%0 Journal Article %T Exact spin-cluster ground states in a mixed diamond chain %A Ken'ichi Takano %A Hidenori Suzuki %A Kazuo Hida %J Physics %D 2008 %I arXiv %R 10.1103/PhysRevB.80.104410 %X The mixed diamond chain is a frustrated Heisenberg chain composed of successive diamond-shaped units with two kinds of spins of magnitudes S and S/2 (S: integer). Ratio $lambda$ of two exchange parameters controls the strength of frustration. With varying $lambda$, the Haldane state and several spin cluster states appear as the ground state. A spin cluster state is a tensor product of exact local eigenstates of cluster spins. We prove that a spin cluster state is the ground state in a finite interval of $lambda$. For S=1, we numerically determine the total phase diagram consisting of five phases. %U http://arxiv.org/abs/0811.1320v2