Thermal Characterization of a Hall Effect Thruster
2008-03-01
Material Curie Temperature Iron 770 °C Nickel 358 °C Cobalt 1130 °C Gadolinium 20 °C Terfenol 380-430 °C Alnico 850 °C Hard Ferrites 400-700...C Barium Ferrite 450 °C Hall Effect thrusters generally use iron magnets with a Curie temperature of 770 °C. Decreasing the magnetic strength
Characterization of Hall effect thruster propellant distributors with flame visualization
NASA Astrophysics Data System (ADS)
Langendorf, S.; Walker, M. L. R.
2013-01-01
A novel method for the characterization and qualification of Hall effect thruster propellant distributors is presented. A quantitative measurement of the azimuthal number density uniformity, a metric which impacts propellant utilization, is obtained from photographs of a premixed flame anchored on the exit plane of the propellant distributor. The technique is demonstrated for three propellant distributors using a propane-air mixture at reservoir pressure of 40 psi (gauge) (377 kPa) exhausting to atmosphere, with volumetric flow rates ranging from 15-145 cfh (7.2-68 l/min) with equivalence ratios from 1.2 to 2.1. The visualization is compared with in-vacuum pressure measurements 1 mm downstream of the distributor exit plane (chamber pressure held below 2.7 × 10-5 Torr-Xe at all flow rates). Both methods indicate a non-uniformity in line with the propellant inlet, supporting the validity of the technique of flow visualization with flame luminosity for propellant distributor characterization. The technique is applied to a propellant distributor with a manufacturing defect in a known location and is able to identify the defect and characterize its impact. The technique is also applied to a distributor with numerous small orifices at the exit plane and is able to resolve the resulting non-uniformity. Luminosity data are collected with a spatial resolution of 48.2-76.1 μm (pixel width). The azimuthal uniformity is characterized in the form of standard deviation of azimuthal luminosities, normalized by the mean azimuthal luminosity. The distributors investigated achieve standard deviations of 0.346 ± 0.0212, 0.108 ± 0.0178, and 0.708 ± 0.0230 mean-normalized luminosity units respectively, where a value of 0 corresponds to perfect uniformity and a value of 1 represents a standard deviation equivalent to the mean.
Simplifying Nanowire Hall Effect Characterization by Using a Three-Probe Device Design.
Hultin, Olof; Otnes, Gaute; Samuelson, Lars; Storm, Kristian
2017-02-08
Electrical characterization of nanowires is a time-consuming and challenging task due to the complexity of single nanowire device fabrication and the difficulty in interpreting the measurements. We present a method to measure Hall effect in nanowires using a three-probe device that is simpler to fabricate than previous four-probe nanowire Hall devices and allows characterization of nanowires with smaller diameter. Extraction of charge carrier concentration from the three-probe measurements using an analytical model is discussed and compared to simulations. The validity of the method is experimentally verified by a comparison between results obtained with the three-probe method and results obtained using four-probe nanowire Hall measurements. In addition, a nanowire with a diameter of only 65 nm is characterized to demonstrate the capabilities of the method. The three-probe Hall effect method offers a relatively fast and simple, yet accurate way to quantify the charge carrier concentration in nanowires and has the potential to become a standard characterization technique for nanowires.
Planar Hall effect based characterization of spin orbital torques in Ta/CoFeB/MgO structures
NASA Astrophysics Data System (ADS)
Jamali, Mahdi; Zhao, Zhengyang; DC, Mahendra; Zhang, Delin; Li, Hongshi; Smith, Angeline K.; Wang, Jian-Ping
2016-04-01
The spin orbital torques in Ta/CoFeB/MgO structures are experimentally investigated utilizing the planar Hall effect and magnetoresistance measurement. By angular field characterization of the planar Hall resistance at ±current, the differential resistance which is directly related to the spin orbital torques is derived. Upon curve fitting of the analytical formulas over the experimental results, it is found that the anti-damping torque, also known as spin Hall effect, is sizable while a negligible field-like torque is observed. A spin Hall angle of about 18 ± 0.6% is obtained for the Ta layer. Temperature dependent study of the spin orbital torques is also performed. It is found that temperature does not significantly modify the spin Hall angle. By cooling down the sample down to 100 K, the obtained spin Hall angle has a maximum value of about 20.5 ± 0.43%.
INTERMETALLIC COMPOUNDS, *SEMICONDUCTING FILMS, *THIN FILM STORAGE DEVICES, ANTIMONY ALLOYS, CRYSTALLIZATION, ELECTRODES, ELECTROMAGNETIC PROPERTIES, EVAPORATION, HALL EFFECT , HEAT TREATMENT, INDIUM ALLOYS, ELECTRICAL RESISTANCE.
NASA Astrophysics Data System (ADS)
Avdonin, A.; Skupiński, P.; Grasza, K.
2016-02-01
A simple description of the Hall effect in the hopping regime of conductivity in semiconductors is presented. Expressions for the Hall coefficient and Hall mobility are derived by considering averaged equilibrium electron transport in a single triangle of localization sites in a magnetic field. Dependence of the Hall coefficient is analyzed in a wide range of temperature and magnetic field values. Our theoretical result is applied to our experimental data on temperature dependence of Hall effect and Hall mobility in ZnO.
2011-04-01
spin-transfer torque gives rise to magnetization reversal and excitation of spin-waves in ferromagnet /normal- metal / ferromagnet trilayers (F/N/F...applications based on the extraordinary Hall effect (EHE). The work was focused on three major tasks: 1. Preparation and study of CoPd multilayers ...D. Rosenblatt, M. Karpovski and A. Gerber, Reversal of the Extraordinary Hall Effect polarity in thin Co-Pd multilayers ., Appl. Phys. Lett., 96
Optical Hall effect-model description: tutorial.
Schubert, Mathias; Kühne, Philipp; Darakchieva, Vanya; Hofmann, Tino
2016-08-01
The optical Hall effect is a physical phenomenon that describes the occurrence of magnetic-field-induced dielectric displacement at optical wavelengths, transverse and longitudinal to the incident electric field, and analogous to the static electrical Hall effect. The electrical Hall effect and certain cases of the optical Hall effect observations can be explained by extensions of the classic Drude model for the transport of electrons in metals. The optical Hall effect is most useful for characterization of electrical properties in semiconductors. Among many advantages, while the optical Hall effect dispenses with the need of electrical contacts, electrical material properties such as effective mass and mobility parameters, including their anisotropy as well as carrier type and density, can be determined from the optical Hall effect. Measurement of the optical Hall effect can be performed within the concept of generalized ellipsometry at an oblique angle of incidence. In this paper, we review and discuss physical model equations, which can be used to calculate the optical Hall effect in single- and multiple-layered structures of semiconductor materials. We define the optical Hall effect dielectric function tensor, demonstrate diagonalization approaches, and show requirements for the optical Hall effect tensor from energy conservation. We discuss both continuum and quantum approaches, and we provide a brief description of the generalized ellipsometry concept, the Mueller matrix calculus, and a 4×4 matrix algebra to calculate data accessible by experiment. In a follow-up paper, we will discuss strategies and approaches for experimental data acquisition and analysis.
Nonlocal Anomalous Hall Effect.
Zhang, Steven S-L; Vignale, Giovanni
2016-04-01
The anomalous Hall (AH) effect is deemed to be a unique transport property of ferromagnetic metals, caused by the concerted action of spin polarization and spin-orbit coupling. Nevertheless, recent experiments have shown that the effect also occurs in a nonmagnetic metal (Pt) in contact with a magnetic insulator [yttrium iron garnet (YIG)], even when precautions are taken to ensure that there is no induced magnetization in the metal. We propose a theory of this effect based on the combined action of spin-dependent scattering from the magnetic interface and the spin-Hall effect in the bulk of the metal. At variance with previous theories, we predict the effect to be of first order in the spin-orbit coupling, just as the conventional anomalous Hall effect-the only difference being the spatial separation of the spin-orbit interaction and the magnetization. For this reason we name this effect the nonlocal anomalous Hall effect and predict that its sign will be determined by the sign of the spin-Hall angle in the metal. The AH conductivity that we calculate from our theory is in order of magnitude agreement with the measured values in Pt/YIG structures.
Nonlocal Anomalous Hall Effect
NASA Astrophysics Data System (ADS)
Zhang, Steven S.-L.; Vignale, Giovanni
2016-04-01
The anomalous Hall (AH) effect is deemed to be a unique transport property of ferromagnetic metals, caused by the concerted action of spin polarization and spin-orbit coupling. Nevertheless, recent experiments have shown that the effect also occurs in a nonmagnetic metal (Pt) in contact with a magnetic insulator [yttrium iron garnet (YIG)], even when precautions are taken to ensure that there is no induced magnetization in the metal. We propose a theory of this effect based on the combined action of spin-dependent scattering from the magnetic interface and the spin-Hall effect in the bulk of the metal. At variance with previous theories, we predict the effect to be of first order in the spin-orbit coupling, just as the conventional anomalous Hall effect—the only difference being the spatial separation of the spin-orbit interaction and the magnetization. For this reason we name this effect the nonlocal anomalous Hall effect and predict that its sign will be determined by the sign of the spin-Hall angle in the metal. The AH conductivity that we calculate from our theory is in order of magnitude agreement with the measured values in Pt /YIG structures.
Backman, Daniel E; LeSavage, Bauer L; Wong, Joyce Y
2017-01-25
Mismatch of hierarchical structure and mechanical properties between tissue-engineered implants and native tissue may result in signal cues that negatively impact repair and remodeling. With bottom-up tissue engineering approaches, designing tissue components with proper microscale mechanical properties is crucial to achieve necessary macroscale properties in the final implant. However, characterizing microscale mechanical properties is challenging, and current methods do not provide the versatility and sensitivity required to measure these fragile, soft biological materials. Here, we developed a novel, highly sensitive Hall-Effect based force sensor that is capable of measuring mechanical properties of biological materials over wide force ranges (μN to N), allowing its use at all steps in layer-by-layer fabrication of engineered tissues. The force sensor design can be easily customized to measure specific force ranges, while remaining easy to fabricate using inexpensive, commercial materials. Although we used the force sensor to characterize mechanics of single-layer cell sheets and silk fibers, the design can be easily adapted for different applications spanning larger force ranges (>N). This platform is thus a novel, versatile, and practical tool for mechanically characterizing biological and biomimetic materials.
ERIC Educational Resources Information Center
Kunkel, W. B.
1981-01-01
Describes an apparatus and procedure for conducting an undergraduate laboratory experiment to quantitatively study the Hall effect in a plasma. Includes background information on the Hall effect and rationale for conducting the experiment. (JN)
Facility Effect Characterization Test of NASA's HERMeS Hall Thruster
NASA Technical Reports Server (NTRS)
Huang, Wensheng; Kamhawi, Hani; Haag, Thomas W.; Ortega, Alejandro Lopez; Mikellides, Ioannis G.
2016-01-01
A test to characterize the effect of varying background pressure on NASA's 12.5-kW Hall Effect Rocket with Magnetic Shielding had being completed. This thruster is the baseline propulsion system for the Solar Electric Propulsion Technology Demonstration Mission (SEP TDM). Potential differences in thruster performance and oscillation characteristics when in ground facilities versus on-orbit are considered a primary risk for the propulsion system of the Asteroid Redirect Robotic Mission, which is a candidate for SEP TDM. The first primary objective of this test was to demonstrate that the tools being developed to predict the zero-background-pressure behavior of the thruster can provide self-consistent results. The second primary objective of this test was to provide data for refining a physics-based model of the thruster plume that will be used in spacecraft interaction studies. Diagnostics deployed included a thrust stand, Faraday probe, Langmuir probe, retarding potential analyzer, Wien filter spectrometer, and high-speed camera. From the data, a physics-based plume model was refined. Comparisons of empirical data to modeling results are shown.
Nonlocal anomalous Hall effect
NASA Astrophysics Data System (ADS)
Zhang, Shulei; Vignale, Giovanni
Anomalous Hall effect (AHE) is a distinctive transport property of ferromagnetic metals arising from spin orbit coupling (SOC) in concert with spontaneous spin polarization. Nonetheless, recent experiments have shown that the effect also appears in a nonmagnetic metal in contact with a magnetic insulator. The main puzzle lies in the apparent absence of spin polarized electrons in the non-magnetic metal. Here, we theoretically demonstrate that the scattering of electrons from a rough metal-insulator interface is generally spin-dependent, which results in mutual conversion between spin and charge currents flowing in the plane of the layer. It is the current-carrying spin polarized electrons and the spin Hall effect in the bulk of the metal layer that conspire to generate the AH current. This novel AHE differs from the conventional one only in the spatial separation of the SOC and the magnetization, so we name it as nonlocal AHE. In contrast to other previously proposed mechanisms (e.g., spin Hall AHE and magnetic proximity effect (MPE)), the nonlocal AHE appears on the first order of spin Hall angle and does not rely on the induced moments in the metal layer, which make it experimentally detectable by contrasting the AH current directions of two layered structures such as Pt/Cu/YIG and β -Ta/Cu/YIG (with a thin inserted Cu layer to eliminate the MPE). We predict that the directions of the AH currents in these two trilayers would be opposite since the spin Hall angles of Pt and β -Ta are of opposite signs. Work supported by NSF Grants DMR-1406568.
NASA Astrophysics Data System (ADS)
Sinova, Jairo; Valenzuela, Sergio O.; Wunderlich, J.; Back, C. H.; Jungwirth, T.
2015-10-01
Spin Hall effects are a collection of relativistic spin-orbit coupling phenomena in which electrical currents can generate transverse spin currents and vice versa. Despite being observed only a decade ago, these effects are already ubiquitous within spintronics, as standard spin-current generators and detectors. Here the theoretical and experimental results that have established this subfield of spintronics are reviewed. The focus is on the results that have converged to give us the current understanding of the phenomena, which has evolved from a qualitative to a more quantitative measurement of spin currents and their associated spin accumulation. Within the experimental framework, optical-, transport-, and magnetization-dynamics-based measurements are reviewed and linked to both phenomenological and microscopic theories of the effect. Within the theoretical framework, the basic mechanisms in both the extrinsic and intrinsic regimes are reviewed, which are linked to the mechanisms present in their closely related phenomenon in ferromagnets, the anomalous Hall effect. Also reviewed is the connection to the phenomenological treatment based on spin-diffusion equations applicable to certain regimes, as well as the spin-pumping theory of spin generation used in many measurements of the spin Hall angle. A further connection to the spin-current-generating spin Hall effect to the inverse spin galvanic effect is given, in which an electrical current induces a nonequilibrium spin polarization. This effect often accompanies the spin Hall effect since they share common microscopic origins. Both can exhibit the same symmetries when present in structures comprising ferromagnetic and nonmagnetic layers through their induced current-driven spin torques or induced voltages. Although a short chronological overview of the evolution of the spin Hall effect field and the resolution of some early controversies is given, the main body of this review is structured from a pedagogical
Performance and Thermal Characterization of the NASA-300MS 20 kW Hall Effect Thruster
NASA Technical Reports Server (NTRS)
Kamhawi, Hani; Huang, Wensheng; Haag, Thomas; Shastry, Rohit; Soulas, George; Smith, Timothy; Mikellides, Ioannis; Hofer, Richard
2013-01-01
NASA's Space Technology Mission Directorate is sponsoring the development of a high fidelity 15 kW-class long-life high performance Hall thruster for candidate NASA technology demonstration missions. An essential element of the development process is demonstration that incorporation of magnetic shielding on a 20 kW-class Hall thruster will yield significant improvements in the throughput capability of the thruster without any significant reduction in thruster performance. As such, NASA Glenn Research Center and the Jet Propulsion Laboratory collaborated on modifying the NASA-300M 20 kW Hall thruster to improve its propellant throughput capability. JPL and NASA Glenn researchers performed plasma numerical simulations with JPL's Hall2De and a commercially available magnetic modeling code that indicated significant enhancement in the throughput capability of the NASA-300M can be attained by modifying the thruster's magnetic circuit. This led to modifying the NASA-300M magnetic topology to a magnetically shielded topology. This paper presents performance evaluation results of the two NASA-300M magnetically shielded thruster configurations, designated 300MS and 300MS-2. The 300MS and 300MS-2 were operated at power levels between 2.5 and 20 kW at discharge voltages between 200 and 700 V. Discharge channel deposition from back-sputtered facility wall flux, and plasma potential and electron temperature measurements made on the inner and outer discharge channel surfaces confirmed that magnetic shielding was achieved. Peak total thrust efficiency of 64% and total specific impulse of 3,050 sec were demonstrated with the 300MS-2 at 20 kW. Thermal characterization results indicate that the boron nitride discharge chamber walls temperatures are approximately 100 C lower for the 300MS when compared to the NASA- 300M at the same thruster operating discharge power.
