Features of electron-spin-resonance excitation in impure asymmetric two-dimensional structures

The band spin-orbit coupling, which makes it possible for the orbital motion of electrons to affect the spin dynamics, is known to be present in crystals with destroyed mirror symmetry. A framework for analyzing effects of the spin-orbit coupling on spin-dependent electron kinetics is suggested and applied to the electron-spin resonance on an electron gas in an impure asymmetric two-dimensional semiconductor structure. The general case of excitation of the resonance by both the electric and magnetic components of the microwave electromagnetic field is considered and the frequency-dependent tensors of the electric conductivity and spin susceptibility as well as the spin-current-correlation tensors, which additionally characterize the response of a broken-mirror-symmetry conducting media to an external electromagnetic field, are calculated. It is shown that the electric component of the resonant microwave field can excite the resonance more effectively than the magnetic component in spite of a small value of the spin-orbit coupling. The formalism presented allows one to consider the case when an external static magnetic field is arbitrary inclined with respect to the plane of the structure and the cyclotron frequency omega(c) corresponding to the perpendicular component of the field can take any value less that the Fermi energy epsilon(F). It is found that the cyclotron motion not only modifies the spin relaxation time but also has an effect on the spin precession giving rise to a shift of the Larmour frequency. The shift can be positive or negative depending on the sign of g factor of current carriers relative to the sign of their charge. It is shown that due to the cyclotron motion the spin resonance can also take place in the particular case of zero g factor. It is also found that because of the spin-velocity correlations the absorption of the linear polarized radiation can change its value at the magnetic field reversal.