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1دورية أكاديمية
المؤلفون: Chen, Hao, Zhou, Pinjia, Liu, Jiawei, Qiao, Jiabin, Oezyilmaz, Barbaros, Martin, Jens
المصدر: Nature Communications 11 (2020)
مصطلحات موضوعية: graphene, electron, experimental study, geometry, magnetic field, one-dimensional modeling, optimization, polarization, quantum mechanics, stacking, wave propagation
الوقت: 500
الوصف: Sign reversal of Berry curvature across two oppositely gated regions in bilayer graphene can give rise to counter-propagating 1D channels with opposite valley indices. Considering spin and sub-lattice degeneracy, there are four quantized conduction channels in each direction. Previous experimental work on gate-controlled valley polarizer achieved good contrast only in the presence of an external magnetic field. Yet, with increasing magnetic field the ungated regions of bilayer graphene will transit into the quantum Hall regime, limiting the applications of valley-polarized electrons. Here we present improved performance of a gate-controlled valley polarizer through optimized device geometry and stacking method. Electrical measurements show up to two orders of magnitude difference in conductance between the valley-polarized state and gapped states. The valley-polarized state displays conductance of nearly 4e2/h and produces contrast in a subsequent valley analyzer configuration. These results pave the way to further experiments on valley-polarized electrons in zero magnetic field. ; publishedVersion
وصف الملف: application/pdf
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2دورية أكاديمية
المؤلفون: Stephan, C.C., Schmidt, H., Zülicke, C., Matthias, V.
المصدر: JGR : Atmospheres 125 (2020), Nr. 1
مصطلحات موضوعية: Gravity wave propagation, High-resolution climate model, Microwave Limb Sounder, Sudden Stratospheric Warming, Tilt of polar night jet, Zonal asymmetries
الوقت: 550
الوصف: Gravity waves (GWs) are important for coupling the mesosphere to the lower atmosphere during sudden stratospheric warmings (SSWs). Here, a minor SSW is internally generated in a simulation with the upper-atmosphere configuration of the ICOsahedral Nonhydrostatic model. At a horizontal resolution of 20 km the simulation uses no GW drag parameterizations but resolves large fractions of the GW spectrum explicitly, including orographic and nonorographic sources. Consistent with previous studies, the simulated zonal-mean stratospheric warming is accompanied by zonal-mean mesospheric cooling. During the course of the SSW the mesospheric GW momentum flux (GWMF) turns from mainly westward to mainly eastward. Waves of large phase speed (40–80 m s -1) dominate the eastward GWMF during the peak phase of the warming. The GWMF is strongest along the polar night jet axis. Parameterizations of GWs usually assume straight upward propagation, but this assumption is often not satisfied. In the case studied here, a substantial amount of the GWMF is significantly displaced horizontally between the source region and the dissipation region, implying that the local impact of GWs on the mesosphere does not need to be above their local transmission through the stratosphere. The simulation produces significant vertically misaligned anomalies between the stratosphere and mesosphere. Observations by the Microwave Limb Sounder confirm the poleward tilt with height of the polar night jet and horizontal displacements between mesospheric cooling and stratospheric warming patterns. Thus, lateral GW propagation may be required to explain the middle-atmosphere temperature evolution in SSW events with significant zonally asymmetric anomalies. ©2019. The Authors. ; publishedVersion
وصف الملف: application/pdf
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3دورية أكاديمية
المؤلفون: Chen, Hao, Zhou, Pinjia, Liu, Jiawei, Qiao, Jiabin, Oezyilmaz, Barbaros, Martin, Jens
المصدر: Nature Communications 11 (2020)
مصطلحات موضوعية: graphene, electron, experimental study, geometry, magnetic field, one-dimensional modeling, optimization, polarization, quantum mechanics, stacking, wave propagation
الوقت: 500
الوصف: Sign reversal of Berry curvature across two oppositely gated regions in bilayer graphene can give rise to counter-propagating 1D channels with opposite valley indices. Considering spin and sub-lattice degeneracy, there are four quantized conduction channels in each direction. Previous experimental work on gate-controlled valley polarizer achieved good contrast only in the presence of an external magnetic field. Yet, with increasing magnetic field the ungated regions of bilayer graphene will transit into the quantum Hall regime, limiting the applications of valley-polarized electrons. Here we present improved performance of a gate-controlled valley polarizer through optimized device geometry and stacking method. Electrical measurements show up to two orders of magnitude difference in conductance between the valley-polarized state and gapped states. The valley-polarized state displays conductance of nearly 4e2/h and produces contrast in a subsequent valley analyzer configuration. These results pave the way to further experiments on valley-polarized electrons in zero magnetic field. ; publishedVersion
وصف الملف: application/pdf
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4دورية أكاديمية
المؤلفون: Stephan, C.C., Schmidt, H., Zülicke, C., Matthias, V.
