Fysiikan tutkimusseminaari: Elsa Prada (ICMM CSIC, Spain)

Welcome to join us for a research seminar by Dr. Elsa Prada from ICMM CSIC, Spain!

Host: Jose Lado/Correlated Quantum Materials group

Title: Searching for Majorana bound states in superconductor-semiconductor nanostructures

Abstract: 

Hybrid superconductor-semiconductor nanowires have been intensively studied in an effort to create, detect and manipulate Majorana bound states. Traditionally, a superconductor is deposited or grown epitaxially over some of the facets of a semiconductor wire with strong spin-orbit coupling and a Zeeman field is applied to drive the system into the topological regime. One of the drawbacks of this platform is the need to subject the hybrid wire to strong magnetic fields that degrade the superconducting state of the parent superconductor. 

In the last years, new nanowire configurations are being explored that could present some advantages with respect to previous designs. In this talk, I will discuss theoretical and experimental progress on one the most promising proposals: the so-called full-shell hybrid nanowires, where the semiconductor nanowire is fully coated by the superconductor shell. In this wires, the topological transition is not driven by the Zeeman effect, but by the winding of the superconducting phase around the semiconducting core. Compared to their partial-shell counterparts, full-shell nanowires present some advantages that could help to clearly identify the elusive Majorana quasiparticles, such as the operation at smaller magnetic fields and low or zero semiconductor g-factor, and the expected appearance of Majorana zero modes at well-controlled regions of parameter space. 

In this work we critically examine this proposal, finding a very rich spectral phenomenology that combines the Little-Parks modulation of the parent-gap superconductor with flux, the presence of trivial flux-dispersing Caroli-de Gennes-Matricon analog subgap states, and the emergence of Majorana zero modes across finite flux intervals that depend on the transverse wavefunction profile of the charge density in the core section.