Striped phase in a quantum XY model with ring exchange.
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.
Sandvik
A W
AW
Department of Physics, Abo Akademi University, Porthansgatan 3, FIN-20500 Turku, Finland.
Daul
S
S
Singh
R R P
RR
Scalapino
D J
DJ