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, 9 (4), 044205
eCollection

Superconductivity in Heavily Boron-Doped Silicon Carbide

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Superconductivity in Heavily Boron-Doped Silicon Carbide

Markus Kriener et al. Sci Technol Adv Mater.

Abstract

The discoveries of superconductivity in heavily boron-doped diamond in 2004 and silicon in 2006 have renewed the interest in the superconducting state of semiconductors. Charge-carrier doping of wide-gap semiconductors leads to a metallic phase from which upon further doping superconductivity can emerge. Recently, we discovered superconductivity in a closely related system: heavily boron-doped silicon carbide. The sample used for that study consisted of cubic and hexagonal SiC phase fractions and hence this led to the question which of them participated in the superconductivity. Here we studied a hexagonal SiC sample, free from cubic SiC phase by means of x-ray diffraction, resistivity, and ac susceptibility.

Keywords: boron-doped SiC; hexagonal and cubic SiC; type-I superconductor.

Figures

Figure 1
Figure 1
(a) Unit cell of cubic 3C-SiC. The planes mark the three C–Si bilayers forming the unit cell (stacking sequence: ABC – …along 〈111〉 (dotted arrow)). The tetrahedral bond alignment of diamond is emphasized demonstrating the close relation to that structure. (b) Four unit cells of hexagonal 6H-SiC. The six bilayers needed for the unit cell are again denoted by planes (stacking sequence ABCACB – …along 〈001〉 (dotted arrow)). For the drawings the software Vesta was used [12].
Figure 2
Figure 2
(a) Powder x-ray diffraction patterns of boron-doped 6H-SiC. Three phases, 6H-SiC, 15R-SiC, and silicon, are identified. There is no indication for a cubic SiC modification in this sample. The respective data for 3C/6H-SiC : B from [9] is shown in panel (b), for comparison.
Figure 3
Figure 3
Resistivity vs. temperature of 6H-SiC : B (blue symbols) (a) up to room temperature and (b) around Tc. The sample used exhibits a metallic-like temperature dependence in the whole examined temperature range above Tc. At Tc, we detect a sharp drop to zero resistance. The respective data for 3C/6H-SiC : B from [9] are shown for comparison (red symbols), too. Please note that the resistivity data of 3C/6H-SiC : B is multiplied by 10. The dotted line marks the transition; see text.
Figure 4
Figure 4
Temperature dependence of the ac susceptibility χac of 6H-SiC. In (a) the real part χ ′ and in (b) the imaginary part χ ″ are shown. The respective data for 3C/6H-SiC : B from [9] is shown in panels (c) and (d), for comparison. The dotted line in panels (a) and (c) signals the zero-field transition temperature. The arrows in panels (a) and (c) denote the temperature sweep direction; see text.
Figure 5
Figure 5
(a) HT phase diagram of 6H-SiC : B. The dashed lines are fits to the data; see text. The respective data for 3C/6H-SiC : B from [9] is shown in panel (b), for comparison. The lower phase lines Hsc correspond to the ‘supercooling’ effect; see text.

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