Polaron Formation in the Three-Band Peierls-Hubbard Model for Cuprate Superconductors

TL;DR

This study uses exact diagonalization to explore how electron-lattice interactions induce a transition from delocalized to polaronic states in cuprate superconductors, revealing implications for charge mobility.

Contribution

It provides a detailed analysis of polaron formation in the three-band Peierls-Hubbard model, including the effects of fluctuations absent in previous Hartree-Fock studies.

Findings

Transition from delocalized to small polaron behavior with increasing electron-lattice coupling

Fluctuations eliminate the magnetic-nonmagnetic transition seen at Hartree-Fock level

Proximity to the polaron transition suggests high hole mobility in doped cuprates

Abstract

Exact diagonalization calculations show a continuous transition from delocalized to small polaron behavior as a function of intersite electron-lattice coupling. A transition, found previously at Hartree-Fock level [Yonemitsu et al., Phys. Rev. Lett. {\bf 69}, 965 (1992)], between a magnetic and a non magnetic state does not subsist when fluctuations are included. Local phonon modes become softer close to the polaron and by comparison with optical measurements of doped cuprates we conclude that they are close to the transition region between polaronic and non-polaronic behavior. The barrier to adiabatically move a hole vanishes in that region suggesting large mobilities.