title: Striped phase in a quantum XY model with ring exchange.
abstract: We present quantum Monte Carlo results for a square-lattice S=1/2 XY model with a standard nearest-neighbor coupling J and a four-spin ring exchange term K. Increasing K/J, we find that the ground state spin stiffness vanishes at a critical point at which a spin gap opens and a striped bond-plaquette order emerges. At still higher K/J, this phase becomes unstable and the system develops a staggered magnetization. We discuss the quantum phase transitions between these phases.
authors.affiliation: Department of Physics, Abo Akademi University, Porthansgatan 3, FIN-20500 Turku, Finland.
authors.forename: A W
authors.initials: AW
authors.lastname: Sandvik
authors.forename: S
authors.initials: S
authors.lastname: Daul
authors.forename: R R P
authors.initials: RR
authors.lastname: Singh
authors.forename: D J
authors.initials: DJ
authors.lastname: Scalapino