scholarly journals Out-of-equilibrium spin transport in mesoscopic superconductors

2018 ◽  
Vol 376 (2125) ◽  
pp. 20150342 ◽  
Author(s):  
C. H. L. Quay ◽  
M. Aprili
Keyword(s):  
Bound States ◽  
Degrees Of Freedom ◽  
Spin Transport ◽  
Energy Gap ◽  
Particle Density ◽  
Zeeman Splitting ◽  
Quasi Particle ◽  
Particle Spin ◽  
Superconducting Energy Gap ◽  
Mesoscopic Superconductors

The excitations in conventional superconductors, Bogoliubov quasi-particles, are spin- fermions but their charge is energy-dependent and, in fact, zero at the gap edge. Therefore, in superconductors (unlike normal metals) spin and charge degrees of freedom may be separated. In this article, we review spin injection into conventional superconductors and focus on recent experiments on mesoscopic superconductors. We show how quasi-particle spin transport and out-of-equilibrium spin-dependent superconductivity can be triggered using the Zeeman splitting of the quasi-particle density of states in thin-film superconductors with small spin-mixing scattering. Finally, we address the spin dynamics and the feedback of quasi-particle spin imbalances on the amplitude of the superconducting energy gap. This article is part of the theme issue ‘Andreev bound states’.

scholarly journals Charge and spin transport in mesoscopic superconductors

2014 ◽  
Vol 5 ◽  
pp. 180-185 ◽  
Author(s):  
M J Wolf ◽  
F Hübler ◽  
S Kolenda ◽  
D Beckmann
Keyword(s):  
Long Range ◽  
Low Temperatures ◽  
Degrees Of Freedom ◽  
Spin Transport ◽  
Spin Injection ◽  
Zeeman Splitting ◽  
Theoretical Models ◽  
Equilibrium Charge ◽  
Mesoscopic Superconductors ◽  
Metal Detectors

Background: Non-equilibrium charge transport in superconductors has been investigated intensely in the 1970s and 1980s, mostly in the vicinity of the critical temperature. Much less attention has been paid to low temperatures and the role of the quasiparticle spin. Results: We report here on nonlocal transport in superconductor hybrid structures at very low temperatures. By comparing the nonlocal conductance obtained by using ferromagnetic and normal-metal detectors, we discriminate charge and spin degrees of freedom. We observe spin injection and long-range transport of pure, chargeless spin currents in the regime of large Zeeman splitting. We elucidate charge and spin transport by comparison to theoretical models. Conclusion: The observed long-range chargeless spin transport opens a new path to manipulate and utilize the quasiparticle spin in superconductor nanostructures.

scholarly journals Generalized Anderson’s theorem for superconductors derived from topological insulators

2020 ◽  
Vol 6 (9) ◽  
pp. eaay6502 ◽  
Author(s):  
Lionel Andersen ◽  
Aline Ramires ◽  
Zhiwei Wang ◽  
Thomas Lorenz ◽  
Yoichi Ando
Keyword(s):  
Degrees Of Freedom ◽  
Energy Gap ◽  
Energy Scale ◽  
Cooper Pairs ◽  
Topological Superconductors ◽  
Scattering Rate ◽  
Nonmagnetic Impurities ◽  
Superconducting Energy Gap ◽  
Strong Scattering ◽  
Internal Degrees Of Freedom

A well-known result in unconventional superconductivity is the fragility of nodal superconductors against nonmagnetic impurities. Despite this common wisdom, Bi2Se3-based topological superconductors have recently displayed unusual robustness against disorder. Here, we provide a theoretical framework that naturally explains what protects Cooper pairs from strong scattering in complex superconductors. Our analysis is based on the concept of superconducting fitness and generalizes the famous Anderson’s theorem into superconductors having multiple internal degrees of freedom with simple assumptions such as the Born approximation. For concreteness, we report on the extreme example of the Cux(PbSe)5(BiSe3)6 superconductor. Thermal conductivity measurements down to 50 mK not only give unambiguous evidence for the existence of nodes but also reveal that the energy scale corresponding to the scattering rate is orders of magnitude larger than the superconducting energy gap. This provides the most spectacular case of the generalized Anderson’s theorem protecting a nodal superconductor.

scholarly journals Phonon self-energy effects in the superconducting energy gap ofMgB2point-contact spectra

2004 ◽  
Vol 69 (10) ◽  
Author(s):  
I. K. Yanson ◽  
S. I. Beloborod’ko ◽  
Yu. G. Naidyuk ◽  
O. V. Dolgov ◽  
A. A. Golubov
Keyword(s):  
Energy Gap ◽  
Self Energy ◽  
Superconducting Energy Gap

High Tc Oxide Superconductors

MRS Bulletin ◽  
1990 ◽  
Vol 15 (6) ◽  
pp. 31-33
Author(s):  
M. Brian Maple
Keyword(s):  
Physical Properties ◽  
Energy Gap ◽  
Vortex State ◽  
Oxide Superconductors ◽  
High Tc ◽  
Superconducting Energy Gap ◽  
Consistent Picture ◽  
Novel Processing ◽  
Processing Techniques

