Phase fluctuations in conventional superconductors

2021 ◽  
Author(s):  
Pratap Raychaudhuri ◽  
Surajit Dutta
Keyword(s):  
Energy Gap ◽  
Energy Scale ◽  
Bcs Theory ◽  
Superconducting Properties ◽  
Phase Fluctuations ◽  
Low Dimensions ◽  
Superconducting Energy Gap ◽  
Zero Resistance ◽  
Resistance State ◽  
Granular Superconductors

Abstract Within the Bardeen-Cooper-Schrieffer (BCS) theory, superconductivity is entirely governed by the pairing energy scale, which gives rise to the superconducting energy gap, Δ. However, another important energy scale, the superfluid phase stiffness, J, which determines the resilience of the superconductor to phase-fluctuations is normally ignored. The spectacular success of BCS theory owes to the fact that in conventional superconductors J is normally several orders of magnitude larger than Δ and thus an irrelevant energy scale. However, in certain situations such as in the presence of low carrier density, strong disorder, at low-dimensions or in granular superconductors, J can drastically come down and even become smaller than Δ. In such situations, the temperature and magnetic field evolution of superconducting properties is governed by phase fluctuations, which gives rise to novel electronic states where signatures of electronic pairing continue to exist even when the zero resistance state is destroyed. In this article, we will review the recent experimental developments on the study of phase fluctuations in conventional superconductors.

Electron Tunneling in High Tc Superconductors

MRS Bulletin ◽  
1990 ◽  
Vol 15 (6) ◽  
pp. 44-49 ◽  
Author(s):  
J.M. Valles ◽  
R.C. Dynes
Keyword(s):  
Energy Gap ◽  
Electron Tunneling ◽  
Quantitative Description ◽  
Bcs Theory ◽  
Phonon Interaction ◽  
Microscopic Mechanism ◽  
Electron Phonon Interaction ◽  
Current Voltage ◽  
Superconducting Energy Gap ◽  
Electron Phonon Coupling

Electron tunneling measurements have proven enormously valuable in studies of conventional superconductors. Very early measurements confirmed, in an especially convincing way, the existence of the superconducting energy gap, and more detailed studies demonstrated the spectral form of the gap and its temperature dependence. These measurements were instrumental in confirming in some detail the predictions of the Bardeen, Cooper, Schrieffer (BCS) theory of superconductivity in simple metals. For example, it was shown very clearly that the ratio of the energy gap (2Δ) and critical temperature Tc was close to the BCS value (2Δ/kTc = 3.5). As the sophistication of the technique improved, deviations from this BCS weak coupling limit became apparent (2Δ/kTc was measured to be >4 in materials like Pb, for example), and subtle structure in the current-voltage characteristics of tunnel junctions unearthed a signature of the electron-phonon interaction—the microscopic mechanism responsible for superconductivity in these traditional materials. Through a quantitative analysis of this structure, people were able to extract a function α2(ω)F(ω), which is the phonon density of states F(ω) modulated by the electron-phonon coupling function α2(ω). This function gave a quantitative description of the electron-phonon interaction and confirmed beyond a doubt that the electron-phonon interaction was responsible for superconductivity.

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.

The Superconducting Energy Gap of Rb3C60 as measured by IR Transmission in Thin Films

1994 ◽  
Vol 359 ◽  
Author(s):  
Daniel Koller ◽  
Michael C. Martin ◽  
Laszlo Mihaly
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Energy Gap ◽  
Bcs Theory ◽  
Infrared Transmission ◽  
Film Resistivity ◽  
Resistivity Measurements ◽  
Superconducting Energy Gap ◽  
Ir Transmission

ABSTRACTThe superconducting energy gap of Rb3C60 has been measured by infrared transmission through a thin film. Resistivity measurements on the same samples in situ indicate a transition to superconductivity at the expected temperature, ∼30K, with distinct gap features appearing in the transmission below this temperature. The results are interpreted in terms of the BCS theory.

scholarly journals Superfluid density from magnetic penetration depth measurements in Nb–Cu 3D nano-composite films

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Chandan Gupta ◽  
Pradnya Parab ◽  
Sangita Bose
Keyword(s):  
Film Thickness ◽  
Energy Gap ◽  
Composite Films ◽  
Nano Particles ◽  
Imaginary Component ◽  
Nano Composite ◽  
Phase Fluctuations ◽  
Cu Content ◽  
Superconducting Energy Gap ◽  
Two Peaks

Abstract Superconductivity in 3D Nb–Cu nanocomposite granular films have been studied with varying thickness for two different compositions, Nb rich with 88 at% of Nb and Cu rich with 46 at% of Nb. For both compositions, the superconducting transition temperature (Tc) decreases with decreasing film thickness. For any thickness, doubling the Cu content in the films decreases the Tc by about 2 K. To explore if phase fluctuations play any role in superconductivity in these 3D films, the superfluid stiffness (JS) of the films was measured using low frequency two-coil mutual inductance (M) technique. Interestingly, the measurement of M in magnetic fields showed two peaks in the imaginary component of M for both Nb rich and Cu rich films. The two peaks were associated with the pair-breaking effect of the magnetic field on the intra and inter-granular coupling in these films consisting of random network of superconductor (S) and normal metal (N) nano-particles. Furthermore, JS was seen to decrease with decreasing film thickness and increasing Cu content. However, for all films studied JS remained higher than the superconducting energy gap (∆) indicating that phase fluctuations do not play any role in superconductivity in the film thickness and composition range investigated. Our results indicate that an interplay of quantum size effects (QSE) and superconducting proximity effect (SPE) controls the Tc with composition in these 3D nano-composite films.

SUPERCONDUCTING ENERGY GAP IN FULLERIDES

2008 ◽  
Vol 22 (19) ◽  
pp. 1851-1857
Author(s):  
JIANGWEN WU ◽  
HONGKAI GUO ◽  
QUN WEI ◽  
ZHUQUAN GU
Keyword(s):  
Energy Gap ◽  
Phase Fluctuations ◽  
Calculated Temperature ◽  
Superconducting Energy Gap

In fullerides, the deviation of the superconducting energy gap from BCS prediction, especially close to TC, in experiments is an old, but not well-understood problem. If phase fluctuations are considered, the calculated temperature temperature of the energy gap is accurately consistent with the experimental one, and the deviation of the gap is a certain result.

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

Zero-resistance state of two-dimensional electrons in a quantizing magnetic field

1982 ◽  
Vol 25 (2) ◽  
pp. 1405-1407 ◽  
Author(s):  
D. C. Tsui ◽  
H. L. Störmer ◽  
A. C. Gossard
Keyword(s):  
Magnetic Field ◽  
Two Dimensional ◽  
Zero Resistance ◽  
Resistance State ◽  
Quantizing Magnetic Field

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.

Sign in / Sign up

Export Citation Format

Share Document