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 fluids 1 . Although rapid advances 2 – 7 have occurred in quantum fluid velocity field imaging 8 , 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 NbSe 2 . 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 × 10 7 A cm –2 . The spatial patterns in electronic fluid flow and magneto-hydrodynamics reveal hexagonal structures coaligned to the crystal lattice and quasiparticle bound states 14 , as long anticipated 15 – 18 . These techniques pave the way for electronic fluid flow visualization studies of other charged quantum fluids.