Possible Metastable State Triggered by Competition of Peierls State and Charge Ordered State

TL;DR

This paper investigates the competition between Peierls and charge-ordered states in a one-dimensional model, revealing a metastable state and phase transitions relevant to photoinduced phenomena in certain organic compounds.

Contribution

It introduces a mean-field phase diagram for the Peierls-Hubbard model showing metastable states and phase transitions driven by electron-electron and electron-phonon interactions.

Findings

Identification of a metastable state with local energy minimum.

First-order transition from coexistent to unconventional Peierls state.

Relevance to photoinduced phase phenomena in (EDO-TTF)_{2}PF_{6}.

Abstract

We examine a Peierls ground state and its competing metastable state in the one-dimensional quarter-filled Peierls-Hubbard model with the nearest-neighbor repulsive interaction V and the electron-phonon interaction (\propto 1/K with K being the elastic constant). From the mean-field approach, we obtain the phase diagram for the ground state on the plane of parameters V and K. The coexistent state of the spin-density wave and the charge ordering is realized for large V and K. With decreasing K, it exhibits a first-order phase transition to the unconventional Peierls state which is described by the bond-centered charge-density-wave state. In the large region of the Peierls ground state in the phase diagram, there exists the metastable state where the energy takes a local minimum with respect to the lattice distortion. On the basis of the present calculation, we discuss the photoinduced phase observed in the (EDO-TTF)_{2}PF_{6} compound.