Strongly Anisotropic s-Wave Gaps in Exotic Superconductors

TL;DR

This paper investigates the pairing gap structures in exotic superconductors, revealing that many exhibit strongly anisotropic s-wave gaps, with variations depending on their material class and some notable exceptions.

Contribution

It provides a comprehensive analysis of gap anisotropy in non-cuprate exotic superconductors, highlighting the prevalence of s-wave-like gaps despite strong anisotropy.

Findings

Cubic materials often have highly anisotropic gaps.

Planar materials tend to have even stronger gap anisotropy with possible nodes.

Evidence supports s-wave-like gaps in various exotic superconductors.

Abstract

The exotic superconductors, defined as those which follow the phenomenological trend of Uemura (Tc approximately proportional to penetration depth^-2), presently constitute the most broad and general class of superconductors which can reasonably be considered "similar to the high-Tc cuprates". It is therefore of much interest to determine the forms of their pairing gap functions. We examine evidence for the gap forms in non-cuprate exotics, and demonstrate some general features. The cubic materials often have highly anisotropic gaps. The planar materials tend to have even stronger gap anisotropy, to the extent that they often have gap nodes, but nevertheless they usually have an s-wave-like gap symmetry. There is good evidence for the latter even in the controversial cases of planar organics and nickel borocarbides. Exceptions to these generalizations are also pointed out and discussed.