Electron self-trapping in intermediate-valent SmB6

SmB6 exhibits intermediate valence in the ground state and unusual behavior at low temperatures. The resistivity and the Hall effect cannot be explain ed either by conventional sf hybridization or by hopping transport in an im purity band. At least three different energy scales determine three tempera ture regimes of electron transport in this system. We consider the ground-s tate properties, the soft valence fluctuations, and the spectrum of band ca rriers in n-doped SmB6. The behavior of excess conduction electrons in the presence of soft valence fluctuations, and the origin of the three energy s cales in the spectrum of elementary excitations are discussed. The carriers which determine the low-temperature transport in this system are self-trap ped electron polaron complexes rather than simply electrons in an impurity band. The mechanism of electron trapping is the interaction with soft valen ce fluctuations.