Successive magnetic-phase transitions in a frustrated two-leg spin ladder

フラストレートした2本足スピン梯子系における連続的な磁気相転移

杉本 貴則; 森 道康   ; 遠山 貴己; 前川 禎通

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

Recently, successive phase transitions induced by magnetic field have been observed in a frustrated two-leg spin ladder BiCuPO, in which the frustration is introduced by the next-nearest-neighbor antiferromagnetic exchange interaction in the leg direction. First, we calculate the magnetic-field dependence of magnetization by using density-matrix renormalization-group method. In this calculation, we find a phase transition induced by strong frustration, which does not appear in a non-frustrated two-leg spin ladder. The phase transition emerges as a jump of susceptibility with unsaturated finite magnetization. We also investigate the origin of the phase transition by using the bond-operator mean-field approximation. We conclude that the phase transition is the same type as the Lifshitz transition. Our study is useful to analyze experimental data of BiCuPO.