4,690 research outputs found

    Curvature-enhanced spin-orbit coupling in a carbon nanotube

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    Structure of the spin-orbit coupling varies from material to material and thus finding the correct spin-orbit coupling structure is an important step towards advanced spintronic applications. We show theoretically that the curvature in a carbon nanotube generates two types of the spin-orbit coupling, one of which was not recognized before. In addition to the topological phase-related contribution of the spin-orbit coupling, which appears in the off-diagonal part of the effective Dirac Hamiltonian of carbon nanotubes, there is another contribution that appears in the diagonal part. The existence of the diagonal term can modify spin-orbit coupling effects qualitatively, an example of which is the electron-hole asymmetric spin splitting observed recently, and generate four qualitatively different behavior of energy level dependence on parallel magnetic field. It is demonstrated that the diagonal term applies to a curved graphene as well. This result should be valuable for spintronic applications of graphitic materials.Comment: 6 pages, 4 figures, to be published on Physical Review

    Ballistic spin field-effect transistors: Multichannel effects

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    We study a ballistic spin field-effect transistor (SFET) with special attention to the issue of multi-channel effects. The conductance modulation of the SFET as a function of the Rashba spin-orbit coupling strength is numerically examined for the number of channels ranging from a few to close to 100. Even with the ideal spin injector and collector, the conductance modulation ratio, defined as the ratio between the maximum and minimum conductances, decays rapidly and approaches one with the increase of the channel number. It turns out that the decay is considerably faster when the Rashba spin-orbit coupling is larger. Effects of the electronic coherence are also examined in the multi-channel regime and it is found that the coherent Fabry-Perot-like interference in the multi-channel regime gives rise to a nested peak structure. For a nonideal spin injector/collector structure, which consists of a conventional metallic ferromagnet-thin insulator-2DEG heterostructure, the Rashba-coupling-induced conductance modulation is strongly affected by large resonance peaks that arise from the electron confinement effect of the insulators. Finally scattering effects are briefly addressed and it is found that in the weakly diffusive regime, the positions of the resonance peaks fluctuate, making the conductance modulation signal sample-dependent.Comment: 18 pages, 15 figure

    The usefulness of the Korean version of modified Mini-Mental State Examination (K-mMMSE) for dementia screening in community dwelling elderly people

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    BACKGROUND: We assessed whether the Korean version of modified Mini-Mental State Examination (K-mMMSE) has improved performance as a screening test for cognitive impairment or dementia in a general population compared with the Korean Mini-Mental State Examination (K-MMSE). METHODS: Screening interviews were conducted with people aged 65 and over in Noam-dong, Namwon-city, Jeonbuk province. There were 522 community participants, of whom 235 underwent clinical and neuropsychological examination for diagnosis of dementia and Cognitive Impairment No Dementia (CIND). Sensitivity, specificity and areas under the receiver operating characteristic (ROC) curves for the K-mMMSE and the K-MMSE were the main outcome measures. RESULTS: Cronbach's alpha for the K-mMMSE was 0.91, compared with 0.84 for the K-MMSE. The areas under the ROC curves in identifying all levels of CIND or dementia were 0.91 for the K-mMMSE and 0.89 for the K-MMSE (P < 0.05). For the K-mMMSE, the optimal cut-off score for a diagnosis of CIND was 69/70, which had a sensitivity of 0.86 and a specificity of 0.79, while, for a diagnosis of dementia, the optimal cut-off score of 59/60 had a sensitivity of 0.91 and a specificity of 0.78. The K-mMMSE also had a high test-retest reliability (r = 0.89). CONCLUSION: Our findings indicate that the K-mMMSE is more reliable and valid than the K-MMSE as a cognitive screen in a population based study of dementia. Considering the test characteristics, the K-MMSE and modified version are expected to be optimally used in clinical and epidemiologic fields