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# Inelastic X-ray scattering in YBa2Cu3O6.6 reveals giant phonon anomalies and elastic central peak due to charge-density-wave formation

## Abstract

The electron–phonon interaction is a major factor influencing the competition between collective instabilities in correlated-electron materials, but its role in driving high-temperature superconductivity in the cuprates remains poorly understood. We have used high-resolution inelastic X-ray scattering to monitor low-energy phonons in YBa2Cu3O6.6 (superconducting transition temperature Tc = 61 K), which is close to a charge-density-wave (CDW) instability. Phonons in a narrow range of momentum space around the CDW ordering vector exhibit extremely large superconductivity-induced line-shape renormalizations. These results imply that the electron–phonon interaction has sufficient strength to generate various anomalies in electronic spectra, but does not contribute significantly to Cooper pairing. In addition, a quasi-elastic ‘central peak’ due to CDW nanodomains is observed in a wide temperature range above and below Tc, suggesting that the gradual onset of a spatially inhomogeneous CDW domain state with decreasing temperature is a generic feature of the underdoped cuprates.

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## Acknowledgements

This work was performed at the ID28 (IXS) and ID29 (DS) beamlines of the European Synchrotron Radiation Facility. We gratefully acknowledge L. Braicovich, M. Calandra, R. Comin, A. Damascelli, T. Devereaux, M. H. Julien, A. F. Kemper, G. Khaliullin, O. Gunnarsson, G. A. Sawatzky and R. Zeyher for insightful discussions.

## Author information

Authors

### Contributions

M.L.T., G.G. and B.K. managed the project. T.L. prepared and characterized the single crystal. A.B. performed the diffuse scattering experiment. M.L.T., A.B., S.M.S. and G.D. carried out the IXS experiment. M.L.T., S.M.S. and G.D. analysed the data. R.H. and K-P.B. performed calculations. M.L.T. and B.K. wrote the paper with helpful comments from all co-authors.

### Corresponding authors

Correspondence to M. Le Tacon or B. Keimer.

## Ethics declarations

### Competing interests

The authors declare no competing financial interests.

## Supplementary information

### Supplementary Information

Supplementary Information (PDF 1283 kb)

## Rights and permissions

Reprints and Permissions

Le Tacon, M., Bosak, A., Souliou, S. et al. Inelastic X-ray scattering in YBa2Cu3O6.6 reveals giant phonon anomalies and elastic central peak due to charge-density-wave formation. Nature Phys 10, 52–58 (2014). https://doi.org/10.1038/nphys2805

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