Recent advances in nanoscience have demonstrated that fundamentally new physical phenomena may be found when the size of samples shrinks. In the area of superconductivity, the reduction of sample size has led to the observation of the paramagnetic Meissner effect in micronsize superconductors (1), the quantization of the Bose condensate in submicron samples (2), and ultimately the suppression of superconductivity in nanometer-scale superconductors (3,4). In this regime, it has also been recognized that the sample topology has particularly strong effects on superconductivity, as reflected in the characteristic features of the phase diagrams for singly-and doubly-connected samples (5,6).A unique feature of doubly-connected superconductors (independent of the sample size) is

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We have studied the temperature dependence of the critical current I c of bilayer Pb/Sr 2 RuO 4 /Pb junctions prepared by using a submicron-diameter filament as a shadow mask. Sr 2 RuO 4 , a layered perovskite isostructural with La 2 CuO 4 , has a superconducting transition temperature (T c ) lower than that of Pb. Below the T c of Pb, the critical current I c of the junction was found to increase initially with decreasing temperature. As the temperature was lowered to below the T c of Sr 2 RuO 4 , however, a sharp drop in I c was observed. This downturn in I c suggests that superconductivity in Sr 2 RuO 4 actually suppresses the Josephson coupling between the two Pb electrodes, which are conventional s-wave superconductors. The implications of this unexpected behavior will be explored, in particularly, in the context of the pairing symmetry in Sr 2 RuO 4 .

Resistance of disordered superconducting Au0.7In0.3 cylindrical films was measured as a function of applied magnetic field. In the high-temperature part of the superconducting transition regime, the resistance oscillated with a period of h/2e in the unit of the enclosed magnetic flux. However, at lower temperatures, the resistance peaks split. We argue that this splitting is due to the emergence of an oscillation with a period of h/4e, half of the flux quantum for paired electrons. The possible physical origin of the h/4e resistance oscillation is discussed in the context of new minima in the free energy of a disordered superconducting cylinder.c EDP Sciences

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