Thermal Hall Effect of Magnons
NASA Astrophysics Data System (ADS)
Murakami, Shuichi; Okamoto, Akihiro
2017-01-01
We review recent developments in theories and experiments on the magnon Hall effect. We derive the thermal Hall conductivity of magnons in terms of the Berry curvature of magnonic bands. In addition to the Dzyaloshinskii-Moriya interaction, we show that the dipolar interaction can make the Berry curvature nonzero. We mainly discuss theoretical aspects of the magnon Hall effect and related theoretical works. Experimental progress in this field is also mentioned.
2008-09-23
resistance measurement, in which current sources can share a common ground, the Hall measurement requires electrically isolated current sources. It...8 Figure captions Fig. 1. Measurement setup for the non-switching van der Pauw Hall technique. IAC and IDB are electrically isolated...Longitudinal resistivity (measured along the electrical current) is expected to be an even function of magnetic induction B, whereas the transverse or Hall
Liu, Paul; Skucha, Karl; Megens, Mischa; Boser, Bernhard
2011-10-01
A CMOS Hall-effect sensor chip designed for the characterization and detection of magnetic nanoparticles (MNPs) achieves over three orders of magnitude better temporal resolution than prior solutions based on superconducting quantum interference devices and fluxgate sensors. The sensor relies on wires embedded in the chip to generate a local magnetizing field that is switched OFF rapidly to observe the relaxation field of the MNPs. The CMOS sensor chip, with integrated high-speed readout electronics, occupies 6.25 mm(2). It can be easily integrated with microfluidics and is suitable for lab-on-a-chip and point-of-care applications.
Design and Characterization of a Three-Axis Hall Effect-Based Soft Skin Sensor.
Tomo, Tito Pradhono; Somlor, Sophon; Schmitz, Alexander; Jamone, Lorenzo; Huang, Weijie; Kristanto, Harris; Sugano, Shigeki
2016-04-07
This paper presents an easy means to produce a 3-axis Hall effect-based skin sensor for robotic applications. It uses an off-the-shelf chip and is physically small and provides digital output. Furthermore, the sensor has a soft exterior for safe interactions with the environment; in particular it uses soft silicone with about an 8 mm thickness. Tests were performed to evaluate the drift due to temperature changes, and a compensation using the integral temperature sensor was implemented. Furthermore, the hysteresis and the crosstalk between the 3-axis measurements were evaluated. The sensor is able to detect minimal forces of about 1 gf. The sensor was calibrated and results with total forces up to 1450 gf in the normal and tangential directions of the sensor are presented. The test revealed that the sensor is able to measure the different components of the force vector.
NASA Technical Reports Server (NTRS)
1985-01-01
The experimental procedure consists of the measurement of the Hall coefficient, resistivity, and Hall mobility as a function of temperature of a sample of gallium arsenides before and after irradiation with low and high energy protons. Work has begun on the development of the theory and subsequently experiments will be designed and performed.
Anomalous Josephson Hall effect in magnet/triplet superconductor junctions
NASA Astrophysics Data System (ADS)
Yokoyama, Takehito
2015-11-01
We investigate anomalous Hall effect in a magnet coupled to a triplet superconductor under phase gradient. It is found that the anomalous Hall supercurrent arises from the nontrivial structure of the magnetization. The magnetic structure manifested in the Hall supercurrent is characterized by even order terms of the exchange coupling, essentially different from that discussed in the context of anomalous Hall effect, reflecting the dissipationless nature of the supercurrent. We also discuss a possible candidate for magnetic structure to verify our prediction.
NASA Technical Reports Server (NTRS)
Kamhawi, Hani; Huang, Wensheng; Haag, Thomas; Yim, John; Herman, Daniel; Peterson, Peter Y.; Williams, George J.; Gilland, James; Hofer, Richard; Mikellides, Ioannis
2016-01-01
NASA's Hall Effect Rocket with Magnetic Shielding (HERMeS) 12.5 kW Technology Demonstration Unit-1 (TDU-1) has been the subject of extensive technology maturation in preparation for flight system development. Part of the technology maturation effort included experimental evaluation of the TDU-1 thruster with conducting and dielectric front pole cover materials in two different electrical configurations. A graphite front magnetic pole cover thruster configuration with the thruster body electrically tied to cathode, and an alumina front pole cover thruster configuration with the thruster body floating were evaluated. Both configurations were also evaluated at different facility background pressure conditions to evaluate background pressure effects on thruster operation. Performance characterization tests found that higher thruster performance was attained with the graphite front pole cover configuration with the thruster electrically tied to cathode. A total thrust efficiency of 68% and a total specific impulse of 2,820 s was demonstrated at a discharge voltage of 600 V and a discharge power of 12.5 kW. Thruster stability regimes were characterized with respect to the thruster discharge current oscillations and with maps of the discharge current-voltage-magnetic field (IVB). Analysis of TDU-1 discharge current waveforms found that lower normalized discharge current peak-to-peak and root mean square magnitudes were attained when the thruster was electrically floated with alumina front pole covers. Background pressure effects characterization tests indicated that the thruster performance and stability were mostly invariant to changes in the facility background pressure for vacuum chamber pressure below 1×10-5 Torr-Xe (for thruster flow rates of 20.5 mg/s). Power spectral density analysis of the discharge current waveforms showed that increasing the vacuum chamber background pressure resulted in a higher discharge current dominant breathing mode frequency. Finally, IVB
NASA Technical Reports Server (NTRS)
Woollam, J. A.; Beale, H. A.; Spain, I. L. (Inventor)
1974-01-01
A magnetometer which uses a single crystal of bismuth selenide is described. The rhombohedral crystal structure of the sensing element is analyzed. The method of construction of the magnetometer is discussed. It is stated that the sensing crystal has a positive or negative Hall coefficient and a carrier concentration of about 10 to the 18th power to 10 to the 20th power per cubic centimeter.
Multilayer thin film Hall effect device
NASA Technical Reports Server (NTRS)
Peters, Palmer N. (Inventor); Sisk, R. Charles (Inventor)
1994-01-01
A Hall effect device and a method of obtaining a magnetic field map of a magnetic body with the Hall effect device are presented. The device comprises: (1) a substrate, (2) a first layer having a first Hall coefficient deposited over the substrate, and (3) a second layer having a second Hall coefficient deposited over the first layer, the first and second layers cooperating to create, in the Hall effect device, a third Hall coefficient different from the first and second Hall coefficients. Creation of the third Hall coefficient by cooperation of the first and second layers allows use of materials for the first and second layers that were previously unavailable for Hall effect devices due to their relatively weak Hall coefficient.
Design and Characterization of a Three-Axis Hall Effect-Based Soft Skin Sensor
Tomo, Tito Pradhono; Somlor, Sophon; Schmitz, Alexander; Jamone, Lorenzo; Huang, Weijie; Kristanto, Harris; Sugano, Shigeki
2016-01-01
This paper presents an easy means to produce a 3-axis Hall effect–based skin sensor for robotic applications. It uses an off-the-shelf chip and is physically small and provides digital output. Furthermore, the sensor has a soft exterior for safe interactions with the environment; in particular it uses soft silicone with about an 8 mm thickness. Tests were performed to evaluate the drift due to temperature changes, and a compensation using the integral temperature sensor was implemented. Furthermore, the hysteresis and the crosstalk between the 3-axis measurements were evaluated. The sensor is able to detect minimal forces of about 1 gf. The sensor was calibrated and results with total forces up to 1450 gf in the normal and tangential directions of the sensor are presented. The test revealed that the sensor is able to measure the different components of the force vector. PMID:27070604
NASA Astrophysics Data System (ADS)
Hatakeyama, Tetsuo; Kiuchi, Yuji; Sometani, Mitsuru; Harada, Shinsuke; Okamoto, Dai; Yano, Hiroshi; Yonezawa, Yoshiyuki; Okumura, Hajime
2017-04-01
The effects of nitridation on the density of traps at SiO2/SiC interfaces near the conduction band edge were qualitatively examined using a simple, newly developed characterization method that utilizes Hall effect measurements and split capacitance–voltage measurements. The results showed a significant reduction in the density of interface traps near the conduction band edge as a result of nitridation, but the interface traps were not completely eliminated by nitridation.
Berry curvature and various thermal Hall effects
NASA Astrophysics Data System (ADS)
Zhang, Lifa
2016-10-01
Applying the approach of semiclassical wave packet dynamics, we study various thermal Hall effects where carriers can be electron, phonon, magnon, etc. A general formula of thermal Hall conductivity is obtained to provide an essential physics for various thermal Hall effects, where the Berry phase effect manifests naturally. All the formulas of electron thermal Hall effect, phonon Hall effect, and magnon Hall effect can be directly reproduced from the general formula. It is also found that the Strěda formula can not be directly applied to the thermal Hall effects, where only the edge magnetization contributes to the Hall effects. Furthermore, we obtain a combined formula for anomalous Hall conductivity, thermal Hall electronic conductivity and thermal Hall conductivity for electron systems, where the Berry curvature is weighted by a different function. Finally, we discuss particle magnetization and its relation to angular momentum of the carrier, change of which could induce a mechanical rotation; and possible experiments for thermal Hall effect associated with a mechanical rotation are also proposed.
Planar Hall effect bridge magnetic field sensors
Henriksen, A. D.; Dalslet, B. T.; Skieller, D. H.; Lee, K. H.; Okkels, F.; Hansen, M. F.
2010-07-05
Until now, the planar Hall effect has been studied in samples with cross-shaped Hall geometry. We demonstrate theoretically and experimentally that the planar Hall effect can be observed for an exchange-biased ferromagnetic material in a Wheatstone bridge topology and that the sensor signal can be significantly enhanced by a geometric factor. For the samples in the present study, we demonstrate an enhancement of the sensor output by a factor of about 100 compared to cross-shaped sensors. The presented construction opens a new design and application area of the planar Hall effect, which we term planar Hall effect bridge sensors.
The Other Hall Effect: College Board Physics
ERIC Educational Resources Information Center
Sheppard, Keith; Gunning, Amanda M.
2013-01-01
Edwin Herbert Hall (1855-1938), discoverer of the Hall effect, was one of the first winners of the AAPT Oersted Medal for his contributions to the teaching of physics. While Hall's role in establishing laboratory work in high schools is widely acknowledged, his position as chair of the physics section of the Committee on College Entrance…
Fractional quantum Hall effect revisited
NASA Astrophysics Data System (ADS)
Jacak, J.; Łydżba, P.; Jacak, L.
2015-10-01
The topology-based explanation of the fractional quantum Hall effect (FQHE) is summarized. The cyclotron braid subgroups crucial for this approach are introduced in order to identify the origin of the Laughlin correlations in 2D (two-dimensional) Hall systems. Flux-tubes and vortices for composite fermions in their standard constructions are explained in terms of cyclotron braids. The derivation of the hierarchy of the FQHE is proposed by mapping onto the integer effect within the topology-based approach. The experimental observations of the FQHE supporting the cyclotron braid picture are reviewed with a special attention paid to recent experiments with a suspended graphene. The triggering role of a carrier mobility for organization of the fractional state in Hall configuration is emphasized. The prerequisites for the FQHE are indicated including topological conditions substantially increasing the previously accepted set of physical necessities. The explanation of numerical studies by exact diagonalizations of the fractional Chern insulator states is formulated in terms of the topology condition applied to the Berry field flux quantization. Some new ideas withz regard to the synthetic fractional states in the optical lattices are also formulated.
NASA HERMeS Hall Thruster Electrical Configuration Characterization
NASA Technical Reports Server (NTRS)
Peterson, Peter Y.; Kamhawi, Hani; Huang, Wensheng; Yim, John; Herman, Daniel; Williams, George; Gilland, James; Hofer, Richard
2015-01-01
The NASA Hall Effect Rocket with Magnetic Shielding (HERMeS) 12.5 kW Technology Demonstration Unit-1 (TDU-1) Hall thruster has been the subject of extensive technology maturation in preparation for development into a flight ready propulsion system. Part of the technology maturation was to test the TDU-1 thruster in several ground based electrical configurations to assess the thruster robustness and suitability to successful in-space operation. The ground based electrical configuration testing has recently been demonstrated as an important step in understanding and assessing how a Hall thruster may operate differently in-space compared to ground based testing, and to determine the best configuration to conduct development and qualification testing. This paper describes the electrical configuration testing of the HERMeS TDU-1 Hall thruster in NASA Glenn Research Center's Vacuum Facility 5. The three electrical configurations examined were 1) thruster body tied to facility ground, 2) thruster floating, and 3) thruster body electrically tied to cathode common. The HERMeS TDU-1 Hall thruster was also configured with two different exit plane boundary conditions, dielectric and conducting, to examine the influence on the electrical configuration characterization.
NASA Technical Reports Server (NTRS)
Kamhawi, Hani; Huang, Wensheng; Haag, Thomas; Shastry, Rohit; Thomas, Robert; Yim, John; Herman, Daniel; Williams, George; Myers, James; Hofer, Richard; Mikellides, Ioannis; Sekerak, Michael; Polk, James
2015-01-01
NASA's Space Technology Mission Directorate (STMD) Solar Electric Propulsion Technology Demonstration Mission (SEP/TDM) project is funding the development of a 12.5-kW Hall thruster system to support future NASA missions. The thruster designated Hall Effect Rocket with Magnetic Shielding (HERMeS) is a 12.5-kW Hall thruster with magnetic shielding incorporating a centrally mounted cathode. HERMeS was designed and modeled by a NASA GRC and JPL team and was fabricated and tested in vacuum facility 5 (VF5) at NASA GRC. Tests at NASA GRC were performed with the Technology Development Unit 1 (TDU1) thruster. TDU1's magnetic shielding topology was confirmed by measurement of anode potential and low electron temperature along the discharge chamber walls. Thermal characterization tests indicated that during full power thruster operation at peak magnetic field strength, the various thruster component temperatures were below prescribed maximum allowable limits. Performance characterization tests demonstrated the thruster's wide throttling range and found that the thruster can achieve a peak thruster efficiency of 63% at 12.5 kW 500 V and can attain a specific impulse of 3,000 s at 12.5 kW and a discharge voltage of 800 V. Facility background pressure variation tests revealed that the performance, operational characteristics, and magnetic shielding effectiveness of the TDU1 design were mostly insensitive to increases in background pressure.
Rankin, Richard A.; Kotter, Dale K.
