  Negative differential resistivity (NDR) in a (3+1)-dimensional quantum system
of strongly correlated charge carriers is theoretically reproduced by using the
AdS/CFT correspondence. Our system is microscopically defined, and the analysis
does not rely on any phenomenological models of NDR mechanism. The interaction
between the heat reservoir and the nonequilibrium charge carriers is also taken
into account. The system realizes insulation due to the formation of the
neutral bound states of the charge carriers at low temperatures. However, the
insulation is broken and the field-induced conductor phase appears by applying
the external electric field greater than the critical value. We find that the
NDR appears right above the critical electric field in this phase, and the pair
creation of the charge carriers is crucial to realize the NDR. The present
result suggests a possibility to observe a similar NDR in excitonic insulators
or in the strongly interacting quark-gluon plasma, where the insulation
originates in the formation of the neutral bound states.
