We report a study of the temperature-dependent electrical resistivity, Seebeck coefficient, thermal conductivity, specific heat, and 27 Al nuclear magnetic resonance (NMR) in Heusler-type Ru 2 TaAl, to shed light on its semimetallic behavior. While the temperature dependence of the electrical resistivity exhibits semiconductorlike behavior, the analysis of low-temperature specific heat reveals a residual Fermi-level density of states (DOS). Both observations can be realized by means of a semimetallic scenario with the Fermi energy located in the pseudogap of the electronic DOS. The NMR Knight shift and spin-lattice relaxation rate show activated behavior at higher temperatures, attributing to the thermally excited carriers across a pseudogap in Ru 2 TaAl. From the first-principles band structure calculations, we further provide a clear picture that an indirect overlap between electron and hole pockets is responsible for the formation of a pseudogap in the vicinity of the Fermi level of Ru 2 TaAl. In addition, an effort for improving the thermoelectric performance of Ru 2 TaAl has been made by investigating the thermoelectric properties of Ru 1.95 Ta 1.05 Al. We found significant enhancements in the electrical conductivity and Seebeck coefficient and marked reduction in the thermal conductivity via the off-stoichiometric approach. This leads to an increase in the figure-of-merit ZT value from 6.1 × 10 −4 in Ru 2 TaAl to 3.4 × 10 −3 in Ru 1.95 Ta 1.05 Al at room temperature. In this respect, a further improvement of thermoelectric performance based on Ru 2 TaAl through other off-stoichiometric attempts is highly probable.

Employing the first-principles combined with hybrid functional calculations, the electronic and magnetic properties of GaAs doped with a N 2 molecule are investigated in this work. We find that in Ga 32 As 31 (N 2 ) As the N-N split is able to saturate the dangling bond of Ga atom ,form sp 3 -like hybridization, and simultaneously supply an extra localized electron, leading to a magnetic ground state with a magnetic moment of ∼1µ B . This magnetic ground state is different from previously nonmagnetic results predicted by PBE functional, which results from the self-interaction error inherent in semi-local density functional theory. Moreover, the band gap of magnetic ground state of Ga 32 As 31 (N 2 ) As alloy decreases, which is relative to GaAs . Finally we discuss and explain why the magnetism is not discovered in previous experiments and theories. C 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.