Discovery of Two-Dimensional Quantum Spin Hall Effect in Triangular Transition-Metal Carbides

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 d_z^2, d_xy, and d_x^2-y^2 orbitals to propose QSHE in the triangular lattice, which are driven by a crossing of electronic bands at the \it \Gamma point. Remarkably, 2D oxidized Mxenes W_2M_2C_3 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.