Superconducting Logic Circuits Through Germanium-Based Quantum Devices
The recently discovered superconducting diode effect, where critical currents depend on direction, offers an exciting platform for energy-efficient quantum electronics. This phenomenon has been demonstrated across various platforms, from superconducting circuits to van der Waals heterostructures, revealing rich physics at the intersection of symmetry breaking and superconductivity. Germanium serves as an ideal platform for exploring these phenomena, offering strong spin-orbit coupling and seamless compatibility with existing semiconductor technology. When combined with superconductors, germanium-based devices enable fundamental physics investigations which eventually could lead to applications.
This project aims to harness the superconducting diode effect in germanium-based hybrid devices to develop novel logic circuits. Our research will focus on understanding how the interplay of spin-orbit coupling, magnetic fields, and device geometry creates directional electronic transport. This work bridges fundamental physics and technological implementation, addressing the growing demand for energy-efficient computing solutions.
The experimental program combines advanced fabrication techniques with transport measurements. Through the development of high-quality germanium-superconductor interfaces and gate-tunable structures, we can control the coupling between normal and superconducting regions of the device. This precise control enables optimization of device performance and development of reliable logic elements.
The project benefits from complementary expertise and facilities at Oxford and Cambridge Universities. Students will access state-of-the-art fabrication and measurement capabilities at both institutions while working alongside leading experts in materials science and quantum engineering. This collaborative environment provides excellent preparation for careers in both academic research and industrial R&D.
1. Nadeem, Muhammad, Michael S. Fuhrer, and Xiaolin Wang. "The superconducting diode effect." Nature Reviews Physics 5.10 (2023): 558-577.
2. Mazur, G. P., et al. "Gate-tunable Josephson diode." Phys. Rev. Applied 22, 054034, 2024.
(a) Schematic of a superconducting device featuring an InSb nanowire contacted by aluminum (Al) electrodes, controlled by side gates (VSG) and a top gate (VTG), with a hafnium oxide (HfO2) dielectric layer. Current (I) and voltage (V) are measured to characterize the device.
(b) Cross-sectional view of the hexagonal InSb nanowire device under an applied magnetic field B, decomposed into components (Bx, By, Bz), highlighting the field orientation (θ) and device layers (Ti/Pd substrate and HfO2 insulator).
(c) Voltage (V) vs. current (I) characteristics showing the switching currents (I+SW and I−SW) and retrapping currents (I+rt and I−rt) during forward and reverse sweeps.
(d) Histogram of the positive (|I+SW|) and negative (|I−SW|) switching currents, highlighting their statistical distributions over repeated measurements showing the difference in magnitude for switching currents between sweep directions.
