Abstract
The Josephson effect is a fundamental quantum phenomenon where a dissipationless supercurrent is introduced in a weak link between two superconducting electrodes by Andreev reflections. The physical details and topology of the junction drastically modify the properties of the supercurrent and a strong enhancement of the critical supercurrent is expected to occur when the topology of the junction allows an emergence of Majorana bound states. Here we report charge transport measurements in mesoscopic Josephson junctions formed by InAs nanowires and Ti/Al superconducting leads. Our main observation is a colossal enhancement of the critical supercurrent induced by an external magnetic field applied perpendicular to the substrate. This striking and anomalous supercurrent enhancement cannot be described by any known conventional phenomenon of Josephson junctions. We consider these results in the context of topological superconductivity, and show that the observed critical supercurrent enhancement is compatible with a magnetic field-induced topological transition.
Highlights
The Josephson effect is a fundamental quantum phenomenon where a dissipationless supercurrent is introduced in a weak link between two superconducting electrodes by Andreev reflections
In the first approximation it is known that a magnetic field destroys superconductivity via the orbital and paramagnetic effect, and one would expect a monotonic decay of the critical current by the application of an external field
An experimental exception to this behaviour is represented by field-enhanced superconductivity observed in Josephson junctions made with metallic NWs covered with magnetic impurities
Summary
The Josephson effect is a fundamental quantum phenomenon where a dissipationless supercurrent is introduced in a weak link between two superconducting electrodes by Andreev reflections. Our main observation is a colossal enhancement of the critical supercurrent induced by an external magnetic field applied perpendicular to the substrate This striking and anomalous supercurrent enhancement cannot be described by any known conventional phenomenon of Josephson junctions. Coupling a conventional s-wave superconductor (S) to materials based on helical electrons such as topological insulators or semiconductors with strong spin-orbit (SO) interaction like InAs or InSb nanowires (NWs) leads to an unconventional p-wave superconductor. The latter may undergo a topological transition, and become a topological superconductor (TS) hosting exotic edge states with Majorana-like character[1,2]. No final conclusions can be drawn from such an analysis, we stress that a topological transition appears to be fully compatible from a qualitative point of view with the observed phenomenology: our proposed physical scenario consists of a magnetically driven zero-energy parity crossing of Andreev levels in the junction[21] which is expected to occur for magnetic fields applied perpendicularly to the wire SO axis, exactly as observed in the experiment
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