  Whereas thermal current noise $\langle I^2 \rangle$ in typical conductors is
proportional to temperature $T$, $\langle I^2 \rangle$ in graphene exhibits a
nonlinear $T$ dependence due to the massless nature of individual electrons.
This unique $\langle I^2 \rangle$ arising from individually massless electrons
is intimately linked to the non-zero collective mass of graphene electrons;
namely, $\langle I^2 \rangle$ is set by the equipartition theorem applied to
the collective mass's kinetic energy, with the nonlinear $T$-dependence arising
from the $T$-dependence of the collective mass. This link between thermal
fluctuation and collective dynamics unifies $\langle I^2 \rangle$ in graphene
and typical conductors, while elucidating the uniqueness of the former at the
same time.
