Proximity effect and Majorana bound states in clean semiconductor nanowires coupled to disordered superconductors

Understand

We study a semiconductor wire with strong spin-orbit coupling, which is proximity-coupled to a superconductor with chemical potential disorder.

• When tunneling at the semiconductor- superconductor interface is very weak, it is known that disorder in the superconductor does not affect the induced superconductivity nor, therefore, the effective topological superconductivity that emerges above a critical magnetic field.
• We demonstrate nonperturbatively how this result breaks down with stronger proximity coupling by obtaining the low-energy (i.e., subgap) excitation spectrum through direct numerical diagonalization of an appropriate BdG hamiltonian.
• With strong proximity coupling, we find that disorder in the parent superconductor suppresses the (non- topological) induced gap at zero magnetic field by disordering the induced pair potential.