Evidence for the coexistence of time-reversal symmetry breaking and Bardeen-Cooper-Schrieffer-like superconductivity in La$_{7}$Pd$_{3}$

TL;DR

This study provides evidence that La$_{7}$Pd$_{3}$ is a type-II superconductor exhibiting BCS-like pairing along with time-reversal symmetry breaking, revealing complex superconducting states in noncentrosymmetric materials.

Contribution

The paper demonstrates coexistence of TRSB and BCS-like superconductivity in La$_{7}$Pd$_{3}$, expanding understanding of unconventional superconducting mechanisms.

Findings

La$_{7}$Pd$_{3}$ is a type-II superconductor with a BCS-like gap.

Zero-field $$SR indicates time-reversal symmetry breaking.

Heat capacity and $$SR data support unconventional superconductivity.

Abstract

Time-reversal symmetry breaking (TRSB) with a Bardeen-Cooper-Schrieffer (BCS) -like superconductivity occurs in a small, but growing number of noncentrosymmetric (NCS) materials, although the mechanism is poorly understood. We present heat capacity, magnetization, resistivity, and muon spin resonance/relaxation ($\mu$SR) measurements on polycrystalline samples of NCS La$_{7}$Pd$_{3}$. Transverse-field $\mu$SR and heat capacity data show La$_{7}$Pd$_{3}$ is a type-II superconductor with a BCS-like gap structure, while zero-field $\mu$SR results provide evidence of TRSB. We discuss the implications of these results for both the La$_{7}X_{3}$ (where $X=$ Ni, Pd, Rh, Ir) group of superconductors and other CS and NCS superconductors for which TRSB has been observed.