Magnetic field dependence of the surface reactance of superconducting tin at 174 MHz

The magnetic field dependence of the surface reactance of superconducting tin has been measured at a frequency of 174 MHz. In the perpendicular field configuration (RF and static fields perpendicular to each other) the behaviour observed is approximately that expected from the Ginzburg-Landau theory in the static limit. In the parallel field configuration complicated behaviour is observed, even the sign of the reactance change being different at different temperatures. Near Tc there is a region where the reactance change has approximately linear dependence on the magnitude of the applied field, instead of the quadratic dependence expected in fields that not not too large.