  We predict the emergence of novel collective electronic excitations in warm
dense matter with an inhomogeneous electronic structure based on
first-principles calculations. The emerging modes are controlled by the imposed
perturbation amplitude. They include satellite signals around the standard
plasmon feature, transformation of plasmons to optical modes, and
double-plasmon modes. Most importantly, these modes exhibit a pronounced
dependence on the temperature. This makes them potentially invaluable for the
diagnostics of plasma parameters in the warm dense matter regime. We
demonstrate that these modes can be probed with present experimental
techniques.

Plasma Physics