Speaker: Ilaria Maccari (KTH)
Title: Vortex physics in 2D disordered superconductors
Time: Tuesday 29th of October, Fika 10:30-11:00 , Seminar 11:00-12:00,
Place: Nordita South, room 112:028 .
Abstract:
The study of quasi-two-dimensional (2D) superconductors can hardly avoid to take into account the presence of vortices. Many real systems, of both conventional and unconventional superconductors, undergoes the superconductor-insulator transition via the Brezinskii-Kosterlitz-Thouless (BKT) transition, at which the phase coherence of the condensate is destroyed by means of free-vortices proliferation.
When a finite flux of the magnetic field is applied to the films, the role of vortices becomes even more crucial for the understanding of the superconducting (SC) transition. Indeed, in this case, the transition is no longer driven by the vortex-antivortex unbinding, but rather by the melting of the 2D Abrikosov lattice of vortices. Such melting, as predicted by the BKT theory, afterward refined by Halperin, Nelson and Young (BKTHNY), can occur in two steps via an intermediate state called hexatic phase. In real systems, the observation of the two-step BKTHNY melting could be hindered by the presence of additional ingredients, such as random pinning, and also competing phases. In [1], we have shown that the 2-dimensional vortex lattice in the a-MoGe thin films follows the BKTHNY sequence of melting as the magnetic field is increased. Identifying the signatures of various transitions on the bulk transport properties of the superconductor, we construct a vortex phase diagram for a 2D superconductor. From a theoretical standpoint, the classical XY model with a transverse magnetic field is a very promising candidate to capture the physics experimentally observed and to explore stronger disorder regimes. It constitutes hence a perfect playground for the investigation of the long-standing issue of the emergent glassy-state of the vortex lattice in the presence of disorder.
[1] I. Roy, S. Dutta, A. N. Roy Choudhury, S. Basistha, I. Maccari, S. Mandal, J. Jesudasan, V.Bagwe, C. Castellani, L. Benfatto, P. Raychaudhuri, Phys. Rev. Lett. 122 (4), 047001 (2019)
