Cyclotron resonance on open electron orbits
Аннотация
We study the absorption of electromagnetic waves by metals in an oblique magnetic field when the extremal number of electrons in the open cross-section of the Fermi surface drifts along the sample. The interaction of these electrons with the electromagnetic wave under conditions of the anomalous skin effect leads to the cyclotron resonance when the wave frequency ω is a multiple of the Larmor frequency Ω of the conduction electrons in the magnetic field. The intensity of the resonance is approximately equal to the resonance intensity in a parallel magnetic field. In both cases, the impedance for ω = nΩ has a fractional-power singularity. It is shown that this result, obtained by Lekhtsier and one of the authors {V.G. Peschanskii, and V.S. Lekhtsier, Zh. Éksp. Teor. Fiz. 46, 764 (1964) [Sov. Phys. JETP 19, 520 (1964)]}, is correct for frequencies ω for which r/δ≫ωτ > 1, where δ is the skin depth, and r is the radius of curvature of the electron trajectory in the magnetic field. As either ω or the electron mean free time τ increase, the resonance weakens, and for ωτ≫r/δ, the character of the resonance singularity changes. In thin metallic films when the film thickness d is smaller than the electron orbit diameter D, the orbit is cut off. For d>D +δ, the resonance line shape is the same as in the bulk material. In a narrow range of magnetic fields such that δ >(d–D)> 0, the resonance undergoes substantial changes and vanishes. This last condition gives the accuracy of determination of the diameter of the electron resonance orbit.