AC Non-equilibrium Supercurrents: The Unusually Strong Half-integer Shapiro Step in Mesoscopic SNS Junctions
Abstract
We investigate AC non-equilibrium supercurrents by microwave irradiation of superconducting-normal metal-superconducting (SNS) Josephson junctions, formed by coupling Nb electrodes with a high quality InAs quantum well. A junction fabricated by optical lithography, with a separation of 1.2μm between Nb electrodes exhibits a critical current(I_c) of 75μA at 1.8K. The junction also shows clear sub-gap structure, the hallmark of multiple Andreev reflection. At 4.2K the junction appears resistive (I_c<500nA). Nevertheless, at 4.2K when irradiated with 15GHz this junction clearly shows an integer and, much larger, half-integer Shapiro step. This behavior was first observed in grating arrays of Nb-InAs SNS junctions[1], but the grating made comparison with theory difficult. We compare our results in single junctions with a recent model of non-equilibrium supercurrents in Andreev-coupled SNS junctions[2], and discuss how we distinguish these supercurrents from more conventional nonlinear behavior. ([1] Surface Science v.361-362 306 (1996), [2] cond-mat/9709001). Work supported by ONR and QUEST, an NSF Science and Technology Center.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 1998
- Bibcode:
- 1998APS..MAR.Q3304L