ABSTRACT
In this chapter, the authors show that in the pumped graphene bilayer, the indirect interband radiative transitions accompanied by scattering of carriers by disorder can provide a substantial negative contribution to the terahertz (THz) conductivity. They demonstrate that the indirect interband contribution to the THz conductivity in a graphene bilayer with the extended defects (such as charged impurity clusters) can surpass by several times the fundamental limit associated with the direct interband transitions, and the Drude conductivity as well. The authors show that the intraband radiation absorption in disordered graphene bilayer does not actually pose a problem for the THz lasing. The absence of a band gap in the atomically thin carbon structures, such as graphene and graphene bilayer, enables their applications in different THz and infrared devices. The authors demonstrate that the graphene bilayer with a long-range disorder (nanometre-scale impurity clusters) can exhibit a strong negative THz conductivity with the span two times or more exceeding the fundamental limit.
