Observation of Andreev Reflection Enhanced Shot Noise
P. Dieleman, H.G. Bukkems, T.M. Klapwijk, M. Schicke, and K.H., Gundlach
TL;DR
This study experimentally demonstrates that multiple Andreev reflection processes in superconductor-insulator-superconductor junctions significantly enhance shot noise beyond theoretical predictions, due to charge clustering effects.
Contribution
It provides experimental evidence linking Andreev reflection to shot noise enhancement in NbN/MgO/NbN junctions, highlighting the role of barrier pinholes.
Findings
Shot noise exceeds theoretical expectations.
Charge clustering due to Andreev reflections increases noise.
Voltage-dependent charge transfer enhances shot noise.
Abstract
We have experimentally investigated the quasiparticle shot noise in NbN/MgO/NbN superconductor - insulator - superconductor tunnel junctions. The observed shot noise is significantly larger than theoretically expected. We attribute this to the occurrence of multiple Andreev reflection processes in pinholes present in the MgO barrier. This mechanism causes the current to flow in large charge quanta (Andreev clusters), with a voltage dependent average value of m = 1+ 2 Delta/eV times the electron charge. Because of this charge enhancement effect, the shot noise is increased by the factor m.
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