Meta-Plaquette Expansion for the Triplet Excitation Spectrum in CaV$_4$O$_9$

TL;DR

This paper extends the meta-plaquette expansion to fifth order to analyze the triplet excitation spectrum in CaV$_4$O$_9$, comparing theoretical results with experimental data and exploring phase boundaries.

Contribution

It introduces a higher-order meta-plaquette expansion for the triplet spectrum in a specific Heisenberg model relevant to CaV$_4$O$_9$.

Findings

Extended the expansion to fifth order.

Compared theoretical spectrum with experimental data.

Identified potential phase boundary.

Abstract

We study antiferromagnetic, $S=1/2$ Heisenberg models with nearest and second neighbor interactions on the one-fifth depleted square lattice which describes the spin degrees of freedom in the spin-gap system CaV$_4$O$_9$. The meta-plaquette expansion for the triplet excitation spectrum is extended to fifth order, and the results are compared with experimental data on CaV$_4$O$_9$. We attempt to locate the phase boundary between magnetically ordered and gapped phases.