Quantum phase transitions in trimerized zigzag spin ladders

H. D. ROSALES, D. C. CABRA, M. D. GRYNBERG, G. L. ROSSINI, AND T. VEKUA

PHYSICAL REVIEW B

AMER PHYSICAL SOC

Año: 2007 vol. 75 p. 174446 - 174456

1098-0121

We analyze the effects of a trimerized modulation in a quantum spin S = 2 zigzag ladder at the magnetizationplateau M = 1 / 3. Such periodicity is argued to be stemmed from lattice deformations by phonons. The interplaybetween frustration and exchange modulation is well described by an effective triple sine-Gordon field theoryclose to the homogeneous ladder and by block-spin perturbation theory in the weakly coupled trimer regime.The characteristic triple degeneracy of the ground state for homogeneous ladders gives place to modulationdriven quantum phase transitions, leading to a rich phase diagram including up-up-down, quantum plateau, andgapless plateau states.