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 advances2–7 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 microscopy9–11 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 vortex12,13 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 anticipated15–18. These techniques pave the way for electronic fluid flow visualization studies of other charged quantum fluids. Atomic-scale visualization of the superfluid velocity field, the electron-pair density and the superfluid current density in an electron-pair superfluid surrounding an Abrikosov vortex in a superconducting sample of NbSe2 is demonstrated, using superconducting-tip scanning tunnelling microscopy.