Boundaries, Cusps and Caustics in the Multimagnon Continua of 1D Quantum Spin Systems

TL;DR

This paper explores the singular features like cusps, caustics, and discontinuities in the multimagnon continua of 1D quantum spin systems, with implications for experimental neutron scattering observations.

Contribution

It analyzes the origins of these continuum features and illustrates them using specific models like the alternating Heisenberg chain and two-leg ladder.

Findings

Identification of cusps and caustics in the continuum boundaries

Discontinuities in the density of states and scattering intensity

Application to specific 1D quantum spin models

Abstract

The multimagnon continua of 1D quantum spin systems possess several interesting singular features that may soon be accessible experimentally through inelastic neutron scattering. These include cusps and composition discontinuities in the boundary envelopes of two-magnon continuum states and discontinuities in the density of states, "caustics", on and within the continuum, which will appear as discontinuities in scattering intensity. In this note we discuss the general origins of these continuum features, and illustrate our results using the alternating Heisenberg antiferromagnetic chain and two-leg ladder as examples.