Theory for Spin-Polarized Oscillations in Nonlinear Optics due to Quantum Well States

Using an electronic tight-binding theory we calculate the nonlinear magneto-optical response from an $x-\mathrm{C}\mathrm{u}/\mathrm{Fe}/\mathrm{Cu}\left(001\right)$ film as a function of frequency and Cu overlayer thickness ( $x=3\mathrm{}–25$). We find very strong spin-polarized oscillations with periods of 6 and 11 monolayers due to quantum well states. These oscillations are enhanced by the large density of Fe $d$ states close to the Fermi level acting as intermediate states for frequency doubling. The results show that optical second harmonic generation is a very sensitive probe of electronic structures and is even k sensitive.