Terahertz dispersion and amplification under electron streaming in graphene at 300 K

We interpret the recent observations of Otsuji's team (Sendai) on switching from absorption to amplification at a temperature of $T$ = 300 K during the passage of terahertz radiation through hexagonal boron nitride–graphene sandwiches with multiple gates on the surface with an increase in the electric field in graphene. It is shown that these effects are related to dispersion and negative conductivity near the transit-time frequency of electrons in momentum space under streaming (anisotropic distribution) in graphene in a strong electric field. On the basis of these data, a universal tunable terahertz source is proposed, which has the form of a graphene-containing sandwich with a high-resistance silicon wafer (a cavity) with an applied voltage. This terahertz cavity is a complete analog of the microwave generator implemented on an InP chip by Vorobev's team (St. Petersburg).