  Quadratic detection in linear mesoscopic transport systems produces cross
terms that can be viewed as interference signals reflecting statistical
properties of charge carriers. In electronic systems these cross term
interferences arise from exchange effects due to Pauli principle. Here we
demonstrate fermionic Hanbury Brown and Twiss (HBT) exchange phenomena due to
indistinguishability of charge carriers in a diffusive graphene system. These
exchange effects are verified using current-current cross correlations in
combination with regular shot noise (autocorrelation) experiments at microwave
frequencies. Our results can be modeled using semiclassical analysis for a
square-shaped metallic diffusive conductor, including contributions from
contact transparency. The experimentally determined HBT exchange factor values
lie between the calculated ones for coherent and hot electron transport.
