Universal lower bound on the dissipation of superconductors

Despite their name, not all superconductors have zero resistance below their transition temperature T_c, at least when placed in a sufficiently strong magnetic field. For so-called type 2 superconductors—a class that includes high-temperature cuprate, iron-based, and magnesium diboride superconductors—the field penetrates and forms a lattice of vortices. Each vortex is an eddy of supercurrent that encircles a quantized amount of magnetic flux. Crystal defects, often intentionally introduced, will tend to pin the vortex lattice in place, but a sufficiently high current will force the vortices to move. That motion dissipates energy and manifests itself as a finite resistance. For currents slightly below the threshold, thermal fluctuations can provide the extra kick needed to knock the lattice free. Known as creep, thermally activated vortex motion can limit the operating range in applications such as high-field magnets and power transmission. The discovery of iron-based superconductors a decade ago challenged the...