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Comment: 4 pages, 3 figures. Typos corrected, small but important change in intro. Accepted for publication in Physical Review Letters
Comment: Version to appear in Phys. Rev. B. Improved interface pinning model. Many typos corrected. One figure deleted, one replaced
Comment: 5 pages, 2 figures. To appear in Physical Review Letters
Comment: 5 pages, 1 figure. A Perspective on "Dissipationless Quantum Spin Current at Room Temperature" by Shuichi Murakami, Naoto Nagaosa, and Shou-Cheng Zhang, Science 301, 1348 (2003)
We analyze the range of validity of Thomas Fermi theory for describing charge density modulations induced by external potentials in neutral graphene. We compare exact results obtained from a tight-binding calculation with those of linear response theory and the Thomas Fermi approximation. For experimentally interesting ranges of size and density amplitudes (electron densities less than $\sim 10 ^{11} cm ^{-2}$, and spatial length scales below $\sim 20 nm$), linear response is significantly more accurate than Thomas Fermi theory.
Comment: 36 pages LaTex with 11 postscript figures. Short animations of the collective modes can be found at
Comment: 10 pages, 8 figures included
We present a Hartree-Fock study that incorporates the effects of Landau level mixing and screening due to filled levels into the computation of energies and states of quasiparticles in quantum Hall ferromagnets. We use it to construct a phase diagram for skyrmion stability as a function of magnetic field and Zeeman coupling strengths. We find that Landau level mixing tends to favor spin-polarized quasiparticles, while finite thickness corrections favor skyrmions. Our studies show that skyrmion stability in high Landau levels is very sensitive to the way in which electron-electron interactions are modified by finite thickness, and indicate that it is crucial to use models with realistic short distance behavior to get qualitatively correct results. We find that recent experimental evidence for skyrmions in higher Landau levels cann...
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