Spin Transition in Strongly Correlated Bilayer Two Dimensional Electron Systems

Using a combination of heat pulse and nuclear magnetic resonance techniques we demonstrate that the phase boundary separating the interlayer phase coherent quantum Hall effect at $\nu_T = 1$ in bilayer electron gases from the weakly coupled compressible phase depends upon the spin polarization of the nuclei in the host semiconductor crystal. Our results strongly suggest that, contrary to the usual assumption, the transition is attended by a change in the electronic spin polarization.Comment: 4 pages, 3 postscript figur

Spin Polarizations at and about the Lowest Filled Landau Level

The spin polarization versus temperature at or near a fully filled lowest Landau level is explored for finite-size systems in a periodic rectangular geometry. Our results at $\nu=1$ which also include the finite-thickness correction are in good agreement with the experimental results. We also find that the interacting electron system results are in complete agreement with the results of the sigma model, i.e., skyrmions on a torus have a topological charge of $Q \ge 2$ and the Q=1 solution is like a single spin-flip excitation. Our results therefore provide direct evidence for the skyrmionic nature of the excitations at this filling factor.Comment: 4 pages, REVTEX, and 4 .ps files, To be published in Europhysics Letter

Korringa ratio of ferromagnetically correlated impure metals

The Korringa ratio, $\cal K$, obtained by taking an appropriate combination of the Knight shift and nuclear spin-lattice relaxation time, is calculated at finite temperature, $T$, in the three-dimensional electron gas model, including the electron-electron interaction, $U$, and non-magnetic impurity scatterings. $\cal K$ varies in a simple way with respect to $U$ and $T$; it decreases as $U$ is increased but increases as $T$ is raised. However, $\cal K$ varies in a slightly more complicated way with respect to the impurity scatterings; as the scattering rate is increased, $\cal K$ increases for small $U$ and low $T$, but decreases for large $U$ or high $T$ regime. This calls for a more careful analysis when one attempts to estimate the Stoner factor from $\cal K$.Comment: 7 pages including 3 figures. To be published in Phys. Rev. B, Dec.

Berry Phase Generation and Measurement in a Single Trapped Ion

In this work, we propose a new design of an ion trap which can enable us to generate state specific Berry phase in a single trapped ion. Such a design will enable us to study the physics at the boundary of abelian and non-abelian symmetries and can also have significant impact in quantum computation

A suggested search for 207Pb nuclear Schiff moment in PbTiO3 ferroelectric

We suggest two types of experiments, NMR and macroscopic magnetometry, with solid PbTiO3 to search for the nuclear Schiff moment of 207Pb. Both kinds of experiments promise substantial improvement over the presently achieved sensitivities. Statistical considerations show that the improvement of the current sensitivity can be up to 10 orders of magnitude for the magnetometry experiment and up to 6 orders of magnitude for the NMR experiment. Such significant enhancement is due to the strong internal electric field of the ferroelectric, as well as due to the possibility to cool the nuclear-spin subsystem in the compound down to nanokelvin temperatures.Comment: 4 pages; revised sensitivity estimate for NMR experimen

Resistance spikes and domain wall loops in Ising quantum Hall ferromagnets

We explain the recent observation of resistance spikes and hysteretic transport properties in Ising quantum Hall ferromagnets in terms of the unique physics of their domain walls. Self-consistent RPA/Hartree-Fock theory is applied to microscopically determine properties of the ground state and domain-wall excitations. In these systems domain wall loops support one-dimensional electron systems with an effective mass comparable to the bare electron mass and may carry charge. Our theory is able to account quantitatively for the experimental Ising critical temperature and to explain characteristics of the resistive hysteresis loops.Comment: 4 pages, 3 figure

The apolipoprotein ϵ4 allele in Parkinson\u27s disease with and without dementia

The ϵ4 isoform of apolipoprotein E (Apo-E) may confer genetic susceptibility for familial and sporadic Alzheimer\u27s disease (AD). Because dementia in AD and Parkinson\u27s disease (PD) share many biologic and clinical features, we determined the Apo-E genotypes for 79 patients with PD, 22 of whom were demented, and for 44 age-matched healthy elderly controls from the same community. We hypothesized that if the dementia was similar to AD, there would be a higher allele frequency of apolipoprotein ϵ4 (Apoϵ4) in demented PD patients compared with nondemented PD patients and controls. The ϵ4 allele frequency for PD without dementia was 0.132, for PD with dementia, 0.068, and for controls, 0.102. There was no association between Apoϵ4 and dementia in the PD patients. We conclude that the biologic basis for dementia in PD may differ from that of AD