Negative magnetoresistance slope in superconducting granular films

A phenomenological theory is developed to explain the recently observed negative magnetoresistance slope in ultra-thin granular YBa2Cu2O7 (delta) films. Viewing this system as a two-dimensional array of extended Josephson junctions, we numerically solve the sine-Gordon equations including a viscosity term that increases linearly with the external field. The solution yields a negative magnetoresistance slope setting in at a field that is determined by the geometry and thus independent of temperature, in agreement with the experimental results. (C) 2014 Elsevier B.V. All rights reserved.