Anisotropic Antiferromagnetic Spin Chains in a Transverse Field: Reentrant Behavior of the Staggered Magnetization

We investigate one-dimensional S=1/2 and S=1 antiferromagnetic quantum spin chains with easy-axis anisotropies in a transverse field. We calculate both the uniform magnetization and the staggered magnetization, using a variant of the density matrix renormalization group method. We find that the staggered magnetizations exhibit reentrant behavior as functions of the transverse field, where the competition between the classical Neel order and the quantum fluctuations plays an important role. We also discuss the critical behavior associated with the staggered magnetizations.