  We employ classical molecular dynamics to study the nonlinear thermal
transport in graphene nanoribbons (GNRs). For GNRs under large temperature
biases beyond linear response regime, we have observed the onset of negative
differential thermal conductance (NDTC). NDTC is tunable by varying the manner
of applying the temperature biases. NDTC is reduced and eventually disappears
when the length of the GNR increases. We have also observed NDTC in triangular
GNRs, where NDTC exists only when the heat current is from the narrower to the
wider end. These effects may be useful in nanoscale thermal managements and
thermal signal processing utilizing GNRs.
