Nonequilibrium mesoscopic conductance fluctuations as the origin of 1/f noise in epitaxial graphene

We investigate the $1/f$ noise properties of epitaxial graphene devices at low temperatures as a function of temperature, current, and magnetic flux density. At low currents, an exponential decay of the $1/f$ noise power spectral density with increasing temperature is observed that indicates mesoscopic conductance fluctuations as the origin of $1/f$ noise at temperatures below 50 K. At higher currents, deviations from the typical quadratic current dependence and the exponential temperature dependence occur as a result of nonequilibrium conditions due to current heating. By applying the Kubakaddi theory [S. S. Kubakaddi, Phys. Rev. B 79, 075417 (2009)], a model describing the $1/f$ noise power spectral density of nonequilibrium mesoscopic conductance fluctuations in epitaxial graphene is developed and used to determine the energy loss rate per carrier. In the regime of Shubnikov--de Haas oscillations, a strong increase of $1/f$ noise is observed, which we attribute to an additional conductance fluctuation mechanism due to localized states in quantizing magnetic fields. When the device enters the regime of quantized Hall resistance, the $1/f$ noise vanishes. It reappears if the current is increased and quantum Hall breakdown sets in.