Quantum versus classical polarons in a ferromagnetic CuO$_3$-like chain

TL;DR

This paper provides an exact analysis of quantum and classical polarons in a ferromagnetic CuO$_3$-like chain, highlighting how magnon energies and quantum fluctuations influence quasiparticle formation and spectral properties.

Contribution

It introduces an exact solution for itinerant holes in a ferromagnetic chain and compares quantum and classical spin interactions, revealing the impact of quantum fluctuations on spectral functions.

Findings

Large energy magnons favor quasiparticle existence.

Two quasiparticle states emerge with increasing exchange coupling.

Quantum fluctuations qualitatively alter the spectral function.

Abstract

We present an exact solution for an itinerant hole added into the oxygen orbitals of a CuO$_{3}$-like ferromagnetic chain. Using the Green's function method, the quantum polarons obtained for the Heisenberg SU(2) interaction between localized Cu spins are compared with the polarons in the Ising chain. We find that magnons with large energy are favorable towards quasiparticle existence, even in the case of relatively modest electron-magnon coupling. We observe two quasiparticle states with dispersion $\sim 2t$ each, which emerge from the incoherent continuum when the exchange coupling $J$ increases. Quantum fluctuations in the spin system modify the incoherent part of the spectrum and change the spectral function qualitatively, beyond the bands derived from the perturbation theory.