1. Department of Physics, University of California at Berkeley,
2. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

Correspondence to: Steven G. Louie^1,2 Correspondence and requests for materials should be addressed to S.G.L. (Email: sglouie@berkeley.edu).

Despite over two decades of intense research efforts, the origin of high-temperature superconductivity in the copper oxides remains elusive. Angle-resolved photoemission spectroscopy experiments^{1, 2} have revealed a kink in the dispersion relations (energy versus wavevector) of electronic states in the copper oxides at binding energies of 50-80 meV, raising the hope that this anomaly could be a key to understanding high-temperature superconductivity. The kink is often interpreted in terms of interactions between the electrons and a bosonic field. Although there is no consensus on the nature of the bosons (or even whether a boson model is appropriate), both phonons¹ and spin fluctuations² have been proposed as possible candidates. Here we report first-principles calculations of the role of phonons and the electron–phonon interaction in the photoemission spectra of La_2 - xSr_xCuO₄. Our calculations within the standard formalism demonstrate that the phonon-induced renormalization of the electron energies and the Fermi velocity is almost one order of magnitude smaller than the effect observed in photoemission experiments. Therefore, our result rules out electron–phonon interaction in bulk La_2 - xSr_xCuO₄ as the exclusive origin of the measured kink. Our conclusions are consistent with those reached independently in a recent study³ of the related compound YBa₂Cu₃O₇.

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