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The spin resonance of two-dimensional conduction electrons in a ZnO/MgZnO heterojunction in tilted magnetic fields is studied near the filling factor . The analysis of the spin resonance intensity at various ν values indicates that a phase transition accompanied by drastic change in the spin polarization occurs in a two-dimensional electron system at a certain angle near . For ν values larger than a certain critical value νc, an intense spin resonance is observed, clearly demonstrating that the system turns out to be in a spin-polarized state. For ν < νc, the resonance amplitude drops by more than an order of magnitude, and the spin polarization of the ground state decreases significantly. In the immediate vicinity of the transition, the spin resonance is broadened significantly and split into several independent peaks. Such behavior of the resonance can most likely be explained by the division of the system into domains with different spin polarizations. [ABSTRACT FROM AUTHOR]

The microwave-induced photovoltage in two-dimensional electron systems in an AlAs quantum well and a ZnO/MgZnO heterojunction under the conditions of the quantum Hall effect is investigated. When the magnetic field is varied smoothly at a fixed microwave frequency, a sharp peak corresponding to the spin resonance of two-dimensional conduction electrons occurs in the recorded photovoltage. This is the first observation of spin resonance in two-dimensional electron systems by such a technique. It is demonstrated that this technique can be used both with the Hall bar and Corbino disk configurations of the ohmic contacts to the two-dimensional channel despite the essential difference between these configurations. This technique is compared with the conventional technique for the detection of spin resonance in a two-dimensional electron system by measuring the change in the resistance caused by the absorption of microwave radiation. [ABSTRACT FROM AUTHOR]

The phenomenon of spin resonance of two-dimensional electrons confined in a 16 nm AlAs quantum well is studied in the quantum Hall effect regime near filling factor 1. At a temperature of T = 0.5K, spin resonance is not observed directly at filling factor ν = 1, but it is found already with slight deviation from it and at the increase in the temperature of the sample. The dependence of the resonance amplitude on the filling factor has two maxima near filling factors ν ≈ 0.9,1.1 symmetric with respect to ν = 1. The temperature dependences of the spin resonance amplitude near different filling factors are studied. It occurs that the resonance amplitude decreases with decreasing temperature T directly at filling factor 1. With deviation from it, the character of the temperature dependence changes. At ν ≈ 0.9,1.1, the electron paramagnetic resonance amplitude increases with decreasing T. Near filling factor 1, the temperature dependence of the amplitude is with good accuracy proportional to the temperature derivative of the longitudinal magnetoresistance measured at the same. However, quantitative agreement is violated when ν ≠ 1.These experimental observations indicate that the detection of spin resonance at filling factor 1 is based on the sensitivity of the longitudinal magnetoresistance to heating caused by the resonant absorption of microwave radiation, but this mechanism no longer works when ν ≠ 1. [ABSTRACT FROM AUTHOR]

The nuclear spin dynamics in an asymmetrically doped 16-nm AlAs quantum well grown along the [001] direction has been studied experimentally using the time decay of the Overhauser shift of paramagnetic resonance of conduction electrons. The nonzero spin polarization of nuclei causing the initial observed Overhauser shift is due the relaxation of the nonequilibrium spin polarization of electrons into the nuclear subsystem near electron paramagnetic resonance owing to the hyperfine interaction. The measured relaxation time of nuclear spins near the unity filling factor is (530 ± 30) min at the temperature T = 0.5 K. This value exceeds the characteristic spin relaxation times of nuclei in GaAs/AlGaAs heterostructures by more than an order of magnitude. This fact indicates the decrease in the strength of the hyperfine interaction in the AlAs quantum well in comparison with GaAs/AlGaAs heterostructures. [ABSTRACT FROM AUTHOR]

Electron spin resonance in GaAs/AlGaAs quantum wells in the vicinity of odd filling factors ν = 3, 5, and 7 is investigated. The spin relaxation time of two-dimensional electrons is determined from the width of the microwave resonance absorption line. Dependences of the spin relaxation time on the filling factor, temperature, and orientation of the magnetic field are investigated. The spin relaxation time decreases noticeably upon deviation from odd filling factors, and its maximum value depends on the angle between the magnetic field and the plane of the two-dimensional electron gas. [ABSTRACT FROM AUTHOR]

