangled chains, from frozen glass state to melt liquid state, is a chain-size solitary wave with transverse ripplon-like soft wave. Thus, the order parameter of GT is found. The various currently available GT theories, such as Static Replica, Random First-Order Transition, Potential Energy Landscape, Mode-Coupling and Nanoscale Heterogeneity, can be unified using the additional and instantaneous spin system. GT served as an inspiration and continues to serve as the paradigm in the universal random delocalization transitions from disorder to more disorder until turbulence.
Vu, Hoang Lan; Ng, Kelvin Tsun Wai; Richter, Amy
2017-08-17
Canada has one of the highest waste generation rates in the world. Because of high land availability, land disposal rates in the province of Saskatchewan are high compared to the rest of the country. In this study, landfill gas data was collected at semi-arid landfills in Regina and Saskatoon, Saskatchewan, and curve fitting was carried out to find optimal k and Lo or DOC values using LandGEM, Afvalzorg Simple, and IPCC first order decay models. Model parameters at each landfill were estimated and compared using default k and Lo or DOC values. Methane generation rates were substantially overestimated using default values (with percentage errors from 55 to 135%). The mean percentage errors for the optimized k and Lo or DOC values ranged from 11.60% to 19.93% at the Regina landfill, and 1.65% to 10.83% at the Saskatoon landfill. Finally, the effect of different iterative methods on the curve fitting process was examined. The residual sum of squares for each model and iterative approaches were similar, with the exception of iterative method 1 for the IPCC model. The default values in these models fail to represent landfills located in cold semi-arid climates. The use of site specific data, provided enough information is available regarding waste mass and composition, can greatly help to improve the accuracy of these first order decay models. Copyright © 2017 Elsevier Ltd. All rights reserved.
Iron-Based Superconductors as topological matter
Hu, Jiangping
We show the existence of non-trivial topological properties in Iron-based superconductors. Several examples are provided, including (1) the single layer FeSe grown on SrTiO3 substrate, in which an topological insulator phase exists due to the band inversion at M point; (2) CaFeAs2, a staggered intercalation compound that integrates both quantum spin hall and superconductivity in which the nontrivial topology stems from the chain-like As layers away from FeAs layers; (3) the Fe(Te,Se) thin films in which the nontrivial Z2 topological invariance originates from the parity exchange at Γ point that is controlled by the Te(Se) height; (4 nontrivial topology that is driven by the nematic order in FeSe. These results lay ground for integrating high Tc superconductivity with topological properties to realize new emergent phenomena, such as majorana particles, in iron-based high temperature superconductors
Asymmetric Ferromagnet-Superconductor-Ferromagnet Switch
Energy Technology Data Exchange (ETDEWEB)
Cadden-Zimansky, P.; Bazaliy, Ya.B.; Litvak, L.M.; Jiang, J.S.; Pearson, J.; Gu, J.Y.; You, Chun-Yeol; Beasley, M.R.; Bader, S.D.
2011-11-04
In layered ferromagnet-superconductor-ferromagnet F{sub 1} /S/F{sub 2} structures, the critical temperature T{sub c} of the superconductors depends on the magnetic orientation of the ferromagnetic layers F{sub 1} and F{sub 2} relative to each other. So far, the experimentally observed magnitude of change in T{sub c} for structures utilizing weak ferromagnets has been 2 orders of magnitude smaller than is expected from calculations. We theoretically show that such a discrepancy can result from the asymmetry of F/S boundaries, and we test this possibility by performing experiments on structures where F{sub 1} and F{sub 2} are independently varied. Our experimental results indicate that asymmetric boundaries are not the source of the discrepancy. If boundary asymmetry is causing the suppressed magnitude of T{sub c} changes, it may only be possible to detect in structures with thinner ferromagnetic layers.
Revisiting holographic superconductors with hyperscaling violation
Energy Technology Data Exchange (ETDEWEB)
Pan, Qiyuan [Universidade de Sao Paulo, Instituto de Fisica, C.P. 66318, Sao Paulo (Brazil); Hunan Normal University, Department of Physics, Key Laboratory of Low Dimensional Quantum Structures and Quantum Control of Ministry of Education, Changsha, Hunan (China); Institute of Theoretical Physics, Chinese Academy of Sciences, State Key Laboratory of Theoretical Physics, Beijing (China); Zhang, Shao-Jun [Universidade de Sao Paulo, Instituto de Fisica, C.P. 66318, Sao Paulo (Brazil)
2016-03-15
We investigate the effect of the hyperscaling violation on the holographic superconductors. In the s-wave model, we find that the critical temperature decreases first and then increases as the hyperscaling violation increases, and the mass of the scalar field will not modify the value of the hyperscaling violation which gives the minimum critical temperature. We analytically confirm the numerical results by using the Sturm-Liouville method with the higher order trial function and improve the previous findings in Fan (J High Energy Phys 09:048, 2013). However, different from the s-wave case, we note that the critical temperature decreases with the increase of the hyperscaling violation in the p-wave model. In addition, we observe that the hyperscaling violation affects the conductivity of the holographic superconductors and changes the expected relation in the gap frequency in both s-wave and p-wave models. (orig.)
Energy efficiency of adiabatic superconductor logic
Takeuchi, Naoki; Yamanashi, Yuki; Yoshikawa, Nobuyuki
2015-01-01
Adiabatic superconductor logic (ASL), including adiabatic quantum-flux-parametron (AQFP) logic, exhibits high energy efficiency because its bit energy can be decreased below the thermal energy through adiabatic switching operations. In the present paper, we present the general scaling laws of ASL and compare the energy efficiency of ASL with those of other energy-efficient logics. Also, we discuss the minimum energy-delay product (EDP) of ASL at finite temperature. Our study shows that there is a maximum temperature at which the EDP can reach the quantum limit given by ħ/2, which is dependent on the superconductor material and the Josephson junction quality, and that it is reasonable to operate ASL at cryogenic temperatures in order to achieve an EDP that approaches ħ/2.
