Specific heat andμSR study on the noncentrosymmetric superconductor LaRhSi3

Abstract

We have investigated the superconducting properties of the noncentrosymmetric superconductor LaRhSi${}_{3}$ by performing magnetization, specific heat, electrical resistivity, and muon spin relaxation ($\ensuremath{\mu}$SR) measurements. LaRhSi${}_{3}$ crystallizes with the BaNiSn${}_{3}$-type tetragonal structure (space group $I4 \mathit{mm}$), as confirmed through our neutron diffraction study. Magnetic susceptibility, electrical resistivity and specific heat data reveal a sharp and well-defined superconducting transition at ${T}_{c}=2.16\ifmmode\pm\else\textpm\fi{}0.08$ K. The low-temperature specific heat data reveal that LaRhSi${}_{3}$ is a weakly coupled bulk BCS superconductor and has an $s$-wave singlet ground state with an isotropic energy gap of $~$0.3 meV, $2{\ensuremath{\Delta}}_{0}/{k}_{B}{T}_{c}=3.24$. The specific heat data measured in an applied magnetic field strongly indicate a type I behavior. Type I superconductivity in this compound is also inferred from the Ginzburg-Landau parameter, $\ensuremath{\kappa}=0.25$. Various superconducting parameters, including the electron-phonon coupling strength, penetration depth, and coherence length, characterize LaRhSi${}_{3}$ as a moderate dirty-limit superconductor. A detailed study of the magnetic field-temperature ($H\ensuremath{-}T$) phase diagram is presented and from a consideration of the free energy, the thermodynamic critical field, ${H}_{c0}$, is estimated to be $17.1\ifmmode\pm\else\textpm\fi{}0.1$ mT, which is in very good agreement with that estimated from the transverse field $\ensuremath{\mu}$SR measurement that gives ${H}_{c0}=17.2\ifmmode\pm\else\textpm\fi{}0.1$ mT. The transverse field $\ensuremath{\mu}$SR results are consistent with conventional type I superconductivity in this compound. Further, the zero field $\ensuremath{\mu}$SR results indicate that time-reversal symmetry is preserved when entering the superconducting state, also supporting a singlet pairing superconducting ground state in LaRhSi${}_{3}$.