Title: Probing individual vortices in twisted graphene via a Josephson junction
When: Monday, May 18, 2026, 15:00
Place: Department of Theoretical Condensed Matter Physics, Faculty of Sciences, Module 3, Seminar Room (5th Floor)
Speaker: Marta Perego, ETH Zurich, Ensslin Nanophysics group
Experimentally, magic-angle twisted bilayer and multilayer graphene have been found to exhibit gate-tunable superconducting phases, enabling the realization of monolithic superconducting devices controlled purely by electrostatic gating. However, a consensus on the microscopic mechanisms underlying superconductivity in these materials has yet to emerge. In this talk, we discuss our recent experiments on gate-tunable Josephson junctions in magic-angle twisted four-layer graphene. By using a junction as a sensitive vortex sensor, we detect individual vortices in the superconducting leads, which manifest as abrupt shifts in the Fraunhofer interference pattern. Time-resolved measurements allow us to investigate the dynamics of individual vortices, providing access to the characteristic vortex energy scale and the London penetration depth. Our measurements reveal a high-temperature regime dominated by classical thermal activation over an energy barrier, which crosses over at low temperatures to a regime of macroscopic quantum tunnelling through the barrier.