The anisotropy of the electron g factor is investigated in symmetrically (SQW) and asymmetrically (AQW) doped 20-nm GaAs/AIGaAs quantum wells, grown in the [0011 direction. Applied was the electrically detected electron spin resonance technique. The AQW demonstrates strong twofold in-plane g-factor anisotropy with the 1110] and [11̅0] principal axes. This can be readily ascribed to the internal electric field asymmetry as caused by single-side doping. The SQW is shown to have 10 times as weak (but still detectable) anisotropy with the same principal axes. The linear (in the magnetic field) corrections to the g factor were also carefully measured. The â tensor of these corrections is shown to have at least three different nonzero components, namely, azzz, axxz and ayyz. [ABSTRACT FROM AUTHOR]

The anisotropy of electron g-factor is investigated for several GaAs/AlxGa1-xAs heterostructures using an electrically detected electron spin resonance technique at liquid helium temperature. For a modulation-doped 25-nm single quantum well with electron density n=4×1011 cm-2 we extracted an out-of-plane g-factor value of ∣gzz∣=0.410 and in-plane values of ∣gyy∣=0.359 and ∣gxx∣=0.289. In addition, linear in magnetic field corrections to the g-factor components were also extracted and strong anisotropy in their values was established. [ABSTRACT FROM AUTHOR]

Electron spin resonance in a system of two-dimensional electrons with a high electron mobility has been investigated and the position, width, intensity, and line shape of the resonance microwave absorption have been studied as functions of the filling factor and temperature. It has been shown that the ESR linewidth in high-electron-mobility GaAs/AlGaAs quantum wells may reach 30 MHz, which corresponds to a spin relaxation time of the two-dimensional electrons of 10 ns. The experimental data on the linewidth of the spin resonance at a filling factor of 1 are compared with the theoretical results for various spin relaxation mechanisms. It has been shown that the dominant mechanism of spin relaxation at a filling factor of 1 and a temperature of 1.5–4 K is the mutual scattering of spin excitons. [ABSTRACT FROM AUTHOR]

Abstract Relaxation of nuclear spins located in the vicinity of 2D electron system confined in a 16 nm [001] AlAs/AlGaAs quantum well was studied with the aid of electron spin resonance (ESR) in the regime of integer and fractional quantum Hall effect. Nuclear spin-lattice relaxation time τ was measured from the time decay of the Overhauser shift near different filling factors of the electron system. The resultant dependence of τ on filling factor turned out to be nontrivial. At the temperature 1.5 K τ reached its maximal value at the exact filling ν = 1 and decreased when ν was altered, yet this maximum vanished when the system was cooled down to 0.5 K. The fractional quantum Hall effect state at the filling of 2∕3 was formed at the temperature of 0.5 K, and the development of this state was accompanied by the slowing of the nuclear spin relaxation. This observation suggests the enhancement of energy gap in the spin excitation spectrum of two-dimensional electrons at 2/3 state. Highlights • Nuclear spin dynamics was studied in a wide AlAs quantum well in the regime of QHE. • Non-trivial dependence of nuclear spin relaxation on filling was observed at 0.5 K. • Formation of the fractional QHE resulted into the slowing of nuclear spin relaxation. [ABSTRACT FROM AUTHOR]

The electron spin resonance (ESR) of two-dimensional electrons confined in a high-quality, 16-nm AlAs quantum well was investigated near the filling factor ν = 2/3 of the fractional quantum Hall effect (FQHE). The spin resonance was robust in the vicinity of the fractional filling ν = 2/3, indicating that the ν = 2/3 state is at least partially spin polarized. The formation of the 2/3 FQHE state did not result in any modifications of the ESR linewidth and, hence, of the electron spin relaxation rate. Yet the nuclear spin-lattice relaxation rate extracted from the time decay of the ESR Overhauser shift demonstrated a strong nonmonotonic dependence on the electron filling factor with a minimum near ν = 2/3. This observation suggests the enhancement of the energy gap in the spin excitation spectrum of two-dimensional electrons at the ν = 2/3 state. [ABSTRACT FROM AUTHOR]