Critical currents and vortex-unbinding transitions in quench-condensed ultrathin films of Bismuth and Tin

K. Das Gupta; Swati S. Soman; G. Sambandamurthy; N. Chandrasekhar

doi:10.1103/PhysRevB.66.144512

paper

Critical currents and vortex-unbinding transitions in quench-condensed ultrathin films of Bismuth and Tin

arXiv:cond-mat/0209023 · doi:10.1103/PhysRevB.66.144512

Abstract

We have investigated the I-V characteristics of strongly disordered ultra-thin films of {\it Bi} and {\it Sn} produced by quench-condensation. Our results show that both these sytems can be visualized as strongly disordered arrays of Josephson junctions. The experimentally observed I-V characteristics of these films is hysteretic, when the injected current is ramped from zero to critical current and back. These are remarkably similar to the hysteretic I-V of an underdamped single junction. We show by computer simulations that hysteresis can persist in a very strongly disordered array. It is also possible to estimate the individual junction parameters ( $R$ , $C$ and $I_{c}$ ) from the experimental I-Vs of the film using this model. The films studied are in a regime where the Josephson-coupling energy is larger than the charging energy. We find that a simple relation $I_{c} (T) = I_{c} (0) (1 - (T / T_{c})^{4})$ describes the temperature dependence of the critical current quite accurately for films with sheet resistance $\sim$ 500 $Ω$ or lower. We also find evidence of a vortex-unbindi

To appear in Phys Rev B, October 1 Issue

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Critical currents and vortex-unbinding transitions in quench-condensed ultrathin films of Bismuth and Tin

Abstract

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