Polaronic Self-Localization Effects in the Three Band Peierls Hubbard Model

TL;DR

This study investigates polaron formation in the three-band Peierls-Hubbard model for high-Tc superconductors, revealing how strong electron-lattice coupling leads to hole self-trapping and affects spectral properties.

Contribution

It demonstrates the formation of lattice and electronic small polarons due to strong coupling and analyzes their impact on spectral functions and optical conductivity.

Findings

Hole self-traps form a polaron around Cu sites.

Spectral weight transfer to localized polaron states.

Polaronic shift alone does not explain chemical potential pinning.

Abstract

We have studied the three-band Peierls-Hubbard model describing the Cu-O layers in high-T$_c$ superconductors by using Lanczos diagonalization and assuming infinite mass for the ions. When the system is doped with one hole, and when the electron-lattice coupling is greater than a critical value, we found that the oxygens around one Cu contract and the hole self-traps forming a lattice and electronic small polaron. The self-trapped hole forms a local singlet analogous to the Zhang-Rice singlet in the undeformed lattice. We also studied the single-particle spectral function and the optical conductivity. We have found that the spectral weight, in general, is similar to that found in previous studies where the coupling with the lattice was absent. There is an anomalous transfer of spectral but, contrary to those studies, it goes to these localized polaronic states. However, this polaronic shift does not seem enough by itself to explain the pinning of the chemical potential observed in real materials. We compare our results to those obtained in inhomogeneous Hartree-Fock calculations and we discuss their relation with experiments.