FULL COUNTING STATISTICS OF SUPERCONDUCTOR--NORMAL-METAL HETEROSTRUCTURES

摘要

In 1918 Schottky discovered that the fluctuations in vacuum diodes can be related to the discrete nature of the charge carriers. His observation was that the power spectrum of the current fluctuations gave direct access to the charge e of the discrete carriers responsible for the current. From his theoretical considerations he found a relation between the noise power of the current fluctuations S_I and the average current I, S_I = 2eI,(1) a result nowadays known as the Schottky formula. Its consequence is, that the current noise provides information on the transport process, which is not accessible through conductance measurements only. Studies of the noise properties of tunnel-junctions renewed the interest in noise later. Since about ten years the investigation of transport in quantum coherent structures has boosted the interest in the theory of current noise in mesoscopic structures. Correlations in the transport of fermions have lead to a number of interesting predictions. For example, the noise of a single channel quantum contact of transparency T at zero temperature has the form S_I =2eI(1-T). The noise is thus suppressed below the Schottky value, Eq. (1). The suppression is a direct consequence of the Pauli principle, and is therefore specific to electrons. Particles with bosonic statistics or classical particles show a different behaviour, e. g. for Bosons the noise is enhanced by a factor 1 + T. A convenient measure of the deviation from the Schottky result is the so-called Fano factor F = S_I/2eI.