Anomalous Metallic State in the Vicinity of Metal to Valence-Bond Solid Insulator Transition inLiVS2

Abstract

We investigate ${\mathrm{LiVS}}_2$ and ${\mathrm{LiVSe}}_2$ with a triangular lattice as itinerant analogues of ${\mathrm{LiVO}}_2$ known for the formation of a valence-bond solid (VBS) state out of an $S=1$ frustrated magnet. ${\mathrm{LiVS}}_2$, 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 $T_c\sim 305\mathrm{K}$ 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 ${\mathrm{LiVS}}_2$ has a pseudogap, likely originating from the VBS fluctuation. ${\mathrm{LiVSe}}_2$ was found to be a paramagnetic metal down to 2 K.