Nonequilibrium Majorana fluctuations

Nonequilibrium physics of random events, or fluctuations, is a unique fingerprint of a given system. Here we demonstrate that in noninteracting systems, whose dynamics is driven by Majorana states, the effective charge $e^*$, characterizing the electric current fluctuations, is fractional. This is in contrast to noninteracting Dirac systems with the trivial electronic charge, $e^*=e$. Quite the opposite, in the Majorana state we predict two different fractional effective charges at low and high energies, $e^*_l=e/2$ and $e^*_h=3e/2$, accessible at low and high bias voltages, respectively. We show that while the low energy effective charge $e^*_l$ is sensitive to thermal fluctuations of the current, the high energy effective charge $e^*_h$ is robust against thermal noise. A unique fluctuation signature of Majorana fermions is, therefore, encoded in the high voltage tails of the electric current noise easily accessible in experiments on strongly nonequilibrium systems even at high temperatures.