1997-01-01
The Hall-Effect Arc Protector is used to protect sensitive electronics from high energy arcs. The apparatus detects arcs by monitoring an electrical conductor, of the instrument, for changes in the electromagnetic field surrounding the conductor which would be indicative of a possible arcing condition. When the magnitude of the monitored electromagnetic field exceeds a predetermined threshold, the potential for an instrument damaging are exists and the control system logic activates a high speed circuit breaker. The activation of the breaker shunts the energy imparted to the input signal through a dummy load to the ground. After the arc condition is terminated, the normal signal path is restored.
Rankin, R.A.; Kotter, D.K.
1997-05-13
The Hall-Effect Arc Protector is used to protect sensitive electronics from high energy arcs. The apparatus detects arcs by monitoring an electrical conductor, of the instrument, for changes in the electromagnetic field surrounding the conductor which would be indicative of a possible arcing condition. When the magnitude of the monitored electromagnetic field exceeds a predetermined threshold, the potential for an instrument damaging are exists and the control system logic activates a high speed circuit breaker. The activation of the breaker shunts the energy imparted to the input signal through a dummy load to the ground. After the arc condition is terminated, the normal signal path is restored. 2 figs.
Temperature Stable Hall Effect Sensors
NASA Astrophysics Data System (ADS)
Partin, D. L.; Heremans, J. P.; Schroeder, T.; Thrush, C. M.; Flores, L. A.
2004-03-01
Magnetic field sensors are needed for high accuracy position, angle, force, strain, torque, and current flow measurements. Molecular beam epitaxy was used to grow tellurium-doped indium gallium antimonide thin films. Hall effect sensors made from these films have been studied for their magnetic sensitivity and thermal stability. For a range of alloy composition and n-type doping levels, high magnetic sensitivity from -40°C to +200°C was found with a resolution of better than +/- 0.5 percent over the entire temperature range.
DEVELOPMENT OF IMPROVED HALL EFFECT SENSORS.
HALL EFFECT , MAGNETOMETERS, GAIN, SENSITIVITY, MAGNETIC FIELDS, DETECTION, ELECTROMAGNETIC PROBES, WEIGHT, VOLUME, BATTERY COMPONENTS, INDIUM ALLOYS, ANTIMONY ALLOYS, FERRITES, MANPORTABLE EQUIPMENT.
AN A. C. HALL EFFECT GAUSSMETER,
MEASURING INSTRUMENTS, MEASURING INSTRUMENTS, HALL EFFECT , MAGNETOMETERS, MEASUREMENT, GENERATORS, CIRCUITS, ALTERNATING CURRENT, GERMANIUM, SEMICONDUCTOR DIODES, GALVANOMETERS, VOLTAGE, DIRECT CURRENT, MAGNETIC FIELDS.
Azimuthal Spoke Propagation in Hall Effect Thrusters
2013-08-01
Approved for public release; distribution unlimited. IEPC-2013- Background Pressure Effects on Krypton Hall Effect Thruster Internal Acceleration...Why are we doing this work? – Continued examination of alternative Hall effect thruster propellants: Krypton – Interest in effects of test...Distribution unlimited 2 Photograph of BHT-600 operating on krypton Long exposure photograph of BHT-600 operating on krypton showing extended plume
NASA HERMeS Hall Thruster Electrical Configuration Characterization
NASA Technical Reports Server (NTRS)
Peterson, Peter; Kamhawi, Hani; Huang, Wensheng; Yim, John; Herman, Daniel; Williams, George; Gilland, James; Hofer, Richard
2016-01-01
NASAs Hall Effect Rocket with Magnetic Shielding (HERMeS) 12.5 kW Technology Demonstration Unit-1 (TDU-1) Hall thruster has been the subject of extensive technology maturation in preparation for development into a flight ready propulsion system. Part of the technology maturation was to test the TDU-1 thruster in several ground based electrical configurations to assess the thruster robustness and suitability to successful in-space operation. The ground based electrical configuration testing has recently been demonstrated as an important step in understanding and assessing how a Hall thruster may operate differently in space compared to ground based testing, and to determine the best configuration to conduct development and qualification testing. This presentation will cover the electrical configuration testing of the TDU-1 HERMeS Hall thruster in NASA Glenn Research Centers Vacuum Facility 5. The three electrical configurations examined are the thruster body tied to facility ground, thruster floating, and finally the thruster body electrically tied to cathode common. The TDU-1 HERMeS was configured with two different exit plane boundary conditions, dielectric and conducting, to examine the influence on the electrical configuration characterization.
The quantum Hall effect helicity
Shrivastava, Keshav N.
2015-04-16
The quantum Hall effect in semiconductor heterostructures is explained by two signs in the angular momentum j=l±s and g=(2j+1)/(2l+1) along with the Landau factor (n+1/2). These modifications in the existing theories explain all of the fractional charges. The helicity which is the sign of the product of the linear momentum with the spin p.s plays an important role for the understanding of the data at high magnetic fields. In particular it is found that particles with positive sign in the spin move in one direction and those with negative sign move in another direction which explains the up and down stream motion of the particles.
Quantum Hall effect in quantum electrodynamics
Penin, Alexander A.
2009-03-15
We consider the quantum Hall effect in quantum electrodynamics and find a deviation from the quantum-mechanical prediction for the Hall conductivity due to radiative antiscreening of electric charge in an external magnetic field. A weak dependence of the universal von Klitzing constant on the magnetic field strength, which can possibly be observed in a dedicated experiment, is predicted.
The quantum Hall effects: Philosophical approach
NASA Astrophysics Data System (ADS)
Lederer, P.
2015-05-01
The Quantum Hall Effects offer a rich variety of theoretical and experimental advances. They provide interesting insights on such topics as gauge invariance, strong interactions in Condensed Matter physics, emergence of new paradigms. This paper focuses on some related philosophical questions. Various brands of positivism or agnosticism are confronted with the physics of the Quantum Hall Effects. Hacking's views on Scientific Realism, Chalmers' on Non-Figurative Realism are discussed. It is argued that the difficulties with those versions of realism may be resolved within a dialectical materialist approach. The latter is argued to provide a rational approach to the phenomena, theory and ontology of the Quantum Hall Effects.
Quantum Hall effect in momentum space
NASA Astrophysics Data System (ADS)
Ozawa, Tomoki; Price, Hannah M.; Carusotto, Iacopo
2016-05-01
We theoretically discuss a momentum-space analog of the quantum Hall effect, which could be observed in topologically nontrivial lattice models subject to an external harmonic trapping potential. In our proposal, the Niu-Thouless-Wu formulation of the quantum Hall effect on a torus is realized in the toroidally shaped Brillouin zone. In this analogy, the position of the trap center in real space controls the magnetic fluxes that are inserted through the holes of the torus in momentum space. We illustrate the momentum-space quantum Hall effect with the noninteracting trapped Harper-Hofstadter model, for which we numerically demonstrate how this effect manifests itself in experimental observables. Extension to the interacting trapped Harper-Hofstadter model is also briefly considered. We finally discuss possible experimental platforms where our proposal for the momentum-space quantum Hall effect could be realized.
Observation of the magnon Hall effect.
Onose, Y; Ideue, T; Katsura, H; Shiomi, Y; Nagaosa, N; Tokura, Y
2010-07-16
The Hall effect usually occurs in conductors when the Lorentz force acts on a charge current in the presence of a perpendicular magnetic field. Neutral quasi-particles such as phonons and spins can, however, carry heat current and potentially exhibit the thermal Hall effect without resorting to the Lorentz force. We report experimental evidence for the anomalous thermal Hall effect caused by spin excitations (magnons) in an insulating ferromagnet with a pyrochlore lattice structure. Our theoretical analysis indicates that the propagation of the spin waves is influenced by the Dzyaloshinskii-Moriya spin-orbit interaction, which plays the role of the vector potential, much as in the intrinsic anomalous Hall effect in metallic ferromagnets.
Hall effect degradation of rail gun performance
NASA Astrophysics Data System (ADS)
Witalis, E. A.; Gunnarsson, Patrik
1993-01-01
The paper discusses the Hall effect and shows it to be significant in the low-density and high-field trailing part of a plasma armature. Without the Hall effect a simple armature model is derived. It exhibits properties expected from classical MHD theory and shows that the purely relativistic electric charge buildup on the rails is a fundamental gun property, leading to V(breech) = 1.5 V(muzzle). The mathematics involved in accounting for Hall effect phenomena is described. These are of two types: the Hall-skewing of the armature current and the superimposed plasma flow rotation. For decreasing gun current the two effects efficiently combine to eject armature plasma rearwards, thus creating conditions for arc separation and parasitic arcs.
Piezo Voltage Controlled Planar Hall Effect Devices.
Zhang, Bao; Meng, Kang-Kang; Yang, Mei-Yin; Edmonds, K W; Zhang, Hao; Cai, Kai-Ming; Sheng, Yu; Zhang, Nan; Ji, Yang; Zhao, Jian-Hua; Zheng, Hou-Zhi; Wang, Kai-You
2016-06-22
The electrical control of the magnetization switching in ferromagnets is highly desired for future spintronic applications. Here we report on hybrid piezoelectric (PZT)/ferromagnetic (Co2FeAl) devices in which the planar Hall voltage in the ferromagnetic layer is tuned solely by piezo voltages. The change of planar Hall voltage is associated with magnetization switching through 90° in the plane under piezo voltages. Room temperature magnetic NOT and NOR gates are demonstrated based on the piezo voltage controlled Co2FeAl planar Hall effect devices without the external magnetic field. Our demonstration may lead to the realization of both information storage and processing using ferromagnetic materials.
Piezo Voltage Controlled Planar Hall Effect Devices
NASA Astrophysics Data System (ADS)
Zhang, Bao; Meng, Kang-Kang; Yang, Mei-Yin; Edmonds, K. W.; Zhang, Hao; Cai, Kai-Ming; Sheng, Yu; Zhang, Nan; Ji, Yang; Zhao, Jian-Hua; Zheng, Hou-Zhi; Wang, Kai-You
2016-06-01
The electrical control of the magnetization switching in ferromagnets is highly desired for future spintronic applications. Here we report on hybrid piezoelectric (PZT)/ferromagnetic (Co2FeAl) devices in which the planar Hall voltage in the ferromagnetic layer is tuned solely by piezo voltages. The change of planar Hall voltage is associated with magnetization switching through 90° in the plane under piezo voltages. Room temperature magnetic NOT and NOR gates are demonstrated based on the piezo voltage controlled Co2FeAl planar Hall effect devices without the external magnetic field. Our demonstration may lead to the realization of both information storage and processing using ferromagnetic materials.
Integer Quantum Hall Effect in Trilayer Graphene
NASA Astrophysics Data System (ADS)
Kumar, A.; Escoffier, W.; Poumirol, J. M.; Faugeras, C.; Arovas, D. P.; Fogler, M. M.; Guinea, F.; Roche, S.; Goiran, M.; Raquet, B.
2011-09-01
By using high-magnetic fields (up to 60 T), we observe compelling evidence of the integer quantum Hall effect in trilayer graphene. The magnetotransport fingerprints are similar to those of the graphene monolayer, except for the absence of a plateau at a filling factor of ν=2. At a very low filling factor, the Hall resistance vanishes due to the presence of mixed electron and hole carriers induced by disorder. The measured Hall resistivity plateaus are well reproduced theoretically, using a self-consistent Hartree calculations of the Landau levels and assuming an ABC stacking order of the three layers.
Hall coefficient measurement for nondestructive materials characterization
NASA Astrophysics Data System (ADS)
Nagy, Peter B.
2013-01-01
Although Hall detectors are widely used for magnetic flux density measurements in numerous electromagnetic NDE applications, measurement of the Hall coefficient of metals and their alloys for NDE purposes has not been successfully attempted before. While other intrinsic electric properties, such as electric conductivity and, to a lesser degree, thermoelectric power, are widely used for NDE, Hall coefficient measurements have never been really considered mainly because the measurements are rather difficult to carry out, especially in high-conductivity materials. In contrast to electric conductivity, the Hall coefficient is influenced mainly by the concentration density of the free charge carriers, i.e., electrons in metals, and not so much by their mobility, therefore it could be a valuable addition to our NDE arsenal. We modified the alternating current potential drop (ACPD) method with square-electrode configuration by adding an external bias magnetic field modulation to measure the Hall coefficient. The presence of such a bias field violates the Reciprocity Theorem unless the sign of the magnetic field is switched between the two measurements, which can be exploited to measure the Hall coefficient in the presence of other variations that would otherwise hide it. This new experimental method was tested on paramagnetic alloys and yielded a ±4% reproducibility that probably could be further improved by additional development efforts. As a first step towards illustrating some of the potential applications of this new technique, we have done reversible applied stress measurements in Al 1100 plates and found the sensitivity of the technique to elastic strain surprisingly high.
Observation of a superfluid Hall effect
Jiménez-García, Karina; Williams, Ross A.; Beeler, Matthew C.; Perry, Abigail R.; Phillips, William D.; Spielman, Ian B.
2012-01-01
Measurement techniques based upon the Hall effect are invaluable tools in condensed-matter physics. When an electric current flows perpendicular to a magnetic field, a Hall voltage develops in the direction transverse to both the current and the field. In semiconductors, this behavior is routinely used to measure the density and charge of the current carriers (electrons in conduction bands or holes in valence bands)—internal properties of the system that are not accessible from measurements of the conventional resistance. For strongly interacting electron systems, whose behavior can be very different from the free electron gas, the Hall effect’s sensitivity to internal properties makes it a powerful tool; indeed, the quantum Hall effects are named after the tool by which they are most distinctly measured instead of the physics from which the phenomena originate. Here we report the first observation of a Hall effect in an ultracold gas of neutral atoms, revealed by measuring a Bose–Einstein condensate’s transport properties perpendicular to a synthetic magnetic field. Our observations in this vortex-free superfluid are in good agreement with hydrodynamic predictions, demonstrating that the system’s global irrotationality influences this superfluid Hall signal. PMID:22699494
The Hall effect in star formation
NASA Astrophysics Data System (ADS)
Braiding, C. R.; Wardle, M.
2012-05-01
Magnetic fields play an important role in star formation by regulating the removal of angular momentum from collapsing molecular cloud cores. Hall diffusion is known to be important to the magnetic field behaviour at many of the intermediate densities and field strengths encountered during the gravitational collapse of molecular cloud cores into protostars, and yet its role in the star formation process is not well studied. We present a semianalytic self-similar model of the collapse of rotating isothermal molecular cloud cores with both Hall and ambipolar diffusion, and similarity solutions that demonstrate the profound influence of the Hall effect on the dynamics of collapse. The solutions show that the size and sign of the Hall parameter can change the size of the protostellar disc by up to an order of magnitude and the protostellar accretion rate by 50 per cent when the ratio of the Hall to ambipolar diffusivities is varied between -0.5 ≤ηH/ηA≤ 0.2. These changes depend upon the orientation of the magnetic field with respect to the axis of rotation and create a preferred handedness to the solutions that could be observed in protostellar cores using next-generation instruments such as ALMA. Hall diffusion also determines the strength and position of the shocks that bound the pseudo and rotationally supported discs, and can introduce subshocks that further slow accretion on to the protostar. In cores that are not initially rotating (not examined here), Hall diffusion can even induce rotation, which could give rise to disc formation and resolve the magnetic braking catastrophe. The Hall effect clearly influences the dynamics of gravitational collapse and its role in controlling the magnetic braking and radial diffusion of the field merits further exploration in numerical simulations of star formation.
