Distorted Diamond Chain Research Articles

Inversion phenomena of the anisotropies of the Hamiltonian and the wave-function in the distorted diamond type spin chain

We investigate the ground-state phase diagram of the XXZ version of the S=1/2 distorted diamond chain by the use of degenerate perturbation theory near the truncation point. In case of the XY-like interaction anisotropy, the phase diagram consists of the Néel phase and the spin-fluid phase. For the Ising-like interaction anisotropy case, it consists of three phases: the ferrimagnetic phase, the Néel phase and the spin-fluid phase. The magnetization in the ferrimagnetic phase is 1/3 of the saturation magnetization. The remarkable nature of the phase diagram is the existence of the Néel phase, although the interaction anisotropy is XY-like. And also, the spin-fluid phase appears in spite of the Ising-like interaction anisotropy. We call these regions ‘inversion regions’.

Ground state of an S=1/2 distorted diamond chain in a finite magnetic field

We investigate the ground state magnetization curve of an S=1/2 distorted diamond chain. It is found that, in a certain region of the exchange interaction constants, a (2/3)-plateau appears in addition to a (1/3)-plateau, which appears in a much wider region. In the (2/3)-plateau state the translational symmetry of the Hamiltonian is spontaneously broken. We also discuss the phase diagram on an interaction constant plane that shows the region of the appearance of the (2/3)-plateau.

Spin Gap ofS=1/2Heisenberg Model on Distorted Diamond Chain

We study the spin gap of the S=1/2 Heisenberg model on the distorted diamond chain, which is recently proposed to represent magnetic properties of Cu_3 Cl_6 (H_2 O)_2 2H_8 C_4 SO_2. This model is composed of stacked trimers and has three kinds of exchange interactions J_1, J_2 and J_3. Using the numerical diagonalization, we obtain a contour map of the spin gap in the J_2/J_1-J_3/J_1 plane. We argue possible values of the exchange constants based on the contour map and the observed value of the spin gap.