Introduction to Light Polarization-Dependent Photocurrent—Phenomenology

In this chapter, we mainly provide a necessary background about the phenomenology of low-order non-linear response resulting in a dc photocurrent expression. Briefly, there are two major effects, photogalvanic effect—PGE and photon drag effect—PDE, both having specific conditions for linearly and circularly polarized light irradiation, leading to LPGE, CPGE and LPDE, CPDE currents, respectively. The origin of current due to latter effects is straightforward to understand; namely, the LPDE and CPDE do not require non-centrosymmetry of the material system; they still are dependent on time-reversal symmetry, related to bulk rather than surfaces or interfaces, and expected to vanish at normal incidence. On the other hand, the former effects require at least local non-centrosymmetry; their dependence on time reversal is different, namely the LPGE and CPGE are odd and even under time reversal, respectively. They are rather surface and interface effects, which makes them nonvanishing for normal incidence of light in real material systems with non-negligible field effects and imperfections. All these are related to the geometry of the material system and the light propagation.