Nature of the low-temperature anomalies in the physical properties of the intermediate-valent compound SmB6

The transport properties (Hall coefficient, thermopower, and resistivity) o f high-quality single-crystal samples of the classical mixed-valent compoun d SmB6 are investigated over a broad temperature range (1.6-300 K) in magne tic fields up to 45 T for the first time following the quasioptical measure ments in the 0.6-4.5 meV frequency range [B. Gorshunov, N. Sluchanko, A. Vo lkov et al., submitted to Phys. Rev. B (1998)]. Measurements in the intrins ic conduction region permit determination of the gap width E-g approximate to 20 meV and evaluation of the behavior of the mobility and concentration of light and heavy charge carriers, as well as the temperature dependence o f the carrier relaxation time, in samarium hexaboride. The results of exper imental investigations in the "impurity'' conduction region (E-ex approxima te to 3.5 meV) are discussed within the Kikoin-Mishchenko exciton-polaron m odel of charge fluctuations. Arguments supporting the formation of a metall ic state with an electron-hole liquid in SmB6 at liquid-helium temperatures are presented. (C) 1999 American Institute of Physics. [S1063-7761(99)0140 3-1].