Alternating spin chains with singlet ground states

TL;DR

This paper studies the low-energy excitations of alternating spin chains with singlet ground states, using spin-wave analysis and mapping to the O(3) non-linear sigma model to understand quantum fluctuations and topological effects.

Contribution

It provides a detailed analysis of the spin-wave spectrum and maps the system to a sigma model, revealing how topological properties influence excitation massiveness.

Findings

Identification of conditions for massless versus massive excitations

Mapping of low-energy excitations to the O(3) non-linear sigma model

Insights into the role of topology in quantum spin chains

Abstract

We investigate low-energy properties of the alternating spin chain model composed of spin $s_1$ and $s_2$ with a singlet ground state. After examining the spin-wave spectrum in detail, we map low-energy spin excitations to the O(3) non-linear sigma model in order to take into account quantum fluctuations. Analyzing the topological term in the resulting sigma model, we discuss how the massless or massive excitations are developed, especially according to the topological nature of the alternating spin system.