Superconducting properties of the spin Hall candidate Ta3Sb with eightfold degeneracy

TL;DR

This paper reports the discovery of superconductivity in the topological material Ta3Sb, which exhibits eightfold degeneracy and large spin Hall effect, making it a promising platform for exploring exotic quantum states.

Contribution

It is the first to demonstrate superconductivity in an eightfold degenerate topological fermionic compound with potential for large spin Hall conductance.

Findings

Superconducting transition temperature Tc ~ 0.67 K.

Upper critical field Hc2(0) ~ 0.95 T and coherence length ~18.6 nm.

GL parameter κ ~ 90 indicating an extreme type-II superconductor.

Abstract

We report the synthesis and characterization of phase pure Ta3Sb, a material predicted to be topological with eightfold degenerate fermionic states [Science 353, aaf5037 (2016)] and to exhibit a large spin Hall effect [Sci. Adv. 5, eaav8575 (2019]. We observe superconductivity in Ta3Sb with Tc~ 0.67 K in both electrical resistivity \r{ho}(T) and specific heat C(T) measurements. Field dependent measurements yield the superconducting phase diagram with an upper critical field of Hc2(0) ~ 0.95 T, corresponding to a superconducting coherence length of {\xi} ~18.6 nm. The gap ratio deduced from specific heat anomaly, 2{\Delta}0/kBTc is 3.46, a value close to the Bardeen-Cooper-Schrieffer (BCS) value of 3.53. From a detailed analysis of both the transport and thermodynamic data within the Ginsburg-Landau (GL) framework, a GL parameter of \k{appa} ~90 is obtained identifying Ta3Sb as an extreme type-II superconductor. The observation of superconductivity in an eightfold degenerate fermionic compound with topological surface states and predicted large spin Hall conductance positions Ta3Sb as an appealing platform to further explore exotic quantum states in multifold degenerate systems.