Accession Number : ADA297740

Title :   Ultrasonic Characterization of High Tc and Other Unconventional Superconductors.

Descriptive Note : Annual summary rept. 1 Jun 94-30 Jun 95,

Corporate Author : WISCONSIN UNIV-MILWAUKEE DEPT OF PHYSICS

Personal Author(s) : Levy, Moises

PDF Url : ADA297740

Report Date : 30 JUN 1995

Pagination or Media Count : 8

Abstract : Ultrasonic techniques have been used to characterize the properties of high Tc and other unconventional superconductors. Attenuation and velocity measurements with longitudinal waves have been performed on a large single crystal of La1.85Sr0.15CuO4. Attenuation and velocity signatures have been observed at the superconducting transition, 37K, and at 27K. The effects observed at the lower temperature are produced by magnetic fluctuations due to an antiferromagnetic transition. Longitudinal ultrasonic attenuation and velocity were measured on a single crystal of UPt3 in high magnetic fields up to 23 T at 192 MHz from 2K up to 35K. Below 17 T, an attenuation peak is observed which is associated with the Kondo Effect. Above 17K, a large attenuation peak was discovered which is due to a metamagnetic transition induced by a crossing of a magnetic energy level with the Fermi Energy. The pontoon technique was used to investigate the attenuation of SAW in a single crystal of YBCO and on thin films of YBCO. Peaks in attenuation are observed slightly below Tc which were enhanced and moved to lower temperatures by a magnetic field. These may be due to melting of the magnetic flux lattice. SAW attenuation and velocity data in the films point to a first order phase transition, around 200 K, which may be a structural transition into a piezoelectric state. (AN)

Descriptors :   *COPPER COMPOUNDS, *HIGH TEMPERATURE SUPERCONDUCTORS, *ULTRASONIC TESTS, *SURFACE ACOUSTIC WAVES, PEAK VALUES, MAGNETIC FIELDS, HIGH TEMPERATURE, CRYSTAL LATTICES, THIN FILMS, SINGLE CRYSTALS, FERMI SURFACES, VARIATIONS, TRANSITION TEMPERATURE, ULTRASONICS, PIEZOELECTRIC CRYSTALS, ACOUSTIC ATTENUATION, ACOUSTIC SIGNATURES, ENERGY LEVELS, ACOUSTIC VELOCITY, PONTOONS, SUPERCONDUCTIVITY, POLYCRYSTALLINE, ANTIFERROMAGNETISM.

Subject Categories : Acoustics
      Electricity and Magnetism
      Crystallography

Distribution Statement : APPROVED FOR PUBLIC RELEASE