Ground-state phase diagram of S = 2 quantum spin chain with the XXZ and on-site anisotropies

By use of mainly numerical methods, we investigate the ground-state phase diagram of an S = 2 quantum spin chain with the XXZ and on-site anisotropies described by H = Σ_j(S_j^xS _j+1^x + S^y_jS^y _j+1 + ΔS^z_jS^z_j+1 + D Σ_j(S^z_j)², where Δ denotes the XXZ anisotropy parameter of the nearest-neighbor interactions and D the on-site anisotropy parameter. In the phase diagram with Δ > 0 and D > 0 there appear the XY phase, the Haldane/large-D (LD) phase, the intermediate-D (ID) phase, and the Néel phase. Among them the ID phase was proposed by Oshikawa in 1992 and has been considered to be absent since the DMRG studies in the latter half of 1990's. And also, the Haldane state and the LD state belong to the same phase, which should be named Haldane/LD phase.