Orbital Shift‐Induced Boundary Obstructed Topological Materials with a Large Energy Gap

Abstract

Boundary obstructed topological phases caused by Wannier orbital shift between ordinary atomic sites are proposed, which, however, cannot be indicated by symmetry eigenvalues at high symmetry momenta (symmetry indicators) in bulk. On the open boundary, Wannier charge centers can shift to different atoms from those in bulk, leading to in‐gap surface states, higher‐order hinge states or corner states. To demonstrate such orbital shift‐induced boundary obstructed topological insulators, eight material candidates are predicted, all of which are overlooked in the present topological databases. Metallic surface states, hinge states, or corner states cover the large bulk energy gap (e.g., more than 1 eV in TlGaTe2) at related boundary, which are ready for experimental detection. Additionally, these materials are also fragile topological insulators with hourglass‐like surface states.

Higher-order obstructed atomic insulator phase in pentagonal monolayer PdSe2

“…Several systems with obstructed higher-order phases have been proposed recently. Particular examples are graphdyine [7,8], graphyne [9], phosphorene [10], Xenes [11], transition metal dichalcogenides [12][13][14] and also other families of materials, such as those described in [15][16][17][18]. Along this line, in what follows, we report on the realization of an OAI phase in pentagonal palladium diselenide (PdSe 2 ) in its monolayer form.…”

Topology-Engineered Orbital Hall Effect in Two-Dimensional Ferromagnets

“…Band inversions occur in the + K and − K valleys sequentially, revealing TPTs with increasing ϵ 2 . For ϵ 2 = 3.2 eV, a floating edge state emerges in the insulating gap, which is usually considered as a key signature of the SOTI. − To identify its band topology, a triangular nanoflake with C 3 rotational symmetry is constructed and the energy spectrum is presented in Figure (c). Obviously, around the Fermi level, one observes three states (red dots) with their spatial distribution well localized at the three corners of the nanoflake, verifying the SOTI phase.…”