Star Formation and the Hall Effect
NASA Astrophysics Data System (ADS)
Braiding, Catherine
2011-10-01
Magnetic fields play an important role in star formation by regulating the removal of angular momentum from collapsing molecular cloud cores. Hall diffusion is known to be important to the magnetic field behaviour at many of the intermediate densities and field strengths encountered during the gravitational collapse of molecular cloud cores into protostars, and yet its role in the star formation process is not well-studied. This thesis describes a semianalytic self-similar model of the collapse of rotating isothermal molecular cloud cores with both Hall and ambipolar diffusion, presenting similarity solutions that demonstrate that the Hall effect has a profound influence on the dynamics of collapse. ... Hall diffusion also determines the strength of the magnetic diffusion and centrifugal shocks that bound the pseudo and rotationally-supported discs, and can introduce subshocks that further slow accretion onto the protostar. In cores that are not initially rotating Hall diffusion can even induce rotation, which could give rise to disc formation and resolve the magnetic braking catastrophe. The Hall effect clearly influences the dynamics of gravitational collapse and its role in controlling the magnetic braking and radial diffusion of the field would be worth exploring in future numerical simulations of star formation.
The fluctuation induced Hall effect
Shen, W.; Prager, S.C.
1993-02-01
The fluctuation induced Hall term, {le}{approximately}{ovr J} {times} {approximately}{ovr B}{ge}, has been measured in the MST reversed field pinch. The term is of interest as a possible source of current self-generation (dynamo). It is found to be non-negligible, but small in that it can account for less than 25% of the dynamo driven current.
The fluctuation induced Hall effect
Shen, W.; Prager, S.C.
1993-02-01
The fluctuation induced Hall term, [le][approximately][ovr J] [times] [approximately][ovr B][ge], has been measured in the MST reversed field pinch. The term is of interest as a possible source of current self-generation (dynamo). It is found to be non-negligible, but small in that it can account for less than 25% of the dynamo driven current.
Charge carrier coherence and Hall effect in organic semiconductors.
Yi, H T; Gartstein, Y N; Podzorov, V
2016-03-30
Hall effect measurements are important for elucidating the fundamental charge transport mechanisms and intrinsic mobility in organic semiconductors. However, Hall effect studies frequently reveal an unconventional behavior that cannot be readily explained with the simple band-semiconductor Hall effect model. Here, we develop an analytical model of Hall effect in organic field-effect transistors in a regime of coexisting band and hopping carriers. The model, which is supported by the experiments, is based on a partial Hall voltage compensation effect, occurring because hopping carriers respond to the transverse Hall electric field and drift in the direction opposite to the Lorentz force acting on band carriers. We show that this can lead in particular to an underdeveloped Hall effect observed in organic semiconductors with substantial off-diagonal thermal disorder. Our model captures the main features of Hall effect in a variety of organic semiconductors and provides an analytical description of Hall mobility, carrier density and carrier coherence factor.
Charge carrier coherence and Hall effect in organic semiconductors
Yi, H. T.; Gartstein, Y. N.; Podzorov, V.
2016-03-30
Hall effect measurements are important for elucidating the fundamental charge transport mechanisms and intrinsic mobility in organic semiconductors. However, Hall effect studies frequently reveal an unconventional behavior that cannot be readily explained with the simple band-semiconductor Hall effect model. Here, we develop an analytical model of Hall effect in organic field-effect transistors in a regime of coexisting band and hopping carriers. The model, which is supported by the experiments, is based on a partial Hall voltage compensation effect, occurring because hopping carriers respond to the transverse Hall electric field and drift in the direction opposite to the Lorentz force acting on band carriers. We show that this can lead in particular to an underdeveloped Hall effect observed in organic semiconductors with substantial off-diagonal thermal disorder. Lastly, our model captures the main features of Hall effect in a variety of organic semiconductors and provides an analytical description of Hall mobility, carrier density and carrier coherence factor.
Charge carrier coherence and Hall effect in organic semiconductors
Yi, H. T.; Gartstein, Y. N.; Podzorov, V.
2016-01-01
Hall effect measurements are important for elucidating the fundamental charge transport mechanisms and intrinsic mobility in organic semiconductors. However, Hall effect studies frequently reveal an unconventional behavior that cannot be readily explained with the simple band-semiconductor Hall effect model. Here, we develop an analytical model of Hall effect in organic field-effect transistors in a regime of coexisting band and hopping carriers. The model, which is supported by the experiments, is based on a partial Hall voltage compensation effect, occurring because hopping carriers respond to the transverse Hall electric field and drift in the direction opposite to the Lorentz force acting on band carriers. We show that this can lead in particular to an underdeveloped Hall effect observed in organic semiconductors with substantial off-diagonal thermal disorder. Our model captures the main features of Hall effect in a variety of organic semiconductors and provides an analytical description of Hall mobility, carrier density and carrier coherence factor. PMID:27025354
Hall Effect in Neutron Star Crusts
NASA Astrophysics Data System (ADS)
Gourgouliatos, K. N.; Cumming, A.
2014-08-01
The crust of Neutron Stars can be approximated by a highly conducting solid crystal lattice. The evolution of the magnetic field in the crust is mediated through Hall effect, namely the electric current is carried by the free electrons of the lattice and the magnetic field lines are advected by the electron fluid. Here, we present the results of a time-dependent evolution code which shows the effect Hall drift has in the large-scale evolution of the magnetic field. In particular we link analytical predictions with simulation results. We find that there are two basic evolutionary paths, depending on the initial conditions compared to Hall equilibrium. We also show the effect axial symmetry combined with density gradient have on suppressing turbulent cascade.
Integer quantum Hall effect in graphene
NASA Astrophysics Data System (ADS)
Jellal, Ahmed
2016-04-01
We study the quantum Hall effect in a monolayer graphene by using an approach based on thermodynamical properties. This can be done by considering a system of Dirac particles in an electromagnetic field and taking into account of the edges effect as a pseudo-potential varying continuously along the x direction. At low temperature and in the weak electric field limit, we explicitly determine the thermodynamical potential. With this, we derive the particle numbers in terms of the quantized flux and therefore the Hall conductivity immediately follows.
Piezo Voltage Controlled Planar Hall Effect Devices
Zhang, Bao; Meng, Kang-Kang; Yang, Mei-Yin; Edmonds, K. W.; Zhang, Hao; Cai, Kai-Ming; Sheng, Yu; Zhang, Nan; Ji, Yang; Zhao, Jian-Hua; Zheng, Hou-Zhi; Wang, Kai-You
2016-01-01
The electrical control of the magnetization switching in ferromagnets is highly desired for future spintronic applications. Here we report on hybrid piezoelectric (PZT)/ferromagnetic (Co2FeAl) devices in which the planar Hall voltage in the ferromagnetic layer is tuned solely by piezo voltages. The change of planar Hall voltage is associated with magnetization switching through 90° in the plane under piezo voltages. Room temperature magnetic NOT and NOR gates are demonstrated based on the piezo voltage controlled Co2FeAl planar Hall effect devices without the external magnetic field. Our demonstration may lead to the realization of both information storage and processing using ferromagnetic materials. PMID:27329068
Quantized photonic spin Hall effect in graphene
NASA Astrophysics Data System (ADS)
Cai, Liang; Liu, Mengxia; Chen, Shizhen; Liu, Yachao; Shu, Weixing; Luo, Hailu; Wen, Shuangchun
2017-01-01
We examine the photonic spin Hall effect (SHE) in a graphene-substrate system with the presence of an external magnetic field. In the quantum Hall regime, we demonstrate that the in-plane and transverse spin-dependent splittings in the photonic SHE exhibit different quantized behaviors. The quantized SHE can be described as a consequence of a quantized geometric phase (Berry phase), which corresponds to the quantized spin-orbit interaction. Furthermore, an experimental scheme based on quantum weak value amplification is proposed to detect the quantized SHE in the terahertz frequency regime. By incorporating the quantum weak measurement techniques, the quantized photonic SHE holds great promise for detecting quantized Hall conductivity and the Berry phase. These results may bridge the gap between the electronic SHE and photonic SHE in graphene.
Inverse spin Hall effect by spin injection
NASA Astrophysics Data System (ADS)
Liu, S. Y.; Horing, Norman J. M.; Lei, X. L.
2007-09-01
Motivated by a recent experiment [S. O. Valenzuela and M. Tinkham, Nature (London) 442, 176 (2006)], the authors present a quantitative microscopic theory to investigate the inverse spin-Hall effect with spin injection into aluminum considering both intrinsic and extrinsic spin-orbit couplings using the orthogonalized-plane-wave method. Their theoretical results are in good agreement with the experimental data. It is also clear that the magnitude of the anomalous Hall resistivity is mainly due to contributions from extrinsic skew scattering.
A Small Modular Laboratory Hall Effect Thruster
NASA Astrophysics Data System (ADS)
Lee, Ty Davis
Electric propulsion technologies promise to revolutionize access to space, opening the door for mission concepts unfeasible by traditional propulsion methods alone. The Hall effect thruster is a relatively high thrust, moderate specific impulse electric propulsion device that belongs to the class of electrostatic thrusters. Hall effect thrusters benefit from an extensive flight history, and offer significant performance and cost advantages when compared to other forms of electric propulsion. Ongoing research on these devices includes the investigation of mechanisms that tend to decrease overall thruster efficiency, as well as the development of new techniques to extend operational lifetimes. This thesis is primarily concerned with the design and construction of a Small Modular Laboratory Hall Effect Thruster (SMLHET), and its operation on argon propellant gas. Particular attention was addressed at low-cost, modular design principles, that would facilitate simple replacement and modification of key thruster parts such as the magnetic circuit and discharge channel. This capability is intended to facilitate future studies of device physics such as anomalous electron transport and magnetic shielding of the channel walls, that have an impact on thruster performance and life. Preliminary results demonstrate SMLHET running on argon in a manner characteristic of Hall effect thrusters, additionally a power balance method was utilized to estimate thruster performance. It is expected that future thruster studies utilizing heavier though more expensive gases like xenon or krypton, will observe increased efficiency and stability.
Fractional Quantization of the Hall Effect
DOE R&D Accomplishments Database
Laughlin, R. B.
1984-02-27
The Fractional Quantum Hall Effect is caused by the condensation of a two-dimensional electron gas in a strong magnetic field into a new type of macroscopic ground state, the elementary excitations of which are fermions of charge 1/m, where m is an odd integer. A mathematical description is presented.
Hall Effect Thruster Ground Testing Challenges
2009-08-18
high purity propellent to eliminate the risk of oxidation poisoning the thermionically emitting electron/neutralizer source drive the entire Hall effect...Mason, L., Jankovsky, R., Snyder, J. S., Malone , S., Haas, J., and Gallimore, A. D., “Spacecraft Interaction Test Results for the High Performance
Towards a Better Understanding of the Anomalous Hall Effect
NASA Astrophysics Data System (ADS)
Yue, Di; Jin, Xiaofeng
2017-01-01
Recent experimental efforts to identify the intrinsic and extrinsic contributions in the anomalous Hall effect are reviewed. Benefited from the experimental control of artificial impurity density in single crystalline magnetic thin films, a comprehensive physical picture of the anomalous Hall effect involving multiple competing scattering processes has been established. Some new insights into the microscopic mechanisms of the anomalous Hall effect are discussed.
Improved Hall-Effect Sensors For Magnetic Memories
NASA Technical Reports Server (NTRS)
Wu, Jiin-Chuan; Stadler, Henry L.; Katti, Romney R.; Chen, Y. C.; Bhattacharya, Pallab K.
1993-01-01
High-electron-mobility sensor films deposited on superlattice buffer (strain) layers. Improved Hall-effect sensors offer combination of adequate response and high speed needed for use in micromagnet/Hall-effect random-access memories. Hall-effect material chosen for use in sensors is InAs.
High temperature Hall measurement setup for thin film characterization
NASA Astrophysics Data System (ADS)
Adnane, L.; Gokirmak, A.; Silva, H.
2016-07-01
Hall measurement using the van der Pauw technique is a common characterization approach that does not require patterning of contacts. Measurements of the Hall voltage and electrical resistivity lead to the product of carrier mobility and carrier concentration (Hall coefficient) which can be decoupled through transport models. Based on the van der Paw method, we have developed an automated setup for Hall measurements from room temperature to ˜500 °C of semiconducting thin films of a wide resistivity range. The resistivity of the film and Hall coefficient is obtained from multiple current-voltage (I-V) measurements performed using a semiconductor parameter analyzer under applied constant "up," zero, and "down" magnetic field generated with two neodymium permanent magnets. The use of slopes obtained from multiple I-Vs for the three magnetic field conditions offer improved accuracy. Samples are preferred in square shape geometry and can range from 2 mm to 25 mm side length. Example measurements of single-crystal silicon with known doping concentration show the accuracy and reliability of the measurement.
High temperature Hall measurement setup for thin film characterization.
Adnane, L; Gokirmak, A; Silva, H
2016-07-01
Hall measurement using the van der Pauw technique is a common characterization approach that does not require patterning of contacts. Measurements of the Hall voltage and electrical resistivity lead to the product of carrier mobility and carrier concentration (Hall coefficient) which can be decoupled through transport models. Based on the van der Paw method, we have developed an automated setup for Hall measurements from room temperature to ∼500 °C of semiconducting thin films of a wide resistivity range. The resistivity of the film and Hall coefficient is obtained from multiple current-voltage (I-V) measurements performed using a semiconductor parameter analyzer under applied constant "up," zero, and "down" magnetic field generated with two neodymium permanent magnets. The use of slopes obtained from multiple I-Vs for the three magnetic field conditions offer improved accuracy. Samples are preferred in square shape geometry and can range from 2 mm to 25 mm side length. Example measurements of single-crystal silicon with known doping concentration show the accuracy and reliability of the measurement.
Precise Quantization of Anomalous Hall Effect
NASA Astrophysics Data System (ADS)
Bestwick, Andrew
In the quantum anomalous Hall effect, electron transport in a magnetically-doped topological insulator takes place through chiral, dissipationless edge channels. In this talk, we discuss the behavior of a nearly ideal implementations of the effect in which the Hall resistance is within a part per 10,000 of its quantized value and the longitudinal resistivity can reach below 1 Ω per square. Nearly all Cr-doped topological insulator samples demonstrate extreme temperature dependence that is well-modeled by a small effective gap, allowing control over quantization with an unexpected magnetocaloric effect. We also discuss measurements of new device geometries and non-local resistances that identify the sources of dissipation that limit the effect. (Now at Rigetti Computing).
Improved Readout For Micromagnet/Hall-Effect Memories
NASA Technical Reports Server (NTRS)
Wu, Jiin-Chuan; Stadler, Henry L.; Katti, Romney R.
1993-01-01
Two improved readout circuits for micromagnet/Hall-effect random-access memories designed to eliminate current shunts introducing errors into outputs of older readout circuits. Incorporate additional switching transistors to isolate Hall sensors as needed.
NASA Astrophysics Data System (ADS)
Schöche, S.; Shi, Junxia; Boosalis, A.; Kühne, P.; Herzinger, C. M.; Woollam, J. A.; Schaff, W. J.; Eastman, L. F.; Schubert, M.; Hofmann, T.
2011-02-01
The free-charge carrier mobility, sheet density, and effective mass of a two-dimensional electron gas are exemplarily determined in the spectral range from 640 GHz to 1 THz in a AlGaN/GaN heterostructure using the optical-Hall effect at room temperature. Complementary midinfrared spectroscopic ellipsometry measurements are performed for analysis of heterostructure constituents layer thickness, phonon mode, and free-charge carrier parameters. The electron effective mass is determined to be (0.22±0.04)m0. The high-frequency sheet density and carrier mobility parameters are in good agreement with results from dc electrical Hall effect measurements, indicative for frequency-independent carrier scattering mechanisms of the two-dimensional carrier distribution.
