Microscopic model for Bose-Einstein condensation and quasiparticle decay

Theoretische Physik I, Technische Universität Dortmund - Otto-Hahn Straße 4, 44221 Dortmund, Germany, EU

^a fischer@fkt.physik.tu-dortmund.de
^b goetz.uhrig@tu-dortmund.de

Received: 13 May 2011
Accepted: 21 September 2011

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≈− 2.3 meV, J₂≈1.2 meV, J₃≈2.9 meV and J₄≈− 0.3 meV. 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.