THE FASCINATING NEW PHYSICS OF SOME OLD BCS SUPERCONDUCTORS

2002 ◽  
Vol 16 (20n22) ◽  
pp. 3134-3139
Author(s):  
V. BARZYKIN
Keyword(s):  
Time Reversal ◽  
Order Parameter ◽  
Coulomb Repulsion ◽  
New Physics ◽  
Superconducting Order Parameter ◽  
High Symmetry ◽  
New Materials ◽  
S Wave ◽  
Orbital Magnetism ◽  
Complicated Mechanism

We consider the pairing state due to the usual Bardeen-Cooper-Schrieffer mechanism in substances where the Fermi surface forms pockets around several points of high symmetry. The symmetry imposed on the multiple pocket positions can give rise to a multidimensional nontrivial superconducting order parameter. A complicated mechanism is not required for unusual superconductivity to exist, just the usual phonon attraction and Coulomb repulsion. Time reversal symmetry is broken, so the superconducting state also has orbital magnetism. In some sense, these superconductors are similar to superfluid3 He, which is known to have an 18-dimensional order parameter and a complicated phase diagram. We suggest several candidate substances where ordering of this kind may appear and discuss how these phases may be identified. Superconductivity in these new materials is expected to be much less sensitive to impurities than in other non s-wave superconductors.1

scholarly journals Unusual symmetries of the order parameter in cuprates

2020 ◽  
Vol 2 (4) ◽  
pp. 207-212
Author(s):  
Tran Van Luong ◽  
Nguyen Thi Ngoc Nu
Keyword(s):  
High Temperature ◽  
Order Parameter ◽  
Cuprate Superconductors ◽  
High Temperature Superconductivity ◽  
Spin Fluctuation ◽  
High Temperature Superconductors ◽  
Coulomb Repulsion ◽  
Bcs Theory ◽  
S Wave ◽  
Wave Symmetry

The BCS superconducting theory, introduced by J. Bardeen, L. Cooper and R. Schriffer in 1957, succeeded in describing and satis-factorily explaining the nature of superconductivity for low-temperature superconductors. However, the BCS theory cannot explain the properties of high-temperature superconductors, discovered by J. G. Bednorz and K. A. Müller in 1986. Although scientists have found a lot of new superconductors and their transition temperatures are constantly increasing, most high-temperature superconductors are found by experiment and so far no theory can fully explain their properties. Many previous studies have suggested that the order parameter in high-temperature copper-based superconductors (cuprate superconductors - cuprates) is in the form of d-wave symmetry, but recent results show that the order parameter has an extended s-wave symmetry (extended s wave). Studying the symmetric forms of order parameters in cuprate can contribute to understanding the nature of high-temperature superconductivity. In this article, the authors present an overview of the development of high-temperature supercon-ductors over the past 30 years and explains unusual symmetries of the order parameter in copper-based superconductors. The com-petition of three coupling mechanisms of electrons in cuprates (the mechanism of coupling through coulomb repulsion, electron-phonon mechanism and spin-fluctuation mechanism) affects the unusual symmetry of the order parameter. The solution of the self-consistency equation in simple cases has been found and the ability to move the phase within the superconducting state has been shown.

EFFECT OF LOCAL CORRELATIONS ON s-WAVE SYMMETRY SUPERCONDUCTIVITY

2000 ◽  
Vol 11 (06) ◽  
pp. 1149-1156
Author(s):  
A. A. SCHMIDT ◽  
J. J. RODRÍGUEZ-NÚÑEZ
Keyword(s):  
Critical Temperature ◽  
Order Parameter ◽  
Mean Field ◽  
Coulomb Repulsion ◽  
Coulomb Interactions ◽  
S Wave ◽  
Field Equations ◽  
Wave Channel ◽  
Mean Field Equations ◽  
Local Correlations

We derive superconducting mean-field equations for an attractive interaction V in the s-wave channel when local Coulomb interactions are taken into account for any value of U. Results show that Coulomb repulsion diminishes the critical temperature Tc to the order parameter Δ(T) for values of U ≥ |V|. Furthermore, the results are also quite sensible to band filling. In the presence of local correlations, 2Δ(0)/Tc differs from the BCS ratio since Coulomb interactions affect much more superconducting critical temperature Tc than superconducting order parameter Δ(T). Some consequences of our findings for experimental measurements in narrow band systems are discussed.

scholarly journals Variation of the extended s-wave superconducting order parameter: From s-wave to g-wave

2015 ◽  
Vol 29 (27) ◽  
pp. 1550163
Author(s):  
H. Chung ◽  
N. Kim ◽  
H. Kim
Keyword(s):  
Fermi Surface ◽  
Density Of States ◽  
Power Law ◽  
Order Parameter ◽  
Superconducting Order Parameter ◽  
Text Line ◽  
Superconducting Properties ◽  
Detailed Structure ◽  
S Wave ◽  
Model Order

