Decoupling of Static and Dynamic Charge Correlations revealed by Uniaxial Strain in a Cuprate Superconductor

TL;DR

This study reveals that in a cuprate superconductor, static charge order and dynamic charge excitations are decoupled, with excitations showing isotropic behavior suggestive of quantum criticality, using uniaxial strain and high-resolution RIXS.

Contribution

The paper demonstrates that static charge order and dynamic charge excitations are decoupled, challenging previous assumptions about their relationship in cuprates.

Findings

Charge excitations are isotropic and decoupled from static charge order.

Optical phonon anomalies show no stripe anisotropy.

Charge excitations suggest quantum critical behavior.

Abstract

We use uniaxial strain in combination with ultra-high-resolution Resonant Inelastic X-ray Scattering (RIXS) at the oxygen K- and copper L3-edges to study the excitations stemming from the charge ordering wave vector in La1.875Sr0.125CuO4. By detwinning stripe ordering, we demonstrate that the optical phonon anomalies do not show any stripe anisotropy. The low-energy charge excitations also retain an in-plane four-fold symmetry. As such, we find that both phonon and charge excitations are decoupled entirely from the strength of static charge ordering. The almost isotropic character of charge excitations is indicative of a quantum critical behaviour and remains a possible source for the strange metal properties found in the normal state of cuprate superconductors.