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Observation of photon-assisted noise in a diffusive normal metal-superconductor junction
Kozhevnikov1, Schoelkopf, Prober
1Departments of Physics and Applied Physics, Yale University, New Haven, Connecticut 06520-8284, USA.
Physical Review Letters
|October 6, 2000
Summary
Measurements reveal that the shot noise in diffusive normal metal-superconductor junctions is double that of normal conductors. Photon-assisted processes indicate an effective charge of 2e, confirming Andreev reflection in these superconducting devices.
Area of Science:
- Condensed matter physics
- Quantum electronics
- Superconductivity
Background:
- Understanding noise in electronic devices is crucial for developing sensitive measurement tools.
- Diffusive normal metal-superconductor (N-S) junctions exhibit unique quantum phenomena due to Andreev reflection.
- Nonequilibrium noise measurements probe fundamental charge transport properties.
Purpose of the Study:
- To measure nonequilibrium noise in diffusive N-S junctions under dc bias and ac excitation.
- To investigate the influence of high-frequency ac fields on shot noise characteristics.
- To determine the effective charge of current carriers in N-S junctions.
Main Methods:
- Fabrication and characterization of diffusive normal metal-superconductor junctions.
- Measurement of shot noise under applied dc bias.
- Application of high-frequency ac excitation and analysis of noise spectra.
Main Results:
- Shot noise in diffusive N-S junctions is twice that observed in normal diffusive conductors.
- Features in shot noise spectra at bias voltages |V| = hnu/(2e) indicate photon-assisted processes.
- These features provide evidence for an effective charge of 2e.
Conclusions:
- Andreev reflection in diffusive N-S junctions leads to a doubled shot noise compared to normal conductors.
- Photon-assisted transport phenomena are observed, confirming the role of Cooper pairs.
- The effective charge of current carriers in these junctions is demonstrated to be 2e.
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