Testability issues in Superconductor Electronics
Kerkhoff, Hans G.; Arun, A.J.
2004-01-01
An emerging technology for solutions in high-end applications in computing and telecommunication is superconductor electronics. A system-level study has been carried out to verify the feasibility of DfT in superconductor electronics. In this paper, we present how this can be realized to monitor
Electronic origin of structural transition in 122 Fe based superconductors
Ghosh, Haranath; Sen, Smritijit; Ghosh, Abyay
2017-03-01
Direct quantitative correlations between the orbital order and orthorhombicity is achieved in a number of Fe-based superconductors of 122 family. The former (orbital order) is calculated from first principles simulations using experimentally determined doping and temperature dependent structural parameters while the latter (the orthorhombicity) is taken from already established experimental studies; when normalized, both the above quantities quantitatively corresponds to each other in terms of their doping as well as temperature variations. This proves that the structural transition in Fe-based materials is electronic in nature due to orbital ordering. An universal correlations among various structural parameters and electronic structure are also obtained. Most remarkable among them is the mapping of two Fe-Fe distances in the low temperature orthorhombic phase, with the band energies Edxz, Edyz of Fe at the high symmetry points of the Brillouin zone. The fractional co-ordinate zAs of As which essentially determines anion height is inversely (directly) proportional to Fe-As bond distances (with exceptions of K doped BaFe2As2) for hole (electron) doped materials as a function of doping. On the other hand, Fe-As bond-distance is found to be inversely (directly) proportional to the density of states at the Fermi level for hole (electron) doped systems. Implications of these results to current issues of Fe based superconductivity are discussed.
Peng, Yingying; Meng, Jianqiao; Mou, Daixiang; He, Junfeng; Zhao, Lin; Wu, Yue; Liu, Guodong; Dong, Xiaoli; He, Shaolong; Zhang, Jun; Wang, Xiaoyang; Peng, Qinjun; Wang, Zhimin; Zhang, Shenjin; Yang, Feng; Chen, Chuangtian; Xu, Zuyan; Lee, T K; Zhou, X J
2013-01-01
The parent compound of the copper-oxide high-temperature superconductors is a Mott insulator. Superconductivity is realized by doping an appropriate amount of charge carriers. How a Mott insulator transforms into a superconductor is crucial in understanding the unusual physical properties of high-temperature superconductors and the superconductivity mechanism. Here we report high-resolution angle-resolved photoemission measurement on heavily underdoped Bi₂Sr₂-xLaxCuO(₆+δ) system. The electronic structure of the lightly doped samples exhibit a number of characteristics: existence of an energy gap along the nodal direction, d-wave-like anisotropic energy gap along the underlying Fermi surface, and coexistence of a coherence peak and a broad hump in the photoemission spectra. Our results reveal a clear insulator-superconductor transition at a critical doping level of ~0.10 where the nodal energy gap approaches zero, the three-dimensional antiferromagnetic order disappears, and superconductivity starts to emerge. These observations clearly signal a close connection between the nodal gap, antiferromagnetism and superconductivity.
Coupling spin qubits via superconductors
DEFF Research Database (Denmark)
Leijnse, Martin; Flensberg, Karsten
2013-01-01
We show how superconductors can be used to couple, initialize, and read out spatially separated spin qubits. When two single-electron quantum dots are tunnel coupled to the same superconductor, the singlet component of the two-electron state partially leaks into the superconductor via crossed...... Andreev reflection. This induces a gate-controlled singlet-triplet splitting which, with an appropriate superconductor geometry, remains large for dot separations within the superconducting coherence length. Furthermore, we show that when two double-dot singlet-triplet qubits are tunnel coupled...... to a superconductor with finite charging energy, crossed Andreev reflection enables a strong two-qubit coupling over distances much larger than the coherence length....
Wang, Qisi; Park, J T; Feng, Yu; Shen, Yao; Hao, Yiqing; Pan, Bingying; Lynn, J W; Ivanov, A; Chi, Songxue; Matsuda, M; Cao, Huibo; Birgeneau, R J; Efremov, D V; Zhao, Jun
2016-05-13
An essential step toward elucidating the mechanism of superconductivity is to determine the sign or phase of the superconducting order parameter, as it is closely related to the pairing interaction. In conventional superconductors, the electron-phonon interaction induces attraction between electrons near the Fermi energy and results in a sign-preserved s-wave pairing. For high-temperature superconductors, including cuprates and iron-based superconductors, prevalent weak coupling theories suggest that the electron pairing is mediated by spin fluctuations which lead to repulsive interactions, and therefore that a sign-reversed pairing with an s_{±} or d-wave symmetry is favored. Here, by using magnetic neutron scattering, a phase sensitive probe of the superconducting gap, we report the observation of a transition from the sign-reversed to sign-preserved Cooper-pairing symmetry with insignificant changes in T_{c} in the S-doped iron selenide superconductors K_{x}Fe_{2-y}(Se_{1-z}S_{z})_{2}. We show that a rather sharp magnetic resonant mode well below the superconducting gap (2Δ) in the undoped sample (z=0) is replaced by a broad hump structure above 2Δ under 50% S doping. These results cannot be readily explained by simple spin fluctuation-exchange pairing theories and, therefore, multiple pairing channels are required to describe superconductivity in this system. Our findings may also yield a simple explanation for the sometimes contradictory data on the sign of the superconducting order parameter in iron-based materials.
