Evidence for nonlocal electrodynamics in planar Josephson junctions

摘要

We study temperature dependence of the critical current modulation Ic(H) fortwo types of planar Josephson junctions: a low-Tc Nb/CuNi/Nb and a high-TcYBa2Cu3O7 bicrystal grain-boundary junction. At low T both junctions exhibit aconventional behavior, described by the local sine-Gordon equation. However, atelevated T the behavior becomes qualitatively different: the Ic(H) modulationfield deltaH becomes almost T-independent and neither deltaH nor the criticalfield for penetration of Josephson vortices vanish at Tc. Such an unusualbehavior is in good agreement with theoretical predictions for junctions withnonlocal electrodynamics. We extract absolute values of the London penetrationdepth from our data and show that a crossover from local to nonlocalelectrodynamics occurs with increasing T when London penetration depth becomeslarger than the electrode thickness.