Atomic-scale visualization of electronic fluid flow

The most essential characteristic of any fluid is the velocity field, and this is particularly true for macroscopic quantum fluids¹. Although rapid advances^2–7 have occurred in quantum fluid velocity field imaging⁸, the velocity field of a charged superfluid—a superconductor—has never been visualized. Here we use superconducting-tip scanning tunnelling microscopy^9–11 to image the electron-pair density and velocity fields of the flowing electron-pair fluid in superconducting NbSe₂. Imaging of the velocity fields surrounding a quantized vortex^12,13 finds electronic fluid flow with speeds reaching 10,000 km h^–1. Together with independent imaging of the electron-pair density via Josephson tunnelling, we visualize the supercurrent density, which peaks above 3 × 10⁷ A cm^–2. The spatial patterns in electronic fluid flow and magneto-hydrodynamics reveal hexagonal structures coaligned to the crystal lattice and quasiparticle bound states¹⁴, as long anticipated^15–18. These techniques pave the way for electronic fluid flow visualization studies of other charged quantum fluids.