Spin-orbit interactions of light in isotropic media

Abstract

Introduction Spin-orbit interaction in quantum physics The term spin-orbit interaction (SOI) is known from quantum physics, where it describes the coupling between the spin and orbital angular momentum (AM) of electrons or other quantum particles [1]. The SOI is usually interpreted as an electromagnetic interaction of the moving magnetic moment of the electron with an external electric field. However, in central fields the SOI Hamiltonian becomes proportional to the product of the spin AM (SAM) and orbital AM (OAM). Furthermore, the geometric Berry-phase description of the SOI uncovered that it is basically related to the intrinsic AM properties of the particle and is largely independent of the particular character of interaction with the external field [2–4]. The SOI can take various forms in different systems, but the unifying feature in all cases is the coupling between the spin and momentum of the particle [5]. There are two basic manifestations of the SOI of electrons. First, the SOI brings about the fine splitting of the energy levels in the finite orbital motions, e.g., in potential wells or magnetic fields [1, 6, 7]. This can be regarded as the Berry-phase contribution to the quantization of orbits [8–11]. Second, due to the SOI upon free motion in an external field the electron undergoes a transverse spin-dependent deflection known as the spin Hall effect [4, 5, 12–14]. This effect is a dynamical (transport) manifestation of the Berry phase closely related to the Coriolis effect [15, 16], and conservation of the total AM of the particle [12].