The current-voltage (I-V) characteristics of various MgB2 films have been studied at different magnetic fields parallel to c-axis. At fields \mu0H between 0 and 5T, vortex liquid-glass transitions were found in the I-V isotherms. Consistently, the I-V curves measured at different temperatures show a scaling behavior in the framework of quasi-two-dimension (quasi-2D) vortex glass theory. However, at \mu0 H >= 5T, a finite dissipation was observed down to the lowest temperature here, T=1.7K, and the I-V isotherms did not scale in terms of any known scaling law, of any dimensionality. We suggest that this may be caused by a mixture of \sigma band vortices and \pi band quasiparticles. Interestingly, the I-V curves at zero magnetic field can still be scaled according to the quasi-2D vortex glass formalism, indicating an equivalent effect of self-field due to persistent current and applied magnetic field.
@article{arxiv.0704.0126,
title = {I-V characteristics of the vortex state in MgB2 thin films},
author = {Huan Yang and Ying Jia and Lei Shan and Yingzi Zhang and Hai-Hu Wen and Chenggang Zhuang and Zikui Liu and Qi Li and Yi Cui and Xiaoxing Xi},
journal= {arXiv preprint arXiv:0704.0126},
year = {2008}
}