Puzzle maker in SmB6: accompany-type valence fluctuation state

In recent years, the study on the Kondo insulator SmB6, a strongly correlated electron material with decades-long puzzles, has become one of the most attractive topics again because the discovery of the coexistence of its unusual metallic surface state with an insulating bulk. Many efforts have been made in understanding the corresponding physics behind in SmB6, but some puzzles on it, being hotly debated and argued, has not been solved. In this article, based on the latest progress in our high pressure studies and the accumulating results reported by other groups on SmB6, we propose a notion named as accompany-type valence fluctuation state, which possibly coexists with the Kondo ground state of SmB6. The purpose of this article is to search a common starting point from which most of the accumulated low-temperature phenomena observed by different experimental investigations on SmB6 could be understood in a unified way. Although this notion is only our personal understanding from a phenomenological point of view and may be immature, anyway, we expect that this notion could attract rigorous theoretical interpretations and further experimental investigations, or stimulate better thinking on the physics in SmB6.