Progress of Theoretical Physics Supplement
Finite-Field Ground State of anS= 1 Anisotropic Antiferromagnetic Chain
Takashi Tonegawa, Kouichi Okunishi, Tôru Sakai, Makoto Kaburagi
Abstract
We investigate, using numerical methods, the finite-field ground-state properties of an S = 1 anisotropic antiferromagnetic chain described by the Hamiltonian . It is found that the magnetization jump anomaly (a first-order phase transition) appears in the ground-statemagnetization curve when Δ = 5.0 and −1.50 ≲ D ≲ 1.05; in a certain region of D, the jump starts from a finite value of the magnetization m per spin. We also find that the a second-order phase transition between commensurate and incommensurate gapless phases takes place in the finite-field ground state. The critical point of this transition as well as the values of m at the onset and end of the magnetization jump is summarized in the m versus D phase diagram.