Octa-Kagomé Lattice Compounds Showing Quantum Critical Behaviors: Spin Gap Ground State versus Antiferromagnetic Ordering
Yingying Tang,^† Cheng Peng,^# Wenbin Guo,^† Jun-feng Wang,^‡ Gang Su,^# and Zhangzhen He*,^†
†State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences,
Fuzhou, Fujian 350002, People’s Republic of China
^#Theoretical Condensed Matter Physics and Computational Materials Physics Laboratory, School of Physical Sciences, University of
Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
^‡Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan, Hubei 430074, People’s
Republic of China

Search for a new geometrically frustrated lattice is a great challenge. Herein, we report on a successful synthesis of two new layered compounds BiOCu2(XO3)(SO4)(OH)·H2O [X = Te (1) and Se (2)] with a new type of geometrically frustrated lattice (i.e., the octa-kagomé lattice) between kagomé and star motifs. Magnetic measurements confirmed that 1 exhibits a spin gap ground state, while 2 possesses a typical antiferromagnetic ordering at low-temperature. Such different magnetic behaviors between two isostructural compounds are suggested to originate from a slightly structural modification induced by nonmagnetic XO3 anionic groups. Theoretical simulations suggest that the origin of gapped ground state in 1 may be due to the dimerization of Cu2+ ions, while 2 may break the limiting of such dimerization, leading to an antiferromagnetic ordering.