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

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 𝑑 𝑧 2 , 𝑑𝑥𝑦, 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 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.

Tuning d-orbitals to control spin–orbit coupling in terminated MXenes

“…15,16 Recently, theoretical predictions have identified diverse MXene monolayers as potential 2D TIs, with their surfaces primarily terminated by oxygen (O) and fluorine (F) groups. 17–27 However, due to the relativistic effect, 2D MXene TIs with a large spin–orbit coupling (SOC) effect have mostly been limited to materials with heavy elements. In other words, the dependency on elements is still indispensable for increasing the nontrivial bandgap.…”

Direct tuning of large-gap quantum spin Hall effect in mono transition metal carbide MXenes

“…29–31 The QSH effect has also been theoretically predicted in mono-transition metal MXenes 32,33 and ordered double transition metal MXenes. 34–38 Most theoretical studies have shown that the bandgaps of 2D MXene TIs are generally observed in heavy elements due to their large spin–orbit coupling (SOC) effect. Thus, the most common methods of tuning the bandgaps in MXenes are to change the heavy elements.…”

First-principles study of high performance lithium/sodium storage of Ti3C2T2 nanosheets as electrode materials*

“…Recently, 2D transition metal car-bides/carbonitrides (denoted as MXenes) have attracted significant attention as electrode materials. [10][11][12][13][14][15] MXene can be prepared from the early ternary transition metal carbides, nitrides, or carbonitrides (MAX) by means of the etching approaches, where M is an early transition metal (M = Sc, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W), A is mainly a group IIIA or IVA element (A = Al, Si, Ga, Ge, In, Sn), X is C or/and N, and n = 1, 2 or 3. [16] In the exfoliation process, the A atoms are replaced by T -terminations (T = F, O or OH), leading to functionalized MXene.…”