A New Family of Two‐Dimensional Topological Materials: CdX (X = F, Cl, Br, and I)

Abstract

Two‐dimensional (2D) transition‐metal halides have attracted great interest owing to their versatile applications in electronics, optoelectronics, and renewable energy storage/conversions. Using first‐principles calculations, it is proposed that a new series of 2D transition‐metal halide CdX (X = F, Cl, Br, and I) monolayers with honeycomb lattice structure show topological properties. When omitting the spin–orbital coupling (SOC) effect, all of them behave as Dirac semimetal whose Fermi surface is composed of two Dirac points at high symmetry K and K’ points in Brillouin zone. When considering the SOC effect, CdCl, CdBr, and CdI monolayers behave as topological insulators with global band gap, whereas CdF is converted from Dirac semimetal into topological metal with local band gap. The nontrivial topological properties are further proved by their nontrivial edge states. The fascinating properties of the CdX (X = F, Cl, Br, and I) monolayers show their potential for future quantum computing and next generation of high‐speed electronic devices.

Atomistic designing of 2D quantum materials heterostructures CdF/CrI3 for Berry curvature driven tunable intrinsic anomalous Hall state

“…The CdF band structure shows semimetallic character, with Dirac-like linear dispersive bands above (≈0.25 eV) the Fermi energy at the K point in the BZ, with a small local gap of around 100 meV is opening up in the presence of SOC, ensures the massive Dirac nature. At the Γ point near the Fermi energy parabolic band dispersion, originating from the Cd-5s orbitals, which is consistent with the reported results [59]. On the other side, the CrI 3 band structure shows, as mentioned in the literature, the large global gap of around 1 eV near Fermi energy, with magnetic moment 3.0 µ B /f.u, where the In the band structure of CrI 3 -CdF heterostructures shown in figure 3, we observed few interesting generic features in all the heterostructures.…”

“…For that, we have calculated the Fermi velocity for all the heterostructures. We found that the Fermi velocities are similar order of magnitude (≈10 6 m s −1 ) to that of the isolated CdF mono-layer system [59], even in the heterostructure systems with the presence of magnetic interactions. We have calculated the ratio of Fermi velocities in heterostructure systems with respect to the isolated CdF Fermi velocity.…”

“…Keeping in mind the in-situ experimental difficulties of heterostructures growth the theoretical prediction and designing the heterostructure plays very crucial and important role in development of the field, which are evident by the recent reports of the theoretical predictions of various kinds of heterostructures studies [47][48][49][50][51][52][53][54][55][56][57][58]. A new class of layered halide Dirac materials, CdX (X = F, Cl, Br, I), have been predicted using first-principles density functional theory (DFT) calculations [59], which are yet to be synthesized experimentally. The dynamical stability is ensured via the absence of negative frequency modes in phonon dispersion, thermodynamical stability is ensured via free energy and entropy as a function of temperature, energy stability is ensured via binding energy, and formation energy of CdX [59].…”

“…A new class of layered halide Dirac materials, CdX (X = F, Cl, Br, I), have been predicted using first-principles density functional theory (DFT) calculations [59], which are yet to be synthesized experimentally. The dynamical stability is ensured via the absence of negative frequency modes in phonon dispersion, thermodynamical stability is ensured via free energy and entropy as a function of temperature, energy stability is ensured via binding energy, and formation energy of CdX [59]. This series shows interesting Dirac-like linear bulk band dispersion with a minimal gap at the BZ's high symmetry K point.…”

Two-dimensional MX Dirac materials and quantum spin Hall insulators with tunable electronic and topological properties

“…Notably, novel topological materials within the 2D MX family have been addressed in a few recent reports. [44][45][46][47][48] We emphasize that the physics underlying the formation of Dirac cones in the family of group-II MX compounds identified in our study differs fundamentally from the work of Zhou et al [44], which focuses on transition-metal compounds with band edges that are constructed via localized d electrons. Dirac cone in Cd-based MX compounds, Yi et al [45] attributed the Dirac cones they found to the interaction between the metal s-and anion-p states, which does not reflect the actual orbital interaction in these compounds.…”