講演情報
[9a-E207-7]First Principles Simulation of Topological Edge States in M2M’C2O2 MXenes
〇(M1)Daryl Hong1, Koichi Nakamura1 (1.KUAS)
キーワード：
MXenes、Tight-binding model、Quantum spin Hall insulator
Quantum spin Hall (QSH) insulators have attracted considerable interest as they host robust gapless topological edge states in finite geometries of two-dimensional systems, which have promising applications in low-power electronics and spintronics, motivating the search for experimentally accessible material realizations. The family of M2M'C2O2 (M=Mo, W; M'=Ti, Zr, Hf) MXenes have been predicted to be QSH insulators with sizeable topological band gaps, among which the member Mo2TiC2O2 has been experimentally synthesized recently. However, for M2M'C2O2 to exhibit the QSH phase, the width of the finite system must be large to minimize coupling between edge states on opposite edges which destroys the QSH effect. As such, modelling such finite systems via direct first-principles calculations is computationally restrictive. To overcome this, we constructed a multi-orbital tight-binding model from a minimal basis of maximally localized Wannier functions derived from first-principles band calculations to efficiently model ~10 nm wide nanoribbons. In this study, we investigated the details of the topological edge states present in various semi-infinite M2M'C2O2 nanoribbons with distinct types of symmetric edge terminations. Our results show that the type of nanoribbon edge termination strongly governs both the dispersion and localization length of the edge states. By combining the approaches of diagonalization of the tight-binding Hamiltonian and the transfer matrix formulation, we further investigated the effect of the width of the nanoribbons on the degree of coupling of the edge states and the size of the corresponding small band gap. Furthermore, we computed the spin textures of the edge states which revealed the spin-momentum locking of the edge states.