Browsing by Author "Coskun, UC"

Now showing 1 - 3 of 3
  • Thumbnail Image
    ItemOpen Access
    Pb-Graphene-Pb josephson junctions: Characterization in magnetic field
    (IEEE Transactions on Applied Superconductivity, 2012-06-14) Borzenets, IV; Coskun, UC; Mebrahtu, H; Finkelstein, G
    We fabricate superconductor-graphene-superconductor Josephson junctions with superconducting regions made of lead (Pb). The critical current through graphene may be modulated by the external magnetic field; the resulting Fraunhofer interference pattern shows several periods of oscillations, suggesting that the junction is uniform. Deviations from the perfect Fraunhofer pattern are observed, and their cause is explained by a simulation that takes into account the sample design. © 2002-2011 IEEE.
  • Thumbnail Image
    ItemOpen Access
    Phase diffusion in graphene-based Josephson junctions.
    (Physical review letters, 2011-09-21) Borzenets, IV; Coskun, UC; Jones, SJ; Finkelstein, G
    We report on graphene-based Josephson junctions with contacts made from lead. The high transition temperature of this superconductor allows us to observe the supercurrent branch at temperatures up to ∼2 K, at which point we can detect a small, but nonzero, resistance. We attribute this resistance to the phase diffusion mechanism, which has not been yet identified in graphene. By measuring the resistance as a function of temperature and gate voltage, we can further characterize the nature of the electromagnetic environment and dissipation in our samples.
  • Thumbnail Image
    ItemOpen Access
    Phonon bottleneck in graphene-based Josephson junctions at millikelvin temperatures.
    (Physical review letters, 2013-07-09) Borzenets, IV; Coskun, UC; Mebrahtu, HT; Bomze, Yu V; Smirnov, AI; Finkelstein, G
    We examine the nature of the transitions between the normal and superconducting branches in superconductor-graphene-superconductor Josephson junctions. We attribute the hysteresis between the switching (superconducting to normal) and retrapping (normal to superconducting) transitions to electron overheating. In particular, we demonstrate that the retrapping current corresponds to the critical current at an elevated temperature, where the heating is caused by the retrapping current itself. The superconducting gap in the leads suppresses the hot electron outflow, allowing us to further study electron thermalization by phonons at low temperatures (T≲1 K). The relationship between the applied power and the electron temperature was found to be P∝T3, which we argue is consistent with cooling due to electron-phonon interactions.