Pressure-induced superconductivity in the topological crystalline insulator NaCd4As3

Recently, a united symmetry-protected topological crystalline insulator (TCI) $\mathrm{NaC}{\mathrm{d}}_{4}\mathrm{A}{\mathrm{s}}_{3}$ has been discovered experimentally, which further features a temperature-driven transformation from TCI to TI due to the mirror symmetry broken across a rhombohedral-to-monoclinic structural transition. Here, we report the pressure tuning of structural property and emergence of superconductivity in TCI $\mathrm{NaC}{\mathrm{d}}_{4}\mathrm{A}{\mathrm{s}}_{3}$ by comprehensive high-pressure experiments in diamond-anvil cell. Temperature-dependent Raman measurements show that the structural transition temperature gradually reduces upon compression and is completely suppressed above $\ensuremath{\sim}4$ GPa. The stable rhombohedral phase further undergoes amorphization evidenced by synchrotron x-ray-diffraction result, which sets in at 20.7 GPa and completes at 34.4 GPa. Along with the complete amorphization, the metallization and superconductivity with a critical temperature ${T}_{c}\ensuremath{\sim}2.5$ K appear simultaneously, as observed in transport experiments. We argue that the sudden enhancement in ${T}_{c}$ across 60.0 GPa is likely related to the pressure-driven amorphous polymorphism. Our finding unravels the fundamental structure-property relationship and highly tunable crystallographic symmetry in $\mathrm{NaC}{\mathrm{d}}_{4}\mathrm{A}{\mathrm{s}}_{3}$ by external pressure, potentially sparking further investigations via alternative tuning strategies.