Small phonon contribution to the photoemission kink in the copper oxide superconductors

Abstract

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 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 phonons and spin fluctuations 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 - x)Sr(x)CuO4. 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 - x)Sr(x)CuO4 as the exclusive origin of the measured kink. Our conclusions are consistent with those reached independently in a recent study of the related compound YBa2Cu3O7.

Bosons in high-temperature superconductors: an experimental survey

“…Also, the transport electron-phonon coupling is much smaller than its quasiparticle counterpart which provides a direct explanation of the observation that the resistivity is linear in T in the normal state above T c (Zeyher 1996). Recent local density approximation (LDA) calculations in YBCO (Heid et al 2008(Heid et al , 2009) and in LSCO (Giustino et al 2008) have found however, very small values of the coupling in the d-channel and conclude that the electron-phonon interaction is much too small to provide the glue for Cooper pair formation. Also quasiparticle mass enhancement factor renormalizations are small as is its transport counterpart.…”

Anomalous Doping Variation of the Nodal Low-Energy Feature of Superconducting(Bi,Pb)2(Sr,La)2CuO

“…Previously it was reported that the nodal group velocity within 50 meV of Fermi energy (E F ) is independent of the cuprate family or the number of CuO 2 layers in the crystal unit cell, and it is almost constant across the entire phase diagram [2]. Recent ARPES technique with low-energy photons (hν = 6-8 eV) has extensively improved the momentum and energy resolutions [3,4], and uncovered a remarkable band renormalization very close to the E F (< 20 meV) [5][6][7][8][9][10], in addition to the well-studied kinks seen at 40-80The new fine band-feature (or "low-energy kink") determines the nodal Fermi velocity of Bi2212, thus it is crucial for the understanding of the electronic properties, which are dominated by the conduction electrons close to the E F .A recent theoretical study has suggested that coupling to phonons is too small to produce the observed band renormalization [11]. On the other hand, it has been pointed out that the strong electron correlation or reduced screening can significantly enhance the phononelectron coupling [10,[12][13][14][15].…”

“…A recent theoretical study has suggested that coupling to phonons is too small to produce the observed band renormalization [11]. On the other hand, it has been pointed out that the strong electron correlation or reduced screening can significantly enhance the phononelectron coupling [10,[12][13][14][15].…”

Exciton-Polariton Mediated Superconductivity

“…This instability results in the so-called BCS state (coherent state of Cooper pairs), that leads to a gap in the spectrum of excitations, responsible for superconductivity. In the currently available high-T C superconductors (the cuprates), an electron pairing is also thought to be realized through a mediating boson, although probably not the phonon [13]. Excitons have been proposed as suitable mediating bosons to achieve higher critical temperatures of superconductivity in specially designed heterostructures ([14], see [15] for a review).…”