Determination of the coherence length in high-mobility semiconductor- coupled Josephson weak links

Abstract

A Nb-InAs-Nb superconductor-semiconductor-superconductor weak link based on a high-mobility homoepitaxial n-InAs film was reported recently [Akazaki, Kawakami, and Nittu J. Appl. Phys. 66, 6121 (1989)]. Measurements of the electron concentration, effective mass, and mobility allowed the coherence length in the normal link to be calculated. The mobility was high enough that the dirty limit was not applicable in the temperature range (∼2-7 K) over which the device critical current was measured. The temperature dependence of the critical current could not be fit by the usual theoretical form, even though an expression for the coherence length was used that should be applicable in both the clean and dirty limits. In this paper is demonstrated an excellent fit to the data, obtained by using the magnitude of the coherence length as a fitting parameter and assuming the dirty limit temperature dependence. This implies a coherence length proportional to T-1/2 but far shorter than that calculated from the known material parameters. It is suggested that a different scaling length may apply in high-mobility devices.