Observation of multigap and coherence peak in the noncentrosymmetric superconductor CaPtAs: As75 nuclear quadrupole resonance measurements

We present synthesis and $^{75}$As-nuclear quadrupole resonance (NQR)\nmeasurements for the noncentrosymmetric superconductor CaPtAs with a\nsuperconducting transition temperature $T_c$ of $\\sim 1.5$ K. We discovered two\ndifferent forms of CaPtAs during synthesis; one is a high-temperature\ntetragonal form that was previously reported, and the other is a\nlow-temperature form consistent with the orthorhombic structure of CaPtP.\nAccording to the $^{75}$As-NQR measurement for superconducting tetragonal\nCaPtAs, the nuclear spin-lattice relaxation rate $1/T_1$ has an obvious\ncoherence peak below $T_c$ and does not follow a simple exponential variation\nat low temperatures. These findings indicate that CaPtAs is a multigap\nsuperconductor and a large $s$-wave component.\n