Time dependent weak localization of a 2DEG in the presence of Andreev reflections
- Univ. of California, Santa Barbara, CA (United States); and others
Experiments on superconducting-normal-superconducting, SNS, junctions, comprised of Nb-2D InAs - Nb, exhibit AC currents at v = 4eV/h, twice the Josephson frequency. These currents can be ascribed to time dependent weak localization in the 2D InAs electron gas modulated by the presence of superconducting electrodes. The change of the current-voltage characteristic of a SNS structure under far-infrared (FIR) illumination (180GHz, 300GHz) has been investigated as a function of temperature, FIR power and magnetic field. The sample is an InAs/AlSb quantum well with a 1{mu}m-period Nb grating contacting the InAs. In the experiments a series connection of N = 300 junctions is measured. The differential resistance of the sample shows a very clear subharmonic gap structure, indicating multiple Andreev reflections between the SN-interfaces. Below a temperature of about T = 5K the sample is superconductive. At sufficiently high temperatures (T > 6K) the photoresponse of the sample under FIR illumination exhibits only a single resonance. This resonance is at V = Nhv/4e, that is half the voltage at which the first step of the AC Josephson effect would occur. B.Z. Spivak and D.E. Khmel`nitskii predicted this effect which arises from the quantum correction of the conductivity of a normal state electron gas due to Andreev reflections. Electrons and holes that are Andreev reflected at the superconductor interface acquire a phase shift that is determined by the phase {Phi} of the superconductor. Interference terms of time reversed paths that include Andreev reflections on adjacent superconductor stripes oscillate with 2({Phi}{sub 2}-{Phi}{sub 1}) = 4eVt/h and therefore lead to a time-dependent conductivity. The manifestation of the oscillating conductivity in the experiments is similar to the Shapiro steps of the AC Josephson effect but with twice the frequency. The experiments show that this effect is very sensitive to an applied magnetic field.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States)
- OSTI ID:
- 238894
- Report Number(s):
- BNL-61982-Absts.; CONF-9508156-Absts.; ON: DE96002729; TRN: 96:013388
- Resource Relation:
- Conference: 17. international free electron laser conference, New York, NY (United States), 21-25 Aug 1995; Other Information: PBD: [1995]; Related Information: Is Part Of 17th international free electron laser conference and 2nd international FEL users` workshop. Program and abstracts; PB: 300 p.
- Country of Publication:
- United States
- Language:
- English
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