Mutual influence between current-induced giant magnetoresistance and radiation-induced magnetoresistance oscillations in the GaAs/AlGaAs 2DES

Electromagnetically induced transparency and quantum enhancement of transmission via dressed bloch photons in an array of three-level Λ-type atoms

We investigate the interactions between an array of three-level atoms and two photon fields with distinct frequencies employing quantum electrodynamics (QED). The control beam, as expected, has a considerably higher intensity than the probe beam, and the probe photon's eigenstate notably then appears as a distinctive dressed Bloch wave. We calculate the dispersion relation and quantum amplitude of the probe photons for their transmission. At positions predicting electromagnetically induced transparency (EIT) phenomena, we unveil remarkable enhancements in the transmission of the probe beam. Crucially, these enhancements are intricately linked to the unique characteristics of the dressed Bloch wave eigenstate. Moreover, we demonstrate that modulating frequency and intensity of the control beam and the lattice constant would further tune these enhancements. Our study highlights the crucial role of the dressed Bloch wave eigenstate in substantially amplifying targeted light beams, thereby significantly enhancing the detection sensitivity for minute electromagnetic signals and emphasizing its pivotal role in unveiling intriguing phenomena.

Manipulating quantum interference of dressed photon fields

Through quantum electrodynamics (QED) we investigate the interactions between a three-level atom and two photon fields under perturbation limit. The dispersion relation and (relative) transmission of the probe photons are obtained by calculating the corresponding Feynman diagrams. The quantum interference in this three-level system such as Fano resonance and electromagnetically induced transparency (EIT) can be tuned by varying the intensities of the control and probe beams. Moreover, by considering that the control beam with periodic modulation, that is, the so-called Landau-Zener-Stückelberg (LZS) type source, the accumulated phase after Landau-Zener transitions is found to show the alternating Fano (EIT) lineshapes in the transmission of the probe photons. We further find that the transmissions can become almost stationary in addition to a wide EIT window in time even though the control beam is a LZS-type oscillating source.

Study of narrow negative magnetoresistance effect in ultra-high mobility GaAs/AlGaAs 2DES under microwave photo-excitation

The microwave-induced change in the narrow negative magnetoresistance effect that appears around zero magnetic field in high mobility GaAs/AlGaAs 2DES (≈10⁷ cm²/Vs) is experimentally examined as a function of incident microwave power at a fixed bath temperature. The experimental results indicate that the narrow negative magnetoresistance effect exhibits substantially increased broadening with increasing microwave intensity. These magnetoresistance data were subjected to lineshape fits to extract possible variation of characteristic lengths with microwave intensity; the results suggest that characteristic lengths decrease by up to 50% upon increasing microwave power up to about 8 mW. We also examine the change in effective electron temperature, T_e, due to the photo-excitation in the absence of a magnetic field. Combining these results suggests a correlation between electron heating and the observed change in the fit extracted characteristic lengths.

Microscopic model for radiation-induced magnetoresistance oscillations excited by circularly polarized radiation

We develop a microscopic model to explain the striking result of immunity to the sense of circularly polarized radiation of the photo-excited resistance oscillations in high-mobility 2D electron systems. Our model is based on the radiation-driven electron orbit model, previously developed to explain the photo-induced resistance oscillations and zero resistance states in these systems. According to it, the guiding center of the Landau states when irradiated by circularly polarized radiation performs a circular path driven by radiation. In principle, in an infinite sample, this path is different according to the the sense of circular polarization (left or right). However, the limited size of the sample with the essential role of the edges and the concurrent presence of the Hall electric field tend to quench the displacement of the driven guiding center making nearly equal both trajectories. In the end and in the presence of scattering, the longitudinal irradiated magnetoresistance turns out nearly the same irrespective of the sense of circular radiation.

Photon-Assisted Perfect Conductivity Between Arrays of Two-Level Atoms

We investigate interactions between two (parallel) arrays of two-level atoms (2LA) via photons through quantum electrodynamical interaction with one array (the source array) connected to a particle source, and we study the (photo-)resistivity of the other array (the measured array). The wave function of the interacted photon propagating in an array is a Bloch wave with a gap in its eigenvalue (the photonic dispersion). Due to interactions between arrayed 2LA and the dressed photonic field with non-linear dispersion, the conduction behaviors of the measured array can be very diversified according to the input energy of the particle source connected to the source array, and their relative positions. As a result, the resistivity of the measured array can be zero or negative, and can also be oscillatory with respect to the incoming energy of the particle source of the source array, and the separation between arrays.

Radiation-induced magnetoresistance oscillations in monolayer and bilayer graphene

We examine the characteristics of the microwave/mm-wave/terahertz radiation-induced magnetoresistance oscillations in monolayer and bilayer graphene and report that the oscillation frequency of the radiation-induced magnetoresistance oscillations in the massless, linearly dispersed monolayer graphene system should depend strongly both on the Fermi energy, and the radiation frequency, unlike in the case of the massive, parabolic, GaAs/AlGaAs 2D electron system, where the radiation-induced magnetoresistance oscillation frequency depends mainly on the radiation frequency. This possible dependence of the magnetoresistance oscillation frequency on the Fermi level at a fixed radiation frequency also suggests a sensitivity to the gate voltage in gated graphene, which suggests an in-situ tunable photo-excitation response in monolayer graphene that could be useful for sensing applications. In sharp contrast to monolayer graphene, bilayer graphene is expected to show radiation-induced magnetoresistance oscillations more similar to the results observed in the GaAs/AlGaAs 2D system. Such expectations for the radiation-induced magnetoresistance oscillations are presented here to guide future experimental studies in both of these modern atomic layer material systems.

