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Coherent multiple charge transfer in a superconducting NbN tunnel junction
1Kansai Advanced Research Center, National Institute of Information and Communications Technology, 588-2 Iwaoka, Iwaoka-cho, Nishi-ku, Kobe 651-2492, Japan.
Physical Review Letters
|August 11, 2005
Summary
We observed novel voltage steps in superconducting NbN tunnel junctions, indicating coherent multiple Andreev reflections. This finding advances understanding of quantum transport in Josephson junctions.
Area of Science:
- Solid State Physics
- Quantum Electronics
- Superconductivity
Background:
- Superconducting tunnel junctions are crucial for quantum electronics.
- Understanding charge transport mechanisms is key to developing advanced devices.
- Subharmonic gap structures and photon-assisted tunneling are important phenomena.
Purpose of the Study:
- To investigate shot noise and submillimeter-wave response in NbN tunnel junctions.
- To analyze the effective charge behavior and novel I-V curve features.
- To provide evidence for coherent multiple Andreev reflection processes.
Main Methods:
- Measurement of shot noise and submillimeter-wave response.
- Analysis of current-voltage (I-V) characteristics.
- Fabrication of NbN tunnel junctions with low barrier transparency.
Main Results:
- Observed a steplike function for effective charge as a function of voltage.
- Identified novel voltage steps (spaced by hv/2e) under submillimeter-wave radiation.
- Confirmed overlapping of these novel steps with ordinary photon-assisted tunneling steps (spaced by hv/e).
Conclusions:
- The observed phenomena provide clear evidence of coherent multiple Andreev reflection.
- These results highlight the importance of barrier transparency in NbN tunnel junctions.
- The study contributes to the fundamental understanding of quantum transport in superconducting devices.