Anisotropic dynamical spin-density response in quantum wells with spin-orbit interaction

The electric field-induced spin polarization of a two-dimensional electron gas with spin-orbit interaction is investigated in the frequency domain. We calculate the spin-polarizability tensor using the linear-response theory, taking into account the presence of both Rashba and Dresselhaus spin-orbit couplings. We consider quantum wells grown in the main crystallographic directions and concentrate on the high-frequency response in the collisionless regime. For an anisotropic spin splitting, it is shown that the spin-density response becomes dependent on the direction of the applied electric field and presents characteristic spectral features, in notable contrast to the case of an isotropic spin-orbit coupling. Such behavior is explained in terms of the nonisotropic momentum space available for electric-dipole transitions and the presence of critical points. This anisotropic dynamic response suggests new possibilities of spin manipulation which could find spintronic applications.