# Ballistic superconductivity and tunable $\pi$-junctions in InSb quantum wells

## TL;DR

This paper demonstrates ballistic superconductivity and tunable $$-junctions in InSb quantum wells, revealing new possibilities for studying topological states and quantum phenomena in semiconductor-superconductor hybrid systems.

## Contribution

First experimental realization of superconducting Josephson junctions in high-quality InSb quantum wells with tunable $0$-$$ states and phase diagram mapping.

## Key findings

- Supercurrent transport over several microns in InSb quantum wells.
- Clear signatures of ballistic superconductivity observed.
- Controlled transitions between $0$ and $$ states achieved.

## Abstract

Two-dimensional electron gases (2DEGs) 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 (SOI). InSb is a well-known example of such a strong SOI semiconductor, however hybrid superconducting devices in InSb quantum wells remain unexplored. Here, we interface InSb 2DEGs with a superconductor (NbTiN) to create Josephson junctions (JJs), thus providing the first evidence of induced superconductivity in high quality InSb quantum wells. The JJs support supercurrent transport over several microns and display clear signatures of ballistic superconductivity. Furthermore, we exploit the large Land\'{e} g-factor and gate tunability of the junctions to control the current-phase relation, and drive transitions between the $0$ and $\pi$-states. This control over the free energy landscape allows us to construct a phase diagram identifying these $0$ and $\pi$-regions, in agreement with theory. Our results establish InSb quantum wells as a promising new material platform to study the interplay between superconductivity, SOI and magnetism.