Extended Einstein diffusion-mobility equation for two-dimensional Schr\"odinger-type quantum materials

We present the exact analytical equation of diffusion-mobility for two-dimensional (2D) Schr\"odinger type transport systems, from molecules to materials. The density of electronic states in such Schr\"odinger systems pertains to the 2D non-relativistic carrier dynamics. We implement the Gaussian function into carrier density derivation; accordingly we develop the electronic compressibility and diffusion-mobility for both the generic and the degenerate Fermi systems. This model is originally developed from generalized Einstein relation, along with concern about the thermodynamic effects on many-body interactions. The effect of interactions is included through the imperfect Fermi-gas entropy function. Our extended model explains the cooperative behavior of thermal and electronic counterparts on diffusion-mobility in disordered systems at wide temperature range. Using earlier experimental and theoretical results, we have shown the validity of our extended Einstein model for different 2D degenerate systems. The results validate the original Einstein equation at certain sets of temperature and chemical potential values for different Gaussian variances. Beyond those combinations, the deviation is observed. At very low temperature, the diffusion-mobility depends only on chemical potential, which is the extended Einstein equation for ideal quantum materials.

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