The Paired-Electron Crystal in the Two-Dimensional Frustrated Quarter-Filled Band

TL;DR

This paper investigates a transition from antiferromagnetic to spin-singlet states in a frustrated 1/4-filled band system, revealing a paired-electron crystal state that relates to superconductivity in organic materials.

Contribution

It demonstrates a frustration-induced transition to a paired-electron crystal in a 2D quarter-filled band, linking charge order to superconductivity in organic systems.

Findings

Identifies a transition from Néel antiferromagnetism to a paired-electron crystal.

Describes the paired-electron crystal as a natural state near superconductivity.

Suggests pressure-induced superconductivity arises from a valence bond solid to liquid transition.

Abstract

The competition between antiferromagnetic and spin-singlet ground states within quantum spin models and the 1/2-filled band Hubbard model has received intense scrutiny. Here we demonstrate a frustration-induced transition from N\'{e}el antiferromagnetism to spin-singlet in the interacting 1/4-filled band on an anisotropic triangular lattice. While the antiferromagnetic state has equal charge densities 0.5 on all sites, the spin-singlet state is a paired-electron crystal, with pairs of charge-rich sites separated by pairs of charge-poor sites. The paired-electron crystal provides a natural description of the spin-gapped state proximate to superconductivity in many organic charge-transfer solids. Pressure-induced superconductivity in these correlated-electron systems is likely a transition from the 1/4-filled band valence bond solid to a valence bond liquid.