Current-induced resistive state in cylindrical type-I superconductors

We have investigated the current-induced resistive state in superconducting indium wires through simultaneous measurements of the dc resistive voltage and the electrical noise power as the electrical transport current was increased from zero to beyond the critical value. The experiments were performed in zero applied magnetic field using indium wires with diameters of 0.17-0.52 mm. The measurements were made below the $\ensuremath{\lambda}$ point to discriminate against contributions from thermal fluctuations in the specimens due to nucleate boiling of liquid helium. The noise power was measured in the frequency range 20 Hz-20 kHz. For two specimens with diameters of 0.17 mm, a peak in the noise power was observed at the critical value of the transport current. The noise-power spectrum of one of the smallest-diameter samples showed very weak dependence of noise power on frequency at low frequencies and approximately ${\ensuremath{\omega}}^{\ensuremath{-}2}$ behavior at high frequencies. The magnitude of the noise voltage at the noise-power peak was found to be at most 2.4 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}3}$% of the dc resistive voltage. No ac voltages larger than ${10}^{\ensuremath{-}5}$% of the dc voltage were detectable for samples with diameters of 0.27 and 0.52 mm. Our results cast doubt on the validity of the Gorter dynamic model of the current-induced intermediate state and tend to support a static model of the type first proposed by London.

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