Hybrid superconducting-magnetic memory device using competing order parameters
Baek, Burm; Rippard, William H.; Benz, Samuel P.; Russek, Stephen E.; Dresselhaus, Paul D.
2014-05-01
In a hybrid superconducting-magnetic device, two order parameters compete, with one type of order suppressing the other. Recent interest in ultra-low-power, high-density cryogenic memories has spurred new efforts to simultaneously exploit superconducting and magnetic properties so as to create novel switching elements having these two competing orders. Here we describe a reconfigurable two-layer magnetic spin valve integrated within a Josephson junction. Our measurements separate the suppression in the superconducting coupling due to the exchange field in the magnetic layers, which causes depairing of the supercurrent, from the suppression due to the stray magnetic field. The exchange field suppression of the superconducting order parameter is a tunable and switchable behaviour that is also scalable to nanometer device dimensions. These devices demonstrate non-volatile, size-independent switching of Josephson coupling, in magnitude as well as phase, and they may enable practical nanoscale superconducting memory devices.
Order parameter and density of states in superconducting structures
Energy Technology Data Exchange (ETDEWEB)
Stojkovic, B.P. (Center for the Science and Application of Superconductivity, School of Physics and Astronomy, Univ. of Minnesota, Minneapolis, MN (United States)); Valls, O.T. (Center for the Science and Application of Superconductivity, School of Physics and Astronomy, Univ. of Minnesota, Minneapolis, MN (United States))
1994-02-01
We study superconducting films and layered superconducting-normal metal structures using a purely microscopic, Gor'kov equations based method. We emphasize the case where the coherence length is short. We obtain self-consistent results for the order parameter and the density of states as a function of temperature and geometry. (orig.)
Saari, Timo; Nieminen, Jouko; Bansil, Arun
2017-06-01
Motivated by the recent experiments indicating superconductivity in metal-decorated graphene sheets, we investigate their quasi-particle structure within the framework of an effective tight-binding Hamiltonian augmented by appropriate BCS-like pairing terms for p-type order parameter. The normal state band structure of graphene is modified not only through interaction with adsorbed metal atoms, but also due to the folding of bands at Brillouin zone boundaries resulting from a \\sqrt{3}× \\sqrt{3}R{{30}\\circ} reconstruction. Several different types of pairing symmetries are analyzed utilizing Nambu-Gorkov Green’s function techniques to show that p+\\text{i}p -symmetric nearest-neighbor pairing yields the most enhanced superconducting gap. The character of the order parameter depends on the nature of the atomic orbitals involved in the pairing process and exhibits interesting angular and radial asymmetries. Finally, we suggest a method to distinguish between singlet and triplet type superconductivity in the presence of magnetic substitutional impurities using scanning tunneling spectroscopy.
Arutyunov, K. Yu.; Lehtinen, J. S.; Radkevich, A. A.; Semenov, A. G.; Zaikin, A. D.
2017-11-01
The current-voltage characteristics of superconductor-insulator-semiconductor (S1-I-S2) tunnel junctions, where superconducting electrode S2 is a thin nanowire, are studied experimentally. The observed blurring of the gap singularities is interpreted as a manifestation of the order parameter quantum fluctuations. We propose a model taking into account the broadening of the density of states due to the interaction of electrons with the Mooij-Schön plasmon mode emerging in a quasi-one-dimensional superconducting channel in the regime of quantum fluctuations of the order parameter. The model gives results that are in a reasonable qualitative agreement with the experimental data.
Coexistence of two vector order parameters: a holographic model for ferromagnetic superconductivity
Energy Technology Data Exchange (ETDEWEB)
Amoretti, Andrea [Dipartimento di Fisica, Università di Genova, and I.N.F.N. - Sezione di Genova, via Dodecaneso 33, 16146, Genova (Italy); Braggio, Alessandro [CNR-SPIN, via Dodecaneso 33, 16146, Genova (Italy); Maggiore, Nicola; Magnoli, Nicodemo [Dipartimento di Fisica, Università di Genova, and I.N.F.N. - Sezione di Genova, via Dodecaneso 33, 16146, Genova (Italy); Musso, Daniele [Physique Théorique et Mathématique, Université Libre de Bruxelles, C.P. 231, 1050 Bruxelles (Belgium)
2014-01-13
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 charge/spin 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 spin 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.
DEFF Research Database (Denmark)
Larsen, Jacob; Uranga, B. Mencia; Stieber, G.
2015-01-01
We have studied the magnetic and superconducting properties of Ba(Fe1-xCox)2As2 as a function of temperature and external magnetic field using neutron scattering and muon spin rotation. Below the superconducting transition temperature the magnetic and superconducting order parameters coexist...... and compete. A magnetic field can significantly enhance the magnetic scattering in the superconducting state, roughly doubling the Bragg intensity at 13.5 T. We perform a microscopic modelling of the data by use of a five-band Hamiltonian relevant to iron pnictides. In the superconducting state, vortices can...... slow down and freeze spin fluctuations locally. When such regions couple they result in a long-range ordered antiferromagnetic phase producing the enhanced magnetic elastic scattering in agreement with experiments....
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.
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.
Smylie, M. P.; Claus, H.; Welp, U.; Kwok, W.-K.; Qiu, Y.; Hor, Y. S.; Snezhko, A.
The low-temperature variation of the London penetration depth λ(T) in the candidate topological superconductor NbxBi2Se3 (x =0.25) is reported for several crystals. The measurements were carried out by means of a tunnel-diode oscillator technique in both field orientations (Hrf // c and Hrf // ab planes). All samples exhibited quadratic temperature dependence at low temperatures clearly indicating the presence of point nodes in the superconducting order parameter. The results presented here are not consistent with a complete superconducting gap. We interpret our data on NbxBi2Se3 in terms of a nematic odd-parity spin-triplet pairing state with Eu symmetry. This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, Contract No. DE-AC02-06CH11357. MPS thanks ND Energy for supporting his research and professional development through the ND Energy Postdoctoral Fellowship Program. YSH acknowledges support from National Science Foundation Grant Number DMR-1255607.
Charge order, superconducting correlations, and positive muons
Energy Technology Data Exchange (ETDEWEB)
Sonier, J.E., E-mail: jsonier@sfu.ca
2015-02-15
The recent discoveries of short-range charge-density wave order in the normal state of several hole-doped cuprate superconductors constitute a significant addition to the known intrinsic properties of these materials. Besides likely being associated with the normal-state pseudogap, the charge-density wave order presumably influences the build-up of known superconducting correlations as the temperature is lowered toward the superconducting state. As a pure magnetic probe, muon spin rotation (μ SR) is not directly sensitive to charge order, but may sense its presence via the effect it has on the magnetic dipolar coupling of the muon with the host nuclei at zero or low magnetic field. At higher field where μ SR is completely blind to the effects of charge order, experiments have revealed a universal inhomogeneous normal-state response extending to temperatures well above T{sub c}. The measured inhomogeneous line broadening has been attributed to regions of superconducting correlations that exhibit varying degrees of fluctuation diamagnetism. Here, the compatibility of these results with other measurements showing charge order correlations or superconducting fluctuations above T{sub c} is discussed. - Highlights: • Superconducting fluctuations in high-T cuprates probed by positive muons are discussed. • Superconducting fluctuations are detected at higher temperatures than by other methods. • The muon experiments indicate that the superconducting fluctuations are inhomogeneous. • The compatibility with short-range charge order in the normal state is considered.
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.
Superconducting state parameters of ternary metallic glasses
Indian Academy of Sciences (India)
The well-known empty core (EMC) model potential of Ashcroft was used to study the theoretical investigation of the superconducting state parameters (SSP) viz. electron–phonon coupling ... Most recent local field correction function due to Sarkar et al is used to study the screening influence on the aforesaid properties.
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.
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.
Effective valence as the control parameter of the superconducting ...
African Journals Online (AJOL)
In this paper, we have demonstrated that the effective valence of iron can be used as the control parameter to tune the Tc of this family of superconducting materials. This is achieved by postulating that our model of spin fluctuation which has been used to successfully account for the superconductivity in the cuprates in Ref.
Lattice parameters guide superconductivity in iron-arsenides
Konzen, Lance M. N.; Sefat, Athena S.
2017-03-01
The discovery of superconducting materials has led to their use in technological marvels such as magnetic-field sensors in MRI machines, powerful research magnets, short transmission cables, and high-speed trains. Despite such applications, the uses of superconductors are not widespread because they function much below room-temperature, hence the costly cooling. Since the discovery of Cu- and Fe-based high-temperature superconductors (HTS), much intense effort has tried to explain and understand the superconducting phenomenon. While no exact explanations are given, several trends are reported in relation to the materials basis in magnetism and spin excitations. In fact, most HTS have antiferromagnetic undoped ‘parent’ materials that undergo a superconducting transition upon small chemical substitutions in them. As it is currently unclear which ‘dopants’ can favor superconductivity, this manuscript investigates crystal structure changes upon chemical substitutions, to find clues in lattice parameters for the superconducting occurrence. We review the chemical substitution effects on the crystal lattice of iron-arsenide-based crystals (2008 to present). We note that (a) HTS compounds have nearly tetragonal structures with a-lattice parameter close to 4 Å, and (b) superconductivity can depend strongly on the c-lattice parameter changes with chemical substitution. For example, a decrease in c-lattice parameter is required to induce ‘in-plane’ superconductivity. The review of lattice parameter trends in iron-arsenides presented here should guide synthesis of new materials and provoke theoretical input, giving clues for HTS.
Exotic Magnetic Orders and Their Interplay with Superconductivity
DEFF Research Database (Denmark)
Christensen, Morten Holm
Superconductivity represents one of the most important scientific discoveries of the 20th century. The practical applications are numerous ranging from clean energy storage and MRI machines to quantum computers. However, the low temperatures required for superconductivity prohibits many practical...... will demonstrate that magnetic fluctuations can drive the system to break rotational symmetry prior to the onset of magnetic order, resulting in so-called nematic order. Furthermore I will discuss how the inclusion of an atomic spin-orbit coupling can explain the observation of a reorientation of the magnetic...
Possible coexistence of superconductivity and magnetic order in ...
Indian Academy of Sciences (India)
Abstract. Coexistence of superconductivity and magnetic order has been one of the exciting as- pects of the quaternary borocarbide superconductors. So far, RNi2B2C (R= Tm, Er, Ho and Dy) are the only known magnetic superconductors in this family. Here, we present our resistivity, mag- netization and heat capacity ...
Disorder parameter of dual superconductivity in QCD revisited
Bonati, Claudio; Cossu, Guido; D'Elia, Massimo; di Giacomo, Adriano
2012-03-01
We discover the origin of the pathologies of the disorder parameter used in previous papers to detect dual superconductivity of QCD vacuum, and we remove them by defining an improved disorder parameter. A check of the approach is made by numerical simulations of SU(2) gauge theory, which demonstrate that the approach is consistent and, with it, that deconfinement is a transition from dual superconductor to normal.
Charge ordering phenomena and superconductivity in underdoped cuprates
Energy Technology Data Exchange (ETDEWEB)
Tassini, Leonardo [Bayerische Akademie der Wissenschaften, Muenchen (Germany). Lehrstuhl E23 fuer Technische Physik
2008-01-16
In this thesis electronic properties of two prototypical copper-oxygen superconductors were studied with Raman scattering. The underdoped regime including the onset point of superconductivity p{sub sc1} was investigated. Evidence of quasi one-dimensional (1D) dynamical stripes was found. The 1D structures have a universal preferential orientation along the diagonals of the CuO{sub 2} planes below p{sub sc1}. At p{sub sc1}, lattice and electron dynamics change discontinuously. The results show that charge ordering drives the transition at p{sub sc1} and that the maximal transition temperature to superconductivity at optimal doping T{sub c}{sup MAX} depends on the type of ordering at p{sub sc1}. (orig.)
First-order superconducting transition in the inter-band model
Energy Technology Data Exchange (ETDEWEB)
Gomes da Silva, M. [Universidade Federal do Amazonas, Departamento de Física, 3000, Japiim, 69077-00 Manaus, AM (Brazil); Instituto Federal de Educação Ciência e Tecnologia do Amazonas, Av. 7 de Setembro, 1975 - Centro, Manaus, AM 69020-120 (Brazil); Dinóla Neto, F., E-mail: dinola@ufam.edu.br [Universidade Federal do Amazonas, Departamento de Física, 3000, Japiim, 69077-00 Manaus, AM (Brazil); Padilha, I.T. [Universidade Federal do Amazonas, Departamento de Física, 3000, Japiim, 69077-00 Manaus, AM (Brazil); Ricardo de Sousa, J. [Universidade Federal do Amazonas, Departamento de Física, 3000, Japiim, 69077-00 Manaus, AM (Brazil); National Institute of Science and Technology for Complex Systems, Universidade Federal do Amazonas, 3000, Japiim, 69077-000 Manaus, AM (Brazil); Continentino, M.A. [Centro Brasileiro de Pesquisas Físicas, 22290-180 Rio de Janeiro, RJ (Brazil)
2014-04-01
The comprehension about the theoretical features of superconductivity is an interesting and fundamental topic in condensed matter physics. Several theoretical proposals were considered to describe the new classes of superconducting compounds and alloys. In this work we propose to study a non-conventional superconducting system where the Cooper pairs are formed by fermions from different bands described via two band model with hybridization. In this inter-band scenario we find a first-order phase transition at low temperatures and we observe a tricritical point in the phase diagram. In our description, the control parameter is the hybridization that can be tuned by external pressure. This fact indicates the possibility to observe discontinuities in the SC gap amplitude through applying pressure on the system.
Superconducting quantum simulator for topological order and the toric code
Sameti, Mahdi; Potočnik, Anton; Browne, Dan E.; Wallraff, Andreas; Hartmann, Michael J.
2017-04-01
Topological order is now being established as a central criterion for characterizing and classifying ground states of condensed matter systems and complements categorizations based on symmetries. Fractional quantum Hall systems and quantum spin liquids are receiving substantial interest because of their intriguing quantum correlations, their exotic excitations, and prospects for protecting stored quantum information against errors. Here, we show that the Hamiltonian of the central model of this class of systems, the toric code, can be directly implemented as an analog quantum simulator in lattices of superconducting circuits. The four-body interactions, which lie at its heart, are in our concept realized via superconducting quantum interference devices (SQUIDs) that are driven by a suitably oscillating flux bias. All physical qubits and coupling SQUIDs can be individually controlled with high precision. Topologically ordered states can be prepared via an adiabatic ramp of the stabilizer interactions. Strings of qubit operators, including the stabilizers and correlations along noncontractible loops, can be read out via a capacitive coupling to read-out resonators. Moreover, the available single-qubit operations allow to create and propagate elementary excitations of the toric code and to verify their fractional statistics. The architecture we propose allows to implement a large variety of many-body interactions and thus provides a versatile analog quantum simulator for topological order and lattice gauge theories.
Dynamical generation of superconducting order of different symmetries in hexagonal lattices
Dehghani, Hossein; Mitra, Aditi
2017-11-01
The growth of superconducting order after an interaction quench in a hexagonal lattice is studied. The cases of both time-reversal (TR) preserving graphene, as well as the TR broken Haldane model, are explored. Spin singlet superconducting order is studied where the s ,d +i d , and d -i d wave orders are the irreducible representations of the hexagonal lattice. For small quenches, the d -wave order parameter grows the fastest, a result also expected when the system is in thermal equilibrium. For the TR symmetry preserving case, the growth rate of the two d -wave orders is identical, while the TR-broken case prefers one of the chiral d -wave orders over the other, leading to a TR broken topological superconductor. As the interaction quench becomes larger, a smooth crossover is found where eventually the growth rate of the s wave becomes the largest. Thus for large interaction quenches, the s wave is preferred over the d wave for both TR preserving and TR broken systems. This result is explained in terms of the high energy quasiparticles responsible for the dynamics as the interaction quench amplitude grows. The results are relevant for time-resolved measurements that can probe the symmetry of the superconducting fluctuations in a transient regime.
Superconductivity, spin and charge order, and quantum criticality in correlated electron materials
Directory of Open Access Journals (Sweden)
Chu J.-H.
2012-03-01
Full Text Available We describe recent experiments performed in our laboratory that address spin or charge ordered phases in novel rare earth and actinide based materials and phenomena that emerge when these ordered phases are suppressed toward 0 K by varying an external control parameter such as chemical composition, pressure, or magnetic field. Specific examples discussed include magnetic order, heavy fermion behavior, and unconventional quantum criticality in noncentrosymmetric M2T12P7 compounds (M = rare earth, actinide; T = Co, Fe and the interplay of superconductivity and charge density waves in rare earth tritelluride compounds RTe3 (R = Gd, Tb, Dy.
Superconductivity and spin excitations in orbitally ordered FeSe
Energy Technology Data Exchange (ETDEWEB)
Kreisel, Andreas; Andersen, Brian M. [Niels Bohr Institute, University of Copenhagen (Denmark); Mukherjee, Shantanu [Niels Bohr Institute, University of Copenhagen (Denmark); Dept. of Physics, State University of New York at Binghamton, Binghamton, NY (United States); Hirschfeld, Peter J. [University of Florida, Gainesville, FL (United States)
2016-07-01
We provide a band-structure with low-energy properties consistent with recent photoemission and quantum oscillations measurements on the Fe-based superconductor FeSe, including a mean-field like orbital ordering in the d{sub xz}/d{sub yz} channel, and show that this model also accounts for the temperature dependence of the measured Knight shift and the spin-relaxation rate. An RPA calculation of the dynamical spin susceptibility yields spin excitations which are peaked at wave vector (π,0) in the 1-Fe Brillouin zone, with a broad maximum at energies of order a few meV. Furthermore, the superconducting gap structure obtained from spin fluctuation theory exhibits nodes on the electron pockets, consistent with the 'V'-shaped density of states measured by tunneling spectroscopy on this material. The redistribution of spectral weight in the superconducting state creates a (π,0) ''neutron resonance'' as seen in recent experiments. Comparing to various experimental results, we give predictions for further studies.
Superconductivity and spin excitations in orbitally ordered FeSe
Kreisel, Andreas; Mukherjee, Shantanu; Hirschfeld, P. J.; Andersen, B. M.
We provide a band-structure with low-energy properties consistent with recent photoemission and quantum oscillations measurements on the Fe-based superconductor FeSe, including a mean-field like orbital ordering in the dxz /dyz channel, and show that this model also accounts for the temperature dependence of the measured Knight shift and the spin-relaxation rate. An RPA calculation of the dynamical spin susceptibility yields spin excitations which are peaked at wave vector (π , 0) in the 1-Fe Brillouin zone, with a broad maximum at energies of order a few meV. Furthermore, the superconducting gap structure obtained from spin fluctuation theory exhibits nodes on the electron pockets, consistent with the 'V'-shaped density of states measured by tunneling spectroscopy on this material. The redistribution of spectral weight in the superconducting state creates a (π , 0) ''neutron resonance'' as seen in recent experiments. Comparing to various experimental results, we give predictions for further studies A.K. and B.M.A. acknowledge financial support from a Lundbeckfond fellowship (Grant No. A9318). P.J.H. was partially supported by the Department of Energy under Grant No. DE-FG02-05ER46236.
Kekule versus hidden superconducting order in graphene-like systems : Competition and coexistence
Kunst, Flore K.; Delerue, Christophe; de Morais Smith, Cristiane; Juricic, Vladimir
2015-01-01
We theoretically study the competition between two possible exotic superconducting orders that may occur in graphene-like systems, assuming dominant nearest-neighbor attraction: the gapless hidden superconducting order, which renormalizes the Fermi velocity, and the Kekule order, which opens a
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.
Analysis of Electrical Coupling Parameters in Superconducting Cables
Bottura, L; Rosso, C
2003-01-01
The analysis of current distribution and redistribution in superconducting cables requires the knowledge of the electric coupling among strands, and in particular the interstrand resistance and inductance values. In practice both parameters can have wide variations in cables commonly used such as Rutherford cables for accelerators or Cable-in-Conduits for fusion and SMES magnets. In this paper we describe a model of a multi-stage twisted cable with arbitrary geometry that can be used to study the range of interstrand resistances and inductances that is associated with variations of geometry. These variations can be due to cabling or compaction effects. To describe the variations from the nominal geometry we have adopted a cable model that resembles to the physical process of cabling and compaction. The inductance calculation part of the model is validated by comparison to semi-analytical results, showing excellent accuracy and execution speed.
Faraei, Zahra; Jafari, S. A.
2017-10-01
We find that a conventional s -wave superconductor in proximity to a three-dimensional Dirac material (3DDM), to all orders of perturbation in tunneling, induces a combination of s - and p -wave pairing only. We show that the Lorentz invariance of the superconducting pairing prevents the formation of Cooper pairs with higher orbital angular momenta in the 3DDM. This no-go theorem acquires stronger form when the probability of tunneling from the conventional superconductor to positive and negative energy states of 3DDM are equal. In this case, all the p -wave contribution except for the lowest order, identically vanish and hence we obtain an exact result for the induced p -wave superconductivity in 3DDM. Fierz decomposing the superconducting matrix we find that the temporal component of the vector superconducting order and the spatial components of the pseudovector order have odd-frequency pairing symmetry. We find that the latter is odd with respect to exchange of position and chirality of the electrons in the Cooper pair and is a spin-triplet, which is necessary for NMR detection of such an exotic pseudovector pairing. Moreover, we show that the tensorial order breaks into a polar vector and an axial vector and both of them have conventional pairing symmetry except for being a spin triplet. According to our study, for gapless 3DDM, the tensorial superconducting order will be the only order that is odd with respect to the chemical potential μ . Therefore we predict that a transverse p -n junction binds Majorana fermions. This effect can be used to control the neutral Majorana fermions with electric fields.
Deductive multiscale simulation using order parameters
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.
Val'kov, V. V.; Zlotnikov, A. O.
2017-11-01
We investigate the effect of the intersite Coulomb interaction in a planar system with the triangular lattice on the structure of chiral order parameter Δ( p) in the phase of coexisting superconductivity and noncollinear 120° magnetic ordering. It has been established that the Coulomb correlations in this phase initiate the state where the quasi-momentum dependence Δ( p) can be presented as a superposition of the chiral invariants corresponding to the {d_{{x^2} - {y^2}}} + i{d_{xy}} and p x + ip y symmetry types. It is demonstrated that the inclusion of the Coulomb interaction shifts the Δ( p) nodal point positions and, thereby, changes the conditions for a quantum topological transition.
Thomas, D B
1974-01-01
A short general review is presented of the progress made in applied superconductivity as a result of work performed in connection with the high-energy physics program in Europe. The phenomenon of superconductivity and properties of superconductors of Types I and II are outlined. The main body of the paper deals with the development of niobium-titanium superconducting magnets and of radio-frequency superconducting cavities and accelerating structures. Examples of applications in and for high-energy physics experiments are given, including the large superconducting magnet for the Big European Bubble Chamber, prototype synchrotron magnets for the Super Proton Synchrotron, superconducting d.c. beam line magnets, and superconducting RF cavities for use in various laboratories. (0 refs).
Comparison of coaxial higher order mode couplers for the CERN Superconducting Proton Linac study
AUTHOR|(CDS)2085329; Gerigk, Frank; Van Rienen, Ursula
2017-01-01
Higher order modes (HOMs) may affect beam stability and refrigeration requirements of superconducting proton linacs such as the Superconducting Proton Linac, which is studied at CERN. Under certain conditions beam-induced HOMs can accumulate sufficient energy to destabilize the beam or quench the superconducting cavities. In order to limit these effects, CERN considers the use of coaxial HOM couplers on the cutoff tubes of the 5-cell superconducting cavities. These couplers consist of resonant antennas shaped as loops or probes, which are designed to couple to potentially dangerous modes while sufficiently rejecting the fundamental mode. In this paper, the design process is presented and a comparison is made between various designs for the high-beta SPL cavities, which operate at 704.4 MHz. The rf and thermal behavior as well as mechanical aspects are discussed. In order to verify the designs, a rapid prototype for the favored coupler was fabricated and characterized on a low-power test-stand.
Yeo, Yung K.
Many potential high-temperature superconductivity (HTS) military applications have been demonstrated by low-temperature superconductivity systems; they encompass high efficiency electric drives for naval vessels, airborne electric generators, energy storage systems for directed-energy weapons, electromechanical launchers, magnetic and electromagnetic shields, and cavity resonators for microwave and mm-wave generation. Further HST applications in militarily relevant fields include EM sensors, IR focal plane arrays, SQUIDs, magnetic gradiometers, high-power sonar sources, and superconducting antennas and inertial navigation systems. The development of SQUID sensors will furnish novel magnetic anomaly detection methods for ASW.
Ketterson, John B
2008-01-01
Conceived as the definitive reference in a classic and important field of modern physics, this extensive and comprehensive handbook systematically reviews the basic physics, theory and recent advances in the field of superconductivity. Leading researchers, including Nobel laureates, describe the state-of-the-art in conventional and unconventional superconductors at a particularly opportune time, as new experimental techniques and field-theoretical methods have emerged. In addition to full-coverage of novel materials and underlying mechanisms, the handbook reflects continued intense research into electron-phone based superconductivity. Considerable attention is devoted to high-Tc superconductivity, novel superconductivity, including triplet pairing in the ruthenates, novel superconductors, such as heavy-Fermion metals and organic materials, and also granular superconductors. What’s more, several contributions address superconductors with impurities and nanostructured superconductors. Important new results on...
Superconducting linac beam dynamics with high-order maps for RF resonators
Geraci, A A; Pardo, R C; 10.1016/j.nima.2003.11.177
2004-01-01
The arbitrary-order map beam optics code COSY Infinity has recently been adapted to calculate accurate high-order ion-optical maps for electrostatic and radio-frequency accelerating structures. The beam dynamics of the superconducting low-velocity positive-ion injector linac for the ATLAS accelerator at Argonne National Lab is used to demonstrate some advantages of the new simulation capability. The injector linac involves four different types of superconducting accelerating structures and has a total of 18 resonators. The detailed geometry for each of the accelerating cavities is included, allowing an accurate representation of the on- and off-axis electric fields. The fields are obtained within the code from a Poisson-solver for cylindrically symmetric electrodes of arbitrary geometry. The transverse focusing is done with superconducting solenoids. A detailed comparison of the transverse and longitudinal phase space is made with the conventional ray-tracing code LINRAY. The two codes are evaluated for ease ...
Poole, Charles P; Creswick, Richard J; Prozorov, Ruslan
2014-01-01
Superconductivity, Third Edition is an encyclopedic treatment of all aspects of the subject, from classic materials to fullerenes. Emphasis is on balanced coverage, with a comprehensive reference list and significant graphics from all areas of the published literature. Widely used theoretical approaches are explained in detail. Topics of special interest include high temperature superconductors, spectroscopy, critical states, transport properties, and tunneling. This book covers the whole field of superconductivity from both the theoretical and the experimental point of view. This third edition features extensive revisions throughout, and new chapters on second critical field and iron based superconductors.
Antiferromagnetic order in superconducting UPt[sub 3]: An x-ray magnetic scattering study (invited)
Energy Technology Data Exchange (ETDEWEB)
Isaacs, E.D. (AT T Bell Laboratories, 600 Mountain Avenue, Murray Hill, New Jersey 07974 (United States)); Zschack, P. (Oak Ridge Institute for Science and Education, Brookhaven National Laboratory, Upton, New York 11973 (United States)); Ramirez, A.P.; Oglesby, C.S.; Bucher, E. (AT T Bell Laboratories, 600 Mountain Avenue, Murray Hill, New Jersey 07974 (United States))
1994-11-15
The temperature dependence of the antiferromagnetic order in superconducting UPt[sub 3] has been measured using x-ray resonance magnetic scattering. The magnetic Bragg intensity at [ital Q]=(1/2,0,2) grows linearly from [ital T][sub [ital N
Sacchetti, N.
In this paper a short historical account of the discovery of superconductivity and of its gradual development is given. The physical interpretation of its various aspects took about forty years (from 1911 to 1957) to reach a successful description of this phenomenon in terms of a microscopic theory At the very end it seemed that more or less everything could be reasonably interpreted even if modifications and refinements of the original theory were necessary. In 1986 the situation changed abruptly when a cautious but revolutionary paper appeared showing that superconductivity was found in certain ceramic oxides at temperatures above those up to then known. A rush of frantic experimental activity started world-wide and in less than one year it was shown that superconductivity is a much more widespread phenomenon than deemed before and can be found at temperatures well above the liquid air boiling point. The complexity and the number of the substances (mainly ceramic oxides) involved call for a sort of modern alchemy if compounds with the best superconducting properties are to be manufactured. We don't use the word alchemy in a deprecatory sense but just to emphasise that till now nobody can say why these compounds are what they are: superconductors.
Comparison of coaxial higher order mode couplers for the CERN Superconducting Proton Linac study
Directory of Open Access Journals (Sweden)
K. Papke
2017-06-01
Full Text Available Higher order modes (HOMs may affect beam stability and refrigeration requirements of superconducting proton linacs such as the Superconducting Proton Linac, which is studied at CERN. Under certain conditions beam-induced HOMs can accumulate sufficient energy to destabilize the beam or quench the superconducting cavities. In order to limit these effects, CERN considers the use of coaxial HOM couplers on the cutoff tubes of the 5-cell superconducting cavities. These couplers consist of resonant antennas shaped as loops or probes, which are designed to couple to potentially dangerous modes while sufficiently rejecting the fundamental mode. In this paper, the design process is presented and a comparison is made between various designs for the high-beta SPL cavities, which operate at 704.4 MHz. The rf and thermal behavior as well as mechanical aspects are discussed. In order to verify the designs, a rapid prototype for the favored coupler was fabricated and characterized on a low-power test-stand.
Yadav, Jayprakash; Rafique, S. M.; Kumari, Shanti
2009-10-01
In the present paper some superconducting (SC) state parameters of metals Ga, Cd and In have been studied through Harrison's First Principle [HFP] pseudopotential technique using McMillan's formalism. The impact of choosing two different sets of core energy eigenvalues viz. Herman-Skillman and Clementi (or Experimental) has been studied.
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.
Study of Higher Order Modes in Superconducting Accelerating Structures for Linac Applications
Schuh, Marcel; Welsch, C P
2011-01-01
Higher Order Modes (HOMs) can severely limit the operation of superconducting cavities in a linear accelerator with high beam current, high duty factor and complex pulse structure. Therefore, the full HOM spectrum has to be analysed in detail to identify potentially dangerous modes already during the design phase and to define their damping requirements. For this purpose a dedicated beam dynamics simulation code, Simulation of higher order Mode Dynamics (SMD), focusing on beam-HOM interaction, has been developed in the frame of this project. SMD allows to analyse the beam behaviour under the presence of HOMs, taking into account many important effects, such as for example the HOM frequency spread, beam input jitter, different chopping patterns, as well as klystron and alignment errors. SMD is used to investigate in detail into the effects of HOMs in the Superconducting Proton Linac (SPL) at CERN and in particular their potential to drive beam instabili- ties in the longitudinal and transverse direction. Based...
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.
Enpuku, Keiji; Minotani, Tadashi; Shiraishi, Fumio; Kandori, Atushi
1999-04-01
Critical current fluctuation of bicrystal junctions is estimated from the 1/f flux noise of the superconducting quantum interference device (SQUID) at T=77 K. The relationships between the current fluctuation and junction parameters, such as critical current Io and resistance R, are obtained. The obtained parameter dependence can be well explained by using the parameter dependence of the resistance fluctuation reported by Marx and Gross [Appl. Phys. Lett. 70, 120 (1997)] and the relationship between Io and R obtained for the present junctions. The agreement indicates that the critical current fluctuation is correlated with the resistance fluctuation through the relationship between Io and R.
Energy Technology Data Exchange (ETDEWEB)
Kinion, D; Clarke, J
2008-01-24
The scattering parameters of an amplifier based on a dc Superconducting QUantum Interference Device (SQUID) are directly measured at 4.2 K. The results can be described using an equivalent circuit model of the fundamental resonance of the microstrip resonator which forms the input of the amplifier. The circuit model is used to determine the series capacitance required for critical coupling of the microstrip to the input circuit.
Unconventional superconductivity in honeycomb lattice
Directory of Open Access Journals (Sweden)
P Sahebsara
2013-03-01
Full Text Available The possibility of symmetrical s-wave superconductivity in the honeycomb lattice is studied within a strongly correlated regime, using the Hubbard model. The superconducting order parameter is defined by introducing the Green function, which is obtained by calculating the density of the electrons . In this study showed that the superconducting order parameter appears in doping interval between 0 and 0.5, and x=0.25 is the optimum doping for the s-wave superconductivity in honeycomb lattice.
Goyal, Amit
2013-09-17
Novel articles and methods to fabricate same with self-assembled nanodots and/or nanorods of a single or multicomponent material within another single or multicomponent material for use in electrical, electronic, magnetic, electromagnetic and electrooptical devices is disclosed. Self-assembled nanodots and/or nanorods are ordered arrays wherein ordering occurs due to strain minimization during growth of the materials. A simple method to accomplish this when depositing in-situ films is also disclosed. Device applications of resulting materials are in areas of superconductivity, photovoltaics, ferroelectrics, magnetoresistance, high density storage, solid state lighting, non-volatile memory, photoluminescence, thermoelectrics and in quantum dot lasers.
Asymmetric d-wave superconducting topological insulator in proximity with a magnetic order
Khezerlou, M.; Goudarzi, H.; Asgarifar, S.
2018-02-01
In the framework of the Dirac-Bogoliubov-de Gennes formalism, we investigate the transport properties in the surface of a 3-dimensional topological insulator-based hybrid structure, where the ferromagnetic and superconducting orders are simultaneously induced to the surface states via the proximity effect. The superconductor gap is taken to be spin-singlet d-wave symmetry. The asymmetric role of this gap respect to the electron-hole exchange, in one hand, affects the topological insulator superconducting binding excitations and, on the other hand, gives rise to forming distinct Majorana bound states at the ferromagnet/superconductor interface. We propose a topological insulator N/F/FS junction and proceed to clarify the role of d-wave asymmetry pairing in the resulting subgap and overgap tunneling conductance. The perpendicular component of magnetizations in F and FS regions can be at the parallel and antiparallel configurations leading to capture the experimentally important magnetoresistance (MR) of junction. It is found that the zero-bias conductance is strongly sensitive to the magnitude of magnetization in FS region mzfs and orbital rotated angle α of superconductor gap. The negative MR only occurs in zero orbital rotated angle. This result can pave the way to distinguish the unconventional superconducting state in the relating topological insulator hybrid structures.
The Higher-Order Mode Dampers of the 400 MHz Superconducting LHC Cavities
Häbel, E; Gerigk, F; Zhao, Z T
1997-01-01
The accelerating system of the LHC consists of two structures per beam, each composed of four superconducting single-cell cavities. Their higher-order modes have to be damped sufficiently in order to prevent coupled-bunch instabilities and to limit parasitic mode losses. The first two higher-order modes do not propagate into the beam tubes between the cells. However, strong damping can be obtained with a special dipole mode coupler resonant at both modes. Because of the restricted space, a compact design is used. The other higher-order modes propagate and form coupled modes with unequal field distributions. They are damped by broadband couplers positioned on either side of each cavity cell. We present the design of the higher-order mode couplers together with measurements on a real cavity.
Directory of Open Access Journals (Sweden)
Romain Maurand
2012-02-01
Full Text Available We study a carbon-nanotube quantum dot embedded in a superconducting-quantum-interference-device loop in order to investigate the competition of strong electron correlations with a proximity effect. Depending on whether local pairing or local magnetism prevails, a superconducting quantum dot will exhibit a positive or a negative supercurrent, referred to as a 0 or π Josephson junction, respectively. In the regime of a strong Coulomb blockade, the 0-to-π transition is typically controlled by a change in the discrete charge state of the dot, from even to odd. In contrast, at a larger tunneling amplitude, the Kondo effect develops for an odd-charge (magnetic dot in the normal state, and quenches magnetism. In this situation, we find that a first-order 0-to-π quantum phase transition can be triggered at a fixed valence when superconductivity is brought in, due to the competition of the superconducting gap and the Kondo temperature. The superconducting-quantum-interference-device geometry together with the tunability of our device allows the exploration of the associated phase diagram predicted by recent theories. We also report on the observation of anharmonic behavior of the current-phase relation in the transition regime, which we associate with the two accessible superconducting states. Our results finally demonstrate that the spin-singlet nature of the Kondo state helps to enhance the stability of the 0 phase far from the mixed-valence regime in odd-charge superconducting quantum dots.
Comparison of high order modes damping techniques for 800 MHz single cell superconducting cavities
Shashkov, Ya V; Zobov, M M
2014-01-01
Currently, applications of 800 MHz harmonic cavities in both bunch lengthening and shortening regimes are under consideration and discussion in the framework of the High Luminosity LHC project. In this paper we study electromagnetic characteristics of high order modes (HOM) for a single cell 800 MHz superconducting cavity and arrays of such cavities connected by drifts tubes. Different techniques for the HOM damping such as beam pipe grooves, coaxial-notch loads, fluted beam pipes etc. are investigated and compared. The influence of the sizes and geometry of the drift tubes on the HOM damping is analyzed.
Order formation processes of complex systems including different parity order parameters
Hashizume, Yoichiro; Suzuki, Masuo; Okamura, Soichiro
2014-06-01
In the present study, we focus on the parity of the order parameters and clarify the order formation process in a system including two order parameters. Each order parameter shows different parity under a gauge transformation, namely even and odd order parameters. For example, in a spin-glass model, the even order parameter corresponds to the spin-glass order parameter while the odd one corresponds to the magnetization. We introduce phenomenologically a set of Langevin equations to express the ordering process under a white Gaussian noise. Using two kinds of Fokker-Planck equations, we analyze the order formation process and the entropy production. Furthermore, we show the noise dependence of the onset time.
Parameter identification and synchronization of fractional-order chaotic systems
Yuan, Li-Guo; Yang, Qi-Gui
2012-01-01
The knowledge about parameters and order is very important for synchronization of fractional-order chaotic systems. In this article, identification of parameters and order of fractional-order chaotic systems is converted to an optimization problem. Particle swarm optimization algorithm is used to solve this optimization problem. Based on the above parameter identification, synchronization of the fractional-order Lorenz, Chen and a novel system (commensurate or incommensurate order) is derived using active control method. The new fractional-order chaotic system has four-scroll chaotic attractors. The existence and uniqueness of solutions for the new fractional-order system are also investigated theoretically. Simulation results signify the performance of the work.
Ohgoe, Takahiro; Imada, Masatoshi
2017-11-01
Using a variational Monte Carlo method, we study the competition of strong electron-electron and electron-phonon interactions in the ground state of the Holstein-Hubbard model on a square lattice. At half filling, an extended intermediate metallic or weakly superconducting (SC) phase emerges, sandwiched between antiferromagnetic and charge order (CO) insulating phases. By carrier doping into the CO insulator, the SC order dramatically increases for strong electron-phonon couplings, but is largely hampered by wide phase separation (PS) regions. Superconductivity is optimized at the border to the PS.
Testing for one Generalized Linear Single Order Parameter
DEFF Research Database (Denmark)
Ellegaard, Niels Langager; Christensen, Tage Emil; Dyre, Jeppe
We examine a linear single order parameter model for thermoviscoelastic relaxation in viscous liquids, allowing for a distribution of relaxation times. In this model the relaxation of volume and entalpy is completely described by the relaxation of one internal order parameter. In contrast to prior...... 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...
Dependence of superconducting properties of NbN thin films on sputtering parameters
Khaire, Trupti; Carter, Faustin; Ding, Junjia; Posada, Chrystian; Bender, Amy; Wang, Gensheng; Yefremenko, Volodymyr; Pearson, John; Padin, Steve; Chang, Clarence; Hoffmann, Axel; Novosad, Valentyn; SPT3G Collaboration
Recently, there has been growing interest in utilizing NbN, TiN, NbTiN thin films in superconducting device applications (e.g. detectors for CMB, mm and sub-mm astronomy). In this work, we have fabricated NbN superconducting thin films by DC reactive magnetron sputtering of Nb in the presence of argon and nitrogen gases. We found that the critical temperature of NbN films is sensitive to various deposition parameters like nitrogen flow rate, target voltage, base pressure, RF substrate bias, and the substrate temperature. By studying each of these factors we have been able to create highly reproducible NbN thin films. We obtained a Tc of 15.25 +/-0.25 K for 300 nm thick NbN film grown on silicon substrate at modest temperature of 250 C in the presence of RF substrate bias. We are also investigating the microwave properties of these NbN films at temperatures well below 50 mK by fabricating quarter wavelength CPW resonators out of NbN and characterizing their frequency shifts and quality factors as functions of temperature and power. In this work we present the results of these analyses. This work was supported by BES-DOE Grant DE-AC02-06CH11357.
Rotated stripe order and its competition with superconductivity in La1.88Sr0.12CuO4
Thampy, V.; Dean, M. P. M.; Christensen, N. B.; Steinke, L.; Islam, Z.; Oda, M.; Ido, M.; Momono, N.; Wilkins, S. B.; Hill, J. P.
2014-09-01
We report the observation of a bulk charge modulation in La1.88Sr0.12CuO4 (LSCO) with a characteristic in-plane wave vector of (0.236,±δ), with δ =0.011 r.l.u. The transverse shift of the ordering wave vector indicates the presence of rotated charge-stripe ordering, demonstrating that the charge ordering is not pinned to the Cu-O bond direction. On cooling through the superconducting transition, we find an abrupt change in the growth of the charge correlations and a suppression of the charge order parameter indicating competition between the two orderings. Orthorhombic LSCO thus helps bridge the apparent disparities between the behavior previously observed in the tetragonal "214" cuprates and the orthorhombic yttrium and bismuth-based cuprates and thus lends strong support to the idea that there is a common motif to charge order in all cuprate families.
Superconducting high current magnetic Circuit: Design and Parameter Estimation of a Simulation Model
Kiefer, Alexander; Reich, Werner Dr
The Large Hadron Collider (LHC) utilizes superconducting main dipole magnets that bend the trajectory of the particle beams. In order to adjust the not completely homogeneous magnetic feld of the main dipole magnets, amongst others, sextupole correctcorrector magnets are used. In one of the 16 corrector magnet circuits placed in the LHC, 154 of these sextupole corrector magnets (MCS) are connected in series. This circuit extends on a 3.35 km tunnel section of the LHC. In 2015, at one of the 16 circuits a fault was detected. The simulation of this circuit is helpful for fnding the fault by applying alternating current at different frequencies. Within this Thesis a PSpice model for the simulation of the superconducting corrector magnet circuit was designed. The physical properties of the circuit and its elements were analyzed and implemented. For the magnets and bus-bars, sub-circuits were created which reflect the parasitic effects of electrodynamics and electrostats. The inductance values and capacitance valu...
Charge-order fluctuations and superconductivity in two-dimensional organic metals
Girlando, Alberto; Masino, Matteo; Schlueter, John A.; Drichko, Natalia; Kaiser, Stefan; Dressel, Martin
2014-05-01
We report comprehensive Raman and infrared investigations of charge-order (CO) fluctuations in the organic metal β''-(BEDT-TTF)2SF5CHFSO3 and superconductor β''-(BEDT-TTF)2SF5CH2CF2SO3. The charge-sensitive vibrational bands are analyzed through an extension of the well-known Kubo model for the spectral signatures of an equilibrium between two states. At room temperature, both salts exhibit charge fluctuations between two differently charged molecular states with an exchange frequency of about 6×1011s-1. The exchange rate of the metallic salt remains roughly constant down to 10 K, while in the superconductor, the exchange velocity starts to decrease below 200 K, and a "frozen" charge-ordered state emerges and coexists with the charge-order fluctuation state down to the superconducting temperature. These findings are confronted with other spectroscopic experiments, and a tentative phase diagram is proposed for the β'' BEDT-TTF quarter-filled salts.
Chiaro, B.; Ohya, S.; Megrant, A.; Neill, C.; Barends, R.; Campbell, B.; Chen, Y.; Kelly, J.; Mariantoni, M.; Mutus, J.; O'Malley, P.; Roushan, P.; Sank, D.; Vainsencher, A.; Wenner, J.; White, T.; Palmstrom, C. J.; Mazin, B. A.; Cleland, A. N.; Martinis, J. M.
2013-03-01
Superconducting coplanar waveguide (CPW) resonators are widely used structures in the fields of photon detection and quantum information processing. Recently, there has been a growing interest in titanium nitride (TiN) thin films due to their widely tunable critical temperature, large surface inductance, and ability to produce high intrinsic quality factor (Qi) resonators. We have deposited nearly stoichiometric TiN films on Si substrates by reactive magnetron sputtering. By increasing the deposition pressure and adjusting the N2 flow rate to maintain stoichiometry, the film stress was changed from ~ 100 MPa to > 3000 MPa and the Qi of CPW resonators made from these films increased from ~104 to ~106 for single photon excitations measured at ~ 100 mK. In this talk, we discuss relationships between deposition parameters, film properties, and microwave electrodynamic responses in these resonators. S. O. acknowledges the Japan Society for the Promotion of Sciences (JSPS) for a Postdoctoral Fellowship for Research Abroad.
Natarajan, Anirudh Raju; Thomas, John C.; Puchala, Brian; Van der Ven, Anton
2017-10-01
Accurate thermodynamic descriptions are a key ingredient to kinetic theories that describe the mesoscale evolution of a solid undergoing ordering or decomposition reactions. We introduce a general approach to identify order parameters for order-disorder reactions and to calculate first-principles free-energy surfaces as a function of these order parameters. The symmetry of the disordered phase is used to formulate order parameters as linear combinations of sublattice compositions of a reference supercell. The order parameters can distinguish the disordered phase from the symmetrically equivalent variants of a particular ordered phase. A thermodynamic formalism is then developed to rigorously define a coarse-grained free energy as a function of order parameters. Bias potentials are added to the potential energy to enable sampling of the unstable regions within the order-parameter domain. Monte Carlo sampling in the biased ensemble is combined with free-energy integration to calculate high-temperature free energies. We illustrate the approach by analyzing the free energies of order-disorder transitions on a two-dimensional triangular lattice and in the technologically important Ni-Al alloy.
Superconductivity and charge order near the onset of antiferromagnetism in metals
Energy Technology Data Exchange (ETDEWEB)
Gerlach, Max Henner; Trebst, Simon [University of Cologne (Germany); Schattner, Yonathan; Berg, Erez [Weizmann Insitute of Science, Rehovot (Israel)
2015-07-01
The quantum-critical transition of a system of itinerant electrons into an antiferromagnetically ordered phase has long been believed to play an important role in the physics of superconductors such as the electron-doped cuprates and the iron pnictides. The complete understanding of this quantum-critical point has remained a key challenge for both analytical and numerical approaches. On the computational side, a numerically exact simulation of such fermionic systems via quantum Monte Carlo studies has long been precluded by the infamous negative sign problem. Only recently a way has been found to set up sign-problem-free simulations of lattice models that realize the universal physics close to this phase transition. Building upon this conceptual work, we introduce further improvements to the Monte Carlo sampling techniques adapted to such a model, allowing us to better understand the properties of the quantum-critical point and the instability towards d-wave-like superconductivity in its vicinity. In addition, we study a competing instability towards a charge-density-wave-like order, which we support by a supplementary interaction. Taken together, our results further improve our understanding of the rich physics of a relatively simple single-band electron model appropriate for the cuprates.
Accelerated gravitational-wave parameter estimation with reduced order modeling
Canizares, Priscilla; Gair, Jonathan; Raymond, Vivien; Smith, Rory; Tiglio, Manuel
2014-01-01
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 parameter estimation approaches for such scenarios can lead to computationally intractable problems in practice. 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 studies. By implementing a reduced order quadrature scheme within the LIGO Algorithm Library, we show that Bayesian inference on the 9-dimensional parameter space of non-spinning binary neutron star inspirals can be sped up by a factor of 30 for the early advanced detectors' configurations. This speed-up will increase to about $150$ as the detectors improve their low-frequency limit to 10Hz, reducing to hours analyses which would otherwise take months to complete. Although thes...
Orientational order parameter estimated from molecular polarizabilities - an optical study
Lalitha Kumari, J.; Datta Prasad, P. V.; Madhavi Latha, D.; Pisipati, V. G. K. M.
2012-01-01
An optical study of N-(p-n-alkyloxybenzylidene)-p-n-butyloxyanilines, nO.O4 compounds with the alkoxy chain number n = 1, 3, 6, 7, and 10 has been carried out by measuring the refractive indices using modified spectrometer and direct measurement of birefringence employing the Newton's rings method. Further, the molecular polarizability anisotropies are evaluated using Lippincott δ-function model, the molecular vibration method, Haller's extrapolation method, and scaling factor method. The molecular polarizabilities α e and α 0 are calculated using Vuk's isotropic and Neugebauer anisotropic local field models. The order parameter S is estimated by employing the molecular polarizability values determined from experimental refractive indices and density data and the polarizability anisotropy values. Further, the order parameter S is also obtained directly from the birefringence data. A comparison has been carried out among the order parameter obtained from different ways and the results are compared with the body of the data available in the literature.
Glass-forming liquids: one or more "order" parameters"
DEFF Research Database (Denmark)
Bailey, Nicholas; Christensen, Tage Emil; Jakobsen, Bo
2008-01-01
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...... 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...
Twisted-order parameter applied to dimerized ladders
Energy Technology Data Exchange (ETDEWEB)
Almeida, J; Martin-Delgado, M A [Departamento de Fisica Teorica I, Universidad Complutense, 28040 Madrid (Spain); Sierra, G [Instituto de Fisica Teorica, C.S.I.C.-U.A.M., Madrid (Spain)
2008-12-05
We apply the twisted-order parameter (TOP) for dimerized quantum spin ladders to locate the critical points that separate gapped phases representing quantum spin liquids of various types. Using the density matrix renormalization group (DMRG), method, we find that the TOP is a good order parameter for these systems regardless of the number of legs. As a check, we reproduce with the DMRG and periodic boundary conditions the computations previously done with quantum Monte Carlo for one-dimensional S = 1/2, S = 1, S = 3/2 and S = 2 Heisenberg chains with alternating bonds.
Coexistence of Incommensurate Magnetism and Superconductivity in the Two-Dimensional Hubbard Model.
