Electron-Phonon Driven Spin Frustration in Multi-Band Hubbard Models: MX Chains and Oxide Superconductors

TL;DR

This paper explores how electron-phonon and electron-electron interactions in multi-band models lead to complex, frustrated magnetic states and novel phenomena in 1D and 2D materials, with implications for MX chains and oxide superconductors.

Contribution

It provides a detailed analysis of the interplay between electron-phonon and electron-electron couplings, revealing new frustrated phases and phenomena in multi-band Hubbard models.

Findings

Unusual spin-Peierls and long-period frustrated ground states identified.

Doping can induce spin-charge separation and phase transitions.

Rich phase diagram with experimentally observable consequences.

Abstract

We discuss the consequences of both electron-phonon and electron-electron couplings in 1D and 2D multi-band (Peierls-Hubbard) models. After briefly discussing various analytic limits, we focus on (Hartree-Fock and exact) numerical studies in the intermediate regime for both couplings, where unusual spin-Peierls as well as long-period, frustrated ground states are found. Doping into such phases or near the phase boundaries can lead to further interesting phenomena such as separation of spin and charge, a dopant-induced phase transition of the global (parent) phase, or real-space (``bipolaronic'') pairing. We discuss possible experimentally observable consequences of this rich phase diagram for halogen-bridged, transition metal, linear chain complexes (MX chains) in 1D and the oxide superconductors in 2D.