Although all superconductors screen magnetic fields, many—including high-Tc cuprates and thin-film superconductors—allow a sufficiently strong field to penetrate as quantized vortices, supercurrent eddies that each surround a fixed amount of magnetic flux. As long as the vortices remain stationary, an applied current can flow across the material without resistance. Currents induce a force on a vortex, however, and above some critical current, the vortex will become liberated and dissipate energy as it moves quickly across the material. Just how quickly? Rough calculations suggest that vortices in a thin lead film could reach speeds of 40 km/s, two orders of magnitude faster than the perpendicular supercurrent driving them.
Little theory has been developed for such superfast vortices. But Eli Zeldov (Weizmann Institute of Science) and colleagues now report the first direct microscopic imaging of them. Crucial to the observations was a novel scanning probe: a nanoscale superconducting quantum interference...
