Anomalous metallic state in the vicinity of metal to valence-bond solid insulator transition in LiVS

Katayama, Naoyuki*; Uchida, Masaya*; Hashizume, Daisuke*; Niitaka, Seiji*; Matsuno, Jobu*; Matsumura, Daiju   ; Nishihata, Yasuo; Mizuki, Junichiro; Takeshita, Nao*; Gauzzi, A.*; Nohara, Minoru*; Takagi, Hidenori*

We investigate LiVS and LiVSe with a triangular lattice as itinerant analogues of LiVO known for the formation of a valence-bond solid (VBS) state out of an S = 1 frustrated magnet. LiVS, which is located at the border between a metal and a correlated insulator, shows a first order transition from a paramagnetic metal to a VBS insulator at T 305 K upon cooling. The presence of a VBS state in the close vicinity of insulator-metal transition may suggest the importance of itinerancy in the formation of a VBS state. We argue that the high temperature metallic phase of LiVS has a pseudogap, likely originating from the VBS fluctuation. LiVSe was found to be a paramagnetic metal down to 2 K.