Ground-state phase diagram of the distorted diamond type S=1/2 quantum spin chain with the XXZ anisotropy

We study the ground-state phase diagram of the distorted diamond type S=1/2 quantum spin chain with the XXZ type interaction anisotropy, given byH=J1∑j{h3j−1,3j(Δ)+h3j,3j+1(Δ)}+J2∑jh3j+1,3j+2(Δ)+J3∑j{h3j−2,3j(Δ)+h3j,3j+2(Δ)}where hl,m(Δ)=SlxSmx+SlySmy+ΔSlzSmz, and Δ>0 denotes the XXZ anisotropy. We have used the degenerate perturbation theory, numerically exact diagonalization method, and the level spectroscopy analysis of the diagonalization data. The remarkable nature of the phase diagram is the existence of the inversion areas. Namely, there appears the Néel region even when the interaction is XY-like, and the spin-fluid region when it is Ising-like. This phenomenon is attributed to the interplay among the interaction anisotropy, frustrating interaction, and the trimer nature of the Hamiltonian.