Motional broadening ofFe57Mössbauer-effect resonance in cuprate superconductors

Abstract

The temperature dependence of the ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ resonance in ${\mathrm{YBa}}_2$(${\mathrm{Cu}}_{0.98}$ ${\mathrm{Fe}}_{0.02}$ ${)}_4$ ${\mathrm{O}}_8$ samples shows evidence of a discontinuity in the observed linewidth Γ(T), isomer shift, and quadrupole splitting at ${\mathit{T}}_{\mathit{c}}$. Γ(T) is found to increase precipitously at T<${\mathit{T}}_{\mathit{c}}$ with the excess width ΔΓ(T) thermally activated. This behavior is a signature of a fluctuating electric-field gradient in the planes with the fluctuations slowing down in the superconducting phase.