Specific heat and electronic states of superconducting boron-doped silicon carbide

The discoveries of superconductivity in the heavily-boron doped semiconductors diamond (C:B) in 2004 [Ekimov , Nature (London) 428, 542 (2004)] and silicon (Si:B) in 2006 [Bustarret , Nature (London) 444, 465 (2006)] have renewed the interest in the physics of the superconducting state of doped semiconductors. Recently, we discovered superconductivity in the closely related "mixed" system heavily boron-doped silcon carbide (SiC:B) [Ren , J. Phys. Soc. Jpn. 76, 103710 (2007)]. Interestingly, the latter compound is a type-I superconductor whereas the two aforementioned materials are type II. In this paper, we present an extensive analysis of our recent specific-heat study, as well as the band structure and expected Fermi surfaces. We observe an apparent quadratic temperature dependence of the electronic specific heat in the superconducting state. Possible reasons are a nodal gap structure or a residual density of states due to nonsuperconducting parts of the sample. The basic superconducting parameters are estimated in a Ginzburg-Landau framework. We compare and discuss our results with those reported for C:B and Si:B. Finally, we comment on possible origins of the difference in the superconductivity of SiC:B compared to the two "parent" materials C:B and Si:B.