# I-V characteristics of the vortex state in MgB2 thin films

## TL;DR

This study investigates the I-V characteristics of MgB2 thin films under various magnetic fields, revealing vortex liquid-glass transitions and scaling behaviors consistent with quasi-2D vortex glass theory, with deviations at higher fields suggesting complex vortex dynamics.

## Contribution

It demonstrates the applicability of quasi-2D vortex glass theory to MgB2 thin films and identifies deviations at high magnetic fields indicating mixed vortex states.

## Key findings

- Vortex liquid-glass transitions observed at fields 0-5T.
- Scaling behavior consistent with quasi-2D vortex glass theory at low fields.
- Deviations from scaling at fields >= 5T, suggesting complex vortex dynamics.

## Abstract

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.