We performed high-pressure Raman and resistance measurements on a two-dimensional monoclinic semiconductor GeAs. We discovered a superconductivity that emerges after the insulator-metal transition above 10 GPa, which is related to the structural transition. Our results indicate that the semiconducting monoclinic phase and rocksalt structure phase coexist above 10 GPa and structural transformation to the rocksalt phase is completed above $17\sim 18\mathrm{GPa}$. The maximum superconducting transition temperature $T_c$ is about 8 K close to the structural transition boundary, and the $T_c$ is gradually decreasing at higher pressures. Upon pressure release, the nonpolar rocksalt structure transforms to a polar tetragonal superconducting phase. Our first-principles calculations indicate that the relatively high $T_c$ in the rocksalt phase is mainly due to the enhancement of the electron-phonon coupling. These results show that superconductivity in this material strongly depends on its structure, achieving maximum $T_c$ in a higher-symmetry phase.

• Received 22 October 2019

DOI:https://doi.org/10.1103/PhysRevB.100.214516