Thierry Klein started off with review of superconductivity in covalent bonded materials and row IV systems. He gave example of fullerenes and Si-Clathrates. He then discussed the reasonably recent example of superconductivity in diamond. He motivated that it exected that the el-phonon coupling constant could be as big as 280 meV. He gave a naive estimate forecast of a Tc based on this el-phonon coupling for this sample of 200K.
Was discovered by Ekimov et al. in 2004. It is believed that superconductivity occurs in an sp3 band.
It appears with B doping at the onset of the metal-insulator transition. Tc is NOT 200K in this compound; it is limited to ~10K presumably due to the low charge carrier density.
Diamond superconducting films can also be grown by plasma assisted CVD, which appeared to this blogger to have a max Tc in these films of about 3K. It has also been discovered intercalated graphite has Tc around 11K in 2005. In 2007 they discovered superconductivity in B doped Si.
Gas immersion laser doping is done to increase B concentration of Si. Apparently it is not possible to doped to high enough concentrations in a melt. The necessary concentrations of B are above the solubility limit of B in Si. To this blogger they blast and melt the surface of a Si with a laser. The surface recrystallize under some atmosphere of B which is incident. They can make highly doped B doped Si layer.
At 1% Boron concentrations the transition starts and rises linear. This is difference than diamond, where Tc comes up with an exponent of ~ 0.5. The superconducting transition doesn't coincide with the MIT. That is at much lower concentrations. The max Tc looks to be about 0.5K. The superconductivity in this system is extreme type II. Unlike the case of diamond where k_Fl is about 1, k_Fl in this system is about 10.
Calculations can postdict the superconductivity reasonably, but there is uncertainty about mu* (as there is always). But with a mu* of about 0.14 (typical for metals), they can describe Tc.
Blogged by Peter Armitage
An important piece of information presented by Thierry Klein was that dependence of transition temperature in both doped diamond and doped Si is anomalous in the sense that at low doping Tc was found much above the estimate which follows from the values of dimentionless coupling constant g (known from numerous ab initio computations). Instead of usual exponential dependence, Tc rather scales as g^2. Such a result would follow immediately from the theory of fractal superconductivity presented in the talk by M.Feigelman. Indeed it seems that such an approach could make sense for doped diamond where superconductor-insulator transition occurs right at the mobility edge as function of doping concentration. However, in doped Silicon the SIT occures in the metallic range of doping, and it seems that there is no reason to invoke fractal superconductivity in that case. In any case, the issue of Tc that is much above BCS-type prediction seems rather intriguing.
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