Generalized Form of Response Functions

Abstract

In this chapter we will discuss generalized forms of response functions. This is necessary since we will discuss in the following chapters not only excitations of the solids by electromagnetic radiation. In particular, excitation with charged and neutral particles will be important. In such cases not only the energy but also the momentum of the perturbing probe and of the excited quasi-particles must be discussed. A generalized dielectric function must consider all such excitations.