263 research outputs found
Edge Modes in the Intermediate-D and Large-D Phases of the S=2 Quantum Spin Chain with XXZ and On-Site Anisotropies
We investigate the edge modes at T=0 in the intermediate-D (ID) phase and the
large-D (LD) phase of the S=2 quantum spin chain with the XXZ anisotropy and
the generalized on-site anisotropies by use of the DMRG. There exists a gapless
edge mode in the ID phase, while no gapless edge mode in the LD phase. These
results are consistent with the physical pictures of these phases. We also show
the ground-state phase diagrams obtained by use of the exact diagonalization
and the level spectroscopy analysis.Comment: Submitted to "Proceedings of the International Conference on Strongly
Correlated Electron Systems (SCES2013)
Anomalous behavior of the spin gap of a spin-1/2 two-leg antiferromagnetic ladder with Ising-like rung interactions
Using mainly numerical methods, we investigate the width of the spin gap of a
spin-1/2 two-leg ladder described by \cH= J_\rl \sum_{j=1}^{N/2} [ \vS_{j,a}
\cdot \vS_{j+1,a} + \vS_{j,b} \cdot \vS_{j+1,b} ] + J_\rr \sum_{j=1}^{N/2}
[\lambda (S^x_{j,a} S^x_{j,b} + S^y_{j,a} S^y_{j,b}) + S^z_{j,a} S^z_{j,b}] ,
where denotes the -component of the spin-1/2
operator at the -th site of the chain. We mainly focus on the J_\rr
\gg J_\rl > 0 and case. The width of the spin gap as a
function of anomalously increases near ; for instance,
for when . The gap formation
mechanism is thought to be different for the
cases. Since, in usual cases, the width of the gap becomes zero or small at the
point where the gap formation mechanism changes, the above gap-increasing
phenomenon in the present case is anomalous. We explain the origin of this
anomalous phenomenon by use of the degenerate perturbation theory. We also draw
the ground-state phase diagram.Comment: 4 pages, 11 figures; Proc. "The International Conference on Quantum
Criticality and Novel Phases" (2012), to be published in Phys. Stat. Solidi
Haldane to Dimer Phase Transition in the Spin-1 Haldane System with Bond-Alternating Nearest-Neighbor and Uniform Next-Nearest-Neighbor Exchange Interactions
The Haldane to dimer phase transition is studied in the spin-1 Haldane system with bond-alternating nearest-neighbor and uniform next-nearest-neighbor exchange interactions, where both interactions are antiferromagnetic and thus compete with each other. By using a method of exact diagonalization, the ground-state phase diagram on the ratio of the next-nearest-neighbor interaction constant to the nearest-neighbor one versus the bond-alternation parameter of the nearest-neighbor interactions is determined. It is found that the competition between the interactions stabilizes the dimer phase against the Haldane phase
Spin-charge-orbital ordering on triangle-based lattices
We investigate the ground-state property of an e_g-orbital Hubbard model at
quarter filling on a zigzag chain by exploiting the density matrix
renormalization group method. When two orbitals are degenerate, the zigzag
chain is decoupled to a doble-chain spin system to suppress the spin
frustration due to the spatial anisotropy of the occupied orbital. On the other
hand, when the level splitting is increased and the orbital anisotropy
disappears, a characteristic change in the spin incommnsurability is observed
due to the revival of the spin frustration.Comment: 2 pages, 1 figure, Proceedings of SCES'05 (July 26-30, 2005, Vienna
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