Resumé / Abstract :

Two-dimensional systems coupled to superconductors offer the opportunity to explore a variety of quantum phenomena. These include the study of novel Josephson effects , superconducting correlations in quantum (spin) Hall systems, hybrid superconducting qubits and emergent topological states in semiconductors with spin-orbit interaction. In this talk I will focus on our efforts to develop InSb two-dimensional electron gases (2DEGs) to engineer topological superconductivity.

We show that Josephson junctions in InSb 2DEGs support supercurrent transport over several microns and display clear signatures of ballistic superconductivity. Furthermore, we exploit the large Landé g-factor and gate tunability of the junctions to control the current-phase relation, and drive transitions between the 0 and π-states. This control over the free energy landscape allows us to construct a phase diagram identifying these 0 and π-regions, in agreement with theory. In addition to induced superconductivity I will discuss the operation of stable quantum confined structures (quantum dots - QDs) in these 2DEGs, which are essential elements for the manipulation and readout of topological qubits. We show that the specific material properties of InSb are strongly reflected in the transport through the QD. The small effective mass of InSb ( 0.02 me) results in a large single-particle confinement energy, giving rise to an even-odd variation in the size of the Coulomb diamonds, related to the spin-dependent filling of orbital levels in the QD. Studying the evolution of Coulomb peaks in a magnetic field allows us to determine the ground state spin configuration and directly extract the g-factor ( 30). An important consequence of this large g-factor is that the ground state of the QD changes from a spin-singlet (spin zero) to spin-triplet (spin one) at magnetic fields as low as 0.3 T. Together, these results establish InSb 2DEGs as a promising new platform to study topological superconductivity.

1. Ballistic superconductivity and tunable π-junctions in InSb quantum wells C. T. Ke, C. M. Moehle et al., Nat. Commun. 10, 3764 (2019) arXiv:1902.10742

2. Stable quantum dots in an InSb two-dimensional electron gas I. Kulesh et al., arXiv:1910.07309

Contact : robert.whitney@grenoble.cnrs.fr