We report the first study of the optical conductivity of MgB2 covering the range of its lowest-energy superconducting gap. Terahertz time-domain spectroscopy is utilized to determine the complex, frequency-dependent conductivity sigma(omega) of thin films. The imaginary part reveals an inductive response due to the emergence of the superconducting condensate. The real part exhibits a strong depletion of oscillator strength near 5 meV resulting from the opening of a superconducting energy gap. The gap ratio of 2Delta0/k(B)TC approximately 1.9 is well below the weak-coupling value, pointing to complex behavior in this novel superconductor.
to 39 K in these reports. Here, we report our successful demonstration of the growth of 3 superconducting MgB 2 films using electron beam evaporated B precursor films followed by appropriate post-annealing. We also report results of transport property measurements on these ex-situ grown MgB 2 films. The MgB 2 films had a sharp T c (zero resistance) of 38.0 K with a ∆T c of 0.3 K and a ratio of the room temperature resistivity to the residual resistivity above T c of about 2. The resistivity decreased linearly with temperature indicating that the MgB 2 film is metallic.
Superconducting magnesium diboride films with Tc0∼24 K and sharp transition ∼1 K were prepared on Si by pulsed-laser deposition from stoichiometric MgB2 target. Contrary to previous reports, anneals at 630 °C and a background of 2×10−4 Ar/4%H2 were performed without the requirement of Mg vapor or Mg cap layer. This integration of superconducting MgB2 film on Si may thus prove enabling in superconductor-semiconductor device applications. Images of surface morphology and cross-section profiles by scanning electron microscopy show that the films have a uniform surface morphology and thickness. Energy-dispersive spectroscopy study reveals these films were contaminated with oxygen, originating either from the growth environment or from sample exposure to air. The oxygen contamination may account for the low Tc for those in situ annealed films, while the use of Si as a substrate does not result in a decrease in Tc as compared to other substrates.
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