AC susceptibilities of grain-textured superconductors
Energy Technology Data Exchange (ETDEWEB)
Sakamoto, N. [Department of Electrical Engineering, Kyushu Sangyo University, 2-3-1 Matsukadai, 813-8503 Fukuoka (Japan)], E-mail: saka@te.kyusan-u.ac.jp; Fukuda, Y.; Koga, M.; Akune, T. [Department of Electrical Engineering, Kyushu Sangyo University, 2-3-1 Matsukadai, 813-8503 Fukuoka (Japan); Khan, H.R. [Institut von Ionenstrahl und Vakuum Technologie, 73728 Esslingen (Germany); Lueders, K. [Freie Universitaet Berlin, Arnimallee, Fac.Physik, D-14195 Berlin (Germany)
2008-09-15
In-phase {chi}{sub n}' and out-phase {chi}{sub n}'' components of nth harmonics of AC susceptibility with measuring parameters of a DC magnetic field B{sub dc}, an amplitude B{sub a} and a frequency f of the superimposed AC magnetic fields give substantial information of the superconducting properties. In low-T{sub c} metallic superconductors, {chi}{sub 1}' shows smooth transition and {chi}{sub 1}'' does single peak. High-T{sub c} oxide superconductors with anisotropic and grain-textured structures show deformed complex characteristics. Double peaks in {chi}{sub 1}'' and shoulders in {chi}{sub 1}' appear in AC susceptibility of Hg-1223 superconductors. Instead of simple Bean model, a grained model, where the superconducting grains are immersed in weak superconducting matrix, are proposed. The susceptibilities numerically analyzed using the model show varied and deformed curves and are successfully compared with the measured results.
A Simple Holographic Superconductor with Momentum Relaxation
Kim, Keun-Young; Park, Miok
2015-01-01
We study a holographic superconductor model with momentum relaxation due to massless scalar fields linear to spatial coordinates($\\psi_I = \\beta \\delta_{Ii} x^i$), where $\\beta$ is the strength of momentum relaxation. In addition to the original superconductor induced by the chemical potential($\\mu$) at $\\beta=0$, there exists a new type of superconductor induced by $\\beta$ even at $\\mu=0$. It may imply a new `pairing' mechanism of particles and antiparticles interacting with $\\beta$, which may be interpreted as `impurity'. Two parameters $\\mu$ and $\\beta$ compete in forming superconducting phase. As a result, the critical temperature behaves differently depending on $\\beta/\\mu$. It decreases when $\\beta/\\mu$ is small and increases when $\\beta/\\mu$ is large, which is a novel feature compared to other models. After analysing ground states and phase diagrams for various $\\beta/\\mu$, we study optical electric($\\sigma$), thermoelectric($\\alpha$), and thermal($\\bar{\\kappa}$) conductivities. When the system undergo...
Georgiev, Georgi; Gombos, Erin; McIntyre, Michael; Mattera, Michael; Gati, Peter; Cabrera, Yaniel; Cebe, Peggy
2010-03-01
We studied the effects of multiwalled carbon nanotubes (MWCTs) at low concentrations (0.01 wt %) on the Freedericksz transition of a 4-Cyano-4'-pentylbipenyl (5CB) liquid crystal using transmission ellipsometry. In addition, we calibrated the altitudinal angle of CNTs as a function of the electric field and directed the azimuthal angle which gave us complete control of the 3D orientation of the CNTs. Our results show that in the presence of CNTs the voltage and width for the Freedericksz transition are reduced by a factor of 1.8 as compared to the control electro-optic cell without CNTs. The shift in transition voltage correlates with increase in order parameter of the electro-optic cell as measured by our polarized UV/Vis absorption spectroscopy results. Research supported by: Assumption College Faculty Development Grant, funding for students' stipends, instrumentation and supplies, the NSF Polymers Program of the DME, grant (DMR-0602473) and NASA grant (NAG8-1167).
High temperature superconductors
Paranthaman, Parans
2010-01-01
This essential reference provides the most comprehensive presentation of the state of the art in the field of high temperature superconductors. This growing field of research and applications is currently being supported by numerous governmental and industrial initiatives in the United States, Asia and Europe to overcome grid energy distribution issues. The technology is particularly intended for densely populated areas. It is now being commercialized for power-delivery devices, such as power transmission lines and cables, motors and generators. Applications in electric utilities include current limiters, long transmission lines and energy-storage devices that will help industries avoid dips in electric power.
Antenna applications of superconductors
Hansen, R. C.
1991-09-01
The applicability of superconductors to antennas is examined. Potential implementations that are examined are superdirective arrays; electrically small antennas; tuning and matching of these two; high-gain millimeter-wavelength arrays; and kinetic inductance slow wave structures for array phasers and traveling wave array feeds. It is thought that superdirective arrays and small antennas will not benefit directly, but their tuning/matching networks will undergo major improvements. Miniaturization of antennas will not be aided, but much higher gain millimeter-wave arrays will be realizable. Kinetic inductance slow-wave lines appear advantageous for improved array phasers and time delay, as well as for traveling-wave array feeds.
Nanoscale magnetization of a single vortex in d-wave superconductors
Zakharchuk, I.; Januzaj, A.; Safonchik, M.; Traito, K. B.; Lähderanta, E.
2017-01-01
A finite-size scaling of the nanoscale magnetization m on size averaging R of a single vortex in d-wave bulk superconductor is developed using quasiclassical Eilenberger equations. Nanoscaling is anchoring around the linear London approximation for bulk superconductors. Comparing the results with those obtained in local nonlinear approach demonstrated the importance of the nonlocal contribution. Temperature dependences of two-point correlation function χ(T , R 1 , R 2) = m(T , R 2) / m(0 , R 2) - m(T , R 1) / m(0 , R 1) with R2 > R1 and one-point function χ(T, R1 → ∞, R2) are calculated. It is found that χ(T, R1, R2), R2 > R1, is a nonmonotonous function of temperature and changes sign at high temperatures. This nonmonotonous temperature dependence can be understood as a result of competition between various effects i) Volovik effect and nonlocal corrections to superconducting electron density dominating in low temperature range, and ii) current-induced suppression of the order parameter dominating at high temperatures. The introduced nonmagnetic disorder greatly suppresses the low temperature nonlocal and nonlinear effects, leaving the order parameter effects to prevail in the whole temperature range. Nonlocal pairing and tunneling effects are investigated at the superconductor - normal metal border by considering a d-wave superconducting dot (d-dot) inside a normal diffusive metal. These effects result in a suppression of the supercurrent in the vortex core and are essential in nanodots with relatively small sizes. At sizes larger than a temperature dependent characteristic length the nanoscale physics transforms into bulk solution.
