Abstract
Based on first-principles calculations and tight-binding model analysis, we propose monolayer graphdiyne as a candidate material for a two-dimensional higher-order topological insulator protected by inversion symmetry. Despite the absence of chiral symmetry, the higher-order topology of monolayer graphdiyne is manifested in the filling anomaly and charge accumulation at two corners. Although its low energy band structure can be properly described by the tight-binding Hamiltonian constructed by using only the pz orbital of each atom, the corresponding bulk band topology is trivial. The nontrivial bulk topology can be correctly captured only when the contribution from the core levels derived from px,y and s orbitals are included, which is further confirmed by the Wilson loop calculations. We also show that the higher-order band topology of a monolayer graphdyine gives rise to the nontrivial band topology of the corresponding three-dimensional material, ABC-stacked graphdiyne, which hosts monopole nodal lines and hinge states.
Highlights
Bulk-boundary correspondence is a fundamental property of topological phases
Based on first-principles calculations and tight-binding model analysis, we show that a monolayer graphdiyne (MGD) is a higher-order topological insulators (HOTIs) characterized by a 2D topological invariant w2, that is quantized when the system is invariant under inversion P symmetry
Since spin-orbit coupling (SOC) is negligible, MGD can be regarded as a spinless fermion system
Summary
The gapped bulk states in d-dimensions support metallic states in (d − 1)-dimensional surfaces. The gapless excitations of a HOTI in d-dimensions are localized, instead, in a subspace with a dimension lower than (d − 1), such as corners or hinges, when the global shape of the material preserves the crystalline symmetry relevant to the nontrivial band topology.[1,2,3,4,5,6,7,8,9,10,11] Recently, rhombohedral bismuth has been identified as the first example of 3D HOTIs hosting helical hinge states.[1] there are other candidate materials of 3D HOTIs including SnTe with strain along the (100) direction,[2] transition metal dichalcogenides MoTe2 and WTe2, hosting helical hinge states,[3] and Bi2−xSmxSe3 with chiral hinge states.[4]
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