The electrical resistivity and Hall effect of alkaline-earth-metal hexaboride single crystals are measured as a function of temperature, hydrostatic pressure, and magnetic field. The transport properties vary weakly with the external parameters and are modeled in terms of intrinsic variable-valence defects. These defects can stay either in (1) delocalized shallow levels or in (2) localized levels resonant with the conduction band, which can be neutral or negatively charged. Satisfactory agreement is obtained for electronic transport properties in a broad temperature and pressure range, although fitting the magnetoresistance is less straightforward and a combination of various mechanisms is needed to explain the field and temperature dependences.

We acknowledge support from Grant No. MAT2012-38213-C02-01 from the Ministerio de Economía y Competividad of Spain. Additional support from Diputacion General de Aragon (DGA-CAMRADS) is also acknowledged. Work at Los Alamos was performed under the auspices of the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering. P.F.S.R. acknowledges a Director’s Postdoctoral Fellowship through the LANL LDRD program. P.S. acknowledges the support by the U.S. Department of Energy (BES) under Grant No. DE-FG02-98ER45707.

Peer Reviewed