Peak-effect and surface crystal-glass transition for surface-pinned   vortex array
  We present a theoretical and experimental study of the peak effect in the surface pinning of vortices. It is associated with a sharp transition in the vortex slippage length which we relate to a crossover from a weakly disordered crystal to a surface glass state. Experiments are performed on ion-beam etched Nb crystals. The slippage length is deduced from 1kHz-1MHz linear AC penetration depth measurements. 
Bernard Placais, Norbert Lutke-Entrup, Joel Bellessa, Patrice Mathieu,   Yvan Simon, Edouard Sonin