Magnetization Plateau State Research Articles

DYNAMICAL STRUCTURE FACTORS OF THE S = 1/2 SPIN LADDER SYSTEMS WITH A DIAGONAL INTERACTION IN THE MAGNETIZATION-PLATEAU STATE

We investigate the dynamical structure factors of the S = 1/2 spin ladder systems with a diagonal interaction in the magnetization-plateau state. The results show characteristic behaviors depending on the chain interaction α, the ladder interaction 1 + δ and the diagonal interaction 1 - δ. The large weights are located at q = π, when δ is small. With increasing δ, the wavenumber of the large weights shifts towards q = π/2 taking the incommensurate value. The almost dispersionless behavior comes out at several combinations of α and δ, indicating that the elementary excitation is localized spatially. We discuss our results in comparison with the exact excitation spectrums of the S = 1/2 XXZ model which is an effective Hamiltonian of the present system in α ~ 0 and δ ~ 1. Dynamical structure factors of some S = 1/2 one-dimensional quantum spin systems in the magnetic fields were measured by inelastic neutron-scattering experiments1,2 and it has been shown the theoretical results from the numerical diagonalization of finite systems can explain them.3–5

DYNAMICAL PROPERTIES OF FIELD-INDUCED ORDERED-STATES IN S = 1/2 ONE-DIMENSIONAL QUANTUM SPIN SYSTEMS

We calculate the dynamical structure factors of the magnetization-plateau state in the S = 1/2 bond-alternating spin chain with a next-nearest-neighbor interaction. The results show characteristic behaviors depending on the next-nearest-neighbor interaction and the bond-alternation. We discuss the lower excited states in comparison with the exact excitation spectrums of an effective Hamiltonian.

Dynamics and Incommensurate Spin Correlation of the Magnetization Plateau State in theS=1/2 Bond-Alternating Spin Chain with a Next-Nearest-Neighbor Interaction

We investigate dynamical properties of the magnetization plateau state in the S =1 /2 bond-alternating spin chain with a next-nearest-neighbor interaction. The dynamical struc- ture factor shows characteristic behavior depending on the next-nearest-neighbor interaction α andthe bondalternation δ. The static structure factor takes the largest value at q = π for small δ. With increasing δ, the wave number of the largest value shifts towards q = π/2, taking the incommensurate value. where δ denotes the bond alternation, α denotes the NNN interaction, N is the total number of the site, and H is magnetic field. We set J =1 ,gµB = 1 and ¯ = 1. In magnetic field along the z axis, rotational symmetry around the x and y axes is broken, while that around the z axis remains. Therefore, the Hamiltonian can be classified into the subspace according to the magnetization m = M/N with M = N S z . In the following, we fix M = N/4. In the half-magnetization- plateau state with δ ∼ 1 and α ∼ 0, this Hamiltonian can be mapped onto the one-dimensional (1D) S =1 /2Heisenberg-Ising model in zero field. 2),4) The DSF can be calculated numerically, using a continued fraction based on the Lanczos algorithm. 5) We calculated the transverse DSF S x (q, ω), turning our atten- tion to the behavior of the lowest excitation band. Typical results for the DSF are shown in Figs. 1 (a) and (b). When δ becomes large for given α, the largest intensity in given wave number lies in the lowest excited state. The solid lines represent the exact bounds of the elementary excitation for the effective Hamiltonian obtained by

Dynamical structure factors of the magnetization plateau state in theS=12bond-alternating spin chain with a next-nearest-neighbor interaction

We calculate the dynamical structure factors of the magnetization plateau state in the $S=\frac{1}{2}$ bond-alternating spin chain with a next-nearest-neighbor interaction. The results show characteristic behaviors depending on the next-nearest-neighbor interaction $\ensuremath{\alpha}$ and the bond alternation \ensuremath{\delta}. We discuss the lower excited states in comparison with the exact excitation spectrums of an effective Hamiltonian. From the finite size effects, characteristics of the lowest excited states are investigated. The dispersionless mode of the lowest excitation appears in adequate sets of $\ensuremath{\alpha}$ and \ensuremath{\delta}, indicating that the lowest excitation is localized spatially and forms an isolated mode below the excitation continuum. We further calculate the static structure factors. The largest intensity is located at $q=\ensuremath{\pi}$ for small $\ensuremath{\delta}$ in fixed \ensuremath{\alpha}. With increasing \ensuremath{\delta}, the wave number of the largest intensity shifts towards $q=\ensuremath{\pi}/2,$ taking the incommensurate value.