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

2本足スピン梯子系における磁気励起とフラストレーション効果

杉本 貴則; 森 道康  ; 遠山 貴己; 前川 禎通

Sugimoto, Takanori; Mori, Michiyasu; Toyama, Takami; Maekawa, Sadamichi

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 BiCuPO. 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 BiCuPO.