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Experimental measurements of photoresistivity under terahertz (THz) radiation in low magnetic fields at conditions of cyclotron resonance (CR) in two-dimensional electron system (2DES) of GaAs/AlGaAs nanostructures are presented and discussed. We report the experimental discovery of "CR-vanishing effect" (CRV) in GaAs/AlGaAs heterostructures with high mobility as a well-defined gap on CR-line that is independent on incident THz power. Our analysis shows that the CRV may appear in systems with well correlated state of 2D electrons such as plasma waves and others. Fundamental nature of these correlated states of electrons in 2DES is discussed. Future THz detectors utilizing the new correlated states in 2DES may expand horizons for supersensitive detection in sub-THz and THz frequencies ranges.

HgTe quantum wells with a gapped single Dirac cone electronic dispersion relation have been investigated by THz magneto-photoresponse (PR) and magneto-transport measurements. The QW sample has the conventional band alignment with the well thickness (6.1 nm) slightly smaller than the critical thickness for the topological phase transition. The effective gap of this structure is roughly 10 meV, and the large sheet density ($n_s\approx 1.5\times 10^{16}$ m^-2) of the two-dimensional electron gas (2DEG) results in a very large Fermi energy ($E_F\sim 160$ meV). We have found several interesting effects at these high densities. In this paper we focus on an observed beating of quantum oscillations in the PR signal (at 1.83 THz) and compare it with direct measurements of oscillations in the longitudinal magneto-resistance (R_xx). The mechanism for the PR is cyclotron resonance absorption heating of the electrons (an electron bolometric effect). We attribute the beating to Rashba splitting of the spin states, which is barely observable in direct R_xx measurements under strong gate-induced electric fields.

Inserted narrow InAs quantum wells in InAs/InGaAs/InAlAs heterostructures have been used to achieve higher mobility for high-electron-mobility transistors (HEMTs) with ultra-low-power and low-noise amplification characteristics and for spin-based devices. Due to the large nonparabolicity of the conduction band of InAs and the penetration of the confined electronic envelope function into the adjacent layer(s), accurate calculations of effective mass and g-factor of charge carriers can be problematic. Methods of making precise determinations of the mass and other electronic parameters are thus of interest. We have applied magneto-photoresponse and -transmissions measurements at several THz laser frequencies in concert with dc magnetotransport measurements at low temperature (T = 1.6 K) to determine various electronic parameters (effective mass, carrier density, g-factor, mobility and the quantum scattering time) of the 2DEG in an InAs/In_0.75Ga_0.25As/In_0.75Al_0.25As inserted channel structure. This characterization method can also be used to probe the effect of strain, Rashba field, etc on the properties of charge carriers in such structures.

Large cyclotron-resonance (CR) line splittings have been observed previously in two-dimensional (2D) electrons in AlGaN/GaN and in GaAs/AlGaAs heterojunctions. The features resemble a level anti-crossing and imply a strong interaction with an unknown excitation of the solid. The origin of this phenomenon remains unexplained. This paper reviews the existing data and presents some recently detected correlations of the splitting with other sample parameters.

Observation of band nonparabolicity is difficult because the electron energy in conduction band cannot be controlled widely. Using quantization energy in quantum well (QW) where the eigen energy is changed by QW thickness, nonparabolic effective mass inside a single QW of InGaAs was determined recently, up to 0.5 eV above bandedge. The dependence of effective mass on energy was analyzed and applied to calculate Landau level energy. Calculation fit well with cyclotron resonance experiments. Coupling between skew and normal cyclotron resonance was identified by this analysis.

We investigate the properties of quasi-two-dimensional electrons in AlP quantum wells by measuring cyclotron resonance, quantum Hall effect, and Shubnikov de Haas oscillations in modulation-doped AlP-GaP type-II quantum wells. We find that in wide AlP wells, the lowest conduction band states are in the X_x and X_y valleys transverse to the growth direction, that the valley degeneracy of this state is g_v=2, and that the cyclotron effective mass . These results indicate that the biaxial compressive strain resulting from the lattice mismatch of AlP quantum well with respect to the GaP substrate and barrier layers causes the longitudinal X_z valley to be lifted above the transverse X_x and X_y valleys. Further, the two-fold degeneracy of the X_x and X_y valleys indicates that the conduction band minimum in AlP is located exactly at the X-point of the Brillouin zone.

