NON-PERTURBATIVE EFFECTIVE FIELD THEORY FOR TWO-LEG ANTIFERROMAGNETIC SPIN LADDERS

D.C. CABRA; A. O. DOBRY; G. L. ROSSINI

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

Americal Physical Society

Lugar: New York; Año: 2001 vol. 63 p. 144408 - 144417

0163-1829

                                                  1   We study the long wavelength limit of a spin- 2 Heisenberg antiferromagnetic two-leg ladder, treating the interchain coupling in a nonperturbative way. We perform a mean field analysis and then include the fluctuations in an exact way. This allows for a discussion of the phase diagram of the system and provides an effective-field theory for the low-energy excitations. The coset fermionic Lagrangian obtained corresponds toa perturbed SU(4)  / U(1) conformal field theory CFT . This effective theory is naturally embedded in a SU(2) x Z_2 CFT, where perturbations are easily identified in terms of conformal operators in the two sectors.Crossed and zigzag ladders are also discussed using the same approach.