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 oxides or nitrides have recently attracted interest as alternative plasmonic materials and extremely nonlinear thermal and optical materials. These materials attract research interest because they are CMOS compatible; hence, they can enable new functionalities within existing devices. 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 modeling of LEDD 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 analytical results can easily be applied to any LEDD materials.