A Structural Probe of the Doped Holes in Cuprate Superconductors

TL;DR

This study uses enhanced anomalous x-ray scattering to directly analyze the distribution of doped holes in cuprate superconductors, revealing inhomogeneities and absence of in-plane hole ordering.

Contribution

It demonstrates a method to magnify the scattering contribution of doped holes, enabling direct structural analysis of their distribution in cuprates.

Findings

Detected a depletion zone near the substrate in La2CuO4+x

Found no evidence of in-plane hole ordering

Enhanced scattering technique increases sensitivity by over 10^3

Abstract

An unresolved issue concerning cuprate superconductors is whether the distribution of carriers in the CuO(2) plane is uniform or inhomogeneous. Because the carriers comprise a small fraction of the total charge density and may be rapidly fluctuating, modulations are difficult to detect directly. Here we demonstrate that in anomalous x-ray scattering at the oxygen K edge of the cuprates, the contribution of carriers to the scattering amplitude is selectively magnified 82 times. This enhances diffraction from the doped holes by more than 10^3, permitting direct structural analysis of the superconducting ground state. Scattering from thin films of La(2)CuO(4+x) (Tc = 39 K) at T=(50 +/- 5) K on the reciprocal space intervals (0,0,0.21) -> (0,0,1.21) and (0,0,0.6) -> (0.3,0,0.6) show a rounding of the carrier density near the substrate suggestive of a depletion zone or similar effect. The structure factor for off-specular scattering was less than 3x10-7 e, suggesting an absence of in-plane hole ordering in this material.