Abstract
Hall effect and magnetoresistance measurements were carried out on a single-phase polycrystalline sample of the type-I clathrate Ba${}_{8}$Ge${}_{43}$\ensuremath{\square}${}_{3}$ in the 2--350 K temperature range. These experiments were complemented by electronic band structure and Fermi surface calculations performed by an all-electron, full potential first-principles method. These calculations have revealed the presence of three pieces of the Fermi surface originating from both holelike and electronlike bands crossing the Fermi level suggesting that both types of carriers play a role in the electrical conduction of this material. These results were experimentally confirmed via a strongly temperature-dependent and dominant holelike signal in the Hall coefficient and a breakdown of Kohler's rule in the magnetoresistance data. We analyze the Hall coefficient and magnetoresistance data within the framework of a two-band model with temperature-dependent carrier concentrations and mobilities and discuss its limits in capturing the essential features governing the magnetotransport. Combined with the temperature dependences of the thermopower and the electrical resistivity, all these results suggest that Ba${}_{8}$Ge${}_{43}$\ensuremath{\square}${}_{3}$ can be classified as a nearly compensated semimetal.
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