Using resonant X-ray diffraction and Raman spectroscopy, we study charge correlations and lattice dynamics in two model cuprates, HgBa2CuO4+δ and HgBa2CaCu2O6+δ. We observe a maximum of the characteristic charge order temperature around the same hole concentration (p≈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 CuO2 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 CuO2 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.
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We wish to thank M. Le Tacon, B. Keimer, D. Pelc, and Y. Y. Peng for discussions, and Enrico Schierle for assistance during the experiments at HZB. The work at Peking University was supported by the National Natural Science Foundation of China (Grants No. 11888101 and No. 11874069) and Ministry of Science and Technology of China (Grants No. 2018YFA0305602 and No. 2015CB921302). The work at the University of Minnesota was funded by the Department of Energy through the University of Minnesota Center for Quantum Materials under Grant No. DE-SC-0016371. The work at TU Wien was funded by the European Research Council (ERC Consolidator Grant No. 725521). I.B. was supported by the National Science Center (NCN, Poland) under Grant No. UMO-2019/32/T/ST3/0019. Part of the research described in this Rapid Communication was performed at the Canadian Light Source, a National Research Facility of University of Saskatchewan, which is supported by the Canada Foundation for Innovation (CFI), the Natural Sciences and Engineering Research Council (NSERC), the National Research Council (NRC), the Canadian Institutes of Health Research (CIHR), the Government of Saskatchewan, and the University of Saskatchewan.