The Experts below are selected from a list of 46851 Experts worldwide ranked by ideXlab platform
Gerard Sullivan - One of the best experts on this subject based on the ideXlab platform.
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Robust helical Edge Transport in gated InAs/GaSb bilayers.
Physical Review Letters, 2015Co-Authors: Ivan Knez, Gerard SullivanAbstract:We have engineered electron-hole bilayers of inverted $\mathrm{InAs}/\mathrm{GaSb}$ quantum wells, using dilute silicon impurity doping to suppress residual bulk conductance. We have observed robust helical Edge states with wide conductance plateaus precisely quantized to $2{e}^{2}/h$ in mesoscopic Hall samples. On the other hand, in larger samples the Edge conductance is found to be inversely proportional to the Edge length. These characteristics persist in a wide temperature range and show essentially no temperature dependence. The quantized plateaus persist to a 12 T applied in-plane field; the conductance increases from $2{e}^{2}/h$ in strong perpendicular fields manifesting chiral Edge Transport. Our study presents a compelling case for exotic properties of a one-dimensional helical liquid on the Edge of $\mathrm{InAs}/\mathrm{GaSb}$ bilayers.
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robust helical Edge Transport in gated inas gasb bilayers
Physical Review Letters, 2015Co-Authors: Ivan Knez, Gerard SullivanAbstract:We have engineered electron-hole bilayers of inverted $\mathrm{InAs}/\mathrm{GaSb}$ quantum wells, using dilute silicon impurity doping to suppress residual bulk conductance. We have observed robust helical Edge states with wide conductance plateaus precisely quantized to $2{e}^{2}/h$ in mesoscopic Hall samples. On the other hand, in larger samples the Edge conductance is found to be inversely proportional to the Edge length. These characteristics persist in a wide temperature range and show essentially no temperature dependence. The quantized plateaus persist to a 12 T applied in-plane field; the conductance increases from $2{e}^{2}/h$ in strong perpendicular fields manifesting chiral Edge Transport. Our study presents a compelling case for exotic properties of a one-dimensional helical liquid on the Edge of $\mathrm{InAs}/\mathrm{GaSb}$ bilayers.
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Observation of Edge Transport in the disordered regime of topologically insulating InAs/GaSb quantum wells.
Physical Review Letters, 2014Co-Authors: Ivan Knez, Charles T. Rettner, See-hun Yang, Stuart S. P. Parkin, Gerard SullivanAbstract:We observe Edge Transport in the topologically insulating InAs=GaSb system in the disordered regime. Using asymmetric current paths we show that conduction occurs exclusively along the device Edge, exhibiting a large Hall signal at zero magnetic fields, while for symmetric current paths, the conductance between the two mesoscopicly separated probes is quantized to 2e 2 =h. Both quantized and self-averaged Transport show resilience to magnetic fields, and are temperature independent for temperatures between 20 mK and 1 K.
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observation of Edge Transport in the disordered regime of topologically insulating inas gasb quantum wells
Physical Review Letters, 2014Co-Authors: Ivan Knez, Charles T. Rettner, See-hun Yang, Stuart S. P. Parkin, Gerard SullivanAbstract:We observe Edge Transport in the topologically insulating InAs=GaSb system in the disordered regime. Using asymmetric current paths we show that conduction occurs exclusively along the device Edge, exhibiting a large Hall signal at zero magnetic fields, while for symmetric current paths, the conductance between the two mesoscopicly separated probes is quantized to 2e 2 =h. Both quantized and self-averaged Transport show resilience to magnetic fields, and are temperature independent for temperatures between 20 mK and 1 K.
Ivan Knez - One of the best experts on this subject based on the ideXlab platform.
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Robust helical Edge Transport in gated InAs/GaSb bilayers.
Physical Review Letters, 2015Co-Authors: Ivan Knez, Gerard SullivanAbstract:We have engineered electron-hole bilayers of inverted $\mathrm{InAs}/\mathrm{GaSb}$ quantum wells, using dilute silicon impurity doping to suppress residual bulk conductance. We have observed robust helical Edge states with wide conductance plateaus precisely quantized to $2{e}^{2}/h$ in mesoscopic Hall samples. On the other hand, in larger samples the Edge conductance is found to be inversely proportional to the Edge length. These characteristics persist in a wide temperature range and show essentially no temperature dependence. The quantized plateaus persist to a 12 T applied in-plane field; the conductance increases from $2{e}^{2}/h$ in strong perpendicular fields manifesting chiral Edge Transport. Our study presents a compelling case for exotic properties of a one-dimensional helical liquid on the Edge of $\mathrm{InAs}/\mathrm{GaSb}$ bilayers.
