Fig. 2: Bias dependence of the conductance and giant shot noise in a V/MgO/Fe junction.
a Conductance for a superconductor/ferromagnet (S/F) sample (sketched in the left), above (red) and below (blue) the critical temperature of vanadium, TC, normalized by the conductance at bias V = −5 mV, above the effective superconducting gap, Δ, -e is the electron charge. Inset: TC identified by the measured temperature-dependent subgap conductance. b For the same sample, there is giant shot noise below TC (blue) at low bias, eV < Δ, compared to its value above TC (red), and its corresponding theoretical maximum value given by the Fano factor, F = 1 (green), for the normal state. c The evolution of the shot noise power with frequency, f, and V, shown in the logarithmic scale. The noise spectrum is largely f independent, except near the lowest f. d, e Comparison of the bias-dependent conductance and shot noise with the control V/MgO/Au junction, with the same normalization as in (a). f Schematic role of the MgO/Au nonepitaxial growth leading to the highly textured interface and suppressed filtering due to different orbital symmetries.
