Rotational invariance and order-parameter stiffness in frustrated quantum spin systems

L. O. MANUEL; A. E. TRUMPER; H. A. CECCATTO

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

American Physical Society

Lugar: New York, Estados Unidos de America; Año: 1998 vol. 57 p. 8348 - 8353

0163-1829

We compute, within the Schwinger-boson scheme, the Gaussian-fluctuation corrections to the order parameter stiffness of two frustrated quantum spin systems: the triangular-lattice Heisenberg antiferromagnet and the J1-J2 model on the square lattice. For the triangular-lattice Heisenberg antiferromagnet we found that the corrections weaken the stiffness, but the ground state of the system remains ordered in the classical 120° spiral pattern. In the case of the J1-J2 model, with increasing frustration the stiffness is reduced until it vanishes, leaving a small window 0.53-0.64 where the system has no long-range magnetic order. In addition, we discuss several methodological questions related to the Schwinger-boson approach. In particular, we show that the consideration of finite clusters which require twisted boundary conditions to fit the infinite lattice magnetic order avoids the use of adhoc factors to correct the Schwinger-boson predictions.