Interference of electric-dipole and magnetic-dipole interactions in conduction-electron-spin resonance in InSb

The contributions of the electric-dipole and magnetic-dipole matrix elements to conduction-electron-spin resonance in zinc-blende crystals are investigated theoretically and experimentally. Using time-dependent perturbation analysis, we show that these contributions interfere at the resonance condition, resulting in an anomalous dependence of the resonance intensity on the sign of either the dc magnetic field B${\to }_0$ or the wave vector q→ of the photon. In the context of macroscopic dielectric response, it is shown that the above interference can be represented by time-reversal symmetry associated with the wave vector. The effects of electric-dipole–magnetic-dipole (EDMD) interference at spin resonance have been studied experimentally by far-infrared (FIR) magnetotransmission in a series of InSb samples with various orientations and electron concentrations. Experiments were performed in magnetic fields up to 60 kG in both Voigt and Faraday geometries, at FIR wavelengths 96.5, 118.8, 163, and 251.1 μm, in the temperature range between 2 and 35 K. Measurements of the absorption coefficient as a function of orientation of B${\to }_0$ in (100), (110), (111), and (112) planes, and as a function of the sign of B${\to }_0$ and q→, are in excellent agreement with the predictions of the theory. These experiments provide an elegant method for determining the inversion-asymmetry parameter ${\delta }_0$, yielding a value of 56 a.u. (3.6×${10}^{\mathrm{-}34}$ erg ${\mathrm{cm}}^3$). In addition to the EDMD interference, the FIR magnetotransmission spectra also conclusively demonstrate that the dominant mechanism allowing electric-dipole-excited spin resonance in InSb is inversion asymmetry.