المصدر: JGR : Atmospheres 125 (2020), Nr. 1
مصطلحات موضوعية: Gravity wave propagation, High-resolution climate model, Microwave Limb Sounder, Sudden Stratospheric Warming, Tilt of polar night jet, Zonal asymmetries
الوقت: 550
الوصف: Gravity waves (GWs) are important for coupling the mesosphere to the lower atmosphere during sudden stratospheric warmings (SSWs). Here, a minor SSW is internally generated in a simulation with the upper-atmosphere configuration of the ICOsahedral Nonhydrostatic model. At a horizontal resolution of 20 km the simulation uses no GW drag parameterizations but resolves large fractions of the GW spectrum explicitly, including orographic and nonorographic sources. Consistent with previous studies, the simulated zonal-mean stratospheric warming is accompanied by zonal-mean mesospheric cooling. During the course of the SSW the mesospheric GW momentum flux (GWMF) turns from mainly westward to mainly eastward. Waves of large phase speed (40–80 m s -1) dominate the eastward GWMF during the peak phase of the warming. The GWMF is strongest along the polar night jet axis. Parameterizations of GWs usually assume straight upward propagation, but this assumption is often not satisfied. In the case studied here, a substantial amount of the GWMF is significantly displaced horizontally between the source region and the dissipation region, implying that the local impact of GWs on the mesosphere does not need to be above their local transmission through the stratosphere. The simulation produces significant vertically misaligned anomalies between the stratosphere and mesosphere. Observations by the Microwave Limb Sounder confirm the poleward tilt with height of the polar night jet and horizontal displacements between mesospheric cooling and stratospheric warming patterns. Thus, lateral GW propagation may be required to explain the middle-atmosphere temperature evolution in SSW events with significant zonally asymmetric anomalies. ©2019. The Authors. ; publishedVersion
وصف الملف: application/pdf
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5دورية أكاديمية
المؤلفون: Chen, Hao, Zhou, Pinjia, Liu, Jiawei, Qiao, Jiabin, Oezyilmaz, Barbaros, Martin, Jens
المصدر: Nature Communications 11 (2020)
مصطلحات موضوعية: graphene, electron, experimental study, geometry, magnetic field, one-dimensional modeling, optimization, polarization, quantum mechanics, stacking, wave propagation
الوقت: 500
الوصف: Sign reversal of Berry curvature across two oppositely gated regions in bilayer graphene can give rise to counter-propagating 1D channels with opposite valley indices. Considering spin and sub-lattice degeneracy, there are four quantized conduction channels in each direction. Previous experimental work on gate-controlled valley polarizer achieved good contrast only in the presence of an external magnetic field. Yet, with increasing magnetic field the ungated regions of bilayer graphene will transit into the quantum Hall regime, limiting the applications of valley-polarized electrons. Here we present improved performance of a gate-controlled valley polarizer through optimized device geometry and stacking method. Electrical measurements show up to two orders of magnitude difference in conductance between the valley-polarized state and gapped states. The valley-polarized state displays conductance of nearly 4e2/h and produces contrast in a subsequent valley analyzer configuration. These results pave the way to further experiments on valley-polarized electrons in zero magnetic field. ; publishedVersion
وصف الملف: application/pdf
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6دورية أكاديمية
المؤلفون: Stephan, C.C., Schmidt, H., Zülicke, C., Matthias, V.
