Variational study of the interacting spinless Su-Schrieffer-Heeger model

TL;DR

This paper investigates the phase diagram and polarization properties of the interacting spinless Su-Schrieffer-Heeger model using a variational approach, revealing phase transitions and symmetry-breaking effects due to correlations.

Contribution

It extends the Baeriswyl variational wave function to include alternating hopping, providing new insights into the phase diagram and polarization distribution of the model.

Findings

Identifies a phase transition at lower interaction than previously known.

Reconstructs polarization distribution and observes smooth and discontinuous changes.

Shows correlations break chiral symmetry similarly to a Rice-Mele potential.

Abstract

We study the phase diagram and the total polarization distribution of the Su-Schrieffer-Heeger model with nearest neighbor interaction in one dimension at half-filling. To obtain the ground state wave-function, we extend the Baeriswyl variational wave function to account for alternating hopping parameters. The ground state energies of the variational wave functions compare well to exact diagonalization results. For the case of uniform hopping for all bonds, where it is known that an ideal conductor to insulator transition takes place at finite interaction, we also find a transition at an interaction strength somewhat lower than the known value. The ideal conductor phase is a Fermi sea. The phase diagram in the whole parameter range shows a resemblance to the phase diagram of the Kane-Mele-Hubbard model. We also calculate the gauge invariant cumulants corresponding to the polarization (Zak phase) and use these to reconstruct the distribution of the polarization. We calculate the reconstructed polarization distribution along a path in parameter space which connects two points with opposite polarization in two ways. In one case we cross the metallic phase line, in the other, we go through only insulating states. In the former case, the average polarization changes discontinuously after passing through the metallic phase line, while in the latter the distribution "walks across" smoothly from one polarization to its opposite. This state of affairs suggests that the correlation acts to break the chiral symmetry of the Su-Schrieffer-Heeger model, in the same way as it happens when a Rice-Mele onsite potential is turned on.