Topological superconductors represent a newly predicted phase of matter that is topologically distinct from conventional superconducting condensates of Cooper pairs. As a manifestation of their topological character, topological superconductors support solid-state realizations of Majorana fermions at their boundaries. The recently discovered superconductor Cu(x)Bi(2)Se(3) has been theoretically proposed as an odd-parity superconductor in the time-reversal-invariant topological superconductor class, and point-contact spectroscopy measurements have reported the observation of zero-bias conductance peaks corresponding to Majorana states in this material. Here we report scanning tunneling microscopy measurements of the superconducting energy gap in Cu(x)Bi(2)Se(3) as a function of spatial position and applied magnetic field. The tunneling spectrum shows that the density of states at the Fermi level is fully gapped without any in-gap states. The spectrum is well described by the Bardeen-Cooper-Schrieffer theory with a momentum independent order parameter, which suggests that Cu(x)Bi(2)Se(3) is a classical s-wave superconductor contrary to previous expectations and measurements.
%'e report on a direct kinetic measurement of Cooper-pair breaking in superconducting lead. A 100-fs pulse of visible light was used to excite a thin-film lead sample, while the Cooper-pair density was optically probed using an ultrashort pulse of broadband far-infrared radiation. Subsequent to the absorption of the visible light, a rapid ((1 ps) change in the far-infrared optical transmission was observed, corresponding to the breaking of Cooper pairs and the collapse of the superconducting gap. Thin superconducting lead films have been extensively studied and characterized using far-infrared (FIR) linear spectroscopy. ' The experiments described in Ref. 3 were the first to demonstrate a FIR manifestation of a superconducting energy gap. Refinements in the experimental technique improved the signal to noise and led to the observation of experimental anomalies in Pb films that could be explained by strong-coupled superconducting theory. Time-resolved studies of ultrashort electrical pulse propagation along striplines have also been used to study the linear spectroscopy of superconductors. These latter measurements have demonstrated dispersion and attenuation of electrical pulses consistent with the presence of quasiparticles and a superconducting energy gap. In addition, linear FIR spectroscopy of high-T, materials has been extensively studied by a variety of techniques over the past few years. ' Recently, there has been heightened interest in the
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