Gigahertz Ultrasound in Single Crystal Superconducting YBa2Cu3O7

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Conference Proceeding

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Anisotropic sound propagation at 1 GHz in single-crystal YBa2Cu3O7 is described. Longitudinal phonons have been studied from 0.01 K to 300 K, with emphasis on the temperature region near the superconducting transition Tc at 88 K. A discontinuous sound velocity is observed at Tc for propagation parallel and perpendicular to the c axis. Strain derivatives of Tc are evaluated using mean field theory. Below 1 K the temperature-dependent sound velocity has positive slope, which indicates tunneling of defects.

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