Structural investigation of the bilayer iridate Sr3Ir2O7
  A complete structural solution of the bilayer iridate compound Sr3Ir2O7 presently remains outstanding. Previously reported structures for this compound vary and all fail to explain weak structural violations observed in neutron scattering measurements as well as the presence of a net ferromagnetic moment in the basal plane. In this paper, we present single crystal neutron diffraction and rotational anisotropy second harmonic generation measurements unveiling a lower, monoclinic symmetry inherent to Sr3Ir2O7 . Combined with density functional theory, our measurements identify the correct structural space group as No. 15 (C2/c) and provide clarity regarding the local symmetry of Ir 4+ cations within this spin-orbit Mott material. 
Tom Hogan, Lars Bjaalie, Liuyan Zhao, Carina Belvin, Xiaoping Wang,   Chris G. Van de Walle, David Hsieh, Stephen D. Wilson
cond-mat.str-el cond-mat.supr-con