<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>C</mml:mi><mml:mi>n</mml:mi></mml:msub></mml:math>-symmetric higher-order topological crystalline insulators in atomically thin transition metal dichalcogenides
Shifeng Qian, Gui‐Bin Liu, Cheng‐Cheng Liu, Yugui Yao
Abstract
Based on first-principles calculations and symmetry analysis, we predict atomically thin ($1\ensuremath{-}N$ layers) $2H$ group-VIB transition metal dichalcogenides (TMDs) $M{X}_{2}$ ($M$ = Mo, W; $X$ = S, Se, Te) are large-gap higher-order topological crystalline insulators (HOTCIs) protected by ${C}_{3}$ rotation symmetry. We explicitly demonstrate the nontrivial topological indices and the existence of hallmark corner states with quantized fractional charge for these familiar TMDs with a large bulk optical band gap ($1.64\text{--}1.95\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ for the monolayers), which would facilitate the experimental verification and exploration of the HOTCI states. Furthermore, we find that the well-defined corner states exist in the triangular finite-size flakes with armchair edges of the atomically thin ($1\ensuremath{-}N$ layers) $2H$ group-VIB TMDs, and the corresponding quantized fractional charge is the number of layers $N$ modulo three. The fractional corner charge will double when spin degree of freedom is taken into account.