Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan.
Phys Rev Lett. 2010 Oct 15;105(16):167205. doi: 10.1103/PhysRevLett.105.167205. Epub 2010 Oct 14.
A thorough crystal structure determination at very low temperature of (CuCl)LaNb₂O₇, originally proposed as a spin-1/2 square-lattice antiferromagnet, is reported thanks to the use of single-crystal x-ray diffraction and powder neutron diffraction. State-of-the-art calculations (maximum entropy method) reveal that (CuCl)LaNb₂O₇ is orthorhombic with Pbam symmetry. First-principles calculations demonstrate that the dominant magnetic interactions are antiferromagnetic between fourth nearest neighbors 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.
（CuCl）LaNb₂O₇最初被提出为一个自旋为 1/2 的正方形晶格反铁磁体，通过使用单晶 X 射线衍射和粉末中子衍射，我们在非常低的温度下对其进行了彻底的晶体结构测定。最先进的计算（最大熵法）表明（CuCl）LaNb₂O₇是具有 Pbam 对称的正交晶系。第一性原理计算表明，主要的磁相互作用是通过 Cu-Cl-Cl-Cu 交换路径的第四近邻之间的反铁磁相互作用，这导致了自旋单态的形成。单态之间的两个最强相互作用是铁磁相互作用，这使得（CuCl）LaNb₂O₇成为第一个铁磁耦合 Shastry-Sutherland 量子自旋单态的体系。
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