Henry Legg

In systems with broken inversion and time reversal symmetry magnetochiral anisotropy (MCA) can result in non-reciprocal transport effects.

In the first part of my talk I will consider rectification due to MCA, i.e., a resistance that depends on the direction of current flow and applied magnetic field. Such non-reciprocal responses usually stem from relativistic corrections and are normally very small. I will consider topological insulator nanowire devices where inversion symmetry can be broken artificially due to a non-uniform potential which arises, for instance, by applying a gate voltage below the TI nanowire. As a result of the artificially broken inversion symmetry, a large splitting of the quasi-1D subbands of states with momentum parallel to the nanowire can occur. I will show that this subband splitting should result in an MCA non-reciprocal transport effect when a magnetic field is applied perpendicular to the nanowire axis. The predicted rectification effect, consistent with theory, is observed experimentally in thin bulk-insulating (Bi$_{1−x}$Sb$_x$)$_2$Te$_3$ (BST) TI nanowires and found to be several orders of magnitude larger than previously reported MCA rectification effects.

In the second half of my talk I will also show that, in proximity with a superconductor, MCA in TI (and Rashba) nanowires should result in a superconducting diode effect when the magnetic field is applied perpendicular to the nanowire. That is, a difference in critical current that depends on the direction of current flow. Furthermore, a strong dependence of the SC diode effect on an additional component of magnetic field applied parallel to the nanowire as well as on the position of the chemical potential can be used to detect that a device is in the region of parameter space where the phase transition to topological superconductivity and associated Majorana bound states are expected to arise.

References:
https://www.nature.com/articles/s41565-022-01124-1
https://arxiv.org/abs/2205.12939