November 16 - Time reversal symmetry breaking in high temperature superconductor circuits
Annelle Eben, student, Calvin College Engineering Department
Professor Stephen Remillard, Physics Department, Hope College
Movies running backwards portray events some of which are indistinguishable from forward, and some of which make no sense in reverse. Those events which make no sense in reverse are driven by non-conservative forces, such as the friction that grinds motion to a halt. The irreversibility of a non-conservative force indicates a one-way transfer of energy from one form into another, more commonly called dissipation. Superconducting materials are so valuable technologically because they do not dissipate electrical energy, and yet experimental evidence that the superconductor does not look the same when time runs backwards reveals the presence of dissipative currents. Using as samples commercial devices that were manufactured from high temperature superconducting wafers, the breaking of time reversal symmetry has been detected through the measurement of the distortion in microwave signals passing through the devices. Causes of both intrinsic (e.g. within the superconducting state) and extrinsic (e.g. material defects) nature are being considered, and time reversal symmetry breaking could prove a valuable tool for hunting down and eliminating the sources of dissipation in these technologically important materials.