Emergent many-body composite excitations of interacting spin-1/2 trimers

TL;DR

This paper reports the discovery of novel composite quasiparticles called doublons and quartons in a spin-1/2 trimer-chain antiferromagnet, advancing understanding of emergent excitations in topologically nontrivial quantum spin systems.

Contribution

It introduces and characterizes new quasiparticles arising from topological excitations in a periodic exchange interaction spin system, supported by experimental and theoretical analysis.

Findings

Identification of doublons and quartons as emergent quasiparticles

Agreement between neutron scattering data and DMRG calculations

Observation of a topologically protected 1/3 magnetization plateau

Abstract

Understanding exotic forms of magnetism in quantum spin systems is an emergent topic of modern condensed matter physics. Quantum dynamics can be described by particle-like carriers of information, known-as quasiparticles that appear from the collective behaviour of the underlying system. Spinon excitations, governing the excitations of quantum spin-systems, have been accurately calculated and precisely verified experimentally for the antiferromagnetic chain model. However, identification and characterization of novel quasiparticles emerging from the topological excitations of the spin system having periodic exchange interactions are yet to be obtained. Here, we report the identification of emergent composite excitations of the novel quasiparticles doublons and quartons in spin-1/2 trimer-chain antiferromagnet Na2Cu3Ge4O12 (having periodic intrachain exchange interactions J1-J1-J2) and its topologically protected quantum 1/3 magnetization-plateau state. The characteristic energies, dispersion relations, and dynamical structure factor of neutron scattering as well as macroscopic quantum 1/3 magnetization-plateau state are in good agreement with the state-of-the-art dynamical density matrix renormalization group calculations.