Electronic structure investigation of novel superconductors
Energy Technology Data Exchange (ETDEWEB)
Buling, Anna
2014-05-15
The discovery of superconductivity in iron-based pnictides in 2008 gave rise to a high advance in the research of high-temperature superconductors. But up to now there is no generally admitted theory of the non-BCS mechanism of these superconductors. The electron and hole doped Ba122 (BaFe{sub 2}As{sub 2}) compounds investigated in this thesis are supposed to be suitable model systems for studying the electronic behavior in order to shed light on the superconducting mechanisms. The 3d-transition metal doped Ba122 compounds are investigated using the X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES) and X-ray magnetic circular dichroism (XMCD), while the completely hole doped K122 is observed using XPS. The experimental measurements are complemented by theoretical calculations. A further new class of superconductors is represented by the electride 12CaO*7Al{sub 2}O{sub 3}: Here superconductivity can be realized by electrons accommodated in the crystallographic sub-nanometer-sized cavities, while the mother compound is a wide band gap insulator. Electronic structure investigations, represented by XPS, XAS and resonant X-ray photoelectron spectroscopy (ResPES), carried out in this work, should help to illuminate this unconventional superconductivity and resolve a debate of competing models for explaining the existence of superconductivity in this compound.
Institute of Scientific and Technical Information of China (English)
B. Kutlu; M. Civi
2006-01-01
@@ We study the order parameter probability distribution at the critical point for the three-dimensional spin-1/2 and spin-1 Ising models on the simple cubic lattice under periodic boundary conditions.
Neutron and Synchrotron X-Ray Scattering Studies of Superconductors
Energy Technology Data Exchange (ETDEWEB)
Tranquada,J.M.
2008-09-01
Superconductors hold the promise for a more stable and efficient electrical grid, but new isotropic, high-temperature superconductors are needed in order to reduce cable manufacturing costs. The effort to understand high-temperature superconductivity, especially in the layered cuprates, provides guidance to the search for new superconductors. Neutron scattering has long provided an important probe of the collective excitations that are involved in the pairing mechanism. For the cuprates, neutron and x-ray diffraction techniques also provide information on competing types of order, such as charge and spin stripes, that appear to be closely connected to the superconductivity. Recently, inelastic x-ray scattering has become competitive for studying phonons and may soon provide valuable information on electronic excitations. Examples of how these techniques contribute to our understanding of superconductivity are presented.
Neutron and synchrotron x-ray scattering studies of superconductors
Energy Technology Data Exchange (ETDEWEB)
Tranquada, J.M.
2008-10-15
Superconductors hold the promise for a more stable and efficient electrical grid, but new isotropic, high-temperature superconductors are needed in order to reduce cable manufacturing costs. The effort to understand high-temperature superconductivity, especially in the layered cuprates, provides guidance to the search for new superconductors. Neutron scattering has long provided an important probe of the collective excitations that are involved in the pairing mechanism. For the cuprates, neutron and x-ray diffraction techniques also provide information on competing types of order, such as charge and spin stripes that appear to be closely connected to the superconductivity. Recently, inelastic x-ray scattering has become competitive for studying phonons and may soon provide valuable information on electronic excitations. Examples of how these techniques contribute to our understanding of superconductivity are presented. (au)
Superconductor digital electronics: Scalability and energy efficiency issues (Review Article)
Tolpygo, Sergey K.
2016-05-01
Superconductor digital electronics using Josephson junctions as ultrafast switches and magnetic-flux encoding of information was proposed over 30 years ago as a sub-terahertz clock frequency alternative to semiconductor electronics based on complementary metal-oxide-semiconductor (CMOS) transistors. Recently, interest in developing superconductor electronics has been renewed due to a search for energy saving solutions in applications related to high-performance computing. The current state of superconductor electronics and fabrication processes are reviewed in order to evaluate whether this electronics is scalable to a very large scale integration (VLSI) required to achieve computation complexities comparable to CMOS processors. A fully planarized process at MIT Lincoln Laboratory, perhaps the most advanced process developed so far for superconductor electronics, is used as an example. The process has nine superconducting layers: eight Nb wiring layers with the minimum feature size of 350 nm, and a thin superconducting layer for making compact high-kinetic-inductance bias inductors. All circuit layers are fully planarized using chemical mechanical planarization (CMP) of SiO2 interlayer dielectric. The physical limitations imposed on the circuit density by Josephson junctions, circuit inductors, shunt and bias resistors, etc., are discussed. Energy dissipation in superconducting circuits is also reviewed in order to estimate whether this technology, which requires cryogenic refrigeration, can be energy efficient. Fabrication process development required for increasing the density of superconductor digital circuits by a factor of ten and achieving densities above 107 Josephson junctions per cm2 is described.
Directory of Open Access Journals (Sweden)
Yan Peng
2017-02-01
Full Text Available We investigate holographic phase transitions with dark matter sector in the AdS soliton background away from the probe limit. In cases of weak backreaction, we find that the larger coupling parameter α makes the gap of condensation shallower and the critical chemical potential keeps as a constant. In contrast, for very heavy backreaction, the dark matter sector could affect the critical chemical potential and the order of phase transitions. We also find the jump of the holographic topological entanglement entropy corresponds to a first order transition between superconducting states in this model with dark matter sector. More importantly, for certain sets of parameters, we observe novel phenomenon of retrograde condensation. In a word, the dark matter sector provides richer physics in the phase structure and the holographic superconductor properties are helpful in understanding dark matter.
