Observation of a new high-pressure semimetal phase of GaAs from pressure dependence of the thermopower

We report the use of the thermopower technique (Seebeck effect) as an effective tool for discovery of 'hidden' (for standard techniques, like x-ray, synchrotron, Raman, etc) phases of substances. Applying the thermopower technique to a set of GaAs single crystals pressurized in a sintered diamond anvil cell, we found an unknown high-pressure semimetal phase with the electron type of conductivity, similar to that recently discovered in ZnTe. A possible crystal structure of this phase is discussed. The pressure-temperature (P-T) phase diagrams of GaAs and ZnTe are compared.