Temperature dependence of spin polarizations at higher Landau Levels

We report our results on temperature dependence of spin polarizations at $\nu=1$ in the lowest as well as in the next higher Landau level that compare well with recent experimental results. At $\nu=3$, except having a much smaller magnitude the behavior of spin polarization is not much influenced by higher Landau levels. In sharp contrast, for filling factor $\nu=\frac83$ we predict that unlike the case of $\nu=\frac23$ the system remains fully spin polarized even at vanishingly small Zeeman energies.Comment: 4 pages, REVTEX, and 3 .ps files, To be published in Physical Review Letter

On the effect of far impurities on the density of states of two-dimensional electron gas in a strong magnetic field

The effect of impurities situated at different distances from a two-dimensional electron gas on the density of states in a strong magnetic field is analyzed. Based on the exact result of Brezin, Gross, and Itzykson, we calculate the density of states in the whole energy range, assuming the Poisson distribution of impurities in the bulk. It is shown that in the case of small impurity concentration the density of states is qualitatively different from the model case when all impurities are located in the plane of the two-dimensional electron gas.Comment: 6 pages, 1 figure, submitted to JETP Letter

Harmonic Solid Theory of Photoluminescence in the High Field Two-Dimensional Wigner Crystal

Motivated by recent experiments on radiative recombination of two-dimensional electrons in acceptor doped GaAs-AlGaAs heterojunctions as well as the success of a harmonic solid model in describing tunneling between two-dimensional electron systems, we calculate within the harmonic approximation and the time dependent perturbation theory the line shape of the photoluminescence spectrum corresponding to the recombination of an electron with a hole bound to an acceptor atom. The recombination process is modeled as a sudden perturbation of the Hamiltonian for the in-plane degrees of freedom of the electron. We include in the perturbation, in addition to changes in the equilibrium positions of electrons, changes in the curvatures of the harmonically approximated potential. The computed spectra have line shapes similar to that seen in a recent experiment. The spectral width, however, is roughly a factor of 3 smaller than that seen in experiment if one assumes a perfect Wigner crystal for the initial state state of the system, whereas a simple random disorder model yields a width a factor of 3 too large. We speculate on the possible mechanisms that may lead to better quantitative agreement with experiment.Comment: 22 pages, RevTex, 8 figures. Submitted to the Physical Review

Magnetic phenomena at and near nu =1/2 and 1/4: theory, experiment and interpretation

I show that the hamiltonian theory of Composite Fermions (CF) is capable of yielding a unified description in fair agreement with recent experiments on polarization P and relaxation rate 1/T_1 in quantum Hall states at filling nu = p/(2ps+1), at and near nu = 1/2 and 1/4, at zero and nonzero temperatures. I show how rotational invariance and two dimensionality can make the underlying interacting theory behave like a free one in a limited context.Comment: Latex 4 pages, 2 figure

Spin-flip and spin-wave excitations in arbitrarily polarized quantum Hall states

We study spin-flip and spin-wave excitations for arbitrarily polarized quantum Hall states by employing a fermionic Chern-Simons gauge theory in the low Zeeman energy limit. We show that the spin-flip correlation functions do not get renormalized by the fluctuations of Chern-Simons gauge field. As a consequence, the excitations for a given integer quantum Hall state are identical to fractional quantum Hall states in the lowest Landau level having the same numerator equal to the integer quantum Hall state. Fully and partially polarized states possess only spin-wave excitations while spin-flip excitations are possible for all states, irrespective of their polarizations.Comment: 19 pages, 8 postscript figure

Anisotropy of Magnetoresistance Hysteresis around the ν=2/3\nu=2/3 Quantum Hall State in Tilted Magnetic Field

We present an anisotropy of the hysteretic transport around the spin transition point at Landau level filling factor $\nu=2/3$ in tilted magnetic field. When the direction of the in-plane component of the magnetic field $B_{\parallel}$ is normal to the probe current $I$, a strong hysteretic transport due to the current-induced nuclear spin polarization occurs. When $B_{\parallel}$ is parallel to $I$, on the other hand, the hysteresis almost disappears. We also demonstrate that the nuclear spin-lattice relaxation rate $T_{1}^{-1}$ at the transition point increases with decreasing angle between the directions of $B_{\parallel}$ and $I$. These results suggest that the morphology of electron spin domains around $\nu =2/3$ is affected by the current direction.Comment: 4 pages, 4 figure

Tunneling Between a Pair of Parallel Hall Droplets

In this paper, we examine interwell tunneling between a pair of fractional quantum Hall liquids in a double quantum well system in a tilted magnetic field. Using a variational Monte Carlo method, we calculate moments of the intra-Landau level tunneling spectrum as a function of in-plane field component $B_{\parallel}$ and interwell spacing $d$. This is done for variety of incompressible states including a pair of $\nu=1/3$ layers ([330]), pair of $\nu=1/5$ layers ([550]), and Halperin's [331] state. The results suggest a technique to extract interwell correlations from the tunneling spectral data.Comment: 21 pages and 8 figures (included), RevTeX, preprint no. UCSDCU

Quantization of the Hall conductivity well beyond the adiabatic limit in pulsed magnetic fields

We measure the Hall conductivity, $\sigma_{xy}$, on a Corbino geometry sample of a high-mobility AlGaAs/GaAs heterostructure in a pulsed magnetic field. At a bath temperature about 80 mK, we observe well expressed plateaux in $\sigma_{xy}$ at integer filling factors. In the pulsed magnetic field, the Laughlin condition of the phase coherence of the electron wave functions is strongly violated and, hence, is not crucial for $\sigma_{xy}$ quantization.Comment: 4 pages, 4 figures, submitted to PR

Effect of a tilted magnetic field on the orientation of Wigner crystals

We study the effect of a tilted magnetic field on the orientation of Wigner crystals by taking account of the width of a quantum well in the $z$-direction. It is found that the cohesive energy of the electronic crystal is always lower for the $[110]$ direction parallel to the in-plane field. In a realistic sample, a domain structure forms in the electronic solid and each domain orients randomly when the magnetic field is normal to the quantum well. As the field is tilted an angle, the electronic crystal favors to align along a preferred direction which is determined by the in-plane magnetic field. The orientation stabilization is strengthened for wider quantum wells as well as for larger tilted angles. Possible consequence of the tilted field on the transport property in the electronic solid is discussed