Optical absorption of light carrying orbital angular momentum by semiconductors: free-particle quantum kinetics

We develop a free-carrier theory of the optical absorption of light carrying orbital angular momentum (twisted light) by bulk and quasi-two-dimensional semiconductors. We obtain the optical transition matrix elements for Bessel-mode twisted light and use them to calculate the wave function of photo-excited electrons to first-order in the vector potential of the laser [1]. We then pose the problem of the quantum kinetics of interband transitions in terms of the Heisenberg equations of motion of the electron populations, and interband and intraband coherences [2]. We solve the equations of motion in the low-excitation regime, and obtain analytical expressions for the coherences and populations; with these, we calculate the orbital angular momentum transferred from the light to the electrons and the paramagnetic and diamagnetic electric current densities. \\[4pt] [1] G.\ F.\ Quinteiro and P.\ I.\ Tamborenea, EPL {\bf 85}, 47001 (2009).\\[0pt] [2] G.\ F.\ Quinteiro and P.\ I.\ Tamborenea, Phys.\ Rev.\ B {\bf 82}, 125207 (2010).