Magnetization process of S=1/2 XXZ chain in a periodic magnetic field

The magnetization process of S = 1/2 XXZ chain, exposed to a periodic field , have been studied with use of density matrix renormalization group (DMRG) method and Jordan-Wigner fermion mean field approximation. In this study, the DMRG calculation has been performed mainly in case of periodic field wi th a period four times the lattice spacing. The magnetization curves for va rious values of Ising anisotropy Delta and amplitude of periodic field lamb da are obtained, exhibiting a plateau for a suitable set of values of Delta and lambda. A phase diagram on the plane of Delta and the uniform field h, or on the plane of Delta and lambda has been constructed to show the condi tion for the 'plateau phase' to appear. These results are well interpreted in terms of the renormalized energy band of JW-fermions, moving in a self-c onsistent periodic field.