Local Lattice Instability and Superconductivity in La$_{1.85}$Sr$_{0.15}$Cu$_{1-x}$M$_x$O$_4$ (M=Mn, Ni, and Co)

TL;DR

This study investigates how substituting Mn, Ni, and Co into La$_{1.85}$Sr$_{0.15}$CuO$_4$ affects local lattice structures and superconductivity, revealing that lattice instability is crucial for superconducting behavior.

Contribution

It demonstrates that Ni and Co suppress local lattice instability more than Mn, linking lattice perturbations to the suppression of superconductivity in cuprates.

Findings

Ni and Co substitution strongly suppresses lattice instability.

Lattice instability correlates with superconductivity.

Mn substitution causes minimal perturbation.

Abstract

Local lattice structures of La$_{1.85}$Sr$_{0.15}$Cu$_{1-x}$M$_x$O$_4$ (M=Mn, Ni, and Co) single crystals are investigated by polarized extended x-ray absorption fine structure (EXAFS). The local lattice instability at low temperature is described by in-plane Cu-O bond splitting. We find that substitution of Mn for Cu causes little perturbation of local lattice instability while Ni and Co substitution strongly suppresses the instability. The suppression of superconductivity by Cu-site substitution is related to the perturbation of lattice instability, indicating that local lattice instability (polaron) plays an important role in superconductivity.