Evidence for the coexistence of time-reversal symmetry breaking and Bardeen-Cooper-Schrieffer-like superconductivity in La7Pd3

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 ($\ensuremath{\mu}\mathrm{SR}$) measurements on polycrystalline samples of NCS ${\mathrm{La}}_{7}{\mathrm{Pd}}_{3}$. Transverse-field $\ensuremath{\mu}\mathrm{SR}$ and heat capacity data show ${\mathrm{La}}_{7}{\mathrm{Pd}}_{3}$ is a type-II superconductor with a BCS-like gap structure, while zero-field $\ensuremath{\mu}\mathrm{SR}$ results provide evidence of TRSB. We discuss the implications of these results for both the ${\mathrm{La}}_{7}{X}_{3}$ (where $X=$ Ni, Pd, Rh, Ir) group of superconductors and other CS and NCS superconductors for which TRSB has been observed.