Quantum phase transitions in trimerized zig-zag spin ladder

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

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

American Physical Society

Lugar: Ridge, New York; Año: 2007 vol. 75 p. 1 - 10

0163-1829

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