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We analyze the electronic transport through a double quantum dot in the regime where spin blockade occurs. Our model includes a self-consistent description of the electrons and nuclei spin dynamics and their interplay within the double dot. Our results indicate that the current leakage experimentally observed in the spin-blockade region of the current-voltage curve, occurs due to spin-flip processes induced by hyperfine interaction through Overhauser effect between the electrons and nuclei spins.

We present an effective Hamiltonian for a bilayer quantum Hall system at filling factor $\nu=1$ neglecting charge fluctuations. Our model is formulated in terms of spin and pseudospin operators and is an exact representation of the system within the above approximation. We analyze its low-lying excitations in terms of spin-wave theory. Moreover we add to previous first-principle exact-diagonalization studies concentrating on the quantum phase transition seen in this system., Comment: Four pages, proceedings for EP2DS-14, Prague 2001

The close analogy between two-dimensional electron system states and conventional itinerant ferromagnets is used to analyze ordered many-body states in the integer quantum Hall regime. The possibility of in situ tuning between easy-plane and easy-axis quantum Hall ferromagnets is discussed for biased bilayer systems with total filling factor ν =3. Recent experiments on Ising quantum Hall systems are explained in terms of their unique domain wall physics. Issues including Ising critical temperatures, hysteresis loops and transport anisotropies are addressed using a combination of the self-consistent field technique, Hartree–Fock/RPA approximation, and exact diagonalization of the many-body Hamiltonian.

We investigate collective spin fluctuations in ferromagnetic (III, Mn)V semiconductors. Our analysis is based on a model with kinetic-exchange coupling between localized Mn spins and valence-band carriers. We derive an independent spin-wave theory to determine the spin-wave spectrum and extract the spin stiffness. Differences between a two-band and a more sophisticated six-band model for the valence-band carriers are discussed. We use these results and Monte-Carlo simulations to demonstrate that collective fluctuations, neglected by mean-field theory, become increasingly important in limiting the Curie temperature when the density of states is large.

We present a theory of carrier-induced ferromagnetism in diluted magnetic semiconductors (III,Mn)V which allows for arbitrary itinerant-carrier spin polarization and dynamic correlations. Both ingredients, which are absent in an RKKY description, are essential in identifying the system's elementary excitations and describing their properties. We find a branch of gapped collective modes, in addition to the spin waves and Stoner continuum which occur in metallic ferromagnets. We determine the low-temperature spin stiffness and derive, in different regimes, its dependence on the exchange coupling between magnetic ions and free carriers, as well as on the effective band mass.

We report on detailed Hartree–Fock calculations of the unidirectional charge density wave orientation energy induced by a tilted magnetic field. We find that for current experimental samples stripes are oriented perpendicular to the in-plane field, consistent with experiment. For wider two-dimensional electron systems we predict tilt-induced stripe states with variable anisotropy energy sign.

We report experimental evidence of the first-order phase transitions in the two-dimensional electron gas formed in a gated wide GaAs/AlGaAs quantum well at even-integer quantum-Hall states. At the filling factor values of ν=2,4 and low temperatures, crossing of Landau levels through the application of the gate bias yields a suppression of the quantum-Hall-state excitation gap and hysteretical behaviour of the diagonal resistivity in up and down sweeps of the magnetic field. Detailed many-body calculations indicate the occurrence of a first-order phase transition and allow the determination of the exact properties of the electron ground states involved in the transition.

We present a mean-field theory of free-carrier-induced ferromagnetism in semiconductors. Our approach allows spatial patterning, free-carrier spin polarization, finite temperature, and free-carrier exchange and correlation to be accounted for self-consistently. The model is applied on an MnxGa1−xAs/GaAs superlattice with alternating ferromagnetic and paramagnetic layers and we demonstrate the possibility of semiconductor magnetoresistance systems with designed properties.

We have investigated the dynamical properties of edge excitations in the (fractional) quantum-Hall regime for a sharp confining potential, emphasizing the effects resulting from the presence of long-range interaction. Our study uses chiral-Luttinger-liquid models that are motivated by the close analogy between the physics of edge excitations and that of plasmons in quasi-one-dimensional electron systems. We find that incorporating realistic long-range interaction is especially important for multi-branch edges. Results are presented for the tunneling-IV-curve power-law exponent and the two-terminal conductance.

In this work the tunneling current through a weakly coupled DQDs in an external B DC is analyzed. We propose a model which includes hyperfine interaction. The time evolution for electronic charge occupations and for the nuclei polarizations in each dot is obtained by means of rate equations which are self-consistently solved. We analyze the current in the SB region as a function of B DC and observe hysteretic behavior for magnetic fields corresponding to the crossings between triplet and singlet states. Bistability is also produced for the induced nuclei spin polarizations within each quantum dot.