Two-dimensional Weyl half-semimetal and tunable quantum anomalous Hall effect

Abstract

We propose a new topological quantum state of matter-the two-dimensional (2D) Weyl half semimetal (WHS), which features 2D Weyl points at Fermi level belonging to a single spin channel, such that the low-energy electrons are described by fully spin-polarized 2D Weyl fermions. We predict its realization in the ground state of monolayer PtCl3. We show that the material is a half metal with an in-plane magnetization, and its Fermi surface consists of a pair of fully spin-polarized Weyl points protected by a mirror symmetry, which are robust against spin-orbit coupling. Remarkably, we show that the WHS state is a critical state at the topological phase transition between two quantum anomalous Hall insulator phases with opposite Chern numbers, such that a switching between quantum anomalous Hall states can be readily achieved by rotating the magnetization direction. Our findings demonstrate that WHS offers new opportunity to control the chiral edge channels, which will be useful for designing new topological electronic devices.

Rational boundary charge in one-dimensional systems with interaction and disorder

“…This pins Q B (ϕ) to quantized plateaus which change abruptly by ±e/2 at gap closing points. This leads to Weyl semimetal physics since edge modes connecting the gap closing points play the role of Dirac arcs, analog to other recent realizations of Weyl semimetal physics in two-dimensional systems [69,[102][103][104][105]. Despite the fact that in this case the Chern number vanishes (leading to zero Hall current), we find a nontrivial quantization effect of the boundary charge Q B .…”

Spin-orbit coupling and linear crossings of dipolar magnons in van der Waals antiferromagnets

“…This leads to chirality of −1 for both nodal points. The nonzero chirality, the linear crossing, and the twofold degeneracy together indicate that these nodal points can be regarded as a magnon analog of the 2D Weyl points recently proposed in an electronic system [19].…”

“…Figure 3(a) shows that another two nodal points at the zone boundary both have winding number +1, compensating the chirality from k ± near valley. In contrast to the 3D Weyl points, which are robust against any perturbation [21][22][23][24], the 2D Weyl points can be gapped by particular perturbation [19]. In the present case, for example, the inclusion of a nonvanishing ω H due to an out-of-plane magnetic field, according to the effective Hamiltonian Eq.…”

“…(41), we find that all four nodal points near K (K ) valley have the same chirality of +1 (−1). By considering their twofold degeneracy and the linear dispersion nearby, we conclude that these nodal points are also 2D Weyl points [19]. FIG.…”

Weyl Fermions in VI3 Monolayer

“…Recently, WSMs in two-dimensional (2D) materials and magnetic materials have received increasing interests. For 2D WSMs, the interest arises from the promising applications in spintronic nanodevices (You et al, 2019 ). For magnetic WSMs, the interest comes from the novel interplay between the non-trivial band topology and the magnetic ordering (Xu et al, 2011 ; Kübler and Felser, 2016 ; Wang et al, 2016 ; Chen et al, 2019 ; He et al, 2019 ; Jin et al, 2020 ; Meng et al, 2020a , b , c ).…”