2D electron-phonon physics from first-principles
Reduced dimensionality has consequences for phonons and electron-phonon interactions. So does the use of gates to dope the layer within the typical field-effect setups used in experiments. In this second lecture, I will describe density-functional perturbation approaches developed to explore those consequences. First-principles results will be supported by analytical models and intuitive explanation of the mechanisms at play. I will first present the general physics of polar-optical phonons, relevant for any semiconductor with more than one element. The energetics and electron-phonon interactions associated with those modes strongly depends on dimensionality and the environment. I will then discuss different consequences of field-effect doping, from standard free-carrier screening to more subtle and surprising mechanisms in transition-metal dichalcogenides and graphene. Finally, I will discuss remote electron-phonon interactions in van der Waals heterostructures. Indeed, the proximity of the different layers stacked on top of each other implies the possibility for the phonons of one layer to interact with the electrons of another.