Quantum entanglement of XY-type spin dimers in Shastry-Sutherland lattice

We report a comprehensive study on the origin of the enigmatic disordered ground state within the Shastry-Sutherland lattice BaCe2ZnS5, at low temperatures. The magnetization and heat capacity data show a lack of magnetic ordering down to 73 mK. We use CrysFieldExplorer to compute single-ion anisotropy g-tensor and deploy a localized spin dimer model which can accurately reproduce the dynamic structure factor of the neutron data, magnetization and heat capacity data. Remarkably, the intra-dimer exchange interaction shows strong XY-type anisotropy in a local reference frame and the ground state of BaCe2ZnS5 is in an entangled state (|↑↑> - |↓↓>)/sqrt(2) in a global reference frame. This is in contrast to the singlet dimer state obtained for Heisenberg interactions. These results confirms that BaCe2ZnS5 is in a quantum paramagnet state consisting of entangled spin dimer states. The parameterized Hamiltonian enables the possibility to explore complex spin dynamics in the SU(N) regime.