Confinement of fractional quantum number particles in a condensed matter system

TL;DR

This paper investigates the confinement of fractional quantum number particles in condensed matter systems, specifically spinons in weakly-coupled spin ladders, using neutron scattering experiments to observe their energy-dependent behavior.

Contribution

It provides experimental evidence of spinon confinement in a weakly-coupled ladder system, bridging the gap between isolated chains and strongly-coupled systems.

Findings

High-energy spectral function resembles that of individual chains

Low-energy excitations are dominated by strongly-coupled chain behavior

Demonstrates confinement of fractional particles in a condensed matter system

Abstract

The idea of confinement states that in certain systems constituent particles can be discerned only indirectly being bound by an interaction whose strength increases with increasing particle separation. Though the most famous example is the confinement of quarks to form baryons and mesons in (3+1)-dimensional Quantum Chromodynamics, confinement can also be realized in the systems of condensed matter physics such as spin-ladders which consist of two spin-1/2 antiferromagnetic chains coupled together by spin exchange interactions. Excitations of individual chains (spinons) carrying spin S=1/2, are confined even by an infinitesimal interchain coupling. The realizations studied so far cannot illustrate this process due to the large strength of their interchain coupling which leaves no energy window for the spinon excitations of individual chains. Here we present neutron scattering experiments for a weakly-coupled ladder material. At high energies the spectral function approaches that of individual chains; at low energies it is dominated by spin 0,1 excitations of strongly-coupled chains.