• A K Gupta

      Articles written in Pramana – Journal of Physics

    • Harmonic generation in superconducting Bi(Pb)SrCaCuO thick films

      S K Shrivastava Neeraj Khare A K Gupta

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      We present a detailed study of harmonic generation in Bi(Pb)SrCaCuO superconducting thick film prepared by screen printing technique. A comparative study of amplitude of harmonics of two films of different Jc have been carried out. The variation of amplitudes of the harmonics are studied as a function of magnitude of ac and dc field. The temperature dependence of amplitude of third harmonic (V3) is studied with increasing amplitude as well as frequency of ac field. These results are analyzed in the frame work of critical state model. V3-T curve also indicates the presence of two phases in Bi(Pb)SrCaCuO film.

    • Anomalous density of states in hybrid normal metal-superconductor bilayers

      A K Gupta L Crétinon B Pannetier H Courtois

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      In contact with a superconductor, the Andreev reflection of the electrons locally modifies the N metal electronic properties, including the local density of states (LDOS). We investigated the LDOS in superconductor-normal metal (Nb-Au) bilayers using a very low temperature (60 mK) STM on the normal metal side. High resolution tunneling spectra measured on the Au surface show a clear proximity effect with an energy gap of reduced amplitude compared to the bulk Nb gap. The dependence of this mini-gap width with the normal metal thickness is discussed in terms of the Thouless energy. Within the mini-gap, the density of states does not reach zero and shows clear sub-gap features. We compare the experimental spectra with the well-established quasi-classical theory.

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