In memory of Leonid Veniaminovich Keldysh. From the archive
Coherent states of excitons
L.V. Keldysh Lebedev Physical Institute, Russian Academy of Sciences, Leninsky prosp. 53, Moscow, 119991, Russian Federation
The concept of a coherent exciton state is formulated. It is shown that for this state the macroscopic wave function may be introduced which satisfies a nonlinear equation of the type familiar in the phenomenological theory of a superfluid liquid. The corresponding nondissipative flux is the flux of energy. For excitons interacting with an electromagnetic field, a coupled system of Maxwell equations and Ginzburg—Pitaevskii (phenomenological theory of Bose liquid) type equations is obtained.