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 and silicon (Si:B) in 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). Interestingly, the latter compound is a type-I superconductor whereas the two aforementioned materials are type-II (compare Z.A. Ren et al., J. Phys. Soc. Jpn. 76, 103710 (2007)). 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 non-superconducting 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.

Figure: Electronic specific heat of SiC-1: The red symbols denote the data in zero magnetic field. The blue refer to data measured in a magnetic field H=200 Oe > Hc, representing the normal-state specific heat. The lines are fits to the data assuming an isotropic BCS-like gap (dashed line) and a nodal gap structure (dotted line). The dashed-dotted horizontal line denotes the value of the Sommerfeld parameter in the normal-conducting state γn. The two other γ values are estimates in the BCS-model and denote the superconducting γs and a possible residual Sommerfeld parameter γres; compare the discussion in the paper.

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M. Kriener, Y. Maeno, T. Oguchi, Z. -A. Ren, J. Kato, T. Muranaka, and J. Akimitsu
Phys. Rev. B 78 024517 July 2008