Difference in Bose-Einstein condensation of conserved and unconserved particles

2012/06/12 by V. I. Yukalov
Physics and Astronomy · #Cold Atom Physics and Bose-Einstein Condensates #Collective behavior #Condensation #Conserved quantity #Magnon #Non-equilibrium thermodynamics #Quantum Electrodynamics and Casimir Effect #Quasiparticle #Strong Light-Matter Interactions #cond-mat.quant-gas #cond-mat.stat-mech

paper · pdf · doi:10.1134/s1054660x12070171

published as Laser Phys. 22 (2012) 1145-1168 · Review article, 47 pages, 1 figure

openalex publication_date 2012/06/12 · arxiv created 2012/07/19 · arxiv updated 2015/06/05 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05

Abstract

The peculiarities in the Bose-Einstein condensation of particles and quasiparticles are discussed. The difference between the condensation of conserved and unconserved particles is analyzed. A classification of quasiparticles is given. The emphasis is made on the ability of particles and quasiparticles to condense. Illustrations include: general Bose-condensed atomic systems, such as ensembles of trapped atoms, Bose gases with conserved and unconserved number of atoms, vibrating atoms in double-well lattices, Holstein-Primakoff magnons, Schwinger bosons, slave bosons, and the condensation of singletons and triplons. The basic difference is that the system of particles, whose total number is conserved, can form equilibrium as well as nonequilibrium condensates, while unconserved particles can condense only in a nonequilibrium system subject to external pumping supporting the density of these particles sufficient for their condensation. The examples of such a nonequilibrium condensation of unconserved particles are the Bose-Einstein condensation of excitons, polaritons, and photons. Elementary collective excitations, such as bogolons and phonons, being self-consistently defined, do not condense. Magnons cannot condense in equilibrium systems. Controversies, existing in literature with regard to the Bose-Einstein condensation of some quasiparticles, are explained. Pushing a system out of equilibrium may favor the condensation of unconserved quasiparticles, but suppresses the condensate fraction of conserved particles.

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