The Polaron-Like Nature of an Electron Coupled to Phonons

Physical Review B, 2004

Here we analyze the effects of an electron-phonon interaction on the one-electron spectral weight A(k, ω) of a d x 2 -y 2 superconductor. We study the case of an Einstein phonon mode with various momentum-dependent electron-phonon couplings and compare the structure produced in A(k, ω) with that obtained from coupling to the magnetic π-resonant mode. We find that if the strength of the interactions are adjusted to give the same renormalization at the nodal point, the differences in A(k, ω) are generally small but possibly observable near k = (π, 0).

EPL (Europhysics Letters), 2013

Polarons and electron-phonon interactions PACS 72.10.Di -Scattering by phonons, magnons, and other nonlocalized excitations PACS 63.20.kd -Phonon-electron interactions

Japanese Journal of Applied Physics, 1987

The popular idea of Tc max\doteq30–40K for electron-phonon (E-P) mechanism is based on an estimation of E-P coupling strength in usual cation metallic solids. However, we have made a model study of the interaction of itinerant electrons with anion cores, Y–Ba–Cu–O is believed to be the case, in LMTO formulation. It turns out that anion repulsive core favours the high angular momentum hybridization of the itinerant wave-function around it. Thus, we will have a strong E-P coupling of λ\doteq1.3 with optical ω\doteq77mev so a Tc of the order of 90K.

physica status solidi (b), 2005

We discuss the interplay between electron-electron and electron-phonon interactions for alkali-doped fullerides and high temperature superconductors. Due to the similarity of the electron and phonon energy scales, retardation effects are small for fullerides. This raises questions about the origin of superconductivity, since retardation effects are believed to be crucial for reducing effects of the Coulomb repulsion in conventional superconductors. We demonstrate that by treating the electron-electron and electronphonon interactions on an equal footing, superconductivity can be understood in terms of a local pairing. The Jahn-Teller character of the important phonons in fullerides plays a crucial role for this result. To describe effects of phonons in cuprates, we derive a t-J model with phonons from the three-band model. Using exact diagonalization for small clusters, we find that the anomalous softening of the half-breathing phonon as well as its doping dependence can be explained. By comparing the solution of the t-J model with the Hartree-Fock approximation for the three-band model, we address results obtained in the localdensity approximation for cuprates. We find that genuine many-body results, due to the interplay between the electron-electron and electron-phonon interactions, play an important role for the the results in the t-J model.

Pramana, 1987

It is proposed that phonon induced mechanism is capable of explaining the observed range of T, for the newly discovered high temperature superconductor within the Allen.and ~y n e s strong coupling theory.

Physical review, 2020

Physical Review B, 2013

We study the Holstein-Hubbard model at half filling to explore ordered phases including superconductivity (SC), antiferromagnetism (AF), and charge order (CO) in situations where the electron-electron and electron-phonon interactions are strong (∼ electronic bandwidth). The model is solved in the dynamical mean-field approximation using a continuous-time quantum Monte Carlo impurity solver. We determine the superconducting transition temperature (Tc) and the SC order parameter and show that the phonon-induced retardation or the strong Coulomb interaction leads to a significant reduction and shift of the Tc dome if one interprets the system as having an effective static interaction U eff given by the Hubbard U reduced by the phonon-mediated attraction in the static limit. This behavior is analyzed by comparison to an effective static model in the polaron representation with a reduced bandwidth. We also determine the finite-temperature phase diagram including AF and CO. In the moderate-coupling regime, there is a hysteretic region of AF and CO around U eff = 0, while the two phases are separated by a paramagnetic metal in the weak-coupling regime and a paramagnetic insulator in the strong coupling regime.

Nature, 2007

The idea of superconductivity without the mediating role of lattice vibrations (phonons) has a long history. It was realized soon after the publication of the Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity 50 years ago that a full treatment of both the charge and spin degrees of freedom of the electron predicts the existence of attractive components of the effective interaction between electrons even in the absence of lattice vibrations--a particular example is the effective interaction that depends on the relative spins of the electrons. Such attraction without phonons can lead to electronic pairing and to unconventional forms of superconductivity that can be much more sensitive than traditional (BCS) superconductivity to the precise details of the crystal structure and to the electronic and magnetic properties of a material.

Physical Review B, 1991

The infrared absorption of the 155-cm c-axis mode of YBa2Cu307 is calculated on the basis of an anharmonic-electron-phonon-interaction model and a large enhancement of its intensity is obtained. A double-well potential in the electron-phonon interaction gives the right order of magnitude for shifts in the bridging O(4) position in agreement with recent extended x-ray-absorption fine-structure data. Electron-density-two-phonon-interaction terms are derived which represent a violation of the Migdal theorem and a BCS-type superconducting state with nonlinearly enhanced electron-phonon coupling is expected together with an anisotropy of the superconducting energy gap.

Nature