Optical spectroscopy study on pressure-induced phase transitions in the three-dimensional Dirac semimetal Cd$_3$As$_2$

摘要

We report a room-temperature optical reflectivity study performed on[112]-oriented Cd$_3$As$_2$ single crystals over a broad energy range underexternal pressure up to 10 GPa. The abrupt drop of the band dispersionparameter ($z$-parameter) and the interruption of the gradual redshift of thebandgap at $\sim$4~GPa confirms the structural phase transition from atetragonal to a monoclinic phase in this material. The pressure-inducedincrease of the overall optical conductivity at low energies and the continuousredshift of the high-energy bands indicate that the system evolves towards atopologically trivial metallic state, although a complete closing of the bandgap could not be observed in the studied pressure range. Furthermore, adetailed investigation of the low-pressure regime suggests the possibleexistence of an intermediate state between 2 and 4~GPa , that might be aprecursor of the structural phase transition or due to the lifted degeneracy ofthe Dirac nodes. Several optical parameters show yet another anomaly at 8~GPa,where low-temperature superconductivity was found in an earlier study.