Anomalous Ion-Channeling Behavior Across the Superconducting Transition in High-T(sub C) Materials.

摘要

Axial channeling scans with minimum RBS yields of (le)2% were obtained for 1.5 MeV (sup 4)He ions incident along the c-axis in YBa(sub 2)Cu(sub 3)O(sub 7-(delta)) and ErBa(sub 2)Cu(sub 3)O(sub 7-(delta)) single crystals. Large variations in the FWHM of the (001) channeling dip were observed for temperatures between 30 and 300 K. An abrupt, (approximately)8% increase was measured as the temperature was lowered through the superconducting transition (T(sub c)); the relative increase across T(sub c) in the width of the axial dip was even larger for angles of incidence less than the critical angle. A simple analytical procedure for polyatomic materials yields isotropic, average thermal vibrational amplitudes that agree well with considerably less precise neutron powder diffraction results on sintered samples. The individual contribution to the angular channeling dip from the row of Er and Ba atoms parallel to the c-axis can be isolated in the RBS scans of the Er compound. This separation reveals normal (Debye-type) behavior for atoms in the Er-Ba row, demonstrating that the anomalous changes are due solely to atomic displacements in the Cu-O row. Finally, x-ray studies using specimens with different O stoichiometries reveal that the anomalous change in the FWHM shifts in temperature in direct proportion to the change in T.