Decoupling of static and dynamic charge correlations revealed by uniaxial strain in a cuprate superconductor

We use uniaxial strain in combination with ultra-high-resolution resonant inelastic x-ray scattering (RIXS) at the oxygen- K and copper- L 3 edges to study the excitations stemming from the charge ordering wave vector in La 1.875 Sr 0.125 CuO 4 . 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 fourfold 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 behavior and remains a possible source for the strange metal properties found in the normal state of cuprate superconductors.