Variation in Superconducting Symmetry against Pressure on Noncentrosymmetric Superconductor Cd${}_2$Re${}_2$O${}_7$ Revealed by ${}^{185\mathrm{/}187}$Re Nuclear Quadrupole Resonance

We performed ${}^{185\mathrm{/}187}$Re nuclear quadrupole resonance (NQR) measurements under pressure to investigate the superconducting properties of noncentrosymmetric superconductor Cd${}_2$Re${}_2$O${}_7$ under various crystal structures. The pressure dependence of superconducting transition temperature $T_{\mathrm{c}}$ determined through ac susceptibility measurements is consistent with the results of previous resistivity measurements [T. C. Kobayashi $et al$., J. Phys. Soc. Jpn. 80, 023715 (2011).]. Below 2.2 GPa, in the nuclear spin-lattice relaxation rate $1\mathrm{/}{T}_1$, a clear coherence peak was observed just below $T_{\mathrm{c}}$, indicating conventional $s$-wave superconductivity. In contrast, the coherence peak disappears at 3.1 GPa, suggesting a change in superconducting symmetry to the $p$-wave dominant state against pressure.