The optical Su-Schrieffer-Heeger model on a triangular lattice

TL;DR

This study investigates the optical SSH model on a triangular lattice using quantum Monte Carlo, revealing doping-dependent phase transitions including bond-order-wave and superconducting phases, with no magnetic correlation enhancement.

Contribution

It provides the first detailed analysis of the triangular lattice optical SSH model, identifying doping-dependent phase transitions and the absence of magnetic correlations.

Findings

At one-quarter filling, a metal-insulator transition to a bond-order-wave phase occurs.

At three-quarters filling, transitions to BOW and s-wave superconducting phases are observed.

No evidence of enhanced magnetic correlations was found in the model.

Abstract

We study the triangular lattice optical Su-Schrieffer-Heeger (SSH) model using determinant quantum Monte Carlo. By varying the model's carrier concentration, electron-phonon coupling strength, and phonon energy $\Omega$, we identify two doping regimes of interest. At one-quarter filling ($\langle n\rangle = 0.5$), corresponding to the case of a circular noninteracting Fermi surface, we find evidence for a metal to insulating bond-order-wave (BOW) phase transition that breaks a local $C_6$ rotational symmetry. Conversely, at three-quarters filling ($\langle n\rangle = 1.5$), corresponding to a hexagonal Fermi surface, we find evidence for transitions to another BOW phase for small $\Omega$ and an $s$-wave superconducting phase for sufficiently large $\Omega$. This tendency toward pairing appears to be associated with the possibility of a sign change in the effective intersite hopping, which can occur for sufficiently large lattice displacements. We also find no evidence for enhanced magnetic correlations in the model, contrary to what has been reported for square lattice SSH models.