Slow spin relaxation in a quantum Hall ferromagnet state
Electron spin relaxation in a spin-polarized quantum Hall state is studied. Long spin-relaxation times that are at least an order of magnitude longer than those measured in previous experiments were observed and explained within the spin-exciton relaxation formalism. The absence of any dependence of the spin-relaxation time on the electron temperature and on the spin-exciton density, and a specific dependence on the magnetic field indicate a definite relaxation mechanism—spin-exciton annihilation mediated by spin-orbit coupling and a smooth random potential.
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.
An unusual behavior of the exchange energy scale of a quantum Hall ferromagnet with ν=1 was found in strongly correlated two-dimensional electron systems based on MgZnO/ZnO heterostructures. The exchange contribution, entering the energy of a collective excitation, was probed by means of inelastic light scattering. It was established that, in a wide range of electron densities corresponding to the Wigner-Seitz parameter 7<rs<11, this contribution is on the order of the cyclotron energy, which is notably different from the typical scale of e2/ɛℓB that is typical for weakly interacting systems. The same trend was confirmed via numerical calculations.
The recent experimental studies of extremely long-lived macroscopic ensembles of spin-cyclotron excitons (magnetoexcitons) which have to obey the Bose-Einstein statistics signal the emergence of an excitonic coherent phase. In the present paper the theory of a weakly interacting Bose gas of spin-cyclotron excitations is developed in terms of a virial correction to the single-magnetoexciton energy. The condition for coherent-incoherent phase transition is discussed. It is expected to be strongly related to the studied long-distance interexcitonic correlations. The results obtained theoretically are discussed in terms of their agreement with specific experimental data.
The dynamics of a two-component Davydov-Scott (DS) soliton with a small mismatch of the initial location or velocity of the high-frequency (HF) component was investigated within the framework of the Zakharov-type system of two coupled equations for the HF and low-frequency (LF) fields. In this system, the HF field is described by the linear Schrödinger equation with the potential generated by the LF component varying in time and space. The LF component in this system is described by the Korteweg-de Vries equation with a term of quadratic influence of the HF field on the LF field. The frequency of the DS soliton`s component oscillation was found analytically using the balance equation. The perturbed DS soliton was shown to be stable. The analytical results were confirmed by numerical simulations.
Radiation conditions are described for various space regions, radiation-induced effects in spacecraft materials and equipment components are considered and information on theoretical, computational, and experimental methods for studying radiation effects are presented. The peculiarities of radiation effects on nanostructures and some problems related to modeling and radiation testing of such structures are considered.