Peierls ground state and excitations in the electron-lattice correlated system (EDO-TTF)_{2}X

TL;DR

This study explores the Peierls state in (EDO-TTF)_{2}X, revealing how electron correlation and electron-phonon interactions lead to charge disproportionation, metastable states, and low-energy soliton excitations, with implications for photoinduced phases.

Contribution

The paper introduces an extended Peierls-Holstein-Hubbard model that captures charge disproportionation and metastable states in (EDO-TTF)_{2}X, and analyzes soliton excitations and their energies.

Findings

Reproduces experimental charge disproportionation patterns.

Identifies a metastable state with local energy minima.

Shows soliton excitations from metastable states have lower energy.

Abstract

We investigate the exotic Peierls state in the one-dimensional organic compound (EDO-TTF)_{2}X, wherein the Peierls transition is accompanied by the bending of molecules and also by a fourfold periodic array of charge disproportionation along the one-dimensional chain. Such a Peierls state, wherein the interplay between the electron correlation and the electron-phonon interaction takes an important role, is examined based on an extended Peierls-Holstein-Hubbard model that includes the alternation of the elastic energies for both the lattice distortion and the molecular deformation. The model reproduces the experimentally observed pattern of the charge disproportionation and there exists a metastable state wherein the energy takes a local minimum with respect to the lattice distortion and/or molecular deformation. Furthermore, we investigate the excited states for both the Peierls ground state and the metastable state by considering the soliton formation of electrons. It is shown that the soliton excitation from the metastable state costs energy that is much smaller than that of the Peierls state, where the former is followed only by the charge degree of freedom and the latter is followed by that of spin and charge. Based on these results, we discuss the exotic photoinduced phase found in (EDO-TTF)_{2}PF_{6}.