SPIN-PEIERLS STATES IN HIGH MAGNETIC-FIELDS

We study numerically the magnetization process of the S = 1/2 antiferr omagnetic chain with spin-lattice coupling, which modifies the exchang e coupling constants. It is shown by diagonalizing the Hamiltonian of the finite-size system with an open boundary condition that, in zero f ield, the ground state is a singlet dimer state, which is stabilized b y the lattice dimerization, while, in relatively high fields, the syst em becomes magnetized in such a way that the magnetization appears as a domain wall between singlet dimers relaxing the lattice dimerization near the wall. The result is discussed in connection with the experim ental result of the spin-Peierls system, CuGeO3. (C) 1998 Elsevier Sci ence B.V. All rights reserved.