Fine structure of cyclotron resonance in a two-dimensional electron system

Abstract

It is established that cyclotron resonance (CR) in a high-quality GaAs/AlGaAs two-dimensional electron system (2DES) originates as a pure resonance, that does not hybridize with dimensional magnetoplasma excitations. The magnetoplasma resonances form a fine structure of the CR. The observed fine structure of the CR results from the interplay between coherent radiative and incoherent collisional mechanisms of 2D plasma relaxation. We show that the range of 2DES filling factors from which the phenomenon arises is intimately connected to the fundamental fine-structure constant.Cyclotron resonance (CR) spectroscopy is the most direct and convenient method of characterizing the Fermi surface and determining the effective mass of semiconductors [1][2][3]. In a two-dimensional electron system (2DES), a perpendicular magnetic field quenches the inplane motion of electrons into cyclotron orbits. In turn, if the phase and polarization of the incident electromagnetic radiation are synchronized with the electron orbital motion, CR is triggered. The first observation of CR in 2DESs was reported for charged carriers in an inversion layer on Si [4, 5]. Subsequently, CR spectroscopy has been successfully applied to research on many two-dimensional systems, for example, isotropic 2D carriers in GaAs heterostructures [6][7][8], composite fermions [9], heavy fermions in MgZnO/ZnO heterojunctions [10,11], and anisotropic heavy fermions in AlAs quantum wells [12,13].It is widely believed that the cyclotron resonance originates from the dimensional magnetoplasma resonance [15,16,20]. The frequency of the hybrid cyclotron magnetoplasma mode is described by the equationwhere ω c = eB/m * c is the cyclotron frequency, and ω p is the dimensional plasmon frequency [17] (Gaussian units are used in this Letter unless otherwise stated):Here, n s and m * are the density and the effective mass of the 2D electrons, and ε is the effective permittivity of the surrounding medium. For a narrow 2DES stripe of width W , the plasmon wavevector can be approximately described by q = πN/W (N = 1, 2, . . . is the number of the plasmon harmonic).Contrary to general believe, we discovered that the CR originates as a pure resonance, that does not hybridize with dimensional magnetoplasma excitations. The CR rises as a single peak with superimposed contribution from different dimensional magnetoplasma modes. Therefore, initially the CR line shape exhibits a multipeak structure. We show that the CR fine structure is resolved when the coherent radiative 2D plasma relaxation dominates the incoherent collisional damping. In large samples, this regime appears when the 2D conductivity 2πσ xx is much larger than c. Moreover, the range of 2DES filling factors ν in which the CR fine structure necessarily arises is dictated by the relation 2πσ xy > c. The latter can be rewritten very elegantly as ν > 1/α, where α = e 2 / c ≈ 1/137 is the fundamental fine-structure constant.Experiments were performed on a set of high-quality GaAs/AlGaAs single quantum wells with a well w...

A place for two-dimensional plasmonics in electromagnetic wave detection

“…For a fundamental mode with nearly-sinusoidal current distribution one can estimate j 2 ω (r) / j ω (r) 2 = π 2 /8 ∼ 1. The inverse quadratic scaling of radiated power with wavelength is in agreement with recent experimental measurements [49].…”

Gate and magnetic field tunable ultrastrong coupling between a magnetoplasmon and the optical mode of an LC cavity

“…This is often considered as a hybridization of the plasmon with the cyclotron dispersion [16,17,29]. More recent microwave experiments show that these excitations are coexisting [30,31], but the cyclotron transition remains very hard to observe if nearby the MP resonance due to screening of the incident electric field.…”

Resistively detected high-order magnetoplasmons in a high-quality two-dimensional electron gas

“…While some photoresistance measurements revealed either only the fundamental [1] or the lowest few odd-order MPR modes [4], another study [6] reported MPR modes with n = 1, 2, 3, 4. Higher order (n 10) MPR have been observed in microwave absorption [14] and spatially resolved photoluminescence [15] and, more recently, even higher modes have been detected in photovoltage [16,17] and differential luminescence spectra [18].…”

“…At high n, the superradiant rate drops rapidly due to the decay of coherence length L n ∼ w/n [18] and the MPR width is governed by the incoherent rate γ. Therefore, small incoherent scattering rate is another essential ingredient for the detection of high-order MPR.…”

“…1(a) also originates from photoresistance, identifying its exact nature is left for future studies. One possible origin is the plasmon-photon mode hybridization which leads to crossing of magnetoplasmon dispersion with cyclotron lines [18,27].…”