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robust helical Edge Transport in gated inas gasb bilayers
Physical Review Letters, 2015Co-Authors: Ivan Knez, Gerard SullivanAbstract:We have engineered electron-hole bilayers of inverted $\mathrm{InAs}/\mathrm{GaSb}$ quantum wells, using dilute silicon impurity doping to suppress residual bulk conductance. We have observed robust helical Edge states with wide conductance plateaus precisely quantized to $2{e}^{2}/h$ in mesoscopic Hall samples. On the other hand, in larger samples the Edge conductance is found to be inversely proportional to the Edge length. These characteristics persist in a wide temperature range and show essentially no temperature dependence. The quantized plateaus persist to a 12 T applied in-plane field; the conductance increases from $2{e}^{2}/h$ in strong perpendicular fields manifesting chiral Edge Transport. Our study presents a compelling case for exotic properties of a one-dimensional helical liquid on the Edge of $\mathrm{InAs}/\mathrm{GaSb}$ bilayers.
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Observation of Edge Transport in the disordered regime of topologically insulating InAs/GaSb quantum wells.
Physical Review Letters, 2014Co-Authors: Ivan Knez, Charles T. Rettner, See-hun Yang, Stuart S. P. Parkin, Gerard SullivanAbstract:We observe Edge Transport in the topologically insulating InAs=GaSb system in the disordered regime. Using asymmetric current paths we show that conduction occurs exclusively along the device Edge, exhibiting a large Hall signal at zero magnetic fields, while for symmetric current paths, the conductance between the two mesoscopicly separated probes is quantized to 2e 2 =h. Both quantized and self-averaged Transport show resilience to magnetic fields, and are temperature independent for temperatures between 20 mK and 1 K.
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observation of Edge Transport in the disordered regime of topologically insulating inas gasb quantum wells
Physical Review Letters, 2014Co-Authors: Ivan Knez, Charles T. Rettner, See-hun Yang, Stuart S. P. Parkin, Gerard SullivanAbstract:We observe Edge Transport in the topologically insulating InAs=GaSb system in the disordered regime. Using asymmetric current paths we show that conduction occurs exclusively along the device Edge, exhibiting a large Hall signal at zero magnetic fields, while for symmetric current paths, the conductance between the two mesoscopicly separated probes is quantized to 2e 2 =h. Both quantized and self-averaged Transport show resilience to magnetic fields, and are temperature independent for temperatures between 20 mK and 1 K.
Weston M. Stacey - One of the best experts on this subject based on the ideXlab platform.
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Analysis of toroidal phasing of resonant magnetic perturbation effects on Edge Transport in the DIII-D tokamak
Physics of Plasmas, 2013Co-Authors: T. M. Wilks, Weston M. Stacey, T.e. EvansAbstract:Resonant Magnetic Perturbation (RMP) fields produced by external control coils are considered a viable option for the suppression of Edge Localized Modes in present and future tokamaks. In DIII-D, the RMPs are generated by six pairs of I-coils, each spanning 60° in toroidal angle, with the currents flowing in opposite directions in adjacent pairs of I-coils. Reversal of the currents in all I-coils, which produces a 60° toroidal shift in the RMP field configuration, generates uniquely different Edge pedestal profiles of the density, temperature, and rotation velocities, implying different effects on the related Edge Transport phenomena caused by the difference in toroidal phase of the I-coil currents. The diffusive and non-diffusive Transport effects of this RMP toroidal phase reversal are analyzed by comparing the ion and electron heat diffusivities, angular momentum Transport frequencies, ion diffusion coefficients, and the particle pinch velocities interpreted from the measured profiles for the two phases of the I-coil currents.
