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Sampled CW Measurements on Single Crystals of YBa2Cu3O(7-delta) and Bi2Sr2CaCu2O8

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Sampled Continuous Wave technique was found most suitable for investigating small single crystals of YBa2Cu3O7-delta and Bi2Sr2CaCu2O8. A unique bonding technique has been developed where the sample is pressed on to the transducer with few threads of very thin GE varnish and the transducer is mounted between parallel gold wires and a soft spring to oscillate freely. It has been found that only an optimal coupling between sample and transducer can bring out various features in the mixed phase of the of these high Tsub c superconducting crystals. The results of attenuation measurements on different single crystals of YBa2Cu3O7-delta and Bi2Sr2CaCu2O8 using such technique at frequencies of 3 MHz and 5 MHz and in magnetic field up to 1.6T will be presented. Early work on untwined YBCO revealed pronounced field dependent attenuation changes that were indicative of transitions from soft vortex system at low fields to a rigid vortex system at high fields. In addition, for untwinned YBCO, ultrasonic signatures of melting transition and possibly depinning transition of the flux line lattice were observed below the critical temperature. For twinned YBCO crystal and BSCCO crystal, sharp field dependent attenuation drops were observed below the critical temperature and are easily identifiable with the normal-superconducting transition. In addition, in the superconducting mixed state there were field dependent transitions analogous to the melting transition of the flux lattice. This melting phenomenon was also investigated extensively for YBCO using ac-susceptometry technique.

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  • Crystallography
  • Radiofrequency Wave Propagation

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