# Theory of triangular lattice quasi-one-dimensional charge-transfer solids

## TL;DR

This paper uses a 1/4-filled band Hubbard model to better explain the magnetic and superconducting properties of quasi-one-dimensional triangular lattice charge-transfer solids, challenging previous models.

## Contribution

It introduces a 1/4-filled band Hubbard model focusing on monomer sites, successfully reproducing experimental results and supporting a valence bond theory of superconductivity.

## Key findings

- Spin gap transition linked to two-dimensional paired-electron crystal formation.
- Prediction of charge-ordering and period doubling accompanying the spin gap.
- Enhanced superconducting pairing correlations with Hubbard repulsion.

## Abstract

Recent investigations of the magnetic properties and the discovery of superconductivity in quasi-one-dimensional triangular lattice organic charge-transfer solids have indicated the severe limitations of the effective 1/2-filled band Hubbard model for these and related systems. Our computational studies of these materials within a 1/4-filled band Hubbard model in which the organic monomer molecules, and not their dimers, constitute the sites of the Hamiltonian are able to reproduce the experimental results. We ascribe the spin gap transition in kappa-(BEDT-TTF)_2B(CN)_4 to the formation of a two-dimensional paired-electron crystal and make the testable prediction that the spin gap will be accompanied by charge-ordering and period doubling in two directions. We find enhancement of the long-range component of superconducting pairing correlations by the Hubbard repulsive interaction for band parameters corresponding to kappa-(BEDT-TTF)_2CF_3SO_3. The overall results strongly support a valence bond theory of superconductivity we have proposed recently.