Seminar of Department of Experimental Physics - Denis Kochan (9.6.2022)
Thursday 9.6.2022 at 14:00 Lecture room C
By: František Herman
Denis Kochan (University of Regensburg & Institute of Physics, SAS Bratislava):
Anisotropic vortex squeezing in Rashba superconductors: a manifestation of Lifshitz invariants
Most 2D superconductors are of type II, i.e., they are penetrated by quantized vortices when exposed to out-of-plane magnetic fields. In a presence of a supercurrent, a Lorentz-like force acts on the vortices, leading to drift and dissipation. The current-induced vortex motion is impeded by pinning at defects. Usually, the pinning strength decreases upon any type of pair-breaking interaction that perturbs a system.
In the talk, I will discuss surprising experimental evidence showing an unexpected enhancement of pinning in synthetic Rashba 2D superconductors when applying an in-plane magnetic field. When rotating the in-plane component of the field with respect to the driving current, the vortex inductance turns out to be highly anisotropic. We explain this phenomenon as a direct manifestation of the Lifshitz invariant that is allowed in the Ginzburg-Landau free energy by symmetry when space-inversion and time-reversal symmetries are broken. As demonstrated in our experiment [arXiv:2201.02512], elliptic squeezing of vortices---an inherent property of the non-centrosymmetric superconducting condensate--- provides access to fundamentally new property of Rashba superconductors, and offers an entirely novel approach to vortex manipulation.
The talk is intended to be pedagogical and as pedestrian, as it can be. I will in introduce and motivate concepts of the Lifshitz invariants, the superconducting diode effect, and, generally, a notion of the non-centrosymmetric superconductivity.