Theoretical seminar | 19 May 2021

In my talk, I will discuss topological phases in a three-dimensional topological insulator (TI) wire with a non-uniform chemical potential induced by gating across the cross-section [1]. This inhomogeneity in chemical potential lifts the degeneracy between two one-dimensional surface state subbands. A magnetic field applied along the wire, due to orbital effects, breaks time-reversal symmetry and lifts the Kramers degeneracy at zero-momentum. If placed in proximity to an s-wave superconductor, the system can be brought into a topological phase at relatively weak magnetic fields. Majorana bound states (MBSs), localized at the ends of the TI wire, emerge and are present for an exceptionally large region of parameter space in realistic systems. Unlike in previous proposals, these MBSs occur without the requirement of a vortex in the superconducting pairing potential, which represents a significant simplification for experiments. Our results open a pathway to the realisation of MBSs in present day TI wire devices. In the second part of my talk, I will switch from non-interacting systems, in which one neglects effects of strong electron-electron interactions, to interacting systems and, thus, to exotic fractional phases. In particular, I will focus on second-order TIs [2-5] and discuss two-dimensional fractional second-order topological superconductors, hosting zero-energy parafermion corner states.

1. H. F. Legg, D. Loss, and J. Klinovaja, arXiv:2103.13412
2. Y. Volpez, D. Loss, and J. Klinovaja, Phys. Rev. Lett. 122,126402 (2019).
3. C.-H. Hsu, P. Stano, J. Klinovaja, and D. Loss, Phys. Rev. Lett. 121,196801 (2018).
4. K. Laubscher, D. Loss, and J. Klinovaja, Phys. Rev. Research 1, 032017(R) (2019).
5. K. Laubscher, D. Loss, and J. Klinovaja, Phys. Rev. Research 2, 013330 (2020).