arXiv subjects

Swati S. Soman

Publications and source records attributed to Swati S. Soman.

4 recordsLinked to original sources

arXiv2002

Insulator superconductor transition on solid inert gas substrates

We present observations of the insulator-superconductor transition in ultrathin films of Bi on solid xenon condensed on quartz and on Ge on quartz. The relative permeability $ε_{r}$ ranges from 1.5 for Xe to 15 for Ge. Though we find screening effects as expected, the I-S transition is robust, and unmodified by the substrate. The resistance separatrix is found to be close to $h/4e^2$ and the crossover thickness close to 25 $Å$ for all substrates. I-V studies and Aslamazov-Larkin analyses indicate superconductivity is inhomogeneous. The transition is best described in terms of a percolation model.

cond-mat.supr-con↗

arXiv2002

Vortices and the mixed state of ultrathin Bi films

Current-voltage (I-V) characteristics of quench condensed, superconducting, ultrathin Bi films in a magnetic field are reported. These show hysteresis for all films, grown both with and without thin Ge underlayers. Films on Ge underlayers, close to superconductor-insulator transition, show a peak in the critical current, indicating a structural transformation of the vortex solid. These underlayers, used to make the films more homogeneous, are found to be more effective in pinning the vortices. The upper critical fields ($B_{c2}$) of these films are determined from the resistive transitions in perpendicular magnetic field. The temperature dependence of the upper critical field is found to differ significantly from Ginzburg-Landau theory, after modifications for disorder.

cond-mat.supr-con↗

arXiv2002

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

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

cond-mat.supr-con↗

arXiv2000

Possible robust insulator-superconductor transition on solid inert gas and other substrates

We present observations of the insulator-superconductor transition in ultrathin films of Bi on amorphous quartz, quartz coated with Ge, and for the first time, solid xenon condensed on quartz. The relative permeability $ε_r$ ranges from 1.5 for Xe to 15 for Ge. Though we find screening effects as expected, the I-S transition is robust, and unmodified by the substrate. The resistance separatrix is found to be close to h/4e^2 and the crossover thickness close to $\rm 25 Å$ for all substrates. I-V studies and Aslamazov-Larkin analyses indicate superconductivity is inhomogeneous. The transition can be understood in terms of a percolation model.

cond-mat.supr-con↗