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Spontaneous Edge Transport barrier formation due to suppression of Edge thermal instabilities as a low–high trigger mechanism in tokamaks
Physics of Plasmas, 2002Co-Authors: Weston M. StaceyAbstract:Models for the calculation of Edge temperature gradients, of growth rates of Edge thermal instabilities, and of the enhancement of Edge Transport coefficients due to thermal instability growth rates have been coupled. The composite model predicts the existence of threshold values of the Edge power flux at which the Edge Transport coefficients sharply decrease and the Edge temperature gradients sharply increase; i.e., an Edge Transport barrier forms. Predicted consequences of this Transport barrier formation are found to be qualitatively consistent with phenomena observed experimentally in conjunction with the L–H (low-to-high) transition. It is suggested that this spontaneous formation of an Edge Transport barrier due to suppression of an Edge thermal instability could be a trigger mechanism for the L–H transition in tokamaks.
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Thermal instabilities in the Edge Transport barrier
Physics of Plasmas, 1999Co-Authors: Weston M. StaceyAbstract:A linear analysis of the Edge Transport barrier identifies localized, two-dimensional (radial-perpendicular) thermal instabilities driven by both impurity radiation and atomic (ionization/charge-exchange/elastic scattering) cooling and suppressed by conductive and convective heat Transport. These instabilities are stabilized by sufficiently large values of the Edge temperature gradient. Numerical calculations indicate that such instabilities would be expected for Edge conditions (electron, impurity and neutral atom densities, temperatures, gradient scale lengths) typical of current tokamak experiments.
Shun-qing Shen - One of the best experts on this subject based on the ideXlab platform.
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Hidden Edge Dirac point and robust quantum Edge Transport in InAs/GaSb quantum wells
Physical Review B, 2018Co-Authors: Song-bo Zhang, Shun-qing ShenAbstract:The robustness of quantum Edge Transport in InAs/GaSb quantum wells in the presence of magnetic fields raises an issue on the fate of topological phases of matter under time-reversal symmetry breaking. A peculiar band structure evolution in InAs/GaSb quantum wells is revealed: the electron subbands cross the heavy hole subbands but anticross the light hole subbands. The topologically protected band crossing point (Dirac point) of the helical Edge states is pulled to be close to and even buried in the bulk valence bands when the system is in a deeply inverted regime, which is attributed to the existence of the light hole subbands. A sizable Zeeman energy gap verified by the effective $g$ factors of Edge states opens at the Dirac point by an in-plane or perpendicular magnetic field; however, it can also be hidden in the bulk valance bands. This provides a plausible explanation for the recent observation on the robustness of quantum Edge Transport in InAs/GaSb quantum wells subjected to strong magnetic fields.
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hidden Edge dirac point and robust quantum Edge Transport in inas gasb quantum wells
Physical Review B, 2018Co-Authors: Song-bo Zhang, Shun-qing ShenAbstract:The robustness of quantum Edge Transport in InAs/GaSb quantum wells in the presence of magnetic fields raises an issue on the fate of topological phases of matter under time-reversal symmetry breaking. A peculiar band structure evolution in InAs/GaSb quantum wells is revealed: the electron subbands cross the heavy hole subbands but anticross the light hole subbands. The topologically protected band crossing point (Dirac point) of the helical Edge states is pulled to be close to and even buried in the bulk valence bands when the system is in a deeply inverted regime, which is attributed to the existence of the light hole subbands. A sizable Zeeman energy gap verified by the effective $g$ factors of Edge states opens at the Dirac point by an in-plane or perpendicular magnetic field; however, it can also be hidden in the bulk valance bands. This provides a plausible explanation for the recent observation on the robustness of quantum Edge Transport in InAs/GaSb quantum wells subjected to strong magnetic fields.
Katsumi Ida - One of the best experts on this subject based on the ideXlab platform.
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Role of electric field curvature in the formation of Edge Transport barrier in the JT-60U tokamak
Plasma Physics and Controlled Fusion, 2017Co-Authors: K. Kamiya, Katsumi Ida, Kimitaka Itoh, S.-i. Itoh, Tatsuya KobayashiAbstract:Based on the high-resolution spectroscopic measurements of the radial electric field (E r) in the JT-60U tokamak, we have identified the mechanisms centered around the role of the E r-curvature on the Edge Transport barrier (ETB) formation. In addition, we recognized a new role of the E r-shear for the expansion of pedestal width, compensating an unfavorable effect of the E r-curvature having its sign dependence on the turbulence Transport. We found a new interesting phenomenon of very slow out-of-phase oscillations between the E r and ion temperature gradient in the frequency range of 30–50 Hz, preceding the slow L-H transition, which can demonstrate a causality test of the ETB formation in association with the non-uniformity E r-effects. A critical condition for the E r-bifurcations is also discussed.