Yamase, Hiroyuki; Eberlein, Andreas; Metzner, Walter
2016-03-04
We analyze the competition of magnetism and superconductivity in the two-dimensional Hubbard model with a moderate interaction strength, including the possibility of incommensurate spiral magnetic order. Using an unbiased renormalization group approach, we compute magnetic and superconducting order parameters in the ground state. In addition to previously established regions of Néel order coexisting with d-wave superconductivity, the calculations reveal further coexistence regions where superconductivity is accompanied by incommensurate magnetic order.
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......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...... (corresponding to a system where the centroid is coupled to a second macroscopic variable), predicts transient and asymptotic properties of the dynamics of the centroid. Phase transitions appear as macroscopic bifurcations. Collective properties arising in the transient, and particularly critical perturbations...
Energy Technology Data Exchange (ETDEWEB)
Li, Y. M. [Peking University, Beijing (China); Thomas Jefferson National Accelerator Facility, Newport News, VA (United States); Liu, Kexin [Peking University, Beijing (China); Geng, Rongli [Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)
2014-02-01
Multipacting (MP) in higher-order-mode (HOM) couplers of the International Linear Collider (ILC) baseline cavity and the Continuous Electron Beam Accelerator Facility (CEBAF) 12 GeV upgrade cavity is studied by using the ACE3P suites, developed by the Advanced Computations Department at SLAC. For the ILC cavity HOM coupler, the simulation results show that resonant trajectories exist in three zones, corresponding to an accelerating gradient range of 0.6-1.6 MV/m, 21-34 MV/m, 32-35 MV/m, and > 40MV/m, respectively. For the CEBAF 12 GeV upgrade cavity HOM coupler, resonant trajectories exist in one zone, corresponding to an accelerating gradient range of 6-13 MV/m. Potential implications of these MP barriers are discussed in the context of future high energy pulsed as well as medium energy continuous wave (CW) accelerators based on superconducting radio frequency cavities. Frequency scaling of MP's predicted in HOM couplers of the ILC, CBEAF upgrade, SNS and FLASH third harmonic cavity is given and found to be in good agreement with the analytical result based on the parallel plate model.
M2 tidal parameter modulation revealed by superconducting gravimeter time series
Meurers, Bruno; Van Camp, Michel; Francis, Olivier; Pálinkáš, Vojtech
2016-04-01
Analyzing consecutive and independent 1-yr data sets of 10 European superconducting gravimeters (SG) reveals statistically significant temporal variations of M2 tidal parameters. Both common short-term ( 2 yr) features are identified in all SG time series but one. The averaged variations of the amplitude factor are about 0.2 per mille. The path of load vector variations equivalent to the temporal changes of tidal parameters suggests the presence of an 8.85 yr modulation (lunar perigee). The tidal waves having the potential to modulate M2 with this period belong to the 3rd degree constituents. Their amplitude factors turn out to be much closer to body tide model predictions than that of the main 2nd degree M2, which indicates ocean loading for 3rd degree waves to be less prominent than for 2nd degree waves within the M2 group. These two different responses to the loading suggest that the observed long-term modulation is more due to insufficient frequency resolution of limited time series rather than to time variable loading. Presently, SG gravity time series are still too short to prove if time variable loading processes are involved too as in case of the annual M2 modulation known to appear for analysis intervals of less than 1 yr. The observed variations provide an upper accuracy limit for Earth model validation and permit estimating the temporal stability of SG scale factors and assessing the quality of gravity time series.
Temporal variation of tidal parameters in superconducting gravimeter time-series
Meurers, Bruno; Van Camp, Michel; Francis, Olivier; Pálinkáš, Vojtech
2016-04-01
Analysing independent 1-yr data sets of 10 European superconducting gravimeters (SG) reveals statistically significant temporal variations of M2 tidal parameters. Both common short-term (2 yr) features are identified in all SG time-series but one. The averaged variations of the amplitude factor are about 0.2‰. The path of load vector variations equivalent to the temporal changes of tidal parameters suggests the presence of an 8.85 yr modulation (lunar perigee). The tidal waves having the potential to modulate M2 with this period belong to the 3rd degree constituents. Their amplitude factors turn out to be much closer to body tide model predictions than that of the main 2nd degree M2, which indicates ocean loading for 3rd degree waves to be less prominent than for 2nd degree waves within the M2 group. These two different responses to the loading suggest that the observed modulation is more due to insufficient frequency resolution of limited time-series rather than to time variable loading. Presently, SG gravity time-series are still too short to prove if time variable loading processes are involved too as in case of the annual M2 modulation known to appear for analysis intervals of less than 1 yr. Whatever the variations are caused by, they provide the upper accuracy limit for earth model validation and permit estimating the temporal stability of SG scale factors and assessing the quality of gravity time-series.
Anyonic order parameters for discrete gauge theories on the lattice
Bais, F.A.; Romers, J.C.
2009-01-01
We present a new family of gauge invariant non-local order parameters Delta(A)(alpha) for (non-abelian) discrete gauge theories on a Euclidean lattice, which are in one-to-one correspondence with the excitation spectrum that follows from the representation theory of the quantum double D(H) of the
Self-assembled fluids with order-parameter- dependent mobility ...
Indian Academy of Sciences (India)
process, the structure factor exhibits multiscaling behavior with characteristic length scale. (t/ ln t)1/2(2α+3). The order-parameter-dependent mobility is found to slow down the rate of coarsening. Keywords. Morphological instability; phase changes; nonequilibrium; irreversible ther- modynamics. PACS Nos 47.20.Hw; 05.70.
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.
Order parameter prediction from molecular dynamics simulations in proteins
Perilla, Juan R
2011-01-01
A molecular understanding of how protein function is related to protein structure will require an ability to understand large conformational changes between multiple states. Unfortunately these states are often separated by high free energy barriers and within a complex energy landscape. This makes it very difficult to reliably connect, for example by all-atom molecular dynamics calculations, the states, their energies and the pathways between them. A major issue needed to improve sampling on the intermediate states is an order parameter -- a reduced descriptor for the major subset of degrees of freedom -- that can be used to aid sampling for the large conformational change. We present a novel way to combine information from molecular dynamics using non-linear time series and dimensionality reduction, in order to quantitatively determine an order parameter connecting two large-scale conformationally distinct protein states. This new method suggests an implementation for molecular dynamics calculations that ma...
Spin-fluctuation mediated superconductivity and magnetic order in the cuprate La1.88Sr0.12CuO4
DEFF Research Database (Denmark)
Rømer, Astrid Tranum
High-temperature superconductivity in cuprates emerges as one out of many electronic phases when doping the antiferromagnetic Mott insulator La2CuO4 away from half _lling. The description of the superconducting phase is therefore complicated by intertwined electronic orders that compete...... with superconductivity. However, it is possible that the tendency towards additional ordering phenomena is a necessary condition for unconventional superconductivity to develop. Indeed most superconductors discovered throughout the last 29 years, including also the recently discovered class of iron-based superconductors......, show a very rich electronic phase diagram. A common feature that characterizes both cuprates, heavy fermions, and iron pnictides is the proximity to magnetic order. Therefore, the idea of spin-uctuation mediated pairing is a popular paradigm proposed for unconventional superconductivity. A _ngerprint...
Mixed-parity superconductivity in centrosymmetric crystals
Sergienko, I. A.
2003-01-01
A weak-coupling formalism for superconducting states possessing both singlet (even parity) and triplet (odd parity) components of the order parameter in centrosymmetric crystals is developed. It is shown that the quasiparticle energy spectrum may be non-degenerate even if the triplet component is unitary. The superconducting gap of a mixed-parity state may have line nodes in the strong spin-orbit coupling limit. The pseudospin carried by the superconducting electrons is calculated, from which...
Microstrip superconducting quantum interference device amplifier: Operation in higher-order modes
Mück, Michael; Schmidt, Bernd; Clarke, John
2017-07-01
DC Superconducting Quantum Interference Devices (SQUIDs) are widely used to amplify low-level, radio frequency (rf) electrical signals. SQUID amplifiers offer low noise, high gain, and low power dissipation. One method of implementing a SQUID rf amplifier for frequencies from a few hundred megahertz to several gigahertz is to operate the integrated input coil on top of the SQUID washer as a microstrip resonator. This is achieved by applying the input signal between one end of the coil and the SQUID washer, which acts as a groundplane; the other end of the coil is left open. Substantial levels of gain can be achieved from the microstrip SQUID amplifier for a signal frequency at the fundamental resonant frequency of the microstrip, at which the length of the microstrip is equal to one-half wavelength, λ/2. Since the length of the microstrip has to be made shorter for higher frequencies, however, the mutual inductance between a SQUID with a given geometry and the microstrip—and thus the gain—decreases with increasing frequency. We show that a significantly enhanced gain can be achieved by operating the microstrip resonator in higher-order modes, for example, with a microstrip length of 3λ/2 or 5λ/2, provided the winding sense of the microstrip for each consecutive λ/2 section is reversed. For a 4λ/2 resonator, we demonstrate a gain of 24 dB at 2.6 GHz, an increase in gain of about 10 dB compared to a λ/2 resonator on a SQUID of the same geometry and characteristics.
Coupling of structure to magnetic and superconducting orders in quasi-one-dimensional K2Cr3As3
Taddei, K. M.; Zheng, Q.; Sefat, A. S.; de la Cruz, C.
2017-11-01
Quasi-one-dimensional A2Cr3As3 (with A =K , Cs, Rb) is an intriguing new family of superconductors which exhibit many similar features to the cuprate and iron-based unconventional superconductor families. Yet, in contrast to these systems, no charge or magnetic ordering has been observed which could provide the electronic correlations presumed necessary for an unconventional superconducting pairing mechanism—an absence which defies predictions of first-principles models. We report the results of neutron scattering experiments on polycrystalline K2Cr3As3 (Tc˜7 K ) which probed the low-temperature dynamics near Tc. Neutron diffraction data evidence a subtle response of the nuclear lattice to the onset of superconductivity while inelastic scattering reveals a highly dispersive column of intensity at the commensurate wave vector q =(00 1/2 ) which loses intensity beneath Tc—indicative of short-range magnetic fluctuations. Using linear spin-wave theory, we model the observed scattering and suggest a possible structure to the short-range magnetic order. These observations suggest that K2Cr3As3 is in close proximity to a magnetic instability and that the incipient magnetic order both couples strongly to the lattice and competes with superconductivity, in direct analogy with the iron-based superconductors.
Emergent Higgsless Superconductivity
Directory of Open Access Journals (Sweden)
Cristina Diamantini M.
2017-01-01
Full Text Available We present a new Higgsless model of superconductivity, inspired from anyon superconductivity but P- and T-invariant and generalizable to any dimension. While the original anyon superconductivity mechanism was based on incompressible quantum Hall fluids as average field states, our mechanism involves topological insulators as average field states. In D space dimensions it involves a (D-1-form fictitious pseudovector gauge field which originates from the condensation of topological defects in compact lowenergy effective BF theories. There is no massive Higgs scalar as there is no local order parameter. When electromagnetism is switched on, the photon acquires mass by the topological BF mechanism. Although the charge of the gapless mode (2 and the topological order (4 are the same as those of the standard Higgs model, the two models of superconductivity are clearly different since the origins of the gap, reflected in the high-energy sectors are totally different. In 2D thi! s type of superconductivity is explicitly realized as global superconductivity in Josephson junction arrays. In 3D this model predicts a possible phase transition from topological insulators to Higgsless superconductors.
Thermal nanostructure: An order parameter multiscale ensemble approach
Cheluvaraja, S.; Ortoleva, P.
2010-01-01
Deductive all-atom multiscale techniques imply that many nanosystems can be understood in terms of the slow dynamics of order parameters that coevolve with the quasiequilibrium probability density for rapidly fluctuating atomic configurations. The result of this multiscale analysis is a set of stochastic equations for the order parameters whose dynamics is driven by thermal-average forces. We present an efficient algorithm for sampling atomistic configurations in viruses and other supramillion atom nanosystems. This algorithm allows for sampling of a wide range of configurations without creating an excess of high-energy, improbable ones. It is implemented and used to calculate thermal-average forces. These forces are then used to search the free-energy landscape of a nanosystem for deep minima. The methodology is applied to thermal structures of Cowpea chlorotic mottle virus capsid. The method has wide applicability to other nanosystems whose properties are described by the CHARMM or other interatomic force field. Our implementation, denoted SIMNANOWORLD™, achieves calibration-free nanosystem modeling. Essential atomic-scale detail is preserved via a quasiequilibrium probability density while overall character is provided via predicted values of order parameters. Applications from virology to the computer-aided design of nanocapsules for delivery of therapeutic agents and of vaccines for nonenveloped viruses are envisioned. PMID:20170252
Thermal nanostructure: An order parameter multiscale ensemble approach
Cheluvaraja, S.; Ortoleva, P.
2010-02-01
Deductive all-atom multiscale techniques imply that many nanosystems can be understood in terms of the slow dynamics of order parameters that coevolve with the quasiequilibrium probability density for rapidly fluctuating atomic configurations. The result of this multiscale analysis is a set of stochastic equations for the order parameters whose dynamics is driven by thermal-average forces. We present an efficient algorithm for sampling atomistic configurations in viruses and other supramillion atom nanosystems. This algorithm allows for sampling of a wide range of configurations without creating an excess of high-energy, improbable ones. It is implemented and used to calculate thermal-average forces. These forces are then used to search the free-energy landscape of a nanosystem for deep minima. The methodology is applied to thermal structures of Cowpea chlorotic mottle virus capsid. The method has wide applicability to other nanosystems whose properties are described by the CHARMM or other interatomic force field. Our implementation, denoted SIMNANOWORLD™, achieves calibration-free nanosystem modeling. Essential atomic-scale detail is preserved via a quasiequilibrium probability density while overall character is provided via predicted values of order parameters. Applications from virology to the computer-aided design of nanocapsules for delivery of therapeutic agents and of vaccines for nonenveloped viruses are envisioned.
Multicomponent order parameter and penetration depth of YBCO single crystals
Nefyodov, Yu. A.; Golubov, Alexandre Avraamovitch; Trunin, M.R.; Béal-Monod, M.T.
2000-01-01
We have analyzed the possible temperature variation of the penetration depth λ(T) in the (d+s)-wave superconductivity model of hybrid pairing, which accounts for the high Tc cuprates with an orthorhombic distortion. The slope of the Δλ(T)∝T for TTc and its dependence on the Δs/Δd admixture in the
Gomes, N; Clay, R T; Mazumdar, S
2013-09-25
A frustrated, effective ½-filled band Hubbard-Heisenberg model has been proposed for describing the strongly dimerized charge-transfer solid families κ-(ET)2X and Z[Pd(dmit)2]2. In addition to showing unconventional superconductivity, these materials also exhibit antiferromagnetism, candidate spin-liquid phases, and, in the case of Z=EtMe3P, a spin-gapped phase that has sometimes been referred to as a valence bond solid. We show that neither superconductivity nor the valence bond order phase occurs within the Hubbard-Heisenberg model. We suggest that a description based on ¼-filling, that is reached when the carrier concentration per molecule instead of per dimer is considered, thus may be appropriate.
Gomes, N.; Clay, R. T.; Mazumdar, S.
2013-09-01
A frustrated, effective \\frac{1}{2}-filled band Hubbard-Heisenberg model has been proposed for describing the strongly dimerized charge-transfer solid families κ-(ET)2X and Z[Pd(dmit)2]2. In addition to showing unconventional superconductivity, these materials also exhibit antiferromagnetism, candidate spin-liquid phases, and, in the case of Z=EtMe3P, a spin-gapped phase that has sometimes been referred to as a valence bond solid. We show that neither superconductivity nor the valence bond order phase occurs within the Hubbard-Heisenberg model. We suggest that a description based on \\frac{1}{4}-filling, that is reached when the carrier concentration per molecule instead of per dimer is considered, thus may be appropriate.
Kaplan, C. Nadir; Hinczewski, Michael; Berker, A. Nihat
2009-06-01
For a variety of quenched random spin systems on an Apollonian network, including ferromagnetic and antiferromagnetic bond percolation and the Ising spin glass, we find the persistence of ordered phases up to infinite temperature over the entire range of disorder. We develop a renormalization-group technique that yields highly detailed information, including the exact distributions of local magnetizations and local spin-glass order parameters, which turn out to exhibit, as function of temperature, complex and distinctive tulip patterns.
Superconducting Vortex with Antiferromagnetic Core
Energy Technology Data Exchange (ETDEWEB)
Arovas, D.P. [Department of Physics, University of California at San Diego, La Jolla, California 92093 (United States); Berlinsky, A.J.; Kallin, C.; Zhang, S. [Department of Physics, Stanford University, Stanford, California 94305 (United States)
1997-10-01
We show that a superconducting vortex in underdoped high T{sub c} superconductors could have an antiferromagnetic core. This type of vortex configuration arises as a topological solution in the recently constructed SO(5) nonlinear {sigma} model and in Landau-Ginzburg theory with competing antiferromagnetic and superconducting order parameters. Experimental detection of this type of vortex by muon spin resonance and neutron scattering is proposed. {copyright} {ital 1997} {ital The American Physical Society}
Superconductivity and magnetic ordering in the mixed ternary Er xY 1-xRh 1.1Sn 3.6 system
Houwman, E. P.; van de Pasch, A. W. M.; Flokstra, J.
1987-07-01
The superconducting transition temperature Tc as well as the magnetic ordering temperature Tm have been determined in the mixed ternary compound Er xY 1-xRh 1.1Sn 3.6 as a function of the Er concentration. Tc decreases from 3.13 K for YRh 1.1Sn 3.6 to 1.1K for ErRh 1.1Sn 3.6. Reentrant superconductivity has been found for x > 0.6. The application of the models of Abrikosov and Gorkov, Maekawa and Tachiki, and Roshen and Ruvalds to this system is discussed. Tc as function of the concentration x is best described by the model of Roshen and Ruvalds assuming a ferromagnetic interaction between the spins. The parameter I2N(0), arising from electron spin, is found to be 0.088 K. The ferromagnetic ordering temperature dependence is described by the theory of Oguchi and Ono, using an effective coordination number z = 6 and an exchange constant of J‧ = 0.30 K.
Kernel methods for interpretable machine learning of order parameters
Ponte, Pedro; Melko, Roger G.
2017-11-01
Machine learning is capable of discriminating phases of matter, and finding associated phase transitions, directly from large data sets of raw state configurations. In the context of condensed matter physics, most progress in the field of supervised learning has come from employing neural networks as classifiers. Although very powerful, such algorithms suffer from a lack of interpretability, which is usually desired in scientific applications in order to associate learned features with physical phenomena. In this paper, we explore support vector machines (SVMs), which are a class of supervised kernel methods that provide interpretable decision functions. We find that SVMs can learn the mathematical form of physical discriminators, such as order parameters and Hamiltonian constraints, for a set of two-dimensional spin models: the ferromagnetic Ising model, a conserved-order-parameter Ising model, and the Ising gauge theory. The ability of SVMs to provide interpretable classification highlights their potential for automating feature detection in both synthetic and experimental data sets for condensed matter and other many-body systems.
Connectivity and superconductivity
Rubinstein, Jacob
2000-01-01
The motto of connectivity and superconductivity is that the solutions of the Ginzburg--Landau equations are qualitatively influenced by the topology of the boundaries, as in multiply-connected samples. Special attention is paid to the "zero set", the set of the positions (also known as "quantum vortices") where the order parameter vanishes. The effects considered here usually become important in the regime where the coherence length is of the order of the dimensions of the sample. It takes the intuition of physicists and the awareness of mathematicians to find these new effects. In connectivity and superconductivity, theoretical and experimental physicists are brought together with pure and applied mathematicians to review these surprising results. This volume is intended to serve as a reference book for graduate students and researchers in physics or mathematics interested in superconductivity, or in the Schrödinger equation as a limiting case of the Ginzburg--Landau equations.
The Ramachandran Number: An Order Parameter for Protein Geometry.
Mannige, Ranjan V; Kundu, Joyjit; Whitelam, Stephen
2016-01-01
Three-dimensional protein structures usually contain regions of local order, called secondary structure, such as α-helices and β-sheets. Secondary structure is characterized by the local rotational state of the protein backbone, quantified by two dihedral angles called ϕ and ψ. Particular types of secondary structure can generally be described by a single (diffuse) location on a two-dimensional plot drawn in the space of the angles ϕ and ψ, called a Ramachandran plot. By contrast, a recently-discovered nanomaterial made from peptoids, structural isomers of peptides, displays a secondary-structure motif corresponding to two regions on the Ramachandran plot [Mannige et al., Nature 526, 415 (2015)]. In order to describe such 'higher-order' secondary structure in a compact way we introduce here a means of describing regions on the Ramachandran plot in terms of a single Ramachandran number, [Formula: see text], which is a structurally meaningful combination of ϕ and ψ. We show that the potential applications of [Formula: see text] are numerous: it can be used to describe the geometric content of protein structures, and can be used to draw diagrams that reveal, at a glance, the frequency of occurrence of regular secondary structures and disordered regions in large protein datasets. We propose that [Formula: see text] might be used as an order parameter for protein geometry for a wide range of applications.
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)
Energy Technology Data Exchange (ETDEWEB)
Zhang, Pei
2013-02-15
Higher order modes (HOM) are electromagnetic resonant fields. They can be excited by an electron beam entering an accelerating cavity, and constitute a component of the wakefield. This wakefield has the potential to dilute the beam quality and, in the worst case, result in a beam-break-up instability. It is therefore important to ensure that these fields are well suppressed by extracting energy through special couplers. In addition, the effect of the transverse wakefield can be reduced by aligning the beam on the cavity axis. This is due to their strength depending on the transverse offset of the excitation beam. For suitably small offsets the dominant components of the transverse wakefield are dipole modes, with a linear dependence on the transverse offset of the excitation bunch. This fact enables the transverse beam position inside the cavity to be determined by measuring the dipole modes extracted from the couplers, similar to a cavity beam position monitor (BPM), but requires no additional vacuum instrumentation. At the FLASH facility in DESY, 1.3 GHz (known as TESLA) and 3.9 GHz (third harmonic) cavities are installed. Wakefields in 3.9 GHz cavities are significantly larger than in the 1.3 GHz cavities. It is therefore important to mitigate the adverse effects of HOMs to the beam by aligning the beam on the electric axis of the cavities. This alignment requires an accurate beam position diagnostics inside the 3.9 GHz cavities. It is this aspect that is focused on in this thesis. Although the principle of beam diagnostics with HOM has been demonstrated on 1.3 GHz cavities, the realization in 3.9 GHz cavities is considerably more challenging. This is due to the dense HOM spectrum and the relatively strong coupling of most HOMs amongst the four cavities in the third harmonic cryo-module. A comprehensive series of simulations and HOM spectra measurements have been performed in order to study the modal band structure of the 3.9 GHz cavities. The dependencies of
Multicritical behavior in models with two competing order parameters.
Eichhorn, Astrid; Mesterházy, David; Scherer, Michael M
2013-10-01
We employ the nonperturbative functional renormalization group to study models with an O(N(1) ⊕O(N)(2)) symmetry. Here different fixed points exist in three dimensions, corresponding to bicritical and tetracritical behavior induced by the competition of two order parameters. We discuss the critical behavior of the symmetry-enhanced isotropic, the decoupled and the biconical fixed point, and analyze their stability in the N(1),N(2) plane. We study the fate of nontrivial fixed points during the transition from three to four dimensions, finding evidence for a triviality problem for coupled two-scalar models in high-energy physics. We also point out the possibility of noncanonical critical exponents at semi-Gaussian fixed points and show the emergence of Goldstone modes from discrete symmetries.
DEFF Research Database (Denmark)
Toft, Katrine Nørgaard
The field-induced magnetic structures of ErNi2B2C and TmNi2B2C in are especially interesting because the field suppresses the superconducting order parameter and therefore the magnetic properties can be studied while varying the strength ofsuperconductivity. ErNi2B2C: For magnetic fields along all...... three symmetry directions, the observed magnetic structures have a period corresponding to the Fermi surface nesting structure. The phase diagrams present all the observed magnetic structures.Two results remain unresolved: 1. When applying the magnetic field along [010], the minority domain (QNB = (0,Q......,0) with moments perpendicular to the field) shows no signs of hysteresis. I expected it to be a meta-stable state, which would be graduallysuppressed by a magnetic field, and when decreasing the field it would not reappear until some small field of approximately 0.1 T. 2. When the field is applied...
Superconducting (Li,Fe)OHFeSe Film of High Quality and High Critical Parameters
Huang, Yulong; Feng, Zhongpei; Ni, Shunli; Li, Jun; Hu, Wei; Liu, Shaobo; Mao, Yiyuan; Zhou, Huaxue; Zhou, Fang; Jin, Kui; Wang, Huabing; Yuan, Jie; Dong, Xiaoli; Zhao, Zhongxian
2017-06-01
A superconducting film of (Li1-x Fe x )OHFeSe is reported for the first time. The thin film exhibits a small in-plane crystal mosaic of 0.22°, in terms of the full width at half maximum of the x-ray rocking curve, and an excellent out-of-plane orientation by x-ray φ-scan. Its bulk superconducting transition temperature {T}{{c}} of 42.4 K is characterized by both zero electrical resistance and diamagnetization measurements. The upper critical field {H}{{c}2} is estimated to be 79.5 T and 443 T for the magnetic field perpendicular and parallel to the ab plane, respectively. Moreover, a large critical current density {J}{{c}} of a value over 0.5 MA/cm2 is achieved at ˜20 K. Such a (Li1-x Fe x )OHFeSe film is therefore not only important to the fundamental research for understanding the high-{T}{{c}} mechanism, but also promising in the field of high-{T}{{c}} superconductivity application, especially in high-performance electronic devices and large scientific facilities such as superconducting accelerator. Supported by the National Basic Research Program of China under Grant No 2017YFA0303000, the National Natural Science Foundation of China under Grant Nos 11574370, 11234006 and 61501220, the Strategic Priority Research Program and Key Research Program of Frontier Sciences of the Chinese Academy of Sciences under Grant Nos QYZDY-SSW-SLH001, QYZDY-SSW-SLH008 and XDB07020100.
Fukazawa, H; Yamada, K
2003-01-01
We evaluate the dominant superconducting pairing symmetry in 3-dimensional cubic lattice structures within the third-order perturbation theory with respect to the on-site coulomb repulsion. We show that the third-order vertex correction term, which has a critical contribution to the p-wave state in the 2-dimensional systems, is also important in the 3-dimensional system. In the three dimensional systems, we obtain the superconducting transition temperature T sub c about one-order lower than that in 2-dimensional systems. This result suggests that magnetic ground states are dominant in the usual 3-dimensional system in accordance with the experimental observation. However there exist heavy fermion systems where the magnetic order is suppressed by the Kondo effect. Thus, our theory can be applied to the heavy fermion system and well explain the superconductivity in the system. (author)
Superconductivity, Mott-Hubbard states, and molecular orbital order in intercalated fullerides
Iwasa, Y
2003-01-01
This article reviews the current status of chemically doped fullerene superconductors and related compounds, with particular focus on Mott-Hubbard states and the role of molecular orbital degeneracy. Alkaline-earth metal fullerides produce superconductors of several kinds, all of which have states with higher valence than (C sub 6 sub 0) sup 6 sup - , where the second lowest unoccupied molecular orbital (the LUMO + 1 state) is filled. Alkali-metal-doped fullerides, on the other hand, afford superconductors only at the stoichiometry A sub 3 C sub 6 sub 0 (A denotes alkali metal) and in basically fcc structures. The metallicity and superconductivity of A sub 3 C sub 6 sub 0 compounds are destroyed either by reduction of the crystal symmetry or by change in the valence of C sub 6 sub 0. This difference is attributed to the narrower bandwidth in the A sub 3 C sub 6 sub 0 system, causing electronic instability in Jahn-Teller insulators and Mott-Hubbard insulators. The latter metal-insulator transition is driven by...
Crisan, Mircea
1989-01-01
This book discusses the most important aspects of the theory. The phenomenological model is followed by the microscopic theory of superconductivity, in which modern formalism of the many-body theory is used to treat most important problems such as superconducting alloys, coexistence of superconductivity with the magnetic order, and superconductivity in quasi-one-dimensional systems. It concludes with a discussion on models for exotic and high temperature superconductivity. Its main aim is to review, as complete as possible, the theory of superconductivity from classical models and methods up t
Why we still don`t know the symmetry of the order parameter in high temperature superconductors
Energy Technology Data Exchange (ETDEWEB)
Klemm, R.A. [Argonne National Lab., IL (United States). Materials Science Div.
1997-03-01
One of the most elusive topics in the study of high temperature superconductors (HTCS) is the orbital symmetry of the superconducting order parameter {Delta}. The low temperature T behavior observed in many experiments suggests that {Delta} might exhibit line nodes, as expected for d{sub x}{sub {minus}y}2 orbital symmetry. However, such behavior also arises from intrinsic proximity coupling and surface states, etc. The paramagnetic Meissner effect, once cited as indirect evidence for a d-wave {Delta}, was recently observed in Nb. Some phase-sensitive Josephson junction experiments gave strong evidence for a substantial isotropic, or s-wave, component to {Delta}, whereas others supported the above d-wave form. However, such experiments are intrinsically unreliable in experimental geometries with sample corners, or with meandering grain boundary junctions and stoichiometry inhomogeneities. Finally, the pseudogap observed recently in underdoped HTCS could arise from a charge-density wave.
Effects of spin-flip scattering on the dynamics of the superconducting order parameter
Energy Technology Data Exchange (ETDEWEB)
Aspen, F.E.
1980-06-01
Measurements of the imaginary part of the pair-field susceptibility X'' have been carried out on dirty-limit Al-Er alloy films. Aluminum films with erbium concentrations of up to one atomic percent were incorporated as the low T/sub c/ film of an asymmetric Josephson junction. The excess current I/sub ex/ due to pair tunneling was measured as a function of the bias voltage V and of the magnetic field H, applied in the plane of the junction, at temperatures within 20% of the critical temperature T/sub c/. Comparison to theory was facilitated by noting that X''(..omega..,k) varies as I/sub ex/(V,H) where the frequency ..omega.. and wave-number k are related to V and H via the Josephson relations.
Spectral characteristics of the coherent dynamics of the order parameter in superconducting nanorods
Energy Technology Data Exchange (ETDEWEB)
Kettmann, P.; Hannibal, S. [Institut für Festkörpertheorie, Westfälische Wilhelms-Universität Münster, Münster,48149 (Germany); Croitoru, M.D., E-mail: mikhail.croitoru@uni-bayreuth.de [3Departamento de Física, Universidade Federal de Pernambuco, Recife, Pernambuco,50670-901 (Brazil); Vagov, A.; Axt, V.M. [Theoretische Physik III, Universität Bayreuth, 95440,Bayreuth (Germany); Kuhn, T. [Institut für Festkörpertheorie, Westfälische Wilhelms-Universität Münster, Münster,48149 (Germany)
2017-02-15
Highlights: • Within the density-matrix formalism based on the Bogoliubov-de Gennes equations approach we investigate the dynamics of the nonequilibrium BCS pairing induced by a sudden change of the coupling constant in quasi-1D and quasi-0D samples. • We demonstrate that two different dynamical regimes of the amplitude of the BCS gap can be distinguished: an initially damped oscillation in the case of short quantum wires and purely irregular dynamics in the case of nanorods. • We explain this transition on the basis of linearized equations of motion and linke it to the properties of the single-particle energies in the corresponding regimes. - Abstract: Within the density-matrix formalism based on the Bogoliubov-de Gennes equations approach we investigate the dynamics of the non-equilibrium BCS pairing induced by a sudden change of the coupling constant in quasi-1D and quasi-0D samples. We demonstrate that two different dynamical regimes of the amplitude of the BCS gap can be distinguished: an initially damped oscillation in the case of short quantum wires and purely irregular dynamics in the case of nanorods.
Improved Parameter Estimation for First-Order Markov Process
Directory of Open Access Journals (Sweden)
Deepak Batra
2009-01-01
Full Text Available This correspondence presents a linear transformation, which is used to estimate correlation coefficient of first-order Markov process. It outperforms zero-forcing (ZF, minimum mean-squared error (MMSE, and whitened least-squares (WTLSs estimators by controlling output noise variance at the cost of increased computational complexity.
Parameter identification of commensurate fractional-order chaotic system via differential evolution
Tang, Yinggan; Zhang, Xiangyang; Hua, Changchun; Li, Lixiang; Yang, Yixian
2012-01-01
Chaos can be observed in fractional-order nonlinear systems with appropriate orders. The knowledge about the parameters and orders are the basis of the control and synchronization of fractional-order chaotic systems. In this Letter, the problem of parameter identification of commensurate fractional-order chaotic systems is investigated. By treating the orders as additional parameters, the parameters and orders are identified together through minimizing an objective function. Differential evolution algorithm, a powerful and robust evolutionary algorithm, is applied to search the optimal solution of the objective function. Numerical simulations and comparisons with genetic algorithm (GA) demonstrate the effectiveness of the proposed method.
Hneda, Marlon Luiz; da Silva Berchon, Luciano; Pureur, Paulo; das Neves Vieira, Valdemar; Jaeckel, Sandra Teixeira; Dias, Fábio Teixeira; Menegotto Costa, Rosângela
2017-04-01
Fluctuation conductivity is experimentally studied in the genuine critical region near the superconducting transition of YBa2Cu3O7 - δ, YBa2Cu2.985Fe0.015O7 - δ and Y0.95Ca0.05Ba2Cu3O7 - δ single crystal samples. Two fluctuation regimes where the electrical conductivity diverges as a power-law of the reduced temperature were systematically observed. In the first regime, farther from the critical temperature Tc, the transition behaves as predicted by the thermodynamics of the three dimensional-XY (3D-XY) universality class characteristic of a second-order phase transition. In the asymptotic regime closer to Tc a power-law regime characterized by a much smaller exponent is observed. The smallest value ever reported for the fluctuation conductivity exponent in the high-Tc superconductors is obtained for the Fe- and Ca-doped systems. We suggest that the regime beyond 3D-XY is a crossover towards a weakly first-order transition induced by internal magnetic excitations.
Fente, Antón; Correa-Orellana, Alexandre; Böhmer, Anna E.; Kreyssig, Andreas; Ran, S.; Bud'ko, Sergey L.; Canfield, Paul C.; Mompean, Federico J.; García-Hernández, Mar; Munuera, Carmen; Guillamón, Isabel; Suderow, Hermann
2018-01-01
We show that biaxial strain induces alternating tetragonal superconducting and orthorhombic nematic domains in Co-substituted CaFe2As2 . We use atomic force, magnetic force, and scanning tunneling microscopy to identify the domains and characterize their properties, finding in particular that tetragonal superconducting domains are very elongated, more than several tens of micrometers long and about 30 nm wide; have the same Tc as unstrained samples; and hold vortices in a magnetic field. Thus, biaxial strain produces a phase-separated state, where each phase is equivalent to what is found on either side of the first-order phase transition between antiferromagnetic orthorhombic and superconducting tetragonal phases found in unstrained samples when changing Co concentration. Having such alternating superconducting domains separated by normal conducting domains with sizes of the order of the coherence length opens opportunities to build Josephson junction networks or vortex pinning arrays and suggests that first-order quantum phase transitions lead to nanometric-size phase separation under the influence of strain.
Juntunen, K I; Tuoriniemi, J T
2004-10-08
We have discovered spontaneous ordering of nuclear spins in lithium metal by NMR measurements at very low temperatures. In low magnetic fields, Blithium at normal pressure down to T(e) approximately 100 microK (B<10 nT).
Parameter identification of commensurate fractional-order chaotic system via differential evolution
Energy Technology Data Exchange (ETDEWEB)
Tang, Yinggan, E-mail: ygtang@yahoo.cn [Institute of Electrical Engineering, Yanshan University, Qinhuangdao, Hebei 066004 (China); National Engineering Research Center for Equipment and Technology of Cold Strip Rolling (China); Zhang, Xiangyang; Hua, Changchun [Institute of Electrical Engineering, Yanshan University, Qinhuangdao, Hebei 066004 (China); Li, Lixiang; Yang, Yixian [Research Center on Fictitious Economy and Data Science, Chinese Academy of Sciences, Beijing 100190 (China)
2012-01-09
Chaos can be observed in fractional-order nonlinear systems with appropriate orders. The knowledge about the parameters and orders are the basis of the control and synchronization of fractional-order chaotic systems. In this Letter, the problem of parameter identification of commensurate fractional-order chaotic systems is investigated. By treating the orders as additional parameters, the parameters and orders are identified together through minimizing an objective function. Differential evolution algorithm, a powerful and robust evolutionary algorithm, is applied to search the optimal solution of the objective function. Numerical simulations and comparisons with genetic algorithm (GA) demonstrate the effectiveness of the proposed method. -- Highlights: ► We study the parameter identification problem of fractional order chaotic system. ► The orders and the parameters can be identified simultaneously. ► Numerical results verify the effectiveness of the proposed method.
Zhang, P; Jones, R M; Flisgen, T; Van Rienen, U; Shinton, I R R
2013-01-01
Higher order mode (HOM) beam position monitors (BPM) are being developed for the 3.9 GHz third harmonic superconducting accelerating cavities at FLASH. The transverse beam position in a cavity can be determined utilizing beam-excited HOMs based on dipole components. The existing couplers used for HOM suppression provide necessary signals. The diagnostics principle is similar to a cavity BPM, but requires no additional vacuum instruments on the linac. The challenges of HOM-BPM for 3.9 GHz cavities lie in the dense HOM spectrum arising from the coupling of the majority HOMs amongst the four cavities in the cryo-module ACC39. HOMs with particularly promising diagnostics features were evaluated using a spectrum analyzer and custom-built test electronics with various data analysis techniques, data reduction was focused on. After careful theoretical and experimental assessment of the HOM spectrum, multi-cavity modes in the region of 5 GHz were chosen to provide a global position over the complete module with superi...
Zhang, P; Baboi, Nicoleta
2012-01-01
Higher order modes (HOM) are electromagnetic resonant fields. They can be excited by an electron beam entering an accelerating cavity, and constitute a component of the wakefield. This wakefield has the potential to dilute the beam quality and, in the worst case, result in a beam-break-up instability. It is therefore important to ensure that these fields are well suppressed by extracting energy through special couplers. In addition, the effect of the transverse wakefield can be reduced by aligning the beam on the cavity axis. This is due to their strength depending on the transverse offset of the excitation beam. For suitably small offsets the dominant components of the transverse wakefield are dipole modes, with a linear dependence on the transverse offset of the excitation bunch. This fact enables the transverse beam position inside the cavity to be determined by measuring the dipole modes extracted from the couplers, similar to a cavity beam position monitor (BPM), but requires no additional vacuum instrum...
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.
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.
On the control parameters of the quasi-one dimensional superconductivity in Sc{sub 3}CoC{sub 4}
Energy Technology Data Exchange (ETDEWEB)
Eickerling, Georg; Hauf, Christoph; Scheidt, Ernst-Wilhelm; Reichardt, Lena; Schneider, Christian; Scherer, Wolfgang [Institut fuer Physik, Universitaet Augsburg, Universitaetstrasse 1, 86179 Augsburg (Germany); Munoz, Alfonso [Departamento de Fisica Fundamental II, Instituto de Materiales y Nanotecnologia, Universidad de La Laguna, Tenerife (Spain); Lopez-Moreno, Sinhue [Escuela Superior Cd. Sahagun, Universidad Autonoma del Estado de Hidalgo, Carretera Cd. Sahagun-Otumba s/n. 43990, Hidalgo (Mexico); Humberto Romero, Aldo [Physics Department, West Virginia University, Morgantown, West Virginia 26506-6315 (United States); Max Planck Institut fuer Mikrostruktur Physik, Weinberg 2, 06120 Halle (Germany); Porcher, Florence; Andre, Gilles [Laboratoire Leon Brillouin, UMR12 CEA-CNRS, Bat 563 CEA Saclay, 91191 Gif sur Yvette Cedex (France); Poettgen, Rainer [Institut fuer Anorganische und Analytische Chemie, Universitaet Muenster, Corrensstrasse 30, 48149 Muenster (Germany)
2013-09-15
Within the series of ternary rare-earth transition metal carbides Sc{sub 3}TC{sub 4} (T = Fe, Co, Ni) only the Co congener displays a structural phase transition at 72 K and an onset of bulk superconductivity at 4.5 K. In this paper we present the results of a detailed analysis of the structural, electronic, and vibrational properties of the low-temperature phase of Sc{sub 3}CoC{sub 4} that represents one of the few well-documented examples of a quasi one-dimensional (1D) superconductor. Variable temperature neutron powder diffraction and low temperature X-ray diffraction experiments were performed in order to confirm the subtle structural distortions during the phase transition. The results of periodic electronic structure calculations indicate, that the structural transition can clearly be identified as a Peierls-type distortion and by a comparison with the isostructural carbide Sc{sub 3}FeC{sub 4} we are able to identify the chemical, electronic, and the vibrational control parameters of the transition. Topological analyses of the electron density distribution and of the valence shell charge concentrations at the cobalt atom finally allow us to directly correlate the changes in the electronic structure due to the Peierls transition in reciprocal space with the according subtle changes in the real space properties of Sc{sub 3}CoC{sub 4}. (Copyright copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Directory of Open Access Journals (Sweden)
Liping Chen
2012-01-01
between the fractional-order chaotic Chen system and the fractional-order chaotic Lü system with unknown parameters is achieved. Theoretical analysis and numerical simulations are presented to demonstrate the validity and feasibility of the proposed method.
Schemm, E R; Gannon, W J; Wishne, C M; Halperin, W P; Kapitulnik, A
2014-07-11
Models of superconductivity in unconventional materials can be experimentally differentiated by the predictions they make for the symmetries of the superconducting order parameter. In the case of the heavy-fermion superconductor UPt3, a key question is whether its multiple superconducting phases preserve or break time-reversal symmetry (TRS). We tested for asymmetry in the phase shift between left and right circularly polarized light reflected from a single crystal of UPt3 at normal incidence and found that this so-called polar Kerr effect appears only below the lower of the two zero-field superconducting transition temperatures. Our results provide evidence for broken TRS in the low-temperature superconducting phase of UPt3, implying a complex two-component order parameter for superconductivity in this system. Copyright © 2014, American Association for the Advancement of Science.
Order parameter anisotropy of MgB2 using specific heat jump of ...
Indian Academy of Sciences (India)
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 ...
Kotegawa, Hisashi; Nakahara, Shingo; Akamatsu, Rui; Tou, Hideki; Sugawara, Hitoshi; Harima, Hisatomo
2015-03-01
Pressure-induced superconductivity was recently discovered in the binary helimagnet CrAs. We report the results of measurements of nuclear quadrupole resonance for CrAs under pressure. In the vicinity of the critical pressure Pc between the helimagnetic (HM) and paramagnetic (PM) phases, a phase separation is observed. The large internal field remaining in the phase-separated HM state indicates that the HM phase disappears through a strong first-order transition. This indicates the absence of a quantum critical point in CrAs; however, the nuclear spin-lattice relaxation rate 1 /T1 reveals that substantial magnetic fluctuations are present in the PM state. The absence of a coherence effect in 1 /T1 in the superconducting state provides evidence that CrAs is the first Cr-based unconventional superconductor.
Superconductivity and magnetic ordering in the mixed ternary ErxY1−xRh1.1Sn3.6 system
Houwman, Evert Pieter; van de Pasch, A.W.M.; Flokstra, Jakob
1987-01-01
The superconducting transition temperature Tc as well as the magnetic ordering temperature Tm have been determined in the mixed ternary compound ErxY1−xRh1.1Sn3.6 as a function of the Er concentration. Tc decreases from 3.13 K for YRh1.1Sn3.6 to 1.1K for ErRh1.1Sn3.6. Reentrant superconductivity has been found for x > 0.6. The application of the models of Abrikosov and Gorkov, Maekawa and Tachiki, and Roshen and Ruvalds to this system is discussed. Tc as function of the concentration x is bes...
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.
Yokoyama, T.; Reutlinger, Johannes; Belzig, Wolfgang; Nazarov, Y.V.
2017-01-01
We consider the spectrum of Andreev bound states (ABSs) in an exemplary four-terminal superconducting structure where four chaotic cavities are connected by quantum point contacts to the terminals and to each other forming a ring. We nickname the resulting device 4T-ring. Such a tunable device
Gonnelli, R. S.; Daghero, D.; Tortello, M.; Ummarino, G. A.; Bukowski, Z.; Karpinski, J.; Reuvekamp, P. G.; Kremer, R. K.; Profeta, G.; Suzuki, K.; Kuroki, K.
2016-05-01
Iron-based compounds (IBS) display a surprising variety of superconducting properties that seems to arise from the strong sensitivity of these systems to tiny details of the lattice structure. In this respect, systems that become superconducting under pressure, like CaFe2As2, are of particular interest. Here we report on the first directional point-contact Andreev-reflection spectroscopy (PCARS) measurements on CaFe2As2 crystals under quasi-hydrostatic pressure, and on the interpretation of the results using a 3D model for Andreev reflection combined with ab-initio calculations of the Fermi surface (within the density functional theory) and of the order parameter symmetry (within a random-phase-approximation approach in a ten-orbital model). The almost perfect agreement between PCARS results at different pressures and theoretical predictions highlights the intimate connection between the changes in the lattice structure, a topological transition in the holelike Fermi surface sheet, and the emergence on the same sheet of an order parameter with a horizontal node line.
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.
Xue, Dingyü; Li, Tingxue
2017-04-27
The parameter optimization method for multivariable systems is extended to the controller design problems for multiple input multiple output (MIMO) square fractional-order plants. The algorithm can be applied to search for the optimal parameters of integer-order controllers for fractional-order plants with or without time delays. Two examples are given to present the controller design procedures for MIMO fractional-order systems. Simulation studies show that the integer-order controllers designed are robust to plant gain variations. Copyright © 2017 ISA. Published by Elsevier Ltd. All rights reserved.
Newhouse, Vernon L
1975-01-01
Applied Superconductivity, Volume II, is part of a two-volume series on applied superconductivity. The first volume dealt with electronic applications and radiation detection, and contains a chapter on liquid helium refrigeration. The present volume discusses magnets, electromechanical applications, accelerators, and microwave and rf devices. The book opens with a chapter on high-field superconducting magnets, covering applications and magnet design. Subsequent chapters discuss superconductive machinery such as superconductive bearings and motors; rf superconducting devices; and future prospec
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.
Energy Technology Data Exchange (ETDEWEB)
Weber, F.
2007-11-02
The present thesis concentrates on the signatures of strong electron-phonon coupling in phonon properties measured by inelastic neutron scattering. The inelastic neutron scattering experiments were performed on the triple-axis spectrometers 1T and DAS PUMA at the research reactors in Saclay (France) and Munich (Germany), respectively. The work is subdivided into two separate chapters: In the first part, we report measurements of the lattice dynamical properties, i.e. phonon frequency, linewidth and intensity, of the conventional, i.e. phonon-mediated, superconductor YNi{sub 2}B{sub 2}C of the rare-earth-borocarbide family. The detailed check of theoretical predictions for these properties, which were calculated in the theory group of our institute, was one major goal of this work. We measured phonons in the normal state, i.e. T>T{sub c}, for several high symmetry directions up to 70 meV. We were able to extract the full temperature dependence of the superconducting energy gap 2{delta}(T) from our phonon scans with such accuracy that even deviations from the weak coupling BCS behaviour could be clearly observed. By measuring phonons at different wave vectors we demonstrated that phonons are sensitive to the gap anisotropy under the precondition, that different phonons get their coupling strength from different parts of the Fermi surface. In the second part, we investigated the properties of Mn-O bond-stretching phonons in the bilayer manganite La{sub 2-2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7}. At the doping level x=0.38 this compound has an ferromagnetic groundstate and exhibits the so-called colossal magnetoresistance effect in the vicinity of the Curie temperature T{sub C}. The atomic displacement patterns of the investigated phonons closely resemble possible Jahn-Teller distortions of the MnO{sub 6} octahedra, which are introduced in this compound by the Jahn-Teller active Mn{sup 3+} ions. We observed strong renormalizations of the phonon frequencies and clear peaks of
Analytic Estimate of the Order Parameter for Magnetic Charge Condensation in QCD
Di Giacomo, Adriano
2006-01-01
The order parameter for monopole condensation is computed in terms of gauge invariant field strength correlators. Important properties emerge of the correlators in the confined phase, which could not be extracted by existing numerical determinations on the lattice.
Health Parameter Estimation with Second-Order Sliding Mode Observer for a Turbofan Engine
National Research Council Canada - National Science Library
Xiaodong Chang; Jinquan Huang; Feng Lu
2017-01-01
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...
A Simple Method for Estimation of Parameters in First order Systems
DEFF Research Database (Denmark)
Niemann, Hans Henrik; Miklos, Robert
2014-01-01
A simple method for estimation of parameters in first order systems with time delays is presented in this paper. The parameter estimation approach is based on a step response for the open loop system. It is shown that the estimation method does not require a complete step response, only a part of...
Yang, Ze-Lei; Zha, Guo-Qiao; Zhou, Shi-Ping
2018-01-01
The flux-dependent evolution of vortex states in nanoscale superconducting noncircular systems is investigated based on the Bogoliubov-de Gennes theory. For a superconductor with the coherence length comparable to the Fermi wavelength, the spatial variations of the superconducting order parameter are very sensitive to the finite size of the sample. With increasing the applied flux, the superconducting state and the normal state can alternately appear in small squares, and a remarkable intermittent superconducting behavior for the ground-state transition is found. Moreover, when the square size is enlarged, the asymmetric single-vortex and multivortex states as well as the vortex-antivortex pairs can emerge as the metastable or ground states, arising from the effect of strong quantum confinement.
Yang, Li-xin; Jiang, Jun
2014-05-01
This paper investigates the adaptive synchronization in the drive-response fractional-order dynamical networks with uncertain parameters. By means of both the stability theory of fractional-order differential system and the adaptive control technique, a novel adaptive synchronization controller is developed with a more general and simpler analytical expression, which does not contain the parameters of the complex network, and effective adaptive laws of parameters. Furthermore, the very strong and conservative uniformly Lipschitz condition on the node dynamics of complex network is released. To demonstrate the validity of the proposed method, the examples for the synchronization of systems with the chaotic and hyper-chaotic node dynamics are presented.
