Condensed Matter Seminar: Fragility of the dissipationless state in clean two-dimensional superconductors

Abstract:

Dissipationless charge transport is one of the defining properties of superconductors, but the interplay between dimensionality and disorder in determining the onset of dissipation remains an open theoretical and experimental problem.  I will present measurements of the dissipation phase diagrams of superconductors in the two dimensional (2D) limit, layer by layer, down to a monolayer in the presence of temperature (T), magnetic field (B), and current (I) in 2H-NbSe2. Our results show that the phase-diagram strongly depends on the thickness even in the 2D limit. At four layers we can define a finite region in the I-B phase diagram where dissipationless transport exists at T=0. At even smaller thicknesses, this region shrinks in area until in a monolayer it approaches a single point defined by I=B=T=0. In applied field, we show that time-dependent-Ginzburg-Landau (TDGL) simulations that describe dissipation by vortex motion, qualitatively reproduce our experimental I-B phase diagram. We show that by using non-local transport and TDGL calculations that we can engineer charge flow and create phase boundaries between dissipative and dissipationless transport regions in a single sample, demonstrating control over non-equilibrium states of matter.

I will also show new results which we understand as a new flow regime in which vortices move in channels and their mobility is strongly influenced by thermal fluctuations. The fluctuations are observed to block vortex motion decreasing the measured resistance with increased temperature.  

Event Organizer: Dr. Moshe Ben Shalom