Fragile superconductivity in a Dirac metal

TL;DR

This study investigates the superconducting properties of LaCuSb2, a Dirac semimetal, revealing pressure sensitivity, anisotropic superconductivity types, and evidence for multigap behavior linked to Dirac fermions, suggesting potential topological superconductivity.

Contribution

It provides the first detailed analysis of superconductivity in LaCuSb2, highlighting pressure effects, anisotropic behavior, and multigap features related to Dirac fermions.

Findings

Superconductivity in LaCuSb2 is suppressed by pressure.

Magnetization shows Type-II behavior along the a-axis and Type-I along the c-axis.

Specific heat indicates multigap superconductivity with deviations from single-gap BCS theory.

Abstract

Studying superconductivity in Dirac semimetals is an important step in understanding quantum matter with topologically non-trivial order parameters. We report on the properties of the superconducting phase in single crystals of the Dirac material LaCuSb2 prepared by the self-flux method. We find that chemical and hydrostatic pressure drastically suppress the superconducting transition. Furthermore, due to large Fermi surface anisotropy, magnetization and muon spin relaxation measurements reveal Type-II superconductivity for applied magnetic fields along the $a$-axis, and Type-I superconductivity for fields along the $c$-axis. Specific heat confirms the bulk nature of the transition, and its deviation from single-gap $s$-wave BCS theory suggests multigap superconductivity. Our tight-binding model points to an anisotropic gap function arising from the spin-orbital texture near the Dirac nodes, providing an explanation for the appearance of an anomaly in specific heat well below $T_c$. Given the existence of superconductivity in a material harboring Dirac fermions, LaCuSb2 proves an interesting material candidate in the search for topological superconductivity.