Excitation Spectrum for Quantum Spin Systems with Ladder, Plaquette and Mixed-Spin Structures

TL;DR

This paper uses series expansion techniques to analyze the excitation spectrum of 2D quantum spin systems with ladder, plaquette, and mixed-spin structures, accurately determining phase boundaries and improving previous phase diagrams.

Contribution

It introduces a refined method for calculating phase boundaries in complex quantum spin systems using excitation spectrum analysis.

Findings

Accurate determination of spin excitation gaps.

Improved phase diagram compared to previous susceptibility-based results.

Clear identification of phase boundary between spin-gap and ordered phases.

Abstract

By using the series expansion techniques, we study the excitation spectrum for the two-dimensional quantum spin systems with ladder, plaquette and mixed-spin structures. We calculate the spin excitation gap and thus determine the phase boundary between the spin-gap phase and the magnetically ordered phase rather precisely. It is found that the phase diagram obtained improves fairly well the one previously obtained via the ground-state susceptibility.