We present far-infrared cyclotron resonance measurements on a strongly coupled symmetric GaAs/GaAlAs double quantum well sample. Cyclotron resonance is measured at several discrete wavelengths and tilt angles of the sample with respect to the magnetic field. The width and strength of the resonance peaks depend strongly on the tilt angle and the laser wavelength, demonstrating the complexity of this system.

We discuss recent measurements of the interband spectrocopy of carbon nanotubes and studies of cyclotron resonance in graphene, using these to examine the possible dependence of the band structure of graphene on the number of layers present and the role of Coulomb interactions. Cyclotron resonances gives a value for the electron velocity at the Dirac point of 1.093×10⁶ ms^-1, which is ~ 20% larger than would be expected from deductions of the band structure of carbon nanotubes. In addition, a significant asymmetry exists between band structure for electrons and holes, which gives rise to a 5% difference between the velocities at energies of 125 meV away from the Dirac point.

In two-dimensional (2D) electron systems in a magnetic field, the Coulomb interaction among charge carriers, under Landau quantization, essentially governs a variety of many-body phenomena while there are also phenomena, such as the (integer) quantum Hall effect, that appear unaffected by the interaction. It is pointed out that the response of 2D electrons to spatially-uniform potentials and fields enjoys a long-wavelength gauge symmetry, associated with cyclotron motion of electrons, that leaves the Coulomb interaction invariant and that thus naturally explains why cyclotron resonance (as implied by Kohn’s theorem) and the quantized Hall conductance appear insensitive to the interaction. It is discussed, in the light of this new long-wavelength gauge symmetry, how Dirac electrons in graphene and conventional 2D electrons differ in cyclotron-resonance characteristics and the quantum Hall effect.

We study the weakly damped electromagnetic waves in strongly anisotropic organic conductors with the chain-like character of the intermolecular overlapping at various orientations of an external magnetic field and wave vector. We obtain the analytical expressions for the spectra of the collective modes in a number of limiting cases, in particular, the dispersion relations in a short-wavelength limit when the eigen frequencies are not close to the resonance frequency and its harmonics. The numerical analysis giving full enough description of the dispersion of the weakly damped eigenmodes is presented. We find the spectrum of the eigenmodes owing to electron oscillations along the least conductivity direction. We show that if the orientation of the wave vector k is not too close to the least conductivity direction, the dependence of the eigen frequencies on k has pronounced oscillatory character.

The structure and features of spatially-confined states in the presence of a tilted magnetic field are theoretically investigated. The electron states in single- and double-quantum wells are described using the variational method. It is shown that the finite ratio of magnetic length to the width of heterostructure could not be neglected in the strong tilted magnetic field. The electronic structure of broken-gap heterostructures is considered similar to the case of usual double-quantum-well with the high narrow barrier. It is shown that tilted magnetic field can eliminate the strong coupling between two degenerated electron states or those of the electron and hole. The existence of such an effect is in accordance with cyclotron resonance studies of InAs/GaSb heterostructures.

We present a theoretical and experimental study on electronic and magneto-optical properties of p-type paramagnetic InMnAs dilute magnetic semiconductor (DMS) alloys in ultrahigh (> 100 T) external magnetic fields (B). Theoretical calculations are based on an 8-band Pidgeon–Brown model which is generalized to include the wavevector dependence of the electronic states along B as well as s–d and p–d exchange interactions with localized Mnd-electrons. The spin-dependent electronic structure as a function of Mn doping is computed and the dependence of the valence band structure on parameters such as the sp–d exchange interaction strength and effective masses in paramagnetic p-InMnAs alloys are examined. The cyclotron resonance (CR) and magneto-optical properties of InMnAs are calculated using Fermi's golden rule. Two strong CR peaks are observed in p-type InMnAs alloys which correspond to the transitions within either heavy-hole (HH) or light-hole (LH) Landau levels. Furthermore, we also observed strong resonance absorption for electron-active polarization which can occur in p-type semiconductors originating from transitions between the light and heavy hole Landau levels.

