Discovery of Two-Dimensional Quantum Spin Hall Effect in Triangular Transition-Metal Carbides**Supported by the Natural Science Foundation of Shandong Province under Grant No ZR2018MA033, and the National Natural Science Foundation of China under Grant No 11274143.

Abstract

Though the quantum spin Hall effect (QSHE) in two-dimensional (2D) crystals has been widely explored, the experimental realization of quantum transport properties is only limited to HgTe/CdTe or InAs/GaSb quantum wells. Here we employ a tight-binding model on the basis of dz2, dxy, and dx2−y2 orbitals to propose QSHE in the triangular lattice, which are driven by a crossing of electronic bands at the Γ point. Remarkably, 2D oxidized Mxenes W2M2C3 are ideal materials with nontrivial gap of 0.12 eV, facilitating room-temperature observations in experiments. We also find that the nontrivially topological properties of these materials are sensitive to the cooperative effect of the electron correlation and spin-orbit coupling. Due to the feasible exfoliation from its 3D MAX phase, our work paves a new direction towards realizing QSHE with low dissipation.