Hermash K. Electromagnetic properties of electron-hole counterflow superconductors with the Dirac spectrum of charge carriers.

The thesis is dedicated to the theoretical study of electromagnetic properties of double layer graphene systems and heterostructures based on topological insulators with electron-hole pairing. It is established that the electron-hole pairing in the double layer graphene system leads to the complete (at zero temperature) or partial (at nonzero temperature) suppression of screening of the electrical field of a point charge. It is predicted the appearence of peaks in reflection and absorption of an electromagnetic wave at the frequency w=2D (2D is the gap in the quasiparticle spectrum). It is shown that the electron-hole pairing leads to splitting of the surface optical plasmon TM-mode in the double layer graphene system into two branches: a low-energy (weakly damped, w<2D) and high-energy (strongly damped, w>2D) ones. On the example of a double layer graphene system, it is found that the Anderson–Bogoliubov, Schmid and Carlson–Goldman collective modes can exist in the counterflow superconductor. It is revealed that electron-hole pairing causes a significant increase in the intensity of the third harmonic generation. The conditions of the appearing of the state with electron-hole pairing in heterostructures based on topological insulator in a magnetic field were determined and the temperature of transition of a gas of electron-hole pairs into the superfluid state was found.