Self-assembled fluids with order-parameter-dependent mobility: The ...
Indian Academy of Sciences (India)
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 ...
Three Order Parameters in Quantum XZ Spin-Oscillator Models with Gibbsian Ground States
Directory of Open Access Journals (Sweden)
Wolodymyr I. Skrypnik
2008-01-01
Full Text Available Quantum models on the hyper-cubic d-dimensional lattice of spin-1/2 particles interacting with linear oscillators are shown to have three ferromagnetic ground state order parameters. Two order parameters coincide with the magnetization in the first and third directions and the third one is a magnetization in a continuous oscillator variable. The proofs use a generalized Peierls argument and two Griffiths inequalities. The class of spin-oscillator Hamiltonians considered manifest maximal ordering in their ground states. The models have relevance for hydrogen-bond ferroelectrics. The simplest of these is proven to have a unique Gibbsian ground state.
Parameter Sensitivity Analysis for Fractional-Order Modeling of Lithium-Ion Batteries
Directory of Open Access Journals (Sweden)
Daming Zhou
2016-02-01
Full Text Available This paper presents a novel-fractional-order lithium-ion battery model that is suitable for use in embedded applications. The proposed model uses fractional calculus with an improved Oustaloup approximation method to describe all the internal battery dynamic behaviors. The fractional-order model parameters, such as equivalent circuit component coefficients and fractional-order values, are identified by a genetic algorithm. A modeling parameters sensitivity study using the statistical Multi-Parameter Sensitivity Analysis (MPSA method is then performed and discussed in detail. Through the analysis, the dynamic effects of parameters on the model output performance are obtained. It has been found out from the analysis that the fractional-order values and their corresponding internal dynamics have different degrees of impact on model outputs. Thus, they are considered as crucial parameters to accurately describe a battery’s dynamic voltage responses. To experimentally verify the accuracy of developed fractional-order model and evaluate its performance, the experimental tests are conducted with a hybrid pulse test and a dynamic stress test (DST on two different types of lithium-ion batteries. The results demonstrate the accuracy and usefulness of the proposed fractional-order model on battery dynamic behavior prediction.
Zenkov, S. A.
2017-10-01
The article describes the method of defining rational parameters for excavator buckets vibrating devices in order to reduce soil adhesion under various operating conditions. The method includes limits formation, calculating geometric parameters of curved mold concentrator for excavator buckets with magnetostriction vibration exciters; calculating parameters of acoustic influence equipment; calculating power demand of equipment, defining adhesive forces of soil to buckets with given values of external factors; defining equipment operation mode (turn-on frequency, exposure time). Suggested method enables one to define required parameters of vibrating equipment to excavator buckets during the design phase.
On the Calculation of Acyl Chain Order Parameters from Lipid Simulations.
Piggot, Thomas J; Allison, Jane R; Sessions, Richard B; Essex, Jonathan W
2017-11-14
For molecular dynamics simulations of biological membrane systems to live up to the potential of providing accurate atomic level detail into membrane properties and functions, it is essential that the force fields used to model such systems are as accurate as possible. One membrane property that is often used to assess force field accuracy is the carbon-hydrogen (or carbon-deuterium) order parameters of the lipid tails, which can be accurately measured using experimental NMR techniques. There are a variety of analysis tools available to calculate these order parameters from simulations and it is essential that these computational tools work correctly to ensure the accurate assessment of the simulation force fields. In this work we compare many of these computational tools for calculating the order parameters of POPC membranes. While tools that work on all-atom systems and tools that work on saturated lipid tails in general work extremely well, we demonstrate that the majority of the tested tools that calculate the order parameters for unsaturated united-atom lipid tails do so incorrectly. We identify tools that do perform accurate calculations and include one such program with this work, enabling rapid and accurate calculation of united-atom lipid order parameters. Furthermore, we discuss cases in which it is nontrivial to appropriately predict the unsaturated carbon order parameters in united-atom systems. Finally, we examine order parameter splitting for carbon 2 in sn-2 lipid chains, demonstrating substantial deviations from experimental values in several all-atom and united-atom lipid force fields.
Wagner, Jacob W.; Dannenhoffer-Lafage, Thomas; Jin, Jaehyeok; Voth, Gregory A.
2017-07-01
Order parameters (i.e., collective variables) are often used to describe the behavior of systems as they capture different features of the free energy surface. Yet, most coarse-grained (CG) models only employ two- or three-body non-bonded interactions between the CG particles. In situations where these interactions are insufficient for the CG model to reproduce the structural distributions of the underlying fine-grained (FG) model, additional interactions must be included. In this paper, we introduce an approach to expand the basis sets available in the multiscale coarse-graining (MS-CG) methodology by including order parameters. Then, we investigate the ability of an additive local order parameter (e.g., density) and an additive global order parameter (i.e., distance from a hard wall) to improve the description of CG models in interfacial systems. Specifically, we study methanol liquid-vapor coexistence, acetonitrile liquid-vapor coexistence, and acetonitrile liquid confined by hard-wall plates, all using single site CG models. We find that the use of order parameters dramatically improves the reproduction of structural properties of interfacial CG systems relative to the FG reference as compared with pairwise CG interactions alone.
Odd triplet superconductivity in ultrasmall quantum dots
Energy Technology Data Exchange (ETDEWEB)
Weiss, Stephan; Koenig, Juergen [Theoretische Physik, Universitaet Duisburg-Essen and CENIDE (Germany); Sothmann, Bjoern [Institut fuer Theoretische Physik und Astrophysik, Universitaet Wuerzburg (Germany)
2016-07-01
We report on the possibility to create odd frequency Cooper pairs in proximized interacting quantum dots attached to ferromagnetic leads. Spin blockade effects together with induced superconductivity allow electron pairs with same spin at different times to carry superconducting correlations. Besides the conventional finite singlet pairing amplitude on the dot, only odd frequency triplet pairing is possible here. This is in contrast to the double dot case. We demonstrate how the order parameter for odd-frequency triplet pairing as well as the differential Andreev conductance are influenced when tuning gate and/or bias voltages, the angle of magnetizations of the leads and the coupling to the nearby superconductor.
Density of states for systems with multiple order parameters: a constrained Wang-Landau method
Chan, Chor-Hoi; Brown, Gregory; Rikvold, Per Arne
2017-11-01
A macroscopically constrained Wang-Landau Monte Carlo method was recently proposed to calculate the joint density of states (DOS) for systems with multiple order parameters. Here we demonstrate results for a nearest-neighbor Ising antiferromagnet with ferromagnetic long-range interactions (a model spin-crossover material). Its two relevant order parameters are the magnetization M and the staggered magnetization M s. The joint DOS, g(E, M, M s) where E is the total system energy, is calculated for zero external field and long-range interaction strength, and then obtained for arbitrary values of these two field-like model parameters by a simple transformation of E. Illustrations are shown for several parameter sets.
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
General two-order-parameter Ginzburg-Landau model with quadratic and quartic interactions.
Ivanov, I P
2009-02-01
The Ginzburg-Landau model with two-order parameters appears in many condensed-matter problems. However, even for scalar order parameters, the most general U(1)-symmetric Landau potential with all quadratic and quartic terms contains 13 independent coefficients and cannot be minimized with straightforward algebra. Here, we develop a geometric approach that circumvents this computational difficulty and allows one to study properties of the model without knowing the exact position of the minimum. In particular, we find the number of minima of the potential, classify explicit symmetries possible in this model, establish conditions when and how these symmetries are spontaneously broken, and explicitly describe the phase diagram.
Machine learning of explicit order parameters: From the Ising model to SU(2) lattice gauge theory
Wetzel, Sebastian J.; Scherzer, Manuel
2017-11-01
We present a solution to the problem of interpreting neural networks classifying phases of matter. We devise a procedure for reconstructing the decision function of an artificial neural network as a simple function of the input, provided the decision function is sufficiently symmetric. In this case one can easily deduce the quantity by which the neural network classifies the input. The method is applied to the Ising model and SU(2) lattice gauge theory. In both systems we deduce the explicit expressions of the order parameters from the decision functions of the neural networks. We assume no prior knowledge about the Hamiltonian or the order parameters except Monte Carlo-sampled configurations.
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.
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.
On the parameter estimation of first order IMA model corrupted with AR
African Journals Online (AJOL)
On the parameter estimation of first order IMA model corrupted with AR (1) errors. D Eni, S A Mahmud. Abstract. No Abstract. Global Journal of Pure and Applied Physics Vol. 14 (1) 2008 pp. 115-120. Full Text: EMAIL FULL TEXT EMAIL FULL TEXT · DOWNLOAD FULL TEXT DOWNLOAD FULL TEXT.
Order parameter anisotropy of MgB2 using specific heat jump of ...
Indian Academy of Sciences (India)
Order parameter anisotropy of MgB2 using specific heat jump of layered superconductors. I N ASKERZADE1 2. 1Department of Physics, Faculty of Sciences, Ankara University, 06100-Tando˘gan-Ankara, Turkey. 2Institute of Physics, Azerbaijan National Academy of Sciences, H-Cavid 33, Baku-370143,. Azerbaijan.
Directory of Open Access Journals (Sweden)
Zhibo Cheng
2014-01-01
Full Text Available We investigate a class of variable coefficients singular third-order differential equation with superlinearity or sublinearity assumptions at infinity for an appropriately chosen parameter. By applications of Green’s function and the Krasnoselskii fixed point theorem, sufficient conditions for the existence of positive periodic solutions are established.
Tepper, H.L.; Scheinhardt-Engels, S.M.; Briels, Willem J.
2003-01-01
A method is presented to design order parameters that can be used as discriminator in two-phase crystal-liquid molecular dynamics simulations. The proposed methodology is an extension to molecular crystal structures of a previously introduced discriminator for the atomic fcc environment [Phys. Rev.
Frank, T.D.; Friedrich, R.; Beek, P.J.
2006-01-01
We address two questions that are central to understanding human motor control variability: what kind of dynamical components contribute to motor control variability (i.e., deterministic and/or random ones), and how are those components structured? To this end, we derive a stochastic order parameter
Spinor order parameter and equilibrium states of spin s = 1 Bose systems
Glushchenko, A. V.; Kovalevsky, M. Yu.
2017-09-01
The problem of classification of degenerate equilibrium states in spin s = 1 systems with the phase and magnetic symmetries simultaneously broken is considered. An assumption about the residual symmetry of degenerate equilibrium states and the transformation properties of the spinor order-parameter operator under transformations generated by additive integrals of motion yields equations that classify its equilibrium values. The anisotropic structure of the equilibrium values of the order parameter is presented in terms of the parameters of the residual symmetry generator. Based on the model with a separated condensate, the structure of the densities of the magnetic additive integrals of motion in the equilibrium state is revealed. A comparison is made with the results of existing studies on superfluid spin s = 1 systems.
Yokoyama, Tomohiro; Reutlinger, Johannes; Belzig, Wolfgang; Nazarov, Yuli V.
2017-01-01
We consider the spectrum of Andreev bound states (ABSs) in an exemplary four-terminal superconducting structure where four chaotic cavities are connected by quantum point contacts to the terminals and to each other forming a ring. We nickname the resulting device 4T-ring. Such a tunable device can be realized in a 2D electron gas-superconductor or a graphene-based hybrid structure. We concentrate on the limit of a short structure and large conductance of the point contacts where there are many ABS in the device forming a quasicontinuous spectrum. The energies of the ABS can be tuned by changing the superconducting phases of the terminals. We observe the opening and closing of gaps in the spectrum upon changing the phases. This concerns the usual proximity gap that separates the levels from zero energy as well as less usual "smile" gaps that split the levels of the quasicontinuous spectrum. We demonstrate a remarkable crossover in the overall spectrum that occurs upon changing the ratio of conductances of the inner and outer point contacts. At big values of the ratio (closed limit), the levels exhibit a generic behavior expected for the spectrum of a disordered system manifesting level repulsion and Brownian "motion" upon changing the phases. At small values of the ratio (open limit), the levels are squeezed into narrow bunches separated by wide smile gaps. Each bunch consists of almost degenerate ABS formed by Andreev reflection between two adjacent terminals. We study in detail the properties of the spectrum in the limit of a small ratio, paying special attention to the crossings of bunches. We distinguish two types of crossings: (i) with a regular phase dependence of the levels and (ii) crossings where the Brownian motion of the levels leads to an apparently irregular phase dependence. We work out a perturbation theory that explains the observations both at a detailed level of random scattering in the device and at a phenomenological level of positively defined
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.
Directory of Open Access Journals (Sweden)
Xiaomin Tian
2014-01-01
Full Text Available The complex modified projective synchronization (CMPS between fractional-order chaotic real and complex systems is investigated for the first time. The parameters of both master and slave systems are assumed to be unknown in advance; moreover, the slave system is perturbed by unknown but bounded external disturbances. The master and slave systems that achieved CMPS can be synchronized up to a complex constant matrix. On the basis of frequency distributed model of fractional integrator and Lyapunov stability theory, a robust adaptive control law is designed to realize the CMPS for two different types of fractional-order chaotic systems. Meanwhile, to deal with these unknown parameters, some fractional-order type parametric update laws are provided. An example is given to demonstrate the effectiveness and feasibility of the proposed synchronization scheme.
Flisgen, Thomas
2015-01-01
The modeling of large chains of superconducting cavities with couplers is a challeng- ing task in computational electrical engineering. The direct numerical treatment of these structures can easily lead to problems with more than ten million degrees of freedom. Problems of this complexity are typically solved with the help of parallel programs running on supercomputing infrastructures. However, these infrastructures are expensive to purchase, to operate, and to maintain. The aim of this thesis is to introduce and to validate an approach which allows for modeling large structures on a standard workstation. The novel technique is called State-Space Concatena- tions and is based on the decomposition of the complete structure into individual segments. The radio-frequency properties of the generated segments are described by a set of state-space equations which either emerge from analytical considera- tions or from numerical discretization schemes. The model order of these equations is reduced...
Beaulieu, Alexandre; Bossé, Dominick; Micheau, Philippe; Avoine, Olivier; Praud, Jean-Paul; Walti, Hervé
2012-02-01
This study presents a methodology for applying the forced-oscillation technique in total liquid ventilation. It mainly consists of applying sinusoidal volumetric excitation to the respiratory system, and determining the transfer function between the delivered flow rate and resulting airway pressure. The investigated frequency range was f ∈ [0.05, 4] Hz at a constant flow amplitude of 7.5 mL/s. The five parameters of a fractional order lung model, the existing "5-parameter constant-phase model," were identified based on measured impedance spectra. The identification method was validated in silico on computer-generated datasets and the overall process was validated in vitro on a simplified single-compartment mechanical lung model. In vivo data on ten newborn lambs suggested the appropriateness of a fractional-order compliance term to the mechanical impedance to describe the low-frequency behavior of the lung, but did not demonstrate the relevance of a fractional-order inertance term. Typical respiratory system frequency response is presented together with statistical data of the measured in vivo impedance model parameters. This information will be useful for both the design of a robust pressure controller for total liquid ventilators and the monitoring of the patient's respiratory parameters during total liquid ventilation treatment. © 2011 IEEE
Experimental results on the nature of the superconducting-insulating transition in two dimensions
Energy Technology Data Exchange (ETDEWEB)
Hebard, A.F. [AT& T Bell Laboratories, Murray Hill, NJ (United States)
1994-12-31
Experiments probing the competition between superconductivity and disorder in two-dimensional thin-film systems, although not completely understood, have given fascinating glimpses of subtle and unexpected quantum processes and associated phase transitions. There is a general consensus that a superconducting-insulating transition does occur, although there is some disagreement on details. Much of this disagreement arises from the wide disparity in the physical characteristics of the thin-film systems that have been studied and the number of ways in which parameters can be varied to experimentally traverse the boundary between the superconducting and insulating phases. In this paper, salient experimental results pertaining to the superconducting-insulating transition will be summarized and placed into context with respect to available theoretical prescriptions. Close attention will be paid to the evidence for a boson-dominated transition in which fluctuations in the phase rather than the magnitude of the superconducting order parameter dominate.
From superconductivity near a quantum phase transition to superconducting graphite
Directory of Open Access Journals (Sweden)
S. S. Saxena
2006-09-01
Full Text Available The collapse of antiferromagnetic order as a function of some quantum tuning parameter such as carrier density or hydrostatic pressure is often accompanied by a region of superconductivity. The corresponding phenomenon in the potentially simpler case of itinerant-electron ferromagnetism, however, remains more illusive. In this paper we consider the reasons why this may be so and summaries evidence suggesting that the obstacles to observing the phenomenon are apparently overcome in a few metallic ferromagnets. A new twist to the problem presented by the recent discoveries in ferroelectric symmetric systems and new graphite intercalate superconductors will also be discussed.
Robust Stability Analysis of Fractional-Order Hopfield Neural Networks with Parameter Uncertainties
Directory of Open Access Journals (Sweden)
Shuo Zhang
2014-01-01
Full Text Available The issue of robust stability for fractional-order Hopfield neural networks with parameter uncertainties is investigated in this paper. For such neural system, its existence, uniqueness, and global Mittag-Leffler stability of the equilibrium point are analyzed by employing suitable Lyapunov functionals. Based on the fractional-order Lyapunov direct method, the sufficient conditions are proposed for the robust stability of the studied networks. Moreover, robust synchronization and quasi-synchronization between the class of neural networks are discussed. Furthermore, some numerical examples are given to show the effectiveness of our obtained theoretical results.
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.
Shah, A A; Xing, W W; Triantafyllidis, V
2017-04-01
In this paper, we develop reduced-order models for dynamic, parameter-dependent, linear and nonlinear partial differential equations using proper orthogonal decomposition (POD). The main challenges are to accurately and efficiently approximate the POD bases for new parameter values and, in the case of nonlinear problems, to efficiently handle the nonlinear terms. We use a Bayesian nonlinear regression approach to learn the snapshots of the solutions and the nonlinearities for new parameter values. Computational efficiency is ensured by using manifold learning to perform the emulation in a low-dimensional space. The accuracy of the method is demonstrated on a linear and a nonlinear example, with comparisons with a global basis approach.
Effect of dislocations on the structural order parameter in a crystal upon torsional strain
Zavorotnev, Yu. D.; Zakharov, A. Yu.; Metlov, L. S.
2017-11-01
The interaction of the structural subsystem with dislocations upon applying an elastic torsional strain has been studied. The consideration is performed in the terms of the Landau phenomenological theory with the refusal from the approximation that the irreducible vector magnitudes are constant. It is shown that additional spatial amplitude and frequency oscillations related to the change in the magnitudes of the structural order parameter and the dislocation density appear.
On the relationship between NMR-derived amide order parameters and protein backbone entropy changes.
Sharp, Kim A; O'Brien, Evan; Kasinath, Vignesh; Wand, A Joshua
2015-05-01
Molecular dynamics simulations are used to analyze the relationship between NMR-derived squared generalized order parameters of amide NH groups and backbone entropy. Amide order parameters (O(2) NH ) are largely determined by the secondary structure and average values appear unrelated to the overall flexibility of the protein. However, analysis of the more flexible subset (O(2) NH entropy than that reported by the side chain methyl axis order parameters, O(2) axis . A calibration curve for backbone entropy vs. O(2) NH is developed, which accounts for both correlations between amide group motions of different residues, and correlations between backbone and side chain motions. This calibration curve can be used with experimental values of O(2) NH changes obtained by NMR relaxation measurements to extract backbone entropy changes, for example, upon ligand binding. In conjunction with our previous calibration for side chain entropy derived from measured O(2) axis values this provides a prescription for determination of the total protein conformational entropy changes from NMR relaxation measurements. © 2015 Wiley Periodicals, Inc.
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.
Coarse-graining for fast dynamics of order parameters in the phase-field model
Jou, D.; Galenko, P. K.
2018-01-01
In standard descriptions, the master equation can be obtained by coarse-graining with the application of the hypothesis of full local thermalization that is equivalent to the local thermodynamic equilibrium. By contrast, fast transformations proceed in the absence of local equilibrium and the master equation must be obtained with the absence of thermalization. In the present work, a non-Markovian master equation leading, in specific cases of relaxation to local thermodynamic equilibrium, to hyperbolic evolution equations for a binary alloy, is derived for a system with two order parameters. One of them is a conserved order parameter related to the atomistic composition, and the other one is a non-conserved order parameter, which is related to phase field. A microscopic basis for phenomenological phase-field models of fast phase transitions, when the transition is so fast that there is not sufficient time to achieve local thermalization between two successive elementary processes in the system, is provided. In a particular case, when the relaxation to local thermalization proceeds by the exponential law, the obtained coarse-grained equations are related to the hyperbolic phase-field model. The solution of the model equations is obtained to demonstrate non-equilibrium phenomenon of solute trapping which appears in rapid growth of dendritic crystals. This article is part of the theme issue `From atomistic interfaces to dendritic patterns'.
Quantum phase fluctuations and density of states in superconducting nanowires
Radkevich, Alexey; Semenov, Andrew G.; Zaikin, Andrei D.
2017-08-01
We argue that quantum fluctuations of the phase of the order parameter may strongly affect the electron density of states (DOS) in ultrathin superconducting wires. We demonstrate that the effect of such fluctuations is equivalent to that of a quantum dissipative environment formed by soundlike plasma modes propagating along the wire. We derive a nonperturbative expression for the local electron DOS in superconducting nanowires which fully accounts for quantum phase fluctuations. At any nonzero temperature these fluctuations smear out the square-root singularity in DOS near the superconducting gap and generate quasiparticle states at subgap energies. Furthermore, at sufficiently large values of the wire impedance this singularity is suppressed down to T =0 in which case DOS tends to zero at subgap energies and exhibits the power-law behavior above the gap. Our predictions can be directly tested in tunneling experiments with superconducting nanowires.
Dynamic properties of superconducting weak links
Schmid, Albert; Schön, Gerd; Tinkham, Michael
1980-06-01
A comprehensive theoretical picture of the dynamic properties of the order parameter and the quasiparticles in superconducting short weak links is presented. Both diffusion and inelastic scattering are found to be important in relaxing nonequilibrium populations. At low voltages a dissipative current, which is considerably larger than the normal ohmic current, is found and at higher voltages the maximum supercurrent is enhanced. These effects describe quantitatively well the foot structure in the I-V characteristic observed experimentally by Octavio, Skocpol, and Tinkham.
Superconducting spoke cavities for high-velocity applications
Energy Technology Data Exchange (ETDEWEB)
Hopper, Christopher S. [Old Dominion U.; Delayen, Jean R. [Old Dominion U., JLAB
2013-10-01
To date, superconducting spoke cavities have been designed, developed, and tested for particle velocities up to {beta}{sub 0}~0.6, but there is a growing interest in possible applications of multispoke cavities for high-velocity applications. We have explored the design parameter space for low-frequency, high-velocity, double-spoke superconducting cavities in order to determine how each design parameter affects the electromagnetic properties, in particular the surface electromagnetic fields and the shunt impedance. We present detailed design for cavities operating at 325 and 352 MHz and optimized for {beta}{sub 0}~=0.82 and 1.
DEFF Research Database (Denmark)
Mozhaev, P. B.; Ovsyannikov, G. A.; Skov, Johannes
1999-01-01
The effect of the laser sputtering parameters on the crystal properties of CeO2 buffer layers grown on a (1 (1) under bar 02) sapphire substrate and on the properties of superconducting YBa2Cu3Ox thin films are investigated. It is shown that (100) and (111) CeO2 growth is observed, depending...
Directory of Open Access Journals (Sweden)
Li Junyi
2015-01-01
Full Text Available A fractional order PID (FOPID controller, which is suitable for control system designing for being insensitive to the variation in system parameter, is proposed for hydroturbine governing system in the paper. The simultaneous optimization for several parameters of controller, that is, Ki, Kd, Kp, λ, and μ, is done by a recently developed metaheuristic nature-inspired algorithm, namely, the firefly algorithm (FA, for the first time, where the selecting, moving, attractiveness behavior between fireflies and updating of brightness, and decision range are studied in detail to simulate the optimization process. Investigation clearly reveals the advantages of the FOPID controller over the integer controllers in terms of reduced oscillations and settling time. The present work also explores the superiority of FA based optimization technique in finding optimal parameters of the controller. Further, convergence characteristics of the FA are compared with optimum integer order PID (IOPID controller to justify its efficiency. What is more, analysis confirms the robustness of FOPID controller under isolated load operation conditions.
Superconducting linacs: some recent developments
Energy Technology Data Exchange (ETDEWEB)
Bollinger, L.M.
1985-01-01
The paper is a review of superconducting linacs that are of interest for heavy-ion acceleration. Most of the paper is concerned with energy boosters for projectiles from tandem electrostatic accelerators, the only application for which superconducting linacs are now used for heavy-ion acceleration. There is also a brief discussion of the concept of a superconducting injector linac being developed as a replacement of the tandem in a multi-stage acceleration system. Throughout, the emphasis is on the technology of the superconducting linac, including some attention to the relationships between resonator design parameters and accelerator performance characteristics. 21 refs., 14 figs., 3 tabs.
Nanoscale high-temperature superconductivity
Energy Technology Data Exchange (ETDEWEB)
Mohanty, P.; Wei, J.Y.T.; Ananth, V.; Morales, P.; Skocpol, W
2004-08-01
We discuss the exciting prospects of studying high-temperature superconductivity in the nanometer scale from the perspective of experiments, theory and simulation. In addition to enabling studies of novel quantum phases in an unexplored regime of system dimensions and parameters, nanoscale high-temperature superconducting structures will allow exploration of fundamental mechanisms with unprecedented insight. The prospects include, spin-charge separation, detection of electron fractionalization via novel excitations such as vison, stripe states and their dynamics, preformed cooper pairs or bose-condensation in the underdoped regime, and other quantum-ordered states. Towards this initiative, we present the successful development of a novel nanofabrication technique for the epitaxial growth of nanoscale cuprates. Combining the techniques of e-beam lithography and nanomachining, we have been able to fabricate the first generation of high-temperature superconducting nanoscale devices, including Y-junctions, four-probe wires and rings. Their initial transport characterization and scanning tunneling microscopy reveal the integrity of the crystal structure, grown on nanometer scale lateral dimensions. Here, we present atomic force micrographs and electrical characterization of a few nanoscale YBa{sub 2}Cu{sub 3}O{sub 7} (YBCO) samples.
Tight-binding description of intrinsic superconducting correlations in multilayer graphene
Muñoz, W. A.; Covaci, L.; Peeters, F. M.
2013-04-01
Using highly efficient GPU-based simulations of the tight-binding Bogoliubov-de Gennes equations we solve self-consistently for the pair correlation in rhombohedral (ABC) and Bernal (ABA) multilayer graphene by considering a finite intrinsic s-wave pairing potential. We find that the two different stacking configurations have opposite bulk/surface behavior for the order parameter. Surface superconductivity is robust for ABC stacked multilayer graphene even at very low pairing potentials for which the bulk order parameter vanishes, in agreement with a recent analytical approach. In contrast, for Bernal stacked multilayer graphene, we find that the order parameter is always suppressed at the surface and that there exists a critical value for the pairing potential below which no superconducting order is achieved. We considered different doping scenarios and find that homogeneous doping strongly suppresses surface superconductivity while nonhomogeneous field-induced doping has a much weaker effect on the superconducting order parameter. For multilayer structures with hybrid stacking (ABC and ABA) we find that when the thickness of each region is small (few layers), high-temperature surface superconductivity survives throughout the bulk due to the proximity effect between ABC/ABA interfaces where the order parameter is enhanced.
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.
Marinelli; Mercuri
2000-02-01
Photopyroelectric measurements of the anisotropy in the thermal conductivity Deltak vs temperature in the nCB (n=5,ellipsis,9) series are reported. The data have been used to deduce the behavior of the orientational order parameter Q close to the nematic-isotropic (N-I) and smectic A-nematic (A-N) phase transitions, respectively. It has been shown that near the N-I transition the data for 5CB and 6CB are consistent with the so-called "tricritical hypothesis," which predicts beta=0.25. This is not true for 7CB and 8CB in which the order parameter exhibits a behavior that could be caused by the presence of fluctuations that become increasingly important when the transition temperature is approached. A very simple model, which takes into account the contribution of fluctuations to the orientational order, has been developed close to the A-N transition and it has been shown that it is in good agreement with the experimental results. A semiquantitative explanation for the observed behavior in compounds with different nematic range has been also given.
Superconducting heavy-ion accelerating structures
Energy Technology Data Exchange (ETDEWEB)
Shepard, K.W.
1996-08-01
This paper briefly reviews the technical history of superconducting ion-accelerating structures. Various superconducting cavities currently used and being developed for use in ion linacs are discussed. Principal parameters and operational characteristics of superconducting structures in active use at various heavy-ion facilities are described.
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%.
Topological insulator in the core of the superconducting vortex in graphene.
Herbut, Igor F
2010-02-12
The core of the vortex in a general superconducting order parameter in graphene is argued to be ordered, with the possible local order parameters forming the algebra U(1) x Cl(3). A sufficiently strong Zeeman coupling of the magnetic field of the vortex to the electron spin breaks the degeneracy in the core in favor of the anomalous quantum Hall state. I consider a variety of superconducting condensates on the honeycomb lattice and demonstrate the surprising universality of this result. A way to experimentally determine the outcome of the possible competition between different types of orders in the core is proposed.
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.
Directory of Open Access Journals (Sweden)
Nils E. R. Zimmermann
2017-11-01
Full Text Available Structure–property relationships form the basis of many design rules in materials science, including synthesizability and long-term stability of catalysts, control of electrical and optoelectronic behavior in semiconductors, as well as the capacity of and transport properties in cathode materials for rechargeable batteries. The immediate atomic environments (i.e., the first coordination shells of a few atomic sites are often a key factor in achieving a desired property. Some of the most frequently encountered coordination patterns are tetrahedra, octahedra, body and face-centered cubic as well as hexagonal close packed-like environments. Here, we showcase the usefulness of local order parameters to identify these basic structural motifs in inorganic solid materials by developing classification criteria. We introduce a systematic testing framework, the Einstein crystal test rig, that probes the response of order parameters to distortions in perfect motifs to validate our approach. Subsequently, we highlight three important application cases. First, we map basic crystal structure information of a large materials database in an intuitive manner by screening the Materials Project (MP database (61,422 compounds for element-specific motif distributions. Second, we use the structure-motif recognition capabilities to automatically find interstitials in metals, semiconductor, and insulator materials. Our Interstitialcy Finding Tool (InFiT facilitates high-throughput screenings of defect properties. Third, the order parameters are reliable and compact quantitative structure descriptors for characterizing diffusion hops of intercalants as our example of magnesium in MnO2-spinel indicates. Finally, the tools developed in our work are readily and freely available as software implementations in the pymatgen library, and we expect them to be further applied to machine-learning approaches for emerging applications in materials science.
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
Higgsless superconductivity from topological defects in compact BF terms
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M. Cristina Diamantini
2015-02-01
Full Text Available We present a new Higgsless model of superconductivity, inspired from anyon superconductivity but P- and T-invariant and generalisable to any dimension. While the original anyon superconductivity mechanism was based on incompressible quantum Hall fluids as average field states, our mechanism involves topological insulators as average field states. In D space dimensions it involves a (D−1-form fictitious pseudovector gauge field which originates from the condensation of topological defects in compact low-energy effective BF theories. In the average field approximation, the corresponding uniform emergent charge creates a gap for the (D−2-dimensional branes via the Magnus force, the dual of the Lorentz force. One particular combination of intrinsic and emergent charge fluctuations that leaves the total charge distribution invariant constitutes an isolated gapless mode leading to superfluidity. The remaining massive modes organise themselves into a D-dimensional charged, massive vector. There is no massive Higgs scalar as there is no local order parameter. When electromagnetism is switched on, the photon acquires mass by the topological BF mechanism. Although the charge of the gapless mode (2 and the topological order (4 are the same as those of the standard Higgs model, the two models of superconductivity are clearly different since the origins of the gap, reflected in the high-energy sectors are totally different. In 2D this type of superconductivity is explicitly realised as global superconductivity in Josephson junction arrays. In 3D this model predicts a possible phase transition from topological insulators to Higgsless superconductors.
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
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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.
Hao, Qun; Li, Tengfei; Hu, Yao
2018-01-01
Surface parameters are the properties to describe the shape characters of aspheric surface, which mainly include vertex radius of curvature (VROC) and conic constant (CC). The VROC affects the basic properties, such as focal length of an aspheric surface, while the CC is the basis of classification for aspheric surface. The deviations of the two parameters are defined as surface parameter error (SPE). Precisely measuring SPE is critical for manufacturing and aligning aspheric surface. Generally, SPE of aspheric surface is measured directly by curvature fitting on the absolute profile measurement data from contact or non-contact testing. And most interferometry-based methods adopt null compensators or null computer-generated holograms to measure SPE. To our knowledge, there is no effective way to measure SPE of highorder aspheric surface with non-null interferometry. In this paper, based on the theory of slope asphericity and the best compensation distance (BCD) established in our previous work, we propose a SPE measurement method for high-order aspheric surface in partial compensation interferometry (PCI) system. In the procedure, firstly, we establish the system of two element equations by utilizing the SPE-caused BCD change and surface shape change. Then, we can simultaneously obtain the VROC error and CC error in PCI system by solving the equations. Simulations are made to verify the method, and the results show a high relative accuracy.
Mazdouri, Behnam; Mohammad Hassan Javadzadeh, S.
2017-09-01
Superconducting materials are intrinsically nonlinear, because of nonlinear Meissner effect (NLME). Considering nonlinear behaviors, such as harmonic generation and intermodulation distortion (IMD) in superconducting structures, are very important. In this paper, we proposed distributed nonlinear circuit model for superconducting split ring resonators (SSRRs). This model can be analyzed by using Harmonic Balance method (HB) as a nonlinear solver. Thereafter, we considered a superconducting metamaterial filter which was based on split ring resonators and we calculated fundamental and third-order IMD signals. There are good agreement between nonlinear results from proposed model and measured ones. Additionally, based on the proposed nonlinear model and by using a novel method, we considered nonlinear effects on main parameters in the superconducting metamaterial structures such as phase constant (β) and attenuation factor (α).
Evidence for competing order parameters in the paramagnetic phase of layered manganites.
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Berger, A.; Mitchell, J. F.; Miller, D. J.; Bader, S. D.
2000-11-08
The magnetic field and temperature dependence of the magnetic susceptibility and magnetization is studied for the ferromagnetic layered manganites SrO(La{sub t{minus}x}Sr{sub x}MnO{sub 3}){sub 2} in the composition range x = 0.32-0.40. In the paramagnetic phase, the susceptibility exhibits an anomalous maximum at an intermediate magnetic field value. The size of this field-induced susceptibility enhancement increases dramatically with x from 10% for x = 0.32 to 160% for x = 0.40. The temperature dependence of the effect shows a maximum at T {approx} 1.1 T{sub c} for all x. Quantitative analysis in terms of the Landau theory of phase transitions enables us to identify a distortion of the free energy F in the paramagnetic phase that is associated with the susceptibility anomaly. This free energy distortion corresponds to a magnetic system that approaches a first order magnetic phase transition as the temperature is lowered towards T{sub c}. Such a behavior is indicative of a second, competing order parameter, which is identified as the recently observed charge density wave. In the immediate vicinity of T{sub c}, the anomaly disappears and the system seems to undergo a more conventional second order paramagnetic-ferromagnetic phase transition.
Hébert, Charles-David; Sémon, Patrick; Tremblay, A.-M. S.
2015-11-01
Layered organic superconductors of the BEDT family are model systems for understanding the interplay of the Mott transition with superconductivity, magnetic order, and frustration, ingredients that are essential to understand superconductivity also in the cuprate high-temperature superconductors. Recent experimental studies on a hole-doped version of the organic compounds reveals an enhancement of superconductivity and a rapid crossover between two different conducting phases above the superconducting dome. One of these phases is a Fermi liquid, the other not. Using plaquette cellular dynamical mean field theory with state-of-the-art continuous-time quantum Monte Carlo calculations, we study this problem with the two-dimensional Hubbard model on the anisotropic triangular lattice. Phase diagrams as a function of temperature T and interaction strength U /t are obtained for anisotropy parameters t'=0.4 t ,t'=0.8 t and for various fillings. As in the case of the cuprates, we find, at finite doping, a first-order transition between two normal-state phases. One of theses phases has a pseudogap while the other does not. At temperatures above the critical point of the first-order transition, there is a Widom line where crossovers occur. The maximum (optimal) superconducting critical temperature Tcm at finite doping is enhanced by about 25% compared with its maximum at half filling and the range of U /t where superconductivity appears is greatly extended. These results are in broad agreement with experiment. Also, increasing frustration (larger t'/t ) significantly reduces magnetic ordering, as expected. This suggests that for compounds with intermediate to high frustration, very light doping should reveal the influence of the first-order transition and associated crossovers. These crossovers could possibly be even visible in the superconducting phase through subtle signatures. We also predict that destroying the superconducting phase by a magnetic field should reveal the
McKenzie, Ross Hugh
A brief overview of past experimental and theoretical investigations of the linear and nonlinear interaction of zero sound with the order parameter collective modes in superfluid ^3He-B is given before introducing the quasiclassical (QC) theory of superfluid ^3He. A new approach to calculating the linear and nonlinear response is presented. The QC propagator is calculated by expanding the low energy Dyson's equation in powers of the nonequilibrium self energy. The expression given for the expansion coefficients, involving products of pairs of equilibrium Green's functions, has a simple diagrammatic representation, and establishes a connection between the QC theory and other theoretical formalisms which have been used to investigate the collective modes. It is shown that the expansion coefficients satisfy Onsager-like relations and some identities required by gauge and galilean invariance. Consequently, this new approach to deriving dynamical equations for the collective modes is more efficient and transparent than solving the QC transport equations. This new approach is used to investigate the linear coupling of zero sound to the order parameter collective modes in weakly inhomogeneous superfluid ^3 He. It makes tractable the treatment of (nonlinear) parametric processes involving zero sound and the collective modes. It is shown that the approximate particle-hole symmetry of the ^3He Fermi liquid determines important selection rules for nonlinear acoustic processes, just as it is well known to do for linear processes. Analogues with nonlinear optics guide the derivation, solution and interpretation of the dynamical equations for a three-wave resonance between two zero sound waves and the J = 2 ^+ order parameter collective mode. It is shown that stimulated Raman scattering and two phonon absorption of zero sound by the J = 2^+ collective mode should be observable when the pump sound wave has energy density larger than about one percent of the superfluid
Positron annihilation in superconductive metals
Energy Technology Data Exchange (ETDEWEB)
Dekhtjar, I.J.
1969-03-10
A correlation is shown between the parameters of superconductive metals and those of positron annihilation. Particular attention is paid to the density states obtained from the electron specific heat.
Parameter Sensitivity of High–Order Equivalent Circuit Models Of Turbine Generator
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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.
The Lichnerowicz-Weitzenboeck formula and superconductivity
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Vargas-Paredes, Alfredo A.; Doria, Mauro M. [Departamento de Fisica dos Solidos, Universidade Federal do Rio de Janeiro, 21941-972 Rio de Janeiro (Brazil); Neto, Jose Abdala Helayeel [Centro Brasileiro de Pesquisas Fisicas, 22290-160 Rio de Janeiro RJ (Brazil)
2013-01-15
We derive the Lichnerowicz-Weitzenboeck formula for the two-component order parameter superconductor, which provides a twofold view of the kinetic energy of the superconductor. For the one component order parameter superconductor we review the connection between the Lichnerowicz-Weitzenboeck formula and the Ginzburg-Landau theory. For the two-component case we claim that this formula opens a venue to describe inhomogeneous superconducting states intertwined by spin correlations and charged dislocation. In this case the Lichnerowicz-Weitzenboeck formula displays local rotational and electromagnetic gauge symmetry (SU(2) Circled-Times U(1)) and relies on local commuting momentum and spin operators. The order parameter lives in a space with curvature and torsion described by Elie Cartan geometrical formalism. The Lichnerowickz-Weitzenboeck formula leads to first order differential equations that are a three-dimensional version of the Seiberg-Witten equations.
Gambling with Superconducting Fluctuations
Foltyn, Marek; Zgirski, Maciej
2015-08-01
Josephson junctions and superconducting nanowires, when biased close to superconducting critical current, can switch to a nonzero voltage state by thermal or quantum fluctuations. The process is understood as an escape of a Brownian particle from a metastable state. Since this effect is fully stochastic, we propose to use it for generating random numbers. We present protocol for obtaining random numbers and test the experimentally harvested data for their fidelity. Our work is prerequisite for using the Josephson junction as a tool for stochastic (probabilistic) determination of physical parameters such as magnetic flux, temperature, and current.
Energy Technology Data Exchange (ETDEWEB)
Chaillout, C.; Alario-Franco, M.A.; Capponi, J.J.; Chenavas, J.; Hodeau, J.L.; Marezio, M.
1987-11-01
Diffuse scattering streaks or bands have been observed in electron diffraction photographs for samples belonging to the superconducting system Ba/sub 2/YCu/sub 3/O/sub 7-//sub x/ (0less than or equal toxless than or equal to1). In-situ experiments show that this diffuse scattering can be associated with short-range ordering of oxygen vacancies. The same vacancy ordering occurs in previously reduced samples. Three types of diffuse scattering are observed, each corresponding to a short-range-order scheme.
Kim, Taehee; Shibuya, Kazuo; Doi, Koichiro; Aoyama, Yuichi; Hayakawa, Hideaki
2010-05-01
The free core nutation (FCN), also refered to as the nearly diurnal free wobble, is due to the pressure coupling between the liquid core and the solid mantle. The FCN enhances the resonance with the diurnal earth tide. Investigation of resonance parameters of FCR (eigenperiod, quality factor Q, and resonance strength) is essential for the Earth's deep interior dynamics and structure. The eigenperiod directly depends on the core-mantle boundary (CMB) ellipticity and on the mantle's inelasticity. The quality factor Q is a direct consequence of damping mechanisms inside the Earth (Sasao et al., 1980; Sasao and Wahr, 1981; Florsch and Hinderer, 2000). For determining theseresonance parameters, the tidal gravimetric factor based on superconducting gravimeter (SG) data is used. We used the gravity data of 4 stations, from 1992 through 2002 at Syowa Station, from 1997 through 2007 at Strasbourg, from 1998 through 2007 at Metsahovi, from 2000 through 2006 at Sutherland, of the GGP Data Center. The tidal gravity parameters were determined using the BAYTAP-G software package (Ishiguro et al., 1981; Tamura et al., 1991). In this study, we focused on the influence of ocean loading effect on precise estimation of FCN parameters. The global ocean tidal models, CSR4.0 (Eanes and Bettadpur, 1999), GOT99.2b (Ray, 1999), FES2004 (Lyard et al., 2006) and TPXO7.1 (Egbert and Erofeeva, 2002) models are tested. These models are accomodated to the GOTIC2 for ocean loading estimation program (Matsumoto et al. 2001). The quality factor Q is dependent on the phase delay of the tidal waves, that means the imaginary part of gravimetric factor corrected for ocean loading effect is an important point for this inverse problem(Florsch and Hinderer, 2000). We present how much the accuracy of FCR parameters can be improved by adopting proper ocean models to each station (Le provost et al., 2001). For this work, we have applied minor waves for ocean loading correction (Matsumoto, 2003), and the
Sultan, Mohammad M; Kiss, Gert; Shukla, Diwakar; Pande, Vijay S
2014-12-09
Given the large number of crystal structures and NMR ensembles that have been solved to date, classical molecular dynamics (MD) simulations have become powerful tools in the atomistic study of the kinetics and thermodynamics of biomolecular systems on ever increasing time scales. By virtue of the high-dimensional conformational state space that is explored, the interpretation of large-scale simulations faces difficulties not unlike those in the big data community. We address this challenge by introducing a method called clustering based feature selection (CB-FS) that employs a posterior analysis approach. It combines supervised machine learning (SML) and feature selection with Markov state models to automatically identify the relevant degrees of freedom that separate conformational states. We highlight the utility of the method in the evaluation of large-scale simulations and show that it can be used for the rapid and automated identification of relevant order parameters involved in the functional transitions of two exemplary cell-signaling proteins central to human disease states.
Asami, Sam; Reif, Bernd
2017-09-21
The measurement of dipolar couplings among directly bonded nuclei yields direct information on the amplitude of dynamic processes in the solid-state. For a reliable motional analysis using, e.g., the model-free approach, a correct quantification of the absolute values of these order parameters is absolutely essential. In the absence of a reference value for the rigid limit, too low dipolar coupling values might be misinterpreted as motion. Therefore, a detailed understanding of the effects that influence the quantification of the experimental order parameters is necessary. We compare here REDOR and CPPI derived order parameters assessed in 1H-detected experiments, and discuss the influence of remote protons and rf inhomogeneity on the extracted dipolar coupling constant for MAS rotation frequencies in the range 20-100 kHz. Experimental results are furthermore compared with the order parameter obtained from a molecular dynamics simulation. We find that fast magic-angle spinning up to 100 kHz can yield artifact-free REDOR based 1H,15N order parameters for perdeuterated and 100% amide back-exchanged proteins, and potentially even in uniformly protonated samples. We believe that awareness of systematic errors introduced by the measurement and in the analysis of order parameters will yield a better understanding of the dynamic properties of a protein derived from solid-state NMR observables.
Superconductivity in quantum wires: A symmetry analysis
Samokhin, K. V.
2017-10-01
We study properties of quantum wires with spin-orbit coupling and time reversal symmetry breaking, in normal and superconducting states. Electronic band structures are classified according to quasi-one-dimensional magnetic point groups, or magnetic classes. The latter belong to one of three distinct types, depending on the way the time reversal operation appears in the group elements. The superconducting gap functions are constructed using antiunitary operations and have different symmetry properties depending on the type of the magnetic point group. We obtain the spectrum of the Andreev boundary modes near the end of the wire in a model-independent way, using the semiclassical approach with the boundary conditions described by a phenomenological scattering matrix. Explicit expressions for the bulk topological invariants controlling the number of the boundary zero modes are presented in the general multiband case for two types of the magnetic point groups with real order parameters, corresponding to DIII and BDI symmetry classes.
Meissner effect in superconducting microtraps
Energy Technology Data Exchange (ETDEWEB)
Cano, Daniel
2009-04-30
This thesis investigates the impact of the Meissner effect on magnetic microtraps for ultracold atoms near superconducting microstructures. This task has been accomplished both theoretically and experimentally. The Meissner effect distorts the magnetic fields near superconducting surfaces, thus altering the parameters of magnetic microtraps. Both computer simulations and experimental measurements demonstrate that the Meissner effect shortens the distance between the magnetic microtrap and the superconducting surface, reduces the magnetic-field gradients and dramatically lowers the trap depth. A novel numerical method for calculating magnetic fields in atom chips with superconducting microstructures has been developed. This numerical method overcomes the geometrical limitations of other calculation techniques and can solve superconducting microstructures of arbitrary geometry. The numerical method has been used to calculate the parameters of magnetic microtraps in computer-simulated chips containing thin-film wires. Simulations were carried out for both the superconducting and the normal-conducting state, and the differences between the two cases were analyzed. Computer simulations have been contrasted with experimental measurements. The experimental apparatus generates a magnetic microtrap for ultracold Rubidium atoms near a superconducting Niobium wire of circular cross section. The design and construction of the apparatus has met the challenge of integrating the techniques for producing atomic quantum gases with the techniques for cooling solid bodies to cryogenic temperatures. By monitoring the position of the atom cloud, one can observe how the Meissner effect influences the magnetic microtrap. (orig.)
Birman, Joseph L.; Izyumov, Yuri A.
1980-02-01
We formulate the thermodynamic theory of phase transitions in magnetically ordered systems in terms of a tensor, or coupled, order parameter. This basis is constructed by coupling atomic spin and lattice displacement. Symmetry lowering is predicted at the second-order phase transition point (tricritical points are not considered here). Lower-symmetry phases should in general be classified according to the Shubnikov symmetry space group Sh, which will reveal the total broken symmetry due to the coupled order parameter. In case the apparatus is "blind" to one portion of the order parameter: either spin or displacement, the apparent symmetry group will not be Sh, but a related space group, which will reveal "partial information." Comparing this formulation and the usual (uncoupled) theory, new results are obtained here: for example "pseudoscalar order parameters" can arise and different "symmetry-broken" groups. An illustration is given by applying the formulation to the spinel-structure space group: O7h-Fd3m. It is conjectured that for TbNi2 the tensor order parameter Γ1- may be relevant, so that the phase transition which has been identified as O7h-->Sh101166 may actually be O7h-->Sh132227, caused by a pseudoscalar.
DEFF Research Database (Denmark)
Gammel, P.L.; Barber, B.P.; Ramirez, A.P.
1999-01-01
The flux line form factor in small angle neutron scattering and transport data determines the superconducting length scares and critical fields in single crystal ErNi2B2C. For H parallel to c, the coherence length xi increases and the penetration depth lambda decreases when crossing T-N = 6.0 K...
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.
Niobium superconducting rf cavity fabrication by electrohydraulic forming
Cantergiani, E.; Léaux, F.; Perez Fontenla, A.T.; Prunet, S.; Dufay-Chanat, L.; Koettig, T.; Bertinelli, F.; Capatina, O.; Favre, G.; Gerigk, F.; Jeanson, A. C.; Fuzeau, J.; Avrillaud, G.; Alleman, D.; Bonafe, J.; Marty, P.
2016-01-01
Superconducting rf (SRF) cavities are traditionally fabricated from superconducting material sheets or made of copper coated with superconducting material, followed by trim machining and electron-beam welding. An alternative technique to traditional shaping methods, such as deep-drawing and spinning, is electrohydraulicforming (EHF). InEHF, half-cells areobtainedthrough ultrahigh-speed deformation ofblank sheets, using shockwaves induced in water by a pulsed electrical discharge. With respect to traditional methods, such a highly dynamic process can yield interesting results in terms of effectiveness, repeatability, final shape precision, higher formability, and reduced springback. In this paper, the first results of EHFon high purity niobium are presented and discussed. The simulations performed in order to master the multiphysics phenomena of EHF and to adjust its process parameters are presented. The microstructures of niobium half- cells produced by EHFand by spinning have been compared in terms of damage...
