High-pressure phases of Weyl semimetals NbP, NbAs, TaP, and TaAs

In this study, we used the crystal structure search method and first-principles calculations to systematically explore the high-pressure phase diagrams of the TaAs family (NbP, NbAs, TaP, and TaAs). Our calculation results show that NbAs and TaAs have similar phase diagrams, the same structural phase transition sequence I4(1)md -> P (6) over bar m2 -> P2(1)/c -> Pm (3) over barm, and slightly different transition pressures. The phase transition sequence of NbP and TaP differs somewhat from that of NbAs and TaAs, in which new structures emerge, such as the Cmcm structure in NbP and the Pmmn structure in TaP. Interestingly, we found that in the electronic structure of the high-pressure phase P (6) over bar m2-NbAs, there are coexisting Weyl points and triple degenerate points, similar to those found in high-pressure P (6) over bar m2-TaAs.