Fragility of the dissipationless state in a clean two-dimensional superconductor 2H-NbSe2
In my talk, I will tell about my interest in emergent phenomena and how the extreme tunability of 2D materials is an unprecedented tool-box to investigate emergent and novel physical phenomena. I will discuss the importance of scanning probes and my plan to establish a new scanning platform based on 2D materials. I will then talk about my work in Columbia on an air-sensitive van der Waals superconductor 2H-NbSe2. How we established a new technique to contact and preserve the material. That we resolved a 20-year-old open question regarding the nature of an anomalous metallic state in the superconducting dome of thin-film superconductors (in collaboration with Danny Shahar, Weizmann). We found that in both 2H-NbSe2 and amorphous InOx, the anomalous metallic state was a non-equilibrium steady-state driven by electronic noise. With no added noise, I will present measurements of the dissipation phase diagrams of superconductivity 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.
If time permits, I will show new results which we understand as a blockade of vortex transport due to thermal fluctuations.
 Nano Letters 2018
 Science Advances 2019
 Nature Physics 2019
 In submission to PRL, arXiv:1909.08469