Competition between superconductivity and magnetism in ferromagnet/superconductor heterostructures
Izyumov, Y A; Khusainov, M G
2002-01-01
The mutual influence of superconductivity and magnetism in FS systems, i.e. systems of alternating ferrimagnetic (F) and superconducting (S) layers, is comprehensively reviewed. For systems with ferromagnetic metal (FM) layers, a theory of the proximity effect is constructed. For a FM/S bilayer and a FM/S superlattice, a boundary-value problem involving finite FM/S boundary transparency and the diffusion and wave modes of quasi-particle motion is formulated; and the critical temperature T sub c is calculated as a function of FM- and S-layer thickness. Possible mutual accommodation scenarios for superconducting and magnetic order parameters are found, the corresponding phase diagrams are plotted, and experimental results explained. The results of the theory of the Josephson effect for S/F/S-contacts are presented and the application of the theory of spin-depending transport to F/S/F contacts is discussed. Application aspects of the subject are examined
Superconductivity in an Inhomogeneous Bundle of Metallic and Semiconducting Nanotubes
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Ilya Grigorenko
2013-01-01
Full Text Available Using Bogoliubov-de Gennes formalism for inhomogeneous systems, we have studied superconducting properties of a bundle of packed carbon nanotubes, making a triangular lattice in the bundle's transverse cross-section. The bundle consists of a mixture of metallic and doped semiconducting nanotubes, which have different critical transition temperatures. We investigate how a spatially averaged superconducting order parameter and the critical transition temperature depend on the fraction of the doped semiconducting carbon nanotubes in the bundle. Our simulations suggest that the superconductivity in the bundle will be suppressed when the fraction of the doped semiconducting carbon nanotubes will be less than 0.5, which is the percolation threshold for a two-dimensional triangular lattice.
Phase transitions in hybrid SFS structures with thin superconducting layers
Samokhvalov, A. V.
2017-11-01
Calculations of critical temperature T c of the phase transition to superconducting state of a superconductor/ ferromagnet/superconductor (SFS) hybrid structure with proximity effect is performed on the base of linearized Usadel equations. It is shown that the proximity effect between S and F metals and the exchange interaction can induce an inhomogeneous superconducting state with longitudinal to layers Δ ∝ exp( ipz) modulation of the superconductivity order parameter, which is characterized by nonzero value of the wave number p, describing the Larkin-Ovchinnikov-Fulde-Ferrell instability. Influence of this instability on transitions between 0- and π-states of the SFS structure is studied. It is shown that the 0-π transition is accompanied by a nonmonotonic dependence of both the critical temperature T c and the effective penetration depth Λ of the magnetic field into the hybrid structure on the characteristic size of the ferromagnetic region.
Energy Technology Data Exchange (ETDEWEB)
Senaris-Rodriguez, M.A.; Alario-Franco, M.A. (Universidad Complutense, Madrid (Spain))
1993-09-01
Electron diffraction and high resolution electron microscopy studies on La[sub 2[minus]x]K[sub x]CuO[sub 4] superconducting samples (x = .22 and x = .27) reveal that the microstructure of these materials is very complex due to a partial ordering between the La and K cations. This ordering presents different characteristics along each of the three space directions: it is long range in two directions, and along one of these (the [00l]) it is incommensurably modulate; in the third direction it is short range, with a coherence length of [approx equal]23-40 [angstrom].
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.
On the interplay of superconductivity and magnetism
Powell, B J
2002-01-01
We explore the exchange field dependence of the Hubbard model with a attractive, effective, pairwise, nearest neighbour interaction via the Hartree-Fock-Gorkov approximation. We derive a Ginzburg-Landau theory of spin triplet superconductivity in an exchange field. For microscopic parameters which lead to ABM phase superconductivity in zero field, the Ginzburg-Landau theory allows both an axial (A, A sub 1 or A sub 2) solution with the vector order parameter, d(k), perpendicular to the field, H, and an A phase solution with d(k) parallel to H. We study the spin-generalised Bogoliubov-de Gennes (BdG) equations for this model with parameters suitable for strontium ruthenate (Sr sub 2 RuO sub 4). The A sub 2 phase is found to be stable in a magnetic field. However, in the real material, spin-orbit coupling could pin the order parameter to the crystallographic c-axis which would favour the A phase for fields parallel to the c-axis. We show that the low temperature thermodynamic behaviour in a magnetic field could...
Pogrebna, A; Mertelj, T; Vujičić, N; Cao, G; Xu, Z A; Mihailovic, D
2015-01-13
Ferromagnetism and superconductivity are antagonistic phenomena. Their coexistence implies either a modulated ferromagnetic order parameter on a lengthscale shorter than the superconducting coherence length or a weak exchange coupling between the itinerant superconducting electrons and the localized ordered spins. In some iron based pnictide superconductors the coexistence of ferromagnetism and superconductivity has been clearly demonstrated. The nature of the coexistence, however, remains elusive since no clear understanding of the spin structure in the superconducting state has been reached and the reports on the coupling strength are controversial. We show, by a direct optical pump-probe experiment, that the coupling is weak, since the transfer of the excess energy from the itinerant electrons to ordered localized spins is much slower than the electron-phonon relaxation, implying the coexistence without the short-lengthscale ferromagnetic order parameter modulation. Remarkably, the polarization analysis of the coherently excited spin wave response points towards a simple ferromagnetic ordering of spins with two distinct types of ferromagnetic domains.
Coherence properties in superconducting flux qubits
Energy Technology Data Exchange (ETDEWEB)
Spilla, Samuele
2015-02-16
The research work discussed in this thesis deals with the study of superconducting Josephson qubits. Superconducting qubits are solid-state artificial atoms which are based on lithographically defined Josephson tunnel junctions properties. When sufficiently cooled, these superconducting devices exhibit quantized states of charge, flux or junction phase depending on their design parameters. This allows to observe coherent evolutions of their states. The results presented can be divided into two parts. In a first part we investigate operations of superconducting qubits based on the quantum coherence in superconducting quantum interference devices (SQUID). We explain experimental data which has been observed in a SQUID subjected to fast, large-amplitude modifications of its effective potential shape. The motivations for this work come from the fact that in the past few years there have been attempts to interpret the supposed quantum behavior of physical systems, such as Josephson devices, within a classical framework. Moreover, we analyze the possibility of generating GHZ states, namely maximally entangled states, in a quantum system made out of three Josephson qubits. In particular, we investigate the possible limitations of the GHZ state generation due to coupling to bosonic baths. In the second part of the thesis we address a particular cause of decoherence of flux qubits which has been disregarded until now: thermal gradients, which can arise due to accidental non equilibrium quasiparticle distributions. The reason for these detrimental effects is that heat currents flowing through Josephson tunnel junctions in response to a temperature gradient are periodic functions of the phase difference between the electrodes. The phase dependence of the heat current comes from Andreev reflection, namely an interplay between the quasiparticles which carry heat and the superconducting condensate which is sensitive to the superconducting phase difference. Generally speaking
PREFACE: Superconducting materials Superconducting materials
Charfi Kaddour, Samia; Singleton, John; Haddad, Sonia
2011-11-01
The discovery of superconductivity in 1911 was a great milestone in condensed matter physics. This discovery has resulted in an enormous amount of research activity. Collaboration among chemists and physicists, as well as experimentalists and theoreticians has given rise to very rich physics with significant potential applications ranging from electric power transmission to quantum information. Several superconducting materials have been synthesized. Crucial progress was made in 1987 with the discovery of high temperature superconductivity in copper-based compounds (cuprates) which have revealed new fascinating properties. Innovative theoretical tools have been developed to understand the striking features of cuprates which have remained for three decades the 'blue-eyed boy' for researchers in superconductor physics. The history of superconducting materials has been notably marked by the discovery of other compounds, particularly organic superconductors which despite their low critical temperature continue to attract great interest regarding their exotic properties. Last but not least, the recent observation of superconductivity in iron-based materials (pnictides) has renewed hope in reaching room temperature superconductivity. However, despite intense worldwide studies, several features related to this phenomenon remain unveiled. One of the fundamental key questions is the mechanism by which superconductivity takes place. Superconductors continue to hide their 'secret garden'. The new trends in the physics of superconductivity have been one of the two basic topics of the International Conference on Conducting Materials (ICoCoM2010) held in Sousse,Tunisia on 3-7 November 2010 and organized by the Tunisian Physical Society. The conference was a nice opportunity to bring together participants from multidisciplinary domains in the physics of superconductivity. This special section contains papers submitted by participants who gave an oral contribution at ICoCoM2010
Harris, A. B.
2017-08-01
For the case of Mn2GeO4 we characterize the complex magnetic phase that exists at temperatures below 5.5 K by order parameters for both the commensurate and the incommensurate ordering. For the incommensurate ordering we are forced to consider the transformation properties which interrelate magnetic modes at different noncollinear members of the star of the incommensurate wave vector. The known transformation properties of the underlying magnetic wave functions are used to deduce the transformation properties of the order parameters. These results are applied to construct the high-order invariants in the free energy which have been used elsewhere to describe the characteristics of switching between different domains. The properties of different domains are discussed in detail.
Deformation limits on two-parameter fracture mechanics in terms of higher order asymptotics
Crane, D. L.; Anderson, T. L.
1994-09-01
This report addresses the limitations of two-parameter fracture mechanics. We performed an asymptotic analysis of the general power series representation of the crack tip stress potential in an elastic plastic material that obeys a Ramberg-Osgood constitutive law. Expansion of the power series over a substantial number of terms yields. only three independent coefficients for low. and medium-hardening materials. The first independent The second and third independent coefficients, K2 and K4 are a function of geometry and loading level. A two-parameter theory implies that the crack tip stress fields have two degrees of freedom, but the asymptotic analysis implies that three parameters are required to characterize near-tip conditions. Thus two-parameter fracture theory is a valid engineering model only when there is an approximately unique relationship between K2 and K4. We performed elastic-plastic finite element analyses on several geometries and evaluated K2 and K4 as a function of deformation level. A reference,two-parameter solution (which gives a unique relation between K2 and K4) was provided by the modified boundary layer (MBL) geometry. Results indicate that the near tip stresses in all but the deeply cracked SENT (a/W-.5.O.9) and SENT (a/W-0.9) lend themselves to a two-parameter characterization. However, the deeply cracked SENT and SENT specimens maintain a high level of constraint to relatively large deformation levels. Thus single-parameter fracture mechanics is fairly robust for these high constraint geometries, but two-parameter theory is of little value when constraint loss eventually occurs.
Superconductivity of Thin Film Intermetallic Compounds.
1985-09-15
D-RISE 2?I SUPERCONDUCTIVITY OF THIN FILM INTERMETLLIC COMPOUNDS I/i. (U) MINNESOTR UNIV MINNERPOLIS SCHOOL OF PHYSICS AND RSTRONOMY R M GOLDMRN 15...parameters to either higher temperatures of higher critical fields. Materials under study are the superconducting Chevrel phase compounds, selected Heavy...superconducting field effect. Processing of the Chevrel Phase I compounds is carried out in a multi-source deposition system. The latter has been upgraded and
Nanoscale superconducting memory based on the kinetic inductance of asymmetric nanowire loops
Murphy, Andrew; Averin, Dmitri V.; Bezryadin, Alexey
2017-06-01
The demand for low-dissipation nanoscale memory devices is as strong as ever. As Moore’s law is staggering, and the demand for a low-power-consuming supercomputer is high, the goal of making information processing circuits out of superconductors is one of the central goals of modern technology and physics. So far, digital superconducting circuits could not demonstrate their immense potential. One important reason for this is that a dense superconducting memory technology is not yet available. Miniaturization of traditional superconducting quantum interference devices is difficult below a few micrometers because their operation relies on the geometric inductance of the superconducting loop. Magnetic memories do allow nanometer-scale miniaturization, but they are not purely superconducting (Baek et al 2014 Nat. Commun. 5 3888). Our approach is to make nanometer scale memory cells based on the kinetic inductance (and not geometric inductance) of superconducting nanowire loops, which have already shown many fascinating properties (Aprili 2006 Nat. Nanotechnol. 1 15; Hopkins et al 2005 Science 308 1762). This allows much smaller devices and naturally eliminates magnetic-field cross-talk. We demonstrate that the vorticity, i.e., the winding number of the order parameter, of a closed superconducting loop can be used for realizing a nanoscale nonvolatile memory device. We demonstrate how to alter the vorticity in a controlled fashion by applying calibrated current pulses. A reliable read-out of the memory is also demonstrated. We present arguments that such memory can be developed to operate without energy dissipation.
Directory of Open Access Journals (Sweden)
Yan Yan
2016-01-01
Full Text Available This paper deals with the synchronization of a class of fractional order chaotic systems with unknown parameters and external disturbance. Based on the Lyapunov stability theory, a fractional order sliding mode is constructed and a controller is proposed to realize chaos synchronization. The presented method not only realizes the synchronization of the considered chaotic systems but also enhances the robustness of sliding mode synchronization. Finally, some simulation results demonstrate the effectiveness and robustness of the proposed method.
On the parameter estimation of first order IMA model corrupted with ...
African Journals Online (AJOL)
In this paper, we showed how the autocovariance functions can be used to estimate the true parameters of IMA(1) models corrupted with white noise . We performed simulation studies to demonstrate our findings. The simulation studies showed that under the presence of errors in not more than 30% of total data points, our ...
Directory of Open Access Journals (Sweden)
Yutaka Nishio
2012-11-01
Full Text Available The metallic state of the molecular conductor β-(meso-DMBEDT-TTF2X (DMBEDT-TTF = 2-(5,6-dihydro-1,3-dithiolo[4,5-b][1,4]dithiin-2-ylidene-5,6-dihydro-5,6-dimethyl-1,3-dithiolo[4,5-b][1,4]dithiin, X = PF6, AsF6 is transformed into the checkerboard-type charge-ordered state at around 75–80 K with accompanying metal-insulator (MI transition on the anisotropic triangular lattice. With lowering temperatures, the magnetic susceptibility decreases gradually and reveals a sudden drop at the MI transition. By applying pressure, the charge-ordered state is suppressed and superconductivity appears in β-(meso-DMBEDT-TTF2AsF6 as well as in the reported β-(meso-DMBEDT-TTF2PF6. The charge-ordered spin-gapped state and the pressure-induced superconducting state are discussed through the paired-electron crystal (PEC model, where the spin-bonded electron pairs stay and become mobile in the crystal, namely the valence-bond solid (VBS and the resonant valence bonded (RVB state in the quarter-filled band structure.
Superconducting states of pure and doped graphene.
Uchoa, Bruno; Castro Neto, A H
2007-04-06
We study the superconducting phases of the two-dimensional honeycomb lattice of graphene. We find two spin singlet pairing states; s wave and an exotic p+ip that is possible because of the special structure of the honeycomb lattice. At half filling, the p+ip phase is gapless and superconductivity is a hidden order. We discuss the possibility of a superconducting state in metal coated graphene.
Superconducting states of pure and doped graphene
Uchoa, Bruno; Neto, A. H. Castro
2006-01-01
We study the superconducting phases of the two-dimensional honeycomb lattice of graphene. We find two spin singlet pairing states, s-wave and an exotic $p+ip$ that is possible because of the special structure of the honeycomb lattice. At half filling, the $p+ip$ phase is gapless and superconductivity is a hidden order. We discuss the possibility of a superconducting state in metal coated graphene.
Allen-Perkins, Alfonso; de Assis, Thiago Albuquerque; Pastor, Juan Manuel; Andrade, Roberto F. S.
2017-10-01
This work considers the time scales associated with the global order parameter and the interlayer synchronization of coupled Kuramoto oscillators on multiplexes. For two-layer multiplexes with an initially high degree of synchronization in each layer, the difference between the average phases in each layer is analyzed from two different perspectives: the spectral analysis and the nonlinear Kuramoto model. Both viewpoints confirm that the prior time scales are inversely proportional to the interlayer coupling strength. Thus, increasing the interlayer coupling always shortens the transient regimes of both the global order parameter and the interlayer synchronization. Surprisingly, the analytical results show that the convergence of the global order parameter is faster than the interlayer synchronization, and the latter is generally faster than the global synchronization of the multiplex. The formalism also outlines the effects of frequencies on the difference between the average phases of each layer, and it identifies the conditions for an oscillatory behavior. Computer simulations are in fairly good agreement with the analytical findings, and they reveal that the time scale of the global order parameter is half the size of the time scale of the multiplex, if not smaller.
DEFF Research Database (Denmark)
Maragakis, Paul; Lindorff-Larsen, Kresten; Eastwood, Michael P
2008-01-01
A molecular-level understanding of the function of a protein requires knowledge of both its structural and dynamic properties. NMR spectroscopy allows the measurement of generalized order parameters that provide an atomistic description of picosecond and nanosecond fluctuations in protein structu...
Borsche, Raul; Kall, Jochen
2016-12-01
In this paper we construct high order finite volume schemes on networks of hyperbolic conservation laws with coupling conditions involving ODEs. We consider two generalized Riemann solvers at the junction, one of Toro-Castro type and a solver of Harten, Enquist, Osher, Chakravarthy type. The ODE is treated with a Taylor method or an explicit Runge-Kutta scheme, respectively. Both resulting high order methods conserve quantities exactly if the conservation is part of the coupling conditions. Furthermore we present a technique to incorporate lumped parameter models, which arise from simplifying parts of a network. The high order convergence and the robust capturing of shocks are investigated numerically in several test cases.
Directory of Open Access Journals (Sweden)
Heng Liu
2017-01-01
Full Text Available We investigate the synchronization problem of fractional-order chaotic systems with input saturation and unknown external disturbance by means of adaptive fuzzy control. An adaptive controller, accompanied with fractional adaptation law, is established, fuzzy logic systems are used to approximate the unknown nonlinear functions, and the fractional Lyapunov stability theorem is used to analyze the stability. This control method can realize the synchronization of two fractional-order chaotic or hyperchaotic systems and the synchronization error tends to zero asymptotically. Finally, we show the effectiveness of the proposed method by two simulation examples.
Recent advances in fullerene superconductivity
Margadonna, S
2002-01-01
Superconducting transition temperatures in bulk chemically intercalated fulleride salts reach 33 K at ambient pressure and in hole-doped C sub 6 sub 0 derivatives in field-effect-transistor (FET) configurations, they reach 117 K. These advances pose important challenges for our understanding of high-temperature superconductivity in these highly correlated organic metals. Here we review the structures and properties of intercalated fullerides, paying particular attention to the correlation between superconductivity and interfullerene separation, orientational order/disorder, valence state, orbital degeneracy, low-symmetry distortions, and metal-C sub 6 sub 0 interactions. The metal-insulator transition at large interfullerene separations is discussed in detail. An overview is also given of the exploding field of gate-induced superconductivity of fullerenes in FET electronic devices.
Jacobi, Nicole; Herich, Lena
2016-10-01
There are conflicting data regarding the role of serum ferritin (SF) as surrogate parameter for iron overload as an independent prognostic factor for outcome after allogeneic stem cell transplantation (SCT). Superconducting quantum interference device (SQUID) biomagnetic liver susceptometry, a noninvasive measurement of iron overload, allows measurement of the interference of an exteriorly applied small but highly constant magnetic field by the paramagnetic liver storage iron. By measuring the true iron load of patients through SQUID, we wanted to assess the effect of iron overload on patients undergoing SCT. We conducted a single-center retrospective analysis (1994-2010), comparing the effect of SF and liver iron content measured by SQUID shortly before transplantation on overall survival (OS), event-free survival (EFS), and transplant-related mortality (TRM) in 142 patients (median age 54.5 yr, range 5.6-75 yr) undergoing SCT (80% reduced intensity regimen). Patients were subdivided into five groups: myelodysplastic syndrome, de novo acute myeloid leukemia (AML), secondary AML, primary myelofibrosis, and others. Correlation between SF and SQUID was significant (r = 0.6; P 1000 ng/mL (P = 0.003). A significant association between SQUID and fungal infection was also seen (P = 0.004). For patients with SQUID ≥1000, the risk of proven fungal infection was increased 3.08-fold (95% CI 1.43-6.63). A similar association between SF >1000 and fungal infection was shown (P = 0.01). In univariate analysis, age was a prognostic factor for TRM (P = 0.034, HR 1.04, CI 1.00-1.08). SF ≥1000 was associated with OS (P = 0.033, HR 2.09, CI 1.06-4.11) and EFS (P = 0.016, HR 2.15, 95% CI 1.15-4.10). In multivariate analysis on EFS, only age and SF >1000 remained as independent factors (HR 1.027, P = 0.040, 95% CI 1.001-1.054 and HR 2.058, P = 0.034, 95% CI 1.056-4.008, respectively). The multivariate analysis on TRM left age and SQUID values ≥1000 in the final model (HR 1.045, P
Single gap s-wave superconductivity in Nb{sub 2}PdS{sub 5}
Energy Technology Data Exchange (ETDEWEB)
Shruti [School of Physical Sciences, JNU, New Delhi (India); Goyal, R.; Awana, V.P.S. [CSIR-National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi 110012 (India); Patnaik, S., E-mail: spatnaik@mail.jnu.ac.in [School of Physical Sciences, JNU, New Delhi (India)
2016-05-15
Highlights: • In this paper, we report on pairing symmetry and superconducting gap in recently discovered superconductor Nb2PdS5. • This is a remarkable superconductor with highest ever reported Hc2/Tc ratio of ∼3. • In some theoretical studies, such effects have been ascribed to multiband effects and possible p-wave superconductivity. • However our penetration depth data is well ascribed to a single gap nodeless S-wave superconductivity. - Abstract: Superconducting order parameter and its symmetry are important parameters towards deciphering the pairing mechanism in newly discovered superconducting systems. We report a study on penetration depth measurement on Nb{sub 2}PdS{sub 5} that has recently been reported with extremely high upper critical field with possible triplet pairing mechanism. Our data show that at low temperatures the change in penetration depth Δλ is best fitted with BCS s-wave model for single gap with zero-temperature value of the superconducting energy gap Δ{sub 0} = 1.05 meV, corresponding to the ratio 2Δ{sub 0}/k{sub B}T{sub c} = 3.9 ± 0.18. The superfluid density in the entire temperature range is well described by single gap with gap ratio 2Δ{sub 0}/k{sub B}T{sub c} = 4.1 ± 0.13 for λ(0) = 225 nm.
Energy Technology Data Exchange (ETDEWEB)
Wilczek, F. [Institute for Advanced Study, Princeton, NJ (United States)
1997-09-22
The asymptotic freedom of QCD suggests that at high density - where one forms a Fermi surface at very high momenta - weak coupling methods apply. These methods suggest that chiral symmetry is restored and that an instability toward color triplet condensation (color superconductivity) sets in. Here I attempt, using variational methods, to estimate these effects more precisely. Highlights include demonstration of a negative pressure in the uniform density chiral broken phase for any non-zero condensation, which we take as evidence for the philosophy of the MIT bag model; and demonstration that the color gap is substantial - several tens of MeV - even at modest densities. Since the superconductivity is in a pseudoscalar channel, parity is spontaneously broken.
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.)
Picco, M.; Ritort, F.; Sales, M.
The use of parameters measuring order-parameter fluctuations (OPF) has been encouraged by the recent results reported in referenece [2,3] which show that two of these parameters, G and Gc, take universal values in the . In this paper we present a detailed study of parameters measuring OPF for two mean-field models with and without time-reversal symmetry which exhibit different patterns of replica symmetry breaking below the transition: the Sherrington-Kirkpatrick model with and without a field and the Ising p-spin glass (p = 3). We give numerical results and analyze the consequences which replica equivalence imposes on these models in the infinite volume limit. We give evidence for the transition in each system and discuss the character of finite-size effects. Furthermore, a comparative study between this new family of parameters and the usual Binder cumulant analysis shows what kind of new information can be extracted from the finite T behavior of these quantities. The two main outcomes of this work are: 1) Parameters measuring OPF give better estimates than the Binder cumulant for Tc and even for very small systems they give evidence for the transition. 2) For systems with no time-reversal symmetry, parameters defined in terms of connected quantities are the proper ones to look at.
Temperature Dependence of Energy Gap in the Superconducting State in URu2Si2
Bourdarot, Frederic; Hassinger, Elena; Raymond, Stephane; Aoki, Dai; Taufour, Valentin; Flouquet, Jacques
2010-09-01
The excitation spectrum of URu2Si2 in the superconducting state has been investigated by a precise neutron-scattering experiment. A weak but clear positive energy shift of ˜40 μeV has been detected in the superconducting phase (at T=400 mK) for the resonance at Q0 = (1,0,0). For the resonance at Q1 = (0.6,0,0), a two times smaller shift is observed but with an incertitude of the same order than this shift. This result is in agreement with our previous results indicating that the wave-vector Q0 is connected with the order parameters of the hidden order and of superconductivity.
Guguchia, Z.; Adachi, T.; Shermadini, Z.; Ohgi, T.; Chang, J.; Bozin, E. S.; von Rohr, F.; dos Santos, A. M.; Molaison, J. J.; Boehler, R.; Koike, Y.; Wieteska, A. R.; Frandsen, B. A.; Morenzoni, E.; Amato, A.; Billinge, S. J. L.; Uemura, Y. J.; Khasanov, R.
2017-09-01
High-pressure neutron powder diffraction, muon-spin rotation, and magnetization studies of the structural, magnetic, and the superconducting properties of the Ce-underdoped superconducting (SC) electron-doped cuprate system with the Nd2CuO4 (the so-called T')structure T '-Pr1.3 -xLa0.7CexCuO4 with x =0.1 are reported. A strong reduction of the in-plane and out-of-plane lattice constants is observed under pressure. However, no indication of any pressure-induced phase transition from T'to the K2NiF4 (the so-called T) structure is observed up to the maximum applied pressure of p = 11 GPa. Large and nonlinear increase of the short-range magnetic order temperature Tso in T '-Pr1.3 -xLa0.7CexCuO4 (x =0.1 ) was observed under pressure. Simultaneous pressure causes a nonlinear decrease of the SC transition temperature Tc. All these experiments establish the short-range magnetic order as an intrinsic and competing phase in SC T '-Pr1.3 -xLa0.7CexCuO4 (x =0.1 ). The observed pressure effects may be interpreted in terms of the improved nesting conditions through the reduction of the in-plane and out-of-plane lattice constants upon hydrostatic pressure.
Intermediate coupled superconductivity in yttrium intermetallics
Sharma, Ramesh; Ahmed, Gulzar; Sharma, Yamini
2017-09-01
Non-magnetic YIn3, LaIn3 and LuIn3 with a superconducting transition temperature Tc of 0.78, 0.71 and 0.24 K were investigated for superconductivity. Similarly, rare-earth compound LaSn3 has been reported to exhibit superconductivity around 6.25 K, whereas the non-magnetic YSn3 is a superconductor with Tc of 7 K. The substitution of 13th group In-atoms by 14th group Sn-atoms is seen to enhance Tc by nearly one order, although the lattice parameters increase by ∼1.0% in YSn3 compared to YIn3 compound. It is observed from the ground state properties that the slight difference in the energy band structures of YIn3, YIn2Sn and YSn3 gives rise to various complex Fermi surfaces which are multiply connected and exhibit vast differences. The Fermi level lies on a sharp peak in YSn3 which has a higher density of states N(EF), whereas Fermi level lies on the shoulder of a sharp peak in YIn3. The electron localization function (ELF) and difference charge density maps clearly illustrate the difference in the nature of bonding; the Ysbnd Sn bonds are clearly more ionic (due to larger bond length) than Ysbnd In bonds. These results are consistent with the Bader charges which show loss of charges from Y-atoms and a gain of charges by In/Sn atoms. The dynamical properties also clearly illustrate the difference in the nature of bonds in YX3 intermetallics. A softening of the lowermost acoustic modes is observed in YIn3, whereas all the modes in YSn3 are observed to have positive frequencies which imply its greater stability. Since λel-ph instability in phonon modes due to stronger Ysbnd In and Insbnd In bonds in YIn3 may be the cause of lower Tc and filamentary nature of superconductivity. Insertion of Sn-atom in the YIn3 lattice further consolidates the superconducting nature due to increase in N(EF) and γ (electronic component of specific heat), along with lowering of the frequency of imaginary modes from 5.6 THz to 1.5-0.6 THz. Thus Tc is directly related to the valence
Midya, Jiarul; Majumder, Suman; Das, Subir K
2015-08-01
Behavior of two-time autocorrelation during the phase separation in solid binary mixtures is studied via numerical solutions of the Cahn-Hilliard equation as well as Monte Carlo simulations of the Ising model. Results are analyzed via state-of-the-art methods, including the finite-size scaling technique. Full forms of the autocorrelation in space dimensions 2 and 3 are obtained empirically. The long-time behavior is found to be power law, with exponents unexpectedly higher than the ones for the ferromagnetic ordering. Both Cahn-Hilliard and Ising models provide consistent results.
Fechete, R; Demco, D E; Blümich, B
2003-12-01
The angular distribution function of collagen fibrils in a sheep Achilles tendon was investigated by (1)H NMR of multipolar spin states represented by dipolar-encoded longitudinal magnetization and double-quantum filtered signals. For the first time the angular distribution function based on the Legendre moment expansion is used. Order parameters were obtained from the anisotropy of (1)H residual dipolar couplings of bond water, which were determined model-free from the excitation efficiency of the multipolar spin states and from double-quantum filtered line splitting. The orientation distribution function of collagen fibrils in Achilles tendon measured from the anisotropy of the residual dipolar couplings is characterized by the average values of beta0 = 1.8+/-0.2 degrees and order parameters [P2] = 0.93+/-0.04, [P4] = 0.78+/-0.04 and [P6] = 0.58+/-0.04. The order of many biological tissues in the presence of ageing, injuries or regeneration can be quantified by the order parameters of the angular distribution function. Copyright 2003 John Wiley & Sons, Ltd.
Method of superconducting joint and its measurement
Energy Technology Data Exchange (ETDEWEB)
Kim, Woo Gon; Lee, Ho Jin; Hong, Gye Won [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)
1994-04-01
The development of joint techniques for superconducting wires is essential to fabricate the high quality superconducting magnet. In this report, the various joining methods and their measuring techniques were reviewed. In order to fabricate a precise superconducting magnet, joining and measuring experiment by using the field decay technique carried out. The contact resistance of coupled specimens with joint was measured as 3.0 x 10{sup -15} ohm at 1 Tesla which is lower than that of the real operating condition of MRI magnet. It is expected that these data can be used to design and fabricate the superconducting magnets successfully. (Author) 12 refs., 20 figs., 2 tabs.
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.
Theoretical analyses of superconductivity in iron based ...
African Journals Online (AJOL)
This paper focuses on the theoretical analysis of superconductivity in iron based superconductor Ba1−xKxFe2As2. After reviewing the current findings on this system, we suggest that phononexciton combined mechanism gives a right order of superconducting transition temperature (TC) for Ba1−xKxFe2As2 . By developing ...
Geneva University - Superconducting flux quantum bits: fabricated quantum objects
2007-01-01
Ecole de physique Département de physique nucléaire et corspusculaire 24, Quai Ernest-Ansermet 1211 GENEVE 4 Tél: (022) 379 62 73 Fax: (022) 379 69 92 Lundi 29 janvier 2007 COLLOQUE DE LA SECTION DE PHYSIQUE 17 heures - Auditoire Stueckelberg Superconducting flux quantum bits: fabricated quantum objects Prof. Hans Mooij / Kavli Institute of Nanoscience, Delft University of Technology The quantum conjugate variables of a superconductor are the charge or number of Cooper pairs, and the phase of the order parameter. In circuits that contain small Josephson junctions, these quantum properties can be brought forward. In Delft we study so-called flux qubits, superconducting rings that contain three small Josephson junctions. When a magnetic flux of half a flux quantum is applied to the loop, there are two states with opposite circulating current. For suitable junction parameters, a quantum superposition of those macroscopic states is possible. Transitions can be driven with resonant microwaves. These quantum ...
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. Copyright © 2012 ISA. Published by Elsevier Ltd. All rights reserved.
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.
Directory of Open Access Journals (Sweden)
Al-Sawalha M. Mossa
2016-01-01
Full Text Available The objective of this article is to implement and extend applications of adaptive control to anti-synchronize different fractional order chaotic and hyperchaotic dynamical systems. The sufficient conditions for achieving anti–synchronization are derived by using the Lyapunov stability theory and an analytic expression of the controller with its adaptive laws of parameters is shown. Theoretical analysis and numerical simulations are shown to verify the results.
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.
Al-Sawalha, M. Mossa; Al-Sawalha, Ayman
2016-01-01
The objective of this article is to implement and extend applications of adaptive control to anti-synchronize different fractional order chaotic and hyperchaotic dynamical systems. The sufficient conditions for achieving anti-synchronization are derived by using the Lyapunov stability theory and an analytic expression of the controller with its adaptive laws of parameters is shown. Theoretical analysis and numerical simulations are shown to verify the results.
Hannibal, S.; Kettmann, P.; Croitoru, M. D.; Axt, V. M.; Kuhn, T.
2018-01-01
We present a numerical study of the Higgs mode in an ultracold confined Fermi gas after an interaction quench and find a dynamical vanishing of the superfluid order parameter. Our calculations are done within a microscopic density-matrix approach in the Bogoliubov-de Gennes framework which takes the three-dimensional cigar-shaped confinement explicitly into account. In this framework, we study the amplitude mode of the order parameter after interaction quenches starting on the BCS side of the BEC-BCS crossover close to the transition and ending in the BCS regime. We demonstrate the emergence of a dynamically vanishing superfluid order parameter in the spatiotemporal dynamics in a three-dimensional trap. Further, we show that the signal averaged over the whole trap mirrors the spatiotemporal behavior and allows us to systematically study the effects of the system size and aspect ratio on the observed dynamics. Our analysis enables us to connect the confinement-induced modifications of the dynamics to the pairing properties of the system. Finally, we demonstrate that the signature of the Higgs mode is contained in the dynamical signal of the condensate fraction, which, therefore, might provide a new experimental access to the nonadiabatic regime of the Higgs mode.
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.)
Goodkind, J. M.
1982-01-01
The superconducting gravimeter was developed and applied to field measurements. The stability of the instrument yielded the highest precision measurements of the Earth tides ever attained. It revealed unprecedented details about the effect of the atmosphere on gravity. Secular variations in gravity and the stability of the instruments were measured by comparing records from co-located instruments. These efforts have resulted in substantial reductions in the noise level at very low frequencies so that the peak differences between two instruments at the same location can be reduced to 0.1 micron gal.
Mohebbi, Akbar; Dehghan, Mehdi
2010-12-01
The problem of finding the solution of partial differential equations with source control parameter has appeared increasingly in physical phenomena, for example, in the study of heat conduction process, thermo-elasticity, chemical diffusion and control theory. In this paper we present a high order scheme for determining unknown control parameter and unknown solution of parabolic inverse problem with both integral overspecialization and overspecialization at a point in the spatial domain. In these equations, we first approximate the spatial derivative with a fourth order compact scheme and reduce the problem to a system of ordinary differential equations (ODEs). Then we apply a fourth order boundary value method for the solution of resulting system of ODEs. So the proposed method has fourth order accuracy in both space and time components and is unconditionally stable due to the favorable stability property of boundary value methods. Several numerical examples and also some comparisons with other methods in the literature will be investigated to confirm the efficiency of the new procedure.
Ergül, Adem
2009-01-01
The objective of this thesis is to evaluate a generic process for fabrication and characterization of the Superconductive coplanar waveguide (CPW) resonators. Superconductive CPW resonators with various lengths and shapes are designed to investigate their electrical and magnetic properties as well as resonance properties and sensitivities. In the first part of thesis, two different models are introduced in order to estimate the nonlinear kinetic inductance of a superconducting CPW resonator. ...
Tam, Ka-Ming; Tsai, Shan-Wen; Campbell, David K.
2014-01-01
The search for realistic one-dimensional (1D) models that exhibit dominant superconducting (SC) fluctuations effects has a long history. In these 1D systems, the effects of commensurate band fillings—strongest at half-filling—and electronic repulsions typically lead to a finite charge gap and the favoring of insulating density wave ordering over superconductivity. Accordingly, recent proposals suggesting a gapless metallic state in the Holstein-Hubbard (HH) model, possibly superconducting, have generated considerable interest and controversy, with the most recent work demonstrating that the putative dominant superconducting state likely does not exist. In this paper we study a model with nonlocal electron-phonon interactions, in addition to electron-electron interactions. This model unambiguously possesses dominant superconducting fluctuations at half filling in a large region of parameter space. Using both the numerical multi-scale functional renormalization group (MFRG) for the full model and an analytic conventional renormalization group for a bosonized version of the model, we demonstrate the existence of these dominant SC fluctuations and show that they arise because the spin-charge coupling at high energies is weakened by the nonlocal electron-phonon interaction and the charge gap is destroyed by the resultant suppression of the Umklapp process. The existence of the dominant SC pairing instability in this half-filled 1D system suggests that nonlocal boson-mediated interactions may be important in the superconductivity observed in the organic superconductors.
Cirelli, Giuseppe Luigi; Consoli, Simona; Juanicó, Marcelo
2009-01-01
The operational parameter MRT%FE, representing the mean residence time of different ages fractions of effluent within a completely mixed reactor, was evaluated and integrated with first order kinetics. The parameter was used to model Escherichia coli concentrations in a municipal wastewater reservoir managed under different operating conditions (continuous and discontinuous). The study was conducted during 2004-2005 in a reservoir receiving effluents from the activated sludge treatment plant of Caltagirone (Eastern Sicily - Italy). The analytical approach is applied to the hydraulic state variables of the system (daily stored volumes, inlet and outlet flows), and the physical-chemical (pH, temperature, EC, TSS, BOD(5), COD) and bacteriological wastewater parameters (E. coli, FC, FS). In order to evaluate the reliability of the proposed approach, predicted E. coli concentrations within the reservoir were compared with measured ones by the correlation coefficient, F-test and Sperman's index. The study included the evaluation of die-off coefficient K(T) (d(-1)), light extinction coefficient K (m(-1)) and their relationships with climatic factors. Results of the study confirm that E. coli removal is related to the fractions of fresh effluent remaining each day within the reservoir with MRT%FE of about 5-8d, significantly lower than the nominal detention time (about 27d). The E. coli die-off coefficient (K(T)) was higher during system discontinuous operations and correlated with incident solar radiation and water temperature.
100 years of superconductivity
Rogalla, Horst
2011-01-01
Even a hundred years after its discovery, superconductivity continues to bring us new surprises, from superconducting magnets used in MRI to quantum detectors in electronics. 100 Years of Superconductivity presents a comprehensive collection of topics on nearly all the subdisciplines of superconductivity. Tracing the historical developments in superconductivity, the book includes contributions from many pioneers who are responsible for important steps forward in the field.The text first discusses interesting stories of the discovery and gradual progress of theory and experimentation. Emphasizi
Transition between different quantum states in a mesoscopic system: The superconducting ring
Energy Technology Data Exchange (ETDEWEB)
Horane, E.M. [Instituto Balseiro, Universidad Nacional de Cuyo and Comision Nacional de Energia Atomica, 8400 Bariloche (Argentina); Castro, J.I. [Departamento Fisico-Quimica, Facultad Filosofia Humanidades y Artes, Universidad Nacional de San Juan, San Juan (Argentina); Buscaglia, G.C.; Lopez, A. [Instituto Balseiro, and Centro Atomico Bariloche, Universidad Nacional de Cuyo and Comision Nacional de Energia Atomica, 8400 Bariloche (Argentina)
1996-04-01
We investigate the thermodynamic properties of a superconducting ring, both analytically and numerically, relying upon the Ginzburg-Landau theory. We find that modulated solutions for the order parameter play a role in describing the thermodynamic transitions between consecutive modes of uniform order parameter, associated with different quantum numbers. Exact expressions for these solutions are given in terms of elliptic functions. We identify the family of energy extrema which, being saddle points of the energy in the functional space of the distributions of the order parameter, represent the energy barrier to be overcome for transitions between different solutions. {copyright} {ital 1996 The American Physical Society.}
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.
The superconducting state of Holstein model using dynamical mean field theory
Lin, Chungwei; Wang, Bingnan; Teo, Koon
To enhance the superconducting temperature within the conventional superconductors, we solve the Holstein model, where conduction electrons are coupled to some boson field, using dynamical mean field theory (DMFT) with the configuration interaction impurity solver. Thanks to the non-perturbative nature of DMFT, we determine the zero-temperature order parameter for a wide range of boson energies to find the optimal range for superconductivity. This is beyond the Migdal-Eliashberg theory where the boson energy is assumed to be small compared to the Fermi energy. The effect of Hubbard on-site repulsion will be also discussed.
Theory of High-T{sub c} Superconducting Cuprates Based on Experimental Evidence
Abrikosov, A. A.
1999-12-10
A model of superconductivity in layered high-temperature superconducting cuprates is proposed, based on the extended saddle point singularities in the electron spectrum, weak screening of the Coulomb interaction and phonon-mediated interaction between electrons plus a small short-range repulsion of Hund's, or spin-fluctuation, origin. This permits to explain the large values of T{sub c}, features of the isotope effect on oxygen and copper, the existence of two types of the order parameter, the peak in the inelastic neutron scattering, the positive curvature of the upper critical field, as function of temperature etc.
Vasta, M.; Roberts, J. B.
1998-06-01
Methods for using fourth order spectral quantities to estimate the unknown parameters in non-linear, randomly excited dynamic systems are developed. Attention is focused on the case where only the response is measurable and the excitation is unmeasurable and known only in terms of a stochastic process model. The approach is illustrated through application to a non-linear oscillator with both non-linear damping and stiffness and with excitation modelled as a stationary Gaussian white noise process. The methods have applications in studies of the response of structures to random environmental loads, such as wind and ocean wave forces.
Ito, Reika; Yoshidome, Takashi
2018-01-01
Markov state models (MSMs) are a powerful approach for analyzing the long-time behaviors of protein motion using molecular dynamics simulation data. However, their quantitative performance with respect to the physical quantities is poor. We believe that this poor performance is caused by the failure to appropriately classify protein conformations into states when constructing MSMs. Herein, we show that the quantitative performance of an order parameter is improved when a manifold-learning technique is employed for the classification in the MSM. The MSM construction using the K-center method, which has been previously used for classification, has a poor quantitative performance.
Anomalous superconductivity near the Mott transition
Tremblay, Andre-Marie
2006-03-01
High-temperature superconductivity appears near an antiferromagnetic Mott insulating phase and a normal phase with a pseudogap. It was suggested early on by Anderson that the strong-coupling limit of the Hubbard model should contain the main physics. It is only recently that we have begun to have access to sufficiently accurate algorithms and powerful enough computers to begin to extract the main features of the phase diagram of high-temperature superconductors from the Hubbard model in a nearly quantitative manner. In this talk, the zero temperature phase diagram of the two-dimensional Hubbard model is discussed based on several ``quantum cluster'' approaches, mainly Variational Cluster Perturbation Theory [1] and Cellular Dynamical Mean Field Theory [2], that shall be introduced. The overall ground state phase diagram of the high-temperature superconductors as well as the asymmetric one-particle excitation spectra for both hole- and electron-doping are reproduced. The d-wave order parameter is found to assume a dome shape as a function of doping and to scale like the magnetic exchange coupling J for U comparable to the bandwidth. We stress the features of superconductivity that are non-BCS like due to the proximity to the Mott insulator. In stark contrast with BCS theory, the superconducting gap can decrease monotonically at the same time as the d-wave order parameter increases away from half-filling. Also, d-wave superconductivity is driven by a lowering of kinetic energy instead of potential energy, in conformity with experiments on cuprates. The pseudogap [3-5] and results of other approaches will also be briefly touched upon. [1] David S'en'echal, P.-L. Lavertu, M.-A. Marois, and A.- M.S. Tremblay, Phys. Rev. Lett. 94, 156404 (2005). [2] S. S. Kancharla, M. Civelli, M. Capone, B. Kyung, D. Senechal, G. Kotliar, A.-M.S. Tremblay, cond-mat/0508205. [3] B. Kyung, S.S. Kancharla, D. S'en'echal, A.-M.S. Tremblay, M. Civelli, and G. Kotliar cond-mat/0502565 [4] B
Superconducting micronets: The Wheatstone bridge
Energy Technology Data Exchange (ETDEWEB)
Ammann, C.; Erdoes, P. [Institute of Theoretical Physics, University of Lausanne, CH-1015 Lausanne (Switzerland); Haley, S.B. [Department of Electrical and Computer Engineering, University of California, Davis, California 95616 (United States)
1995-05-01
Using the Ginzburg-Landau theory, a particular superconducting (sc) micronet, called the Wheatstone bridge, is studied. This planar micronet is made of two nodes connected by three thin sc wires. A magnetic field is applied perpendicularly to its plane. The sc-normal second-order phase transition is characterized by only two configurations of the order parameter: {ital cphi}{sub {ital A}}={ital cphi}{sub {ital B}} and {ital cphi}{sub {ital A}}={minus}{ital cphi}{sub {ital B}}, where {ital cphi}{sub {ital A}} and {ital cphi}{sub {ital B}} are the order parameters at the nodes. For temperatures near {ital T}{sub {ital c}}, we show that only the {ital cphi}{sub {ital A}}={ital cphi}{sub {ital B}} configuration is admissible for fluxes near {Phi}={ital n}{Phi}{sub 0}, where {ital n} is an integer and {Phi}{sub 0} is the flux quantum. Finally, the exact solution of the nonlinear Ginzburg-Landau equations for one-dimensional systems is numerically fitted to the boundary conditions of the Wheatstone bridge for the two configurations {ital cphi}{sub {ital A}}={ital cphi}{sub {ital B}} and {ital cphi}{sub {ital A}}={minus}{phi}{sub {ital B}}. Graphs of the Gibbs energy and of the spontaneous supercurrent, which for these two configurations is always a screening supercurrent, are given as functions of the total flux. A discontinuous transition between configurations occurs as a function of the flux.
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. Copyright © 2016 John Wiley & Sons, Ltd.
Superconductivity in compensated and uncompensated semiconductors
Directory of Open Access Journals (Sweden)
Youichi Yanase and Naoyuki Yorozu
2008-01-01
Full Text Available We investigate the localization and superconductivity in heavily doped semiconductors. The crossover from the superconductivity in the host band to that in the impurity band is described on the basis of the disordered three-dimensional attractive Hubbard model for binary alloys. The microscopic inhomogeneity and the thermal superconducting fluctuation are taken into account using the self-consistent 1-loop order theory. The superconductor-insulator transition accompanies the crossover from the host band to the impurity band. We point out an enhancement of the critical temperature Tc around the crossover. Further localization of electron wave functions leads to the localization of Cooper pairs and induces the pseudogap. We find that both the doping compensation by additional donors and the carrier increase by additional acceptors suppress the superconductivity. A theoretical interpretation is proposed for the superconductivity in the boron-doped diamond, SiC, and Si.
Bothner, D.; Wiedmaier, D.; Ferdinand, B.; Kleiner, R.; Koelle, D.
2017-09-01
We experimentally investigate superconducting coplanar waveguide resonators in external magnetic fields and present two strategies to reduce field-induced dissipation channels and resonance frequency shifts. One of our approaches is to significantly reduce the superconducting ground-plane areas, which leads to reduced magnetic-field focussing and thus to lower effective magnetic fields inside the waveguide cavity. By this measure, the field-induced losses can be reduced by more than one order of magnitude in mT out-of-plane magnetic fields. When these resonators are additionally coupled inductively instead of capacitively to the microwave feed lines, an intrinsic closed superconducting loop is effectively shielding the heart of the resonator from magnetic fields by means of flux conservation. In total, we achieve a reduction of the field-induced resonance frequency shift by up to 2 orders of magnitude. We combine systematic parameter variations on the experimental side with numerical magnetic-field calculations to explain the effects of our approaches and to support our conclusions. The presented results are relevant for all areas, where high-performance superconducting resonators need to be operated in magnetic fields, e.g., for quantum hybrid devices with superconducting circuits or electron spin resonance detectors based on coplanar waveguide cavities.
Energy Technology Data Exchange (ETDEWEB)
Keidel, Felix; Burset, Pablo; Trauzettel, Bjoern [Institute of Theoretical Physics and Astrophysics, University of Wuerzburg, 97074 Wuerzburg (Germany); Crepin, Francois [Laboratoire de Physique Theorique de la Matiere Condensee, UPMC, Sorbonne Universites, 75252 Paris (France)
2016-07-01
The scientific interest in Quantum Spin Hall systems is far from declining. While these certainly are fascinating by themselves, there is plenty of new and exciting physics to arise when superconductivity and ferromagnetism are brought into the game. The strong constraint of helicity in the edge states of a two-dimensional topological insulator is responsible for an intimate relation between the allowed scattering processes in a hybrid junction and the parameters of the system, namely the superconducting order parameter and the magnetic field. In our work, we study a helical liquid in proximity to a conventional s-wave superconductor and ferromagnetic insulators by means of a Green's function analysis. The ferromagnet gives rise to sub-gap Andreev/Majorana bound states and non-local crossed Andreev reflection (CAR), both of which decisively affect the pairing and transport properties of the junction. As a result, the simple s-wave symmetry of the superconductor is enriched and unconventional odd-frequency triplet superconductivity emerges. Strikingly, we have identified a setup that favors CAR over electron co-tunneling and may allow for the indirect measurement of the symmetries of the superconducting order parameter.
Training and magnetic field measurements of the ANKA superconducting undulator
Energy Technology Data Exchange (ETDEWEB)
Saez de Jauregui, David; Baumbach, Tilo; Casalbuoni, Sara; Gerstl, Stefan; Hagelstein, Michael [Karlsruhe Institute of Technology (KIT), Karlsruhe (Germany); Boffo, Cristian; Walter, Wolfgang [Babcock Noell GmbH, Wuerzburg (Germany)
2011-07-01
In 2011 a 1.5 m long superconducting undulator with a period length of 15mm is scheduled to be installed in ANKA. This insertion device is planned to be the light source of the new beamline NANO for high resolution X-ray diffraction. The key specifications of the system are an undulator parameter K higher than 2 (for a magnetic gap of 5mm) and a phase error smaller than 3.5 degrees. In order to characterize the magnetic field properties of the superconducting coils local field measurements have been performed by moving a set of Hall probes on a sledge in a liquid helium bath. The results of these investigations are presented.
