Collaborating with Prof. Wegscheider’s group at ETH Zurich, we developed high-quality InAs/Al heterostructures, screening over 26 wafers and achieving electron mobilities consistently above 60,000 cm²/Vs. This collaboration also led to breakthroughs in understanding epitaxial growth, including interfaces between Al and Nb, which are crucial for achieving stable hybrid systems. These advancements are expected to enhance device reproducibility and performance in future applications.
We conducted extensive studies on planar Josephson junctions fabricated from these heterostructures. These experiments unveiled new phenomena related to phase dynamics in the presence of large in-plane magnetic fields and interactions with microwave radiation. The insights gained are essential for realizing topological states, particularly by clarifying how spin-orbit interactions and orbital magnetic fields influence superconducting properties and switching currents.
Expanding on theoretical proposals, we explored multiterminal Josephson junctions, focusing on three-lead and four-lead configurations. These complex devices required the integration of superconducting loops and flux-bias lines, combined with precise DC filtering. The results allowed us to map the density of states in a synthetic two-dimensional phase space, demonstrating the formation of novel Andreev bands and controlled Andreev molecules. In systems with strong spin-orbit coupling, we observed spin-splitting and parity transitions, aligning with theoretical models. This work could lead to a new class of quantum devices where information is stored in spin states but manipulated using superconducting qubit technology.
Additionally, we developed flip-chip packaging techniques to combine microwave resonators with planar Josephson junctions on III-V materials, using vacuum-mediated inductive coupling. This integration enabled high-resolution measurements of Andreev spectra and fast dynamics in InAs and Ge-based systems. The approach is highly promising for future experiments targeting the spectroscopy of Floquet-Andreev states and exploring new material platforms.
Furthermore, the project fostered significant interdisciplinary collaboration, enabling new studies on the effects of high-energy electrons on mesoscopic superconductors and the microscopic origins of the superconducting diode effect in conventional materials.