Destruction of the Fractional Quantum Hall Effect by Disorder
DOE R&D Accomplishments Database
Laughlin, R. B.
1985-07-01
It is suggested that Hall steps in the fractional quantum Hall effect are physically similar to those in the ordinary quantum Hall effect. This proposition leads to a simple scaling diagram containing a new type of fixed point, which is identified with the destruction of the fractional states by disorder. 15 refs., 3 figs.
Intrinsic spin and orbital angular momentum Hall effect.
Zhang, S; Yang, Z
2005-02-18
A generalized definition of intrinsic and extrinsic transport coefficients is introduced. We show that transport coefficients from the intrinsic origin are solely determined by local electronic structure, and thus the intrinsic spin Hall effect is not a transport phenomenon. The intrinsic spin Hall current is always accompanied by an equal but opposite intrinsic orbital angular momentum Hall current. We prove that the intrinsic spin Hall effect does not induce a spin accumulation at the edge of the sample or near the interface.
Current Distributions in Quantum Hall Effect Devices
Cage, M. E.
1997-01-01
This paper addresses the question of how current is distributed within quantum Hall effect devices. Three types of flow patterns most often mentioned in the literature are considered. They are: (1) skipping orbits along the device periphery (which arise from elastic collisions off hard-walled potentials); (2) narrow conducting channels along the device sides (which are presumed to be generated from confining potentials); and (3) currents distributed throughout the device (which are assumed to arise from a combination of confining and charge-redistribution potentials). The major conclusions are that skipping orbits do not occur in quantum Hall effect devices, and that nearly all of the externally applied current is located within the device interior rather than along the device edges. PMID:27805115
Developments in the quantum Hall effect.
von Klitzing, Klaus
2005-09-15
The most important applications of the quantum Hall effect (QHE) are in the field of metrology. The observed quantization of the resistance is primarily used for the reproduction of the SI unit ohm, but is also important for high precision measurements of both the fine structure constant and the Planck constant. Some current QHE research areas include the analysis of new electron-electron correlation phenomena and the development of a more complete microscopic picture of this quantum effect. Recently, scanning force microscopy (SFM) of the potential distribution in QHE devices has been used to enhance the microscopic understanding of current flow in quantum Hall systems. This confirms the importance of the theoretically predicted stripes of compressible and incompressible electronic states close to the boundary of the QHE devices.
Mode Transitions in Hall Effect Thrusters
2013-07-01
Astronautics Mode Transitions in Hall Effect Thrusters Michael J. Sekerak 1 , Benjamin W. Longmier 2 and Alec D. Gallimore 3 University of Michigan...nude Faraday probe, retarding potential analyzer and cylindrical Langmuir prove, Brown showed the transition from “low-current” to “high-current...thank two former PEPL students: Dr. Robert Lobbia for development of the HDLP; and Dr. Michael McDonald for development of the FastCam Analysis
High temperature Hall-effect apparatus
NASA Technical Reports Server (NTRS)
Wood, C.; Lockwood, A.; Chmielewski, A.; Parker, J.; Zoltan, A.
1984-01-01
A high-temperature Hall-effect apparatus is described which allows measurements up to temperatures greater than 1200 K using the van der Pauw method. The apparatus was designed for measurements on refractory materials having high charge carrier concentrations and generally low mobilities. Pressure contacts are applied to the samples. Consequently, special contacting methods, peculiar to a specific sample material, are not required. The apparatus has been semiautomated to facilitate measurements. Results are presented on n- and p-type silicon.
Generic superweak chaos induced by Hall effect.
Ben-Harush, Moti; Dana, Itzhack
2016-05-01
We introduce and study the "kicked Hall system" (KHS), i.e., charged particles periodically kicked in the presence of uniform magnetic (B) and electric (E) fields that are perpendicular to each other and to the kicking direction. We show that for resonant values of B and E and in the weak-chaos regime of sufficiently small nonintegrability parameter κ (the kicking strength), there exists a generic family of periodic kicking potentials for which the Hall effect from B and E significantly suppresses the weak chaos, replacing it by "superweak" chaos (SWC). This means that the system behaves as if the kicking strength were κ^{2} rather than κ. For E=0, SWC is known to be a classical fingerprint of quantum antiresonance, but it occurs under much less generic conditions, in particular only for very special kicking potentials. Manifestations of SWC are a decrease in the instability of periodic orbits and a narrowing of the chaotic layers, relative to the ordinary weak-chaos case. Also, for global SWC, taking place on an infinite "stochastic web" in phase space, the chaotic diffusion on the web is much slower than the weak-chaos one. Thus, the Hall effect can be relatively stabilizing for small κ. In some special cases, the effect is shown to cause ballistic motion for almost all parameter values. The generic global SWC on stochastic webs in the KHS appears to be the two-dimensional closest analog to the Arnol'd web in higher dimensional systems.
Quantum anomalous Hall effect in real materials
NASA Astrophysics Data System (ADS)
Zhang, Jiayong; Zhao, Bao; Zhou, Tong; Yang, Zhongqin
2016-11-01
Under a strong magnetic field, the quantum Hall (QH) effect can be observed in two-dimensional electronic gas systems. If the quantized Hall conductivity is acquired in a system without the need of an external magnetic field, then it will give rise to a new quantum state, the quantum anomalous Hall (QAH) state. The QAH state is a novel quantum state that is insulating in the bulk but exhibits unique conducting edge states topologically protected from backscattering and holds great potential for applications in low-power-consumption electronics. The realization of the QAH effect in real materials is of great significance. In this paper, we systematically review the theoretical proposals that have been brought forward to realize the QAH effect in various real material systems or structures, including magnetically doped topological insulators, graphene-based systems, silicene-based systems, two-dimensional organometallic frameworks, quantum wells, and functionalized Sb(111) monolayers, etc. Our paper can help our readers to quickly grasp the recent developments in this field. Project supported by the National Basic Research Program of China (Grant No. 2011CB921803), the National Natural Science Foundation of China (Grant No. 11574051), the Natural Science Foundation of Shanghai, China (Grant No. 14ZR1403400), and Fudan High-end Computing Center, China.
Anisotropic Spin Hall Effect from First Principles
NASA Astrophysics Data System (ADS)
Freimuth, Frank; Blügel, Stefan; Mokrousov, Yuriy
2011-03-01
We present first principles calculations of the intrinsic non-dissipative spin Hall conductivity (SHC) for 3 d , 4 d and 5 d transition metals focusing in particular on the anisotropy of the SHC in nonmagnetic hcp metals and in antiferromagnetic Cr. For the metals of this study we generally find large anisotropies. We derive the general relation between the SHC vector and the direction of spin-polarization and discuss its consequences for hcp metals. Especially, it is predicted that for systems where the SHC changes sign due to the anisotropy the spin Hall effect may be tuned such that the spin polarization is parallel either to the electric field or to the spin current. Additionally, we describe our computational method [2,3] emphasizing the Wannier interpolation technique and the definition of the conserved spin current. This work is supported by the DFG Project MO 1731/3-1 and HGF-YIG grant VH-NG-513.
Background Pressure Effects on Krypton Hall Effect Thruster Internal Acceleration
2013-08-01
Technical Paper 3. DATES COVERED (From - To) August 2013- September 2013 4. TITLE AND SUBTITLE Background Pressure Effects on Krypton Hall Effect...Conference 2013, Washington, D.C., 6-10 October 2013. 14. ABSTRACT This study uses krypton propellant in a medium power Hall effect to amplify the...effect of background pressure due to the greater mobility of neutral krypton compared to neutral xenon. The use of krypton amplifies the effect of
Mode Transitions in Hall Effect Thrusters
NASA Technical Reports Server (NTRS)
Sekerak, Michael J.; Longmier, Benjamin W.; Gallimore, Alec D.; Brown, Daniel L.; Hofer, Richard R.; Polk, James E.
2013-01-01
Mode transitions have been commonly observed in Hall Effect Thruster (HET) operation where a small change in a thruster operating parameter such as discharge voltage, magnetic field or mass flow rate causes the thruster discharge current mean value and oscillation amplitude to increase significantly. Mode transitions in a 6-kW-class HET called the H6 are induced by varying the magnetic field intensity while holding all other operating parameters constant and measurements are acquired with ion saturation probes and ultra-fast imaging. Global and local oscillation modes are identified. In the global mode, the entire discharge channel oscillates in unison and azimuthal perturbations (spokes) are either absent or negligible. Downstream azimuthally spaced probes show no signal delay between each other and are very well correlated to the discharge current signal. In the local mode, signals from the azimuthally spaced probes exhibit a clear delay indicating the passage of "spokes" and are not well correlated to the discharge current. These spokes are localized oscillations propagating in the ExB direction that are typically 10-20% of the mean value. In contrast, the oscillations in the global mode can be 100% of the mean value. The transition between global and local modes occurs at higher relative magnetic field strengths for higher mass flow rates or higher discharge voltages. The thrust is constant through mode transition but the thrust-to-power decreased by 25% due to increasing discharge current. The plume shows significant differences between modes with the global mode significantly brighter in the channel and the near-field plasma plume as well as exhibiting a luminous spike on thruster centerline. Mode transitions provide valuable insight to thruster operation and suggest improved methods for thruster performance characterization.
Hall Effect Measured Using a Waveguide Tee
NASA Astrophysics Data System (ADS)
Coppock, Joyce; Anderson, James; Johnson, William
2013-03-01
We describe a simple microwave apparatus to measure the Hall effect in semiconductor wafers. The advantage of this technique is that it does not require contacts on the sample, unlike the Van der Pauw method.[1] Our method consists of placing the semiconductor wafer into a slot cut in an X-band waveguide tee and placing the tee in the center of an electromagnet. The next step is to inject power into two arms of the tee and to balance the output so that no power comes out of the third arm of the tee at zero magnetic field. Application of a nonzero magnetic field gives a Hall signal that is linear in the magnetic field and which reverses phase when the magnetic field is reversed. We use a network analyzer to measure the ratio of the Hall signal to the input power. This method yields the semiconductor mobility in the wafer, which we can compare for calibration purposes with mobility data from our Van der Pauw measurements. This talk presents data for silicon and germanium samples doped with boron or phosphorus. Preliminary measurements on doped III-V semiconductor samples will also be presented.
Hall effect in two-dimensional composites
NASA Astrophysics Data System (ADS)
Christiansson, H.
1997-07-01
Conduction in a two-component composite film, subject to a magnetic field, is treated numerically with an interface integral equation method. The composite is chosen to be a square array of starfish-shaped inclusions in an anisotropic matrix. Highly accurate calculations are performed and used to investigate microstructure-independent relations between the effective conductivity tensor elements. Asymptotic studies of closely spaced superconducting and insulating disks in an anisotropic matrix verify theoretical results. All the results in this paper are valid for the analog to the Hall effect in heat conduction, the Righi-Leduc effect.
Excitons in the Fractional Quantum Hall Effect
DOE R&D Accomplishments Database
Laughlin, R. B.
1984-09-01
Quasiparticles of charge 1/m in the Fractional Quantum Hall Effect form excitons, which are collective excitations physically similar to the transverse magnetoplasma oscillations of a Wigner crystal. A variational exciton wavefunction which shows explicitly that the magnetic length is effectively longer for quasiparticles than for electrons is proposed. This wavefunction is used to estimate the dispersion relation of these excitons and the matrix elements to generate them optically out of the ground state. These quantities are then used to describe a type of nonlinear conductivity which may occur in these systems when they are relatively clean.
Comparing Hall Effect and Field Effect Measurements on the Same Single Nanowire.
Hultin, Olof; Otnes, Gaute; Borgström, Magnus T; Björk, Mikael; Samuelson, Lars; Storm, Kristian
2016-01-13
We compare and discuss the two most commonly used electrical characterization techniques for nanowires (NWs). In a novel single-NW device, we combine Hall effect and back-gated and top-gated field effect measurements and quantify the carrier concentrations in a series of sulfur-doped InP NWs. The carrier concentrations from Hall effect and field effect measurements are found to correlate well when using the analysis methods described in this work. This shows that NWs can be accurately characterized with available electrical methods, an important result toward better understanding of semiconductor NW doping.
A Hall effect angle detector for solid-state NMR.
Mamone, Salvatore; Dorsch, André; Johannessen, Ole G; Naik, Manoj V; Madhu, P K; Levitt, Malcolm H
2008-01-01
We describe a new method for independent monitoring of the angle between the spinning axis and the magnetic field in solid-state NMR. A Hall effect magnetic flux sensor is fixed to the spinning housing, so that a change in the stator orientation leads to a change in the angle between the Hall plane and the static magnetic field. This leads to a change in the Hall voltage generated by the sensor when an electric current is passed through it. The Hall voltage may be measured externally by a precision voltmeter, allowing the spinning angle to be measured non-mechanically and independent of the NMR experiment. If the Hall sensor is mounted so that the magnetic field is approximately parallel to the Hall plane, the Hall voltage becomes highly sensitive to the stator orientation. The current angular accuracy is around 10 millidegrees. The precautions needed to achieve higher angular accuracy are described.
Guterding, Daniel; Jeschke, Harald O.; Valentí, Roser
2016-01-01
Electronic states with non-trivial topology host a number of novel phenomena with potential for revolutionizing information technology. The quantum anomalous Hall effect provides spin-polarized dissipation-free transport of electrons, while the quantum spin Hall effect in combination with superconductivity has been proposed as the basis for realizing decoherence-free quantum computing. We introduce a new strategy for realizing these effects, namely by hole and electron doping kagome lattice Mott insulators through, for instance, chemical substitution. As an example, we apply this new approach to the natural mineral herbertsmithite. We prove the feasibility of the proposed modifications by performing ab-initio density functional theory calculations and demonstrate the occurrence of the predicted effects using realistic models. Our results herald a new family of quantum anomalous Hall and quantum spin Hall insulators at affordable energy/temperature scales based on kagome lattices of transition metal ions. PMID:27185665
NASA Astrophysics Data System (ADS)
Guterding, Daniel; Jeschke, Harald O.; Valentí, Roser
2016-05-01
Electronic states with non-trivial topology host a number of novel phenomena with potential for revolutionizing information technology. The quantum anomalous Hall effect provides spin-polarized dissipation-free transport of electrons, while the quantum spin Hall effect in combination with superconductivity has been proposed as the basis for realizing decoherence-free quantum computing. We introduce a new strategy for realizing these effects, namely by hole and electron doping kagome lattice Mott insulators through, for instance, chemical substitution. As an example, we apply this new approach to the natural mineral herbertsmithite. We prove the feasibility of the proposed modifications by performing ab-initio density functional theory calculations and demonstrate the occurrence of the predicted effects using realistic models. Our results herald a new family of quantum anomalous Hall and quantum spin Hall insulators at affordable energy/temperature scales based on kagome lattices of transition metal ions.
Guterding, Daniel; Jeschke, Harald O; Valentí, Roser
2016-05-17
Electronic states with non-trivial topology host a number of novel phenomena with potential for revolutionizing information technology. The quantum anomalous Hall effect provides spin-polarized dissipation-free transport of electrons, while the quantum spin Hall effect in combination with superconductivity has been proposed as the basis for realizing decoherence-free quantum computing. We introduce a new strategy for realizing these effects, namely by hole and electron doping kagome lattice Mott insulators through, for instance, chemical substitution. As an example, we apply this new approach to the natural mineral herbertsmithite. We prove the feasibility of the proposed modifications by performing ab-initio density functional theory calculations and demonstrate the occurrence of the predicted effects using realistic models. Our results herald a new family of quantum anomalous Hall and quantum spin Hall insulators at affordable energy/temperature scales based on kagome lattices of transition metal ions.