A whale better adjusts the biosonar to ordered rather than to random changes in the echo parameters.
Supin, Alexander Ya; Nachtigall, Paul E; Breese, Marlee
2012-09-01
A false killer whale's (Pseudorca crassidens) sonar clicks and auditory evoked potentials (AEPs) were recorded during echolocation with simulated echoes in two series of experiments. In the first, both the echo delay and transfer factor (which is the dB-ratio of the echo sound-pressure level to emitted pulse source level) were varied randomly from trial to trial until enough data were collected (random presentation). In the second, a combination of the echo delay and transfer factor was kept constant until enough data were collected (ordered presentation). The mean click level decreased with shortening the delay and increasing the transfer factor, more at the ordered presentation rather than at the random presentation. AEPs to the self-heard emitted clicks decreased with shortening the delay and increasing the echo level equally in both series. AEPs to echoes increased with increasing the echo level, little dependent on the echo delay at random presentations but much more dependent on delay with ordered presentations. So some adjustment of the whale's biosonar was possible without prior information about the echo parameters; however, the availability of prior information about echoes provided additional whale capabilities to adjust both the transmitting and receiving parts of the biosonar.
Superconducting Continuous Graphene Fibers via Calcium Intercalation.
Liu, Yingjun; Liang, Hui; Xu, Zhen; Xi, Jiabin; Chen, Genfu; Gao, Weiwei; Xue, Mianqi; Gao, Chao
2017-04-25
Superconductors are important materials in the field of low-temperature magnet applications and long-distance electrical power transmission systems. Besides metal-based superconducting materials, carbon-based superconductors have attracted considerable attention in recent years. Up to now, five allotropes of carbon, including diamond, graphite, C60, CNTs, and graphene, have been reported to show superconducting behavior. However, most of the carbon-based superconductors are limited to small size and discontinuous phases, which inevitably hinders further application in macroscopic form. Therefore, it raises a question of whether continuously carbon-based superconducting wires could be accessed, which is of vital importance from viewpoints of fundamental research and practical application. Here, inspired by superconducting graphene, we successfully fabricated flexible graphene-based superconducting fibers via a well-established calcium (Ca) intercalation strategy. The resultant Ca-intercalated graphene fiber (Ca-GF) shows a superconducting transition at ∼11 K, which is almost 2 orders of magnitude higher than that of early reported alkali metal intercalated graphite and comparable to that of commercial superconducting NbTi wire. The combination of lightness and easy scalability makes Ca-GF highly promising as a lightweight superconducting wire.
Anderson, Janet S; Hernández, Griselda; LeMaster, David M
2017-07-11
Protein molecular dynamics interpretation of the standard R1, R2, and heteronuclear NOE relaxation measurements has typically been limited to a single S2 order parameter which is often insufficient to characterize the rich content of these NMR experiments. In the absence of exchange linebroadening, an optimized reduced spectral density analysis of these measurements can yield spectral density values at three distinct frequencies. Surprisingly, these three discrete spectral density values have proven to be sufficient for a Larmor frequency-selective order parameter analysis of the 223 methine and methylene H-C bonds of the B3 domain of Protein G (GB3) to accurately back-calculate the entire curve of the corresponding bond vector autocorrelation functions upon which the NMR relaxation behavior depends. The 13C relaxation values calculated from 2 μs of CHARMM36 simulation trajectories yielded the corresponding autocorrelation functions to an average rmsd of 0.44% with only three bond vectors having rmsd errors slightly greater than 1.0%. Similar quality predictions were obtained using the CHARMM22/CMAP, AMBER ff99SB, and AMBER ff99SB-ILDN force fields. Analogous predictions for the backbone 15N relaxation values were 3-fold more accurate. Excluding seven residues for which either experimental data is lacking or previous MD studies have indicated markedly divergent dynamics predictions, the CHARMM36-derived and experimentally derived 15N relaxation values for the remaining 48 amides of GB3 agree to an average of 0.016, 0.010, and 0.020 for the fast limit (Sf2) and Larmor frequency-selective (SH2 and SN2) order parameters, respectively. In contrast, for a substantial fraction of side chain positions, the statistical uncertainties obtained in the relaxation value predictions from each force field were appreciably less than the much larger differences predicted among these force fields, indicating a significant opportunity for experimental NMR relaxation measurements to
Directory of Open Access Journals (Sweden)
Yucel Yildirim
2011-09-01
Full Text Available A generic theory of the quasiparticle superconducting gap in underdoped cuprates is derived in the strong-coupling limit, and found to describe the experimental “second gap” in absolute scale. In drastic contrast to the standard pairing gap associated with Bogoliubov quasiparticle excitations, the quasiparticle gap is shown to originate from anomalous kinetic (scattering processes, with a size unrelated to the pairing strength. Consequently, the k dependence of the gap deviates significantly from the pure d_{x^{2}-y^{2}} wave of the order parameter. Our study reveals a new paradigm for the nature of the superconducting gap, and is expected to reconcile numerous apparent contradictions among existing experiments and point toward a more coherent understanding of high-temperature superconductivity.
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. Copyright © 2016 ISA. Published by Elsevier Ltd. All rights reserved.
Kundin, Julia
2017-06-01
The present paper proposes an extension to the phase-field model of Kobayashi, Warren and Carter (KWC) as described in (Warren et al 2002 Acta Mater.) to incorporate the recrystallization process which occurs during heat treatments of alloy systems with predeformed defect structure. The standard KWC model is extended by an additional order parameter for recrystallized grains and describes the general results for the steady-state moving boundary. The simulation results of the initial grain growth and recrystallization process in various systems show that the extended phase-field model is able to describe the influence of the initial grain boundaries on the recrystallization kinetics and to incorporate the misorientation dependency of the low angle grain boundary mobility which strongly influences the orientation distribution in the resulting microstructure.
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.
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...
Overview on superconducting photoinjectors
Arnold, A.; Teichert, J.
2011-02-01
The success of most of the proposed energy recovery linac (ERL) based electron accelerator projects for future storage ring replacements (SRR) and high power IR-free-electron lasers (FELs) largely depends on the development of an appropriate source. For example, to meet the FEL specifications [J. W. Lewellen, Proc. SPIE Int. Soc. Opt. Eng.PSISDG0277-786X 5534, 22 (2004)10.1117/12.557378] electron beams with an unprecedented combination of high brightness, low emittance (0.1μmrad), and high average current (hundreds of mA) are required. An elegant way to create a beam of such quality is to combine the high beam quality of a normal conducting rf photoinjector with the superconducting technology, i.e., to build a superconducting rf photoinjector (SRF gun). SRF gun R&D programs based on different approaches have been launched at a growing number of institutes and companies (AES, Beijing University, BESSY, BNL, DESY, FZD, TJNAF, Niowave, NPS, Wisconsin University). Substantial progress was achieved in recent years and the first long term operation was demonstrated at FZD [R. Xiang , in Proceedings of the 31st International Free Electron Laser Conference (FEL 09), Liverpool, UK (STFC Daresbury Laboratory, Warrington, 2009), p. 488]. In the near future SRF guns are expected to play an important role for linac-driven FEL facilities. In this paper we will review the concepts, the design parameters, and the status of the major SRF gun projects.
Simple Superconducting "Permanent" Electromagnet
Israelson, Ulf E.; Strayer, Donald M.
1992-01-01
Proposed short tube of high-temperature-superconducting material like YBa2Cu3O7 acts as strong electromagnet that flows as long as magnetic field remains below critical value and temperature of cylinder maintained sufficiently below superconducting-transition temperature. Design exploits maximally anisotropy of high-temperature-superconducting material.
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.
Wu, Jia Lin
2013-06-01
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
2017-11-01
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.
metrological performance improvement of a superconducting cable test station
Montenero, Giuseppe; Ballarino, Amalia
The work presented in this PhD thesis concerns the metrological performance improvement of a superconducting cable test station based on superconducting transformers. The main cable’s parameter to be assessed –as a function of temperature and magnetic field– is the critical current, i.e. beyond this limit the phase transition to the normal state occurs. Ramping the current at levels in the order of the tens of kA can be achieved with superconducting transformers at moderate capital and operational cost. But, issues such as (i) accurate/precise measurements and (ii) monitoring of the secondary current during the device operation have to be addressed. In this regard, the goals of the thesis are the design, prototyping, and validation of a new cryogenic current transducer and effective monitoring system for test stations transformer-based. Among the available transducers for current sensing at room temperature, the DC current transformer (DCCT) provides measurement accuracy in the order of the hundreds of ...
Superconducting Bolometer Array Architectures
Benford, Dominic J.; Chervenak, James A.; Irwin, Kent D.; Moseley, S. H., Jr.; Shafer, Richard A.; Staguhn, Johannes G.; Wollack, Ed
2003-02-01
The next generation of far-infrared and submillimeter instruments require large arrays of detectors containing thousands of elements. These arrays will necessarily be multiplexed, and superconducting bolometer arrays are the most promising present prospect for these detectors. We discuss our current research into superconducting bolometer array technologies, which has recently resulted in the first multiplexed detections of submillimeter light and the first multiplexed astronomical observations. Prototype arrays containing 512 pixels are in production using the Pop-Up Detector (PUD) architecture, which can be extended easily to 1000 pixel arrays. Planar arrays of close-packed bolometers are being developed for the GBT and for future space missions. For certain applications, such as a slewed far-infrared sky survey, feedhorn-coupling of a large sparsely-filled array of bolometers is desirable, and is being developed using photolithographic feedhorn arrays. Individual detectors have achieved a Noise Equivalent Power (NEP) of ~10-17 W/√Hz at 300mK, but several orders of magnitude improvement are required and can be reached with existing technology. The testing of such ultralow-background detectors will prove difficult, as this requires optical loading of below 1fW. Antenna-coupled bolometer designs have advantages for large format array designs at low powers due to their mode selectivity. We also present a design and preliminary results for an enhanced-dynamic-range transition edge sensor suitable for broadband ultralow-background detectors.
Enhanced superconductivity of fullerenes
Energy Technology Data Exchange (ETDEWEB)
Washington, II, Aaron L.; Teprovich, Joseph A.; Zidan, Ragaiy
2017-06-20
Methods for enhancing characteristics of superconductive fullerenes and devices incorporating the fullerenes are disclosed. Enhancements can include increase in the critical transition temperature at a constant magnetic field; the existence of a superconducting hysteresis over a changing magnetic field; a decrease in the stabilizing magnetic field required for the onset of superconductivity; and/or an increase in the stability of superconductivity over a large magnetic field. The enhancements can be brought about by transmitting electromagnetic radiation to the superconductive fullerene such that the electromagnetic radiation impinges on the fullerene with an energy that is greater than the band gap of the fullerene.
Superconducting material development
1987-09-01
A superconducting compound was developed that showed a transition to a zero-resistance state at 65 C, or 338 K. The superconducting material, which is an oxide based on strontium, barium, yttrium, and copper, continued in the zero-resistance state similar to superconductivity for 10 days at room temperature in the air. It was also noted that measurements of the material allowed it to observe a nonlinear characteristic curve between current and voltage at 65 C, which is another indication of superconductivity. The research results of the laboratory experiment with the superconducting material will be published in the August edition of the Japanese Journal of Applied Physics.
Robb, Daniel T.; Ostrander, Aaron
2014-02-01
We present numerical evidence for an extended order parameter and conjugate field for the dynamic phase transition in a Ginzburg-Landau mean-field model driven by an oscillating field. The order parameter, previously taken to be the time-averaged magnetization, comprises the deviations of the Fourier components of the magnetization from their values at the critical period. The conjugate field, previously taken to be the time-averaged magnetic field, comprises the even Fourier components of the field. The scaling exponents β and δ associated with the extended order parameter and conjugate field are shown numerically to be consistent with their values in the equilibrium mean-field model.
Li, Jun; Ji, Min; Schwarz, Tobias; Ke, Xiaoxing; Van Tendeloo, Gustaaf; Yuan, Jie; Pereira, Paulo J.; Huang, Ya; Zhang, Gufei; Feng, Hai-Luke; Yuan, Ya-Hua; Hatano, Takeshi; Kleiner, Reinhold; Koelle, Dieter; Chibotaru, Liviu F.; Yamaura, Kazunari; Wang, Hua-Bing; Wu, Pei-Heng; Takayama-Muromachi, Eiji; Vanacken, Johan; Moshchalkov, Victor V.
2015-01-01
The determination of the pairing symmetry is one of the most crucial issues for the iron-based superconductors, for which various scenarios are discussed controversially. Non-magnetic impurity substitution is one of the most promising approaches to address the issue, because the pair-breaking mechanism from the non-magnetic impurities should be different for various models. Previous substitution experiments demonstrated that the non-magnetic zinc can suppress the superconductivity of various iron-based superconductors. Here we demonstrate the local destruction of superconductivity by non-magnetic zinc impurities in Ba0.5K0.5Fe2As2 by exploring phase-slip phenomena in a mesoscopic structure with 119 × 102 nm2 cross-section. The impurities suppress superconductivity in a three-dimensional ‘Swiss cheese'-like pattern with in-plane and out-of-plane characteristic lengths slightly below ∼1.34 nm. This causes the superconducting order parameter to vary along abundant narrow channels with effective cross-section of a few square nanometres. The local destruction of superconductivity can be related to Cooper pair breaking by non-magnetic impurities. PMID:26139568
Smart monitoring system based on adaptive current control for superconducting cable test
Arpaia, Pasquale; Ballarino, Amalia; Daponte, Vincenzo; Montenero, Giuseppe; Svelto, Cesare
2014-12-01
A smart monitoring system for superconducting cable test is proposed with an adaptive current control of a superconducting transformer secondary. The design, based on Fuzzy Gain Scheduling, allows the controller parameters to adapt continuously, and finely, to the working variations arising from transformer nonlinear dynamics. The control system is integrated in a fully digital control loop, with all the related benefits, i.e., high noise rejection, ease of implementation/modification, and so on. In particular, an accurate model of the system, controlled by a Fuzzy Gain Scheduler of the superconducting transformer, was achieved by an experimental campaign through the working domain at several current ramp rates. The model performance was characterized by simulation, under all the main operating conditions, in order to guide the controller design. Finally, the proposed monitoring system was experimentally validated at European Organization for Nuclear Research (CERN) in comparison to the state-of-the-art control system [P. Arpaia, L. Bottura, G. Montenero, and S. Le Naour, "Performance improvement of a measurement station for superconducting cable test," Rev. Sci. Instrum. 83, 095111 (2012)] of the Facility for the Research on Superconducting Cables, achieving a significant performance improvement: a reduction in the system overshoot by 50%, with a related attenuation of the corresponding dynamic residual error (both absolute and RMS) up to 52%.
Vortex-core order and field-driven supersolidity
Karmakar, Madhuparna; Menon, Gautam I.; Ganesh, R.
2017-11-01
Superconductivity occurs in the proximity of other competing orders in a wide variety of materials. Such competing phases may reveal themselves when superconductivity is locally suppressed by a magnetic field in the core of a vortex. We explore the competition between superconductivity and charge density wave order in the attractive Hubbard model on a square lattice. Using Bogoliubov-de Gennes mean-field theory, we study how vortex structures form and evolve as the magnetic flux is tuned. Each vortex seeds a charge density wave region whose size is determined by the energy cost of the competing phase. The vortices form a lattice whose lattice parameter shrinks with increasing flux. Eventually, their charge-ordered cores overlap, leading to a field-driven coexistence phase exhibiting both macroscopic charge order and superconductivity—a "supersolid." Ultimately, superconductivity disappears via a first-order phase transition into a purely charge-ordered state. We demonstrate that the Hubbard model maps to a strong-coupling field theory with a constant-squared-sum constraint. We argue that such a constraint necessarily leads to ordered-vortex cores and field-driven coexistence. The coexistence phase can be interpreted as a crystalline arrangement of meron defects in a pseudospin description. We construct a phase diagram using t', the next-nearest-neighbor hopping, to tune the competition between phases.
Flükiger, R.; Spina, T.; Cerutti, F.; Ballarino, A.; Scheuerlein, C.; Bottura, L.; Zubavichus, Y.; Ryazanov, A.; Svetogovov, R. D.; Shavkin, S.; Degtyarenko, P.; Semenov, Y.; Senatore, C.; Cerny, R.
2017-05-01
Nb3Sn platelets with thicknesses between 0.12 and 0.20 mm produced by a high isostatic pressure process at 1250 °C were irradiated at 300 K with 12 MeV protons. The effects of irradiation on the lattice parameter a, the atomic order parameter S and the transition temperature T c were measured as a function of proton fluence. In view of the presence of multiple energy radiation sources in future accelerators, the present proton data are compared with neutron irradiation data from the literature. The fluences for both types of radiation were replaced by the dpa number, the ‘displacements per atom’, calculated using the FLUKA code, which is proportional to the number of radiation induced Frenkel defects. It was found that the variation of both a and S for Nb3Sn after proton and neutron irradiation as a function of dpa fall almost on the same curve, in analogy to the recently reported correlation between T c and the dpa number. By a simultaneous irradiation of two adjacent thin Nb3Sn platelets, we have shown that this correlation is not only valid for the state of ‘steady energy loss’ (protons traveling through the first platelet) but also for the state of higher damage at the Bragg peak (second platelet). It follows that the number of radiation induced Frenkel defects in the A15 grains, calculated via the dpa number, can be considered as a ‘universal’ parameter, allowing the calculation of the variation of T c, a and S of Nb3Sn under the effect of multiple high energy radiation sources, as in future superconducting accelerators.
Tunable superconducting phase transition in metal-decorated graphene sheets.
Kessler, B M; Girit, C O; Zettl, A; Bouchiat, V
2010-01-29
We have produced graphene sheets decorated with a nonpercolating network of nanoscale tin clusters. These metal clusters both efficiently dope the graphene substrate and induce long-range superconducting correlations. We find that despite structural inhomogeneity on mesoscopic length scales (10-100 nm), this material behaves electronically as a homogenous dirty superconductor with a field-effect tuned Berezinskii-Kosterlitz-Thouless transition. Our facile self-assembly method establishes graphene as an ideal tunable substrate for studying induced two-dimensional electronic systems at fixed disorder and our technique can readily be extended to other order parameters such as magnetism.
Directory of Open Access Journals (Sweden)
Jose Luis Rivera
2015-01-01
Full Text Available The critical point affects the coexistence behavior of the vapor-liquid equilibrium densities. The length of the critical influence zone is under debate because for some properties, like shear viscosity, the extension is only a few degrees, while for others, such as the density order parameter, the critical influence zone covers up to hundreds of degrees below the critical temperature. Here we show that, for ethane, the experimental critical influence zone covers a wide zone of tens of degrees (below the critical temperature down to a transition temperature, at which the apparent critical influence zone vanishes, and the transition temperature can be predicted through a pressure analysis of the coexisting bulk liquid phase, using a simple molecular potential. The liquid phases within the apparent critical influence zone show low densities, making them behave internally like their corresponding vapor phases. Therefore, Molecular Dynamics simulations reveal that the experimentally observed wide extension of the critical influence zone is the result of a vapor-like effect due to low bulk liquid phase densities.
Superconducting states of the quasi-2D Holstein model: effects of vertex and non-local corrections
Energy Technology Data Exchange (ETDEWEB)
Hague, J P [Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH (United Kingdom)
2005-09-21
I investigate superconducting states in a quasi-2D Holstein model using the dynamical cluster approximation. The effects of spatial fluctuations (non-local corrections) are examined and approximations neglecting and incorporating lowest order vertex corrections are computed. The approximation is expected to be valid for electron-phonon couplings of less than the bandwidth. The phase diagram and superconducting order parameter are calculated. Effects which can only be attributed to theories beyond Migdal-Eliashberg theory are present. In particular, the order parameter shows momentum dependence on the Fermi surface with a modulated form and s-wave order is suppressed at half-filling. The results are discussed in relation to Hohenberg's theorem and the Bardeen-Cooper-Schrieffer approximation.
Tight-binding description of intrinsic superconducting correlations in multilayer graphene
Munoz, W. A.; Covaci, L.; Peeters, F. M.
2013-01-01
Using highly efficient GPU-based simulations of the tight-binding Bogoliubov-de Gennes equations we solve self-consistently for the pair correlation in rhombohedral (ABC) and Bernal (ABA) multilayer graphene by considering a finite intrinsic s-wave pairing potential. We find that the two different stacking configurations have opposite bulk/surface behavior for the order parameter. Surface superconductivity is robust for ABC stacked multilayer graphene even at very low pairing potentials for w...
Superconductivity theory applied to the periodic table of the elements
Energy Technology Data Exchange (ETDEWEB)
Elifritz, T.L. [Information Corporation, Madison, WI (United States)
1994-12-31
The modern theory of superconductivity, based upon the BCS to Bose-Einstein transition, is applied to the periodic table of the elements, in order to isolate the essential features of high temperature superconductivity and to predict its occurrence within the periodic table. It is predicted that Sodium-Ammonia, Sodium Zinc Phosphide and Bismuth (I) Iodide are promising materials for experimental explorations of high temperature superconductivity.
Superconductivity theory applied to the periodic table of the elements
Elifritz, Thomas Lee
1995-01-01
The modern theory of superconductivity, based upon the BCS to Bose-Einstein transition is applied to the periodic table of the elements, in order to isolate the essential features of of high temperature superconductivity and to predict its occurrence with the periodic table. It is predicted that Sodium-Ammonia, Sodium Zinc Phosphide and Bismuth (I) Iodide are promising materials for experimental explorations of high temperature superconductivity.
Zhang, P; Jones, R M
2012-01-01
An electron beam entering an accelerating cavity excites a wakefield. This wakefield can be decomposed into a series of multi-poles or modes. The dominant component of the transverse wakefield is dipole. This report summarizes the higher order mode (HOM) signals of the third harmonic cavities of FLASH measured at various stages: transmission measurements in the single cavity test stand at Fermilab, at CMTB (Cryo-Module Test Bench) and at FLASH, and beam-excited measurements at FLASH. Modes in the first two dipole bands and the fifth dipole band have been identified using a global Lorentzian fit technique. The beam-pipe modes at approximately 4 GHz and some modes in the fifth dipole band have been observed as localized modes, while the first two dipole bands, containing some strong coupling cavity modes, propagate. This report also presents the dependence of the localized dipole modes on the transverse beam position. Linear dependence for various modes has been observed. This makes them suitable for beam posit...
Energy Technology Data Exchange (ETDEWEB)
Zhang, Pei [Manchester Univ. (United Kingdom); Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Baboi, Nicoleta [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Jones, Roger M. [The Cockcroft Institute, Daresbury (United Kingdom)
2012-06-15
An electron beam entering an accelerating cavity excites a wakefield. This wakefield can be decomposed into a series of multi-poles or modes. The dominant component of the transverse wakefield is dipole. This report summarizes the higher order mode (HOM) signals of the third harmonic cavities of FLASH measured at various stages: transmission measurements in the single cavity test stand at Fermilab, at CMTB (Cryo- Module Test Bench) and at FLASH, and beam-excited measurements at FLASH. Modes in the first two dipole bands and the fifth dipole band have been identified using a global Lorentzian fit technique. The beam-pipe modes at approximately 4 GHz and some modes in the fifth dipole band have been observed as localized modes, while the first two dipole bands, containing some strong coupling cavity modes, propagate. This report also presents the dependence of the localized dipole modes on the transverse beam position. Linear dependence for various modes has been observed. This makes them suitable for beam position diagnostics. These modes, together with some propagating, strong coupling modes, have been considered in the design of a dedicated electronics for beam diagnostics with HOMs for the third harmonic cavities.
Modeling of planar quasi-TEM superconducting transmission lines
Antsos, Dimitrios; Chew, Wilbert; Riley, A. L.; Hunt, Brian D.; Foote, Marc C.; Bajuk, Louis J.; Rascoe, Daniel L.; Cooley, Thomas W.
1992-01-01
An application of the phenomenological loss equivalence method (Lee and Itoh, 1989) in modeling the microwave behavior of planar quasi-TEM superconducting transmission lines is presented. For validation of the model, data are used from measurements of a YBCO superconducting thin-film coplanar-waveguide lowpass filter on a lanthanum aluminate substrate. Measured and modeled S-parameters of an existing superconducting coplanar waveguide lowpass filter agree to within 0.3 dB in magnitude and 0.5 radians in phase. Extracted values for penetration depth and real part of the conductivity of the superconducting film are within 10 percent of other researchers' findings.
Niobium superconducting rf cavity fabrication by electrohydraulic forming
Directory of Open Access Journals (Sweden)
E. Cantergiani
2016-11-01
Full Text Available Superconducting rf (SRF cavities are traditionally fabricated from superconducting material sheets or made of copper coated with superconducting material, followed by trim machining and electron-beam welding. An alternative technique to traditional shaping methods, such as deep-drawing and spinning, is electrohydraulic forming (EHF. In EHF, half-cells are obtained through ultrahigh-speed deformation of blank sheets, using shockwaves induced in water by a pulsed electrical discharge. With respect to traditional methods, such a highly dynamic process can yield interesting results in terms of effectiveness, repeatability, final shape precision, higher formability, and reduced springback. In this paper, the first results of EHF on high purity niobium are presented and discussed. The simulations performed in order to master the multiphysics phenomena of EHF and to adjust its process parameters are presented. The microstructures of niobium half-cells produced by EHF and by spinning have been compared in terms of damage created in the material during the forming operation. The damage was assessed through hardness measurements, residual resistivity ratio (RRR measurements, and electron backscattered diffraction analyses. It was found that EHF does not worsen the damage of the material during forming and instead, some areas of the half-cell have shown lower damage compared to spinning. Moreover, EHF is particularly advantageous to reduce the forming time, preserve roughness, and to meet the final required shape accuracy.
Niobium superconducting rf cavity fabrication by electrohydraulic forming
Cantergiani, E.; Atieh, S.; Léaux, F.; Perez Fontenla, A. T.; Prunet, S.; Dufay-Chanat, L.; Koettig, T.; Bertinelli, F.; Capatina, O.; Favre, G.; Gerigk, F.; Jeanson, A. C.; Fuzeau, J.; Avrillaud, G.; Alleman, D.; Bonafe, J.; Marty, P.
2016-11-01
Superconducting rf (SRF) cavities are traditionally fabricated from superconducting material sheets or made of copper coated with superconducting material, followed by trim machining and electron-beam welding. An alternative technique to traditional shaping methods, such as deep-drawing and spinning, is electrohydraulic forming (EHF). In EHF, half-cells are obtained through ultrahigh-speed deformation of blank sheets, using shockwaves induced in water by a pulsed electrical discharge. With respect to traditional methods, such a highly dynamic process can yield interesting results in terms of effectiveness, repeatability, final shape precision, higher formability, and reduced springback. In this paper, the first results of EHF on high purity niobium are presented and discussed. The simulations performed in order to master the multiphysics phenomena of EHF and to adjust its process parameters are presented. The microstructures of niobium half-cells produced by EHF and by spinning have been compared in terms of damage created in the material during the forming operation. The damage was assessed through hardness measurements, residual resistivity ratio (RRR) measurements, and electron backscattered diffraction analyses. It was found that EHF does not worsen the damage of the material during forming and instead, some areas of the half-cell have shown lower damage compared to spinning. Moreover, EHF is particularly advantageous to reduce the forming time, preserve roughness, and to meet the final required shape accuracy.
Efficient Measurement of Superconducting Resonators
Sendelbach, Steven; Stoutimore, Micah; Strong, Josh; Naaman, Ofer; Campbell, Brooks; Martinis, John
2014-03-01
S-parameter measurements of high-Q superconducting resonators at single-photon drive powers often require significant averaging with associated long acquisition time. We have developed a procedure for optimizing the frequency sweep-plan of the measurement, and found that an appropriate choice of frequencies has a significant impact on its efficiency. An optimized sweep-plan design offers up to a factor of two reduction in the variance of extracted parameters, in comparison to a linear sweep-plan having the same total acquisition time. We experimentally compare the performance of the optimized and linear sweeps in measurements of high-Q aluminum CPW resonators.
Overview on superconducting photoinjectors
Directory of Open Access Journals (Sweden)
A. Arnold
2011-02-01
Full Text Available The success of most of the proposed energy recovery linac (ERL based electron accelerator projects for future storage ring replacements (SRR and high power IR–free-electron lasers (FELs largely depends on the development of an appropriate source. For example, to meet the FEL specifications [J. W. Lewellen, Proc. SPIE Int. Soc. Opt. Eng. 5534, 22 (2004PSISDG0277-786X10.1117/12.557378] electron beams with an unprecedented combination of high brightness, low emittance (0.1 μmrad, and high average current (hundreds of mA are required. An elegant way to create a beam of such quality is to combine the high beam quality of a normal conducting rf photoinjector with the superconducting technology, i.e., to build a superconducting rf photoinjector (SRF gun. SRF gun R&D programs based on different approaches have been launched at a growing number of institutes and companies (AES, Beijing University, BESSY, BNL, DESY, FZD, TJNAF, Niowave, NPS, Wisconsin University. Substantial progress was achieved in recent years and the first long term operation was demonstrated at FZD [R. Xiang et al., in Proceedings of the 31st International Free Electron Laser Conference (FEL 09, Liverpool, UK (STFC Daresbury Laboratory, Warrington, 2009, p. 488]. In the near future SRF guns are expected to play an important role for linac-driven FEL facilities. In this paper we will review the concepts, the design parameters, and the status of the major SRF gun projects.
Frontiers in Superconducting Materials
Narlikar, Anant V
2005-01-01
Frontiers in Superconducting Materials gives a state-of-the-art report of the most important topics of the current research in superconductive materials and related phenomena. It comprises 30 chapters written by renowned international experts in the field. It is of central interest to researchers and specialists in Physics and Materials Science, both in academic and industrial research, as well as advanced students. It also addresses electronic and electrical engineers. Even non-specialists interested in superconductivity might find some useful answers.
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.
Amini Sabegh, Z.; Vafafard, A.; Maleki, M. A.; Mahmoudi, M.
2015-08-01
We study the interaction of the microwave fields with an array of superconducting phase quantum circuits. It is shown that the different four-level configurations i.e. cascade, N-type, diamond, Y-type and inverted Y-type systems can be obtained in the superconducting phase quantum circuits by keeping the third order of the Josephson junction potential expansion whereas by dropping the third order term, just the cascade configuration can be established. We study the propagation and amplification of a microwave field in a four-level cascade quantum system, which is realized in an array of superconducting phase quantum circuits. We find that by increasing the microwave pump tones feeding the system, the normal dispersion switches to the anomalous and the gain-assisted superluminal microwave propagation is obtained in an array of many superconducting phase quantum circuits. Moreover, it is demonstrated that the stimulated microwave field is generated via four-wave mixing without any inversion population in the energy levels of the system (amplification without inversion) and the group velocity of the generated pulse can be controlled by the external oscillating magnetic fluxes. We also show that in some special set of parameters, the absorption-free superluminal generated microwave propagation is obtained in superconducting phase quantum circuit system.
Canko, Osman; Keskin, Mustafa
Analytical expressions of the order parameters near the transition temperatures in the spin-3/2 Ising system with bilinear (J) and biquadratic (K) interactions are presented for various values of J/K. First, we obtain the free energy expression and the equations to determine order parameters by using the mean-field approximation. Then, the order parameters are expressed in the vicinity of the transition temperatures in which these expressions are very important to study the dynamics of the system by means of Onsager's theory of irreversible thermodynamics. Hence, we investigate the phase transitions occurring in the system and also obtain two tricritical points analytically. Finally, the specific heat and magnetic susceptibility are calculated and an argument about the critical exponents at the second-order phase transitions and tricritical points is given.
Fundamentals of Superconducting Nanoelectronics
Sidorenko, Anatolie
2011-01-01
This book demonstrates how the new phenomena in superconductivity on the nanometer scale (FFLO state, triplet superconductivity, Crossed Andreev Reflection, synchronized generation etc.) serve as the basis for the invention and development of novel nanoelectronic devices and systems. It demonstrates how rather complex ideas and theoretical models, like odd-pairing, non-uniform superconducting state, pi-shift etc., adequately describe the processes in real superconducting nanostructues and novel devices based on them. The book is useful for a broad audience of readers, researchers, engineers, P
Feedback Control of Loaded Q Values of the Superconducting Cavities at FLASH
Cichalewski, W.; Branlard, J.; Schlarb, H.; Carwardine, J.; Napieralski, A.
2013-12-01
The well-established technology of superconducting niobium cavities (TESLA - TeV-Energy Superconducting Linear Accelerator) finds an increasing number of applications for linear accelerators in high-energy physics experiments. Together with cavity design and manufacturing, control systems for accelerating field parameters were developed. The digital control system developed for cryomodule operation at the Free Electron Laser in Hamburg (FLASH) is able to perform field amplitude and phase regulation with the precision requested for the multiple user experiments carried at FLASH and according to the required laser light parameters. While new experiments (like the International Linear Collider or the European X-FEL) are based on the same technology (and similar control systems), they require additional levels of controlling superconducting structures parameters in order to comply with tighter power budget overheads and finer field regulation requirements. Consequently, the possibility of controlling such parameters as cavity loaded quality factor or resonance frequency is becoming more attractive. The necessity and the benefits of regulating these parameters have been described in and . In this paper, we describe the algorithm for feedback control of the loaded Q in TESLA cavities by means of motor control of the fundamental power coupler.
Magnetic levitation force between a superconducting bulk magnet and a permanent magnet
Wang, J. J.; He, C. Y.; Meng, L. F.; Li, C.; Han, R. S.; Gao, Z. X.
2002-01-01
The current density in a disk-shaped superconducting bulk magnet and the magnetic levitation force exerted on the superconducting bulk magnet by a cylindrical permanent magnet are calculated from first principles. The effect of the superconducting parameters of the superconducting bulk is taken into account by assuming the voltage-current law and the material law. The magnetic levitation force is dominated by the remnant current density, which is induced by switching off the applied magnetizi...
Directory of Open Access Journals (Sweden)
Grzegorz Tarczyński
2012-01-01
Full Text Available The paper presents an analysis of the impact of the number of picking aisles, slots in a rack, the size of pick lists, and the routing method on the performance of the order picking process. In the analysis, the forklift truck's maneuvers such as turns back and turns aside, omitted by some scientists, are considered. Although only random storage assignment is examined in this paper, the possible congestion effect is considered. Experiments were performed by the use of simulations. (original abstract
Barnes, G J
2000-01-01
are clearly revealed. Once this has been achieved, further studies indicate the most desirable parameters which are expected to optimise the performance. In recent years, the possibility of incorporating type-ll superconducting materials into engineering power applications such as motors, generators, bearings and levitation systems has attracted much attention. However, in order to fully develop the potential of using these relatively new materials in such applications, suitable computational modelling is required. The aim of the research presented in this thesis was to further the development of electrical machines incorporating high temperature superconductors (HTSs) by formulating and then implementing mathematical models. After identifying and justifying necessary assumptions, two such models are developed: the first deriving from the ideas of fluxon motion leading to a finite difference scheme, and the second deriving from more fundamental macroscopic ideas of induced currents leading to a finite element...
Quantum acoustics with superconducting qubits
Chu, Yiwen; Kharel, Prashanta; Renninger, William H.; Burkhart, Luke D.; Frunzio, Luigi; Rakich, Peter T.; Schoelkopf, Robert J.
2017-10-01
Mechanical objects have important practical applications in the fields of quantum information and metrology as quantum memories or transducers for measuring and connecting different types of quantum systems. The field of electromechanics is in pursuit of a robust and highly coherent device that couples motion to nonlinear quantum objects such as superconducting qubits. Here, we experimentally demonstrate a high-frequency bulk acoustic wave resonator that is strongly coupled to a superconducting qubit using piezoelectric transduction with a cooperativity of 260. We measure qubit and mechanical coherence times on the order of 10 microseconds. Our device requires only simple fabrication methods and provides controllable access to a multitude of phonon modes. We demonstrate quantum control and measurement on gigahertz phonons at the single-quantum level.
Energy Technology Data Exchange (ETDEWEB)
1979-01-01
The purpose of this project is to investigate the suitability of using a superconducting fault current limiter (SCFCL) in conjunction with other superconducting apparatus or transmission lines. Literature search, consultation, analysis and experimentation are to be carried out to derive a set of operational parameters for a SCFCL and to answer key questions as to the feasibility of a superconducting element to meet these performance objectives. During the first quarter year of effort, substantial progress has been made on several of these program tasks. A comprehensive search of the literature on SCFCL devices and applications was initiated; the references which were obtained to date are evaluated within a framework into which additional references can be added as they are received. Consultation with key researchers has occurred to supplement and update the literature search. Device analyses have also been started in order to determine to what extent the various proposed SCFCL devices meet the requirements of the power system.
Pressure induced Superconductivity in the Charge Density Wave Compound Tritelluride
Energy Technology Data Exchange (ETDEWEB)
Hamlin, J.J.; Zocco, D.A.; Sayles, T.A.; Maple, M.B.; /UC, Davis; Chu, J.-H.; Fisher, I.R.; /Stanford U., Geballe Lab.
2010-02-15
A series of high-pressure electrical resistivity measurements on single crystals of TbTe{sub 3} reveal a complex phase diagram involving the interplay of superconducting, antiferromagnetic and charge density wave order. The onset of superconductivity reaches a maximum of almost 4 K (onset) near {approx} 12.4 GPa.
Extreme sensitivity of superconductivity to stoichiometry in Fe1+?Se
McQueen, T.M.; Huang, Q.; Ksenofontov, V.; Felser, C.; Xu, Q.; Zandbergen, H.; Hor, Y.S.; Allred, J.; Williams, A.J.; Qu, D.; Checkelsky, J.; Ong, N.P.; Cava, R.J.
2009-01-01
The recently discovered iron arsenide superconductors appear to display a universal set of characteristic features, including proximity to a magnetically ordered state and robustness of the superconductivity in the presence of disorder. Here we show that superconductivity in Fe1+?Se, which can be
DEFF Research Database (Denmark)
Chang, J.; Blackburn, E.; Holmes, A. T.
2012-01-01
Superconductivity often emerges in the proximity of, or in competition with, symmetry-breaking ground states such as antiferromagnetism or charge density waves (CDW). A number of materials in the cuprate family, which includes the high transition-temperature (high-Tc) superconductors, show spin a...... scales, and the high-Tc superconductivity forms from a pre-existing CDW environment. Our results provide a mechanism for the formation of small Fermi surface pockets, which explain the negative Hall and Seebeck effects and the ‘Tc plateau’ in this material when underdoped.......Superconductivity often emerges in the proximity of, or in competition with, symmetry-breaking ground states such as antiferromagnetism or charge density waves (CDW). A number of materials in the cuprate family, which includes the high transition-temperature (high-Tc) superconductors, show spin...
The relationship of structure to superconductivity in the Pr-Ba-Cu-O system
Energy Technology Data Exchange (ETDEWEB)
Minseo, Park [Iowa State Univ., Ames, IA (United States)
1994-05-10
The relation of structure to lack of superconductivity in Pr-Ba-Cu-O was systematically investigated. First, the phase equilibria of this system was studied to find the processing parameters which maximize the cation-site ordering between Pr and Ba ions. Second, a comparative study between superconducting Nd-Ba-Cu-0 and non- superconducting Pr-Ba-Cu-0 was performed by forming solid-solution Nd- Pr-Ba-Cu-0. The relation between structure and superconductivity in Ndb_{1-x}Pr_{x}Ba_{2}Cu_{3}O_{7-δ} is investigated. T_{c} decreases monotonically with increasing x and superconductivity disappears at around x=0.3-0.4. T_{c} is enhanced by 10K when the sample is processed at an oxygen partial pressure (PO_{2}) of 0.01 atm, followed by oxygenation at 450C. Depression of (T_{c}) as a function of x and PO _{2} is explained in terms of a charge-transfer model. It is suggested that destruction of superconductivity in the RE_{1-x}Pr_{x}Ba_{2}CU_{3}O_{7-δ} (RE=rare-earth) system can be viewed as disruption of four-fold planar coordinated Cu ions in the chain-site due to permanent occupation of extra Pr ions on Ba sites.
Gaillard, Pierre
2015-04-01
In this paper, we construct new deformations of the Akhmediev-Peregrine (AP) breather of order N (or APN breather) with 2N-2 real parameters. Other families of quasirational solutions of the nonlinear Schrödinger (NLS) equation are obtained. We evaluate the highest amplitude of the modulus of the AP breather of order N; we give the proof that the highest amplitude of the APN breather is equal to 2N+1. We get new formulas for the solutions of the NLS equation, which are different from these already given in previous works. New solutions for the order 8 and their deformations according to the parameters are explicitly given. We simultaneously get triangular configurations and isolated rings. Moreover, the appearance for certain values of the parameters and of new configurations of concentric rings are underscored.
Superconducting cavities for LEP
CERN PhotoLab
1983-01-01
Above: a 350 MHz superconducting accelerating cavity in niobium of the type envisaged for accelerating electrons and positrons in later phases of LEP. Below: a small 1 GHz cavity used for investigating the surface problems of superconducting niobium. Albert Insomby stays on the right. See Annual Report 1983 p. 51.
Academic training: Applied superconductivity
2007-01-01
LECTURE SERIES 17, 18, 19 January from 11.00 to 12.00 hrs Council Room, Bldg 503 Applied Superconductivity : Theory, superconducting Materials and applications E. PALMIERI/INFN, Padova, Italy When hearing about persistent currents recirculating for several years in a superconducting loop without any appreciable decay, one realizes that we are dealing with a phenomenon which in nature is the closest known to the perpetual motion. Zero resistivity and perfect diamagnetism in Mercury at 4.2Â K, the breakthrough during 75 years of several hundreds of superconducting materials, the revolution of the "liquid Nitrogen superconductivity"; the discovery of still a binary compound becoming superconducting at 40 K and the subsequent re-exploration of the alreadyÂ known superconducting materials: Nature discloses drop by drop its intimate secrets and nobody can exclude that the last final surprise must still come. After an overview ofÂ phenomenology and basic theory of superconductivity, the lectures for this a...
Bernard, Philippe
1999-01-01
It was 20 years ago when the research and development programme for LEP superconducting cavities was initiated. It lasted about 10 years. Today, my aim is not to tell you in great detail about the many innovations made thanks to our research, but I would like to point out some milestones in the development of superconducting cavities where Emilio's influence was particularly important.
Pérot, J
1981-01-01
Discusses the use of large superconducting magnets in the areas of particle physics, thermonuclear fusion, and magnetohydrodynamics. In addition to considering the physics of the superconducting state, the article considers machines such as BEBC (Big European Bubble Chamber) at CERN, the LINAC at SLAC and possible Tokamak applications. The future application of superconductors to high speed trains is discussed. (0 refs).
Superconducting wind turbine generators
DEFF Research Database (Denmark)
Abrahamsen, Asger Bech; Mijatovic, Nenad; Seiler, Eugen
2010-01-01
We have examined the potential of 10 MW superconducting direct drive generators to enter the European offshore wind power market and estimated that the production of about 1200 superconducting turbines until 2030 would correspond to 10% of the EU offshore market. The expected properties of future......, the main challenge of the superconducting direct drive technology is to prove that the reliability is superior to the alternative drive trains based on gearboxes or permanent magnets. A strategy of successive testing of superconducting direct drive trains in real wind turbines of 10 kW, 100 kW, 1 MW and 10...... offshore turbines of 8 and 10 MW have been determined from an up-scaling of an existing 5 MW turbine and the necessary properties of the superconducting drive train are discussed. We have found that the absence of the gear box is the main benefit and the reduced weight and size is secondary. However...
Directory of Open Access Journals (Sweden)
M.P. Kozlovskii
2010-01-01
Full Text Available The present work is devoted to the investigation of the 3D Ising-like model in the presence of an external field in the vicinity of critical point. The method of collective variables is used. General expressions for the order parameter and susceptibility are calculated as functions of temperature and the external field as well as scaling functions of that are explicitly obtained. The results are compared with the ones obtained within the framework of parametric representation of the equation of state and Monte Carlo simulations. New expression for the exit point from critical regime of the order parameter fluctuations is proposed and used for the calculation.
Angle-resolved photoemission studies of the superconducting gap symmetry in Fe-based superconductors
Directory of Open Access Journals (Sweden)
Y.-B. Huang
2012-12-01
Full Text Available The superconducting gap is the fundamental parameter that characterizes the superconducting state, and its symmetry is a direct consequence of the mechanism responsible for Cooper pairing. Here we discuss about angle-resolved photoemission spectroscopy measurements of the superconducting gap in the Fe-based high-temperature superconductors. We show that the superconducting gap is Fermi surface dependent and nodeless with small anisotropy, or more precisely, a function of the momentum location in the Brillouin zone. We show that while this observation seems inconsistent with weak coupling approaches for superconductivity in these materials, it is well supported by strong coupling models and global superconducting gaps. We also suggest that a smaller lifetime of the superconducting Cooper pairs induced by the momentum dependent interband scattering inherent to these materials could affect the residual density of states at low energies, which is critical for a proper evaluation of the superconducting gap.
Beam heat load in superconducting wigglers
Casalbuoni, S.
2013-04-22
The beam heat load is a fundamental input parameter for the design of superconducting wigglers since it is needed to specify the cooling power. In this presentation I will review the possible beam heat load sources and the measurements of beam heat load performed and planned onto the cold vacuum chambers installed at different synchrotron light sources.
Attenuation in Superconducting Circular Waveguides
Directory of Open Access Journals (Sweden)
K. H. Yeap
2016-09-01
Full Text Available We present an analysis on wave propagation in superconducting circular waveguides. In order to account for the presence of quasiparticles in the intragap states of a superconductor, we employ the characteristic equation derived from the extended Mattis-Bardeen theory to compute the values of the complex conductivity. To calculate the attenuation in a circular waveguide, the tangential fields at the boundary of the wall are first matched with the electrical properties (which includes the complex conductivity of the wall material. The matching of fields with the electrical properties results in a set of transcendental equations which is able to accurately describe the propagation constant of the fields. Our results show that although the attenuation in the superconducting waveguide above cutoff (but below the gap frequency is finite, it is considerably lower than that in a normal waveguide. Above the gap frequency, however, the attenuation in the superconducting waveguide increases sharply. The attenuation eventually surpasses that in a normal waveguide. As frequency increases above the gap frequency, Cooper pairs break into quasiparticles. Hence, we attribute the sharp rise in attenuation to the increase in random collision of the quasiparticles with the lattice structure.
Oxide-based platform for reconfigurable superconducting nanoelectronics.
Veazey, Joshua P; Cheng, Guanglei; Irvin, Patrick; Cen, Cheng; Bogorin, Daniela F; Bi, Feng; Huang, Mengchen; Bark, Chung-Wung; Ryu, Sangwoo; Cho, Kwang-Hwan; Eom, Chang-Beom; Levy, Jeremy
2013-09-20
We report quasi-1D superconductivity at the interface of LaAlO3 and SrTiO3. The material system and nanostructure fabrication method supply a new platform for superconducting nanoelectronics. Nanostructures having line widths w ~ 10 nm are formed from the parent two-dimensional electron liquid using conductive atomic force microscope lithography. Nanowire cross-sections are small compared to the superconducting coherence length in LaAlO3/SrTiO3, placing them in the quasi-1D regime. Broad superconducting transitions versus temperature and finite resistances in the superconducting state well below Tc ≈ 200 mK are observed, suggesting the presence of fluctuation- and heating-induced resistance. The superconducting resistances and V-I characteristics are tunable through the use of a back gate. Four-terminal resistances in the superconducting state show an unusual dependence on the current path, varying by as much as an order of magnitude. This new technology, i.e., the ability to 'write' gate-tunable superconducting nanostructures on an insulating LaAlO3/SrTiO3 'canvas', opens possibilities for the development of new families of reconfigurable superconducting nanoelectronics.
Quantum Memristors with Superconducting Circuits.
Salmilehto, J; Deppe, F; Di Ventra, M; Sanz, M; Solano, E
2017-02-14
Memristors are resistive elements retaining information of their past dynamics. They have garnered substantial interest due to their potential for representing a paradigm change in electronics, information processing and unconventional computing. Given the advent of quantum technologies, a design for a quantum memristor with superconducting circuits may be envisaged. Along these lines, we introduce such a quantum device whose memristive behavior arises from quasiparticle-induced tunneling when supercurrents are cancelled. For realistic parameters, we find that the relevant hysteretic behavior may be observed using current state-of-the-art measurements of the phase-driven tunneling current. Finally, we develop suitable methods to quantify memory retention in the system.
Wysokiński, Marcin M; Kaczmarczyk, Jan
2017-03-01
We investigate the effect of the electron-hole (e-h) symmetry breaking on d-wave superconductivity induced by non-local effects of correlations in the generalized Hubbard model. The symmetry breaking is introduced in a two-fold manner: by the next-to-nearest neighbor hopping of electrons and by the charge-bond interaction-the off-diagonal term of the Coulomb potential. Both terms lead to a pronounced asymmetry of the superconducting order parameter. The next-to-nearest neighbor hopping enhances superconductivity for h-doping, while diminishes it for e-doping. The charge-bond interaction alone leads to the opposite effect and, additionally, to the kinetic-energy gain upon condensation in the underdoped regime. With both terms included, with similar amplitudes, the height of the superconducting dome and the critical doping remain in favor of h-doping. The influence of the charge-bond interaction on deviations from [Formula: see text] symmetry of the shape of the gap at the Fermi surface in the momentum space is briefly discussed.
Ogata, M.; Matsue, H.; Yamashita, T.; Hasegawa, H.; Nagashima, K.; Maeda, T.; Matsuoka, T.; Mukoyama, S.; Shimizu, H.; Horiuchi, S.
2016-05-01
Energy storage systems are necessary for renewable energy sources such as solar power in order to stabilize their output power, which fluctuates widely depending on the weather. Since ‘flywheel energy storage systems’ (FWSSs) do not use chemical reactions, they do not deteriorate due to charge or discharge. This is an advantage of FWSSs in applications for renewable energy plants. A conventional FWSS has capacity limitation because of the mechanical bearings used to support the flywheel. Therefore, we have designed a superconducting magnetic bearing composed of a superconducting coil stator and a superconducting bulk rotor in order to solve this problem, and have experimentally manufactured a large scale FWSS with a capacity of 100 kWh and an output power of 300 kW. The superconducting magnetic bearing can levitate 4 tons and enables the flywheel to rotate smoothly. A performance confirmation test will be started soon. An overview of the superconducting FWSS is presented in this paper.