We investigate evolution of properties of an extended [Formula: see text]-wave superconductor, when the order parameter varies from an [Formula: see text]-wave to a [Formula: see text]-wave continuously, by using a model order parameter [Formula: see text]. The evolution of the gap amplitude, the density of states and the specific heat are mainly focused on. For [Formula: see text], due to the existence of a finite sized gap, the characteristic behaviors more or less follow those of the [Formula: see text]-wave. Sudden changes in the characteristic behaviors come out for [Formula: see text], due to appearances of nodes. For [Formula: see text], point nodes in the order parameter on the Fermi surface appear, while for [Formula: see text], line nodes appear. Although they are different kinds of nodes which would usually induce different power-law dependencies in superconducting properties, interestingly enough, they give rise to the same characteristic behavior. The detailed structure of the point nodes for [Formula: see text] is investigated, and it is explained why they lead to the same dependence as the line nodes.

INELASTIC NEUTRON SCATTERING FROM ANISOTROPIC SUPERCONDUCTORS

2002 ◽  
Vol 16 (20n22) ◽  
pp. 3062-3065
Author(s):  
P. S. RISEBOROUGH
Keyword(s):  
Order Parameter ◽  
Inelastic Neutron Scattering ◽  
Particle Density ◽  
Coulomb Repulsion ◽  
Inelastic Neutron ◽  
Superconducting Order Parameter ◽  
Collective Excitations ◽  
Quasi Particle ◽  
Anisotropic Superconductors ◽  
Magnetic Fluctuation

The magnetic fluctuation spectra are calculated for various phases of anisotropic superconductors. Both singlet and triplet superconducting phases can support antiferromagnetic fluctuations for small values of the Coulomb repulsion, the spectra show power law frequency dependencies due to the nodes in the superconducting order parameter. For larger strengths of the Coulomb interaction, low energy critically damped collective excitations develop from the quasi-particle density of states in the gap. The q and ω dependence of the spectra can be used to deduce the character of the superconducting order parameter.

Description and symmetry of aperiodic crystals

2018 ◽  
Author(s):  
Ted Janssen ◽  
Gervais Chapuis ◽  
Marc de Boissieu
Keyword(s):  
Time Reversal ◽  
Mathematical Concept ◽  
New Materials ◽  
Magnetic Systems ◽  
Atomic Structures ◽  
Modulated Phases ◽  
Quasiperiodic Functions ◽  
Aperiodic Crystals ◽  
Superspace Description

This chapter first introduces the mathematical concept of aperiodic and quasiperiodic functions, which will form the theoretical basis of the superspace description of the new recently discovered forms of matter. They are divided in three groups, namely modulated phases, composites, and quasicrystals. It is shown how the atomic structures and their symmetry can be characterized and described by the new concept. The classification of superspace groups is introduced along with some examples. For quasicrystals, the notion of approximants is also introduced for a better understanding of their structures. Finally, alternatives for the descriptions of the new materials are presented along with scaling symmetries. Magnetic systems and time-reversal symmetry are also introduced.

scholarly journals Unsplit superconducting and time reversal symmetry breaking transitions in Sr2RuO4 under hydrostatic pressure and disorder

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Vadim Grinenko ◽  
Debarchan Das ◽  
Ritu Gupta ◽  
Bastian Zinkl ◽  
Naoki Kikugawa ◽  
...  
Keyword(s):  
Hydrostatic Pressure ◽  
Symmetry Breaking ◽  
Time Reversal ◽  
Order Parameter ◽  
Muon Spin Rotation ◽  
Horizontal Line ◽  
Time Reversal Symmetry ◽  
Zero Field ◽  
Symmetry Protected ◽  
Line Node

AbstractThere is considerable evidence that the superconducting state of Sr2RuO4 breaks time reversal symmetry. In the experiments showing time reversal symmetry breaking, its onset temperature, TTRSB, is generally found to match the critical temperature, Tc, within resolution. In combination with evidence for even parity, this result has led to consideration of a dxz ± idyz order parameter. The degeneracy of the two components of this order parameter is protected by symmetry, yielding TTRSB = Tc, but it has a hard-to-explain horizontal line node at kz = 0. Therefore, s ± id and d ± ig order parameters are also under consideration. These avoid the horizontal line node, but require tuning to obtain TTRSB ≈ Tc. To obtain evidence distinguishing these two possible scenarios (of symmetry-protected versus accidental degeneracy), we employ zero-field muon spin rotation/relaxation to study pure Sr2RuO4 under hydrostatic pressure, and Sr1.98La0.02RuO4 at zero pressure. Both hydrostatic pressure and La substitution alter Tc without lifting the tetragonal lattice symmetry, so if the degeneracy is symmetry-protected, TTRSB should track changes in Tc, while if it is accidental, these transition temperatures should generally separate. We observe TTRSB to track Tc, supporting the hypothesis of dxz ± idyz order.

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