Energy Technology Data Exchange (ETDEWEB)
Peng, Yan, E-mail: yanpengphy@163.com [School of Mathematical Sciences, Qufu Normal University, Qufu, Shandong 273165 (China); School of Mathematics and Computer Science, Shaanxi Sci-Tech University, Hanzhong, Shaanxi 723000 (China); Pan, Qiyuan, E-mail: panqiyuan@126.com [Department of Physics, Key Laboratory of Low Dimensional Quantum Structures and Quantum Control of Ministry of Education, Hunan Normal University, Changsha, Hunan 410081 (China); Liu, Yunqi, E-mail: liuyunqi@hust.edu.cn [School of Physics, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China)
2017-02-15
We investigate holographic phase transitions with dark matter sector in the AdS soliton background away from the probe limit. In cases of weak backreaction, we find that the larger coupling parameter α makes the gap of condensation shallower and the critical chemical potential keeps as a constant. In contrast, for very heavy backreaction, the dark matter sector could affect the critical chemical potential and the order of phase transitions. We also find the jump of the holographic topological entanglement entropy corresponds to a first order transition between superconducting states in this model with dark matter sector. More importantly, for certain sets of parameters, we observe novel phenomenon of retrograde condensation. In a word, the dark matter sector provides richer physics in the phase structure and the holographic superconductor properties are helpful in understanding dark matter.
Peng, Yan; Pan, Qiyuan; Liu, Yunqi
2017-02-01
We investigate holographic phase transitions with dark matter sector in the AdS soliton background away from the probe limit. In cases of weak backreaction, we find that the larger coupling parameter α makes the gap of condensation shallower and the critical chemical potential keeps as a constant. In contrast, for very heavy backreaction, the dark matter sector could affect the critical chemical potential and the order of phase transitions. We also find the jump of the holographic topological entanglement entropy corresponds to a first order transition between superconducting states in this model with dark matter sector. More importantly, for certain sets of parameters, we observe novel phenomenon of retrograde condensation. In a word, the dark matter sector provides richer physics in the phase structure and the holographic superconductor properties are helpful in understanding dark matter.
Pair correlations in iron-based superconductors: Quantum Monte Carlo study
Energy Technology Data Exchange (ETDEWEB)
Kashurnikov, V.A.; Krasavin, A.V., E-mail: avkrasavin@gmail.com
2014-08-01
The new generalized quantum continuous time world line Monte Carlo algorithm was developed to calculate pair correlation functions for two-dimensional FeAs-clusters modeling of iron-based superconductors using a two-orbital model. The data obtained for clusters with sizes up to 10×10 FeAs-cells favor the possibility of an effective charge carrier's attraction that is corresponding the A{sub 1g}-symmetry, at some parameters of interaction. The analysis of pair correlations depending on the cluster size, temperature, interaction, and the type of symmetry of the order parameter is carried out. - Highlights: • New generalized quantum continuous time world line Monte Carlo algorithm is developed. • Pair correlation functions for two-dimensional FeAs-clusters are calculated. • Parameters of two-orbital model corresponding to attraction of carriers are defined.
Flux pinning in superconductors
Matsushita, Teruo
2014-01-01
The book covers the flux pinning mechanisms and properties and the electromagnetic phenomena caused by the flux pinning common for metallic, high-Tc and MgB2 superconductors. The condensation energy interaction known for normal precipitates or grain boundaries and the kinetic energy interaction proposed for artificial Nb pins in Nb-Ti, etc., are introduced for the pinning mechanism. Summation theories to derive the critical current density are discussed in detail. Irreversible magnetization and AC loss caused by the flux pinning are also discussed. The loss originally stems from the ohmic dissipation of normal electrons in the normal core driven by the electric field induced by the flux motion. The readers will learn why the resultant loss is of hysteresis type in spite of such mechanism. The influence of the flux pinning on the vortex phase diagram in high Tc superconductors is discussed, and the dependencies of the irreversibility field are also described on other quantities such as anisotropy of supercondu...
Flux Pinning in Superconductors
Matsushita, Teruo
2007-01-01
The book covers the flux pinning mechanisms and properties and the electromagnetic phenomena caused by the flux pinning common for metallic, high-Tc and MgB2 superconductors. The condensation energy interaction known for normal precipitates or grain boundaries and the kinetic energy interaction proposed for artificial Nb pins in Nb-Ti, etc., are introduced for the pinning mechanism. Summation theories to derive the critical current density are discussed in detail. Irreversible magnetization and AC loss caused by the flux pinning are also discussed. The loss originally stems from the ohmic dissipation of normal electrons in the normal core driven by the electric field induced by the flux motion. The readers will learn why the resultant loss is of hysteresis type in spite of such mechanism. The influence of the flux pinning on the vortex phase diagram in high Tc superconductors is discussed, and the dependencies of the irreversibility field are also described on other quantities such as anisotropy of supercondu...
Hybrid superconductor magnet bearings
Chu, Wei-Kan
1995-01-01
Hybrid superconductor magnet bearings (HSMB's) utilize high temperature superconductors (HTS's) together with permanent magnets to form a frictionless interface between relatively rotating parts. They are low mass, stable, and do not incur expenditure of energy during normal operation. There is no direct physical contact between rotor and stator, and hence there is no wear and tear. However, just as any other applications of HTS's, it requires a very cold temperature to function. Whereas this might be perceived as a disadvantage on earth, it is of no great concern in space or on the moon. To astronomers, the moon is an excellent site for an observatory, but the cold and dusty vacuum environment on the moon precludes the use of mechanical bearings on the telescope mounts. Furthermore, drive mechanisms with very fine steps, and hence bearings with extremely low friction are needed to track a star from the moon, because the moon rotates very slowly. All aspects considered, the HSMB is about the only candidate that fits in naturally. Here, we present a design for one such bearing, capable of supporting a telescope that weighs about 3 lbs on Earth.
