Atomic-scale Visualization of Electronic Fluid Flow

Although rapid advances have occurred in quantum fluid flow imaging, the velocity field v(r) of a charged superfluid - a superconductor - had never been visualized. We used superconductive–tip scanning tunneling microscopy to image the electron-pair density ρ_s(r) and velocity v_s(r) fields of the flowing electron-pair fluid in superconducting NbSe₂. Imaging v_s(r) surrounding a quantized vortex finds speeds reaching 10,000 km/hr. Together with independent imaging of ρ_s(r) via Josephson tunneling, we visualize the supercurrent density j_s(r)≡ ρ_s(r)v_s(r), which peaks above 3×10⁷ A/cm². The spatial patterns in electron-pair fluid flow and magneto-hydrodynamics reveal hexagonal structures co-aligned to the crystal lattice and quasiparticle bound states, as long anticipated from NbSe₂ crystal symmetry. This demonstration of atomic-scale imaging of v_s(r) for charged superfluid paves the way for electronic fluid flow visualization in other quantum fluids.

Published Article - Nature Materials 20, 1480 - August 2021