Quantum phase transitions in trimerized zig-zag spin ladders

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

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

American Physical Society

Lugar: New York; Año: 2007 vol. 75 p. 174446 - 174455

0163-1829

We analyze the effects of a trimerized modulation in a quantum spin $S= rac12$ zig-zag ladder at themagnetization plateau $M=1/3$. Such periodicity is argued to be stemmed from latticedeformations by phonons. The interplaybetween frustration and exchange modulation is well described by an effectivetriple sine-Gordon field theory close to the homogeneous ladder and by block-spin perturbation theoryin the weakly coupled trimers regime.The characteristic triple degeneracy of the ground state for homogeneous ladders givesplace to modulation driven quantum phase transitions, leading to a rich phase diagramincluding up-up-down, quantum plateau and gapless plateau states.