Strain-induced structural change and nearly-commensurate diffuse scattering in the model high-temperature superconductor HgBa$_2$CuO$_{4+\delta}$

TL;DR

This study examines how strain affects the structure and charge correlations in HgBa₂CuO₄+δ, revealing strain-induced diffuse scattering linked to nearly-commensurate charge modulations, independent of superconductivity.

Contribution

It provides new insights into strain-induced structural and charge correlation changes in a high-temperature superconductor, supported by experimental and simulation data.

Findings

Strain causes a 0.9% increase in Cu-O distance along c at 1.1% a-axis compression.

Detected diffuse scattering indicates a nearly-commensurate charge modulation.

Charge order signal is insensitive to superconducting transition.

Abstract

We investigate the strain response of underdoped HgBa$_2$CuO$_{4+\delta}$ (Hg1201), by synchrotron X-ray diffraction and corresponding simulations of thermal diffuse scattering. The compression in the crystallographic $a$ direction leads to relatively small expansion in the $b$ and $c$ directions, with Poisson ratios $\nu_{ba}$=0.16 and $\nu_{ca}$=0.11, respectively. However, the Cu-O distance in the $c$ direction exhibits a notable 0.9% increase at 1.1% $a$-axis compression. We further find strain-induced diffuse scattering which corresponds to a new type of two-dimensional charge correlation. Interestingly, this signal is insensitive to the onset of superconductivity and instead corresponds to a short-range, nearly commensurate modulation with a wave vector close to (0.5, 0, 0) and a correlation length of approximately four unit cells. It closely resembles the charge order theoretically predicted in the phase diagram of the spin-liquid model with resonating valence bonds on a square lattice.