Pressure and inversion symmetry breaking field-driven first-order phase transition and formation of Dirac circle in perovskites

Through model Hamiltonian studies and first-principle electronic structure calculations, we have examined the effect of inversion symmetry breaking (ISB) field and hydrostatic pressure on the band topology of halide perovskites by taking MAPbI3 as a representative. Our study shows that while hydrostatic pressure induces normal to topological insulator continuous phase transition, the ISB field makes it first order. The pressure smoothly reduces the normal band gap, and without ISB, the system achieves a gapless state before it produces a nontrivial band gap with inverted characters. The ISB field does not stabilize the gapless state, and therefore, the discontinuity in the band gap with pressure gives rise to the first-order transition. Furthermore, in the nontrivial phase, the ISB field forms an invariant surface Dirac circle in the neighborhood of TRIM, which is the first of its kind. The circle is formed due to interpenetration of Dirac cones resembling the band topology of AA-stacked bilayer graphene.