Vortex Tunneling and Critical State
In 2D superconductors with thicknesses much less than the London Penetration Depth λ, vortex dynamics will dominate the transport properties because the superconductor can no longer effectively screen magnetic fields. In a recent study, we observed nonzero voltage in the I-V curves at subcritical current values. The voltage in this regime depends exponentially on the current and takes on values three orders of magnitude lower than those typically seen in the normal state near the canonical critical current (mV vs. μV)! The signal is believed to arise from vortices moving on the order kilometers per second. These results provide evidence for vortex flow across a constriction as well as macroscopic quantum tunneling of a single vortex. In the latter regime, the tunneling is expected to be overdamped and corresponds to the real-sapce tunneling of a topological excitation. This is fundamentally different from the tunneling behavior observed in an underdamped Josephson Junction.
Motivated by these exciting results, we are actively developing new experiments to probe the exotic behavior of complex oxide interfaces and how they may be integrated with other superconducting technologies.
Anisotropic Superconductivity at KTaO3 (111) Interfaces
Superconducting effects in 2D materials have been shown to host exotic states not found in higher dimensional systems. Most 2D superconductors are made from materials that are conducting in their normal state, such as Al thin films or more exotic systems like magic-angle graphene. Counterintuitively however, the interface of the insulators KTaO3 and LaSrMnO3 has been shown to host a superconducting electron gas with exotic properties. Work performed in the Finkelstein lab has measured the anisotropic transport properties of the superconducting state, hinting at the rich physics that could be present in this system. The kinetic inductance in this system is expected to be very extremely high due to the 2D nature whilst KTaO3 itself has a high dielectric constant(~4000) at low temperatures. Therefore we are able to modulate the superconducting state by applying a gate voltage, despite the high carrier density (~1013cm-2).These properties of high kinetic inductance and gate tunability make KTaO3 heterostructures a promising platform for a novel, scalable superconducting qubit system.
Transport measurements directed along different crystallographic directions. The increased critical temperature and critical field along the [112] direction relative to the [110] direction are strong indications of anisotropic superconductivity. The origin of these properties is not well understood and is subject to further research.
This work is performed in collaboration with the Kumah Lab and Ahadi Lab at Duke University and Ohio State University, respectively. The KTaO3 heterostructures are grown in an oxide molecular-beam epitaxy system whilst low temperature transport measurements are performed in a dilution refrigerator in the Finkelstien lab. Current research is directed towards fabricating devices in KTaO3 heterostructures which will be sensitive to the exotic superconducting state as well as devices that may have a more practical application, such as superconducting qubits. We are also exploring more novel oxide materials which may host more robust and exotic superconducting states.
Corresponding grad students: Ryan Henderson (ryan.henderson@duke.edu ) and Jordan McCourt (recently graduated) (jordan.mccourt@duke.edu)
Related Publications
Vortex Tunneling and Critical State in an Oxide Heterostructure
J. McCourt, R. Henderson, J. Chiles, C. Chen, Shama, D. Kumah, Vadim Geshkenbein, G. Finkelstein
arXiv preprint (2026)
Superconductivity of spin-orbit coupled BaBi3 formed by in situ reduction of bismuthate films
Shama, J. McCourt, M. Baksi, G. Finkelstein, D. P. Kumah
Physical Review Materials (2025)
Electrostatic Control of Quantum Phases in KTaO3-based Planar Constrictions
J. McCourt, E. G. Arnault, M. Baksi, S. J. Poage, S. Salmani-Rezaie, K. Ahadi, D. P. Kumahm G. Finkelstein
Nano Letters (2025)
Anisotropic superconductivity at KTaO3 (111) interfaces
Ethan G Arnault, Athby H Al-Tawhid, Salva Salmani-Rezaie, David A Muller, Divine P Kumah, Mohammad S Bahramy, Gleb Finkelstein, Kaveh Ahadi
Science Advances (2023)
