Cluster-Based Haldane State in an Edge-Shared Tetrahedral Spin-Cluster Chain: Fedotovite K2Cu3O(SO4)3

Fedotovite K2Cu3O(SO4)(3) is a candidate of new quantum spin systems, in which the edge-shared tetrahedral ( EST) spin clusters consisting of Cu2+ are connected by weak intercluster couplings forming a one-dimensional array. Comprehensive experimental studies by magnetic susceptibility, magnetization, heat capacity, and inelastic neutron scattering measurements reveal the presence of an effective S = 1 Haldane state below T congruent to 4 K. Rigorous theoretical studies provide an insight into the magnetic state of K2Cu3O(SO4)(3) : an EST cluster makes a triplet in the ground state and a one-dimensional chain of the EST induces a cluster-based Haldane state. We predict that the cluster-based Haldane state emerges whenever the number of tetrahedra in the EST is even.