المصدر: JGR : Atmospheres 125 (2020), Nr. 1
مصطلحات موضوعية: Gravity wave propagation, High-resolution climate model, Microwave Limb Sounder, Sudden Stratospheric Warming, Tilt of polar night jet, Zonal asymmetries
الوقت: 550
الوصف: Gravity waves (GWs) are important for coupling the mesosphere to the lower atmosphere during sudden stratospheric warmings (SSWs). Here, a minor SSW is internally generated in a simulation with the upper-atmosphere configuration of the ICOsahedral Nonhydrostatic model. At a horizontal resolution of 20 km the simulation uses no GW drag parameterizations but resolves large fractions of the GW spectrum explicitly, including orographic and nonorographic sources. Consistent with previous studies, the simulated zonal-mean stratospheric warming is accompanied by zonal-mean mesospheric cooling. During the course of the SSW the mesospheric GW momentum flux (GWMF) turns from mainly westward to mainly eastward. Waves of large phase speed (40–80 m s -1) dominate the eastward GWMF during the peak phase of the warming. The GWMF is strongest along the polar night jet axis. Parameterizations of GWs usually assume straight upward propagation, but this assumption is often not satisfied. In the case studied here, a substantial amount of the GWMF is significantly displaced horizontally between the source region and the dissipation region, implying that the local impact of GWs on the mesosphere does not need to be above their local transmission through the stratosphere. The simulation produces significant vertically misaligned anomalies between the stratosphere and mesosphere. Observations by the Microwave Limb Sounder confirm the poleward tilt with height of the polar night jet and horizontal displacements between mesospheric cooling and stratospheric warming patterns. Thus, lateral GW propagation may be required to explain the middle-atmosphere temperature evolution in SSW events with significant zonally asymmetric anomalies. ©2019. The Authors. ; publishedVersion
وصف الملف: application/pdf
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7دورية أكاديمية
المؤلفون: Chen, Hao, Zhou, Pinjia, Liu, Jiawei, Qiao, Jiabin, Oezyilmaz, Barbaros, Martin, Jens
المصدر: Nature Communications 11 (2020)
مصطلحات موضوعية: graphene, electron, experimental study, geometry, magnetic field, one-dimensional modeling, optimization, polarization, quantum mechanics, stacking, wave propagation
الوقت: 500
الوصف: Sign reversal of Berry curvature across two oppositely gated regions in bilayer graphene can give rise to counter-propagating 1D channels with opposite valley indices. Considering spin and sub-lattice degeneracy, there are four quantized conduction channels in each direction. Previous experimental work on gate-controlled valley polarizer achieved good contrast only in the presence of an external magnetic field. Yet, with increasing magnetic field the ungated regions of bilayer graphene will transit into the quantum Hall regime, limiting the applications of valley-polarized electrons. Here we present improved performance of a gate-controlled valley polarizer through optimized device geometry and stacking method. Electrical measurements show up to two orders of magnitude difference in conductance between the valley-polarized state and gapped states. The valley-polarized state displays conductance of nearly 4e2/h and produces contrast in a subsequent valley analyzer configuration. These results pave the way to further experiments on valley-polarized electrons in zero magnetic field. ; publishedVersion
وصف الملف: application/pdf
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8دورية أكاديمية
المؤلفون: Stephan, C.C., Schmidt, H., Zülicke, C., Matthias, V.
