Using inelastic neutron scattering, x-ray, neutron diffraction, and the first-principle calculation techniques, we show that the crystal structure of the two-dimensional quantum spin system (CuCl)LaNb2O7 is orthorhombic with Pbam symmetry in which CuCl4O2 octahedra are tilted from their high symmetry positions and the Cu2+(s=1/2) ions form a distorted square lattice. The dominant magnetic interactions are the fourth nearest neighbor antiferromagnetic interactions with a Cu-Cl--Cl-Cu exchange path, which lead to the formation of spin singlets. The two strongest interactions between the singlets are ferromagnetic, which makes (CuCl)LaNb2O7 the first system of ferromagnetically coupled Shastry-Sutherland quantum spin singlets.
@article{arxiv.1006.0755,
title = {Ferromagnetically coupled Shastry-Sutherland quantum spin singlets in (CuCl)LaNb$_2$O$_7$},
author = {C. Tassel and J. Kang and C. Lee and O. Hernandez and Y. Qiu and W. Paulus and E. Collet and B. Lake and T. Guidi and M. -H. Whangbo and C. Ritter and H. Kageyama and S. -H. Lee},
journal= {arXiv preprint arXiv:1006.0755},
year = {2015}
}