Detailed numerical simulations of intrinsic Josephson junctions of high temperature superconductors under external electromagnetic radiation are performed taking into account a charge imbalance effect. We demonstrate that the charge imbalance is responsible for a slope in the Shapiro step the value of which increases with a nonequilibrium parameter. Coupling between junctions leads to the distribution of the slope's values along the stack. The nonperiodic boundary conditions shift the Shapiro step in IV-characteristics from the canonical position determined by Vss=ℏf/(2e), where f is a frequency of external radiation. This fact makes ambiguous the interpretation of the experimentally found Shapiro step shift by the charge imbalance effect.
@article{arxiv.1601.04456,
title = {Shapiro Step at Nonequilibrium Conditions},
author = {Yu. M. Shukrinov and M. Nashaat and K. V. Kulikov and R. Dawood and H. El Samman and Th. M. El Sherbini},
journal= {arXiv preprint arXiv:1601.04456},
year = {2016}
}