The Enabling Electronic Motif for Topological Insulation in ABO₃ Perovskites

Abstract

Stable oxide topological insulators (TIs) have been sought for years, but none have been found; whereas heavier (selenides, tellurides) chalcogenides can be TIs. The basic contradiction between topological insulation and thermo dynamic stability is pointed out, offering a narrow window of opportunity. The electronic motif is first identified and can achieve topological band inversion in ABO 3 as a lonepair, electronrich B atom (e.g., Te, I, Bi) at the octahedral site. Then, twelve ABO 3 compounds are designed in the assumed cubic perovskite structure, which satisfy this electronic motif and are indeed found by density function theory calculations to be TIs. Next, it is illustrated that poorly screened ionic oxides with large inversion energies undergo energy lowering atomic distortions that destabilize the cubic TI phase and remove band inversion. The coexistence windows of topological band inversion and structure stability can nevertheless be expanded under moderate pressures (15 and 35 GPa, respectively, for BaTeO 3 and RbIO 3 ). This study traces the principles needed to design stable oxide topological insulators at ambient pressures as a) a search for oxides with small inversion energies; b) design of large inversionenergy oxide TIs that can be stabilized by pressure; and c) a search for covalent oxides where TIremoving atomic displacements can be effectively screened out.

Topological Insulators versus Topological Dirac Semimetals in Honeycomb Compounds

“…Similar to the BiA 6 B 3 motifs discussed above, in Ref. 28 , a BO 6 motif is found to be responsible for the band inversion in ABO 3 TI's. Furthermore, it is found that large enough distortions to the BO 6 motif can remove the band inversion, and once the distortions are partially or fully restored (e.g.…”

“…Furthermore, highly symmetrized structure of the XA 6 B 3 motif increases state repulsions shifting VBM (CBM) up (down) and thus helps form band inversions, analogous to the highly symmetrical BO 6 motif in ABO 3 TI's. 28 In Figure 3, we see a TI to narrow-gap (~14 meV) normal insulator transition along with the cation substitution from KCaBi to KBaBi, which could be related to the variation of the motif sizes and shapes due to cation variations. Orbital-projected band structure of NaCaBi in the honeycomb (S1) structure (see Figure S2 in Supporting Information for the band-inverted electronic structure of NaCaBi from HSE06 22 ); (b) KBaBi (S1); (c) NaSrBi in the S2 structure (see Figure 3b); (d) NaBaBi (S2).…”

Antidoping in Insulators and Semiconductors Having Intermediate Bands with Trapped Carriers

“…In summary, there are cases where the presence of doped free carriers can change the structure and symmetry of host solid lattice structure itself [38], or create self-trapped lattice polarons, or develop local, charge-compensating centers [39,40] that lead to the stagnation of EF ("pinning") even if carriers are added. Anti-doping represents perhaps the most extreme form of non-rigid response of D(ε) to doping, reversing entirely the expected trend-reducing, rather than increasing conductivity by doping.…”

Heusler, Weyl and Berry

“…In this review, we introduce the Berry curvature as one guiding principle to explain topological phenomena in Heusler compounds. This principle can further be used to explore other tunable material classes with novel properties, e.g., perovskites [38][39][40] and shandites [41][42][43][44][45]…”