Radiative Processes, Spin Currents, Vortices

This chapter deals with developments that have their origin in subjects introduced in Chaps. 1 and 2. Gravitational Berry phases enable the formulation of an EFA which alters the dispersion relations of the particles interacting with the gravitational field. Hence, processes normally forbidden for kinematical reasons become physical in the presence of a gravitational field, as shown in Sect. 6.1. Section 6.2 deals with spin currents. These are currents in which the flow of spin can be separated from that of charge. This possibility has stimulated interest in fundamental spin physics. Spin control is an important issue in spin-based electronics and in all phenomena based on spin transport and dynamics. EFA makes possible the investigation of the transfer of angular momentum between external non-inertial fields and electron spins by means of the spin current tensor. The wave functions considered in Chap. 1 contain singularities that give rise to vortices. These are of interest in astrophysics, dark matter physics, and laboratory experiments. They are considered in Sect. 6.3. Some aspects of Zitterbewegung, or trembling motion, are studied in Sect. 6.4. In 1930, Schroedinger found that the electron velocity is not a constant of motion. Such an effect in vacuo must be quantum in nature. The expected trembling frequency and amplitude are not attainable with present experimental means. Zitterbewegung is a subject of intense interest in solid-state physics where its presence has been studied in crystalline solids, semiconductors, and graphene [1].