Speaker
Description
Dirac crystals are zero-bandgap semiconductors in which the valence and conduction bands are linear over the crystal momentum (and, therefore, non-dispersive) in the proximity of the Fermi level at the Brillouin zone boundary. They are therefore the quantum material analogue of the Dirac cone of light in special relativity. To understand a number of different properties of 2D Dirac crystals (including their electron-related lattice thermal conductivity) demands models that consider the interaction between valence electrons and acoustic phonons beyond perturbation theory in these strongly correlated quantum systems. It is commonly assumed that the exceptionally high thermal conductivity of two-dimensional (2D) Dirac crystals is due to nearly ideal phonon gases. Therefore, electron-phonon collisions, when present, may control the thermal transport. Nonetheless, their accurate description beyond first-order collisions has seldom been undertaken. The Fermi level, and therefore the concentration of conduction electrons in 2D Dirac crystals can be tuned by many forms of doping, which also controls the acoustic phonon scattering rate by electrons.
Here, we are using a modified formulation of the Lindhard model for electron screening by phonons in strongly correlated systems to demonstrate that a proportional relationship exists between electron-lattice thermal conductivity and the phonon scattering rate, for bands of electrons and phonons that are linear over the crystal momentum. Furthermore, although the phonon scattering rate is usually calculated in the literature only at the first-order degree (i.e., with EP-E and E-EP processes consisting of 2 electrons and 1 phonon) we are here presenting an accurate expression for the phonon scattering rate and the electron-phonon interaction that is calculated at the higher order, where electron-in/phonon-in, electron-out/phonon-out (EP-EP) processes are also considered. We show that, even at temperatures as small as 300 K, the EP-EP* become critical in the accurate determination of the phonon scattering rates and, therefore the electron-lattice thermal transport. Collectively, our work points at the necessity of an accurate description of the electron-phonon interaction to comprehensively understand the electron-related lattice properties of strongly-correlated 2D Dirac crystals.
Keyword-1 | 2D Dirac crystalas |
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Keyword-2 | Electron-phonon interaction |
Keyword-3 | Theoretical condensed matter |