  The shot noise in tunneling experiments reflects the Poissonian nature of the
tunneling process. The shot noise power is proportional to both the magnitude
of the current and the effective charge of the carrier. Shot noise spectroscopy
thus enables, in principle, to determine the effective charge q of the charge
carriers that tunnel. This can be used to detect electron pairing in
superconductors: in the normal state, the noise corresponds to single electron
tunneling (q = 1e), while in the paired state, the noise corresponds to q = 2e.
Here, we use a newly developed amplifier to reveal that in typical mesoscopic
superconducting junctions, the shot noise does not reflect the signatures of
pairing and instead stays at a level corresponding to q = 1e. We show that
transparency can control the shot noise and this q = 1e is due to the large
number of tunneling channels with each having very low transparency. Our
results indicate that in typical mesoscopic superconducting junctions one
should expect q = 1e noise, and lead to design guidelines for junctions that
allow the detection of electron pairing.
