Full counting statistics for unconventional superconductor junctions
Tim Kokkeler
Donostia International Physics Center (DIPC), 20018 Donostia–San Sebastián, Spain
University of Twente, 7522 NB Enschede, The Netherlands
Noise power in hybrid junctions is a useful tool to reveal properties that can not be studied through the conductance alone. For instance, noise measurements show that transport carriers in conventional superconductors have charge 2e. At finite temperatures, next to the shot noise, also thermal noise plays an important role. We present a full counting statistics theory for unconventional superconductor / normal metal junctions of different types, incorporating the effect
of thermal noise on the differential Fano factor, the ratio of differential noise power and conductance. In junctions with unconventional superconductors there may exist surface Andreev bound states, which strongly impact the noise of the system, depending on their dispersion. If they are dispersionless, a negative differential Fano factor appears at finite temperatures, that is, the noise decreases with increasing voltage. In contrast, in the presence of dispersive surface Andreev bound states, the noise power always increases with voltage, but for finite temperatures there are local minima in the differential noise at those voltages corresponding to the extrema of the surface Andreev bound state spectrum. Our results highlight the importance of finite temperature effects in noise power measurements for potential unconventional superconductors, offering new means to determine pairing symmetries in unconventional superconductors.
[1] Kokkeler, T.H., Golubov, A.A., Bergeret, F. S. & Tanaka, Y., (2024). Full counting statistics for unconventional superconductor junctions,
