Superconductivity in heavily boron-doped silicon carbide

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.

Superconductivity in carrier-doped silicon carbide

“…In preliminary ac susceptibility results (T-scan and H-scan), small hysteresis between cooling and warming process was observed ( T ∼0.02 K at H = 100 Oe, H ∼19 Oe at T = 0.26 K) [38]. Concentration of crystal defects and impurities should be reduced in SiC:Al for a more detailed study of the superconductivity.…”

“…Table 1 lists preliminary specific heat coefficients γ n [38]; basic normal-state parameters: Fermi wave number k F , effective mass m * , Fermi velocity v F , mean free path l; as well as superconducting state parameters: penetration depth λ, coherence length ξ and Ginzburg-Landau parameter κ GL . Those parameters were estimated as described in [39].…”

Recent advances in superconductivity of covalent superconductors

“…Therefore, this theory hardly applies to diamond (or Si), as recently admitted by the author himself [17]. However, this theory might be valid for SiC where superconductivity has been recently observed for much lower dopant concentrations $0.25% [23].…”

Superconductivity in covalent semiconductors

“…The low-temperature part is usually scanned several times under different values of applied magnetic field, in order to check for hysteresis and to deduce the extrapolated value of the upper critical magnetic field H 2 (for type-II superconductor) at which superconductivity vanishes at 0 K. The wide temperature scan is also used to evaluate the residual resistivity ratio, which is often taken as ratio of resistivity at 300 K to resistivity at a temperature slightly above T . This ratio may relate to the material puritylower value means lower purity [20,21]. Resistance behavior at T > T indicates whether material is metal-like ( R/ T > 0) or semiconductor-like ( R/ T < 0).…”

“…Therefore, samples containing mostly 6H-SiC or 3C-SiC were prepared for the following experiments [20,21]. Also, the boron doping, which was used initially by example of Ekimov et al, was extended to aluminum.…”