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UBC Theses and Dissertations

Superconductivity in thin films Chaudhari, Ram Das


The critical, currents and magnetic fields required to destroy superconductivity have been measured for thin films of indium and tin in the thickness range of 585 Å to 3600 Å, The measurements were made in the region close to the transition temperature, T[subscript c] . The critical current measurements on a 585 Å thick indium film are the first reported which combine the use of a compensated geometry avoiding the difficulties associated with specimen edges, and fast rising current pulses in which the transition is not obscured by specimen heating. The fast current pulses used had a rise time of 7 nanoseconds. It was found that the temperature dependence of the critical currents in the region near the transition temperature, 0 ⋜ ΔT ⋜ 0.15°K is in. agreement with the Ginzburg-Landau theory. For a number of films the critical currents were measured using pulses having a rise time of 1.2 microseconds. The critical currents have been found to vary linear 1 with the film thickness, in agreement with the G-L theory. Measurements with fast pulses seem to indicate the existence of a transition delay of about 7 nanoseconds, independent of the current amplitudes. The transition from the superconducting to the normal state immediately following the transition delay appears to be very fast. For the critical field data, the temperature dependence is in accordance with the G-L theory in the range 0⋜ΔT ⋜ 0.3°K for both indium and tin films. The effective penetration depth calculated in the manner of Ittner, and Douglass and Blumberg was found to be dependent on the thickness and the mean free path. The critical magnetic fields were found to be inversely proportional to the film thickness in agreement with G-L theory.

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