Superconducting Properties on Two-dimensional Quasicrystal (Ta${}_{0.95}$Cu${}_{0.05}$)${}_{1.6}$Te Studied with ${}^{125}$Te-NMR

Physical properties in the normal and superconducting (SC) state are investigated with ${}^{125}$Te-nuclear magnetic resonance (NMR) measurements in a quasicrystal $(\mathrm{T}{\mathrm{a}}_{0.95}\mathrm{C}{\mathrm{u}}_{0.05}{)}_{1.6}\mathrm{T}\mathrm{e}$, which was a recently discovered superconductor with the SC transition temperature $T_{\mathrm{c}}$ = 0.94 K. The nuclear spin-lattice relaxation rate $1\mathrm{/}{T}_1$ shows a coherence peak just below $T_{\mathrm{c}}$, followed by an exponential decrease down to 0.1 K. The overall temperature dependence of $1\mathrm{/}{T}_1$ is in good agreement with an $s$-wave SC model with a SC gap slightly smaller than the BCS value. However, the coherence peak is unusually small, which may be attributable to a reduced Bogoliubov peak theoretically predicted for quasicrystals. Furthermore, ${}^{125}$Te-NMR spectra show almost no broadening nor shift in the SC state, suggesting that an unusual SC state such as parity mixing might be realized in the Ta${}_{1.6}$Te superconductor.