Nobuyasu Haga

NMR Relaxation Rate of (quasi-)One-Dimensional Spin-Gapped Systems in Magnetic Fields

The NMR relaxation rates of (quasi-)one-dimensional spin-gapped systems such as the S =1/2 spin ladder with a diagonal interaction and the Haldane-gap system are investigated at low temperatures in...

Dynamical structure factors of S = 1 2 two-leg spin-ladder systems

We investigate the dynamical properties of

Optical absorption spectra in SrCu 2 O 3 two-leg spin ladder

S=\frac{1}{2}

Dynamical structure factors of the magnetization plateau state in the S = 1 2 bond-alternating spin chain with a next-nearest-neighbor interaction

two-leg spin-ladder systems. In a strong-coupling region, an isolated mode appears in the lowest excited states, while in a weak-coupling region, an isolated mode is reduced and the lowest excited states become a lower bound of the excitation continuum. We find in the system with equal intrachain and interchain couplings that due to a cyclic four-spin interaction, the distribution of the weights for the dynamical structure factor and characteristics of the lowest excited states are strongly influenced. The dynamical properties of the two systems proposed for

Optical absorption of two-leg spin ladder systems

{\mathrm{SrCu}}_{2}{\mathrm{O}}_{3}

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

are also discussed.

Dynamics of S = 1/2 Two-Leg Spin Ladder Systems

We calculate the phonon-assisted optical-absorption spectra in SrCu 2 O 3 two-leg spin-ladder systems. The results for two models proposed for SrCu 2 O 3 are compared. In the model including the effects of a cyclic four-spin interaction, the shoulder structure appears at ∼978 cm - 1 and the peak appears at ∼1975 cm - 1 in the spectrum for polarization of the electric field parallel to the legs. In the other model which describes a pure two-leg ladder, the peak appears around the lower edge of the spectrum at ∼1344 cm - 1 . The feature can be effective in determining the proper model for SrCu 2 O 3 .

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 bond-alternating spin chain with a next-nearest-neighbor interaction. The results show characteristic behaviors depending on the next-nearest-neighbor interaction a and the bond alternation δ. 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 a and δ, 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 = π for small δ in fixed a. With increasing δ, the wave number of the largest intensity shifts towards q=π/2, taking the incommensurate value.

Optical absorption spectra inSrCu2O3two-leg spin ladder

Abstract We calculate the optical absorption spectrums for the S= 1 2 two-leg spin ladder systems using continued fraction method based on Lanczos algorithm. We use two sets of parameters suggested for an S= 1 2 two-leg spin ladder material SrCu2O3. We find that due to a cyclic four-spin interaction the dispersion curve becomes flatter and hence, the large peak structure appears in the optical absorption spectrums.

Optical absorption of S= 1 2 two-leg spin ladder systems

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