Entropy Driven Dimerization in a One-Dimensional Spin-Orbital Model

TL;DR

This paper investigates a one-dimensional spin-orbital model relevant to cubic vanadates, revealing entropy-driven dimerization phenomena and phase transitions influenced by Hund's coupling and temperature.

Contribution

It introduces a new understanding of temperature-driven dimerization in a spin-orbital system, highlighting the role of entropy in phase stability.

Findings

Dimerization occurs at small Hund's coupling J_H due to spin-orbital interactions.

A uniform ferromagnetic phase emerges above a critical J_H at zero temperature.

Temperature induces dimerization in the ferromagnetic phase through entropy effects.

Abstract

We study a new version of the one-dimensional spin-orbital model with spins S=1 relevant to cubic vanadates. At small Hund's coupling J_H we discover dimerization in a pure electronic system solely due to a dynamical spin-orbital coupling. Above a critical value J_H, a uniform ferromagnetic state is stabilized at zero temperature. More surprisingly, we observe a temperature driven dimerization of the ferrochain, which occurs due to a large entropy released by dimer states. This dynamical dimerization seems to be the mechanism driving the peculiar intermediate phase of YVO_3.