The layered antiferromagnetic MnBi₂Te₄ films have been proposed to be an intrinsic quantum anomalous Hall (QAH) insulator with a large gap. It is crucial to open a magnetic gap of surface states. However, recent experiments have observed gapless surface states, indicating the absence of out-of-plane surface magnetism, and thus, the quantized Hall resistance can only be achieved at the magnetic field above 6 T. We propose to induce out-of-plane surface magnetism of MnBi₂Te₄ films via the magnetic proximity with magnetic insulator CrI₃. A strong exchange bias of ∼40 meV originates from the long Cr-e_g orbital tails that hybridize strongly with Te p orbitals. By stabilizing surface magnetism, the QAH effect can be realized in the MnBi₂Te₄/CrI₃ heterostructure. Moreover, the high–Chern number QAH state can be achieved by controlling external electric gates. Thus, the MnBi₂Te₄/CrI₃ heterostructure provides a promising platform to realize the electrically tunable zero-field QAH effect.

The growing diversity of topological classes leads to ambiguity between classes that share similar boundary phenomenology. This is the status of bulk bismuth. Recent studies have classified it as either a strong or a higher-order topological insulator, both of which host helical modes on their boundaries. We resolve the topological classification of bismuth by spectroscopically mapping the response of its boundary modes to a screw-dislocation. We find that the one-dimensional mode, on step-edges, extends over a wide energy range and does not open a gap near the screw-dislocations. This signifies that this mode binds to the screw-dislocation, as expected for a material with nonzero weak indices. We argue that the small energy gap, at the time reversal invariant momentum L, positions bismuth within the critical region of a topological phase transition between a higher-order topological insulator and a strong topological insulator with nonzero weak indices.

The discovery of topological Weyl semimetals has revealed opportunities to realize several extraordinary physical phenomena in condensed matter physics. Specifically, Weyl semimetals with strong spin-orbit coupling, broken inversion symmetry, and novel spin textures are predicted to exhibit a large spin Hall effect that can efficiently convert the charge current to a spin current. Here, we report a direct experimental observation of large spin Hall and inverse spin Hall effects in the Weyl semimetal ${\mathrm{WTe}}_2$ at room temperature obeying the Onsager reciprocity relation. We demonstrate the detection of a pure spin current generated by the spin Hall phenomenon in ${\mathrm{WTe}}_2$ by making a van der Waals heterostructure with graphene, taking advantage of its long spin coherence length and spin transmission at the heterostructure interface. These experimental findings, well supported by ab initio calculations, show a large charge-spin conversion efficiency in ${\mathrm{WTe}}_2$, which can pave the way for the utilization of spin-orbit-induced phenomena in spintronic memory and logic circuit architectures.

The anomalous Lorenz ratio of the topological antiferromagnet Mn ₃ Ge becomes lower than the Sommerfeld value above 100 K.