Ground state of a quantum mixed spin-((1)/(2))-((1)/(2))-1-1 chain with uniaxial single-ion-type anisotropy

Effect of the uniaxial single-ion-type anisotropy for the S=1 spins on the ground state of a quantum mixed spin-((1)/(2))-((1)/(2))-1-1 chain is discussed. It is found that, when the ground state in the case of no anisotropy is of the Haldane-phase character, the anisotropy causes a second-order phase transition accompanying the disappearance of the string order