We study an isotropic Heisenberg spin-
21 model on a trellis ladder which is composed of two ${J}_{1}\ensuremath{-}{J}_{2}$ zigzag ladders interacting through antiferromagnetic rung coupling
J3.
J1 and
J2 are ferromagnetic zigzag spin interaction between two legs and antiferromagnetic interaction along each leg of a zigzag ladder. A quantum phase diagram of this model is constructed using the density matrix renormalization group method and linearized spin-wave analysis. In the small
J2 limit, a short-range striped collinear phase is found in the presence of
J3, whereas, in the large
J2/J3 limit, a noncollinear quasi-long-range phase is found. The system shows a short-range noncollinear state in the large
J3 limit. The short-range-order phase is the dominant feature of this phase diagram. We also show that the results obtained by DMRG and linearized spin-wave analysis show a similar phase boundary between the collinear striped and noncollinear short-range phases, and the collinear phase region shrinks with increasing
J3. We apply this model to understand the magnetic properties of
CaV2O5 and also fit the experimental data of susceptibility and magnetization. We note that
J3 is a dominant interaction in this material, whereas
J1 and
J2 are approximately half of
J3. The variation of magnetic specific heat capacity as a function of temperature for various external magnetic fields is also predicted.
We analyze the effects of a trimerized modulation in a quantum spin
S=21 zigzag 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 trimer 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.
The effect of next-nearest-neighbor hopping
t2 on the ground-state phase diagram of the one-dimensional Kondo lattice is studied with density-matrix renormalization-group techniques and by comparing with the phase diagram of the classical-spin variant of the same model. For a finite
t2, i.e., for a zigzag-ladder geometry, indirect antiferromagnetic interactions between the localized spins are geometrically frustrated. We demonstrate that
t2 at the same time triggers several magnetic phases which are absent in the model with nearest-neighbor hopping only. For strong
J, we find a transition from antiferromagnetic to incommensurate magnetic short-range order, which can be understood entirely in the classical-spin picture. For weaker
J, a spin-dimerized phase emerges, which spontaneously breaks the discrete translation symmetry. The phase is not accessible to perturbative means but is explained, on a qualitative level, by the classical-spin model as well. Spin dimerization alleviates magnetic frustration and is interpreted as a key to understand the emergence of quasi-long-range spiral magnetic order, which is found at weaker couplings. The phase diagram at weak
J, with gapless quasi-long-range order on top of the twofold degenerate spin-dimerized ground state, competing with a nondegenerate phase with gapped spin (and charge) excitations, is unconventional and eludes an effective low-energy spin-only theory.