Breakdown of a Magnetization Plateau in Ferrimagnetic Mixed Spin-(1/2,S) Heisenberg Chains Due to a Quantum Phase Transition Towards the Luttinger Spin Liquid

摘要

Magnetization curves of the ferrimagnetic mixed spin-(1/2,S) Heisenbergchains are calculated with the help of density-matrix renormalization groupmethod for several quantum spin numbers S=1, 3/2, 2 and 5/2. It is shown thatthe ferrimagnetic mixed spin-(1/2,S) Heisenberg chains exhibit irrespective ofthe spin value S exactly one intermediate magnetization plateau, which can beidentified with the gapped Lieb-Mattis ferrimagnetic ground state. Themagnetization plateau due to the Lieb-Mattis ferrimagnetism breaks down at aquantum phase transition towards the Luttinger spin liquid, which ischaracterized by a continuous change of the magnetization with the magneticfield until another quantum critical point is reached at the saturation field.