Topological superconductivity in an ultrathin, magnetically-doped topological insulator proximity coupled to a conventional superconductor

TL;DR

This paper investigates topological superconductivity in magnetically-doped ultrathin topological insulator films coupled to superconductors, analyzing phase diagrams and the persistence of induced superconductivity under strong magnetic fields.

Contribution

It provides a detailed phase diagram for magnetically-doped thin film TI-superconductor systems and explores the robustness of induced superconductivity due to spin-momentum locking.

Findings

Phase diagram as a function of hybridization gap, Zeeman energy, and chemical potential.

Persistence of s-wave order parameter at large Zeeman energies.

Guidelines for experimental observation of topological superconductivity.

Abstract

As a promising candidate system to realize topological superconductivity, the system of a 3D topological insulator (TI) grown on top of the s-wave superconductor has been extensively studied. To access the topological superconductivity experimentally, the 3D TI sample must be thin enough to allow for Cooper pair tunneling to the exposed surface of TI. The use of magnetically ordered dopants to break time-reversal symmetry may allow the surface of a TI to host Majorana fermion, which are believed to be a signature of topological superconductivity. In this work, we study a magnetically-doped thin film TI-superconductor hybrid systems. Considering the proximity induced order parameter in thin film of TI, we analyze the gap closing points of the Hamiltonian and draw the phase diagram as a function of relevant parameters: the hybridization gap, Zeeman energy, and chemical potential of the TI system. Our findings provide a useful guide in choosing relevant parameters to facilitate the observation of topological superconductivity in thin film TI-superconductor hybrid systems. In addition, we further perform numerical analysis on a TI proximity coupled to a s-wave superconductor and find that, due to the spin-momentum locked nature of the surface states in TI, the induced s-wave order parameter of the surface states persists even at large magnitude of the Zeeman energy.