We present a comprehensive structural study on perovskite-type 6H-Ba3CuSb2O9, which exhibits a spin-orbital short-range ordering on a honeycomb-based lattice. By combining synchrotron x-ray diffraction, electron spin resonance, ultrasound measurement
and Raman spectroscopy, we found that the static Jahn-Teller distortion is absent down to the lowest temperature in the present material, indicating orbital ordering is strongly suppressed. We discuss such an unusual state is realized with the help of spin degree of freedom, leading to a spin-orbital entangled liquid state.
We investigate LiVS2 and LiVSe2 with a triangular lattice as itinerant analogues of LiVO2, known for the formation of valence bond solid (VBS) state out of S = 1 frustrated magnet. LiVS2, which is located at the border between a metal and a correlate
d insulator, shows a first ordered transition from a paramagnetic metal to a VBS insulator at Tc ~ 305 K upon cooling. The presence of VBS state in the close vicinity of insulator-metal transition may suggest the importance of itinerancy in the formation of VBS state. We argue that the high temperature metallic phase of LiVS2 has a pseudo-gap, likely originating from the VBS fluctuation. LiVSe2 was found to be a paramagnetic metal down to 2 K.
We report a novel superconducting (SC) and antiferromagnetic (AF) hybrid state in SrFe2As2 revealed by 75As nuclear magnetic resonance (NMR) experiments on a single crystal under highly hydrostatic pressure up to 7 GPa. The NMR spectra at 5.4 GPa ind
icate simultaneous development of the SC and AF orders below 30 K. The nuclear spin-lattice relaxation rate in the SC domains shows a substantial residual density of states, suggesting proximity effects due to spontaneous formation of a nano-scale SC/AF hybrid structure. This entangled behavior is a remarkable example of a self-organized heterogeneous structure in a clean system.
