Giant magnetochiral anisotropy from quantum-confined surface states of topological insulator nanowires

Wireless technology relies on the conversion of alternating electromagnetic fields into direct currents, a process known as rectification. Although rectifiers are normally based on semiconductor diodes, quantum mechanical non-reciprocal transport effects that enable a highly controllable rectification were recently discovered. One such effect is magnetochiral anisotropy (MCA)6,7,8,9, in which the resistance of a material or a device depends on both the direction of the current flow and an applied magnetic field. However, the size of rectification possible due to MCA is usually extremely small because MCA relies on inversion symmetry breaking that leads to the manifestation of spin–orbit coupling, which is a relativistic effect. In typical materials, the rectification coefficient γ due to MCA is usually ∣γ∣ ≲ 1 A⁻¹ T⁻¹ and the maximum values reported so far are ∣γ∣ ≈ 100 A⁻¹ T⁻¹ in carbon nanotubes and ZrTe₅. Here, to overcome this limitation, we artificially break the inversion symmetry via an applied gate voltage in thin topological insulator (TI) nanowire heterostructures and theoretically predict that such a symmetry breaking can lead to a giant MCA effect. Our prediction is confirmed via experiments on thin bulk-insulating (Bi_1−xSb_x)₂Te₃ (BST) TI nanowires, in which we observe an MCA consistent with theory and ∣γ∣ ≈ 100,000 A⁻¹ T⁻¹, a very large MCA rectification coefficient in a normal conductor.