# Spin and Charge Fluctuations near Metal-Insulator Transition in Dimer-Type Molecular Solid

## TL;DR

This paper investigates spin and charge fluctuations near the metal-insulator transition in a molecular dimer solid using an extended Hubbard model and variational Monte Carlo, revealing dominant polar-charge fluctuations near the phase boundary.

## Contribution

It introduces a detailed analysis of competing electronic phases in a molecular dimer system, highlighting the prominence of polar-charge fluctuations near the transition.

## Key findings

- Polar-charge fluctuation is dominant over a wide parameter range.
- Charge fluctuations are enhanced near the phase boundary.
- Spin fluctuations remain almost unchanged near the transition.

## Abstract

Spin and charge fluctuations at vicinity of metal-to-Mott insulator transitions are studied in an organic solid with molecular dimers. The extended Hubbard model taking account of the internal electronic degree of freedom in a molecular dimer is analyzed using the variational Monte Carlo method. Three kinds of the electronic phases, i.e. a metallic phase, an antiferromagnetic insulating phase and a polar charge ordered phase, compete with each other in the ground state. It is found that the polar-charge fluctuation is dominant in a wide range of the molecular dimerization and Coulomb interaction amplitudes, and is enhanced remarkably near the metal-insulator phase boundary, in which the spin fluctuation is almost unchanged. Implication for the $\kappa$-type BEDT-TTF salts is discussed.