  Thermal runaway occurs when a rise in system temperature results in heat
generation rates exceeding dissipation rates. Here we demonstrate that thermal
runaway occurs in thermal radiative systems, given a sufficient level of
negative differential thermal emission. By exploiting the insulator-to-metal
phase transition of vanadium dioxide, we show that a small increase in heat
generation (e.g., 10 nW/mm2) can result in a large change in surface
temperature (e.g., ~35 K), as the thermal emitter switches from high emissivity
to low emissivity. While thermal runaway is typically associated with
catastrophic failure mechanisms, detailed understanding and control of this
phenomenon may give rise to new opportunities in infrared sensing, camouflage,
and rectification.