Volumetric Hall effect tomography--a feasibility study.
Wen, H
1999-07-01
Hall effect imaging is an ultrasound-based method of mapping spatial variations in the dielectric constants of an acoustically-uniform sample. This paper presents three-dimensional Hall effect images of phantoms obtained by scanning a single transducer across a two-dimensional grid, effectively simulating two-dimensional phased-array signal reception. The experiments demonstrate the feasibility of volumetric Hall effect tomography and show the advantage of volumetric scans over planar scans. The images reflect several limitations of the current scanning method and point to directions for further hardware development. The inherent limitations of Hall effect imaging are also discussed in light of these results.
Volumetric Hall Effect Tomography – A Feasibility Study
Wen, Han
2010-01-01
Hall effect imaging is an ultrasound-based method of mapping spatial variations in the dielectric constants of an acoustically-uniform sample. This paper presents three-dimensional Hall effect images of phantoms obtained by scanning a single transducer across a two-dimensional grid, effectively simulating two-dimensional phased-array signal reception. The experiments demonstrate the feasibility of volumetric Hall effect tomography and show the advantage of volumetric scans over planar scans. The images reflect several limitations of the current scanning method and point to directions for further hardware development. The inherent limitations of Hall effect imaging are also discussed in light of these results. PMID:10604800
Faster Hall-Effect Current-Measuring Circuit
NASA Technical Reports Server (NTRS)
Sullender, Craig C.; Johnson, Daniel D.; Walker, Daniel D.
1993-01-01
Current-measuring circuit operates on Hall-effect-sensing and magnetic-field-nulling principles similar to those described in article, "Nulling Hall-Effect Current-Measuring Circuit" (LEW-15023), but simpler and responds faster. Designed without feedback loop, and analog pulse-width-modulated output indicates measured current. Circuit measures current at frequency higher than bandwidth of its Hall-effect sensor.
MAGNETORESISTANCE AND HALL EFFECT IN SINGLE CRYSTALS OF ALUMINUM
ALUMINUM, *SINGLE CRYSTALS, CRYSTALS, HALL EFFECT , IMPURITIES, LOW PRESSURE, MAGNETIC FIELDS, MAGNETIC PROPERTIES, PARTICLE TRAJECTORIES, ELECTRICAL RESISTANCE, SOLID STATE PHYSICS, SURFACE PROPERTIES.
Charge carrier coherence and Hall effect in organic semiconductors
Yi, H. T.; Gartstein, Y. N.; Podzorov, V.
2016-03-30
Hall effect measurements are important for elucidating the fundamental charge transport mechanisms and intrinsic mobility in organic semiconductors. However, Hall effect studies frequently reveal an unconventional behavior that cannot be readily explained with the simple band-semiconductor Hall effect model. Here, we develop an analytical model of Hall effect in organic field-effect transistors in a regime of coexisting band and hopping carriers. The model, which is supported by the experiments, is based on a partial Hall voltage compensation effect, occurring because hopping carriers respond to the transverse Hall electric field and drift in the direction opposite to the Lorentz force actingmore » on band carriers. We show that this can lead in particular to an underdeveloped Hall effect observed in organic semiconductors with substantial off-diagonal thermal disorder. Lastly, our model captures the main features of Hall effect in a variety of organic semiconductors and provides an analytical description of Hall mobility, carrier density and carrier coherence factor.« less
Topological Hall Effect in Skyrmions: A Nonequilibrium Coherent Transport Approach
NASA Astrophysics Data System (ADS)
Yin, Gen; Zang, Jiadong; Lake, Roger
2014-03-01
Skyrmion is a topological spin texture recently observed in many materials with broken inversion symmetry. In experiments, one effective method to detect the skyrmion crystal phase is the topological Hall measurement. At adiabatic approximation, previous theoretical studies show that the Hall signal is provided by an emergent magnetic field, which explains the topological Hall effect in the classical level. Motivated by the potential device application of skyrmions as digital bits, it is important to understand the topological Hall effect in the mesoscopic level, where the electron coherence should be considered. In this talk, we will discuss the quantum aspects of the topological Hall effect on a tight binding setup solved by nonequilibrium Green's function (NEGF). The charge distribution, Hall potential distribution, thermal broadening effect and the Hall resistivity are investigated in detail. The relation between the Hall resistance and the DM interaction is investigated. Driven by the spin transferred torque (SST), Skyrmion dynamics is previously studied within the adiabatic approximation. At the quantum transport level, this talk will also discuss the non-adiabatic effect in the skyrmion motion with the presence of the topological Hall effect. This material is based upon work supported by the National Science Foundation under Grant Nos. NSF 1128304 and NSF 1124733. It was also supported in part by FAME, one of six centers of STARnet, an SRC program sponsored by MARCO and DARPA.
NASA Astrophysics Data System (ADS)
Owerre, S. A.
2016-07-01
Quite recently, the magnon Hall effect of spin excitations has been observed experimentally on the kagome and pyrochlore lattices. The thermal Hall conductivity κxy changes sign as a function of magnetic field or temperature on the kagome lattice, and κxy changes sign upon reversing the sign of the magnetic field on the pyrochlore lattice. Motivated by these recent exciting experimental observations, we theoretically propose a simple realization of the magnon Hall effect in a two-band model on the honeycomb lattice. The magnon Hall effect of spin excitations arises in the usual way via the breaking of inversion symmetry of the lattice, however, by a next-nearest-neighbour Dzyaloshinsky-Moriya interaction. We find that κxy has a fixed sign for all parameter regimes considered. These results are in contrast to the Lieb, kagome, and pyrochlore lattices. We further show that the low-temperature dependence on the magnon Hall conductivity follows a T2 law, as opposed to the kagome and pyrochlore lattices. These results suggest an experimental procedure to measure thermal Hall conductivity within a class of 2D honeycomb quantum magnets and ultracold atoms trapped in a honeycomb optical lattice.
Universality in the Fractional Quantum Hall effect
NASA Astrophysics Data System (ADS)
Fradkin, Eduardo; Lopez, Ana
1993-11-01
In this lectures we review the fermion field theoretic approach to the Fractional Quantum Hall Effect and use it to discuss the origin of its remarkable universality. We discuss the semiclassical expansion around the average field approximation (AFA). We reexamine the AFA and the role of fluctuations. We argue that, order-by-order in the semiclassical expansion, the response functions obey the correct symmetry properties required by Galilean and Gauge Invariance and by the incompressibility of the fluid. In particular, we find that the low-momentum limit of the semiclassical approximation to the response functions is exact and that it saturates the f-sum rule. We discuss the nature of the spectrum of collective excitations of FQHE systems in the low-momentum limit. We applied these results to the problem of the screening of external charges and fluxes by the electron fluid, and obtained asymptotic expressions of the charge and current density profiles, for different types of interactions. The universality of the FQHE is demonstrated by deriving the form of the wave function of the ground state at long distances. We show that the wave functions of the fluid ground states of Fractional Quantum Hall systems, in the thermodynamic limit, are universal at long distances and that they have a generalized Laughlin form. This universality is a consequence of the analytic properties of the equal-time density correlation functions at long distances.
Hall Effect Measured Using a Waveguide Tee
NASA Astrophysics Data System (ADS)
Coppock, Joyce; Anderson, James; Johnson, William
2014-03-01
We describe a simple microwave apparatus to measure the Hall effect in semiconductor wafers. The advantage of this technique is that it does not require contacts on the sample or the use of a resonant cavity. Our method consists of placing the semiconductor wafer into a slot cut in an X-band waveguide tee, which lies in the center of an electromagnet, injecting power into the two opposing arms of the tee, and measuring the output at the third arm. Application of a magnetic field gives a Hall signal that is linear in the magnetic field and which reverses phase when the magnetic field is reversed. This method yields the semiconductor mobility, which we can compare for calibration purposes with mobility data from direct-current (Van der Pauw1) measurements. We are in the process of modeling the system using a finite-difference time-domain (FDTD) simulation to better understand the behavior of the electric fields inside the sample. Resistivity data is obtained by measuring the microwave reflection coefficient of the sample. This talk presents data for silicon and germanium samples doped with boron or phosphorus. Measured mobilities ranged from 270-3000 cm2/V.s . 1L. J. van der Pauw, PhilipsResearchReports 13, 1 (1958)
Intrinsic valley Hall effect in graphene
NASA Astrophysics Data System (ADS)
Yang, Mou; Zhang, Wen-Lian; Liu, Hai; Bai, Yan-Kui
2017-04-01
If electrons are incident from an armchair graphene ribbon into the bulk graphene region, the electronic diffraction occurs. Because of the different triangular wrapping of the energy dispersion between valleys K and K ‧ , the electrons of valley K tend to be diffracted to one side and those of valley K ‧ to the other side. When the current is injected from the armchair ribbon of a four-terminal graphene device, the major portion of the incident current of valley K flows through one side arm and the minor portion through the other side arm. The ratio between them is derived to be 1 + 4 E / 3 in the low energy limit, where E is the energy in units of hopping parameter. The major arm for valley K is the minor arm for valley K ‧ . This results in the rise of the valley Hall effect, which is an intrinsic property of graphene stemming from the different electronic structure of the two valleys. The valley Hall conductance is calculated to be (2 E / 3)G0 with G0 being the conductance supported by the injection ribbon.
Quantum Hall Effect and Quillen Metric
NASA Astrophysics Data System (ADS)
Klevtsov, Semyon; Ma, Xiaonan; Marinescu, George; Wiegmann, Paul
2017-02-01
We study the generating functional, the adiabatic curvature and the adiabatic phase for the integer quantum Hall effect (QHE) on a compact Riemann surface. For the generating functional we derive its asymptotic expansion for the large flux of the magnetic field, i.e., for the large degree k of the positive Hermitian line bundle L k . The expansion consists of the anomalous and exact terms. The anomalous terms are the leading terms of the expansion. This part is responsible for the quantization of the adiabatic transport coefficients in QHE. We then identify the non-local (anomalous) part of the expansion with the Quillen metric on the determinant line bundle, and the subleading exact part with the asymptotics of the regularized spectral determinant of the Laplacian for the line bundle L k , at large k. Finally, we show how the generating functional of the integer QHE is related to the gauge and gravitational (2+1)d Chern-Simons functionals. We observe the relation between the Bismut-Gillet-Soulé curvature formula for the Quillen metric and the adiabatic curvature for the electromagnetic and geometric adiabatic transport of the integer Quantum Hall state. We then obtain the geometric part of the adiabatic phase in QHE, given by the Chern-Simons functional.
Geometric spin Hall effect of light with inhomogeneous polarization
NASA Astrophysics Data System (ADS)
Ling, Xiaohui; Zhou, Xinxing; Yi, Xunong
2017-01-01
The spin Hall effect of light originates from spin-orbit interaction of light, which manifests two types of geometric phases. In this paper, we report the observation of a geometric spin Hall effect by generating a light beam with inhomogeneous polarization distribution. Unlike the previously reported geometric spin Hall effect observed in a tilted beam-detector system, which is believed to result from an effective spin-redirection Berry geometric phase, the geometric spin Hall effect demonstrated here is attributed to an effective, spatially varying Pancharatnam-Berry geometric phase generated by the inhomogeneous polarization geometry. Our further experiments show that the geometric spin Hall effect can be tuned by tailoring the polarization geometry of light, demonstrating the spin states of photons can be steered with a great flexibility.
Gauge Physics of Spin Hall Effect
Tan, Seng Ghee; Jalil, Mansoor B. A.; Ho, Cong Son; Siu, Zhuobin; Murakami, Shuichi
2015-01-01
Spin Hall effect (SHE) has been discussed in the context of Kubo formulation, geometric physics, spin orbit force, and numerous semi-classical treatments. It can be confusing if the different pictures have partial or overlapping claims of contribution to the SHE. In this article, we present a gauge-theoretic, time-momentum elucidation, which provides a general SHE equation of motion, that unifies under one theoretical framework, all contributions of SHE conductivity due to the kinetic, the spin orbit force (Yang-Mills), and the geometric (Murakami-Fujita) effects. Our work puts right an ambiguity surrounding previously partial treatments involving the Kubo, semiclassical, Berry curvatures, or the spin orbit force. Our full treatment shows the Rashba 2DEG SHE conductivity to be instead of −, and Rashba heavy hole instead of −. This renewed treatment suggests a need to re-derive and re-calculate previously studied SHE conductivity. PMID:26689260
Photonic versus electronic quantum anomalous Hall effect
NASA Astrophysics Data System (ADS)
Bleu, O.; Solnyshkov, D. D.; Malpuech, G.
2017-03-01
We derive the diagram of the topological phases accessible within a generic Hamiltonian describing quantum anomalous Hall effect for photons and electrons in honeycomb lattices in the presence of a Zeeman field and spin-orbit coupling (SOC). The two cases differ crucially by the winding number of their SOC, which is 1 for the Rashba SOC of electrons, and 2 for the photon SOC induced by the energy splitting between the TE and TM modes. As a consequence, the two models exhibit opposite Chern numbers ±2 at low field. Moreover, the photonic system shows a topological transition absent in the electronic case. If the photonic states are mixed with excitonic resonances to form interacting exciton-polaritons, the effective Zeeman field can be induced and controlled by a circularly polarized pump. This new feature allows an all-optical control of the topological phase transitions.
Gauge Physics of Spin Hall Effect.
Tan, Seng Ghee; Jalil, Mansoor B A; Ho, Cong Son; Siu, Zhuobin; Murakami, Shuichi
2015-12-22
Spin Hall effect (SHE) has been discussed in the context of Kubo formulation, geometric physics, spin orbit force, and numerous semi-classical treatments. It can be confusing if the different pictures have partial or overlapping claims of contribution to the SHE. In this article, we present a gauge-theoretic, time-momentum elucidation, which provides a general SHE equation of motion, that unifies under one theoretical framework, all contributions of SHE conductivity due to the kinetic, the spin orbit force (Yang-Mills), and the geometric (Murakami-Fujita) effects. Our work puts right an ambiguity surrounding previously partial treatments involving the Kubo, semiclassical, Berry curvatures, or the spin orbit force. Our full treatment shows the Rashba 2DEG SHE conductivity to be [formula in text] instead of [formula in text], and Rashba heavy hole [formula in text] instead of [formula in text]. This renewed treatment suggests a need to re-derive and re-calculate previously studied SHE conductivity.
Gauge Physics of Spin Hall Effect
NASA Astrophysics Data System (ADS)
Tan, Seng Ghee; Jalil, Mansoor B. A.; Ho, Cong Son; Siu, Zhuobin; Murakami, Shuichi
2015-12-01
Spin Hall effect (SHE) has been discussed in the context of Kubo formulation, geometric physics, spin orbit force, and numerous semi-classical treatments. It can be confusing if the different pictures have partial or overlapping claims of contribution to the SHE. In this article, we present a gauge-theoretic, time-momentum elucidation, which provides a general SHE equation of motion, that unifies under one theoretical framework, all contributions of SHE conductivity due to the kinetic, the spin orbit force (Yang-Mills), and the geometric (Murakami-Fujita) effects. Our work puts right an ambiguity surrounding previously partial treatments involving the Kubo, semiclassical, Berry curvatures, or the spin orbit force. Our full treatment shows the Rashba 2DEG SHE conductivity to be instead of -, and Rashba heavy hole instead of -. This renewed treatment suggests a need to re-derive and re-calculate previously studied SHE conductivity.
