Observation of a local structural change at Tc for Tl2Ba2CaCu2O8 by pulsed neutron diffraction

Abstract

Deviations in atomic positions from those of the average crystallographic structure of superconducting ${\mathrm{Tl}}_2$ ${\mathrm{ba}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$ were studied by pair-distribution function (PDF) analysis of pulsed-neutron-scattering data. The PDF shows a clear change in the local structure at the onset of superconductivity. In addition to the previously observed local displacements of Tl and O within the Tl-O sheets, correlated displacements of O and Cu perpendicular to the Cu-O plane have been found. The arrangement of the O atoms appears to be different above and below ${\mathit{T}}_{\mathit{c}}$.