Doping-dependent phonon anomaly and charge-order phenomena in the HgBa$_{2}$CuO$_{4+\delta}$ and HgBa$_{2}$CaCu$_{2}$O$_{6+\delta}$

TL;DR

This study reveals doping-dependent charge order and lattice anomalies in cuprates HgBa$_{2}$CuO$_{4+ extdelta}$ and HgBa$_{2}$CaCu$_{2}$O$_{6+ extdelta}$, indicating an intrinsic link between lattice dynamics and charge correlations.

Contribution

It provides new insights into the doping dependence of charge order and lattice anomalies, highlighting their emergence prior to static charge correlation formation in cuprates.

Findings

Maximum charge order temperature at p ≈ 0.09 in both compounds

Lattice anomalies occur at room temperature, before static charge correlations

Charge order driven by fundamental changes in lattice and electronic properties

Abstract

Using resonant X-ray diffraction and Raman spectroscopy, we study charge correlations and lattice dynamics in two model cuprates, HgBa$_{2}$CuO$_{4+\delta}$ and HgBa$_{2}$CaCu$_{2}$O$_{6+\delta}$. We observe a maximum of the characteristic charge order temperature around the same hole concentration ($p \approx 0.09$) in both compounds, and concomitant pronounced anomalies in the lattice dynamics that involve the motion of atoms in and/or adjacent to the CuO$_2$ layers. These anomalies are already present at room temperature, and therefore precede the formation of the static charge correlations, and we attribute them to an instability of the CuO$_2$ layers. Our finding implies that the charge order in the cuprates is an emergent phenomenon, driven by a fundamental variation in both lattice and electronic properties as a function of doping.