Microscopic model for Bose-Einstein condensation and quasiparticle decay

TL;DR

This paper develops a detailed microscopic model for the magnetic excitations and Bose-Einstein condensation phenomena in the quantum antiferromagnet IPA-CuCl3, using neutron scattering and susceptibility data.

Contribution

It provides the first quantitative determination of magnetic couplings in IPA-CuCl3, modeling it as coupled asymmetric S=1/2 Heisenberg ladders.

Findings

Quantitative magnetic couplings J1, J2, J3, J4 determined

Model explains field dependence of condensed phase modes

Model matches temperature dependence of the energy gap

Abstract

Sufficiently dimerized quantum antiferromagnets display elementary S=1 excitations, triplon quasiparticles, protected by a gap at low energies. At higher energies, the triplons may decay into two or more triplons. A strong enough magnetic field induces Bose-Einstein condensation of triplons. For both phenomena the compound IPA-CuCl3 is an excellent model system. Nevertheless no quantitative model was determined so far despite numerous studies. Recent theoretical progress allows us to analyse data of inelastic neutron scattering (INS) and of magnetic susceptibility to determine the four magnetic couplings J1=-2.3meV, J2=1.2meV, J3=2.9meV and J4=-0.3meV. These couplings determine IPA-CuCl3 as system of coupled asymmetric S=1/2 Heisenberg ladders quantitatively. The magnetic field dependence of the lowest modes in the condensed phase as well as the temperature dependence of the gap without magnetic field corroborate this microscopic model.