Quantum Melting of Magnetic Order in an Organic Dimer-Mott Insulating System

TL;DR

This paper investigates how quantum entanglement between spin and charge in an organic dimer-Mott insulator leads to the melting of magnetic order, suggesting a possible quantum spin liquid state.

Contribution

It introduces a low energy model with antisymmetric exchange interactions and analyzes magnetic phase stability using spin-wave and Schwinger-boson theories, revealing mechanisms for magnetic melting.

Findings

Antisymmetric exchange favors 90° spin configurations.

Spin-charge interactions destabilize magnetic order near phase merging.

Implications for quantum spin liquid states in organic materials.

Abstract

Quantum entanglement effects between the electronic spin and charge degrees of freedom are examined in an organic molecular solid, termed a dimer-Mott insulating system, in which molecular dimers are arranged in a crystal as fundamental units. A low energy effective model includes an antisymmetric exchange interaction, as one of the dominant magnetic interactions. This interaction favors a 90 degree spin configuration, and competes with the Heisenberg-type exchange interaction. Stabilities of the magnetic ordered phases are examined by using the spin-wave theory, as well as the Schwinger-boson theory. It is found that the spin-charge interaction promotes an instability of the long-range magnetic ordered state around a parameter region where two spin-spiral phases are merged. Implication for the quantum spin liquid state observed in $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$ is discussed.