The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Naoto Nagaosa - One of the best experts on this subject based on the ideXlab platform.
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shift charge and spin photocurrents in dirac surface states of topological insulator
Physical Review B, 2017Co-Authors: Takahiro Morimoto, Naoto NagaosaAbstract:The generation of photocurrent in condensed matter is of main interest for photovoltaic and optoelectronic applications. Shift current, a nonlinear photoresponse, has attracted recent intensive attention as a dominant player of bulk photovoltaic effect in ferroelectric materials. In three dimensional topological insulators $\text{Bi}_2\text{X}_3$ (X: Te, Se), we find that Dirac surface states with a hexagonal warping term carry shift current by linearly polarized light. In addition, shift spin-current is introduced with the time-reversal symmetry breaking perturbation. The estimate for the magnitudes of the shift charge- and spin-currents are 0.13$I_0$ and 0.21$I_0$(nA/m) with the intensity of light $I_0$ measured in $(\text{W}/\text{m}^2)$, respectively, which can offer a useful method to generate these currents efficiently.
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shift charge and spin photocurrents in dirac surface states of topological insulator
Physical Review B, 2017Co-Authors: Kun Woo Kim, Takahiro Morimoto, Naoto NagaosaAbstract:The generation of photocurrent in condensed matter is of main interest for photovoltaic and optoelectronic applications. Shift current, a nonlinear photoresponse, has attracted recent intensive attention as a dominant player of bulk photovoltaic effect in ferroelectric materials. In three-dimensional topological insulators ${\text{Bi}}_{2}{X}_{3}$ ($X=\text{Te}$, Se), we find that Dirac surface states with a hexagonal warping term support shift current by linearly polarized light. Moreover, we study ``shift spin current'' that arises in Dirac surface states by introducing time-reversal symmetry breaking perturbation. The estimate for the magnitudes of the shift charge and spin current densities are $0.13{I}_{0}$ and $0.40{I}_{0}$ (nA/m) for ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ with the intensity of light ${I}_{0}$ measured in $(\text{W}/{\text{m}}^{2})$, respectively, which can offer a useful method to generate these currents efficiently.
Peter Thier - One of the best experts on this subject based on the ideXlab platform.
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Haarmeier T: Disturbed overt but normal covert shifts of attention in adult cerebellar patients
2015Co-Authors: Heidrun Golla, Peter Thier, Thomas HaarmeierAbstract:In an attempt to provide a common denominator for cognitive deficits observed in cerebellar patients, it has been suggested that they might be secondary to impaired control of attention, a ‘dysmetria of attention’, conceptually analogous to motor dysmetria. Albeit appealing and quite influential, the concept of attentional dysmetria as a consequence of cerebellar disease remains controversial. In an attempt to test this concept in a direct way, we compared the performance of patients with cerebellar disorders to that of normal controls on tasks requiring either overt or covert shifts of spatial attention. In the first experiment, visually guided saccades, i.e. overt shifts of spatial attention, were elicited. In the second experiment, covert shifts of attention were evoked by the need to discriminate the orientation of a Landolt C observed during controlled fixation and presented in the same locations as the saccade targets in the previous experiment. The allocation of attention was assessed by comparing acuity thresholds determined with and without spatial cueing. The patients exhib-ited dysmetric saccades as reflected by larger absolute position errors or a higher number of corrective saccades compared to controls. In contrast, the ability to shift attention covertly was unimpaired in the patients, as indicated by a robust improvement in visual acuity induced by spatial cueing which did not differ from the one observed in the controls and which was independent of the range of SOAs (stimulus onset asynchronies) tested. Finally, the individual amount of saccadic dysmetria did not correlate with the individua
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neuron specific contribution of the superior colliculus to overt and covert shifts of attention
Nature Neuroscience, 2004Co-Authors: Alla Ignashchenkova, Peter W Dicke, Thomas Haarmeier, Peter ThierAbstract:Neuron-specific contribution of the superior colliculus to overt and covert shifts of attention
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neuron specific contribution of the superior colliculus to overt and covert shifts of attention
Nature Neuroscience, 2004Co-Authors: Alla Ignashchenkova, Peter W Dicke, Thomas Haarmeier, Peter ThierAbstract:The analysis of a peripheral visual location can be improved in two ways: either by orienting one's gaze (usually by making a foveating saccade) or by 'covertly' shifting one's attention to the peripheral location without making an eye movement. The premotor theory of attention holds that saccades and spatial shifts of attention share a common functional module with a distinct neuronal basis. Using single-unit recording from the brains of trained rhesus monkeys, we investigated whether the superior colliculus, the major subcortical center for the control of saccades, is part of this shared network for attention and saccades. Here we show that a distinct type of neuron in the intermediate layer of the superior colliculus, the visuomotor neuron, which is known to be centrally involved in the preparation of saccades, is also active during covert shifts of attention.
Steven Yantis - One of the best experts on this subject based on the ideXlab platform.
