Gap properties of SmB6 and YbB12:: Electrical resistivity and tunnelling spectroscopy studies

We report results of electrical resistivity studies below 100 K and tunnelling spectroscopy studies at 4.2 K for SmB6 and YbB12 samples. The resistivity results of both systems exhibit temperature activated behavior with several activation energies. The tunnelling studies show a non-zero differential conductance at and in the vicinity of zero bias voltage, indicating a presence of the states in the gap region. Results can be plausibly understood within the conception of "classical" heavily doped semiconductors, however, the shapes of differential conductance curves reminiscent of correlation pseudogap (like in FeSi) existence. (c) 2006 Elsevier B.V. All rights reserved.