We have performed flux noise and AC-susceptibility measurements on two 400 nm thick MgB2 films. Both measurement techniques give information about the vortex dynamics in the sample, and hence the superconducting transition, and can be linked to each other through the fluctuation-dissipation-theorem. The transition widths for the two films are 0.3 and 0.8 K, respectively, and the transitions show a multi step-like behavior in the AC-susceptibility measurements. The same phenomenon is observed in the flux noise measurements through a change in the frequency dependence of the spectral density at each step in the transition. The results are discussed and interpreted in terms of vortices carrying an arbitrary fraction of a flux quantum as well as in terms of different macroscopic regions in the films having slightly different compositions, and hence, different critical temperatures.
@article{arxiv.cond-mat/0303337,
title = {Flux Noise in MgB2 Thin Films},
author = {Orjan Festin and Peter Svedlindh and W. N. Kang and Eun-Mi Choi and Sung-Ik Lee},
journal= {arXiv preprint arXiv:cond-mat/0303337},
year = {2009}
}
Comments
8 pages, 4 figures, conference contribution to "Fluctuations and Noise", Santa Fe, New mexico 1-4 june 2003