Specific heat and μsR study on the noncentrosymmetric superconductor LaRhSi₃

We have investigated the superconducting properties of the noncentrosymmetric superconductor LaRhSi₃ by performing magnetization, specific heat, electrical resistivity, and muon spin relaxation (μSR) measurements. LaRhSi₃ crystallizes with the BaNiSn ₃-type tetragonal structure (space group I4 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±0.08 K. The low-temperature specific heat data reveal that LaRhSi₃ is a weakly coupled bulk BCS superconductor and has an s-wave singlet ground state with an isotropic energy gap of ~0.3 meV, 2Δ₀/k_BT_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, κ=0.25. Various superconducting parameters, including the electron-phonon coupling strength, penetration depth, and coherence length, characterize LaRhSi₃ as a moderate dirty-limit superconductor. A detailed study of the magnetic field-temperature (H-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±0.1 mT, which is in very good agreement with that estimated from the transverse field μSR measurement that gives H_c0=17.2±0.1 mT. The transverse field μSR results are consistent with conventional type I superconductivity in this compound. Further, the zero field μSR results indicate that time-reversal symmetry is preserved when entering the superconducting state, also supporting a singlet pairing superconducting ground state in LaRhSi₃.