Nonequilibrium transport in mesoscopic multi-terminal SNS Josephson junctions

Abstract

We report the results of several nonequilibrium experiments performed on superconducting/normal/superconducting (S/N/S) Josephson junctions containing either one or two extra terminals that connect to normal reservoirs. Currents injected into the junctions from the normal reservoirs induce changes in the electron energy distribution function, which can change the properties of the junction. A simple experiment performed on a 3-terminal sample demonstrates that quasiparticle current and supercurrent can coexist in the normal region of the S/N/S junction. When larger voltages are applied to the normal reservoir, the sign of the current-phase relation of the junction can be reversed, creating a "π-junction." We compare quantitatively the maximum critical currents obtained in 4-terminal π-junctions when the voltages on the normal reservoirs have the same or opposite sign with respect to the superconductors. We discuss the challenges involved in creating a "Zeeman" π-junction with a parallel applied magnetic field and show in detail how the orbital effect suppresses the critical current. Finally, when normal current and supercurrent are simultaneously present in the junction, the distribution function develops a spatially inhomogeneous component that can be interpreted as an effective temperature gradient across the junction, with a sign that is controllable by the supercurrent. Taken as a whole, these experiments illustrate the richness and complexity of S/N/S Josephson junctions in nonequilibrium situations. PACS numbers: 74.50.+r, 85.25.Am, 85.25.Cp

Nonlocal correlations in a proximity-coupled normal-metal

“…At lower temperatures, however, they show a weaker temperature dependence. This latter behavior has been observed previously by other groups, 24 and arises from the reduction of I c due to the nonequilibrium quasiparticle distribution introduced by I qp .…”

“…In SNS structures with Josephson coupling between two superconducting electrodes, supercurrents and quasiparticle currents can coexist in a proximity-coupled normal metal over distances much longer than ξ S . [22][23][24] As the superconducting electrodes S 1 and S 2 are Josephson-coupled at low enough temperatures, they are at the same electrochemical potential, which we take to be 0 here for simplicity. A finite potential V applied to the current injection electrode N 1 will drive a quasiparticle current I qp into the proximity-coupled normal metal as shown in Fig.…”

Intrinsic spin-orbit interaction in diffusive normal wire Josephson weak links: Supercurrent and density of states

“…Similar physics as in the superconductorferromagnet-superconductor case can be envisaged as long as the orbital effect of the magnetic field is weak enough [8,9] and does not limit the supercurrent. Such a situation takes place especially in narrow nanowires, where the spinsplitting field in combination with the Rashba-type spin-orbit (SO) interaction has been used in an effort to take these wires to the limit of topological superconductivity [10][11][12] for the detection of Majorana-type excitations at the edges of the wires.…”

Origin of Hysteresis in a Proximity Josephson Junction

“…Nevertheless, a significant hysteresis is routinely observed in lateral junctions as soon as their critical current is large: once the junction has switched to the resistive branch, it does not recover the superconducting state until the bias current is decreased to a significantly smaller retrapping current I r . This observation does not depend on the nature of the weak link, as was observed early in superconducting constrictions and microbridges [2 -4], and more recently in superconducting nanowires [5], normal metals [6,7], twodimensional electron gases [8], semiconductor nanowires [9], carbon nanotubes [10], and graphene [11]. Two main explanations have been proposed.…”