Exponential decrease of the collective vortex state energy with layer number in 2H-NbSe2

In the last years, a new generation of superconductors truly in the two-dimensional limit has been discovered in van der Waals materials. Recently, it has been shown that these type-II SCs can be extremely sensitive to external perturbation which pushes the system into a non-equilibrium steady state exhibiting metallic-like behavior [1]. Here we study the equilibrium and non-equilibrium phase diagrams of few-layered 2H-NbSe2 with minimal external perturbations. At finite magnetic field we observe a current-induced crossover to a non-activated metallic-like regime with a critical current that reduces with layer number. We discuss our results both phenomenologically and in the vortex picture which we compare with time-dependent Ginzburg-Landau simulations. In the vortex-picture we attribute the crossover to a transition from a pinned to unpinned vortex liquid. Finally, we demonstrate that by spreading non-uniform currents, we stabilize different vortex steady states in different spatial locations, potentially leading to novel interfaces.

[1] - Tamir, I., Benyamini, A. et al. Sensitivity of the Superconducting State in Thin Films. (2018)