Nonlinear mesoscopic transport in a strongly cooperative electron system: The La0.67Ca0.33MnO3 microbridge.

We investigate the electrical transport in mesoscopic structures of La0.7Ca0.3MnO3 in the regime of the metal-insulator transition by fabricating microbridges from strained and unstrained thin films. We measure current-voltage characteristics as function of temperature and in high magnetic fields. For strained films we find nonlinear effects in the steep part of the transition characterized by a differential resistance with a strong peak around zero applied current, and saturation at higher currents after a resistance drop of up to 60%. We propose that this nonlinear behavior is associated with the melting of the insulating state by injecting charge carriers, signaling the occurrence of an intervening phase that involves the formation of short-range polaron correlations. [ABSTRACT FROM AUTHOR]