المصدر: JGR : Atmospheres 125 (2020), Nr. 1
مصطلحات موضوعية: Gravity wave propagation, High-resolution climate model, Microwave Limb Sounder, Sudden Stratospheric Warming, Tilt of polar night jet, Zonal asymmetries
الوقت: 550
الوصف: Gravity waves (GWs) are important for coupling the mesosphere to the lower atmosphere during sudden stratospheric warmings (SSWs). Here, a minor SSW is internally generated in a simulation with the upper-atmosphere configuration of the ICOsahedral Nonhydrostatic model. At a horizontal resolution of 20 km the simulation uses no GW drag parameterizations but resolves large fractions of the GW spectrum explicitly, including orographic and nonorographic sources. Consistent with previous studies, the simulated zonal-mean stratospheric warming is accompanied by zonal-mean mesospheric cooling. During the course of the SSW the mesospheric GW momentum flux (GWMF) turns from mainly westward to mainly eastward. Waves of large phase speed (40–80 m s -1) dominate the eastward GWMF during the peak phase of the warming. The GWMF is strongest along the polar night jet axis. Parameterizations of GWs usually assume straight upward propagation, but this assumption is often not satisfied. In the case studied here, a substantial amount of the GWMF is significantly displaced horizontally between the source region and the dissipation region, implying that the local impact of GWs on the mesosphere does not need to be above their local transmission through the stratosphere. The simulation produces significant vertically misaligned anomalies between the stratosphere and mesosphere. Observations by the Microwave Limb Sounder confirm the poleward tilt with height of the polar night jet and horizontal displacements between mesospheric cooling and stratospheric warming patterns. Thus, lateral GW propagation may be required to explain the middle-atmosphere temperature evolution in SSW events with significant zonally asymmetric anomalies. ©2019. The Authors. ; publishedVersion
وصف الملف: application/pdf
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9دورية أكاديمية
المؤلفون: Chen, Hao, Zhou, Pinjia, Liu, Jiawei, Qiao, Jiabin, Oezyilmaz, Barbaros, Martin, Jens
المصدر: Nature Communications 11 (2020)
مصطلحات موضوعية: graphene, electron, experimental study, geometry, magnetic field, one-dimensional modeling, optimization, polarization, quantum mechanics, stacking, wave propagation
الوقت: 500
الوصف: Sign reversal of Berry curvature across two oppositely gated regions in bilayer graphene can give rise to counter-propagating 1D channels with opposite valley indices. Considering spin and sub-lattice degeneracy, there are four quantized conduction channels in each direction. Previous experimental work on gate-controlled valley polarizer achieved good contrast only in the presence of an external magnetic field. Yet, with increasing magnetic field the ungated regions of bilayer graphene will transit into the quantum Hall regime, limiting the applications of valley-polarized electrons. Here we present improved performance of a gate-controlled valley polarizer through optimized device geometry and stacking method. Electrical measurements show up to two orders of magnitude difference in conductance between the valley-polarized state and gapped states. The valley-polarized state displays conductance of nearly 4e2/h and produces contrast in a subsequent valley analyzer configuration. These results pave the way to further experiments on valley-polarized electrons in zero magnetic field. ; publishedVersion
وصف الملف: application/pdf
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10دورية أكاديمية
المؤلفون: Stephan, C.C., Schmidt, H., Zülicke, C., Matthias, V.
المصدر: JGR : Atmospheres 125 (2020), Nr. 1
مصطلحات موضوعية: Gravity wave propagation, High-resolution climate model, Microwave Limb Sounder, Sudden Stratospheric Warming, Tilt of polar night jet, Zonal asymmetries
الوقت: 550
الوصف: Gravity waves (GWs) are important for coupling the mesosphere to the lower atmosphere during sudden stratospheric warmings (SSWs). Here, a minor SSW is internally generated in a simulation with the upper-atmosphere configuration of the ICOsahedral Nonhydrostatic model. At a horizontal resolution of 20 km the simulation uses no GW drag parameterizations but resolves large fractions of the GW spectrum explicitly, including orographic and nonorographic sources. Consistent with previous studies, the simulated zonal-mean stratospheric warming is accompanied by zonal-mean mesospheric cooling. During the course of the SSW the mesospheric GW momentum flux (GWMF) turns from mainly westward to mainly eastward. Waves of large phase speed (40–80 m s -1) dominate the eastward GWMF during the peak phase of the warming. The GWMF is strongest along the polar night jet axis. Parameterizations of GWs usually assume straight upward propagation, but this assumption is often not satisfied. In the case studied here, a substantial amount of the GWMF is significantly displaced horizontally between the source region and the dissipation region, implying that the local impact of GWs on the mesosphere does not need to be above their local transmission through the stratosphere. The simulation produces significant vertically misaligned anomalies between the stratosphere and mesosphere. Observations by the Microwave Limb Sounder confirm the poleward tilt with height of the polar night jet and horizontal displacements between mesospheric cooling and stratospheric warming patterns. Thus, lateral GW propagation may be required to explain the middle-atmosphere temperature evolution in SSW events with significant zonally asymmetric anomalies. ©2019. The Authors. ; publishedVersion
وصف الملف: application/pdf