Cyclotron resonance in the high mobility GaAs/AlGaAs 2D electron system over the microwave, mm-wave, and terahertz- bands

The reflected microwave power from the photo-excited high mobility GaAs/AlGaAs 2D device has been measured over the wide frequency band spanning from 30 to 330 GHz simultaneously along with diagonal magnetoresistance as a function of the magnetic field. Easily distinguishable resonances in the reflected power signal are observed at the same magnetic fields as a reduced amplitude in the Shubnikov-de Haas (SdH) oscillations of the diagonal magnetoresistance. The reflection resonances with concurrent amplitude reduction in SdH oscillations are correlated with cyclotron resonance induced by microwave, mm-wave, and terahertz photoexcitation. The magnetoplasma effect was also investigated. The results suggest a finite frequency zero-magnetic-field intercept, providing an estimate for the plasma frequency. The experimentally measured plasma frequency appears to be somewhat lower than the estimated plasma frequency for these Hall bars. The results, in sum, are consistent with an effective mass ratio of m*/m = 0.067, the standard value, even in these high mobility GaAs/AlGaAs devices, at very large filling factors. Preliminary findings from this article have been published as conference proceedings, see Kriisa, A., et al., J. of Phys. Conf. Ser. 864, 012057 (2017).

Electron heating induced by an ac-bias current in the regime of Shubnikov-de Haas oscillation in the high mobility GaAs/Al x Ga1-x As two-dimensional electron system

The magnetotransport properties of the high mobility GaAs/AlGaAs two-dimensional electron gas systems have been examined to determine the influence of the ac current bias on the carrier temperature. The changes in the line shape of Shubnikov-de Haas oscillations in the longitudinal magnetoresistance ([Formula: see text]) were followed as a function of the ac current bias in the temperature range of [Formula: see text] in order to determine the carrier heating effect due to the ac bias. The lineshape analysis of these oscillations indicates that the carrier temperature of the two-dimensional electron system is linearly proportional to the ac bias current.

Coherent backscattering in quasi-ballistic ultra-high mobility GaAs/AlGaAs 2DES

A small and narrow negative-magnetoresistance (MR) effect that appears about null magnetic field over the interval −0.025 ≤ B ≤ 0.025 T in magnetotransport studies of the GaAs/AlGaAs 2D system with μ ≈ 10⁷cm²/Vs is experimentally examined as a function of the sample temperature, T. The temperature dependent magnetoresistance data were fit using the Hikami et al. theory, without including the spin-orbit correction, to extract the inelastic length, l_i, which decreases rapidly with increasing temperature. It turns out that l_i < l_e, where l_e is the elastic length, for all T. Thus, we measured the single particle lifetime, τ_s, and the single particle mean free path l_s = v_Fτ_s. A comparison between l_i and l_s indicates that l_i > l_s. The results suggest that the observed small and narrow magnetoresistance effect about null magnetic field could be a manifestation of coherent backscattering due to small angle scattering from remote ionized donors in the high mobility GaAs/AlGaAs 2DES.

B-periodic oscillations in the Hall-resistance induced by a dc-current-bias under combined microwave-excitation and dc-current bias in the GaAs/AlGaAs 2D system

We report the observation of dc-current-bias-induced B-periodic Hall resistance oscillations and Hall plateaus in the GaAs/AlGaAs 2D system under combined microwave radiation- and dc bias excitation at liquid helium temperatures. The Hall resistance oscillations and plateaus appear together with concomitant oscillations also in the diagonal magnetoresistance. The periods of Hall and diagonal resistance oscillations are nearly identical, and source power (P) dependent measurements demonstrate sub-linear relationship of the oscillation amplitude with P over the span 0 < P ≤ 20 mW.

Magnetoresistance and robust resistivity plateau in MoAs2

We have grown the MoAs2 single crystal which crystallizes in a monoclinic structure with C2/m space group. Transport measurements show that MoAs2 displays a metallic behavior at zero field and undergoes a metal-to-semiconductor crossover at low temperatures when the applied magnetic field is over 5 T. A robust resistivity plateau appears below 18 K and persists for the field up to 9 T. A large positive magnetoresistance (MR), reaching about 2600% at 2 K and 9 T, is observed when the field is perpendicular to the current. The MR becomes negative below 40 K when the field is rotated to be parallel to the current. The Hall resistivity shows the non-linear field-dependence below 70 K. The analysis using two-band model indicates a compensated electron-hole carrier density at low temperatures. A combination of the breakdown of Kohler's rule, the abnormal drop and the cross point in Hall data implies that a possible Lifshitz transition has occurred between 30 K and 60 K, likely driving the compensated electron-hole density, the large MR as well as the metal-semiconductor transition in MoAs2. Our results indicate that the family of centrosymmetric transition-metal dipnictides has rich transport behavior which can in general exhibit variable metallic and topological features.

Radiation-induced resistance oscillations in 2D electron systems with strong Rashba coupling

We present a theoretical study on the effect of radiation on the mangetoresistance of two-dimensional electron systems with strong Rashba spint-orbit coupling. We want to study the interplay between two well-known effects in these electron systems: the radiation-induced resistance oscillations and the typical beating pattern of systems with intense Rashba interaction. We analytically derive an exact solution for the electron wave function corresponding to a total Hamiltonian with Rashba and radiation terms. We consider a perturbation treatment for elastic scattering due to charged impurities to finally obtain the magnetoresistance of the system. Without radiation we recover a beating pattern in the amplitude of the Shubnikov de Hass oscillations: a set of nodes and antinodes in the magnetoresistance. In the presence of radiation this beating pattern is strongly modified following the profile of radiation-induced magnetoresistance oscillations. We study their dependence on intensity and frequency of radiation, including the teraherzt regime. The obtained results could be of interest for magnetotransport of nonideal Dirac fermions in 3D topological insulators subjected to radiation.