Topological states in superconducting two-dimensional electron gases

ended

I will experimentally investigate hybrid superconductor/semiconductor devices for realizing novel topological states of matter, with interest both in fundamental physics and quantum computing applications. Common denominator of the proposed experiments is a regime where the characteristic energy scales of the system, namely Fermi energy, spin orbit interaction correction, superconducting gap and Zeeman splitting are comparable to each other, resulting in unique and mostly uncharted physical territories. Differently from the most widespread use of semiconductor nanowires coupled to superconductors, I will employ novel hybrid two-dimensional electron gases (2DEGs) where the superconductor is grown in-situ and matched to the semiconductor lattice. This novel system was mainly developed by the team I supervise, during the last two years. Compared to the conventional nanowire-based approach, hybrid 2DEGs are readily available, characterized by very low disorder and more amenable to complex sample designs. The work will focus on: 1) Taking full advantage of the planar geometry to study spatial and non-local properties of individual Majorana wires, as well as branched geometries. These experiments will constitute critical tests to establish if the commonly observed zero bias peaks are indeed associated with Majorana modes and pave the way to complex networks of interacting Majorana wires, a requirement for quantum computing. 2) Studying topological phenomena in multi-terminal Josephson junctions (JJs), with particular emphasis on tuning the superconducting phase difference across electrodes pairs. Topological JJs offer a new and possibly advantageous path forward to create and manipulate Majorana modes not explored up to date, including the possibility to reach the topological regime for vanishing small external magnetic fields, useful for applications. Success of the proposal will constitute a key step forward towards topological quantum computing.