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

TL;DR

This study uses $^{125}$Te-NMR to investigate the superconducting properties of a two-dimensional quasicrystal, revealing an s-wave gap with an unusually small coherence peak and suggesting possible unconventional superconductivity.

Contribution

First detailed NMR analysis of superconductivity in a 2D quasicrystal, showing conventional s-wave behavior with unique features indicating unconventional pairing.

Findings

Observation of a coherence peak just below $T_c$

Exponential decrease of $1/T_1$ consistent with s-wave gap

No significant spectral broadening in the superconducting state

Abstract

Physical properties in the normal and superconducting (SC) state are investigated with $^{125}$Te-nuclear magnetic resonance (NMR) measurements in a quasicrystal $\mathrm{(Ta_{0.95}Cu_{0.05})_{1.6}Te}$, which was a recently discovered superconductor with the SC transition temperature $T_{\mathrm{c}}$ = 0.94 K. The nuclear spin-lattice relaxation rate $1/T_1$ shows a coherence peak just below $T_{\mathrm{c}}$, followed by an exponential decrease down to 0.1 K. The overall temperature dependence of $1/T_1$ 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.