Second-neighbor electron hopping and pressure induced topological quantum phase transition in insulating cubic perovskites

Abstract

Perovskite structure is one of the five symmetry families suitable for exhibiting topological insulator phase. However, none of the halides and oxides stabilizing in this structure exhibit the same. Through density functional calculations on cubic perovskites (CsSnX3; X = Cl, Br, and I), we predict a band insulator -Dirac semimetal -topological insulator phase transition with uniform compression. With the aid of a Slater-Koster tight binding Hamiltonian, we show that, apart from the valence electron count, the band topology of these perovksites is determined by five parameters involving electron hopping among the Sn-{s, p} orbitals. These parameters monotonically increase with pressure to gradually transform the positive band gap to a negative one and thereby enable the quantum phase transition. The universality of the mechanism of phase transition is established by examining the band topology of Bi based oxide perovskites. Dynamical stability of the halides against pressure strengthens the experimental relevance.

Defining the topological influencers and predictive principles to engineer the band structure of halide perovskites

“…Though the universality of the band structure arises from the nearest-neighbor B-{s, p}-X-p covalent interactions as discussed in the previous paragraph, the second neighbor B-{s, p}-B-{s, p} interactions are found to be the driving force for engineering the bandgap as well as construing non-trivial phases [13]. In the ground state, the second neighbor interaction strength is less than 1eV (almost one-third of nearest neighbor interaction) [13,19] which can be varied and made anisotropic easily through strain and will be discussed in the following sub-section.…”

“…Considering the α-phase, for any halide and oxide perovskites ABX 3 we have shown that bonding and antibonding bands emerge out of strong B-{s, p}-X-p nearest neighbor covalent interactions. [13,19] The anti-bonding and bonding bands are separated by a set of X-p dominated non-bonding bands. Furthermore, both bonding and antibonding spectrum have four bands with the lower one is formed by the B-s-X-p hybridized states and the upper three are formed by the B-p-X-p hyrbridized states.…”

“…The symmetry altering structural modifications invite changes in the interplay of lattice, orbital and spin degrees of freedom to manifest trivial and non-trivial electronic phases. Studies suggest that if A is inorganic elements like Cs and Rb, then the centrosymmetric structure stabilizes [12] and in such a situation while, covalent interaction among the B and X states tune the bandgap (E g ), the strength of atomic spin-orbit coupling become deterministic towards tailoring non-trivial topological phases such as topological insulator [9,13]. However, if A is an organic element like MA (CH 3 NH 3 ) and FA (CH(NH 2 ) 2 )the inversion symmetry breaks down and therefore both atomic SOC and Rashba SOC -that inflicts the spin-split in the momentum space -become deterministic in tailoring the electronic behavior of these quantum materials [14,15].…”

“…Specific to the studies of band topology in inorganic halide perovskites, the literature, focusing on the high temperature cubic phase, hypothesizes a pressure induced phase transition from the normal insulator (NI) to topological insulator (TI) phase via an accidental Dirac * nandab@iitm.ac.in semimetal (DSM) phase [9,13]. However, experimentally halide perovskites are known to demonstrate structural polymorphs with temperature governing their stability.…”

“…The universality of the electronic structure of perovskite members as explained in our earlier works [13,19] enables us to examine a single compound rather than the whole family and extract the insight into the band struc-ture with regard to the anisotropic structural distortions. In this paper, it is achieved by carrying out DFT calculations on CsSnI 3 polymorphs.…”