Bipolaron liquids at strong Peierls electron-phonon couplings

TL;DR

This study uses the DMRG method to show that one-dimensional Peierls electron-phonon systems are generally stable against phase separation at low densities, supporting the potential for bipolaron-based high-temperature superconductivity.

Contribution

It demonstrates the stability of bipolaron liquids in the Peierls model at low densities, contrasting with other electron-phonon models, and explores conditions for phase separation.

Findings

Bipolaron liquids are stable at low electron densities.

Phase separation occurs only at large couplings where linear approximation fails.

Stability extends up to quarter filling, suggesting relevance for superconductivity.

Abstract

We use the Density Matrix Renormalization Group method to study a one-dimensional chain with Peierls electron-phonon coupling, which describes the modulation of the electron hopping by lattice distortions. We demonstrate that this system is stable against phase separation in the dilute density limit. We only find phase separation numerically for large couplings for which the linear approximation for the electron-phonon coupling becomes invalid; this behavior can be stabilized in a narrow sliver of the physical parameter space if the dispersion of the phonons is carefully tuned. These results indicate that in the dilute electron density limit, Peierls bipolaron liquids are generically stable, unlike in other models of electron-phonon coupling. We show that this behavior extends to finite carrier concentrations of up to quarter filling. This stability of low-density, light-mass bipolaron liquids in the Peierls model opens a path to high-$T_c$ superconductivity based on a bipolaronic mechanism, in higher dimensions.