Nontrivial ferrimagnetism of the Heisenberg model on the Union Jack strip lattice

摘要

We study the ground-state properties of the S=1/2 antiferromagneticHeisenberg model on the Union Jack strip lattice by using theexact-diagonalization and density matrix renormalization group methods. Weconfirm a region of the intermediate-magnetization state between the Neel-likespin liquid state and the conventional ferrimagnetic state of Lieb-Mattis type.In the intermediate-state, we find that the spontaneous magnetization changesgradually with respect to the strength of the inner interaction. In addition,the local magnetization clearly shows an incommensurate modulation withlong-distance periodicity in the intermediate-magnetization state. Thesecharacteristic behaviors lead to the conclusion that theintermediate-magnetization state is the non-Lieb-Mattis ferrimagnetic one. Wealso discuss the relationship between the ground-state properties of the S=1/2antiferromagnetic Heisenberg model on the original Union Jack lattice and thoseon our strip lattice.