Scaling of nonlinear complex susceptibility applied to the study of type-II superconductors

Different chi measurements can be collapsed into a single universal curve i f plotted against the scaling variable h(omega (overbar)/omega)(1/sigma) or , more generally, h/Jd, where J(T, B, omega) is a frequency dependent shiel ding current density, d is the sample half-width and h is the AC field ampl itude. We have tested these scaling laws for two Nb samples, one melt textu red YBCO sample, and one Er123 single crystal. Further, we found that J(T,B , omega) for Er123 displays a behavior closely related to the second magnet ization peak (fishtail effect), observed in M x H curves. Our results are s atisfactorily interpreted in terms of vortex dynamic models. (C) 2001 Elsev ier Science B.V. All rights reserved.