1984-10-09
Order Statistics. Wiley. 12] Epstein, S. S., M. Small, J. Kaplan and N. Mantel (1963). Photodynamic bioassays of benzo(a)pyrene using paramecium ... caudatum . Jour. Natl. Cancer Inst., 31: 163-168. [3] Epstein, S. S., E. Savicki and H. L. Falk (1965). Photodynamic bioassay of polycyclic atmospheric
Loops and Strings in a Superconducting Lattice Gauge Simulator.
Brennen, G K; Pupillo, G; Rico, E; Stace, T M; Vodola, D
2016-12-09
We propose an architecture for an analog quantum simulator of electromagnetism in 2+1 dimensions, based on an array of superconducting fluxonium devices. The encoding is in the integer (spin-1) representation of the quantum link model formulation of compact U(1) lattice gauge theory. We show how to engineer Gauss' law via an ancilla mediated gadget construction, and how to tune between the strongly coupled and intermediately coupled regimes. The witnesses to the existence of the predicted confining phase of the model are provided by nonlocal order parameters from Wilson loops and disorder parameters from 't Hooft strings. We show how to construct such operators in this model and how to measure them nondestructively via dispersive coupling of the fluxonium islands to a microwave cavity mode. Numerical evidence is found for the existence of the confined phase in the ground state of the simulation Hamiltonian on a ladder geometry.
Loops and Strings in a Superconducting Lattice Gauge Simulator
Brennen, G. K.; Pupillo, G.; Rico, E.; Stace, T. M.; Vodola, D.
2016-12-01
We propose an architecture for an analog quantum simulator of electromagnetism in 2 +1 dimensions, based on an array of superconducting fluxonium devices. The encoding is in the integer (spin-1) representation of the quantum link model formulation of compact U (1 ) lattice gauge theory. We show how to engineer Gauss' law via an ancilla mediated gadget construction, and how to tune between the strongly coupled and intermediately coupled regimes. The witnesses to the existence of the predicted confining phase of the model are provided by nonlocal order parameters from Wilson loops and disorder parameters from 't Hooft strings. We show how to construct such operators in this model and how to measure them nondestructively via dispersive coupling of the fluxonium islands to a microwave cavity mode. Numerical evidence is found for the existence of the confined phase in the ground state of the simulation Hamiltonian on a ladder geometry.
Energy Technology Data Exchange (ETDEWEB)
Hao, L. [Department of Physics, Tohoku University, Aramaki-aza-aoba, Aoba-ku, Sendai 980-8578 (Japan); Iwasa, K. [Department of Physics, Tohoku University, Aramaki-aza-aoba, Aoba-ku, Sendai 980-8578 (Japan)]. E-mail: iwasa@iiyo.phys.tohoku.ac.jp; Kuwahara, K. [Department of Physics, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397 (Japan); Kohgi, M. [Department of Physics, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397 (Japan); Sugawara, H. [Department of Mathematical and Natural Sciences, Tokushima University Tokushima 770-8502 (Japan); Aoki, Y. [Department of Physics, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397 (Japan); Sato, H. [Department of Physics, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397 (Japan); Matsuda, T.D. [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai 319-119 (Japan); Mignot, J.-M. [Laboratoire Leon Brillouin, CEA-CRNS, CEA/Saclay, 91191 Gif sur Yvette Cedex (France); Gukasov, A. [Laboratoire Leon Brillouin, CEA-CRNS, CEA/Saclay, 91191 Gif sur Yvette Cedex (France); Nishi, M. [Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581 (Japan)
2005-04-30
The order parameters in the antiferro-quadrupolar (AFQ) ordered phase of PrFe{sub 4}P{sub 12} have been investigated by polarized neutron diffraction measurement. By observing the interference effect of scattering amplitudes from the Fe-ion displacement and the antiferromagnetic component induced by the magnetic field applied along the [0,0,1] axis, we conclude that the dominant ordered quadrupole is O{sub 2}{sup 0} in the low-temperature phase. By inelastic neutron scattering experiment for a single-crystal sample, we observed sharp magnetic excitations in the AFQ-ordered phase, whose maximum intensity appears at the Brillouin zone center and minimum at the zone boundary. This fact indicates the existence of ferromagnetic correlation between Pr ions in the AFQ-ordered phase.
Directory of Open Access Journals (Sweden)
Chaojun Wu
2015-01-01
Full Text Available An efficient approach of inverse optimal control and adaptive control is developed for global asymptotic stabilization of a novel fractional-order four-wing hyperchaotic system with uncertain parameter. Based on the inverse optimal control methodology and fractional-order stability theory, a control Lyapunov function (CLF is constructed and an adaptive state feedback controller is designed to achieve inverse optimal control of a novel fractional-order hyperchaotic system with four-wing attractor. Then, an electronic oscillation circuit is designed to implement the dynamical behaviors of the fractional-order four-wing hyperchaotic system and verify the satisfactory performance of the controller. Comparing with other fractional-order chaos control methods which may have more than one nonlinear state feedback controller, the inverse optimal controller has the advantages of simple structure, high reliability, and less control effort that is required and can be implemented by electronic oscillation circuit.
Microwave mode structure of superconducting metamaterial resonators
Wang, Haozhi; Rouxinol, Francisco; Lahaye, Matthew; Plourde, Britton
2015-03-01
Arrays of lumped circuit elements can be used to form metamaterial resonant structures that exhibit novel behavior compared to resonators made from conventional distributed transmission lines. By engineering the parameters and configurations of the lumped elements composing the unit cell of such a metamaterial resonator, one can generate spectra with wide stop-bands as well as pass-bands with dense microwave modes. If the metamaterials are fabricated from superconducting traces, the losses can be low enough to allow for these dense modes to be resolved and potentially coupled to quantum systems, such as superconducting qubits. We will present our low-temperature measurements of a variety of superconducting metamaterial resonators and we will compare these with numerical simulations of the microwave properties.
Material Specific Design for Room Temperature Superconductivity
Isikaku-Ironkwe, O.-Paul; Ofe, Uko; Oriaku, Chijioke; Asiegbu, Dan; Oguzi, Emeka
2012-02-01
The transition temperature, Tc, of superconductors has been increased sevenfold from 23K in Nb3Ge to 164K in Hg-1223. A further two-fold increase would get us to above room temperature superconductivity. Studying high temperature superconductors (HTSCs), we have developed a formula that expresses Tc in terms of electronegativity, valence electrons, Ne, atomic number, Z, formula mass and a coupling constant, Ko. We observe an increasing linear relationship between Tc and Ko. Ko also correlates with formula mass and atomic number and the number of atoms in the compound. By our formula, Hg-1223 has Ko = 70. We propose, using our design algorithm, that room temperature superconductivity may be realized in a system with ko = 160; electronegativity = 2.5, Ne/Sqrt Z = 0.8. We proceed to show combinations of oxides and elements that will yield the required parameters for synthesizing reproducible room temperature superconductivity.
Superconducting state parameters of ternary metallic glasses
Indian Academy of Sciences (India)
Administrator
pseudopotential to ternary metallic glasses involves the assumption of pseudoions with average properties, which are assumed to replace three types of ions in the ternary systems, and a gas of free electrons is assumed to perme- ate through them. The electron–pseudoion is accounted by the pseudopotential, and the ...
Directory of Open Access Journals (Sweden)
Meiqiang Feng
2014-01-01
Full Text Available The author considers an impulsive boundary value problem involving the one-dimensional p-Laplacian -(φp (u′′=λωtft,u, 00 and μ>0 are two parameters. Using fixed point theories, several new and more general existence and multiplicity results are derived in terms of different values of λ>0 and μ>0. The exact upper and lower bounds for these positive solutions are also given. Moreover, the approach to deal with the impulsive term is different from earlier approaches. In this paper, our results cover equations without impulsive effects and are compared with some recent results by Ding and Wang.
Intrinsic superconductivity in ABA-stacked trilayer graphene
Directory of Open Access Journals (Sweden)
Haiwen Liu
2012-12-01
Full Text Available We study the phonon-mediated superconductivity in light doped ABA-stacked trilayer graphene system by means of two theoretical models. We find superconducting transition temperature TC can be greatly enlarged by tuning the Fermi energy away from neutral point. Utilizing realistic parameters, we find Tc is approximately 1 K even under weak doping condition EF = 0.1 eV. Specifically, we give out the analytical expression for superconductivity gap △ and superconducting transition temperature Tc for negative-U Hubbard model. Further, we consider the thermal fluctuation and calculate the Berezinskii-Kosterlitz-Thouless critical temperature TBKT. Besides, we consider a two-band BCS model in comparision with the negative-U Hubbard model. The results for both models are qualitatively consistent. Our study provides a promising possibility for realizing intrinsic superconductivity in multilayer graphene systems.
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......We report on small-angle neutron scattering studies of the intrinsic vortex lattice (VL) structure in detwinned YBa2Cu3O7 at 2 K, and in fields up to 10.8 T. Because of the suppressed pinning to twin-domain boundaries, a new distorted hexagonal VL structure phase is stabilized at intermediate...
Energy Technology Data Exchange (ETDEWEB)
Bhattacharyay, A [Department of Chemistry, University of Warwick (United Kingdom)
2008-03-21
The mixed states of superconducting (SC) and normal (N) phases in one-dimensional systems are characterized by several phase slips and localization of the order parameter of the SC phase. The phenomenon is explained on the basis of a complex Ginzburg Landau (CGL) model. We present a simple analysis of the system on multiple scales to capture localization and phase slips when phases coexist. (fast track communication)
Superconducting permanent magnets
Energy Technology Data Exchange (ETDEWEB)
Wipf, S.L.; Laquer, H.L.
1989-03-01
The concept of superconducting permanent magnets with fields trapped in shells or cylinders of Type II superconductors is an old one. Unfortunately, the low values of 0.5 to 1T for the first flux jump field, which is independent of the actual current density, have frustrated its implementation with classical Type II superconductors. The fact that the flux jump fields for high temperature superconductors should be an order of magnitude larger at liquid nitrogen temperatures allows us to reconsider these options. Analysis of the hysteresis patterns, based on the critical state model, shows that, if the dimensions are chosen so that the sample is penetrated at a field B/sub p/, which is equal to or just less than the first flux jump field, B/sub fj/, a temporarily applied field of 2B/sub fj/ will trap 0.5 B/sub fj/. Thus for a 90 K superconductor with a B/sub fj/ of 6T, a permanent field of 3 T should be trapped, with an energy product of 1.8 MJ/m/sup 3/ (225 MG . Oe). This is five times as large as for the best permanent magnet materials. The authors discuss means to verify the analysis and the limitations imposed by the low critical current densities in presently available high temperature superconductors.
Superconducting micronets: A state-variable approach
Energy Technology Data Exchange (ETDEWEB)
Fink, H.J.; Haley, S.B. (Department of Electrical Engineering and Computer Science, University of California, Davis, Davis, California 95616 (USA))
1991-05-01
A state-variable formulation of the nonlinear Ginzburg-Landau equations for superconducting micronets is introduced. The state variables are the Cooper-pair density {ital N}, kinetic energy {ital E}, and the imaginary part {ital I} of the Cooper-pair momentum density {ital scrP}. Purely algebraic relations among the state variables are derived, and several fundamental properties of micronets are proven. The current density {ital J}=Re{ital scrP} is given by {ital J}{sup 2}={ital NE}{minus}{ital I}{sup 2}, where {ital I}=Im{ital scrP}. For the limit {ital N}{much lt}1, a quasilinear theory yields the superfluid velocity {ital Q} as the only relevant transport parameter at the phase-transition boundary. Applying the full nonlinear theory, the maximum supercurrent that can be injected into a microladder is calculated as a function of normalized nodal spacing {ital scrL}/{xi}({ital T}) and magnetic flux {phi} for low magnetic fields, where {xi}({ital T}) is the temperature-dependent coherence length. The critical current {ital J}{sub {ital c}} approaches zero at a new temperature-critical flux boundary, {phi}{sub {ital c}1}({ital T}), which is first order and distinct from the second-order phase-transition boundary, {phi}{sub {ital c}2}({ital T}).
High specific heat superconducting composite
Steyert, Jr., William A.
1979-01-01
A composite superconductor formed from a high specific heat ceramic such as gadolinium oxide or gadolinium-aluminum oxide and a conventional metal conductor such as copper or aluminum which are insolubly mixed together to provide adiabatic stability in a superconducting mode of operation. The addition of a few percent of insoluble gadolinium-aluminum oxide powder or gadolinium oxide powder to copper, increases the measured specific heat of the composite by one to two orders of magnitude below the 5.degree. K. level while maintaining the high thermal and electrical conductivity of the conventional metal conductor.
Superconductivity fundamentals and applications
Buckel, Werner
2004-01-01
This is the second English edition of what has become one of the definitive works on superconductivity in German -- currently in its sixth edition. Comprehensive and easy to understand, this introductory text is written especially with the non-specialist in mind. The authors, both long-term experts in this field, present the fundamental considerations without the need for extensive mathematics, describing the various phenomena connected with the superconducting state, with liberal insertion of experimental facts and examples for modern applications. While all fields of superconducting phenomena are dealt with in detail, this new edition pays particular attention to the groundbreaking discovery of magnesium diboride and the current developments in this field. In addition, a new chapter provides an overview of the elements, alloys and compounds where superconductivity has been observed in experiments, together with their major characteristics. The chapter on technical applications has been considerably expanded...
Superconducting detectors in astronomy
Rahman, F.
2006-08-01
Radiation detectors based on superconducting phenomena are becoming increasingly important for observational astronomy. Recent developments in this important field, together with relevant background, are described here. After a general introduction to superconductivity and the field of superconductor-based radiation sensors, the main detector types are examined with regard to their physical form, operating principles and principal advantages. All major forms of superconducting detectors used in contemporary research such as tunnelling detectors, mixers, hot-electron bolometers and transition edge sensitive devices are discussed with an emphasis on how more recent developments are overcoming the shortcomings of the previous device generations. Also, discussed are new ideas in superconducting detector technology that may find applications in the coming years.
Superconducting metamaterial transmission line
Rouxinol, Francisco; Wang, Haozhi; Plourde, B. L. T.
2014-03-01
Left-handed metamaterials are artificial composite structures with unusual properties. Such systems have a wide range of potential applications in photonics. We are developing transmission lines composed of superconducting metamaterials using thin-film lumped circuit elements. Such structures allow for the possibility of generating novel transmission spectra with a high density of modes in some frequency ranges and stop-bands in others. We discuss possible couplings of these lines to superconducting qubits in circuit QED architectures.
Superconducting Wind Turbine Generators
Yunying Pan; Danhzen Gu
2016-01-01
Wind energy is well known as a renewable energy because its clean and less polluted characteristic, which is the foundation of development modern wind electricity. To find more efficient wind turbine is the focus of scientists around the world. Compared from conventional wind turbines, superconducting wind turbine generators have advantages at zero resistance, smaller size and lighter weight. Superconducting wind turbine will inevitably become the main trends in this area. This paper intends ...
Superconducting circuits for quantum information: an outlook.
Devoret, M H; Schoelkopf, R J
2013-03-08
The performance of superconducting qubits has improved by several orders of magnitude in the past decade. These circuits benefit from the robustness of superconductivity and the Josephson effect, and at present they have not encountered any hard physical limits. However, building an error-corrected information processor with many such qubits will require solving specific architecture problems that constitute a new field of research. For the first time, physicists will have to master quantum error correction to design and operate complex active systems that are dissipative in nature, yet remain coherent indefinitely. We offer a view on some directions for the field and speculate on its future.
One- and two-center ETF-integrals of first order in relativistic calculation of NMR parameters
Slevinsky, R. M.; Temga, T.; Mouattamid, M.; Safouhi, H.
2010-06-01
The present work focuses on the analytical and numerical developments of first-order integrals involved in the relativistic calculation of the shielding tensor using exponential-type functions as a basis set of atomic orbitals. For the analytical development, we use the Fourier integral transformation and practical properties of spherical harmonics and the Rayleigh expansion of the plane wavefunctions. The Fourier transforms of the operators were derived in previous work and they are used for analytical development. In both the one- and two-center integrals, Cauchy's residue theorem is used in the final developments of the analytical expressions, which are shown to be accurate to machine precision.
Superconducting transmission line particle detector
Gray, Kenneth E.
1989-01-01
A microvertex particle detector for use in a high energy physic collider including a plurality of parallel superconducting thin film strips separated from a superconducting ground plane by an insulating layer to form a plurality of superconducting waveguides. The microvertex particle detector indicates passage of a charged subatomic particle by measuring a voltage pulse measured across a superconducting waveguide caused by the transition of the superconducting thin film strip from a superconducting to a non-superconducting state in response to the passage of a charged particle. A plurality of superconducting thin film strips in two orthogonal planes plus the slow electromagnetic wave propogating in a superconducting transmission line are used to resolve N.sup.2 ambiguity of charged particle events.
Universal phase diagrams with superconducting domes for electronic flat bands
Löthman, Tomas; Black-Schaffer, Annica M.
2017-08-01
Condensed matter systems with flat bands close to the Fermi level generally exhibit, due to their very large density of states, extraordinarily high critical ordering temperatures of symmetry-breaking orders, such as superconductivity and magnetism. Here we show that the critical temperatures follow one of two universal curves with doping away from a flat band depending on the ordering channel, which completely dictates both the general order competition and the phase diagram. Notably, we find that orders in the particle-particle channel (superconducting orders) survive decisively farther than orders in the particle-hole channel (magnetic or charge orders) because the channels have fundamentally different polarizabilities. Thus, even if a magnetic or charge order initially dominates, superconducting domes are still likely to exist on the flanks of flat bands. We apply these general results to both the topological surface flat bands of rhombohedral ABC-stacked graphite and to the Van Hove singularity of graphene.
Superconducting Fullerene Nanowhiskers
Directory of Open Access Journals (Sweden)
Yoshihiko Takano
2012-04-01
Full Text Available We synthesized superconducting fullerene nanowhiskers (C_{60}NWs by potassium (K intercalation. They showed large superconducting volume fractions, as high as 80%. The superconducting transition temperature at 17 K was independent of the K content (x in the range between 1.6 and 6.0 in K-doped C_{60} nanowhiskers (K_{x}C_{60}NWs, while the superconducting volume fractions changed with x. The highest shielding fraction of a full shielding volume was observed in the material of K_{3.3}C_{60}NW by heating at 200 °C. On the other hand, that of a K-doped fullerene (K-C_{60} crystal was less than 1%. We report the superconducting behaviors of our newly synthesized K_{x}C_{60}NWs in comparison to those of K_{x}C_{60} crystals, which show superconductivity at 19 K in K_{3}C_{60}. The lattice structures are also discussed, based on the x-ray diffraction (XRD analyses.
Development of innovative superconducting DC power cable
Energy Technology Data Exchange (ETDEWEB)
Matsushita, Teruo; Kiuchi, Masaru [Dept. of Computer Science and Electronics Kyushu Institute of Technology, Iizuka (Japan)
2017-09-15
It is required to reduce the cost of superconducting cable to realize a superconducting DC power network that covers a wide area in order to utilize renewable energy. In this paper a new concept of innovative cable is introduced that can enhance the current-carrying capacity even though the same superconducting tape is used. Such a cable can be realized by designing an optimal winding structure in such a way that the angle between the tape and magnetic field becomes small. This idea was confirmed by preliminary experiments for a single layer model cable made of Bi-2223 tapes and REBCO coated conductors. Experiments of three and four layer cables of practical sizes were also done and it was found that the current-carrying capacity increased as theoretically predicted. If the critical current properties of commercial superconducting tapes are further improved in a parallel magnetic field, the enhancement will become pronounced and this technology will surely contribute to realization of superconducting DC power network.
Summer Course on the Science and Technology of Superconductivity
Gregory, W D; Mathews, W N; The science and technology of superconductivity
1973-01-01
Since the discovery of superconductivity in 1911 by H. Kamerlingh Onnes, of the order of half a billion dollars has been spent on research directed toward understanding and utiliz ing this phenomenon. This investment has gained us fundamental understanding in the form of a microscopic theory of superconduc tivity. Moreover, superconductivity has been transformed from a laboratory curiosity to the basis of some of the most sensitive and accurate measuring devices known, a whole host of other elec tronic devices, a soon-to-be new international standard for the volt, a prototype generation of superconducting motors and gener ators, and magnets producing the highest continuous magnetic fields yet produced by man. The promise of more efficient means of power transmission and mass transportation, a new generation of superconducting motors and generators, and computers and other electronic devices with superconducting circuit elements is all too clear. The realization of controlled thermonuclear fu...
Yokoyama, Sho; Kojima, Takashi; Kaga, Tatsushi; Ichikawa, Kazuo
2015-12-23
We report three asteroid hyalosis cases in which internal higher-order aberrations (HOAs) were improved concomitant with improved visual symptoms after vitrectomy. Cases 1 and 2 reported severe floaters and glare disability, although their visual acuities were fairly good. Case 3 showed poor visual acuity since this patient also suffered from mild macular degeneration. For these three asteroid hyalosis cases, we were unsure if treatment with vitrectomy could improve visual symptoms. Therefore, we measured internal HOAs with an aberrometer, and found that the internal HOA values in these cases were high. We suspected that internal high HOAs values were associated with visual disturbance, and performed vitrectomy. After the vitrectomy, the internal HOA values in these three asteroid hyalosis cases markedly decreased, and visual symptoms improved. These observations suggested that measurement of internal HOAs may be useful to determine the indication for vitrectomy. 2015 BMJ Publishing Group Ltd.
Impact of iron-site defects on superconductivity in LiFeAs
Aluru, R.; Wahl, P.; Chi, S.; Liang, R.; Hardy, W. N.; Bonn, D. A.; Kreisel, A.; Andersen, B. M.; Singh, U. R.; Nelson, R.; Berlijn, T.; Ku, W.; Hirschfeld, P. J.
In iron-based high temperature superconductors the symmetry of the order parameter still remains a controversial topic where for the same compound sign changing and non sign-changing order parameters have been proposed theoretically. Among the iron-based superconductors, LiFeAs takes a special role (together with FeSe) by being a stoichiometric superconductor, minimizing intrinsic scattering. Here, we study engineered iron-site defects in LiFeAs by low temperature scanning tunneling microscopy and spectroscopy (STM/STS). The tunneling spectra obtained on individual defects show signatures of impurity bound states. A detailed comparison of the tunneling spectra measured on impurities with theoretical simulations enables us to draw conclusions about the superconducting order parameter in LiFeAs. Studying Ni, Co, Mn impurities and native defects, we find a continuous evolution from negligible impurity bound states at the smaller gap edge to detectable states as the scattering potential increases.
Ramezanpour, B.; Mahmoudi Chenari, Hossein; Sadigh, M. Khadem
2017-11-01
In this work, undoped and Mn-doped PbS/PVA nanocomposite films have been successfully fabricated using the simple solution-casting method. Their crystalline structure was examined by X-ray powder diffraction (XRD). XRD pattern show the formation of cubic structure of PbS for Mn-doped PbS in PVA matrix. Microstructure parameters of Mn-doped PbS/PVA nanocomposite films were obtained through the size-strain plot (SSP) method. The thermal stability of the nanocomposite film was determined using Thermogravimetric analysis (TGA). Furthermore, Z-scan technique was used to investigate the optical nonlinearity of nanocomposite films by a continuous-wave laser irradiation at the wavelength of 655 nm. This experimental results show that undoped PbS/PVA nanocomposite films indicate high nonlinear absorption characteristics. Moreover, the nanocomposite films with easy preparation characteristics, high thermal stability and nonlinear absorption properties can be used as an active element in optics and photonic devices.
Robust determination of the superconducting gap sign structure via quasiparticle interference
Energy Technology Data Exchange (ETDEWEB)
Altenfeld, Dustin [Institut fuer Theoretische Physik III, Ruhr-Universitaet Bochum, D-44801 Bochum (Germany); Hirschfeld, Peter [Department of Physics, University of Florida, Gainesville, Florida 32611 (United States); Eremin, Ilya [Institut fuer Theoretische Physik III, Ruhr-Universitaet Bochum, D-44801 Bochum (Germany); Kazan Federal University, Kazan 420008 (Russian Federation); Mazin, Igor [Naval Research Laboratory, Code 6393, Washington, DC 20375 (United States)
2016-07-01
Using an electronic theory, we present a qualitative description to identify sign changes of the superconducting order parameter via quasiparticle interference (QPI) measurement in Fe-based superconductors (FeSc). In particular, we point out that the temperature dependence of the momentum-integrated QPI data can be used to differentiate between s{sub +-} and s{sub ++} states in a system with typical iron pnictide Fermi surface. We show that the signed symmetrized and antisymmetrized QPI maps are useful to obtain a characteristic signature of a gap sign change or lack thereof, starting from two-band model up to ab initio based band structure calculation. We further suggest this method as a robust way of the determination of the superconducting gap sign structure in experiment and discuss its application to the LiFeAs compounds.
DEFF Research Database (Denmark)
Vinckx, W.; Vanacken, J.; Moshchalkov, V.V.
2007-01-01
Vortex pinning in a superconducting Nb thin film deposited on an anodically grown alumina template is investigated. Anodic oxidation of aluminium layers permits under specific conditions the formation of highly ordered porous alumina, a membrane-like structure consisting of triangular arrays...... of parallel pores. Its pore diameter and interpore distance are set by careful tuning of the anodization parameters. A superconducting Nb thin film is deposited directly onto the alumina film. The porous alumina acts as a template and it allows Nb to form a periodic pinning array during its growth. Pinning...... force vs. field measurements derived from magnetization measurements, show matching effects in fields up to 1 T. We demonstrate that the anodic alumina template with 50 nm interpore spacing provides enhanced vortex pinning in a large field and temperature range....
Spatial modulation patterns in two-dimensional Fulde-Ferrell-Larkin-Ovchinnikov superconductivity
Kanao, Taro; Ogata, Masao
2012-12-01
FFLO superconductivity breaks the intrinsic translational symmetry and has spatially modulated order parameters. Determining its spatial modulation patterns is one of the fundamental problems concerning FFLO superconductivity. Preceding studies based on Ginzburg-Landau expansion showed that, in isotropic two-dimensional systems, patterns such as stripe, triangle, square and hexagon, are realized depending on the temperature and the applied magnetic field. However, Ginzburg-Landau expansion is not applicable at low temperatures, and another approach is necessary. In this research, based on Bogoliubov-de Gennes equations we investigate the patterns at zero temperature. By calculating free energies, we show that many patterns tend to be degenerate in contrast to the distinct energy difference at finite temperatures.
Using LSTM recurrent neural networks for detecting anomalous behavior of LHC superconducting magnets
Wielgosz, Maciej
2017-09-21
The superconducting LHC magnets are coupled with an electronic monitoring system which records and analyses voltage time series reflecting their performance. A currently used system is based on a range of preprogrammed triggers which launches protection procedures when a misbehavior of the magnets is detected. All the procedures used in the protection equipment were designed and implemented according to known working scenarios of the system and are updated and monitored by human operators. This paper proposes a novel approach to monitoring and fault protection of the Large Hadron Collider (LHC) superconducting magnets which employs state-of-the-art Deep Learning algorithms. Consequently, the authors of the paper decided to examine the performance of LSTM recurrent neural networks for anomaly detection in voltage time series of the magnets. In order to address this challenging task different network architectures and hyper-parameters were used to achieve the best possible performance of the solution. The regre...
Using LSTM recurrent neural networks for monitoring the LHC superconducting magnets
Wielgosz, Maciej; Mertik, Matej
2017-09-21
The superconducting LHC magnets are coupled with an electronic monitoring system which records and analyzes voltage time series reflecting their performance. A currently used system is based on a range of preprogrammed triggers which launches protection procedures when a misbehavior of the magnets is detected. All the procedures used in the protection equipment were designed and implemented according to known working scenarios of the system and are updated and monitored by human operators. This paper proposes a novel approach to monitoring and fault protection of the Large Hadron Collider (LHC) superconducting magnets which employs state-of-the-art Deep Learning algorithms. Consequently, the authors of the paper decided to examine the performance of LSTM recurrent neural networks for modeling of voltage time series of the magnets. In order to address this challenging task different network architectures and hyper-parameters were used to achieve the best possible performance of the solution. The regression re...
Tri-band superconducting filter using stub-loaded stepped-impedance resonators
Energy Technology Data Exchange (ETDEWEB)
Feng, Yuning; Guo, Xubo; Wei, Bin; Zhang, Xiaoping; Song, Fei [Department of Physics, Tsinghua University, Beijing 100084 (China); Xu, Zhan [School of Information and Electronics, Beijing Institute of Technology, Beijing 100081 (China); Cao, Bisong, E-mail: bscao@tsinghua.edu.cn [Department of Physics, Tsinghua University, Beijing 100084 (China)
2015-05-15
Highlights: • A stub-loaded stepped-impedance resonator is proposed to design a tri-band bandpass filter. • The insertion losses are significantly reduced by using high-temperature superconducting thin films. • The measured results exhibit high performance and agree well with the simulated ones. - Abstract: A stub-loaded stepped-impedance resonator (SLSIR) with three resonant modes is proposed to design a tri-band bandpass filter (BPF). The couplings between adjacent resonators at different resonant modes can be controlled independently by properly selecting the geometric parameters of the resonator. A dual-feeding structure is used to realize the required external couplings of the three passbands simultaneously. A fourth-order tri-band BPF with the passbands centered at 1.73, 2.40 and 3.45 GHz, respectively, is successfully designed and fabricated with superconducting thin films. The measured results exhibit high performance and agree well with the simulated ones.
Magnetic and Superconducting Materials at High Pressures
Energy Technology Data Exchange (ETDEWEB)
Struzhkin, Viktor V. [Carnegie Inst. of Washington, Washington, DC (United States)
2015-03-24
The work concentrates on few important tasks in enabling techniques for search of superconducting compressed hydrogen compounds and pure hydrogen, investigation of mechanisms of high-Tc superconductivity, and exploring new superconducting materials. Along that route we performed several challenging tasks, including discovery of new forms of polyhydrides of alkali metal Na at very high pressures. These experiments help us to establish the experimental environment that will provide important information on the high-pressure properties of hydrogen-rich compounds. Our recent progress in RIXS measurements opens a whole field of strongly correlated 3d materials. We have developed a systematic approach to measure major electronic parameters, like Hubbard energy U, and charge transfer energy Δ, as function of pressure. This technique will enable also RIXS studies of magnetic excitations in iridates and other 5d materials at the L edge, which attract a lot of interest recently. We have developed new magnetic sensing technique based on optically detected magnetic resonance from NV centers in diamond. The technique can be applied to study superconductivity in high-TC materials, to search for magnetic transitions in strongly correlated and itinerant magnetic materials under pressure. Summary of Project Activities; development of high-pressure experimentation platform for exploration of new potential superconductors, metal polyhydrides (including newly discovered alkali metal polyhydrides), and already known superconductors at the limit of static high-pressure techniques; investigation of special classes of superconducting compounds (high-Tc superconductors, new superconducting materials), that may provide new fundamental knowledge and may prove important for application as high-temperature/high-critical parameter superconductors; investigation of the pressure dependence of superconductivity and magnetic/phase transformations in 3d transition metal compounds, including
Energy Technology Data Exchange (ETDEWEB)
Tylczyński, Z., E-mail: zbigtyl@amu.edu.pl; Wiesner, M.; Trzaskowska, A.
2016-11-01
Temperature change of piezoelectric properties of (NH{sub 4}){sub 2}CuBr{sub 4}·2H{sub 2}O crystal in the low-temperature ferroelastoelectric phase is studied. The macroscopic order parameter is proved to be the h{sub 36} component of the spontaneous piezoelectric tensor. The critical exponent related with the phase transition is α=0.60±0.05.
Sanchez-Castillo, A; Osipov, M A; Jagiella, S; Nguyen, Z H; Kašpar, M; Hamplovă, V; Maclennan, J; Giesselmann, F
2012-06-01
The orientational order parameters (P{2}) and (P{4}) of the ferroelectric, de Vries-type liquid crystal 9HL have been determined in the SmA and SmC phases by means of polarized Raman spectroscopy, and in the SmA phase using x-ray diffraction. Quantum density functional theory predicts Raman spectra for 9HL that are in good agreement with the observations and indicates that the strong Raman band probed in the experiment corresponds to the uniaxial, coupled vibration of the three phenyl rings along the molecular long axis. The magnitudes of the orientational order parameters obtained in the Raman and x-ray experiments differ dramatically from each other, a discrepancy that is resolved by considering that the two techniques probe the orientational distributions of different molecular axes. We have developed a systematic procedure in which we calculate the angle between these axes and rescale the orientational order parameters obtained from x-ray scattering with results that are then in good agreement with the Raman data. At least in the case of 9HL, the results obtained by both techniques support a "sugar loaf" orientational distribution in the SmA phase with no qualitative difference to conventional smectics A. The role of individual molecular fragments in promoting de Vries-type behavior is considered.
Thermionic current in metal-superconducting semiconductor contact
Kuznetsov, G V
2001-01-01
The thermonuclear mechanism of the carriers transfer from the superconducting semiconductor into the metal is considered. The zonal energy diagram of the n-type metal-superconducting semiconductor is analyzed. The task on calculating the thermal electron current is reduced to determination of the above-the-barrier part of this current. The volt-ampere characteristics of the metal-superconducting semiconductor contact for various intervals of the applied external voltage are considered in detail. The changes in the volt-ampere characteristics are determined by the temperature and the parameter of the superconductor energy gap
Strong single-photon coupling in superconducting quantum magnetomechanics.
Via, Guillem; Kirchmair, Gerhard; Romero-Isart, Oriol
2015-04-10
We show that the inductive coupling between the quantum mechanical motion of a superconducting microcantilever and a flux-dependent microwave quantum circuit can attain the strong single-photon nanomechanical coupling regime with feasible experimental parameters. We propose to use a superconducting strip, which is in the Meissner state, at the tip of a cantilever. A pickup coil collects the flux generated by the sheet currents induced by an external quadrupole magnetic field centered at the strip location. The position-dependent magnetic response of the superconducting strip, enhanced by both diamagnetism and demagnetizing effects, leads to a strong magnetomechanical coupling to quantum circuits.
Kingni, S. T.; Jafari, S.; Simo, H.; Woafo, P.
2014-05-01
This paper proposes a three-dimensional chaotic autonomous system with only one stable equilibrium. This system belongs to a newly introduced category of chaotic systems with hidden attractors. The nonlinear dynamics of the proposed chaotic system is described through numerical simulations which include phase portraits, bifurcation diagrams and new cost function for parameter estimation of chaotic flows. The coexistence of a stable equilibrium point with a strange attractor is found in the proposed system for specific parameters values. The physical existence of the chaotic behavior found in the proposed system is verified by using the Orcard-PSpice software. A good qualitative agreement is shown between the simulations and the experimental results. Based on the Routh-Hurwitz conditions and for a specific choice of linear controllers, it is shown that the proposed chaotic system is controlled to its equilibrium point. Chaos synchronization of an identical proposed system is achieved by using the unidirectional linear and nonlinear error feedback coupling. Finally, the fractional-order form of the proposed system is studied by using the stability theory of fractional-order systems and numerical simulations. A necessary condition for the commensurate fractional order of this system to remain chaotic is obtained. It is found that chaos exists in this system with order less than three.
Fullerides - Superconductivity at the limit
Palstra, Thomas T. M.
The successful synthesis of highly crystalline Cs3C60, exhibiting superconductivity up to a record temperature for fullerides of 38 K, demonstrates a powerful synthetic route for investigating the origin of superconductivity in this class of materials.
Superconductivity in Dirac semimetals
Energy Technology Data Exchange (ETDEWEB)
Hashimoto, Tatsuki; Kobayashi, Shingo [Nagoya University, Nagoya (Japan); Sato, Masatoshi [Kyoto University, Kyoto (Japan)
2016-07-01
In this presentation, we would like to discuss the superconductivity in Dirac semimetals. Dirac semimetal is a material that hosts topologically protected bulk Dirac cones and surface Fermi loop. It has been revealed that the unique spin-orbit interaction in the Dirac semimetals stabilize the unconventional superconductivity. Experimentally, the zero-bias conductance peak that suggests the realization of topological superconductivity has been observed in Cd{sub 3}As{sub 2}. We use a k . p Hamiltonian around Γ point with spin and orbital degrees of freedom to describe the Dirac semimetal. For the model, we propose six types of k-independent pair potentials, where two of them are trivial pairings and others are topological ones. By introducing a single band description of the pair potentials, it is found that the superconducting gap and d-vector have the characteristic structure in each pair potential. To see these, we calculate the electronic specific heat and spin susceptibility and confirm that we can distinguish these superconducting states experimentally. In addition to the bulk physical properties, we also calculate the surface state by using the recursive Green's function method. It is find that either arc or flat shape Andreev bound states appear on the surface depending on the parity of mirror reflection symmetry.
Three-flavor color superconductivity
Energy Technology Data Exchange (ETDEWEB)
Malekzadeh, H.
2007-12-15
I investigate some of the inert phases in three-flavor, spin-zero color-superconducting quark matter: the CFL phase (the analogue of the B phase in superfluid {sup 3}He), the A and A{sup *} phases, and the 2SC and sSC phases. I compute the pressure of these phases with and without the neutrality condition. Without the neutrality condition, after the CFL phase the sSC phase is the dominant phase. However, including the neutrality condition, the CFL phase is again the energetically favored phase except for a small region of intermediate densities where the 2SC/A{sup *} phase is favored. It is shown that the 2SC phase is identical to the A{sup *} phase up to a color rotation. In addition, I calculate the self-energies and the spectral densities of longitudinal and transverse gluons at zero temperature in color-superconducting quark matter in the CFL phase. I find a collective excitation, a plasmon, at energies smaller than two times the gap parameter and momenta smaller than about eight times the gap. The dispersion relation of this mode exhibits a minimum at some nonzero value of momentum, indicating a van Hove singularity. (orig.)
Superconducting Helical Snake Magnet for the AGS
Willen, Erich; Escallier, John; Ganetis, George; Ghosh, Arup; Gupta, Ramesh C; Harrison, Michael; Jain, Animesh K; Luccio, Alfredo U; MacKay, William W; Marone, Andrew; Muratore, Joseph F; Okamura, Masahiro; Plate, Stephen R; Roser, Thomas; Tsoupas, Nicholaos; Wanderer, Peter
2005-01-01
A superconducting helical magnet has been built for polarized proton acceleration in the Brookhaven AGS. This "partial Snake" magnet will help to reduce the loss of polarization of the beam due to machine resonances. It is a 3 T magnet some 1940 mm in magnetic length in which the dipole field rotates with a pitch of 0.2053 degrees/mm for 1154 mm in the center and a pitch of 0.3920 degrees/mm for 393 mm in each end. The coil cross-section is made of two slotted cylinders containing superconductor. In order to minimize residual offsets and deflections of the beam on its orbit through the Snake, a careful balancing of the coil parameters was necessary. In addition to the main helical coils, a solenoid winding was built on the cold bore tube inside the main coils to compensate for the axial component of the field that is experienced by the beam when it is off-axis in this helical magnet. Also, two dipole corrector magnets were placed on the same tube with the solenoid. A low heat leak cryostat was built so that t...
Applied Superconductivity Conference 2014
2015-01-01
Energy Efficiency is a worldwide imperative driven by an increasing awareness of the need to conserve valuable natural resources. Superconductivity, the technology which revolutionized non-invasive medical imaging through MRI starting in the 1980’s, is one of the most promising enablers of energy efficiency in the 21st century. From energy efficient supercomputers to power generation, transmission, and storage, the spectrum of applications of superconductivity is broad in its reach and potential. As ASC comes to Charlotte, site of the hall of fame of NASCAR, our theme, “Race to Energy Efficiency,” is intended to inspire the world experts in superconductivity who will converge to Charlotte to present their latest results, exchange information, network, and plan and project the future breakthroughs.
Hugdal, Henning G.; Sudbø, Asle
2018-01-01
We study the superconducting order in a two-dimensional square lattice Hubbard model with weak repulsive interactions, subject to a Zeeman field and weak Rashba spin-orbit interactions. Diagonalizing the noninteracting Hamiltonian leads to two separate bands, and by deriving an effective low-energy interaction we find the mean field gap equations for the superconducting order parameter on the bands. Solving the gap equations just below the critical temperature, we find that superconductivity is caused by Kohn-Luttinger-type interaction, while the pairing symmetry of the bands is indirectly affected by the spin-orbit coupling. The dominating attractive momentum channel of the Kohn-Luttinger term depends on the filling fraction n of the system, and it is therefore possible to change the momentum dependence of the order parameter by tuning n . Moreover, n also determines which band has the highest critical temperature. Rotating the magnetic field changes the momentum dependence from states that for small momenta reduce to a chiral px±i py type state for out-of-plane fields, to a nodal p -wave-type state for purely in-plane fields.
Towards phase-coherent caloritronics in superconducting circuits
Fornieri, Antonio; Giazotto, Francesco
2017-10-01
The emerging field of phase-coherent caloritronics (from the Latin word calor, heat) is based on the possibility of controlling heat currents by using the phase difference of the superconducting order parameter. The goal is to design and implement thermal devices that can control energy transfer with a degree of accuracy approaching that reached for charge transport by contemporary electronic components. This can be done by making use of the macroscopic quantum coherence intrinsic to superconducting condensates, which manifests itself through the Josephson effect and the proximity effect. Here, we review recent experimental results obtained in the realization of heat interferometers and thermal rectifiers, and discuss a few proposals for exotic nonlinear phase-coherent caloritronic devices, such as thermal transistors, solid-state memories, phase-coherent heat splitters, microwave refrigerators, thermal engines and heat valves. Besides being attractive from the fundamental physics point of view, these systems are expected to have a vast impact on many cryogenic microcircuits requiring energy management, and possibly lay the first stone for the foundation of electronic thermal logic.
Topological strings linking with quasiparticle exchange in superconducting Dirac semimetals
Lopes, Pedro L. e. S.; Teo, Jeffrey C. Y.; Ryu, Shinsei
2017-06-01
We demonstrate a topological classification of vortices in three-dimensional time-reversal invariant topological superconductors based on superconducting Dirac semimetals with an s -wave superconducting order parameter by means of a pair of numbers (NΦ,N ) , accounting how many units NΦ of magnetic fluxes h c /4 e and how many N chiral Majorana modes the vortex carries. From these quantities, we introduce a topological invariant, which further classifies the properties of such vortices under linking processes. While such processes are known to be related to instanton processes in a field theoretic description, we demonstrate here that they are, in fact, also equivalent to the fractional Josephson effect on junctions based at the edges of quantum spin Hall systems. This allows one to consider microscopically the effects of interactions in the linking problem. We therefore demonstrate that associated to links between vortices, one has the exchange of quasiparticles, either Majorana zero modes, or e /2 quasiparticles, which allows for a topological classification of vortices in these systems, seen to be Z8 classified. While NΦ and N are shown to be both even or odd in the weakly interacting limit, in the strongly interacting scenario one loosens this constraint. In this case, one may have further fractionalization possibilities for the vortices, whose excitations are described by SO(3) 3 -like conformal field theories with quasiparticle exchanges of more exotic types.
Electromechanical characterization of superconducting wires and tapes at 77 K
Bjoerstad, Roger
The strain dependency of the critical current in state-of-the-art cuprate high-temperature superconductors (HTS) has been characterized. A universal test machine (UTM) combined with a critical current measurement system has been used to characterize the mechanical and the superconducting properties of conductors immersed in an open liquid nitrogen dewar. A set-up has been developed in order to perform simultaneous measurements of the superconductor lattice parameter changes, critical current, as well as the stress and strain at 77 K in self-field in a high energy synchrotron beamline. The HTS tapes and wires studied were based on YBCO, Bi-2223 and Bi-2212. The YBCO tapes were produced by SuperPower and American Superconductors (AMSC). Two types of Bi-2223 tapes, HT and G, were produced by Sumitomo Electric Industries (SEI). The Bi-2212 wires were produced by Oxford Superconducting Technology (OST) using Nexans granulate precursor, before undergoing a specialized over pressure (OP) processing and heat treatmen...
Khatami, Ehsan
Many properties of the two-dimensional Hubbard model have been explored for the model parameters appropriate for strongly correlated electronic systems, especially cuprate superconductors. Most of the calculations are done using a well-established dynamical cluster quantum Monte Carlo method. Using this method, we investigate the effect of long-range hoppings on superconductivity with and without the presence of phonons on small clusters. The superconducting transition temperature, Tc, is found to generally decrease with a negative next nearest neighbor hopping, t'. In the presence of the Holstein phonons, a finite t' enhances Tc in the under-doped region for the hole-doped system, consistent with band structure calculations and experiment. The validity of the spin-susceptibility-mediated pairing in this model is studied and found to yield symmetries other than d-wave when a finite t' is considered. A new numerical algorithm for solving the embedded cluster problems is introduced, and used to calculate the thermodynamic properties of the model on larger clusters, especially those associated with the quantum critical behavior at finite doping. Our results suggest that the quantum critical point (QCP) which separates the Fermi liquid and pseudogap regions, is the second order terminus of the line of first order phase separation transition in the limit when a positive t' goes to zero. For small t', the superconducting dome is centered at the QCP, suggesting that charge fluctuations might have a role in the pairing mechanism in this model.
Superconductivity in potassium-doped few-layer graphene.
Xue, Mianqi; Chen, Genfu; Yang, Huaixin; Zhu, Yuanhua; Wang, Duming; He, Junbao; Cao, Tingbing
2012-04-18
Here we report the successful synthesis of superconducting potassium-doped few-layer graphene (K-doped FLG) with a transition temperature of 4.5 K, which is 1 order of magnitude higher than that observed in the bulk potassium graphite intercalation compound (GIC) KC(8) (T(c) = 0.39 K). The realization of superconductivity in K-doped FLG shows the potential for the development of new superconducting electronic devices using two-dimensional (2D) graphene as a basis material. © 2012 American Chemical Society
Power Switches Utilizing Superconducting Material for Accelerator Magnets
March, S A; Yang, Y
2009-01-01
Power switches that utilize superconducting material find application in superconducting systems. They can be used for the protection of magnets as a replacement for warm DC breakers, as well as for the replacement of cold diodes. This paper presents a comparison of switches made of various superconducting materials having transport currents of up to 600 A and switching times of the order of milliseconds. The switches operate in the temperature range 4.2-77 K and utilize stainless steel clad YBCO tape and MgB2 tape with a nickel, copper, and iron matrix. Results from simulations and tests are reported.
Energy Technology Data Exchange (ETDEWEB)
Sykora, Steffen; Huebsch, Arnd; Becker, Klaus W. [Institut fuer Theoretische Physik, Technische Universitaet Dresden, 01062 Dresden (Germany)
2008-07-01
The competition of charge-density waves (CDW) and superconductivity (SC) is studied in a two-dimensional half-filled Holstein model by use of the projector-based renormalization method (PRM). As is well known, in one dimension the coupling of electrons to phonons leads to a transition from a metallic to a Peierls distorted insulated state when the coupling exceeds a critical value. On the other hand, in two dimensions the electron-phonon interaction may also be responsible for the formation of Cooper pairs. In this paper, the competing influence of superconductivity and charge order will be discussed for two dimensions. The PRM not only allows to study SC and CDW correlation functions but gives direct access to the order parameters.
A control system for and a method of controlling a superconductive rotating electrical machine
DEFF Research Database (Denmark)
2014-01-01
This invention relates to a method of controlling and a control system (100) for a superconductive rotating electric machine (200) comprising at least one superconductive winding (102; 103), where the control system (100) is adapted to control a power unit (101) supplying during use the at least...... or more actual values (110, 111)of one or more parameters for a given superconductive winding (102; 103), each parameter representing a physical condition of the given superconductive winding (102; 103), and to dynamically derive one or more electrical current values to be maintained in the given...... superconductive winding (102; 103) by the power unit (101) where the one or more electrical current values is/are derived taking into account the received one or more actual values (110, 111). In this way,greater flexibility and more precise control of the performance of the superconducting rotating electrical...
Energy Technology Data Exchange (ETDEWEB)
Ozer, Mustafa M [ORNL; Thompson, James R [ORNL; Weitering, Harm H [ORNL
2006-01-01
Strong quantum size effects enable the formation of crystalline Pb films that are atomically flat on a macroscopic length scale. The superconducting properties of 5-18-monolayer-(ML) thick Pb films were investigated in a superconducting quantum interference device (SQUID) magnetometer using combined ac and dc methods. Even the thinnest films (5 ML) are extraordinarily robust type-II superconductors. Despite the extreme two-dimensional geometry, the thermodynamic parameters {Tc} and upper critical field H{sub c2} are primarily controlled by the physical boundary conditions of the film and show no evidence for disorder-driven or fluctuation-driven quenching of superconductivity. A magnetically hard critical state is established as a consequence of vortex trapping by quantum growth defects.
High pressure induced superconductivity
Energy Technology Data Exchange (ETDEWEB)
Amaya, K.; Shimizu, K
2003-10-15
We have developed complex extreme condition of very low temperature down to 30 mK and ultra high pressure exceeding 200 GPa by assembling compact diamond anvil cell (DAC) on a powerful {sup 3}He/{sup 4}He dilution refrigerator. We have also developed measuring techniques of electrical resistance, magnetization and optical measurement for the sample confined in the sample space of the DAC. Using the newly developed apparatus and techniques, we have searched for superconductivity in various materials under pressure. In this paper, we will shortly review our newly developed experimental apparatus and techniques and discuss a few examples of pressure induced superconductivity which were observed recently.
Superconducting metamaterials and qubits
Plourde, B. L. T.; Wang, Haozhi; Rouxinol, Francisco; LaHaye, M. D.
2015-05-01
Superconducting thin-film metamaterial resonators can provide a dense microwave mode spectrum with potential applications in quantum information science. We report on the fabrication and low-temperature measurement of metamaterial transmission-line resonators patterned from Al thin films. We also describe multiple approaches for numerical simulations of the microwave properties of these structures, along with comparisons with the measured transmission spectra. The ability to predict the mode spectrum based on the chip layout provides a path towards future designs integrating metamaterial resonators with superconducting qubits.
