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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
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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

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K. Das Gupta, Swati S. Soman, G. Sambandamurthy, N. Chandrasekhar. 2002-09-02. Critical currents and vortex-unbinding transitions in quench-condensed ultrathin films of Bismuth and Tin. https://doi.org/10.1103/physrevb.66.144512

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