Vladimir I. Fal'ko

The Aharonov-Bohm effect in a mesoscopic ring of diluted magnetic alloy

The spin dynamics of magnetic impurities is shown to play a crucial role in mesoscopic effects. It follows from this analysis that the quantum magnetoconductance oscillations in a mesoscopic ring of a diluted magnetic alloy are gradually suppressed in the paramagnetic regime, whereas a strong magnetic field forbids spin-flip processes and restores the mesooptic Aharonov-Bohm oscillations with an amplitude limited by the efficiency of electron escape to the bulk. This effect is examined analytically using a model of a quasi one-dimensional ring joined to the electrodes by tunnelling contacts or short leads.

Inter-Landau-level relaxation in two-dimensional electron gases at high magnetic fields

Inter-Landau-level relaxation in two-dimensional electron and hole gases in high magnetic fields is strongly affected by the extent, lambda(z), of the electronic wavefunction perpendicular to the two-dimensional channel. As the field is increased, the suppression of the one-acoustic-phonon (cyclotron phonon) emission process that occurs when the phonon wavenumber at the cyclotron frequency exceeds lambda(z)-1 causes two-acoustic-phonon emission to replace one-phonon emission as the dominant relaxation process. The field at which this occurs has been calculated. The net reduction in relaxation rate is believed to be partly responsible for the sensitivity of the optical detection of cyclotron resonance in two-dimensional electron gas systems. In zero magnetic field, the two-phonon process should also contribute significantly to the energy and momentum relaxation of hot electrons.

Electron-phonon drag effect at 2D Landau levels

The authors propose a theory of the electron-phonon drag effect in an ideally pure 2D system under a quantizing magnetic field. Two situations are considered, i.e. when phonons are (i) those of a diffusive heat flow and (ii) those of a focused ballistic beam. In the first case, the authors calculate the drag current for different asymptotical temperature intervals and give its relation to the phonon-scattering-induced conductivity. For the 2D gas illuminated by a hot beam of phonons, they analyse the manifestation of their cyclotron absorption both in the drag and in the beam-activated conductivity.

On the resonant tunneling through double-barrier structures in a tilted magnetic field

The influence of a tilted magnetic field on the resonant structure of current-voltage (I-V) characteristics of layered semiconductor systems is analyzed both for the cases of weak and strong magnetic field. The Hall current and a current caused by tunneling assisted shift of cyclotron orbit center are also discussed.

On the relaxation of nuclear polarization near 2D electron gas

We propose a treatment of relaxation of nuclear polarization in electronically poor systems, such as heterostructures, based on the consideration of electrons as provisional spin holders but not as the spin bath. In this case the rate T1(-1) of decay of polarized states of nuclei is determined by the spin-orbital electron-phonon interaction and the conductivity of the electron gas (in open systems). The developed theory can be applied to experiments on nuclear magnetic relaxation in the quantum Hall effect regime.

The fine structure of cyclotron and spin resonances at their crossing: interplay between spin-orbit and Coulomb interactions

We compare the anticrossing of the spin and cyclotron resonances in spin-polarized and non-polarized phases of a two-dimensional electron gas subjected to a strong tilted magnetic field. The spin-orbit coupling splits these resonances into three lines with the gaps between them exactly equal to delta 2n+1=Vso rho F and delta 2n=vso rho F/ square root 2 at odd- and even-integer factors, respectively. The 1/ square root 2 factor difference between the gaps delta 2n and delta 2n+1 arises from the existence of two collective spin-wave-density modes in the polarized phase of interacting electrons in the system with two filled Landau levels. This allows us to predict a new type of spectral Shubnikov-de Haas oscillations, which indicates the re-entrance of the system into the spin-polarized state.

Quantum conductance fluctuations in 3d ballistic adiabatic wires

We predict quantum conductance fluctuations in three-dimensional (3D) adiabatic wires rising from fluctuations in the energy spectrum of size-quantized electron motion across the channel. These fluctuations could be observed as random oscillations in the voltage dependence of the differential conductance dI/dV or the magnetic field dependence. They obey Poisson or Wigner-Dyson statistics depending on the cross sectional shape of the wire and can have an amplitude which exceeds the universal e2/h value.