Superconducting magnetic quadrupole
Energy Technology Data Exchange (ETDEWEB)
Kim, J.W.; Shepard, K.W.; Nolen, J.A.
1995-08-01
A design was developed for a 350 T/m, 2.6-cm clear aperture superconducting quadrupole focussing element for use in a very low q/m superconducting linac as discussed below. The quadrupole incorporates holmium pole tips, and a rectangular-section winding using standard commercially-available Nb-Ti wire. The magnet was modeled numerically using both 2D and 3D codes, as a basis for numerical ray tracing using the quadrupole as a linac element. Components for a prototype singlet are being procured during FY 1995.
Pakmanesh, M. R.; Shamanian, M.
2018-02-01
In this study, the optimization of pulsed Nd:YAG laser welding parameters was done on the lap-joint of a 316L stainless steel foil with the aim of reducing weld defects through response surface methodology. For this purpose, the effects of peak power, pulse-duration, and frequency were investigated. The most important weld defects seen in this method include underfill and undercut. By presenting a second-order polynomial, the above-mentioned statistical method was managed to be well employed to balance the welding parameters. The results showed that underfill increased with the increased power and reduced frequency, it first increased and then decreased with the increased pulse-duration; and the most important parameter affecting it was the power, whose effect was 65%. The undercut increased with the increased power, pulse-duration, and frequency; and the most important parameter affecting it was the power, whose effect was 64%. Finally, by superimposing different responses, improved conditions were presented to attain a weld with no defects.
Theory of spin-fluctuation induced superconductivity in iron-based superconductors
Energy Technology Data Exchange (ETDEWEB)
Zhang, Junhua [Iowa State Univ., Ames, IA (United States)
2011-01-01
In this dissertation we focus on the investigation of the pairing mechanism in the recently discovered high-temperature superconductor, iron pnictides. Due to the proximity to magnetic instability of the system, we considered short-range spin fluctuations as the major mediating source to induce superconductivity. Our calculation supports the magnetic fluctuations as a strong candidate that drives Cooper-pair formation in this material. We find the corresponding order parameter to be of the so-called ss-wave type and show its evolution with temperature as well as the capability of supporting high transition temperature up to several tens of Kelvin. On the other hand, our itinerant model calculation shows pronounced spin correlation at the observed antiferromagnetic ordering wave vector, indicating the underlying electronic structure in favor of antiferromagnetic state. Therefore, the electronic degrees of freedom could participate both in the magnetic and in the superconducting properties. Our work shows that the interplay between magnetism and superconductivity plays an important role to the understanding of the rich physics in this material. The magnetic-excitation spectrum carries important information on the nature of magnetism and the characteristics of superconductivity. We analyze the spin excitation spectrum in the normal and superconducting states of iron pnictides in the magnetic scenario. As a consequence of the sign-reversed gap structure obtained in the above, a spin resonance mode appears below the superconducting transition temperature. The calculated resonance energy, scaled with the gap magnitude and the magnetic correlation length, agrees well with the inelastic neutron scattering (INS) measurements. More interestingly, we find a common feature of those short-range spin fluctuations that are capable of inducing a fully gapped ss state is the momentum anisotropy with elongated span along the direction transverse to the antiferromagnetic momentum
Fe(Se,Te) superconducting quantum interference devices
Sarnelli, E.; Nappi, C.; Leveratto, A.; Bellingeri, E.; Braccini, V.; Ferdeghini, C.
2017-06-01
We have fabricated and analyzed bicrystal grain boundary superconducting quantum interference devices made by Fe(Se,Te) superconductors, grown on [001] tilt SrTiO3 bicrystal substrates. We have realized several devices using the so-called hole-type geometry, with different loop inductances and different junction widths. Modulations of the voltage under an external applied magnetic field have been observed for three samples. Voltage amplitudes of the order of few microvolt have been measured. The maximum magnetic flux-to-voltage transfer parameter value that we have observed has been {V}{{Φ }}=9.4 μ {{V}}/{{{Φ }}}0. The experimental data are analyzed in the famework of existing theoretical models.
Superconducting vortex pinning with artificial magnetic nanostructures.
Energy Technology Data Exchange (ETDEWEB)
Velez, M.; Martin, J. I.; Villegas, J. E.; Hoffmann, A.; Gonzalez, E. M.; Vicent, J. L.; Schuller, I. K.; Univ. de Oviedo-CINN; Unite Mixte de Physique CNRS/Thales; Univ. Paris-Sud; Univ.Complutense de Madrid; Univ. California at San Diego
2008-11-01
This review is dedicated to summarizing the recent research on vortex dynamics and pinning effects in superconducting films with artificial magnetic structures. The fabrication of hybrid superconducting/magnetic systems is presented together with the wide variety of properties that arise from the interaction between the superconducting vortex lattice and the artificial magnetic nanostructures. Specifically, we review the role that the most important parameters in the vortex dynamics of films with regular array of dots play. In particular, we discuss the phenomena that appear when the symmetry of a regular dot array is distorted from regularity towards complete disorder including rectangular, asymmetric, and aperiodic arrays. The interesting phenomena that appear include vortex-lattice reconfigurations, anisotropic dynamics, channeling, and guided motion as well as ratchet effects. The different regimes are summarized in a phase diagram indicating the transitions that take place as the characteristic distances of the array are modified respect to the superconducting coherence length. Future directions are sketched out indicating the vast open area of research in this field.
LHC Report: superconducting circuit powering tests
Mirko Pojer
2015-01-01
After the long maintenance and consolidation campaign carried out during LS1, the machine is getting ready to start operation with beam at 6.5 TeV… the physics community can’t wait! Prior to this, all hardware and software systems have to be tested to assess their correct and safe operation. Most of the cold circuits (those with high current/stored energy) possess a sophisticated magnet protection system that is crucial to detect a transition of the coil from the superconducting to the normal state (a quench) and safely extract the energy stored in the circuits (about 1 GJ per dipole circuit at nominal current). LHC operation relies on 1232 superconducting dipoles with a field of up to 8.33 T operating in superfluid helium at 1.9 K, along with more than 500 superconducting quadrupoles operating at 4.2 or 1.9 K. Besides, many other superconducting and normal resistive magnets are used to guarantee the possibility of correcting all beam parameters, for a total of mo...
The superconductivity in Re-B system
Kawano, A; Takagiwa, H; Muranaka, T; Akimitsu, J
2003-01-01
We present here the low temperature electrical transport and magnetic properties of intermetallic rhenium boride compounds. We newly discovered the superconductivity of Re sub 7 B sub 3 (T sub c = 3.3 K) and its superconducting properties were discussed. We also discussed the physical properties of Re sub 3 B (T sub c = 4.8 K), of which superconductivity was discussed by Strukova et al. The crystal structures of these compounds (Re sub 3 B and Re sub 7 B sub 3) are orthorhombic (space group Cmcm) and hexagonal (P6 sub 3 /mc), respectively, and have different B-B bonds each other. The magnetization (M-H) curves of these compounds show a typical type-II superconducting behavior. The lower critical field, H sub c sub 1 (0), the upper critical field, H sub c sub 2 (0) and the Ginzburg-Landau (GL) parameter, kappa are, 8 mT, 5.2 T and 35 for Re sub 3 B and 6mT, 0.9T and 17 for Re sub 7 B sub 3. (author)
Superconducting proximity effect in clean ferromagnetic layers
Zareyan, M.; Belzig, W.; Nazarov, Yu. V.
2002-01-01
We investigate the superconducting proximity effect in clean ferromagnetic layers with rough boundaries. The subgap density of states is formed by Andreev bound states at energies which depend on trajectory length and the ferromagnetic exchange field. At energies above the gap, the spectrum is governed by resonant scattering states. The resulting density of states, measurable by tunneling spectroscopy, exhibits a rich structure, which allows us to connect the theoretical parameters from exper...
Relativistic quantum teleportation with superconducting circuits.
Friis, N; Lee, A R; Truong, K; Sabín, C; Solano, E; Johansson, G; Fuentes, I
2013-03-15
We study the effects of relativistic motion on quantum teleportation and propose a realizable experiment where our results can be tested. We compute bounds on the optimal fidelity of teleportation when one of the observers undergoes nonuniform motion for a finite time. The upper bound to the optimal fidelity is degraded due to the observer's motion. However, we discuss how this degradation can be corrected. These effects are observable for experimental parameters that are within reach of cutting-edge superconducting technology.
Plasma modes in superconducting wires: Optimized experimental configuration
Energy Technology Data Exchange (ETDEWEB)
Camarota, B.; Parage, F.; Wooldridge, I.; Delsing, P.; Buisson, O.
2000-03-01
An experimental configuration is analyzed in order to study plasma modes in a superconducting wire deposited onto SrTiO{sub 3}. A dispersion relation has been derived by evaluating the effect of environment surrounding the wire. It corresponds to the one-dimensional dispersion law predicted for an isolated superconducting wire. Preliminary measurements are presented. They show 1D plasma modes in the optimized experimental configuration here studied.
Superconducting Magnets for Particle Accelerators
Rossi, L
2012-01-01
Superconductivity has been the most influential technology in the field of accelerators in the last 30 years. Since the commissioning of the Tevatron, which demonstrated the use and operability of superconductivity on a large scale, superconducting magnets and rf cavities have been at the heart of all new large accelerators. Superconducting magnets have been the invariable choice for large colliders, as well as cyclotrons and large synchrotrons. In spite of the long history of success, superconductivity remains a difficult technology, requires adequate R&D and suitable preparation, and has a relatively high cost. Hence, it is not surprising that the development has also been marked by a few setbacks. This article is a review of the main superconducting accelerator magnet projects; it highlights the main characteristics and main achievements, and gives a perspective on the development of superconducting magnets for the future generation of very high energy colliders.
Energy Technology Data Exchange (ETDEWEB)
Moler, Kathryn
2010-08-26
We present scanning SQUID microscopy data on the superconductors Sr{sub 2}RuO{sub 4} (T{sub c} = 1.5 K) and PrOs{sub 4}Sb{sub 12} (T{sub c} = 1.8 K). In both of these materials, superconductivity-related time-reversal symmetry-breaking fields have been observed by muon spin rotation; our aim was to visualize the structure of these fields. However in neither Sr{sub 2}RuO{sub 4} nor PrOs{sub 4}Sb{sub 12} do we observe spontaneous superconductivity-related magnetization. In Sr{sub 2}RuO{sub 4}, many experimental results have been interpreted on the basis of a p{sub x} {+-} ip{sub y} superconducting order parameter. This order parameter is expected to give spontaneous magnetic induction at sample edges and order parameter domain walls. Supposing large domains, our data restrict domain wall and edge fields to no more than {approx}0.1% and {approx}0.2% of the expected magnitude, respectively. Alternatively, if the magnetization is of the expected order, the typical domain size is limited to {approx}30 nm for random domains, or {approx} 500 nm for periodic domains.
Superconductors for superconducting magnets
Larbalestier, David
2011-03-01
Even in 1913 Kamerlingh Onnes envisioned the use of superconductors to create powerful magnetic fields well beyond the capability provided by cooling normal metals with liquid helium. Only some ``bad places'' in his Hg and Pb wires seemed to impede his first attempts at this dream, one that he imagined would be resolved in a few weeks of effort. In fact, of course, resolution required another 50 years and development of both a true understanding of the difference between type I and type II superconductors and the discovery of compounds such as Nb 3 Sn that could remain superconducting to fields as high as 30 T. And then indeed, starting in the 1960s, Onnes's dreams were comfortably surpassed. In the last 45 years virtually all superconducting magnets have been made from just two Nb-base materials, Nb-Ti and Nb 3 Sn. Now it seems that a new generation of magnets based on cuprate high temperature superconductors with fields well above 30 T are possible using Bi-Sr-Ca-Cu-O and the RE-Ba-Cu-O compounds. We hope that a first demonstration of this possibility will be an all-superconducting 32 T magnet with RE-Ba-Cu-O insert that we are building for NHMFL users. The magnet application potential of this new generation of superconducting conductors will be discussed.
Nonlinearities in Microwave Superconductivity
Ledenyov, Dimitri O.; Ledenyov, Viktor O.
2012-01-01
The research is focused on the modeling of nonlinear properties of High Temperature Superconducting (HTS) thin films, using Bardeen, Cooper, Schrieffer and Lumped Element Circuit theories, with purpose to enhance microwave power handling capabilities of microwave filters and optimize design of microwave circuits in micro- and nano- electronics.
High temperature superconducting materials
Energy Technology Data Exchange (ETDEWEB)
Alario-Franco, M.A. [Universidad Complutense de Madrid (Spain). Facultad de Ciencias Quimicas
1995-02-01
The perovskite structure is the basis of all known high-temperature superconducting materials. Many of the most successful (highest T{sub c}) materials are based on mercury and thallium phases but, due to the high toxicity of the component compounds effort has been invested in the substitution of these elements with silver. Progress is reviewed. (orig.)
Superconductivity committee planning report
Energy Technology Data Exchange (ETDEWEB)
1988-11-01
The recent discovery of superconductors that operate at relatively high temperatures has generated a large amount of research which promises to have applications in almost all branches of high technology, notably those in which high electric current densities are used. After a background description of the properties of superconductors, the market for superconductor technology is described from the Canadian perspective. Worldwide markets are growing rapidly and are estimated to total $920 million by 1990, considering only conventional low-temperature superconductors. Applications for superconductivity include the use of thin films and microelectronics, low loss signal transmission, tunnel injections, and sensitive magnetic detectors. Superconducting magnets find application in magnetic separation, magnetic levitation and propulsion, and for energy storage and transmission by power utilities. Research in superconductivity in British Columbia, reviewed in this report, has been under way at 3 universities and 4 or 5 compaines, where a small group of qualified researchers and some high-technology laboratories are focusing on thin-film and electonic applications. The potential market for superconductivity is felt to warrant more effort in British Columbia, and a number of recommendations are made for coordinating and promoting research, funding joint university-industry projects for innovative applications, and facilitating technology transfer.
Checking BEBC superconducting magnet
CERN PhotoLab
1974-01-01
The superconducting coils of the magnet for the 3.7 m Big European Bubble Chamber (BEBC) had to be checked, see Annual Report 1974, p. 60. The photo shows a dismantled pancake. By December 1974 the magnet reached again the field design value of 3.5 T.
Superconducting Quantum Circuits
Majer, J.B.
2002-01-01
This thesis describes a number of experiments with superconducting cir- cuits containing small Josephson junctions. The circuits are made out of aluminum islands which are interconnected with a very thin insulating alu- minum oxide layer. The connections form a Josephson junction. The current trough
Ciovati, G.
2014-07-17
This contribution provides a brief introduction to AC/RF superconductivity, with an emphasis on application to accelerators. The topics covered include the surface impedance of normal conductors and superconductors, the residual resistance, the field dependence of the surface resistance, and the superheating field.
Niobium superconducting cavity
CERN PhotoLab
1980-01-01
This 5-cell superconducting cavity, made from bulk-Nb, stems from the period of general studies, not all directed towards direct use at LEP. This one is dimensioned for 1.5 GHz, the frequency used at CEBAF and also studied at Saclay (LEP RF was 352.2 MHz). See also 7908227, 8007354, 8209255, 8210054, 8312339.
ISR Superconducting Quadrupoles
1977-01-01
Michel Bouvier is preparing for curing the 6-pole superconducting windings inbedded in the cylindrical wall separating liquid helium from vacuum in the quadrupole aperture. The heat for curing the epoxy glue was provided by a ramp of infrared lamps which can be seen above the slowly rotating cylinder. See also 7703512X, 7702690X.
Superconducting doped topological materials
Energy Technology Data Exchange (ETDEWEB)
Sasaki, Satoshi, E-mail: sasaki@sanken.osaka-u.ac.jp [Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047 (Japan); Mizushima, Takeshi, E-mail: mizushima@mp.es.osaka-u.ac.jp [Department of Materials Engineering Science, Osaka University, Toyonaka, Osaka 560-8531 (Japan); Department of Physics, Okayama University, Okayama 700-8530 (Japan)
2015-07-15
Highlights: • Studies on both normal- and SC-state properties of doped topological materials. • Odd-parity pairing systems with the time-reversal-invariance. • Robust superconductivity in the presence of nonmagnetic impurity scattering. • We propose experiments to identify the existence of Majorana fermions in these SCs. - Abstract: Recently, the search for Majorana fermions (MFs) has become one of the most important and exciting issues in condensed matter physics since such an exotic quasiparticle is expected to potentially give rise to unprecedented quantum phenomena whose functional properties will be used to develop future quantum technology. Theoretically, the MFs may reside in various types of topological superconductor materials that is characterized by the topologically protected gapless surface state which are essentially an Andreev bound state. Superconducting doped topological insulators and topological crystalline insulators are promising candidates to harbor the MFs. In this review, we discuss recent progress and understanding on the research of MFs based on time-reversal-invariant superconducting topological materials to deepen our understanding and have a better outlook on both the search for and realization of MFs in these systems. We also discuss some advantages of these bulk systems to realize MFs including remarkable superconducting robustness against nonmagnetic impurities.
Energy Technology Data Exchange (ETDEWEB)
Ciovati, Gianluigi [JLAB
2015-02-01
This contribution provides a brief introduction to AC/RF superconductivity, with an emphasis on application to accelerators. The topics covered include the surface impedance of normal conductors and superconductors, the residual resistance, the field dependence of the surface resistance, and the superheating field.
High temperature superconductivity: Proceedings
Energy Technology Data Exchange (ETDEWEB)
Bedell, K.S.; Coffey, D. (Los Alamos National Lab., NM (USA)); Meltzer, D.E. (Florida Univ., Gainesville, FL (USA)); Pines, D. (Illinois Univ., Urbana, IL (USA)); Schrieffer, J.R. (California Univ., Santa Barbara, CA (USA)) (eds.)
1990-01-01
This book is the result of a symposium at Los Alamos in 1989 on High Temperature Superconductivity. The topics covered include: phenomenology, quantum spin liquids, spin space fluctuations in the insulating and metallic phases, normal state properties, and numerical studies and simulations. (JF)
1995-01-01
Engineers work in a clean room on one of the superconducting cavities for the upgrade to the LEP accelerator, known as LEP-2. The use of superconductors allow higher electric fields to be produced so that higher beam energies can be reached.
Patrice Loiez
1999-01-01
This cross-section through a strand of superconducting matieral as used in the LHC shows the 8000 Niobium-Titanium filaments embedded like a honeycomb in copper. When cooled to 1.9 degrees above absolute zero in the LHC accelerator, these filaments will have zero resistance and so will carry a high electric current with no energy loss.
Electrical Conduction and Superconductivity
Indian Academy of Sciences (India)
Home; Journals; Resonance – Journal of Science Education; Volume 8; Issue 9. Electrical Conduction and Superconductivity. Suresh V Vettoor. General Article Volume 8 Issue 9 September 2003 pp 41-48. Fulltext. Click here to view fulltext PDF. Permanent link: http://www.ias.ac.in/article/fulltext/reso/008/09/0041-0048 ...
Superconducting magnetic energy storage and superconducting self-supplied electromagnetic launcher
Ciceron, Jérémie; Badel, Arnaud; Tixador, Pascal
2017-10-01
Superconductors can be used to build energy storage systems called Superconducting Magnetic Energy Storage (SMES), which are promising as inductive pulse power source and suitable for powering electromagnetic launchers. The second generation of high critical temperature superconductors is called coated conductors or REBCO (Rare Earth Barium Copper Oxide) tapes. Their current carrying capability in high magnetic field and their thermal stability are expanding the SMES application field. The BOSSE (Bobine Supraconductrice pour le Stockage d'Energie) project aims to develop and to master the use of these superconducting tapes through two prototypes. The first one is a SMES with high energy density. Thanks to the performances of REBCO tapes, the volume energy and specific energy of existing SMES systems can be surpassed. A study has been undertaken to make the best use of the REBCO tapes and to determine the most adapted topology in order to reach our objective, which is to beat the world record of mass energy density for a superconducting coil. This objective is conflicting with the classical strategies of superconducting coil protection. A different protection approach is proposed. The second prototype of the BOSSE project is a small-scale demonstrator of a Superconducting Self-Supplied Electromagnetic Launcher (S3EL), in which a SMES is integrated around the launcher which benefits from the generated magnetic field to increase the thrust applied to the projectile. The S3EL principle and its design are presented. Contribution to the topical issue "Electrical Engineering Symposium (SGE 2016)", edited by Adel Razek
Tri-band superconducting filter using stub-loaded stepped-impedance resonators
Feng, Yuning; Guo, Xubo; Wei, Bin; Zhang, Xiaoping; Song, Fei; Xu, Zhan; Cao, Bisong
2015-05-01
A stub-loaded stepped-impedance resonator (SLSIR) with three resonant modes is proposed to design a tri-band bandpass filter (BPF). The couplings between adjacent resonators at different resonant modes can be controlled independently by properly selecting the geometric parameters of the resonator. A dual-feeding structure is used to realize the required external couplings of the three passbands simultaneously. A fourth-order tri-band BPF with the passbands centered at 1.73, 2.40 and 3.45 GHz, respectively, is successfully designed and fabricated with superconducting thin films. The measured results exhibit high performance and agree well with the simulated ones.
3D X-ray micro-tomography for modeling of NB{sub 3}SN multifilamentary superconducting wires
Energy Technology Data Exchange (ETDEWEB)
Tiseanu, Ion [National Institute for Lasers, Plasma and Radiation Physics (NILPRP), Bucharest-Magurele (Romania); Craciunescu, Teddy [National Institute for Lasers, Plasma and Radiation Physics (NILPRP), Bucharest-Magurele (Romania)], E-mail: teddy@infim.ro; Petrisor, Traian [Technical University of Cluj-Napoca (Romania); Corte, Antonio Della [ENEA Frascati (Italy)
2007-10-15
Practical superconducting cables used in large scale applications (e.g. magnets for fusion reactor) consist in superconducting filaments embedded in a normal-conducting matrix. The common technique to reduce the eddy-current losses is to twist the wire and the filaments during the manufacture. This also reduces the time-independent proximity effect between the filaments and its associated loss. Currently, the only method for measuring the twist-pitch consists in evidencing the twisted structure by etching techniques. This method is destructive and does not permit the visualization of the filaments. It is proved in this paper that X-ray micro-tomography permit the non-destructive reconstruction of the 3D image of the ITER-type multifilamentary wire enabling the determination of the number of inter-filament contacts on unite lengths well as the twist-pitch parameter. This can be used to develop a more complex model of the multifilamentary superconducting wire in order to explain the role of the internal wire structure on the superconducting transport properties.
Ultrahigh pressure superconductivity in molybdenum disulfide
Energy Technology Data Exchange (ETDEWEB)
Chi, Zhenhua [Chinese Academy of Sciences (CAS), Hefei (China); Yen, Feihsiang [Chinese Academy of Sciences (CAS), Hefei (China); Peng, Feng [Luoyang Normal Univ., Luoyang (China); Zhu, Jinlong [Univ. of Nevada, Las Vegas, NV (United States); Zhang, Yijin [Univ. of Tokyo, Tokyo (Japan); Chen, Xuliang [Chinese Academy of Sciences (CAS), Hefei (China); Yang, Zhaorong [Chinese Academy of Sciences (CAS), Hefei (China); Nanjing Univ., Nanjing (China); Liu, Xiaodi [Chinese Academy of Sciences (CAS), Hefei (China); Ma, Yaming [Jilin Univ., Changchun (China); Zhao, Yusheng [Univ. of Nevada, Las Vegas, NV (United States); Kagayama, Tomoko [Osaka Univ., Osaka (Japan); Iwasa, Yoshihiro [Univ. of Tokyo, Tokyo (Japan); RIKEN Center for Emergent Matter Science (CEMS), Wako (Japan)
2015-03-18
Superconductivity commonly appears under pressure in charge densit wave (CDW)-bearing transition metal dichalcogenides (TMDs)^{1,2}, but ha emerged so far only via either intercalation with electron donors^{3} or electrostati doping^{4} in CDW-free TMDs. Theoretical calculations have predicted that th latter should be metallized through bandgap closure under pressure^{5,6}, bu superconductivity remained elusive in pristine 2H-MoS_{2} upon substantia compression, where a pressure of up to 60 GPa only evidenced the metalli state^{7,8}. Here we report the emergence of superconductivity in pristine 2H-MoS at 90 GPa. The maximum onset transition temperature T_{c}^{(onset)} of 11.5 K, th highest value among TMDs and nearly constant from 120 up to 200 GPa, is wel above that obtained by chemical doping3 but comparable to that obtained b electrostatic doping4. T_{c}^{(onset)} is more than an order of magnitude larger tha present theoretical expectations, raising questions on either the curren calculation methodologies or the mechanism of the pressure-induced pairin state. Lastly, our findings strongly suggest further experimental and theoretical effort directed toward the study of the pressure-induced superconductivity in all CDWfre TMDs.
d -wave superconductivity in boson+fermion dimer models
Goldstein, Garry; Chamon, Claudio; Castelnovo, Claudio
2017-05-01
We present a slave-particle mean-field study of the mixed boson+fermion quantum dimer model introduced by Punk et al. [Proc. Natl. Acad. Sci. USA 112, 9552 (2015), 10.1073/pnas.1512206112] to describe the physics of the pseudogap phase in cuprate superconductors. Our analysis naturally leads to four charge e fermion pockets whose total area is equal to the hole doping p for a range of parameters consistent with the t -J model for high-temperature superconductivity. Here we find that the dimers are unstable to d -wave superconductivity at low temperatures. The region of the phase diagram with d -wave rather than s -wave superconductivity matches well with the appearance of the four fermion pockets. In the superconducting regime, the dispersion contains eight Dirac cones along the diagonals of the Brillouin zone.
Nematicity, magnetism and superconductivity in FeSe
Böhmer, Anna E.; Kreisel, Andreas
2018-01-01
Iron-based superconductors are well known for their complex interplay between structure, magnetism and superconductivity. FeSe offers a particularly fascinating example. This material has been intensely discussed because of its extended nematic phase, whose relationship with magnetism is not obvious. Superconductivity in FeSe is highly tunable, with the superconducting transition temperature, T c, ranging from 8 K in bulk single crystals at ambient pressure to almost 40 K under pressure or in intercalated systems, and to even higher temperatures in thin films. In this topical review, we present an overview of nematicity, magnetism and superconductivity, and discuss the interplay of these phases in FeSe. We focus on bulk FeSe and the effects of physical pressure and chemical substitutions as tuning parameters. The experimental results are discussed in the context of the well-studied iron-pnictide superconductors and interpretations from theoretical approaches are presented.
Nematicity, magnetism and superconductivity in FeSe.
Böhmer, Anna E; Kreisel, Andreas
2018-01-17
Iron-based superconductors are well known for their complex interplay between structure, magnetism and superconductivity. FeSe offers a particularly fascinating example. This material has been intensely discussed because of its extended nematic phase, whose relationship with magnetism is not obvious. Superconductivity in FeSe is highly tunable, with the superconducting transition temperature, T c, ranging from 8 K in bulk single crystals at ambient pressure to almost 40 K under pressure or in intercalated systems, and to even higher temperatures in thin films. In this topical review, we present an overview of nematicity, magnetism and superconductivity, and discuss the interplay of these phases in FeSe. We focus on bulk FeSe and the effects of physical pressure and chemical substitutions as tuning parameters. The experimental results are discussed in the context of the well-studied iron-pnictide superconductors and interpretations from theoretical approaches are presented.
Directory of Open Access Journals (Sweden)
Samo eLasič
2014-02-01
Full Text Available Diffusion tensor imaging (DTI is the method of choice for non-invasive investigations of the structure of human brain white matter. The results are conventionally reported as maps of the fractional anisotropy (FA, which is a parameter related to microstructural features such as axon density, diameter, and myelination. The interpretation of FA in terms of microstructure becomes ambiguous when there is a distribution of axon orientations within the image voxel. In this paper, we propose a procedure for resolving this ambiguity by determining a new parameter, the microscopic fractional anisotropy (µFA, which corresponds to the FA without the confounding influence of orientation dispersion. In addition, we suggest a method for measuring the orientational order parameter (OP for the anisotropic objects. The experimental protocol is capitalizing on a recently developed diffusion NMR pulse sequence based on magic-angle spinning of the q-vector. Proof-of-principle experiments are carried out on microimaging and clinical MRI equipment using lyotropic liquid crystals and plant tissues as model materials with high µFA and low FA on account of orientation dispersion. We expect the presented method to be especially fruitful in combination with DTI and high angular resolution acquisition protocols for neuroimaging studies of grey and white matter.
A new microwave resonator readout scheme for superconducting qubits
Metcalfe, Michael B.
Quantum computation is a relatively new field of research, which uses the properties of quantum mechanical systems for information processing. While most proposals for constructing such a quantum computer involve using microscopic degrees of freedom such as those of trapped ions or nuclear spins, this thesis concentrates on using the collective electromagnetic response of a macroscopic electrical circuit to construct the fundamental building block of a quantum computer---a qubit. These macroscopic systems are inherently more difficult to protect from decoherence compared to the microscopic qubit systems because of strong environmental coupling through, for example, the measurement leads. However, superconducting quantum circuits should be easier to scale to large multi qubit systems since they involve simple electrical elements, such as inductors and capacitors for coupling qubits. Furthermore, they can be produced using the highly developed fabrication techniques of integrated circuits. One of the outstanding issues in superconducting qubit circuits is to read out the qubit state without introducing excessive noise. Such a readout scheme requires speed, sensitivity and should minimally disturb the qubit state. To meet these requirements we have developed a new type of dispersive bifurcating amplifier, called the cavity bifurcation amplifier (CBA), which consists of a Josephson junction imbedded in a microwave on-chip resonator. The optimum resonator design is based on a simple coplanar waveguide (CPW), imposing a pre-determined frequency and whose other RF characteristics like the quality factor are easily controlled and optimized. The CBA is sensitive to the susceptibility of the superconducting qubit with respect to an external control parameter (e.g., flux) and hence during both qubit manipulation and readout sequences, the qubit can be biased on a so-called "sweet spot", where it is immune to first order fluctuations in this parameter. This readout has no on
Motiei, H.; Jafari, A.; Naderali, R.
2017-02-01
In this paper, two chemically synthesized organic azo dyes, 2-(2,5-Dichloro-phenyazo)-5,5-dimethyl-cyclohexane-1,3-dione (azo dye (i)) and 5,5-Dimethyl-2-tolylazo-cyclohexane-1,3-dione (azo dye (ii)), have been studied from optical Kerr nonlinearity point of view. These materials were characterized by Ultraviolet-visible spectroscopy. Experiments were performed using a continous wave diode-pumped laser at 532 nm wavelength in three intensities of the laser beam. Nonlinear absorption (β), refractive index (n2) and third-order susceptibility (χ (3)) of dyes, were calculated. Nonlinear absorption coefficient of dyes have been calculated from two methods; 1) using theoretical fits and experimental data in the Z-scan technique, 2) using the strength of nonlinearity curves. The values of β obtained from both of the methods were approximately the same. The results demonstrated that azo dye (ii) displays better nonlinearity and has a lower two-photon absorption threshold than azo dye (i). Calculated parameter related to strength of nonlinearity for azo dye (ii) was higher than azo dye (i), It may be due to presence of methyl in azo dye (ii) instead of chlorine in azo dye (i). Furthermore, The measured values of third order susceptibility of azo dyes were from the order of 10-9 esu . These azo dyes can be suitable candidate for optical switching devices.
Superconducting generators for wind turbines: design considerations
DEFF Research Database (Denmark)
Mijatovic, Nenad; Abrahamsen, Asger Bech; Træholt, Chresten
2010-01-01
The harmonic content of high temperature superconductors (HTS) field winding in air-core high temperature superconducting synchronous machine (HTS SM) has been addressed in order to investigate tendency of HTS SM towards mechanical oscillation and additional loss caused by higher flux harmonic....... Both analytical expressions for flux distribution and current sheet distribution have been derived and analyzed. The two main contributors to the AC loss of HTS rotor winding are also identified and their influence addressed on general level....
Theory and technology for superconducting cavities
Lengeler, Herbert
1993-01-01
The course will address Physicist and Engineers who are newcomers in the field of accelerators and accelerating cavities. The elements of RF-Superconductivity will be presented with special relevance to accelerating cavities. The present ststus of achievable accelerating fields and RF losses will be given and their link to the special technologies for cavity fabrication and surface treatments will be stressed. Cavity auxiliaries like main couplers, higher order mode couplers and frequency tuners will be described.
Intertwined Orders in Heavy-Fermion Superconductor CeCoIn_{5}
Directory of Open Access Journals (Sweden)
Duk Y. Kim
2016-12-01
Full Text Available The appearance of spin-density-wave (SDW magnetic order in the low-temperature and high-field corner of the superconducting phase diagram of CeCoIn_{5} is unique among unconventional superconductors. The nature of this magnetic Q phase is a matter of current debate. Here, we present the thermal conductivity of CeCoIn_{5} in a rotating magnetic field, which reveals the presence of an additional order inside the Q phase that is intimately intertwined with the superconducting d-wave and SDW orders. A discontinuous change of the thermal conductivity within the Q phase, when the magnetic field is rotated about antinodes of the superconducting d-wave order parameter, demands that the additional order must change abruptly, together with the recently observed switching of the SDW. A combination of interactions, where spin-orbit coupling orients the SDW, which then selects the secondary p-wave pair-density-wave component (with an average amplitude of 20% of the primary d-wave order parameter, accounts for the observed behavior.
Resonating Valence Bonds and Mean-Field d-Wave Superconductivity in Graphite
Energy Technology Data Exchange (ETDEWEB)
Black-Schaffer, Annica M.
2010-04-27
We investigate the possibility of inducing superconductivity in a graphite layer by electronic correlation effects. We use a phenomenological microscopic Hamiltonian which includes nearest neighbor hopping and an interaction term which explicitly favors nearest neighbor spin-singlets through the well-known resonance valence bond (RVB) character of planar organic molecules. Treating this Hamiltonian in mean-field theory, allowing for bond-dependent variation of the RVB order parameter, we show that both s- and d-wave superconducting states are possible. The d-wave solution belongs to a two-dimensional representation and breaks time reversal symmetry. At zero doping there exists a quantum critical point at the dimensionless coupling J/t = 1.91 and the s- and d-wave solutions are degenerate for low temperatures. At finite doping the d-wave solution has a significantly higher T{sub c} than the s-wave solution. By using density functional theory we show that the doping induced from sulfur absorption on a graphite layer is enough to cause an electronically driven d-wave superconductivity at graphite-sulfur interfaces. We also discuss applying our results to the case of the intercalated graphites as well as the validity of a mean-field approach.
Computation of Superconducting Generators for Wind Turbine Applications
DEFF Research Database (Denmark)
Rodriguez Zermeno, Victor Manuel
The idea of introducing a superconducting generator for offshore wind turbine applications has received increasing support. It has been proposed as a way to meet energy market requirements and policies demanding clean energy sources in the near future. However, design considerations have to take...... of the generator including ramp-up of rotor coils, load connection and change was simulated. Hence, transient hysteresis losses in the superconducting coils were computed. This allowed addressing several important design and performance issues such as critical current of the superconducting coils, electric load......, to the actual generators in the KW (MW) class with an expected cross section in the order of decimeters (meters). This thesis work presents cumulative results intended to create a bottom-up model of a synchronous generator with superconducting rotor windings. In a first approach, multiscale meshes with large...
Review of 2D superconductivity: the ultimate case of epitaxial monolayers
Brun, Christophe; Cren, Tristan; Roditchev, Dimitri
2017-01-01
order to illustrate their specific properties related to quantum-size effects. In the next section 3 we review the growth methods and structural properties of the presented 2DEG surface-confined superconductors. In section 4, we review the electronic structure and Fermi surface properties as measured by macroscopic ARPES and confront them to ab initio DFT calculations based on the characterized atomic structures of the monolayers. The following section 5 reviews the macroscopic properties inferred from in situ electrical transport measurements methods, including attempts to study the Berezinsky-Kosterlitz-Thouless 2D regime. In the last section 6, we summarize the emerging local spectroscopic properties measured by STS. These latter demonstrate variations of the local superconducting properties at a scale much shorter than the superconducting coherence length due to a combined effect of non-magnetic disorder and two-dimensionality. Further peculiar local spectroscopic effects are presented giving evidence for the presence of a mixed singlet-triplet superconducting order parameter induced by the presence of a strong Rashba spin-orbit coupling term at the surface. These local signatures will be discussed along with ARPES and transport measurements in parallel high magnetic field on closely related systems. Finally, we present in anisotropic Pb and In monolayers the peculiar role played by atomic steps on vortex properties, leading to the observation by STS of mixed Abrikosov-Josephson vortices in agreement with in situ macroscopic transport measurements. From the overview of all recent experimental and theoretical results it appears that these surface 2D superconductors, such as one monolayer of Pb on Si(111), are ideal templates to engineer and realize topological superconductivity.
Investigation of superconducting thin film structures prepared by nanoscale wedge polishing
Energy Technology Data Exchange (ETDEWEB)
Pollithy, Martin; Hoefer, Katharina; Schinkel, Uwe; Michalowski, Peter; Grosse, Veit; Schmidl, Frank; Seidel, Paul [FSU Jena, Institute of Solid State Physics, Helmholtzweg 5, D-07743 Jena (Germany); Meier, Dagmar; Shapoval, Tanya [IFW Dresden, Institute for Metallic Materials, PO Box 270116, D-01171 Dresden (Germany)
2009-07-01
The performance of dc-SQUID gradiometers depends very strong on the spread of the critical parameters Ic, Rn and Ls. After the preparation of high temperature superconducting devices it could be useful to tune the superconducting properties by decrease of the film thickness. On the other hand it is often helpful for sensor applications to realise a superconducting thin film structure with a smooth surface to avoid resistive or superconducting shunts in insulating layers on the top of the superconductor. In these investigations we use a mechanical wedge polishing procedure to thin the superconducting devices (microbridges, dc-SQUIDs or dc-SQUID gradiometers) before and/or after the first measurements of the electrical properties. AFM and SEM measurements were done to characterise the film morphology. Temperature dependent measurements of the superconducting properties of microbridges, dc-SQUIDs and dc-SQUID gradiometer structures were realised. We discuss the possibilities and limitations of this procedure.
2017 Gordon Conference on Superconductivity
Energy Technology Data Exchange (ETDEWEB)
Chubukov, Andrey [Univ. of Minnesota, Twin Cities, MN (United States)
2017-11-14
The DOE award was for a 2017 Gordon Research conference on Superconductivity (GRC). The objective of GRC is to interchange the information about the latest theoretical and experimental developments in the area of superconductivity and to select most perspective directions for future research in this area.The goal of the Gordon Conference on Superconductivity is to present and discuss the latest results in the field of modern superconductivity, discuss new ideas and new directions of research in the area. It is a long-standing tradition of the Gordon conference on Superconductivity that the vast majority of participants are junior scientists. Funding for the conference would primarily be used to support junior researchers, particularly from under-represented groups. We had more 10 female speakers, some of them junior researchers, and some funding was used to support these speakers. The conference was held together with Gordon Research Seminar on Superconductivity, where almost all speakers and participants were junior scientists.
Induced superconductivity in graphene grown on rhenium.
Tonnoir, C; Kimouche, A; Coraux, J; Magaud, L; Delsol, B; Gilles, B; Chapelier, C
2013-12-13
We report a new way to strongly couple graphene to a superconductor. The graphene monolayer has been grown directly on top of a superconducting Re(0001) thin film and characterized by scanning tunneling microscopy and spectroscopy. We observed a moiré pattern due to the mismatch between Re and graphene lattice parameters that we have simulated with ab initio calculations. The density of states around the Fermi energy appears to be position dependent on this moiré pattern. Tunneling spectroscopy performed at 50 mK shows that the superconducting behavior of graphene on Re is well described by the Bardeen-Cooper-Schrieffer theory and stands for a very good interface between the graphene and its metallic substrate.
Calculations of superconducting parametric amplifiers performances
Goto, T.; Takeda, M.; Saito, S.; Shimakage, H.
2017-07-01
A superconducting parametric amplifier is an electromagnetic wave amplifier with high-quality characteristics such as a wide bandwidth, an extremely low noise, and a high dynamic range. In this paper, we report on the estimations of a YBCO superconducting parametric amplifier characteristic. The YBCO thin films were deposited on an MgO substrate by a pulsed laser deposition method. Based on the measured YBCO thin film parameters, theoretical calculations were implemented for evaluations of kinetic inductance nonlinearities and parametric gains. The nonlinearity of the YBCO thin film was estimated to be stronger than a single crystal NbTiN thin film. It is indicated that the YBCO parametric amplifier has a potential to be realized the amplifier with the high parametric gain. It is also expected that it could be operated in the range of the high frequency band, at the high temperature, and low applied current.
Statistical mechanics of superconductivity
Kita, Takafumi
2015-01-01
This book provides a theoretical, step-by-step comprehensive explanation of superconductivity for undergraduate and graduate students who have completed elementary courses on thermodynamics and quantum mechanics. To this end, it adopts the unique approach of starting with the statistical mechanics of quantum ideal gases and successively adding and clarifying elements and techniques indispensible for understanding it. They include the spin-statistics theorem, second quantization, density matrices, the Bloch–De Dominicis theorem, the variational principle in statistical mechanics, attractive interaction, and bound states. Ample examples of their usage are also provided in terms of topics from advanced statistical mechanics such as two-particle correlations of quantum ideal gases, derivation of the Hartree–Fock equations, and Landau’s Fermi-liquid theory, among others. With these preliminaries, the fundamental mean-field equations of superconductivity are derived with maximum mathematical clarity based on ...
Superconducting Accelerator Magnets
Mess, K H; Wolff, S
1996-01-01
The main topic of the book are the superconducting dipole and quadrupole magnets needed in high-energy accelerators and storage rings for protons, antiprotons or heavy ions. The basic principles of low-temperature superconductivity are outlined with special emphasis on the effects which are relevant for accelerator magnets. Properties and fabrication methods of practical superconductors are described. Analytical methods for field calculation and multipole expansion are presented for coils without and with iron yoke. The effect of yoke saturation and geometric distortions on field quality is studied. Persistent magnetization currents in the superconductor and eddy currents the copper part of the cable are analyzed in detail and their influence on field quality and magnet performance is investigated. Superconductor stability, quench origins and propagation and magnet protection are addressed. Some important concepts of accelerator physics are introduced which are needed to appreciate the demanding requirements ...
Chen, Xiao-Jia; Struzhkin, Viktor V.; Wu, Zhigang; Somayazulu, Maddury; Qian, Jiang; Kung, Simon; Christensen, Axel Nørlund; Zhao, Yusheng; Cohen, Ronald E.; Mao, Ho-kwang; Hemley, Russell J.
2005-01-01
Detailed study of the equation of state, elasticity, and hardness of selected superconducting transition-metal nitrides reveals interesting correlations among their physical properties. Both the bulk modulus and Vickers hardness are found to decrease with increasing zero-pressure volume in NbN, HfN, and ZrN. The computed elastic constants from first principles satisfy c11 > c12 > c44 for NbN, but c11 > c44 > c12 for HfN and ZrN, which are in good agreement with the neutron scattering data. The cubic δ-NbN superconducting phase possesses a bulk modulus of 348 GPa, comparable to that of cubic boron nitride, and a Vickers hardness of 20 GPa, which is close to sapphire. Theoretical calculations for NbN show that all elastic moduli increase monotonically with increasing pressure. These results suggest technological applications of such materials in extreme environments. PMID:15728352
Superconductivity an introduction
Kleiner, Reinhold
2016-01-01
The third edition of this proven text has been developed further in both scope and scale to reflect the potential for superconductivity in power engineering to increase efficiency in electricity transmission or engines. The landmark reference remains a comprehensive introduction to the field, covering every aspect from fundamentals to applications, and presenting the latest developments in organic superconductors, superconducting interfaces, quantum coherence, and applications in medicine and industry. Due to its precise language and numerous explanatory illustrations, it is suitable as an introductory textbook, with the level rising smoothly from chapter to chapter, such that readers can build on their newly acquired knowledge. The authors cover basic properties of superconductors and discuss stability and different material groups with reference to the latest and most promising applications, devoting the last third of the book to applications in power engineering, medicine, and low temperature physics. An e...
Competition between Superconductivity and Magnetism in Non-centrosymmetric (La1-xCex)NiC2
Katano, Susumu; Shibata, Kohei; Nakashima, Kotaro; Yoshimura, Hideaki; Matsubara, Yohei
2017-10-01
The superconducting and magnetic properties of non-centrosymmetric (La1-xCex)NiC2 solid solutions have been studied by X-ray diffraction, electrical resistivity, specific heat and magnetic measurements. The paramagnetic susceptibility shows that Ce forms localized magnetic moments of about 2.5 μB, the value expected for a Ce3+ free ion, throughout the whole concentration range. With these localized magnetic moments, the superconducting transition temperature Tc of ˜2.8 K for LaNiC2 decreases rapidly, disappearing at about 2 at. % Ce. This marked suppression of Tc by the paramagnetic Ce impurities implies that the system is a BCS-type superconductor with a full energy gap. The substitution of La for Ce also substantially changes the unique magnetism of CeNiC2 that exhibits successive transitions from the paramagnetic state to an incommensurate antiferromagnetic ordering below 20 K, then to a commensurate antiferromagnetic state at 10 K, and further to a ferromagnetic (or ferrimagnetic) order below 2 K. By the substitution of Ce for La the magnetic ordered state appears above around 4 at. % Ce. Some electronic parameters both for the superconducting state and for the magnetic state are estimated from the experimental data, and the electronic characteristics of these states are discussed. On the basis of the results, the phase diagram for temperature vs concentration is constructed.
How to make graphene superconducting
Profeta, Gianni; Calandra, Matteo; Mauri, Francesco
2011-01-01
Graphene is the physical realization of many fundamental concepts and phenomena in solid state-physics, but in the long list of graphene remarkable properties, a fundamental block is missing: superconductivity. Making graphene superconducting is relevant as the easy manipulation of this material by nanolytographic techniques paves the way to nanosquids, one-electron superconductor-quantum dot devices, superconducting transistors at the nano-scale and cryogenic solid-state coolers. Here we exp...
Superconducting metamaterials and qubits
Plourde, B. L. T.; Wang, Haozhi; Rouxinol, Francisco; LaHaye, M. D.
2015-01-01
Superconducting thin-film metamaterial resonators can provide a dense microwave mode spectrum with potential applications in quantum information science. We report on the fabrication and low-temperature measurement of metamaterial transmission-line resonators patterned from Al thin films. We also describe multiple approaches for numerical simulations of the microwave properties of these structures, along with comparisons with the measured transmission spectra. The ability to predict the mode ...
Unconventional superconductivity near inhomogeneities
Energy Technology Data Exchange (ETDEWEB)
Poenicke, A.F.
2008-01-25
After the presentation of a quasi-classical theory the specific heat of Sr{sub 2}RuO{sub 4} is considered. Then tunneling spectroscopy on cuprate superconductors is discussed. Thereafter the subharmonic gap structure in d-wave superconductors is considered. Finally the application of the S-matrix in superconductivity is discussed with spin mixing, CrO{sub 2} as example, and an interface model. (HSI)
Superconducting magnetic energy storage
Energy Technology Data Exchange (ETDEWEB)
Rogers, J.D.; Boenig, H.J.; Hassenzahl, W.V.; Schermer, R.I.
1978-01-01
Long-time varying-daily, weekly, and seasonal-power demands require the electric utility industry to have installed generating capacity in excess of the average load. Energy storage can reduce the requirement for less efficient excess generating capacity used to meet peak load demands. Short-time fluctuations in electric power can occur as negatively damped oscillations in complex power systems with generators connected by long transmission lines. Superconducting inductors with their associated converter systems are under development for both load leveling and transmission line stabilization in electric utility systems. Superconducting magnetic energy storage (SMES) is based upon the phenomenon of the nearly lossless behavior of superconductors. Application is, in principal, efficient since the electromagnetic energy can be transferred to and from the storage coils without any intermediate conversion to other energy forms. Results from a reference design for a 10-GWh SMES unit for load leveling are presented. The conceptual engineering design of a 30-MJ, 10-MW energy storage coil is discussed with regard to system stabilization, and tests of a small scale, 100-KJ SMES system are presented. Some results of experiments are provided from a related technology based program which uses superconducting inductive energy storage to drive fusion plasmas.
Litak, G.; Annett, J. F.; Györffy, B. L.; Wysokiski, K. I.
2004-04-01
Superconductivity in Sr2RuO4 is one of the most interesting phenomena in current condensed matter physics, since it is revealed to be a triplet-pairing state. Our Editor's Choice [1] considers an important problem related to the type of order parameter in this material.The position of line nodes on the Fermi surface, as evident from recent measurements, has been determined for various scenarios shown in the cover picture. Using these models, the temperature dependence of heat capacity and penetration depth has been calculated for easy comparison with experiments.The first author, Grzegorz Litak, is assistant professor at Technical University of Lublin and visiting scientist at the Max Planck Institute in Dresden. He is working on the effect of disorder on correlated and exotic superconductors, nonlinear dynamics, and superconductivity in strontium ruthenate.