Moore, Craig E.; Cardelino, Beatriz H.; Frazier, Donald O.; Niles, Julian; Wang, Xian-Qiang
1997-01-01
Calculations were performed on the valence contribution to the static molecular third-order polarizabilities (gamma) of thirty carbon-cage fullerenes (C60, C70, five isomers of C78, and twenty-three isomers of C84). The molecular structures were obtained from B3LYP/STO-3G calculations. The values of the tensor elements and an associated numerical uncertainty were obtained using the finite-field approach and polynomial expansions of orders four to eighteen of polarization versus static electric field data. The latter information was obtained from semiempirical calculations using the AM1 hamiltonian.
The upper critical field in two-band layered superconductors
Institute of Scientific and Technical Information of China (English)
Liu Min-Xia; Gan Zi-Zhao
2007-01-01
The upper critical field of clean MgB2 is investigated using the two-band layered Ginzburg-Landau (GL) theory.The calculated results are fitted to the experimental data of clean MgB2 crystal very well in a broad temperature range.Based on the GL theory for clean superconductors,a phenomenOlogical theory for dirty superconductor is proposed.Selecting appropriate parameters,two-band layered GL theory is successfully applied to the crystal of Mg(B1-xCx)2 and the neutron irradiation samples of MgB2.
XRD spectra of new YBaCuO superconductors
Indian Academy of Sciences (India)
S Sujinnapram; P Udomsamuthirun; T Kruaehong; T Nilkamjon; S Ratreng
2011-08-01
XRD spectra of new YBaCuO superconductors were studied. There were 2 phases found in our samples, the superconducting phase and the non-superconducting phase. The more non-superconducting phase, the more anisotropy parameters were found. The amount of impurities have no effect on the value of -axis which has a linear relation to the number of Cu-atoms. So the new formula of YBaCuO are the new types of superconductor in this family that have higher -axis than the Y123.
Magnetic response of holographic Lifshitz superconductors: Vortex and Droplet solutions
Energy Technology Data Exchange (ETDEWEB)
Lala, Arindam, E-mail: arindam.lala@bose.res.in
2014-07-30
In this paper a holographic model of s-wave superconductor with anisotropic Lifshitz scaling has been considered. In the presence of an external magnetic field our holographic model exhibits both vortex and droplet solutions. Based on analytic methods we have shown that the anisotropy has no effect on the vortex and droplet solutions whereas it may affect the condensation. Our vortex solution closely resembles the Ginzburg–Landau theory and a relation between the upper critical magnetic field and superconducting coherence length has been speculated from this comparison. Using Sturm–Liouville method, the effect of anisotropy on the critical parameters in insulator/superconductor phase transitions has been analyzed.
Vortex lines in a ferromagnetic spin-triplet superconductor
Institute of Scientific and Technical Information of China (English)
Zhao Li; Yang Jie; Xie Qun-Ying; Tian Miao; Duan Yi-Shi
2012-01-01
Based on Duan's topological current theory,we show that in a ferromagnetic spin-triplet superconductor there is a topological defect of string structures which can be interpreted as vortex lines.Such defects are different from the Abrikosov vortices in one-component condensate systems.We investigate the inner topological structure of the vortex lines.The topological charge density,velocity,and topological current of the vortex lines can all be expressed in terms of δ function,which indicates that the vortices can only arise from the zero points of an order parameter field.The topological charges of vortex lines are quantized in terms of the Hopf indices and Brouwer degrees of φ-mapping.The divergence of the self-induced magnetic field can be rigorously determined by the corresponding order parameter fields and its expression also takes the form of a δ-like function.Finally,based on the implicit function theorem and the Taylor expansion,we conduct detailed studies on the bifurcation of vortex topological current and find different directions of the bifurcation.
Magnetic excitations in iron chalcogenide superconductors.
Kotegawa, Hisashi; Fujita, Masaki
2012-10-01
Nuclear magnetic resonance and neutron scattering experiments in iron chalcogenide superconductors are reviewed to make a survey of the magnetic excitations in FeSe, FeSe1-x Te x and alkali-metal-doped Ax Fe2-y Se2 (A = K, Rb, Cs, etc). In FeSe, the intimate relationship between the spin fluctuations and superconductivity can be seen universally for the variations in the off-stoichiometry, the Co-substitution and applied pressure. The isovalent compound FeTe has a magnetic ordering with different wave vector from that of other Fe-based magnetic materials. The transition temperature Tc of FeSe increases with Te substitution in FeSe1-x Te x with small x, and decreases in the vicinity of the end member FeTe. The spin fluctuations are drastically modified by the Te substitution. In the vicinity of the end member FeTe, the low-energy part of the spin fluctuation is dominated by the wave vector of the ordered phase of FeTe; however, the reduction of Tc shows that it does not support superconductivity. The presence of same wave vector as that of other Fe-based superconductors in FeSe1-x Te x and the observation of the resonance mode demonstrate that FeSe1-x Te x belongs to the same group as most of other Fe-based superconductors in the entire range of x, where superconductivity is mediated by the spin fluctuations whose wave vector is the same as the nesting vector between the hole pockets and the electron pockets. On the other hand, the spin fluctuations differ for alkali-metal-doped Ax Fe2-y Se2 and FeSe or other Fe-based superconductors in their wave vector and strength in the low-energy part, most likely because of the different Fermi surfaces. The resonance mode with different wave vector suggests that Ax Fe2-y Se2 has an exceptional superconducting symmetry among Fe-based superconductors.
Materials design for new superconductors.
