22,563 research outputs found

    Broken-Symmetry States of Dirac Fermions in Graphene with A Partially Filled High Landau Level

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    We report on numerical study of the Dirac fermions in partially filled N=3 Landau level (LL) in graphene. At half-filling, the equal-time density-density correlation function displays sharp peaks at nonzero wavevectors ±q\pm {\bf q^{*}}. Finite-size scaling shows that the peak value grows with electron number and diverges in the thermodynamic limit, which suggests an instability toward a charge density wave. A symmetry broken stripe phase is formed at large system size limit, which is robust against purturbation from disorder scattering. Such a quantum phase is experimentally observable through transport measurements. Associated with the special wavefunctions of the Dirac LL, both stripe and bubble phases become possible candidates for the ground state of the Dirac fermions in graphene with lower filling factors in the N=3 LL.Comment: Contains are slightly changed. Journal reference and DOI are adde

    Odd-Integer Quantum Hall Effect in Graphene: Interaction and Disorder Effects

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    We study the competition between the long-range Coulomb interaction, disorder scattering, and lattice effects in the integer quantum Hall effect (IQHE) in graphene. By direct transport calculations, both ν=1\nu=1 and ν=3\nu=3 IQHE states are revealed in the lowest two Dirac Landau levels. However, the critical disorder strength above which the ν=3\nu=3 IQHE is destroyed is much smaller than that for the ν=1\nu=1 IQHE, which may explain the absence of a ν=3\nu=3 plateau in recent experiments. While the excitation spectrum in the IQHE phase is gapless within numerical finite-size analysis, we do find and determine a mobility gap, which characterizes the energy scale of the stability of the IQHE. Furthermore, we demonstrate that the ν=1\nu=1 IQHE state is a Dirac valley and sublattice polarized Ising pseudospin ferromagnet, while the ν=3\nu=3 state is an xyxy plane polarized pseudospin ferromagnet.Comment: 5 pages, 5 figure

    Importance of risk management

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    Financial crises ; Risk management

    Iterative Multiuser Minimum Symbol Error Rate Beamforming Aided QAM Receiver

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    A novel iterative soft interference cancellation (SIC) aided beamforming receiver is developed for high-throughput quadrature amplitude modulation systems. The proposed SIC based minimum symbol error rate (MSER) multiuser detection scheme guarantees the direct and explicit minimization of the symbol error rate at the output of the detector. Adopting the extrinsic information transfer (EXIT) chart technique, we compare the EXIT characteristics of an iterative MSER multiuser detector (MUD) with those of the conventional minimum mean-squared error (MMSE) detector. As expected, the proposed SIC-MSER MUD outperforms the SIC-MMSE MUD. Index Terms—Beamforming, iterative multiuser detection, minimum symbol error rate, quadrature amplitude modulation

    Symmetric complex-valued RBF receiver for multiple-antenna aided wireless systems

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    A nonlinear beamforming assisted detector is proposed for multiple-antenna-aided wireless systems employing complex-valued quadrature phase shift-keying modulation. By exploiting the inherent symmetry of the optimal Bayesian detection solution, a novel complex-valued symmetric radial basis function (SRBF)-network-based detector is developed, which is capable of approaching the optimal Bayesian performance using channel-impaired training data. In the uplink case, adaptive nonlinear beamforming can be efficiently implemented by estimating the system’s channel matrix based on the least squares channel estimate. Adaptive implementation of nonlinear beamforming in the downlink case by contrast is much more challenging, and we adopt a cluster-variationenhanced clustering algorithm to directly identify the SRBF center vectors required for realizing the optimal Bayesian detector. A simulation example is included to demonstrate the achievable performance improvement by the proposed adaptive nonlinear beamforming solution over the theoretical linear minimum bit error rate beamforming benchmark

    Minimum Symbol Error Rate Turbo Multiuser Beamforming Aided QAM Receiver

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    This paper studies a novel iterative soft interference cancellation (SIC) aided beamforming receiver designed for highthroughput quadrature amplitude modulation systems communicating over additive white Gaussian noise channels. The proposed linear SIC aided minimum symbol error rate (MSER) multiuser detection scheme guarantees the direct and explicit minimisation of the symbol error rate at the output of the detector. Based on the extrinsic information transfer (EXIT) chart technique, we compare the EXIT characteristics of an iterative MSER multiuser detector (MUD) with those of the conventional minimum mean squared error (MMSE) detector. As expected, the proposed SICMSER MUD outperforms the SIC aided MMSE MUD
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