Local Lattice Distortion in Superconducting Cuprates Studied by XAS

Abstract

In-plane local distortion in cuprates characterized by strong doping and temperature dependence is a signature of polaron (bipolaron). The nature of dynamic lattice response in relation to the onset of superconductivity was probed by polarized x-ray absorption spectroscopy (XAS), for pure and magnetic impurity-doped MxLa1.85Sr0.15Cu1-xO4 (M=Mn, Ni, Co, x<0.05) single crystals grown by a TSFZ method. The results confirm that the dynamical anti Jahn-Teller (AJT) distorted domains maximize at Tdmax~Tconset, which is described by the disappearance of the Cu-O(1) bond alternation upon the completion of phase coherence (onset of superconductivity). In contrast to the Ni and Co dopings which quickly suppress superconductivity by magnetic pair breaking, the Mn doping shows sustainable superconductivity i.e., a constant Tdmax and Tconset upto x=0.03 with the presence of dynamical AJT distortion. The results suggest that the dynamical AJT type distortion with either Q2 or pseudo JT symmetry extending over the basal plane could be a prerequisite for high temperature superconductivity.