Norman, M R
2016-07-01
Since the announcement in 2011 of the Materials Genome Initiative by the Obama administration, much attention has been given to the subject of materials design to accelerate the discovery of new materials that could have technological implications. Although having its biggest impact for more applied materials like batteries, there is increasing interest in applying these ideas to predict new superconductors. This is obviously a challenge, given that superconductivity is a many body phenomenon, with whole classes of known superconductors lacking a quantitative theory. Given this caveat, various efforts to formulate materials design principles for superconductors are reviewed here, with a focus on surveying the periodic table in an attempt to identify cuprate analogues.
Materials design for new superconductors
Norman, M. R.
2016-07-01
Since the announcement in 2011 of the Materials Genome Initiative by the Obama administration, much attention has been given to the subject of materials design to accelerate the discovery of new materials that could have technological implications. Although having its biggest impact for more applied materials like batteries, there is increasing interest in applying these ideas to predict new superconductors. This is obviously a challenge, given that superconductivity is a many body phenomenon, with whole classes of known superconductors lacking a quantitative theory. Given this caveat, various efforts to formulate materials design principles for superconductors are reviewed here, with a focus on surveying the periodic table in an attempt to identify cuprate analogues.
TECHNICAL TRAINING SEMINAR: High Temperature Superconductors: Progress and Issues
Davide Vitè
2002-01-01
Monday 24 June from 14:30 to 15:30 - Training Centre Auditorium - bldg. 593-11 High Temperature Superconductors: Progress and Issues Prof. Jan Evetts / UNIVERSITY OF CAMBRIDGE, Department of Materials Science and Metallurgy, UK Grappling with grain boundaries: Current transport processes in granular High Temperature Superconductors (HTS) The development of High Temperature Superconductors, seen from a materials scientist's point of view, is relevant to the superconductivity community at CERN: their possible high current applications can include high performance magnets for future accelerators. There is an urgent need to develop a quantitative description of HTS conductors in terms of their complex anisotropy, inhomogeneity and dimensionality. This is essential both for the practical specification of a conductor and for charting routes to conductor optimisation. The critical current, the n-value, dissipation and quenching characteristics are amongst most important parameters that make up an engineering specifi...
Vortices in high-performance high-temperature superconductors
Kwok, Wai-Kwong; Welp, Ulrich; Glatz, Andreas; Koshelev, Alexei E.; Kihlstrom, Karen J.; Crabtree, George W.
2016-11-01
The behavior of vortex matter in high-temperature superconductors (HTS) controls the entire electromagnetic response of the material, including its current carrying capacity. Here, we review the basic concepts of vortex pinning and its application to a complex mixed pinning landscape to enhance the critical current and to reduce its anisotropy. We focus on recent scientific advances that have resulted in large enhancements of the in-field critical current in state-of-the-art second generation (2G) YBCO coated conductors and on the prospect of an isotropic, high-critical current superconductor in the iron-based superconductors. Lastly, we discuss an emerging new paradigm of critical current by design—a drive to achieve a quantitative correlation between the observed critical current density and mesoscale mixed pinning landscapes by using realistic input parameters in an innovative and powerful large-scale time dependent Ginzburg-Landau approach to simulating vortex dynamics.
Vortices in high-performance high-temperature superconductors.
Kwok, Wai-Kwong; Welp, Ulrich; Glatz, Andreas; Koshelev, Alexei E; Kihlstrom, Karen J; Crabtree, George W
2016-11-01
The behavior of vortex matter in high-temperature superconductors (HTS) controls the entire electromagnetic response of the material, including its current carrying capacity. Here, we review the basic concepts of vortex pinning and its application to a complex mixed pinning landscape to enhance the critical current and to reduce its anisotropy. We focus on recent scientific advances that have resulted in large enhancements of the in-field critical current in state-of-the-art second generation (2G) YBCO coated conductors and on the prospect of an isotropic, high-critical current superconductor in the iron-based superconductors. Lastly, we discuss an emerging new paradigm of critical current by design-a drive to achieve a quantitative correlation between the observed critical current density and mesoscale mixed pinning landscapes by using realistic input parameters in an innovative and powerful large-scale time dependent Ginzburg-Landau approach to simulating vortex dynamics.
The ground state in a spin-one color superconductor
Schmitt, A
2004-01-01
Color superconductors in which quarks of the same flavor form Cooper pairs are investigated. These Cooper pairs carry total spin one. A systematic group-theoretical classification of possible phases in a spin-one color superconductor is presented, revealing parallels and differences to the theory of superfluid $^3$He. General expressions for the gap parameter, the critical temperature, and the pressure are derived and evaluated for several spin-one phases, with special emphasis on the angular structure of the gap equation. It is shown that, in a spin-one color superconductor, the (transverse) A phase is expected to be the ground state. This is in contrast to $^3$He, where the ground state is in the B phase.
Energy Technology Data Exchange (ETDEWEB)
Emamipour, Hamidreza, E-mail: h_emamipour@yahoo.com [Department of Physics, Ilam University, Ilam (Iran, Islamic Republic of); Mehrabzad, Narges [Islamic Azad University, Central Tehran Branch, Tehran (Iran, Islamic Republic of)
2016-07-15
We study tunneling conductance in a quantum wire–insulator–ferromagnetic d-wave superconductor junction. The results show that exchange field of superconductor has a strong impact on tunneling spectra depending on the junction parameters. We have found a gap like structure in the tunneling limit when we have an interface normal to the (100) axis of superconductor. In the case of (110) axis of superconductor, there is not any zero- bias conductance peaks in tunneling spectra. For a metallic junction the dips disappear.
Ndoye, Ibrahima
2014-12-01
In this paper, an adaptive observer design with parameter identification for a nonlinear system with external perturbations and unknown parameters is proposed. The states of the nonlinear system are estimated by a nonlinear observer and the unknown parameters are also adapted to their values. Sufficient conditions for the stability of the adaptive observer error dynamics are derived in terms of linear matrix inequalities. Simulation results for chaotic Lorenz systems with unknown parameters in the presence of external perturbations are given to illustrate the effectiveness of our proposed approach. © 2014 IEEE.
