Condensed Matter Seminar "Ballistic superconductivity and tunable pi-junctions in InSb quantum wells"
Chung Ting Ke (TU Delft)
Superconductor-semiconductor hybrids provide a promising platform for topological superconductivity. Using a 2D electron gas (2DEG) could allow one to create complex networks required for Majorana qubit schemes. There has been a great interest in realizing topological superconductivity in planar Josephson junctions (JJs). The robust topological phase is predicted when the phase of the junction is tuned to pi. The exceptional electronic properties of InSb 2DEGs make it a perfect material to realize this. So far, material challenges have prevented the study of hybrid superconducting devices in InSb 2DEGs. Here, we interface InSb 2DEGs with a superconductor (NbTiN) to create Josephson junctions, thus providing the first evidence of induced superconductivity in high-quality InSb 2DEGs. The JJs support supercurrent transport over several microns and find clear signatures of ballistic superconductivity. We exploit the large Lande g-factor and gate tunability of the junctions to control the current-phase relation and drive transitions between the 0 and pi states. The transition is determined by a simple resonance condition, where the Zeeman energy and Thouless energy become comparable. We demonstrate electromagnetic control of 0-pi transitions. This control over the free energy landscape allows us to construct a phase diagram. Our results establish InSb 2DEGs as a promising new material platform to study the interplay between superconductivity, SOC, and magnetism.