Current-Induced Intermediate State in Superconducting Strips of Lead and Indium
We have investigated the magnetic structure, the electrical resistance, and the electrical noise power spectra in the current-induced intermediate state of superconducting strips of lead and indium. The specimens were microstrips 60–300 µm wide, 0.3–10 µm thick, and 3–6 mm long. The samples were made by vacuum deposition on a glass or fused quartz substrate using starting materials with 99.9999% purity and a tunable mask with two razor blade sections. The samples carried electrical current and voltage leads attached to rather wide sections at both ends of the strip. The experiments were performed in zero applied external magnetic field. Electrical transport currents with an average density up to 106 A/cm2 were applied to the strips. The samples were in direct contact with the liquid helium bath. In order to protect the microstrips against destruction by thermal runaway, a shunt was attached parallel to the sample. The shunt resistance was 3–5 times the normal resistance of the samples at 4.2°K, being at least 1–2 orders of magnitude larger than the current-induced sample resistance for the current range investigated. In the electrical noise power measurements the primary coil of a stepup transformer in the liquid helium bath provided the protective shunt.
KeywordsNoise Power Transport Current Voltage Step Normal Domain Noise Power Spectrum
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