Co-operative density wave and giant spin gap in the quarter-filled zigzag ladder

TL;DR

This paper investigates a quarter-filled zigzag electron ladder model, revealing strong co-operative interactions that lead to a large spin gap and a singlet ground state, relevant for certain organic charge-transfer solids.

Contribution

It introduces a new model for quarter-filled zigzag ladders showing enhanced spin gaps due to co-operative symmetry-breaking interactions.

Findings

Ground state is a singlet with a large spin gap.

Strong co-operative interactions involve charge-ordering and bond distortions.

Model explains high spin-gap transition temperatures in related materials.

Abstract

Strong co-operative interactions occur between four different broken symmetries involving charge-ordering and bond distortions in the quarter-filled correlated zigzag electron ladder. The ground state is singlet, with spin gap several times larger than in the spin-Peierls state of the one-dimensional quarter-filled chain with the same parameters. We propose the quarter-filled zigzag electron ladder model for several different organic charge-transfer solids with coupled pairs of quasi-one-dimensional stacks, the spin-gap transition temperatures in which are unusually high.