Ferroelectric topological superconductor: $\alpha \text{−}{\mathrm{In}}_2{\mathrm{Se}}_3$

A two-dimensional topological superconductor (TSC) represents an exotic quantum material with quasiparticle excitation manifesting in dispersive Majorana modes (DMMs) at the boundaries. A domain-wall DMM can arise at the boundary between two TSC domains with opposite Chern numbers or with a π-phase shift in their pairing gap, which can only be tuned by a magnetic field. Here we propose the concept of a ferroelectric (FE) TSC, which not only enriches the domain-wall DMMs but also significantly makes them electrically tunable. The π-phase shift of the pairing gap is shown to be attained between two TSC domains of opposite FE polarization, and switchable by reversing FE polarizations. In combination with ferromagnetic (FM) polarization, the domain wall can host helical, doubled chiral, and fused DMMs, which can be transferred into each other by changing the direction of the electrical and/or magnetic field. Furthermore, based on first-principles calculations, we demonstrate $\alpha \text{−}{\mathrm{In}}_2{\mathrm{Se}}_3$ to be a promising FE TSC candidate in proximity with a FM layer and a superconductor substrate. We envision that a FE TSC will significantly ease the manipulation of a DMM by electrical field to realize fault-tolerant quantum computation.