We investigate experimentally the electric transport at the insulating side of the superconductor to insulator transition in thin TiN-films. At temperatures T > 50 mK we observe an Arrhenius-type conductance, with an activation energy depending logarithmically on the sample size. At high bias the current voltage (I-V) characteristics display a large current jump into an electron heating dominated regime. For the largest samples, and below 50 mK we observe a low-bias power law I ~ V^alpha characteristics with an exponent alpha > 1 rapidly growing with decreasing temperature, which is expected for a binding-unbinding crossover of the charge-Berezinskii-Kosterlitz-Thouless type.
@article{arxiv.1004.5153,
title = {Intrinsic non-linear conduction in the super-insulating state of thin TiN films},
author = {D. Kalok and A. Bilusic and T. I. Baturina and V. M. Vinokur and C. Strunk},
journal= {arXiv preprint arXiv:1004.5153},
year = {2010}
}