Plaquette Resonating-Valence-Bond Ground State of CaV$_4$O$_9$

TL;DR

This paper proposes a theoretical model explaining the spin gap in CaV$_4$O$_9$ by showing that a plaquette resonating valence bond state on a 1/5-depleted square lattice accounts for the experimental observations.

Contribution

It introduces a model demonstrating that frustration and plaquette RVB states on a depleted lattice can produce a spin gap consistent with experiments.

Findings

The model predicts a sizable spin gap matching experimental data.

Frustrating second neighbor interactions stabilize the quantum disordered state.

The plaquette RVB state is favored on the 1/5-depleted square lattice.

Abstract

A theoretical model is presented to explain the spin gap observed for CaV$_4$O$_9$. The underlying lattice of the 1/5-depleted square lattice favors a formation of plaquette resonating valence bond state. Inclusion of the frustrating second neighbor interaction enhances this tendency, leading to a quantum disordered state of a two dimensional spin-1/2 Heisenberg model with a sufficiently big spin gap compatible with experiments.