Energy Technology Data Exchange (ETDEWEB)
Measson, M.-A. [Departement de Recherche Fondamentale sur la Matiere Condensee, SPSMS, CEA Grenoble, 38054 Grenoble (France)]. E-mail: mmeasson@cea.fr; Brison, J.P. [Centre de Recherches sur les Tres Basses Temperatures, CNRS, 25 avenue des Martyrs, BP166, 38042 Grenoble Cedex (France)]. E-mail: brison@grenoble.cnrs.fr; Seyfarth, G. [Centre de Recherches sur les Tres Basses Temperatures, CNRS, 25 avenue des Martyrs, BP166, 38042 Grenoble Cedex (France); Braithwaite, D. [Departement de Recherche Fondamentale sur la Matiere Condensee, SPSMS, CEA Grenoble, 38054 Grenoble (France); Lapertot, G. [Departement de Recherche Fondamentale sur la Matiere Condensee, SPSMS, CEA Grenoble, 38054 Grenoble (France); Salce, B. [Departement de Recherche Fondamentale sur la Matiere Condensee, SPSMS, CEA Grenoble, 38054 Grenoble (France); Flouquet, J. [Departement de Recherche Fondamentale sur la Matiere Condensee, SPSMS, CEA Grenoble, 38054 Grenoble (France); Lhotel, E. [Centre de Recherches sur les Tres Basses Temperatures, CNRS, 25 avenue des Martyrs, BP166, 38042 Grenoble Cedex (France); Paulsen, C. [Centre de Recherches sur les Tres Basses Temperatures, CNRS, 25 avenue des Martyrs, BP166, 38042 Grenoble Cedex (France); Sugawara, H. [Department of Physics, Tokyo Metropolitan University, Minami-Ohsawa 1-1, Hashioji, Tokyo 192-0397 (Japan); Sato, H. [Department of Physics, Tokyo Metropolitan University, Minami-Ohsawa 1-1, Hashioji, Tokyo 192-0397 (Japan); Canfield, P.C. [Ames Laboratory Department of Physics and Astronomy, Iowa State University, Ames, IA 50011 (United States); Izawa, K. [Institute for Solid State Physics, University of Tokyo, Kashiwanoha 5-1-5 Kashiwa, Chiba 277-8581 (Japan); Matsuda, Y. [Institute for Solid State Physics, University of Tokyo, Kashiwanoha 5-1-5 Kashiwa, Chiba 277-8581 (Japan)
2005-04-30
We present a precise (H-T) phase diagram of the double superconducting transition in the specific heat of the heavy fermion superconductor PrOs{sub 4}Sb{sub 12}, down to 350mK, on a sample which exhibits two sharp distinct anomalies at T{sub c1}=1.89K and T{sub c2}=1.72K. Comparison with an existing phase diagram based on transport measurements will be reviewed. The intrinsic or extrinsic nature of this double transition is discussed in light of some characterisations of the superconducting transition of different samples and with respect to the historical case of UPt{sub 3}. Finally, we give a detailed analysis of H{sub c2} which shows the importance of the multiband character of the electronic structure of PrOs{sub 4}Sb{sub 12} and gives strong support to an even parity order parameter.
Wu, Xiangyang; Tan, Yunfei; Fang, Zhen; Jiang, Donghui; Chen, Zhiyou; Chen, Wenge; Kuang, Guangli
2017-10-01
A large cable-in-conduit-conductor (CICC) test facility has been designed and fabricated at the High Magnetic Field Laboratory of the Chinese Academy of Sciences (CHMFL) in order to meet the test requirement of the conductors which are applied to the future fusion reactor. The critical component of the test facility is an 80 kA superconducting transformer which consists of a multi-turn primary coil and a minor-turn secondary coil. As the current source of the conductor samples, the electromagnetic performance of the superconducting transformer determines the stability and safety of the test facility. In this paper, the key factors and parameters, which have much impact on the performance of the transformer, are analyzed in detail. The conceptual design and optimizing principles of the transformer are discussed. An Electromagnetic-Circuit coupled model built in ANSYS Multiphysics is successfully used to investigate the electromagnetic characterization of the transformer under the dynamic operation condition.
Black-Schaffer, Annica M
2012-11-09
We investigate the effect of edges on the intrinsic d-wave superconducting state in graphene doped close to the van Hove singularity. While the bulk is in a chiral d(x(2)-y(2)) + id(xy) state, the order parameter at any edge is enhanced and has d(x(2)-y(2))-symmetry, with a decay length strongly increasing with weakening superconductivity. No graphene edge is pair breaking for the d((x(2)-y{2)) state, and there are no localized zero-energy edge states. We find two chiral edge modes which carry a spontaneous, but not quantized, quasiparticle current related to the zero-energy momentum. Moreover, for realistic values of the Rashba spin-orbit coupling, a Majorana fermion appears at the edge when tuning a Zeeman field.
Topological Superconductivity in Dirac Semimetals.
Kobayashi, Shingo; Sato, Masatoshi
2015-10-30
Dirac semimetals host bulk band-touching Dirac points and a surface Fermi loop. We develop a theory of superconducting Dirac semimetals. Establishing a relation between the Dirac points and the surface Fermi loop, we clarify how the nontrivial topology of Dirac semimetals affects their superconducting state. We note that the unique orbital texture of Dirac points and a structural phase transition of the crystal favor symmetry-protected topological superconductivity with a quartet of surface Majorana fermions. We suggest the possible application of our theory to recently discovered superconducting states in Cd_{3}As_{2}.
An Analytical Benchmark for the Calculation of Current Distribution in Superconducting Cables
Bottura, L; Fabbri, M G
2002-01-01
The validation of numerical codes for the calculation of current distribution and AC loss in superconducting cables versus experimental results is essential, but could be affected by approximations in the electromagnetic model or incertitude in the evaluation of the model parameters. A preliminary validation of the codes by means of a comparison with analytical results can therefore be very useful, in order to distinguish among different error sources. We provide here a benchmark analytical solution for current distribution that applies to the case of a cable described using a distributed parameters electrical circuit model. The analytical solution of current distribution is valid for cables made of a generic number of strands, subjected to well defined symmetry and uniformity conditions in the electrical parameters. The closed form solution for the general case is rather complex to implement, and in this paper we give the analytical solutions for different simplified situations. In particular we examine the ...
Bhandari, Subodh
There has been a significant growth in the use of UAV helicopters for a multitude of military and civilian applications over the last few years. Due to these numerous applications, from crop dusting to remote sensing, UAV helicopters are now a major topic of interest within the aerospace community. The main research focus is on the development of automatic flight control systems (AFCS). The design of AFCS for these vehicles requires a mathematical model representing the dynamics of the vehicle. The mathematical model is developed either from first-principles, using the equations of motion of the vehicle, or from the flight data, using parameter identification techniques. The traditional six-degrees-of-freedom (6-DoF) dynamics model is not suitable for high-bandwidth control system design. Such models are valid only within the low- to mid-frequency range. The agility and high maneuverability of small-scale helicopters require a high-bandwidth control system for full authority autonomous performance. The design of a high-bandwidth control system in turn requires a high-fidelity simulation model that is able to capture the key dynamics of the helicopter. These dynamics include the rotor dynamics. This dissertation presents the development of a 14-degrees-of-freedom (14-DoF) state-space linear model for the KU Thunder Tiger Raptor 50 UAV helicopter from first-principles and from flight test data using a parameter identification technique for the hovering and forward flight conditions. The model includes rigid body, rotor regressive, rotor inflow, stabilizer bar, and rotor coning dynamics. The model is implemented within The MathWork's MATLAB/Simulink environment. The simulation results show that the high-order model is able to predict the helicopter's dynamics up to the frequency of 30 rad/sec. The main contributions of this dissertation are the development of a high-order simulation model for a small UAV helicopter from first-principles and the identification of a
Murakami, Yuta; Werner, Philipp; Tsuji, Naoto; Aoki, Hideo
2014-03-01
Phonon-mediated superconductivity when, as in the alkali-doped fullerides and aromatic compounds, the Coulomb interaction, electron-phonon coupling and phonon frequencies are all comparable to the electronic band width poses an intriguing question. In order to obtain insights into the superconductivity in this regime, we have analyzed the Holstein-Hubbard model with the dynamical mean-field theory with a continuous-time quantum Monte Carlo impurity solver. We focus on the s-wave superconducting state when the Hubbard repulsion U, the phonon mediated attractive interaction λ and the phonon energy (ω0) are comparable to the bandwidth. A particular interest is the effects of the retardation and the strong Coulomb interaction on the behavior of the transition temperature TC, the superconductivity order parameter and gap in spectrum (Δ). We find that the Tc-dome against Ueff = U - λ significantly deviates from that in the anti-adiabatic limit, and that an effective model in the polaron representation reproduces the effect of the retardation and the Coulomb interaction well even for ω0 smaller than the bandwidth. We also show an unusual isotope effect for fast phonons and deviation of 2 Δ /kBTC from BCS value.
Optimization of superconducting tiling pattern for superconducting bearings
Energy Technology Data Exchange (ETDEWEB)
Hull, John R. (Hinsdale, IL)
1996-01-01
An apparatus and method for reducing magnetic field inhomogeneities which produce rotational loss mechanisms in high temperature superconducting magnetic bearings. Magnetic field inhomogeneities are reduced by dividing high temperature superconducting structures into smaller structures, and arranging the smaller structures into tiers which stagger the magnetic field maximum locations of the smaller structures.
Superconducting Materials: History and the Future
Kitazawa, Koichi
The following sections are included: * The Tc Barrier of BCS Superconductors Till 1986 * Development of low temperature superconductors * Critical temperature 23K of Nb3Ge: Unsurmountable Tc-barrier? * USO: Unidentified Superconducting Object * Discovery, Confirmation and Identification of the High Temperature Superconductors * Further Materials Developments * Unique Electronic Structure in the HTS Cuprates * Characteristics of HTS Superconductivity Phenomenology * Anisotropy factor and crystal structure * Anisotropy and irreversibility * Anisotropy and the first order vortex lattice phase transition * Anisotropy and the dimensional cross over in the low temperature * Future Material Designing * Practical usage of Bi2212 and Bi2223 at 4K, 20K and 77K * Methods to improve the current carrying performance under strong magnetic fields * Rhenium-doped Hg1223 system * Heavily lead-doped Bi2212 system * Trends of the developments of Bi2212 and Bi2223 wires * Non-cuprate materials * Weak Pinning Potential in the Under-Doped Regime * References
Enhancing superconducting critical current by randomness
Wang, Y. L.; Thoutam, L. R.; Xiao, Z. L.; Shen, B.; Pearson, J. E.; Divan, R.; Ocola, L. E.; Crabtree, G. W.; Kwok, W. K.
2016-01-01
The key ingredient of high critical currents in a type-II superconductor is defect sites that pin vortices. Contrary to earlier understanding on nanopatterned artificial pinning, here we show unequivocally the advantages of a random pinscape over an ordered array in a wide magnetic field range. We reveal that the better performance of a random pinscape is due to the variation of its local density of pinning sites (LDOPS), which mitigates the motion of vortices. This is confirmed by achieving even higher enhancement of the critical current through a conformally mapped random pinscape, where the distribution of the LDOPS is further enlarged. The demonstrated key role of LDOPS in enhancing superconducting critical currents gets at the heart of random versus commensurate pinning. Our findings highlight the importance of random pinscapes in enhancing the superconducting critical currents of applied superconductors.
Towards inducing superconductivity into graphene
Efetov, Dmitri K.
Graphenes transport properties have been extensively studied in the 10 years since its discovery in 2004, with ground-breaking experimental observations such as Klein tunneling, fractional quantum Hall effect and Hofstadters butterfly. Though, so far, it turned out to be rather poor on complex correlated electronic ground states and phase transitions, despite various theoretical predictions. The purpose of this thesis is to help understanding the underlying theoretical and experimental reasons for the lack of strong electronic interactions in graphene, and, employing graphenes high tunability and versatility, to identify and alter experimental parameters that could help to induce stronger correlations. In particular graphene holds one last, not yet experimentally discovered prediction, namely exhibiting intrinsic superconductivity. With its vanishingly small Fermi surface at the Dirac point, graphene is a semi-metal with very weak electronic interactions. Though, if it is doped into the metallic regime, where the size of the Fermi surface becomes comparable to the size of the Brillouin zone, the density of states becomes sizeable and electronic interactions are predicted to be dramatically enhanced, resulting in competing correlated ground states such as superconductivity, magnetism and charge density wave formation. Following these predictions, this thesis first describes the creation of metallic graphene at high carrier doping via electrostatic doping techniques based on electrolytic gates. Due to graphenes surface only properties, we are able to induce carrier densities above n>1014 cm-2 (epsilonF>1eV) into the chemically inert graphene. While at these record high carrier densities we yet do not observe superconductivity, we do observe fundamentally altered transport properties as compared to semi-metallic graphene. Here, detailed measurements of the low temperature resistivity reveal that the electron-phonon interactions are governed by a reduced, density
Investigations of the surface resistance of superconducting materials
Junginger, Tobias; Welsch, Carsten
In particle accelerators superconducting RF cavities are widely used to achieve high accelerating gradients and low losses. Power consumption is proportional to the surface resistance RS which depends on a number of external parameters, including frequency, temperature, magnetic and electric field. Presently, there is no widely accepted model describing the increase of Rs with applied field. In the frame of this project the 400 MHz Quadrupole Resonator has been extended to 800 and 1200 MHz to study surface resistance and intrinsic critical RF magnetic field of superconducting samples over a wide parameter range, establishing it as a world-wide unique test facility for superconducting materials. Different samples were studied and it was shown that Rs is mainly caused by the RF electric field in the case of strongly oxidized surfaces. This can be explained by interface tunnel exchange of electrons between the superconductor and localized states in adjacent oxides. For well prepared surfaces, however, the majori...
Nematic topological superconducting phase in Nb-doped Bi2Se3
Shen, Junying; He, Wen-Yu; Yuan, Noah Fan Qi; Huang, Zengle; Cho, Chang-woo; Lee, Seng Huat; Hor, Yew San; Law, Kam Tuen; Lortz, Rolf
2017-10-01
A nematic topological superconductor has an order parameter symmetry, which spontaneously breaks the crystalline symmetry in its superconducting state. This state can be observed, for example, by thermodynamic or upper critical field experiments in which a magnetic field is rotated with respect to the crystalline axes. The corresponding physical quantity then directly reflects the symmetry of the order parameter. We present a study on the superconducting upper critical field of the Nb-doped topological insulator NbxBi2Se3 for various magnetic field orientations parallel and perpendicular to the basal plane of the Bi2Se3 layers. The data were obtained by two complementary experimental techniques, magnetoresistance and DC magnetization, on three different single crystalline samples of the same batch. Both methods and all samples show with perfect agreement that the in-plane upper critical fields clearly demonstrate a two-fold symmetry that breaks the three-fold crystal symmetry. The two-fold symmetry is also found in the absolute value of the magnetization of the initial zero-field-cooled branch of the hysteresis loop and in the value of the thermodynamic contribution above the irreversibility field, but also in the irreversible properties such as the value of the characteristic irreversibility field and in the width of the hysteresis loop. This provides strong experimental evidence that Nb-doped Bi2Se3 is a nematic topological superconductor similar to the Cu- and Sr-doped Bi2Se3.
Dynamic resistance of a high-Tc superconducting flux pump
Jiang, Zhenan; Hamilton, K.; Amemiya, Naoyuki; Badcock, R. A.; Bumby, C. W.
2014-09-01
Superconducting flux pumps enable large currents to be injected into a superconducting circuit, without the requirement for thermally conducting current leads which bridge between the cryogenic environment and room temperature. In this work, we have built and studied a mechanically rotating flux pump which employs a coated conductor high-Tc superconducting (HTS) stator. This flux pump has been used to excite an HTS double pancake coil at 77 K. Operation of the flux pump causes the current within the superconducting circuit to increase over time, before saturating at a limiting value. Interestingly, the superconducting flux pump is found to possess an effective internal resistance, Reff, which varies linearly with frequency, and is two orders of magnitude larger than the measured series resistance of the soldered contacts within the circuit. This internal resistance sets a limit for the maximum achievable output current from the flux pump, which is independent of the operating frequency. We attribute this effect to dynamic resistance within the superconducting stator wire which is caused by the interaction between the DC transport current and the imposed alternating magnetic field. We provide an analytical expression describing the output characteristics of our rotating flux pump in the high frequency limit, and demonstrate that it describes the time-dependent behavior of our experimental circuit. Dynamic resistance is highlighted as a generic issue that must be considered when optimizing the design of an HTS flux pump.
Superconducting bearings for flywheel applications
DEFF Research Database (Denmark)
Abrahamsen, A.B.
2001-01-01
A literature study on the application of superconducting bearings in energy storage flywheel systems. The physics of magnetic levitation and superconductors are presented in the first part of the report, followed by a discussion of the literature found onthe applications of superconducting bearings...
The Danish Superconducting Cable Project
DEFF Research Database (Denmark)
Tønnesen, Ole
1997-01-01
The design and construction of a superconducting cable is described. The cable has a room temperature dielectric design with the cryostat placed inside the electrical insulation.BSCCO 2223 superconducting tapes wound in helix form around a former are used as the cable conductor. Results from...
Beam commissioning for a superconducting proton linac
Wang, Zhi-Jun; He, Yuan; Jia, Huan; Dou, Wei-ping; Chen, Wei-long; Zhang, X. L.; Liu, Shu-hui; Feng, Chi; Tao, Yue; Wang, Wang-sheng; Wu, Jian-qiang; Zhang, Sheng-hu; Zhao, Hong-Wei
2016-12-01
To develop the next generation of safe and cleaner nuclear energy, the accelerator-driven subcritical (ADS) system emerges as one of the most attractive technologies. It will be able to transmute the long-lived transuranic radionuclides produced in the reactors of today's nuclear power plants into shorter-lived ones, and also it will provide positive energy output at the same time. The prototype of the Chinese ADS (C-ADS) proton accelerator comprises two injectors and a 1.5 GeV, 10 mA continuous wave (CW) superconducting main linac. The injector scheme II at the C-ADS demo facility inside the Institute of Modern Physics is a 10 MeV CW superconducting linac with a designed beam current of 10 mA, which includes an ECR ion source, a low-energy beam transport line, a 162.5 MHz radio frequency quadrupole accelerator, a medium-energy beam transport line, and a superconducting half wave resonator accelerator section. This demo facility has been successfully operating with an 11 mA, 2.7 MeV CW beam and a 3.9 mA, 4.3 MeV CW beam at different times and conditions since June 2014. The beam power has reached 28 kW, which is the highest record for the same type of linear accelerators. In this paper, the parameters of the test injector II and the progress of the beam commissioning are reported.
Magnetism and superconductivity in neodymium/lanthanum superlattices
DEFF Research Database (Denmark)
Goff, J.P.; Sarthour, R.S.; McMorrow, Desmond Francis
1997-01-01
bilayers. Magnetization studies reveal the onset of superconductivity at a temperature comparable to bulk DHCP La, and the results suggest coupling across the antiferromagnetic Nd layers. The magnetic structures, investigated using neutron diffraction techniques, resemble those found in bulk Nd....... For the cubic sites of the DHCP structure the magnetic order is confined to individual Nd blocks. However, the magnetic order on the Nd hexagonal sites propagates coherently through the La, even when it becomes superconducting. (C) 1998 Elsevier Science B.V. All rights reserved....
Superconductivity in a chiral nanotube
Qin, F.; Shi, W.; Ideue, T.; Yoshida, M.; Zak, A.; Tenne, R.; Kikitsu, T.; Inoue, D.; Hashizume, D.; Iwasa, Y.
2017-02-01
Chirality of materials are known to affect optical, magnetic and electric properties, causing a variety of nontrivial phenomena such as circular dichiroism for chiral molecules, magnetic Skyrmions in chiral magnets and nonreciprocal carrier transport in chiral conductors. On the other hand, effect of chirality on superconducting transport has not been known. Here we report the nonreciprocity of superconductivity--unambiguous evidence of superconductivity reflecting chiral structure in which the forward and backward supercurrent flows are not equivalent because of inversion symmetry breaking. Such superconductivity is realized via ionic gating in individual chiral nanotubes of tungsten disulfide. The nonreciprocal signal is significantly enhanced in the superconducting state, being associated with unprecedented quantum Little-Parks oscillations originating from the interference of supercurrent along the circumference of the nanotube. The present results indicate that the nonreciprocity is a viable approach toward the superconductors with chiral or noncentrosymmetric structures.
Energy Technology Data Exchange (ETDEWEB)
Pang, C S; Falco, C M; Kampwirth, R T; Schuller, I K; Hudak, J J; Anastasio, T A
1979-01-01
Results of a preliminary investigation of a superconducting notch filter for possible application in the 2 to 30 MHz high frequency (HF) communication band are presented. The circuit was successfully implemented using planar geometry so that closed cycle refrigeration could be used to cool circuits fabricated from high T/sub c/ Nb/sub 3/Sn or Nb/sub 3/Ge thin films. In the present design, circuit Q's of about 2 x 10/sup 3/ were obtained with 50-ohm source and output impedance. (TFD)
Superconductivity in nanowires
Bezryadin, Alexey
2012-01-01
The importance and actuality of nanotechnology is unabated and will be for years to come. A main challenge is to understand the various properties of certain nanostructures, and how to generate structures with specific properties for use in actual applications in Electrical Engineering and Medicine.One of the most important structures are nanowires, in particular superconducting ones. They are highly promising for future electronics, transporting current without resistance and at scales of a few nanometers. To fabricate wires to certain defined standards however, is a major challenge, and so i
100 years of superconductivity
Globe Info
2011-01-01
Public lecture by Philippe Lebrun, who works at CERN on applications of superconductivity and cryogenics for particle accelerators. He was head of CERN’s Accelerator Technology Department during the LHC construction period. Centre culturel Jean Monnet, route de Gex Tuesday 11 October from 8.30 p.m. to 10.00 p.m. » Suitable for all – Admission free - Lecture in French » Number of places limited For further information: +33 (0)4 50 42 29 37
Superconducting gravimeter. Final report
Energy Technology Data Exchange (ETDEWEB)
Goodkind, J.M.
1982-01-01
The superconducting gravimeter was developed and applied to field measurements. The stability of the instrument yielded the highest precision measurements of the Earth tides ever attained. It revealed unprecedented details about the effect of the atmosphere on gravity. Secular variations in gravity and the stability of the instruments were measured by comparing records from co-located instruments. These efforts have resulted in substantial reductions in the noise level at very low frequencies so that the peak differences between two instruments at the same location can be reduced to 0.1 micron gal.
Superconductivity under high pressure
Energy Technology Data Exchange (ETDEWEB)
Amaya, K.; Shimizu, K.; Takeda, K.; Tateiwa, N.; Muramatsu, T.; Ishizuka, M.; Kobayashi, T.C
2003-05-01
In part 1, we review techniques developed in our laboratory for producing the complex extreme condition of very low temperature and ultra-high pressure and those for measuring electrical resistance and magnetization of the sample confined in the extremely small space of the used pressure cell. In part 2, we review our experimental results in search for pressure-induced superconductivity, which have been obtained by the use of developed techniques. Typical examples are shown in the case of simple inorganic and organic molecular crystals, ionic crystals, and magnetic metals.
Introduction to superconductivity
Rose-Innes, A C
1978-01-01
Introduction to Superconductivity differs from the first edition chiefly in Chapter 11, which has been almost completely rewritten to give a more physically-based picture of the effects arising from the long-range coherence of the electron-waves in superconductors and the operation of quantum interference devices. In this revised second edition, some further modifications have been made to the text and an extra chapter dealing with """"high-temperature"""" superconductors has been added. A vast amount of research has been carried out on these since their discovery in 1986 but the results, both
Song, Xiao-Na; Song, Shuai; Tejado Balsera, Inés; Liu, Lei-Po
2017-10-01
This paper investigates the mixed H ∞ and passive projective synchronization problem for fractional-order (FO) memristor-based neural networks. Our aim is to design a controller such that, though the unavoidable phenomena of time-delay and parameter uncertainty are fully considered, the resulting closed-loop system is asymptotically stable with a mixed H ∞ and passive performance level. By combining active and adaptive control methods, a novel hybrid control strategy is designed, which can guarantee the robust stability of the closed-loop system and also ensure a mixed H ∞ and passive performance level. Via the application of FO Lyapunov stability theory, the projective synchronization conditions are addressed in terms of linear matrix inequality techniques. Finally, two simulation examples are given to illustrate the effectiveness of the proposed method. Supported by National Natural Science Foundation of China under Grant Nos. U1604146, U1404610, 61473115, 61203047, Science and Technology Research Project in Henan Province under Grant Nos. 152102210273, 162102410024, and Foundation for the University Technological Innovative Talents of Henan Province under Grant No. 18HASTIT019
Runge, Anne F; Saavedra, S Scott; Mendes, Sergio B
2006-04-06
This article describes two mathematical formalisms for the determination of the second and fourth order parameters of molecular films using optical spectroscopy. Method A uses polarized total internal reflection fluorescence (TIRF) to calculate the second and fourth order parameters, {P2(cos theta)} and {P4(cos theta)}, using an independently determined value for the angle between the absorption and emission dipoles, gamma. Method B uses {P2(cos theta)} obtained from attenuated total reflectance (ATR) data, along with polarized TIRF measurements to calculate {P4(cos theta)} and {cos2 gamma}. The choice of a specific method should rely on experimental considerations. We also present a method to separate the contributions of substrate surface roughness and dipole orientation with respect to the molecular axis from the spectroscopically determined second and fourth order parameters. Finally, a maximum entropy approach for construction of an orientation distribution from order parameters is compared with the commonly used delta and Gaussian distributions.
Interplay between superconductivity and magnetism in iron-based superconductors
Energy Technology Data Exchange (ETDEWEB)
Chubukov, Andrey V [University of Wisconsin
2015-06-10
This proposal is for theoretical work on strongly correlated electron systems, which are at the center of experimental and theoretical activities in condensed-matter physics. The interest to this field is driven fascinating variety of observed effects, universality of underlying theoretical ideas, and practical applications. I propose to do research on Iron-based superconductors (FeSCs), which currently attract high attention in the physics community. My goal is to understand superconductivity and magnetism in these materials at various dopings, the interplay between the two, and the physics in the phase in which magnetism and superconductivity co-exist. A related goal is to understand the origin of the observed pseudogap-like behavior in the normal state. My research explores the idea that superconductivity is of electronic origin and is caused by the exchange of spin-fluctuations, enhanced due to close proximity to antiferromagnetism. The multi-orbital/multi-band nature of FeSCs opens routes for qualitatively new superconducting states, particularly the ones which break time-reversal symmetry. By all accounts, the coupling in pnictdes is below the threshold for Mott physics and I intend to analyze these systems within the itinerant approach. My plan is to do research in two stages. I first plan to address several problems within weak-coupling approach. Among them: (i) what sets stripe magnetic order at small doping, (ii) is there a preemptive instability into a spin-nematic state, and how stripe order affects fermions; (iii) is there a co-existence between magnetism and superconductivity and what are the system properties in the co-existence state; (iv) how superconductivity emerges despite strong Coulomb repulsion and can the gap be s-wave but with nodes along electron FSs, (v) are there complex superconducting states, like s+id, which break time reversal symmetry. My second goal is to go beyond weak coupling and derive spin-mediated, dynamic interaction between
Karlsruhe: En route to a superconducting r.f. separator
1973-01-01
A superconducting r.f. separator is under construction at Karlsruhe for use at the SPS in the beam-line to the Omega spectrometer. Tests on a section of the first 3 m deflector have given results close to the desired parameters.
RSFQ electronics for controlling superconducting polarity switches
Brandel, O.; Wetzstein, O.; May, T.; Toepfer, H.; Ortlepp, T.; Meyer, H.-G.
2012-12-01
Superconducting radiation sensors are of particular interest for imaging applications in the sub-mm wavelength band because of their extraordinary sensitivity. The rising number of sensors integrated in one array entails the requirement of multiplexing techniques in order to reduce the number of wires leading into the cryogenic stage and thus reduce the thermal losses. One kind of promising code division multiplexing technique is based on a current steering switch (CSS), which is composed of two identical superconducting quantum interference devices (SQUIDs) in parallel current paths. One of them is switched from the superconducting into the normal state controlled by the applied magnetic flux. In this way the signal path can be altered and they can act as a polarity switch for analogue signals. We pursue this concept to use rapid single flux quantum (RSFQ) electronics for controlling these switches. As a first step, the SQUIDs of the CSS are inductively coupled to the storing loops of two delay flip flops (DFFs). Thus, one is able to toggle the polarity of the analogue switch by controlling the state of the DFF by RSFQ control signals. The results of simulations and measurements and also margin analyses are discussed.
Chiral magnetic superconductivity
Directory of Open Access Journals (Sweden)
Kharzeev Dmitri E.
2017-01-01
Full Text Available Materials with charged chiral quasiparticles in external parallel electric and magnetic fields can support an electric current that grows linearly in time, corresponding to diverging DC conductivity. From experimental viewpoint, this “Chiral Magnetic Superconductivity” (CMS is thus analogous to conventional superconductivity. However the underlying physics is entirely different – the CMS does not require a condensate of Cooper pairs breaking the gauge degeneracy, and is thus not accompanied by Meissner effect. Instead, it owes its existence to the (temperature-independent quantum chiral anomaly and the conservation of chirality. As a result, this phenomenon can be expected to survive to much higher temperatures. Even though the chirality of quasiparticles is not strictly conserved in real materials, the chiral magnetic superconductivity should still exhibit itself in AC measurements at frequencies larger than the chirality-flipping rate, and in microstructures of Dirac and Weyl semimetals with thickness below the mean chirality-flipping length that is about 1 – 100 μm. In nuclear physics, the CMS should contribute to the charge-dependent elliptic flow in heavy ion collisions.
Overview on superconducting photoinjectors
Arnold, A
2011-01-01
The success of most of the proposed energy recovery linac (ERL) based electron accelerator projects for future storage ring replacements (SRR) and high power IR–free-electron lasers (FELs) largely depends on the development of an appropriate source. For example, to meet the FEL specifications [J.W. Lewellen, Proc. SPIE Int. Soc. Opt. Eng. 5534, 22 (2004)] electron beams with an unprecedented combination of high brightness, low emittance (0.1 µmrad), and high average current (hundreds of mA) are required. An elegant way to create a beam of such quality is to combine the high beam quality of a normal conducting rf photoinjector with the superconducting technology, i.e., to build a superconducting rf photoinjector (SRF gun). SRF gun R&D programs based on different approaches have been launched at a growing number of institutes and companies (AES, Beijing University, BESSY, BNL, DESY, FZD, TJNAF, Niowave, NPS, Wisconsin University). Substantial progress was achieved in recent years and the first long term ...
Additive Manufactured Superconducting Cavities
Holland, Eric; Rosen, Yaniv; Woolleet, Nathan; Materise, Nicholas; Voisin, Thomas; Wang, Morris; Mireles, Jorge; Carosi, Gianpaolo; Dubois, Jonathan
Superconducting radio frequency cavities provide an ultra-low dissipative environment, which has enabled fundamental investigations in quantum mechanics, materials properties, and the search for new particles in and beyond the standard model. However, resonator designs are constrained by limitations in conventional machining techniques. For example, current through a seam is a limiting factor in performance for many waveguide cavities. Development of highly reproducible methods for metallic parts through additive manufacturing, referred to colloquially as 3D printing\\x9D, opens the possibility for novel cavity designs which cannot be implemented through conventional methods. We present preliminary investigations of superconducting cavities made through a selective laser melting process, which compacts a granular powder via a high-power laser according to a digitally defined geometry. Initial work suggests that assuming a loss model and numerically optimizing a geometry to minimize dissipation results in modest improvements in device performance. Furthermore, a subset of titanium alloys, particularly, a titanium, aluminum, vanadium alloy (Ti - 6Al - 4V) exhibits properties indicative of a high kinetic inductance material. This work is supported by LDRD 16-SI-004.
Development of the composite superconducting magnetic bearing for superconducting flywheel
Energy Technology Data Exchange (ETDEWEB)
Nagaya, S.; Komura, K.; Kashima, N.; Kawashima, H.; Unisuga, S.; Kakiuchi, Y
2003-10-15
Superconducting magnetic bearing for flywheel requires the characteristics such as higher stiffness, lower loss and higher stability. There are two types of superconducting magnetic bearings, one is axial gap type and another is radial gap type and the characteristics of these types are quite different. We think that the supporting system of superconducting flywheel should support the rotor at one position near the center of gravity to minimize the cooling energy loss. We propose that the bearing composed of axial gap type and radial gap type is necessary from the result of this investigation, because the characteristics about both types of bearings should be compensated each other.
Discovery of a Superconducting High-Entropy Alloy
Koželj, P.; Vrtnik, S.; Jelen, A.; Jazbec, S.; Jagličić, Z.; Maiti, S.; Feuerbacher, M.; Steurer, W.; Dolinšek, J.
2014-09-01
High-entropy alloys (HEAs) are multicomponent mixtures of elements in similar concentrations, where the high entropy of mixing can stabilize disordered solid-solution phases with simple structures like a body-centered cubic or a face-centered cubic, in competition with ordered crystalline intermetallic phases. We have synthesized an HEA with the composition Ta34Nb33Hf8Zr14Ti11 (in at. %), which possesses an average body-centered cubic structure of lattice parameter a =3.36 Å. The measurements of the electrical resistivity, the magnetization and magnetic susceptibility, and the specific heat revealed that the Ta34Nb33Hf8Zr14Ti11 HEA is a type II superconductor with a transition temperature Tc≈7.3 K, an upper critical field μ0Hc2≈8.2 T, a lower critical field μ0Hc1≈32 mT, and an energy gap in the electronic density of states (DOS) at the Fermi level of 2Δ ≈2.2 meV. The investigated HEA is close to a BCS-type phonon-mediated superconductor in the weak electron-phonon coupling limit, classifying it as a "dirty" superconductor. We show that the lattice degrees of freedom obey Vegard's rule of mixtures, indicating completely random mixing of the elements on the HEA lattice, whereas the electronic degrees of freedom do not obey this rule even approximately so that the electronic properties of a HEA are not a "cocktail" of properties of the constituent elements. The formation of a superconducting gap contributes to the electronic stabilization of the HEA state at low temperatures, where the entropic stabilization is ineffective, but the electronic energy gain due to the superconducting transition is too small for the global stabilization of the disordered state, which remains metastable.
Energy Technology Data Exchange (ETDEWEB)
Lopez Garcia, I.; Escalera Perez, R. [Universidad Autonoma Metropolitana - Azcapotzalco (Mexico)]. E-mail: irvinlopez@yahoo.com; r.escalera@ieee.org; Niewierowicz Swiecicka, T. [Instituto Politecnico Nacional, U.P. Adolfo Lopez Mateos (Mexico)]. E-mail: tniewi@ipn.mx; Campero Littlewood, E.[Universidad Autonoma Metropolitana - Azcapotzalco (Mexico)]. E-mail: ecl@correo.azc.uam.mx
2010-01-15
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 conclusion 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. [Spanish] En este trabajo se presentan los resultados del analisis de sensibilidad parametrica realizado a modelos de circuitos equivalentes de orden superior de un turbogenerador (150 MVA, 120 MW, 13.8 kV y 50 Hz). La representacion del generador sincrono se hace en el espacio de estados, utilizando la teoria de dos ejes (d y a). El objetivo del estudio de sensibilidad es evaluar el impacto que tiene cada uno de los parametros en la respuesta transitoria de los modelos analizados -circuitos equivalentes desde una hasta cinco ramas de amortiguamiento en el eje d y de una a cuatro ramas en el eje q-. En este trabajo el concepto de sensibilidad parametrica se formula en terminos generales, planteando la funcion de sensibilidad a partir de condiciones de cortocircuito en las terminales del generador. Los resultados se presentan senalando el nivel de importancia de cada parametro en el comportamiento del modelo. Los algoritmos utilizados fueron disenados en MATLAB. Asi, este estudio permite inferir aspectos electromagneticos de los
Rotated stripe order and its competition with superconductivity in La_{1.88}Sr_{0.12}CuO_{4}
DEFF Research Database (Denmark)
Thampy, V.; Dean, M. P. M.; Christensen, Niels Bech
2014-01-01
We report the observation of a bulk charge modulation in La1.88Sr0.12CuO4 (LSCO) with a characteristic in-plane wave vector of (0.236,±δ), with δ=0.011 r.l.u. The transverse shift of the ordering wave vector indicates the presence of rotated charge-stripe ordering, demonstrating that the charge...... the apparent disparities between the behavior previously observed in the tetragonal “214” cuprates and the orthorhombic yttrium and bismuth-based cuprates and thus lends strong support to the idea that there is a common motif to charge order in all cuprate families....
Schmidt, R
2000-01-01
The superconducting busbars powering the LHC magnets are highly stabilised with copper to reduce the probability of a quench starting in a busbar and to avoid excessive temperatures after a quench during current discharge. In order to determine the required copper stabilisation and the parameters of the protection system a finite difference program has been developed. The program numerically approximates the heat balance equation and evaluates the temperature profile after a quench as a function of time and space. The approach emphasises the modelling of heat transfer into helium. The evaluation of the temperature includes the entire quench process, i.e., the time for quench detection and the current decay.
Sutherland, Mike; Doiron-Leyraud, Nicolas; Taillefer, Louis; Weller, Thomas; Ellerby, Mark; Saxena, S S
2007-02-09
We report measurements of the in-plane electrical resistivity rho and thermal conductivity kappa of the intercalated graphite superconductor C6Yb down to temperatures as low as Tc/100. When a field is applied along the c axis, the residual electronic linear term kappa0/T evolves in an exponential manner for Hc1
Operational Merits of Maritime Superconductivity
Ross, R.; Bosklopper, J. J.; van der Meij, K. H.
The perspective of superconductivity to transfer currents without loss is very appealing in high power applications. In the maritime sector many machines and systems exist in the roughly 1-100 MW range and the losses are well over 50%, which calls for dramatic efficiency improvements. This paper reports on three studies that aimed at the perspectives of superconductivity in the maritime sector. It is important to realize that the introduction of superconductivity comprises two technology transitions namely firstly electrification i.e. the transition from mechanical drives to electric drives and secondly the transition from normal to superconductive electrical machinery. It is concluded that superconductivity does reduce losses, but its impact on the total energy chain is of little significance compared to the investments and the risk of introducing a very promising but as yet not proven technology in the harsh maritime environment. The main reason of the little impact is that the largest losses are imposed on the system by the fossil fueled generators as prime movers that generate the electricity through mechanical torque. Unless electric power is supplied by an efficient and reliable technology that does not involve mechanical torque with the present losses both normal as well as superconductive electrification of the propulsion will hardly improve energy efficiency or may even reduce it. One exception may be the application of degaussing coils. Still appealing merits of superconductivity do exist, but they are rather related to the behavior of superconductive machines and strong magnetic fields and consequently reduction in volume and mass of machinery or (sometimes radically) better performance. The merits are rather convenience, design flexibility as well as novel applications and capabilities which together yield more adequate systems. These may yield lower operational costs in the long run, but at present the added value of superconductivity rather seems more
Influence of phonon-phonon coupling on superconducting state in honeycomb-type crystal lattice
Drzazga, E. A.; Szczȩśniak, R.; Domagalska, I. A.
2018-01-01
We have taken into account the superconducting state inducing in the crystal lattice of the honeycomb-type. In the framework of the Eliashberg theory, we have determined the thermodynamic properties of the system. The phonon spectral function, which is the input parameter in the Eliashberg equations, has been calculated by using the thermodynamic Green functions. We have considered the model of the coupled Einstein oscillators with frequency ω0 = 100 meV. We have shown that the increasing inter-phonon coupling constant (f) causes the rapid growth of the critical temperature ([TC]max = 36.2 K) just below the maximum value of f equal to 0.25ω0. Simultaneously, the order parameter and the thermodynamic critical field take the values increasingly distant from the predictions of the BCS theory, which results from the strong-coupling and the retardation effects.
Signatures of topological superconductivity
Energy Technology Data Exchange (ETDEWEB)
Peng, Yang
2017-07-19
The prediction and experimental discovery of topological insulators brought the importance of topology in condensed matter physics into the limelight. Topology hence acts as a new dimension along which more and more new states of matter start to emerge. One of these topological states of matter, namely topological superconductors, comes into the focus because of their gapless excitations. These gapless excitations, especially in one dimensional topological superconductors, are Majorana zero modes localized at the ends of the superconductor and exhibit exotic nonabelian statistics, which can be potentially applied to fault-tolerant quantum computation. Given their highly interesting physical properties and potential applications to quantum computation, both theorists and experimentalists spend great efforts to realize topological supercondoctors and to detect Majoranas. In two projects within this thesis, we investigate the properties of Majorana zero modes in realistic materials which are absent in simple theoretical models. We find that the superconducting proximity effect, an essential ingredient in all existing platforms for topological superconductors, plays a significant role in determining the localization property of the Majoranas. Strong proximity coupling between the normal system and the superconducting substrate can lead to strongly localized Majoranas, which can explain the observation in a recent experiment. Motivated by experiments in Molenkamp's group, we also look at realistic quantum spin Hall Josephson junctions, in which charge puddles acting as magnetic impurities are coupled to the helical edge states. We find that with this setup, the junction generically realizes an exotic 8π periodic Josephson effect, which is absent in a pristine Josephson junction. In another two projects, we propose more pronounced signatures of Majoranas that are accessible with current experimental techniques. The first one is a transport measurement, which uses
Superconducting properties of ultra-pure niobium welded joints
Demyanov, S. E.; Kaniukov, E. Yu.; Pobol, I. L.; Yurevich, S. V.; Baturitsky, M. A.; Shirkov, G. D.; Budagov, Yu. A.; Demin, D. L.; Azaryan, N. S.
2015-07-01
An optimal electron-beam welding operating regime for ultra-pure sheet niobium has been developed for use in a superconducting resonator for the International Linear Collider (ILC). The formation of weld joints is studied and their microstructure and microhardness are investigated taking the required geometry of the weld seams into account. Low-temperature electrical measurements in magnetic fields up to 2 T are used to determine the critical parameters of the superconducting transition in the weld area. From the standpoint of the superconducting properties of the resonator, the slight degradation in the characteristics of sheet niobium observed in the thermally affected area (about 10% on average) is not of fundamental importance.
Loss and Inductance Investigation in Superconducting Cable Conductors
DEFF Research Database (Denmark)
Olsen, Søren Krüger; Tønnesen, Ole; Træholt, Chresten
1999-01-01
An important parameter in the design and optimization of a superconducting cable conductor is the control of the current distribution among single tapes and layers. This distribution is to a large degree determined by inductances, since the resistances are low. The self and mutual inductances...... of the layers are therefore studied theoretically. The current distribution between the superconducting layers is monitored as a function of transport current, and the results are compared with the expected current distribution given by our electrical circuit model.The AC-losses are measured as a function...... of transport current and current distribution.This presentation is based on a number of experiments performed on prototype superconducting cable conductors. The critical current (1uV/cm) of the conductor at 77K was 1590 A (cable #1) and 3240 A (cable #2) respectively.At an rms current of 2 kA (50 Hz) the AC...
Pressure-restored superconductivity in Cu-substituted FeSe
Schoop, Leslie M.; Medvedev, Sergey A.; Ksenofontov, Vadim; Williams, Anthony; Palasyuk, Taras; Troyan, Iwan A.; Schmitt, Jennifer; Casper, Frederick; Wang, Changhai; Eremets, Mikhail; Cava, R. J.; Felser, Claudia
2011-11-01
Copper doping of FeSe destroys its superconductivity at ambient pressure, even at low doping levels. Here we report the pressure-dependent transport and structural properties of Fe1.01-xCuxSe with 3% and 4% Cu doping and find that the superconductivity is restored. Metallic resistivity behavior, absent in Cu-doped FeSe, is also restored. At the low pressure of 1.5 GPa, superconductivity is seen at 6 K for 4% Cu doping, somewhat lower than the 8 K Tc of undoped FeSe. Tc reaches its maximum of 31.3 K at 7.8 GPa, lower than the maximum superconducting temperature in the undoped material under pressure (Tc max of 37 K) but still very high. X-ray diffraction shows that applied pressure decreases the lattice parameter in the basal plane, counteracting the structural effect of Cu doping, providing a possible explanation for the restoration of the superconductivity.
Structure and superconductivity of isotope-enriched boron-doped diamond
Directory of Open Access Journals (Sweden)
Evgeny A Ekimov, Vladimir A Sidorov, Andrey V Zoteev, Yury B Lebed, Joe D Thompson and Sergey M Stishov
2008-01-01
Full Text Available Superconducting boron-doped diamond samples were synthesized with isotopes of 10B, 11B, 13C and 12C. We claim the presence of a carbon isotope effect on the superconducting transition temperature, which supports the 'diamond-carbon'-related nature of superconductivity and the importance of the electron–phonon interaction as the mechanism of superconductivity in diamond. Isotope substitution permits us to relate almost all bands in the Raman spectra of heavily boron-doped diamond to the vibrations of carbon atoms. The 500 cm−1 Raman band shifts with either carbon or boron isotope substitution and may be associated with vibrations of paired or clustered boron. The absence of a superconducting transition (down to 1.6 K in diamonds synthesized in the Co–C–B system at 1900 K correlates with the small boron concentration deduced from lattice parameters.
DEFF Research Database (Denmark)
Blackburn, E.; Chang, J.; Hücker, M.
2013-01-01
X-ray diffraction measurements show that the high-temperature superconductor YBa2Cu3O6.54, with ortho-II oxygen order, has charge-density-wave order in the absence of an applied magnetic field. The dominant wave vector of the charge density wave is qCDW=(0,0.328(2),0.5), with the in-plane component...... parallel to the b axis (chain direction). It has a similar incommensurability to that observed in ortho-VIII and ortho-III samples, which have different dopings and oxygen orderings. Our results for ortho-II contrast with recent high-field NMR measurements, which suggest a commensurate wave vector along...
Interpolation of Superconducting Gravity Observations Using Least-Squares Collocation Method
Habel, Branislav; Janak, Juraj
2014-05-01
A pre-processing of the gravity data measured by superconducting gravimeter involves removing of spikes, offsets and gaps. Their presence in observations can limit the data analysis and degrades the quality of obtained results. Short data gaps are filling by theoretical signal in order to get continuous records of gravity. It requires the accurate tidal model and eventually atmospheric pressure at the observed site. The poster presents a design of algorithm for interpolation of gravity observations with a sampling rate of 1 min. Novel approach is based on least-squares collocation which combines adjustment of trend parameters, filtering of noise and prediction. It allows the interpolation of missing data up to a few hours without necessity of any other information. Appropriate parameters for covariance function are found using a Bayes' theorem by modified optimization process. Accuracy of method is improved by the rejection of outliers before interpolation. For filling of longer gaps the collocation model is combined with theoretical tidal signal for the rigid Earth. Finally, the proposed method was tested on the superconducting gravity observations at several selected stations of Global Geodynamics Project. Testing demonstrates its reliability and offers results comparable with the standard approach implemented in ETERNA software package without necessity of an accurate tidal model.
Superconductivity papers database
International Superconductivity Technology Center. Tokyo
This database covers mostly the articles on superconductivity appeared after the advent (1987) of the high Tc in 20 - 50 scientific journals including review papers. In the field of organic conductors, literatures are traced back to the era of TTF-TC 1970s). It contains 1)High Tc, 2) C60 related, 3) Organic Conductors, 4) Non-Oxide Superconductors including the conventional superconductors, 5) Oxide Conductors, and 6) Theory (new field since September 1997). Total number of articles at present amounts to 39,000 (December, 1998). Although the proceedings are out of the list in principle, necessary and important papers by the organizer's view are collected even from the proceedings, since some important proceedings.
The LHC superconducting cavities
Boussard, Daniel; Häbel, E; Kindermann, H P; Losito, R; Marque, S; Rödel, V; Stirbet, M
1999-01-01
The LHC RF system, which must handle high intensity (0.5 A d.c.) beams, makes use of superconducting single-cell cavities, best suited to minimizing the effects of periodic transient beam loading. There will be eight cavities per beam, each capable of delivering 2 MV (5 MV/m accelerating field) at 400 MHz. The cavities themselves are now being manufactured by industry, using niobium-on-copper technology which gives full satisfaction at LEP. A cavity unit includes a helium tank (4.5 K operating temperature) built around a cavity cell, RF and HOM couplers and a mechanical tuner, all housed in a modular cryostat. Four-unit modules are ultimately foreseen for the LHC (two per beam), while at present a prototype version with two complete units is being extensively tested. In addition to a detailed description of the cavity and its ancillary equipment, the first test results of the prototype will be reported.
Superconducting pulsed magnets
CERN. Geneva
2006-01-01
Lecture 1. Introduction to Superconducting Materials Type 1,2 and high temperature superconductors; their critical temperature, field & current density. Persistent screening currents and the critical state model. Lecture 2. Magnetization and AC Loss How screening currents cause irreversible magnetization and hysteresis loops. Field errors caused by screening currents. Flux jumping. The general formulation of ac loss in terms of magnetization. AC losses caused by screening currents. Lecture 3. Twisted Wires and Cables Filamentary composite wires and the losses caused by coupling currents between filaments, the need for twisting. Why we need cables and how the coupling currents in cables contribute more ac loss. Field errors caused by coupling currents. Lecture 4. AC Losses in Magnets, Cooling and Measurement Summary of all loss mechanisms and calculation of total losses in the magnet. The need for cooling to minimize temperature rise in a magnet. Measuring ac losses in wires and in magnets. Lecture 5. Stab...
Ostroumov, Peter
2013-01-01
This article discusses the main building blocks of a superconducting (SC) linac, the choice of SC resonators, their frequencies, accelerating gradients and apertures, focusing structures, practical aspects of cryomodule design, and concepts to minimize the heat load into the cryogenic system. It starts with an overview of design concepts for all types of hadron linacs differentiated by duty cycle (pulsed or continuous wave) or by the type of ion species (protons, H-, and ions) being accelerated. Design concepts are detailed for SC linacs in application to both light ion (proton, deuteron) and heavy ion linacs. The physics design of SC linacs, including transverse and longitudinal lattice designs, matching between different accelerating–focusing lattices, and transition from NC to SC sections, is detailed. Design of high-intensity SC linacs for light ions, methods for the reduction of beam losses, preventing beam halo formation, and the effect of HOMs and errors on beam quality are discussed. Examples are ta...
Superconducting energy storage
Energy Technology Data Exchange (ETDEWEB)
Giese, R.F.
1993-10-01
This report describes the status of energy storage involving superconductors and assesses what impact the recently discovered ceramic superconductors may have on the design of these devices. Our description is intended for R&D managers in government, electric utilities, firms, and national laboratories who wish an overview of what has been done and what remains to be done. It is assumed that the reader is acquainted with superconductivity, but not an expert on the topics discussed here. Indeed, it is the author`s aim to enable the reader to better understand the experts who may ask for the reader`s attention, support, or funding. This report may also inform scientists and engineers who, though expert in related areas, wish to have an introduction to our topic.