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Magnetic excitations and frustration effect in a frustrated two-leg spin-ladder system

杉本貴則; 森道康; 遠山貴己; 前川禎通

no journal, ,

We present numerical study on magnetic excitations in a frustrated two-leg spin-ladder model, an antiferromagnetic ladder with intra-chain next-nearest-neighbour antiferromagnetic exchange interaction. This model is a minimal model describing a low-dimensional quantum spin system BiCu $_{2}$ PO $_{6}$ . We calculate dynamical spin correlation function by using dynamical density-matrix renormalization-group method for some possible phases at zero temperature. We make clear that there are some differences between the magnetic excitations in the zero-temperature phases. The dominant excitations are understood by elementary excitations with spinon and triplon. Especially, bonding mode and anti-bonding mode of triplon in the rung direction are quite different in contrast with the excitations of spinons. Therefore, we insist that the difference of the spectrum weight between the bonding mode and the anti-bonding mode, is important to distinguish the zero- temperature phases. In addition, we examine the anti-bonding mode, so-called bound triplon, in detail. Frustration effect on the bound triplon is also investigated with a perturbation theory from the strong rung limit. Our study is expected to be useful to analyze inelastic neutron scattering data for BiCu $_{2}$ PO $_{6}$ .

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Spin and multipole dynamics of ferromagnetic frustrated chain in high magnetic field

大西弘明

no journal, ,

By exploiting density-matrix renormalization group techniques, we investigate spin and quadrupole dynamical structure factors of a spin- one-dimensional $J_{1}$ - $J_{2}$ Heisenberg model in applied magnetic field. Regarding the spin dynamical structure factor, we can see a difference between the longitudinal $S^{z}(q,omega)$ and the transverse $S^{-}(q,omega)$ : $S^{z}(q,omega)$ exhibits a gapless mode with the shift of the peak position according to magnetization, while $S^{-}(q,omega)$ shows a gapped mode, since a finite energy is required to break a two-magnon bound state. These features should be observed by inelastic neutron scattering experiments. On the other hand, we find a gapless mode in the quadrupole dynamical structure factor $Q^{-}(q,omega)$ , since the two-magnon excitation energy is zero. We will report detailed analyses of the dependence on magnetic field and exchange couplings.