Phase transition induced by magnetic field in a two-leg spin ladder

2本足スピン梯子系における磁場誘起相転移

杉本 貴則; 森 道康  ; 遠山 貴己; 前川 禎通

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

Recently, a successive phase transitions induced by magnetic field has been observed in BiCu2PO6. The experimental study claims that a magnetic anisotropy is an origin of this interesting phenomenon. The existence of the magnetic anisotropy can be confirmed by a splitting of the triplet excitation observed in inelastic neutron scattering experiment without magnetic field. Thus, we numerically study magnetic excitations in a frustrated two-leg spin-ladder system, in which all magnetic exchange interactions. This is a minimal model describing a low-dimensional quantum spin compound, BiCuPO. The dynamical density-matrix renormalization-group method is used to calculate the excitation spectrum in the incommensurate rung-singlet phase without magnetic field. We study the successive phase transitions induced by magnetic field. Two ground- state phases emerge with magnetic field both longitudinal and perpendicular to the leg directions. Therefore, the two phases may occur without magnetic anisotropy. First, we discuss the phase transitions by using density-matrix renormalization-group method without magnetic anisotropy. In addition, we mention effects of anisotropy on phase transitions induced by magnetic field.