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Vortices in superconducting arrays: probing dissipation and interactions Prof. Nadya Mason

Wednesday, May 29, 2019 - 11:15 to 12:30 Auditorium

Superconductivity continues to be an exciting and fertile field of research, with potential applications in energy efficiency and storage. Non-superconducting systems in contact with superconductors have been of particular recent interest, as these proximity-coupled superconductors may show new behaviors or harbor unusual excitations (eg, Majoranas in topological-superconductor systems). A key to understanding and utilizing superconductors is understanding their behavior in magnetic fields, particularly when the field penetrates as quantized tubules of flux, or vortices. In this talk I will show that, although vortices have been studied for many years, measurements of their current-driven dynamics can still lead to new results and understanding. I will discuss transport measurements of current-driven vortices in superconductor-normal-superconductor (SNS) arrays, where we are able to access a number of vortex regimes, and find unusual behavior in the non-equilibrium transitions between vortex states. First, in the low magnetic field regime, we find that the dynamic behavior of vortices is consistent with the presence of time delayed dissipative forces. I will also discuss how at higher magnetic fields, vortex de-pinning occurs in two steps, consistent with a commensurate lattice appearing even for non-commensurate magnetic field values. This two-step behavior is due to strong vortex interactions, and has not previously been observed. Finally, I will discuss measurements of vortex arrays on topological insulators, where we see enhanced dissipation and evidence of unusual charged vortices, predicted as the “Witten effect” in topological systems.