Hall-Effect Thruster Utilizing Bismuth as Propellant
NASA Technical Reports Server (NTRS)
Szabo, James; Gasdaska, Charles; Hruby, Vlad; Robin, Mike
2008-01-01
A laboratory-model Hall-effect spacecraft thruster was developed that utilizes bismuth as the propellant. Xenon was used in most prior Hall-effect thrusters. Bismuth is an attractive alternative because it has a larger atomic mass, a larger electron-impact-ionization cross-section, and is cheaper and more plentiful.
Useful Pedagogical Applications of the Classical Hall Effect
ERIC Educational Resources Information Center
Houari, Ahmed
2007-01-01
One of the most known phenomena in physics is the Hall effect. This is mainly due to its simplicity and to the wide range of its theoretical and practical applications. To complete the pedagogical utility of the Hall effect in physics teaching, I will apply it here to determine the Faraday constant as a fundamental physical number and the number…
25 Years quantum Hall effect: how it all came about
NASA Astrophysics Data System (ADS)
Landwehr, G.
2003-12-01
The quantum Hall effect (QHE) was discovered by Klaus von Klitzing in the spring of 1980. However, the plateaus in the Hall resistance of silicon metal oxide semiconductor devices which can be observed in high magnetic fields at low temperatures showed up several years earlier. The world wide research, which eventually culminated in the discovery, is briefly reviewed. The QHE was not predicted by theory, there were only approximate indications of quantization of the Hall resistance in whole fractions of h/ e2. The exceptional precision of the resistance values of the Hall plateau led very soon to a new resistance standard.
In-plane magnetization-induced quantum anomalous Hall effect.
Liu, Xin; Hsu, Hsiu-Chuan; Liu, Chao-Xing
2013-08-23
The quantum Hall effect can only be induced by an out-of-plane magnetic field for two-dimensional electron gases, and similarly, the quantum anomalous Hall effect has also usually been considered for systems with only out-of-plane magnetization. In the present work, we predict that the quantum anomalous Hall effect can be induced by in-plane magnetization that is not accompanied by any out-of-plane magnetic field. Two realistic two-dimensional systems, Bi2Te3 thin film with magnetic doping and HgMnTe quantum wells with shear strains, are presented and the general condition for the in-plane magnetization-induced quantum anomalous Hall effect is discussed based on the symmetry analysis. Nonetheless, an experimental setup is proposed to confirm this effect, the observation of which will pave the way to search for the quantum anomalous Hall effect in a wider range of materials.
Mesoscopic spin Hall effect in semiconductor nanostructures
NASA Astrophysics Data System (ADS)
Zarbo, Liviu
The spin Hall effect (SHE) is a name given to a collection of diverse phenomena which share two principal features: (i) longitudinal electric current flowing through a paramagnetic semiconductor or metallic sample leads to transverse spin current and spin accumulation of opposite sign at opposing lateral edges; (ii) SHE does not require externally applied magnetic field or magnetic ordering in the equilibrium state of the sample, instead it relies on the presence of spin-orbit (SO) couplings within the sample. This thesis elaborates on a new type of phenomenon within the SHE family, predicted in our recent studies [Phys. Rev. B 72, 075361 (2005); Phys. Rev. Lett. 95, 046601 (2005); Phys. Rev. B 72, 075335 (2005); Phys. Rev. B 73 , 075303 (2006); and Europhys. Lett. 77, 47004 (2007)], where pure spin current flows through the transverse electrodes attached to a clean finitesize two-dimensional electron gas (2DEG) due to unpolarized charge current injected through its longitudinal leads. If transverse leads are removed, the effect manifests as nonequilibrium spin Hall accumulation at the lateral edges of 2DEG wires. The SO coupling driving this SHE effect is of the Rashba type, which arises due to structural inversion asymmetry of semiconductor heterostructure hosting the 2DEG. We term the effect "mesoscopic" because the spin Hall currents and accumulations reach optimal value in samples of the size of the spin precession length---the distance over which the spin of an electron precesses by an angle pi. In strongly SO-coupled structures this scale is of the order of ˜100 nm, and, therefore, mesoscopic in the sense of being much larger than the characteristic microscopic scales (such as the Fermi wavelength, screening length, or the mean free path in disordered systems), but still much smaller than the macroscopic ones. Although the first theoretical proposal for SHE, driven by asymmetry in SO-dependent scattering of spin-up and spin-down electrons off impurities
Magnetic circuit for hall effect plasma accelerator
NASA Technical Reports Server (NTRS)
Manzella, David H. (Inventor); Jacobson, David T. (Inventor); Jankovsky, Robert S. (Inventor); Hofer, Richard (Inventor); Peterson, Peter (Inventor)
2009-01-01
A Hall effect plasma accelerator includes inner and outer electromagnets, circumferentially surrounding the inner electromagnet along a thruster centerline axis and separated therefrom, inner and outer magnetic conductors, in physical connection with their respective inner and outer electromagnets, with the inner magnetic conductor having a mostly circular shape and the outer magnetic conductor having a mostly annular shape, a discharge chamber, located between the inner and outer magnetic conductors, a magnetically conducting back plate, in magnetic contact with the inner and outer magnetic conductors, and a combined anode electrode/gaseous propellant distributor, located at a bottom portion of the discharge chamber. The inner and outer electromagnets, the inner and outer magnetic conductors and the magnetically conducting back plate form a magnetic circuit that produces a magnetic field that is largely axial and radially symmetric with respect to the thruster centerline.
Universal scaling of the anomalous Hall effect
NASA Astrophysics Data System (ADS)
Zhang, Xiaoqian; Wang, Wei; Wang, Kejie; Niu, Wei; Lai, Bolin; Maltby, Nick; Yang, Mao; Gao, Ming; Liu, Wenqing; He, Liang; Zhang, Rong; Xu, Yongbing
2017-04-01
We have undertaken a detailed study of the magneto-transport properties of ultra-thin Fe films epitaxially grown on GaAs (1 0 0). A metal–semiconductor transition has been observed with a critical thickness of 1.25 nm, which was thought to be related to the thermally activated tunneling between metallic clusters. By fitting {ρ\\text{AH}} versus ρ xx2 with the TYJ equation (Tian et al 2009 Phys. Rev. Lett. 103 087206), we found that the magnetization is negligible for the scaling of the anomalous Hall effect in ultra-thin Fe films. Furthermore, the intrinsic term, which is acquired by the linear fitting of {ρ\\text{AH}} versus ρ xx2 , shows an obvious decrease when the film thickness drops below 1.25 nm, which was thought to be related to the fading of the Berry curvature in the ultra-thin film limit.
Cathode Effects in Cylindrical Hall Thrusters
Granstedt, E.M.; Raitses, Y.; Fisch, N. J.
2008-09-12
Stable operation of a cylindrical Hall thruster (CHT) has been achieved using a hot wire cathode, which functions as a controllable electron emission source. It is shown that as the electron emission from the cathode increases with wire heating, the discharge current increases, the plasma plume angle reduces, and the ion energy distribution function shifts toward higher energies. The observed effect of cathode electron emission on thruster parameters extends and clarifies performance improvements previously obtained for the overrun discharge current regime of the same type of thruster, but using a hollow cathode-neutralizer. Once thruster discharge current saturates with wire heating, further filament heating does not affect other discharge parameters. The saturated values of thruster discharge parameters can be further enhanced by optimal placement of the cathode wire with respect to the magnetic field.
Anomalous Hall effect in YIG|Pt bilayers
Meyer, Sibylle Schlitz, Richard; Geprägs, Stephan; Opel, Matthias; Huebl, Hans; Goennenwein, Sebastian T. B.; Gross, Rudolf
2015-03-30
We measure the ordinary and the anomalous Hall effect in a set of yttrium iron garnet|platinum (YIG|Pt) bilayers via magnetization orientation dependent magnetoresistance experiments. Our data show that the presence of the ferrimagnetic insulator YIG leads to an anomalous Hall effect like voltage in Pt, which is sensitive to both Pt thickness and temperature. Interpretation of the experimental findings in terms of the spin Hall anomalous Hall effect indicates that the imaginary part of the spin mixing conductance G{sub i} plays a crucial role in YIG|Pt bilayers. In particular, our data suggest a sign change in G{sub i} between 10 K and 300 K. Additionally, we report a higher order Hall effect contribution, which appears in thin Pt films on YIG at low temperatures.
NASA Astrophysics Data System (ADS)
Gerhardts, Rolf R.
2017-01-01
Recent low-temperature scanning-force-microscopy experiments on narrow Hall bars, under the conditions of the integer quantum Hall effect (IQHE) and its breakdown, have revealed an interesting position dependence of the Hall potential, which changes drastically with the applied magnetic field and the strength of the imposed current through the sample. The present paper shows, that inclusion of Joule heating into an existing self-consistent theory of screening and magneto-transport, which assumes translation invariant Hall bars with a homogeneous background charge due to doping, can explain the experimental results on the breakdown of the IQHE in the so called edge-dominated regime.
Optical Emission Characterization of High-Power Hall Thruster Wear
NASA Technical Reports Server (NTRS)
WIlliams, George J.; Kamhawi, Hani
2013-01-01
Optical emission spectroscopy is employed to correlate BN insulator erosion with high-power operation of the NASA 300M Hall-effect thruster. Actinometry leveraging excited xenon states is used to normalize the emission spectra of ground state boron as a function of thruster operating condition. Trends in the strength of the boron signal are correlated with thruster power, discharge voltage, discharge current and magnetic field strength. The boron signals are shown to trend with discharge current and show weak dependence on discharge voltage. The trends are consistent with data previously collected on the NASA 300M and NASA 457M thrusters but are different from conventional wisdom.
Kim, Sang-Il; Seo, Min-Su; Park, Seung-Young; Kim, Dong-Jun; Park, Byong-Guk
2015-05-07
The dependence of the measured DC voltage on the non-magnetic material (NM) in NM/CoFeB and CoFeB/NM bilayers is studied under ferromagnetic resonance conditions in a TE{sub 011} resonant cavity. The directional change of the inverse spin Hall effect (ISHE) voltage V{sub ISHE} for the stacking order of the bilayer can separate the pure V{sub ISHE} and the anomalous Hall effect (AHE) voltage V{sub AHE} utilizing the method of addition and subtraction. The Ta and Ti NMs show a broad deviation of the spin Hall angle θ{sub ISH}, which originates from the AHE in accordance with the high resistivity of NMs. However, the Pt and Pd NMs show that the kinds of NMs with low resistivity are consistent with the previously reported θ{sub ISH} values. Therefore, the characteristics that NM should simultaneously satisfy to obtain a reasonable V{sub ISHE} value in bilayer systems are large θ{sub ISH} and low resistivity.
High temperature hall effect measurement system design, measurement and analysis
NASA Astrophysics Data System (ADS)
Berkun, Isil
A reliable knowledge of the transport properties of semiconductor materials is essential for the development and understanding of a number of electronic devices. In this thesis, the work on developing a Hall Effect measurement system with software based data acqui- sition and control for a temperature range of 300K-700K will be described. A system was developed for high temperature measurements of materials including single crystal diamond, poly-crystalline diamond, and thermoelectric compounds. An added capability for monitor- ing the current versus voltage behavior of the contacts was used for studying the influence of ohmic and non-ohmic contacts on Hall Effect measurements. The system has been primar- ily used for testing the transport properties of boron-doped single crystal diamond (SCD) deposited in a microwave plasma-assisted chemical vapor deposition (MPCVD) reactor [1]. Diamond has several outstanding properties that are of high interest for its development as an electronic material. These include a relatively wide band gap of 5.5 (eV), high thermal conductivity, high mobility, high saturation velocity, and a high breakdown voltage. For a temperature range of 300K-700K, IV curves, Hall mobilities and carrier concentrations are shown. Temperature dependent Hall effect measurements have shown carrier concentrations from below 1017cm --3 to approximately 1021 cm--3 with mobilities ranging from 763( cm2/V s) to 0.15(cm 2/V s) respectively. Simulation results have shown the effects of single and mixed carrier models, activation energies, effective mass and doping concentrations. These studies have been helpful in the development of single crystal diamond for diode applications. Reference materials of Ge and GaAs were used to test the Hall Effect system. The system was also used to characterize polycrystalline diamond deposited on glass for electrochemical applications, and Mg2(Si,Sn) compounds which are promising candidates of low-cost, light weight and non
Topological insulator in junction with ferromagnets: Quantum Hall effects
NASA Astrophysics Data System (ADS)
Chudnovskiy, A. L.; Kagalovsky, V.
2015-06-01
The ferromagnet-topological insulator-ferromagnet (FM-TI-FM) junction exhibits thermal and electrical quantum Hall effects. The generated Hall voltage and transverse temperature gradient can be controlled by the directions of magnetizations in the FM leads, which inspires the use of FM-TI-FM junctions as electrical and as heat switches in spintronic devices. Thermal and electrical Hall coefficients are calculated as functions of the magnetization directions in ferromagnets and the spin-relaxation time in TI. Both the Hall voltage and the transverse temperature gradient decrease but are not completely suppressed even at very short spin-relaxation times. The Hall coefficients turn out to be independent of the spin-relaxation time for symmetric configuration of FM leads.
Unconventional quantum Hall effect in Floquet topological insulators.
Tahir, M; Vasilopoulos, P; Schwingenschlögl, U
2016-09-28
We study an unconventional quantum Hall effect for the surface states of ultrathin Floquet topological insulators in a perpendicular magnetic field. The resulting band structure is modified by photon dressing and the topological property is governed by the low-energy dynamics of a single surface. An exchange of symmetric and antisymmetric surface states occurs by reversing the light's polarization. We find a novel quantum Hall state in which the zeroth Landau level undergoes a phase transition from a trivial insulator state, with Hall conductivity [Formula: see text] at zero Fermi energy, to a Hall insulator state with [Formula: see text]. These findings open new possibilities for experimentally realizing nontrivial quantum states and unusual quantum Hall plateaus at [Formula: see text].
Magnet/Hall-Effect Random-Access Memory
NASA Technical Reports Server (NTRS)
Wu, Jiin-Chuan; Stadler, Henry L.; Katti, Romney R.
1991-01-01
In proposed magnet/Hall-effect random-access memory (MHRAM), bits of data stored magnetically in Perm-alloy (or equivalent)-film memory elements and read out by using Hall-effect sensors to detect magnetization. Value of each bit represented by polarity of magnetization. Retains data for indefinite time or until data rewritten. Speed of Hall-effect sensors in MHRAM results in readout times of about 100 nanoseconds. Other characteristics include high immunity to ionizing radiation and storage densities of order 10(Sup6)bits/cm(Sup 2) or more.
A non-invasive Hall current distribution measurement system for Hall Effect thrusters
NASA Astrophysics Data System (ADS)
Mullins, Carl Raymond
A direct, accurate method to measure thrust produced by a Hall Effect thruster on orbit does not currently exist. The ability to calculate produced thrust will enable timely and precise maneuvering of spacecraft---a capability particularly important to satellite formation flying. The means to determine thrust directly is achievable by remotely measuring the magnetic field of the thruster and solving the inverse magnetostatic problem for the Hall current density distribution. For this thesis, the magnetic field was measured by employing an array of eight tunneling magnetoresistive (TMR) sensors capable of milligauss sensitivity when placed in a high background field. The array was positioned outside the channel of a 1.5 kW Colorado State University Hall thruster equipped with a center-mounted electride cathode. In this location, the static magnetic field is approximately 30 Gauss, which is within the linear operating range of the TMR sensors. Furthermore, the induced field at this distance is greater than tens of milligauss, which is within the sensitivity range of the TMR sensors. Due to the nature of the inverse problem, the induced-field measurements do not provide the Hall current density by a simple inversion; however, a Tikhonov regularization of the induced field along with a non-negativity constraint and a zero boundary condition provides current density distributions. Our system measures the sensor outputs at 2 MHz allowing the determination of the Hall current density distribution as a function of time. These data are shown in contour plots in sequential frames. The measured ratios between the average Hall current and the discharge current ranged from 0.1 to 10 over a range of operating conditions from 1.3 kW to 2.2 kW. The temporal inverse solution at 2.0 kW exhibited a breathing mode of 37 kHz, which was in agreement with temporal measurements of the discharge current.
