arXiv subjects

Walter Stephan

Publications and source records attributed to Walter Stephan.

4 recordsLinked to original sources

arXiv2000

Dynamical correlations in one-dimensional charge-transfer insulators

The single-particle spectral function and the density response of a two band Emery model for CuO chains is calculated for large on-site Cu repulsion U and large on-site energy difference Δ. For U>>U-Δ>>t the eigenfunctions are products of charge and spin parts, which allows analytical calculation of spectral functions in that limit. For other parameters numerical diagonalization is used. The low energy hole carriers are shown to be the one-dimensional analogs of the Zhang-Rice singlets. The validity of the one-band model is discussed. The results are relevant to the interpretation of photoemission and EELS experiments on SrCuO2 and Sr2CuO3 .

cond-mat.str-el↗

arXiv1999

Small polaron formation in many-particle states of the Hubbard-Holstein model: The one-dimensional case

We investigate polaron formation in a many-electron system in the presence of a local repulsion sufficiently strong to prevent local-bipolaron formation. Specifically, we consider a Hubbard-Holstein model of interacting electrons coupled to dispersionless phonons of frequency $ω_0$. Numerically solving the model in a small one-dimensional cluster, we find that in the nearly adiabatic case $ω_0 < t$, the necessary and sufficient condition for the polaronic regime to occur is that the energy gain in the atomic (i.e., extremely localized) regime ${\cal E}_{pol}$ overcomes the energy of the purely electronic system $ {\cal E}_{el}$. In the antiadiabatic case, $ω_0 > t$, polaron formation is instead driven by the condition of a large ionic displacement $g/ω_0 >1$ ($g$ being the electron-phonon coupling). Dynamical properties of the model in the weak and moderately strong coupling regimes are also analyzed.

cond-mat.str-el↗

arXiv1996

Dynamical density-density correlations in one-dimensional Mott insulators

The dynamical density-density correlation function is calculated for the one-dimensional, half-filled Hubbard model extended with nearest neighbor repulsion using the Lanczos algorithm for finite size systems and analytically for large on site repulsion compared to hopping amplitudes. At the zone boundary an excitonic feature exists for any finite nearest neighbor repulsion and exhausts most of the spectral weight, even for parameters where no exciton is visible at zero momentum.

cond-mat↗

arXiv1996

A new perspective on the Holstein polaron problem

The single-polaron band structure of the Holstein model in one and two dimensions is studied using a new form of resummed strong-coupling perturbation theory. Well converged results are obtained for phonon frequencies of the order of the hopping integral and strong to intermediate electron-phonon coupling. The polaron band structure at intermediate coupling is shown to deviate markedly from that of a nearest-neighbor tight-binding model, and is in fact similar in shape to the prediction of weak-coupling self-consistent perturbation theory.

cond-mat↗