Direct Observation of Magnon Fractionalization in the Quantum Spin Ladder

TL;DR

This study uses inelastic neutron scattering to observe the fractionalization of magnons into spinons in a quantum spin ladder, revealing different excitation spectra across various magnetic field regimes.

Contribution

First direct experimental observation of magnon fractionalization into spinons in a quantum spin ladder under varying magnetic fields.

Findings

Magnon modes are observed at low and high fields in ordered phases.

A spinon continuum appears at intermediate fields in the Luttinger-liquid phase.

Magnetic field tuning drives the fractionalization process.

Abstract

We measure by inelastic neutron scattering the spin excitation spectra as a function of applied magnetic field in the quantum spin-ladder material (C5H12N)2CuBr4. Discrete magnon modes at low fields in the quantum disordered phase and at high fields in the saturated phase contrast sharply with a spinon continuum at intermediate fields characteristic of the Luttinger-liquid phase. By tuning the magnetic field, we drive the fractionalization of magnons into spinons and, in this deconfined regime, observe both commensurate and incommensurate continua.