Multigap superconductivity in locally noncentrosymmetric SrPtAs: An As 75 nuclear quadrupole resonance investigation

We report detailed $^{75}\mathrm{As}$ nuclear quadrupole resonance investigations of the locally noncentrosymmetric superconductor SrPtAs. The spin-lattice relaxation studies prove weakly coupled multigap superconductivity. A retardation of the decay in $1/{T}_{1}T$ evidences a nodeless (fully gapped) superconducting state on the complex multipocket Fermi surface, which is consistent with an anisotropic $s$-wave order parameter and with proposed unconventional $f$-wave and chiral $d$-wave symmetries. A quantitative analysis of these models favors the unconventional $f$-wave state.