Isotropic s-wave superconductivity in the noncentrosymmetric charge density wave superconductor SrPt2As2

Abstract

SrPt2As2 undergoes a structural transition around 470 K (from a high-temperature tetragonal to a low-temperature orthorhombic phase) accompanied by a charge density wave transition and followed by a superconducting transition at much lower temperature (5 K). The superconducting gap symmetry of this noncentrosymmetric compound was investigated in detail by means of muon-spin rotation or relaxation (mu SR) experiments in transverse-field (TF) configuration. The temperature-dependent magnetic penetration depth obtained from the TF-mu SR spectra suggests an isotropic s-wave-type superconducting gap. No observable differences are seen in the asymmetry time spectra collected in zero field above and below the superconducting transition temperature T-c. This strongly suggests the absence of spontaneous magnetic fields in the superconducting state, hence pointing to a preserved time-reversal symmetry below T-c.