Neutron diffraction evidence of microscopic charge inhomogeneities in the CuO2 plane of superconducting La2-xSrxCuO4 (0 < x <0.30)

TL;DR

This study uses neutron diffraction to reveal charge inhomogeneities in the CuO2 planes of La2-xSrxCuO4, showing a transition from inhomogeneous to homogeneous charge states with doping, indicating strong electron-lattice coupling.

Contribution

It provides direct local structural evidence of charge inhomogeneities and their doping-dependent evolution in La2-xSrxCuO4 using neutron pair distribution function analysis.

Findings

Charge inhomogeneities are present at and below optimal doping.

A transition from inhomogeneous to homogeneous charge state occurs above optimal doping.

Strong electron-lattice coupling is indicated by local structural responses.

Abstract

We present local structural evidence supporting the presence of charge inhomogeneities in the CuO2 planes of underdoped La2-xSrxCuO4. High-resolution atomic pair distribution functions have been obtained from neutron powder diffraction data over the range of doping 0 < x < 0.30 at 10 K. Despite the average structure getting less orthorhombic we see a broadening of the in-plane Cu-O bond distribution as a function of doping up to optimal doping. Thereafter the peak abruptly sharpens. Complementary evidence is also evident from the observation of octahedral tilt disorder in the PDF at higher atomic separation. This suggests a crossover from a charge inhomogeneous state at and below optimal doping to a homogeneous charge state above optimal doping. The strong response of the local structure to the charge-state implies a strong electron-lattice coupling in these materials.