This issue of the MRS BULLETIN is devoted to high Tc superconductivity. It is the sequel to a previous series of articles on the same subject which appeared in the MRS BULLETIN in January 1989. While the articles in the January 1989 issue emphasized the families of high Tc superconducting oxides known at that rime, as well as novel processing techniques and thin films, the papers in this issue focus on the physical properties of high Tc oxide superconductors.The quality of polycrystalline and single-crystal bulk and thin-film materials has improved to the point where researchers can now make reliable measurements of many physical properties representative of the intrinsic behavior of these materials. As a result, a broad spectrum of important issues such as the nature of the electronic structure, the type of superconducting electron pairing, the magnitude and temperature dependence of the superconducting energy gap, the behavior of fluxoids in the vortex state, etc., can be addressed meaningfully. Presently emerging is a consistent picture of the physical properties of the high Tc oxides, which will form the foundation to eventually developing an appropriate theory for the normal and superconducting states of these remarkable materials.

scholarly journals Higher derivatives driven symmetry breaking in holographic superconductors

2020 ◽  
Vol 80 (2) ◽  
Author(s):  
Hai-Li Li ◽  
Guoyang Fu ◽  
Yan Liu ◽  
Jian-Pin Wu ◽  
Xin Zhang
Keyword(s):  
High Temperature Superconductor ◽  
Energy Gap ◽  
Coupling Term ◽  
Holographic Superconductor ◽  
Complex Scalar ◽  
Holographic Superconductors ◽  
Higher Derivative ◽  
Superconducting Energy Gap ◽  
Higher Derivatives ◽  
Complex Scalar Field

Abstract In this paper, we construct a novel holographic superconductor from higher derivative (HD) gravity involving a coupling between the complex scalar field and the Weyl tensor. This HD coupling term provides a near horizon effective mass squared, which can violates IR Breitenlohner–Freedman (BF) bound by tuning the HD coupling and induces the instability of black brane such that the superconducting phase transition happens. We also study the properties of the condensation and the conductivity in the probe limit. We find that a wider extension of the superconducting energy gap ranging from 4.6 to 10.5 may provide a novel platform to model and interpret the phenomena in the real materials of high temperature superconductor.

Integrable and chaotic motions of four vortices II. Collision dynamics of vortex pairs

1988 ◽  
Vol 326 (1593) ◽  
pp. 655-696 ◽  
Keyword(s):  
Bound States ◽  
Degrees Of Freedom ◽  
Complex Structure ◽  
Physical Space ◽  
Vantage Point ◽  
Collision Dynamics ◽  
Chaotic Motions ◽  
Vortex Pairs ◽  
Scattering States ◽  
Space Mechanisms

The interaction of two vortex pairs is investigated analytically and by numerical experiments from the vantage point of dynamical-systems theory. Vortex pairs can escape to infinity, so the phase space of this system is unbounded in contrast to that of four identical vortices investigated previously. Chaotic motion is nevertheless possible both for ‘bound states’ of the system and for ‘scattering states’. For the bound states standard Poincare section techniques suffice. For scattering states chaos appears as complex structure in the numerically generated plot of scattering angle against impact parameter. Interpretations of physical space mechanisms leading to chaos are given. Analytical characterizations of the system include a formal reduction to two degrees of freedom by canonical transformations and an identification and discussion of integrable cases of which one is apparently new.

scholarly journals Momentum-resolved superconducting energy gaps of Sr2RuO4 from quasiparticle interference imaging

2020 ◽  
Vol 117 (10) ◽  
pp. 5222-5227 ◽  
Author(s):  
Rahul Sharma ◽  
Stephen D. Edkins ◽  
Zhenyu Wang ◽  
Andrey Kostin ◽  
Chanchal Sow ◽  
...  
Keyword(s):  
Knight Shift ◽  
Energy Gap ◽  
Space Structure ◽  
Superconducting Order Parameter ◽  
Temperature Dependent ◽  
High Precision Measurement ◽  
Quasiparticle Interference ◽  
Energy Gaps ◽  
Superconducting Energy Gap ◽  
Intense Research

Sr2RuO4 has long been the focus of intense research interest because of conjectures that it is a correlated topological superconductor. It is the momentum space (k-space) structure of the superconducting energy gap Δi(k) on each band i that encodes its unknown superconducting order parameter. However, because the energy scales are so low, it has never been possible to directly measure the Δi(k) of Sr2RuO4. Here, we implement Bogoliubov quasiparticle interference (BQPI) imaging, a technique capable of high-precision measurement of multiband Δi(k). At T = 90 mK, we visualize a set of Bogoliubov scattering interference wavevectors qj:j=1−5 consistent with eight gap nodes/minima that are all closely aligned to the (±1,±1) crystal lattice directions on both the α and β bands. Taking these observations in combination with other very recent advances in directional thermal conductivity [E. Hassinger et al., Phys. Rev. X 7, 011032 (2017)], temperature-dependent Knight shift [A. Pustogow et al., Nature 574, 72–75 (2019)], time-reversal symmetry conservation [S. Kashiwaya et al., Phys. Rev B, 100, 094530 (2019)], and theory [A. T. Rømer et al., Phys. Rev. Lett. 123, 247001 (2019); H. S. Roising, T. Scaffidi, F. Flicker, G. F. Lange, S. H. Simon, Phys. Rev. Res. 1, 033108 (2019); and O. Gingras, R. Nourafkan, A. S. Tremblay, M. Côté, Phys. Rev. Lett. 123, 217005 (2019)], the BQPI signature of Sr2RuO4 appears most consistent with Δi(k) having dx2−y2(B1g) symmetry.

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