Magnetic measurement of RF-induced flux lattice annealing (RIFLA) in the electron-doped superconductor Pr$_{1.85}$Ce$_{0.15}$CuO$_{4-y}$.

A strained flux lattice (FL) in a superconductor (SC) can be annealed to a lower free energy by the RF-field used to generate an NMR spin-echo signal [W.G. Clark et al., J. Phys. IV Proceedings \textbf{9}, Pr10-49-52 (1999)]. Here, we report the change in the rf magnetic susceptibility ($\chi )$ in the SC phase of a single crystal of Pr$_{1.85}$Ce$_{0.15}$CuO$_{4-y}$ with a strained FL by successive RIFLA pulses. The distorted FL is prepared by rotating the sample through a small angle in a magnetic field well below the SC transition temperature, leaving the FL pinned in a non-equilibrium configuration. RIFLA pulses then reduce $\chi $, which is measured by the change in the inductance of a coil surrounding the sample using an NMR probe and spectrometer. The interpretation is that shaking the FL by the RF pulses progressively anneals it to a lower free energy configuration, which has a smaller $\chi $. These measurements provide a very sensitive measure of the RIFLA effect. Work at UCLA was supported by NSF Grants DMR-0334869 (WGC) and DMR-0520552 (SEB).