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control of attention shifts between vision and audition in human cortex
The Journal of Neuroscience, 2004Co-Authors: Sarah Shomstein, Steven YantisAbstract:Selective attention contributes to perceptual efficiency by modulating cortical activity according to task demands. Visual attention is controlled by activity in posterior parietal and superior frontal cortices, but little is known about the neural basis of attentional control within and between other sensory modalities. We examined human brain activity during attention shifts between vision and audition. Attention shifts from vision to audition caused increased activity in auditory cortex and decreased activity in visual cortex and vice versa, reflecting the effects of attention on sensory representations. Posterior parietal and superior prefrontal cortices exhibited transient increases in activity that were time locked to the initiation of voluntary attention shifts between vision and audition. These findings reveal that the attentional control functions of posterior parietal and superior prefrontal cortices are not limited to the visual domain but also include the control of crossmodal shifts of attention.
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transient neural activity in human parietal cortex during spatial attention shifts
Nature Neuroscience, 2002Co-Authors: Jens Schwarzbach, Steven Yantis, John T Serences, Robert L Carlson, Michael A Steinmetz, James J PekarAbstract:Observers viewing a complex visual scene selectively attend to relevant locations or objects and ignore irrelevant ones. Selective attention to an object enhances its neural representation in extrastriate cortex, compared with those of unattended objects, via top-down attentional control signals. The posterior parietal cortex is centrally involved in this control of spatial attention. We examined brain activity during attention shifts using rapid, event-related fMRI of human observers as they covertly shifted attention between two peripheral spatial locations. Activation in extrastriate cortex increased after a shift of attention to the contralateral visual field and remained high during sustained contralateral attention. The time course of activity was substantially different in posterior parietal cortex, where transient increases in activation accompanied shifts of attention in either direction. This result suggests that activation of the parietal cortex is associated with a discrete signal to shift spatial attention, and is not the source of a signal to continuously maintain the current attentive state.
Alla Ignashchenkova - One of the best experts on this subject based on the ideXlab platform.
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neuron specific contribution of the superior colliculus to overt and covert shifts of attention
Nature Neuroscience, 2004Co-Authors: Alla Ignashchenkova, Peter W Dicke, Thomas Haarmeier, Peter ThierAbstract:Neuron-specific contribution of the superior colliculus to overt and covert shifts of attention
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neuron specific contribution of the superior colliculus to overt and covert shifts of attention
Nature Neuroscience, 2004Co-Authors: Alla Ignashchenkova, Peter W Dicke, Thomas Haarmeier, Peter ThierAbstract:The analysis of a peripheral visual location can be improved in two ways: either by orienting one's gaze (usually by making a foveating saccade) or by 'covertly' shifting one's attention to the peripheral location without making an eye movement. The premotor theory of attention holds that saccades and spatial shifts of attention share a common functional module with a distinct neuronal basis. Using single-unit recording from the brains of trained rhesus monkeys, we investigated whether the superior colliculus, the major subcortical center for the control of saccades, is part of this shared network for attention and saccades. Here we show that a distinct type of neuron in the intermediate layer of the superior colliculus, the visuomotor neuron, which is known to be centrally involved in the preparation of saccades, is also active during covert shifts of attention.
Takahiro Morimoto - One of the best experts on this subject based on the ideXlab platform.
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shift charge and spin photocurrents in dirac surface states of topological insulator
Physical Review B, 2017Co-Authors: Takahiro Morimoto, Naoto NagaosaAbstract:The generation of photocurrent in condensed matter is of main interest for photovoltaic and optoelectronic applications. Shift current, a nonlinear photoresponse, has attracted recent intensive attention as a dominant player of bulk photovoltaic effect in ferroelectric materials. In three dimensional topological insulators $\text{Bi}_2\text{X}_3$ (X: Te, Se), we find that Dirac surface states with a hexagonal warping term carry shift current by linearly polarized light. In addition, shift spin-current is introduced with the time-reversal symmetry breaking perturbation. The estimate for the magnitudes of the shift charge- and spin-currents are 0.13$I_0$ and 0.21$I_0$(nA/m) with the intensity of light $I_0$ measured in $(\text{W}/\text{m}^2)$, respectively, which can offer a useful method to generate these currents efficiently.
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shift charge and spin photocurrents in dirac surface states of topological insulator
Physical Review B, 2017Co-Authors: Kun Woo Kim, Takahiro Morimoto, Naoto NagaosaAbstract:The generation of photocurrent in condensed matter is of main interest for photovoltaic and optoelectronic applications. Shift current, a nonlinear photoresponse, has attracted recent intensive attention as a dominant player of bulk photovoltaic effect in ferroelectric materials. In three-dimensional topological insulators ${\text{Bi}}_{2}{X}_{3}$ ($X=\text{Te}$, Se), we find that Dirac surface states with a hexagonal warping term support shift current by linearly polarized light. Moreover, we study ``shift spin current'' that arises in Dirac surface states by introducing time-reversal symmetry breaking perturbation. The estimate for the magnitudes of the shift charge and spin current densities are $0.13{I}_{0}$ and $0.40{I}_{0}$ (nA/m) for ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ with the intensity of light ${I}_{0}$ measured in $(\text{W}/{\text{m}}^{2})$, respectively, which can offer a useful method to generate these currents efficiently.
