Interplay of Site and Bond Electron-Phonon Coupling in One Dimension

TL;DR

This study investigates how bond and charge interactions with quantum phonons influence one-dimensional materials, revealing complex phases including metallic states and transitions between insulating states.

Contribution

It provides an exact quantum Monte Carlo analysis of the combined Holstein and SSH couplings, uncovering new metallic phases and transition behaviors.

Findings

Weak coupling leads to a spin-gapped metallic phase.

Strong coupling induces a transition between Peierls insulators.

Quantum phonons enable phases absent in pure models.

Abstract

The interplay of bond and charge correlations is studied in a one-dimensional model with both Holstein and Su-Schrieffer-Heeger (SSH) couplings to quantum phonons. The problem is solved exactly by quantum Monte Carlo simulations. If one of the couplings dominates, the ground state is a Peierls insulator with long-range bond or charge order. At weak coupling, the results suggest a spin-gapped and repulsive metallic phase arising from the competing order parameters and lattice fluctuations. Such a phase is absent from the pure SSH model even for quantum phonons. At strong coupling, evidence for a continuous transition between the two Peierls states is presented.