Dissipative Enhancement of the Supercurrent in Tl2Ba2CaCu2O8 Intrinsic Josephson Junctions

01 January 2009

Warburton PA, Saleem S, Fenton JC, Korsah M, Grovenor CR

Physical review letters Y. 2009, vol. 103, No. 21, [217002.1-217002.4] ISSN : 0031-9007

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In the high-temperature superconductor Tl2Ba2CaCu2O8 the c-axis coherence length (~ 2?) is less than the separation of adajacent cuprate double-planes (~ 15 ?). Hence adjacent cuprate double-planes are intrinsically Josephson-coupled. When the bias current flows perpendicular to the planes, the resulting d.c. current-voltage characteristics resemble those of an array of underdamped Josephson junctions. I will discuss our experiments on sub-micron-scale intrinsic Josephson junctions using Tl2Ba2CaCu2O8 thin films. In addition to observing several well-known Josephson phenomena we have observed a number of effects related to the fact that the dynamics of the intrinsic junctions at the plasma frequency are moderately damped (Q ~ 8) – i.e. falling between the well-understood underdamped and overdamped regimes. This results in a number of counter-intuitive experimental observations including a suppression of thermal fluctuations as the temperature is increased and a shift of the skewness of the switching current distributions from negative at low temperatures to positive at high temperatures. Simulations of the dynamics confirm that these phenomena result from repeated (~103) phase slips as the junction undergoes a transition from the zero-voltage state to the running state. We further show by both experiment [1] and simulation [2] that increased dissipation counter-intuitively increases the supercurrent in the moderate damping regime. This leads to the anomalous switching order often observed in arrays of intrinsic junctions.