Spin-Peierls states in high magnetic fields

We study numerically the magnetization process of the S = 1/2 antiferromagnetic chain with spin-lattice coupling, which modifies the exchange coupling constants. It is shown by diagonalizing the Hamiltonian of the finite-size system with an open boundary condition that, in zero field, the ground state is a singlet dimer state, which is stabilized by the lattice dimerization, while, in relatively high fields, the system 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 experimental result of the spin-Peierls system, CuGeO₃.