The electronic and thermal response of low electron density Drude materials to ultrafast optical illumination

Many low electron density Drude (LEDD) materials such as transparent conductive oxide or nitrides have recently attracted interest as alternative plasmonic materials and future nonlinear optical materials. However, the rapidly growing number of experimental studies has so far not been supported by a systematic theory of the electronic, thermal and optical response of these materials. Here, we use the techniques previously derived in the context of noble metals to go beyond a simple electromagnetic modelling of low electron density Drude materials and provide an electron dynamics model for their electronic and thermal response. We find that the low electron density makes momentum conservation in electron-phonon interactions more important, more complex and more sensitive to the temperatures compared with noble metals; moreover, we find that electron-electron interactions are becoming more effective due to the weaker screening. Most importantly, we show that the low electron density makes the electron heat capacity much smaller than in noble metals, such that the electrons in LEDD materials tend to heat up much more and cool down faster compared to noble metals. While here we focus on indium tin oxide (ITO), our analytic results can be easily applied to any LEDD materials.