From Supersonic Currents to Cavity-Altered Superconductors
Abhay Pasupathy
Columbia University
Wednesday, September 24, 2025
2:00 p.m.
In-person: QNC 1201
Abhay Pasupathy from Columbia University will discuss the use of scan probe microscopy to gain microscopic insight into two separate quantum phenomena.
In the first experiment, we explore how electrons in ultra-clean solids can behave as a viscous fluid, enabling transport far from the textbook ohmic or ballistic regimes. I will discuss a bilayer-graphene electronic de Laval nozzle that accelerates carriers to supersonic speeds, producing a viscous electron shock. Discontinuities in transport and local potential flattening observed by Kelvin probe microscopy are consistent with a compressible, hydrodynamic flow that breaks the electronic sound barrier—opening a path to intrinsically nonlinear devices that exploit shocks.
In the second experiment, I will discuss how we can affect superconductivity by engineering a material’s electromagnetic environment. Using a “dark” hyperbolic cavity formed by hexagonal boron nitride interfaced with the molecular superconductor κ-(BEDT-TTF)₂Cu[N(CN)₂]Br (κ-ET), we realize resonant coupling between hBN hyperbolic modes and a molecular vibration implicated in pairing. We use magnetic-force microscopy to detect the Meissner response at the interface of the two materials. We observe a marked suppression of superfluid density at the interface—an effect absent in non-resonant controls.