Manufacturing a Superconductor in School.
Barrow, John
1989-01-01
Described is the manufacture of a superconductor from a commercially available kit using equipment usually available in schools or easily obtainable. The construction is described in detail including equipment, materials, safety procedures, tolerances, and manufacture. (Author/CW)
Lee, H C; Choi, H Y
2009-11-04
Electronic Raman scattering of two-band superconductors is studied based on the time-dependent Landau-Ginzburg theory. The focus is on the possible features of the π phase shift between the two superconducting order parameters which may be realized in the Fe-pnictides. The Raman response was computed up to the Gaussian fluctuations in the functional integral formalism including the long range Coulomb interaction with the four channels of symmetric and antisymmetric combinations of the phases and amplitudes of the two order parameters. The Raman spectra is found to be composed of the quasiparticle and the phase collective mode contributions without mixing between them. The contributions from the quasiparticle and the symmetric phase collective mode (the Anderson-Bogolyubov mode) are similar to the two-band superconductors without the π phase shift. The antisymmetric phase mode (the Leggett mode) originates from the fluctuations of the relative phase of the two order parameters. It lies between twice the smaller gap and twice the larger gap and is damped by the quasiparticles. However, this mode is eliminated by the long range Coulomb interaction in the zero-wavenumber limit.
Exotic magnetic states in Pauli-limited superconductors.
Kenzelmann, M
2017-03-01
Magnetism and superconductivity compete or interact in complex and intricate ways. Here we review the special case where novel magnetic phenomena appear due to superconductivity, but do not exist without it. Such states have recently been identified in unconventional superconductors. They are different from the mere coexistence of magnetic order and superconductivity in conventional superconductors, or from competing magnetic and superconducting phases in many materials. We describe the recent progress in the study of such exotic magnetic phases, and articulate the many open questions in this field.
Exotic magnetic states in Pauli-limited superconductors
Kenzelmann, M.
2017-03-01
Magnetism and superconductivity compete or interact in complex and intricate ways. Here we review the special case where novel magnetic phenomena appear due to superconductivity, but do not exist without it. Such states have recently been identified in unconventional superconductors. They are different from the mere coexistence of magnetic order and superconductivity in conventional superconductors, or from competing magnetic and superconducting phases in many materials. We describe the recent progress in the study of such exotic magnetic phases, and articulate the many open questions in this field.
Spins in the vortices of a high-temperature superconductor
DEFF Research Database (Denmark)
Lake, B.; Aeppli, G.; Clausen, K.N.
2001-01-01
Neutron scattering is used to characterize the magnetism of the vortices for the optimally doped high-temperature superconductor La2-xSrxCuO4 (x = 0.163) in an applied magnetic field. As temperature is reduced, Low-frequency spin fluctuations first disappear with the loss of vortex mobility......, but then reappear. We find that the vortex state can be regarded as an inhomogeneous mixture of a superconducting spin fluid and a material containing a nearly ordered antiferromagnet. These experiments show that as for many other properties of cuprate superconductors, the important underlying microscopic forces...
Superconductor stripes move on
Energy Technology Data Exchange (ETDEWEB)
Tranquada, J. [Physics Department, Brookhaven National Laboratory, Upton, NY (United States)
1999-11-01
Differences in fundamental assumptions are behind much of the controversy among theorists over the cause of high-temperature superconductivity the absence of resistance to electrical current at temperatures as high as 130 K in layered copper-oxide compounds. One common assumption is that the charge carriers are distributed uniformly throughout the all-important CuO{sub 2} layers. However, there is growing experimental evidence that this is not the case and that 'stripes' of charge form in these puzzling materials. Now a significant step forward in the struggle to understand the behaviour of charge carriers in high-temperature superconductors has been made at the Oak Ridge National Laboratory in the US. (UK)
Flux pinning characteristics and irreversibility line in high temperature superconductors
Matsushita, T.; Ihara, N.; Kiuchi, M.
1995-01-01
The flux pinning properties in high temperature superconductors are strongly influenced by thermally activated flux motion. The scaling relation of the pinning force density and the irreversibility line in various high temperature superconductors are numerically analyzed in terms of the flux creep model. The effect of two factors, i.e., the flux pinning strength and the dimensionality of the material, on these properties are investigated. It is speculated that the irreversibility line in Bi-2212 superconductors is one order of magnitude smaller than that in Y-123, even if the flux pinning strength in Bi-2212 is improved up to the level of Y-123. It is concluded that these two factors are equally important in determination of the flux pinning characteristics at high temperatures.
Inelastic scanning tunneling microscopy in conventional and unconventional superconductors
Energy Technology Data Exchange (ETDEWEB)
Hlobil, Patrik; Schmalian, Joerg; Wulfhekel, Wulf; Jandke, Jasmin [Karlsruhe Institute of Technologie (Germany)
2015-07-01
Electron tunneling spectroscopy has been used extremely successful in order to verify the microscopic phonon pairing mechanism in conventional BCS superconductors using the Eliashberg theory. Nevertheless, earlier theories and experiments focused mainly on elastic tunneling processes. We present, motivated by recent experiments, a theoretical description of inelastic tunneling in STM in which an electrons tunnels from the tip into a BCS superconductor and coherently excites a phonon during the tunneling process. This additional channel enhances the measured conductivity and we show that if the superconductor is in the normal state, within some limitations, the derivative dσ/dV will be proportional to the Eliashberg function α2F. Additionally, the influence of the inelastic contributions on the tunneling spectrum in the superconducting state will be discussed. Finally, we generalize the theory to other bosonic excitations and focus on the question if inelastic tunneling could be used to unveil the electronic pairing mechanism in the iron pnictides.