Progress of Theoretical Physics Supplement

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

Sei-ichiro Suga, Nobuyasu Haga

Published Jan 1, 2002• 0 citations

Abstract

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 structure factor shows characteristic behavior depending on the next-nearest-neighbor interaction α and the bond alternation 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.

DOI: 10.1143/ptps.145.130

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Progress of Theoretical Physics Supplement

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

Sei-ichiro Suga, Nobuyasu Haga

Published Jan 1, 2002• 0 citations

Publisher

Abstract

DOI: 10.1143/ptps.145.130

Related papers

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

Nobuyasu Haga, Sei-ichiro Suga

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.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.

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We investigate the critical properties of the $S=1∕2$ bond-alternating spin chain with a next-nearest-neighbor interaction in magnetic fields. By the numerical calculation and the exact solution based on the effective Hamiltonian, we show that there is a parameter region where the longitudinal incommensurate spin correlation becomes dominant around the half-magnetization of the saturation. Possible interpretations of our results are discussed. We next investigate the effects of the interchain interaction $({J}^{\ensuremath{'}})$. The staggered susceptibility and the uniform magnetization are calculated by combining the density-matrix renormalization group method with the interchain mean-field theory. For the parameters where the dominant longitudinal incommensurate spin correlation appears in the case ${J}^{\ensuremath{'}}=0$, the staggered long-range order does not emerge up to a certain critical value of ${J}^{\ensuremath{'}}$ around the half-magnetization of the saturation. We calculate the static structure factor in such a parameter region. The size dependence of the static structure factor at $k=2{k}_{F}$ implies that the system has a tendency to form an incommensurate long-range order around the half-magnetization of the saturation. We discuss the recent experimental results for the NMR relaxation rate in magnetic fields performed for pentafluorophenyl nitronyl nitroxide.We investigate the critical properties of the $S=1∕2$ bond-alternating spin chain with a next-nearest-neighbor interaction in magnetic fields. By the numerical calculation and the exact solution based on the effective Hamiltonian, we show that there is a parameter region where the longitudinal incommensurate spin correlation becomes dominant around the half-magnetization of the saturation. Possible interpretations of our results are discussed. We next investigate the effects of the interchain interaction $({J}^{\ensuremath{'}})$. The staggered susceptibility and the uniform magnetization are calculated by combining the density-matrix renormalization group method with the interchain mean-field theory. For the parameters where the dominant longitudinal incommensurate spin correlation appears in the case ${J}^{\ensuremath{'}}=0$, the staggered long-range order does not emerge up to a certain critical value of ${J}^{\ensuremath{'}}$ around the half-magnetization of the saturation. We calculate the static structure factor in such a parameter region. The size dependence of the static structure factor at $k=2{k}_{F}$ implies that the system has a tendency to form an incommensurate long-range order around the half-magnetization of the saturation. We discuss the recent experimental results for the NMR relaxation rate in magnetic fields performed for pentafluorophenyl nitronyl nitroxide.

arXiv:cond-mat/0403404Physical Review BAug 25, 200421 citations

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.

We investigate the critical properties of the

S=1∕2

bond-alternating spin chain with a next-nearest-neighbor interaction in magnetic fields. By the numerical calculation and the exact solution based on the effective Hamiltonian, we show that there is a parameter region where the longitudinal incommensurate spin correlation becomes dominant around the half-magnetization of the saturation. Possible interpretations of our results are discussed. We next investigate the effects of the interchain interaction $({J}^{\ensuremath{'}})$. The staggered susceptibility and the uniform magnetization are calculated by combining the density-matrix renormalization group method with the interchain mean-field theory. For the parameters where the dominant longitudinal incommensurate spin correlation appears in the case ${J}^{\ensuremath{'}}=0$, the staggered long-range order does not emerge up to a certain critical value of ${J}^{\ensuremath{'}}$ around the half-magnetization of the saturation. We calculate the static structure factor in such a parameter region. The size dependence of the static structure factor at

k=2{k}_{F}

implies that the system has a tendency to form an incommensurate long-range order around the half-magnetization of the saturation. We discuss the recent experimental results for the NMR relaxation rate in magnetic fields performed for pentafluorophenyl nitronyl nitroxide.