Time-reversal-symmetry breaking and unconventional pairing in the noncentrosymmetric superconductor <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">La</mml:mi><mml:mn>7</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">Rh</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math>
D. Singh, Mathias S. Scheurer, A. D. Hillier, D. T. Adroja, R. P. Singh
Abstract
Noncentrosymmetric superconductors have sparked significant research interests due to their exciting properties, such as the admixture of spin-singlet and spin-triplet pairing. Here we report on the muon spin rotation and relaxation and thermodynamic measurements on the noncentrosymmetric superconductor ${\mathrm{La}}_{7}{\mathrm{Rh}}_{3}$, which show an isotropic superconducting gap but also spontaneous time-reversal-symmetry breaking occurring at the onset of superconductivity. We show that our results pose severe constraints on any microscopic theory of superconductivity in this system. A symmetry analysis identifies ground states compatible with time-reversal-symmetry breaking, and the resulting gap functions are discussed. Furthermore, general energetic considerations indicate the relevance of electron-electron interactions for the pairing mechanism, in accordance with hints of spin fluctuations revealed in susceptibility measurements.