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Simultaneous realization of a high density Edge Transport barrier and an improved L-mode on CHS
Nuclear Fusion, 2009Co-Authors: Takashi Minami, S. Okamura, Tsuyoshi Akiyama, Chihiro Suzuki, Katsumi Ida, M. Isobe, Tetsutarou Oishi, Haruhisa Nakano, Keiji Matsuo, Akihide FujisawaAbstract:An Edge Transport barrier (ETB) formation and an improved L-mode (IL mode) have been simultaneously realized in the high density region ( ) on the Compact Helical System (CHS). When the ETB is formed during the IL mode, the density reduction in the Edge region is suppressed by the barrier formation. As a result of the continuous increase in the temperature by the IL mode, the stored energy during the combined mode increased up to the maximum stored energy (Wp ~ 9.4 kJ) recorded in the CHS experiments. The plasma pressure in the peripheral region increases up to three times compared with the L-mode, and the large Edge plasma pressure gradient is formed accompanying the pedestal structure. This is caused by the anomalous Transport reduction that is confirmed by the sharp drop in the density fluctuation in the Edge region. The neutral particle density reduction in the peripheral region and the metallic impurity accumulation in the core plasma are simultaneously observed during the high density ETB formation.
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Observation of the high-density Edge Transport barrier in CHS using beam emission spectroscopy
Journal of Physics: Conference Series, 2008Co-Authors: Tetsutarou Oishi, Mikio Yoshinuma, T Minami, K. Nagaoka, Katsumi Ida, M. Isobe, Shinichiro Kado, T. Akiyama, C. Suzuki, S. OkamuraAbstract:The formation of an Edge Transport barrier (ETB) has been observed in the high-density region (ne ~ 1.0 × 1020 m-3) of the Compact Helical System (CHS). The high-density ETB is observed in so-called 'reheat mode' discharge, an improved confinement mode in which the temperature increases due to the change of density profile by controlling gas-puff fueling. In the present study, we investigated the behaviour of the density profile and the density fluctuations in the Edge region accompanied by the formation of the high-density ETB using beam emission spectroscopy (BES), and we compared the behaviour with that of the normal ETB transition of CHS. BES has been implemented in CHS to simultaneously measure both local density fluctuations and gradients. It revealed that the density, density gradient, and inverse value of the density scale length increase in the Edge region at both the normal ETB transition and the high-density ETB transition. The turbulence of the frequency at less than 20 kHz is suppressed at the formation of the high-density ETB.
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Characteristics of high density Edge Transport barrier with reheat mode on CHS
Journal of Physics: Conference Series, 2008Co-Authors: T Minami, S. Okamura, K. Nagaoka, Katsumi Ida, M. Isobe, Akihide Fujisawa, Tetsutarou Oishi, Haruhisa Nakano, T. Akiyama, Mikio YoshinumaAbstract:Edge Transport barrier (ETB) formation and a reheat mode have been simultaneously realized on the Compact Helical System (CHS). The new mode is induced by neutral particle reduction in the Edge region, which is caused by shutting off fueling after a strong gas-puffing. When both the reheat mode and the ETB are simultaneously realized, the density reduction is suppressed by the ETB in the peripheral region, and the temperature continues to increase by the reheat mode. This mode provides an enhanced confinement in the high density region (e ~ 1.2 × 1020mr-3) compared to the ETB formation without the reheat mode, because of a large suppression of an anomalous Transport, which is confirmed with fluctuation measurements in the Edge region.
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Scaling of power threshold for Edge Transport barrier formation in CHS with density, magnetic field and magnetic configuration
Plasma Physics and Controlled Fusion, 2006Co-Authors: Tsuyoshi Akiyama, S. Okamura, T. Oishi, Katsumi Ida, K. Toi, Akihide Fujisawa, Takashi Minami, Shinichiro Kado, Masaki Takeuchi, Mikio YoshinumaAbstract:An improved confinement state by the formation of an Edge Transport barrier can be obtained in the compact helical system. A power threshold exists, as is the case for the H-mode in tokamaks. The threshold scales as . These dependences are similar to those in tokamaks. The threshold also depends on magnetic configuration parameters such as the position of the magnetic axis. The absolute value of the threshold is 1–3 times larger than the tokamak H-mode power scaling.
