Eur. Phys. J. B (2017) 90: 217
https://doi.org/10.1140/epjb/e2017-80218-1

Regular Article

Hard-core bosons in flat band systems above the critical density

Institut für Theoretische Physik, University of Heidelberg, Heidelberg, Germany

^a e-mail: mielke@tphys.uni-heidelberg.de

Received: 12 April 2017
Received in final form: 21 July 2017
Published online: 13 November 2017

Abstract

We investigate the behaviour of hard-core bosons in one- and two-dimensional flat band systems, the chequerboard and the kagomé lattice and one-dimensional analogues thereof. The one-dimensional systems have an exact local reflection symmetry which allows for exact results. We show that above the critical density an additional particle forms a pair with one of the other bosons and that the pair is localised. In the two-dimensional systems exact results are not available but variational results indicate a similar physical behaviour.