title: Two-step restoration of SU(2) symmetry in a frustrated ring-exchange magnet.
abstract: We demonstrate the existence of a spin-nematic, moment-free phase in a quantum four-spin ring-exchange model on the square lattice. This unusual quantum state is created by the interplay of frustration and quantum fluctuations that lead to a partial restoration of SU(2) symmetry when going from a four-sublattice orthogonal biaxial Néel order to this exotic uniaxial magnet. A further increase of frustration drives a transition to a fully gapped SU(2) symmetric valence bond crystal.
authors.affiliation: Institut Romand de Recherche Numérique en Physique des Matériaux (IRRMA), PPH-Ecublens, CH-1015 Lausanne, Switzerland.
authors.forename: A
authors.initials: A
authors.lastname: Läuchli
authors.forename: J C
authors.initials: JC
authors.lastname: Domenge
authors.forename: C
authors.initials: C
authors.lastname: Lhuillier
authors.forename: P
authors.initials: P
authors.lastname: Sindzingre
authors.forename: M
authors.initials: M
authors.lastname: Troyer