Large cyclotron-resonance (CR) line splittings have been observed previously in two-dimensional (2D) electrons in AlGaN/GaN and in GaAs/AlGaAs heterojunctions. The features resemble a level anti-crossing and imply a strong interaction with an unknown excitation of the solid. The origin of this phenomenon remains unexplained. This paper reviews the existing data and presents some recently detected correlations of the splitting with other sample parameters.

Observation of band nonparabolicity is difficult because the electron energy in conduction band cannot be controlled widely. Using quantization energy in quantum well (QW) where the eigen energy is changed by QW thickness, nonparabolic effective mass inside a single QW of InGaAs was determined recently, up to 0.5 eV above bandedge. The dependence of effective mass on energy was analyzed and applied to calculate Landau level energy. Calculation fit well with cyclotron resonance experiments. Coupling between skew and normal cyclotron resonance was identified by this analysis.

Experimental measurements of photoresistivity under terahertz (THz) radiation in low magnetic fields at conditions of cyclotron resonance (CR) in two-dimensional electron system (2DES) of GaAs/AlGaAs nanostructures are presented and discussed. We report the experimental discovery of “CR-vanishing effect” (CRV) in GaAs/AlGaAs heterostructures with high mobility as a well-defined gap on CR-line that is independent on incident THz power. Our analysis shows that the CRV may appear in systems with well correlated state of 2D electrons such as plasma waves and others. Fundamental nature of these correlated states of electrons in 2DES is discussed. Future THz detectors utilizing the new correlated states in 2DES may expand horizons for supersensitive detection in sub-THz and THz frequencies ranges.

HgTe quantum wells with a gapped single Dirac cone electronic dispersion relation have been investigated by THz magneto-photoresponse (PR) and magneto-transport measurements. The QW sample has the conventional band alignment with the well thickness (6.1 nm) slightly smaller than the critical thickness for the topological phase transition. The effective gap of this structure is roughly 10 meV, and the large sheet density (n_S ≈ 1.5 × 10¹⁶ m⁻²) of the two-dimensional electron gas (2DEG) results in a very large Fermi energy (E_F ~ 160 meV). We have found several interesting effects at these high densities. In this paper we focus on an observed beating of quantum oscillations in the PR signal (at 1.83 THz) and compare it with direct measurements of oscillations in the longitudinal magneto-resistance (R_xx) The mechanism for the PR is cyclotron resonance absorption heating of the electrons (an electron bolometric effect). We attribute the beating to Rashba splitting of the spin states, which is barely observable in direct R_xx measurements under strong gate-induced electric fields.

Inserted narrow InAs quantum wells in InAs/InGaAs/InAlAs hetrostructures have been used to achieve higher mobility for high-electron-mobility transistors (HEMTs) with ultra-low-power and low-noise amplification characteristics and for spin-based devices. Due to the large nonparabolicity of the conduction band of InAs and the penetration of the confined electronic envelope function into the adjacent layer(s), accurate calculations of effective mass and g-factor of charge carriers can be problematic. Methods of making precise determinations of the mass and other electronic parameters are thus of interest. We have applied magneto-photoresponse and -transmissions measurements at several THz laser frequencies in concert with dc magnetotransport measurements at low temperature (T = 1.6 K) to determine various electronic parameters (effective mass, carrier density, g-factor, mobility and the quantum scattering time) of the 2DEG in an InAs/In_0.75Ga_0.25As/In_0.75Al_0.25As inserted channel structure. This characterization method can also be used to probe the effect of strain, Rashba field, etc on the properties of charge carriers in such structures.