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The spin–orbit interaction in a series of ZnO/MgxZn1 – xO heterojunctions containing a two-dimensional electron system with a wurtzite structure has been studied in detail. The spin–orbit coupling constants have been determined from the analysis of the modification of the single-particle g-factor caused by the spin–orbit interaction in the quantum Hall effect regime. The g-factor has been measured with high accuracy by the electron paramagnetic resonance technique in wide ranges of magnetic fields and electromagnetic frequencies. The spin–orbit coupling constants have been determined for a series of samples with different Mg concentrations, which has allowed us to obtain the dependence of the spin–orbit coupling constant on the two-dimensional electron density n. The measured spin–orbit coupling constant is in the range of 0.5–0.8 meV Å and quite weakly depends on n. The coefficients specifying the linear and cubic contributions to the spin–orbit interaction determined from the approximation of the experimental data are α0 = 0.48 meV Å and γ = 0.12 eV Å3, respectively. These values are correlated with results obtained by other research groups. [ABSTRACT FROM AUTHOR]

In high-quality ZnO/MgxZn1 –xO heterojunctions, microwave-induced magnetoresistance oscillations have been investigated using a contactless technique. The basic detection principle relies on the measurements of a signal transmission in the radio frequency range (f ~ 50 MHz) between two T-shaped antennas, capacitively coupled to a two-dimensional electron system. When the sample is exposed to exciting microwave radiation with the frequency 60–140 GHz in low magnetic fields, at least three oscillations are well resolved in the high-frequency conductivity. The amplitude of the first oscillation is comparable in amplitude to Shubnikov–de Haas oscillations in strong magnetic fields. A significant advantage of this method is the absence of Ohmic contacts or metallization deposited on the sample surface, which provides additional information for understanding the origin of this phenomenon. [ABSTRACT FROM AUTHOR]

Extraordinary multiparticle effects in quantizing magnetic fields that are manifested in strongly interacting two-dimensional electron systems in MgZnO/ZnO heterostructures have been reviewed. They are studied by the method of inelastic light scattering on two-dimensional systems with unique properties: strong Coulomb interaction characterized by the Wigner–Seitz parameters and a high mobility. Studies are focused on the properties of collective excitations in strong magnetic fields corresponding to the integer quantum Hall effect regime. Many results for the structure of the ground state and multiparticle contributions to the energy of collective excitations are far beyond the commonly accepted concepts of the microscopic structure of states of the quantum Hall effect in weakly interacting systems. Although any strict theory of two-dimensional electron systems at is absent, experimental results are adequately described by the calculations by the exact diagonalization method and the Fermi liquid model. [ABSTRACT FROM AUTHOR]

The behavior of the degree of spin polarization and the specific exchange energy near the Hall ferromagnetic state with filling factor ν = 1 in strongly interacting two-dimensional electron systems in MgZnO/ZnO heterostructures is investigated. These characteristics have been determined by measuring the spectra of inelastic light scattering by the collective excitations of the electron system, i.e., spin excitons and cyclotron spin-flip excitons. The intensity of the spin exciton line and the energy of the cyclotron spin-flip exciton line serve as indicators of the spin polarization of the system and the specific exchange energy at the lowest Landau level, respectively. It is found that no depolarization takes place when the filling factor deviates to ν < 1, whereas the system with ν > 1 is depolarized according to the single-particle scenario. The specific exchange energy decreases on both sides of ν = 1. It is shown that a local ferromagnetic order existing at ν = 1 also persists when the temperature is raised to 4.2 K, which is somewhat lower than the Zeeman energy. [ABSTRACT FROM AUTHOR]