Can Quantum Lattice Fluctuations Destroy the Peierls Broken Symmetry Ground State?

TL;DR

This paper investigates whether quantum lattice fluctuations can eliminate the Peierls broken symmetry ground state in one-dimensional systems, finding that bond alternation persists even with gapless, dispersive phonons.

Contribution

The study introduces a more realistic model with gapless, dispersive phonons and uses DMRG to show bond alternation is robust against quantum fluctuations.

Findings

Bond alternation persists for all electron-phonon couplings.

Quantum fluctuations do not destroy the Peierls ground state in the model.

Results challenge previous models with gapped, dispersionless phonons.

Abstract

The study of bond alternation in one-dimensional electronic systems has had a long history. Theoretical work in the 1930s predicted the absence of bond alternation in the limit of infinitely long conjugated polymers; a result later contradicted by experimental investigations. When this issue was re-examined in the 1950s it was shown in the adiabatic limit that bond alternation occurs for any value of electron-phonon coupling. The question of whether this conclusion remains valid for quantized nuclear degrees of freedom was first addressed in the 1980s. Since then a series of numerical calculations on models with gapped, dispersionless phonons have suggested that bond alternation is destroyed by quantum fluctuations below a critical value of electron-phonon coupling. In this work we study a more realistic model with gapless, dispersive phonons. By solving this model with the DMRG method we show that bond alternation remains robust for any value of electron-phonon coupling.