Finite-temperature phase transitions in quasi-one-dimensional molecular conductors

TL;DR

This paper investigates finite-temperature phase transitions in quasi-one-dimensional molecular conductors using a combination of numerical methods and mean-field approximation, revealing complex coexistent states and transitions.

Contribution

It introduces a theoretical framework combining quantum transfer-matrix and mean-field methods to study phase transitions in molecular conductors, including coexistence phenomena.

Findings

Prediction of a coexistent charge order and bond dimerization state.

Identification of finite-temperature charge, dimer Mott, and spin-Peierls transitions.

Discovery of dielectricity in the coexistent state.

Abstract

Phase transitions in 1/4-filled quasi-one-dimensional molecular conductors are studied theoretically on the basis of extended Hubbard chains including electron-lattice interactions coupled by interchain Coulomb repulsion. We apply the numerical quantum transfer-matrix method to an effective one-dimensional model, treating the interchain term within mean-field approximation. Finite-temperature properties are investigated for the charge ordering, the "dimer Mott" transition (bond dimerization), and the spin-Peierls transition (bond tetramerization). A coexistent state of charge order and bond dimerization exhibiting dielectricity is predicted in a certain parameter range, even when intrinsic dimerization is absent.