Properties of Tl2Ba2CaCu2O8 step and bicrystal junctions and dc-SQUIDs on LaAlO3 substrates

Y. F. Chen, Z. G. Ivanov, E. A. Stepantsov, A. Y. Tzalenchuk, S. Zarembinski, A. L. Vasiliev, E. Olsson, H. R. Yi, T. Claeson, L. G. Johansson

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Step and bicrystal Josephson junctions and de SQUIDs in Tl-2212 epitaxial films have been fabricated and studied. The junctions formed on steps with an angle of 68 degrees have hysteretic multi-branch I-V curves and J(c) approximate to 10(3) A/cm(2) at 4K. TEM images show that Tl-2212 forms an a-axis bar-like grain on the step which is surrounded by c-axis oriented film. However, the supercurrent transport at the step is most likely determined by Josephson tunneling between the Cu-O planes in the c-direction of this grain rather than through the 90 degrees a-axis tilted grain boundaries formed at the step edges. The transport measurements on 32 degrees bicrystal junctions showed that such a grain boundary behaves as a Josephson junction with a J(c) of 6 . 10(3)-2 . 10(4) A/cm(2) while the intragrain J(c) was approximate to 2 . 10(6) A/cm(2), both measured at 77K. The critical temperature of the junctions is in the range 89-108K. The critical current is found to be proportional to (1-T/T-c)(2) at temperatures close to T-c, whereas at low temperatures I-c proportional to 1-T/T-c. The flux noise, S-Phi, of de SQUIDs is measured up to 95K in the locked mode without bias reversing. At 77K the white noise level is 50 mu Phi(0)/root Hz. The crossover frequency to 1/f noise is low, about 5Hz, and the flux noise level at 1 Hz is 440 mu Phi(0)/root Hz.
Original languageEnglish
Title of host publicationApplied Superconductivity 1995, Vols. 1 and 2: Vol 1: Plenary Talks and High Current Applications; Vol 2: Small Scale Applications
Number of pages4
Publication statusPublished - 1995

Publication series

NameInstitute of Physics Conference Series

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