Optical detection of spin Hall effect in metals
NASA Astrophysics Data System (ADS)
van T Erve, Olaf; Hanbicki, Aubrey; McCreary, Kathy; Li, Connie; Jonker, Berry
2015-03-01
Here we present room temperature measurements of the spin Hall effect in non-magnetic metals such as Pt and β-W using a standard bench top magneto-optic Kerr effect (MOKE) system. With this system, one can readily determine the angular dependence of the induced polarization on the bias current direction, the orientation of the spin Hall induced polarization, and the sign of the spin Hall angle. When a bias current is applied, the spin Hall effect causes electrons of opposite spin to be scattered in orthogonal directions, resulting in a spin accumulation at the surface of the film. The MOKE signal tracks the applied square wave bias current with an amplitude and phase directly related to the spin Hall angle. Using this technique, we show that the spin-Hall angle of β-W is opposite in sign and significantly larger than that of Pt, and follow the structural phase transition from β-W to α-W as the film is annealed through the dependence of the spin Hall angle on crystal structure. We also use this technique to detect spin diffusion from β-W into Al thin films. This work was supported by internal programs at NRL and the NRL Nanoscience Institute
Hall Effect and Magneto Optical MFL Sensing
NASA Astrophysics Data System (ADS)
Jallouli, Wissem
The need for a reliable sensing tool has stimulated countless researchers to develop techniques trying to extract maximum information. In the field of nondestructive testing (NDT), various sensors have been established to fulfill that function. Examples include the ultrasonic, eddy current, and magnetic flux leakage (MFL) based techniques. Because they are extremely reliable, MFL based techniques represent one of the best inspection technologies. These technologies have numerous applications in diverse domains, including petroleum pipeline and tank inspections, airplane inspections, and production quality control. In this work, we will present two technologies based on MFL technique. The first is the Hall Effect sensor. This device has been extensively developed during the last century, especially after the use of integrated circuit technology. Its reliable results even under extreme conditions made it an extremely useful tool. The second technology is Magneto Optical Imaging. This technique rose very recently, and scientists hold high expectations about its performance once proper techniques are developed. The study of these two sensing devices gives a better understanding of the MFL technique by allowing us to investigate the potential of each technology, experience each in studied conditions to derive its characteristics, and discuss its performance.
Hall effect measurements on InAs nanowires
Bloemers, Ch.; Grap, T.; Lepsa, M. I.; Moers, J.; Gruetzmacher, D.; Lueth, H.; Trellenkamp, St.; Schaepers, Th.
2012-10-08
We have processed Hall contacts on InAs nanowires grown by molecular beam epitaxy using an electron beam lithography process with an extremely high alignment accuracy. The carrier concentrations determined from the Hall effect measurements on these nanowires are lower by a factor of about 4 in comparison with those measured by the common field-effect technique. The results are used to evaluate quantitatively the charging effect of the interface and surface states.
Hall effect measurements on InAs nanowires
NASA Astrophysics Data System (ADS)
Blömers, Ch.; Grap, T.; Lepsa, M. I.; Moers, J.; Trellenkamp, St.; Grützmacher, D.; Lüth, H.; Schäpers, Th.
2012-10-01
We have processed Hall contacts on InAs nanowires grown by molecular beam epitaxy using an electron beam lithography process with an extremely high alignment accuracy. The carrier concentrations determined from the Hall effect measurements on these nanowires are lower by a factor of about 4 in comparison with those measured by the common field-effect technique. The results are used to evaluate quantitatively the charging effect of the interface and surface states.
Hall-Effect Current Sensors For Integrated Circuits
NASA Technical Reports Server (NTRS)
Rippel, Wally E.
1989-01-01
Built-in devices measure direct or alternating currents. Hall-effect sensors placed near constriction in conductor strip. Differential configuration reduces effects of stray magnetic fields, nonlinearities, and changes in temperature. Preliminary design studies and experiments with macroscopic commercial Hall-effect sensors conducted to assess feasibility, limitations, and need for further research and development of this concept. Potential applications include programmable power supplies and protective circuitry.
Elyasi, Mehrdad; Bhatia, Charanjit S.; Yang, Hyunsoo
2015-02-14
We have proposed a method to synchronize multiple spin-transfer torque oscillators based on spin pumping, inverse spin Hall, and spin Hall effects. The proposed oscillator system consists of a series of nano-magnets in junction with a normal metal with high spin-orbit coupling, and an accumulative feedback loop. We conduct simulations to demonstrate the effect of modulated charge currents in the normal metal due to spin pumping from each nano-magnet. We show that the interplay between the spin Hall effect and inverse spin Hall effect results in synchronization of the nano-magnets.
Fractional quantum Hall effect in the absence of Landau levels.
Sheng, D N; Gu, Zheng-Cheng; Sun, Kai; Sheng, L
2011-07-12
It is well known that the topological phenomena with fractional excitations, the fractional quantum Hall effect, will emerge when electrons move in Landau levels. Here we show the theoretical discovery of the fractional quantum Hall effect in the absence of Landau levels in an interacting fermion model. The non-interacting part of our Hamiltonian is the recently proposed topologically non-trivial flat-band model on a checkerboard lattice. In the presence of nearest-neighbouring repulsion, we find that at 1/3 filling, the Fermi-liquid state is unstable towards the fractional quantum Hall effect. At 1/5 filling, however, a next-nearest-neighbouring repulsion is needed for the occurrence of the 1/5 fractional quantum Hall effect when nearest-neighbouring repulsion is not too strong. We demonstrate the characteristic features of these novel states and determine the corresponding phase diagram.
Nulling Hall-Effect Current-Measuring Circuit
NASA Technical Reports Server (NTRS)
Sullender, Craig C.; Vazquez, Juan M.; Berru, Robert I.
1993-01-01
Circuit measures electrical current via combination of Hall-effect-sensing and magnetic-field-nulling techniques. Known current generated by feedback circuit adjusted until it causes cancellation or near cancellation of magnetic field produced in toroidal ferrite core by current measured. Remaining magnetic field measured by Hall-effect sensor. Circuit puts out analog signal and digital signal proportional to current measured. Accuracy of measurement does not depend on linearity of sensing components.
Valleytronics. The valley Hall effect in MoS₂ transistors.
Mak, K F; McGill, K L; Park, J; McEuen, P L
2014-06-27
Electrons in two-dimensional crystals with a honeycomb lattice structure possess a valley degree of freedom (DOF) in addition to charge and spin. These systems are predicted to exhibit an anomalous Hall effect whose sign depends on the valley index. Here, we report the observation of this so-called valley Hall effect (VHE). Monolayer MoS2 transistors are illuminated with circularly polarized light, which preferentially excites electrons into a specific valley, causing a finite anomalous Hall voltage whose sign is controlled by the helicity of the light. No anomalous Hall effect is observed in bilayer devices, which have crystal inversion symmetry. Our observation of the VHE opens up new possibilities for using the valley DOF as an information carrier in next-generation electronics and optoelectronics.
The spin Hall effect in a quantum gas.
Beeler, M C; Williams, R A; Jiménez-García, K; LeBlanc, L J; Perry, A R; Spielman, I B
2013-06-13
Electronic properties such as current flow are generally independent of the electron's spin angular momentum, an internal degree of freedom possessed by quantum particles. The spin Hall effect, first proposed 40 years ago, is an unusual class of phenomena in which flowing particles experience orthogonally directed, spin-dependent forces--analogous to the conventional Lorentz force that gives the Hall effect, but opposite in sign for two spin states. Spin Hall effects have been observed for electrons flowing in spin-orbit-coupled materials such as GaAs and InGaAs (refs 2, 3) and for laser light traversing dielectric junctions. Here we observe the spin Hall effect in a quantum-degenerate Bose gas, and use the resulting spin-dependent Lorentz forces to realize a cold-atom spin transistor. By engineering a spatially inhomogeneous spin-orbit coupling field for our quantum gas, we explicitly introduce and measure the requisite spin-dependent Lorentz forces, finding them to be in excellent agreement with our calculations. This 'atomtronic' transistor behaves as a type of velocity-insensitive adiabatic spin selector, with potential application in devices such as magnetic or inertial sensors. In addition, such techniques for creating and measuring the spin Hall effect are clear prerequisites for engineering topological insulators and detecting their associated quantized spin Hall effects in quantum gases. As implemented, our system realizes a laser-actuated analogue to the archetypal semiconductor spintronic device, the Datta-Das spin transistor.
Hall-Petch effect: Another manifestation of size effect
NASA Astrophysics Data System (ADS)
Li, Yuan; Dunstan, David; Bushby, Andy
In the 1950s, Hall and Petch first established a quantitative relationship, expressed by the famous Hall-Petch equation: σd =σ0 +kHP/√{ d} There is a very large body of experimental data in the literature reinforcing this dependence in a very wide range of metals. Recently, we presented some of the classic data sets which have been considered to confirm the Hall-Petch equation and showed they are equally well consistent with the equation ɛel (d) =ɛ0 +kln/(d) d Eq. 2 is based on critical thickness theory. Fitting to Eq.1 with the exponent 0.5 replaced by the free fitting parameter x, the confidence interval for the exponent is 0.5
Anisotropic intrinsic spin Hall effect in quantum wires.
Cummings, A W; Akis, R; Ferry, D K
2011-11-23
We use numerical simulations to investigate the spin Hall effect in quantum wires in the presence of both Rashba and Dresselhaus spin-orbit coupling. We find that the intrinsic spin Hall effect is highly anisotropic with respect to the orientation of the wire, and that the nature of this anisotropy depends strongly on the electron density and the relative strengths of the Rashba and Dresselhaus spin-orbit couplings. In particular, at low densities, when only one subband of the quantum wire is occupied, the spin Hall effect is strongest for electron momentum along the [N110] axis, which is the opposite of what is expected for the purely 2D case. In addition, when more than one subband is occupied, the strength and anisotropy of the spin Hall effect can vary greatly over relatively small changes in electron density, which makes it difficult to predict which wire orientation will maximize the strength of the spin Hall effect. These results help to illuminate the role of quantum confinement in spin-orbit-coupled systems, and can serve as a guide for future experimental work on the use of quantum wires for spin-Hall-based spintronic applications.
Linear Magnetization Dependence of the Intrinsic Anomalous Hall Effect
Zeng, C.; Yao, Y.; Niu, Q.; Weitering, Harm H
2006-01-01
The anomalous Hall effect is investigated experimentally and theoretically for ferromagnetic thin films of Mn{sub 5}Ge{sub 3}. We have separated the intrinsic and extrinsic contributions to the experimental anomalous Hall effect and calculated the intrinsic anomalous Hall conductivity from the Berry curvature of the Bloch states using first-principles methods. The intrinsic anomalous Hall conductivity depends linearly on the magnetization, which can be understood from the long-wavelength fluctuations of the spin orientation at finite temperatures. The quantitative agreement between theory and experiment is remarkably good, not only near 0 K but also at finite temperatures, up to about -240 K (0.8T{sub c}).
Azimuthal Spoke Propagation in Hall Effect Thrusters
NASA Technical Reports Server (NTRS)
Sekerak, Michael J.; Longmier, Benjamin W.; Gallimore, Alec D.; Brown, Daniel L.; Hofer, Richard R.; Polk, James E.
2013-01-01
Spokes are azimuthally propagating perturbations in the plasma discharge of Hall Effect Thrusters (HETs) that travel in the E x B direction and have been observed in many different systems. The propagation of azimuthal spokes are investigated in a 6 kW HET known as the H6 using ultra-fast imaging and azimuthally spaced probes. A spoke surface is a 2-D plot of azimuthal light intensity evolution over time calculated from 87,500 frames/s videos. The spoke velocity has been determined using three methods with similar results: manual fitting of diagonal lines on the spoke surface, linear cross-correlation between azimuthal locations and an approximated dispersion relation. The spoke velocity for three discharge voltages (300, 400 and 450 V) and three anode mass flow rates (14.7, 19.5 and 25.2 mg/s) yielded spoke velocities between 1500 and 2200 m/s across a range of normalized magnetic field settings. The spoke velocity was inversely dependent on magnetic field strength for low B-field settings and asymptoted at B-field higher values. The velocities and frequencies are compared to standard drifts and plasma waves such as E x B drift, electrostatic ion cyclotron, magnetosonic and various drift waves. The empirically approximated dispersion relation yielded a characteristic velocity that matched the ion acoustic speed for 5 eV electrons that exist in the near-anode and near-field plume regions of the discharge channel based on internal measurements. Thruster performance has been linked to operating mode where thrust-to-power is maximized when azimuthal spokes are present so investigating the underlying mechanism of spokes will benefit thruster operation.
NASA Astrophysics Data System (ADS)
Gallagher, James; Page, Michael; Bhallamudi, Vidya; Brangham, Jack; Meng, Keng Yuan; Esser, Bryan; Wang, Hailong; McComb, Dave; Hammel, Chris; Yang, Fengyuan
B20 phase crystal structures, such as FeGe and MnSi, have been of interest because they enable magnetic skyrmion phases, which can potentially lead to low energy cost spintronic device applications. We report the synthesis of pure phase FeGe epitaxial thin films grown on Si (111) substrates by ultra-high vacuum off-axis magnetron sputtering. The FeGe films were characterized by x-ray diffraction, scanning transmission electron microscopy (STEM) and Hall effect measurements. The topological Hall effect (THE) signals were extracted by subtracting out the anomalous Hall effect and ordinary Hall effect, demonstrating the existence of the skyrmion phase in FeGe films between 5 and 275 K. Topological hall effect was observed at zero field at all temperatures below the Curie temperature, showing the possibility of metastable skymion particles at zero field and high temperatures. We will also discuss the study of dynamics of the ferromagnetic phases using ferromagnetic resonance.
Modulation of effective damping constant using spin Hall effect
Kasai, Shinya Kondou, Kouta; Sukegawa, Hiroaki; Mitani, Seiji; Tsukagoshi, Kazuhito; Otani, Yoshichika
2014-03-03
We have investigated modulation of the effective damping constant α{sub eff} via spin currents through the spin Hall effect for Permalloy/Pt bilayer films with various thicknesses. The observed linear and sinusoidal dependences of current density and field direction on α{sub eff} are in agreement with the analytical model. By comparing the thickness dependence of spin Hall angle obtained from the damping modulation with that previously obtained by spin-torque-induced ferromagnetic resonance, we show that there is no clear extrinsic contribution in the present method. We also show the large modulation of the effective damping constant (down to ∼20%) in the high-current-density region.
Spin Hall effect and spin swapping in diffusive superconductors
NASA Astrophysics Data System (ADS)
Espedal, Camilla; Lange, Peter; Sadjina, Severin; Mal'shukov, A. G.; Brataas, Arne
2017-02-01
We consider the spin-orbit-induced spin Hall effect and spin swapping in diffusive superconductors. By employing the nonequilibrium Keldysh Green's function technique in the quasiclassical approximation, we derive coupled transport equations for the spectral spin and particle distributions and for the energy density in the elastic scattering regime. We compute four contributions to the spin Hall conductivity, namely, skew scattering, side jump, anomalous velocity, and the Yafet contribution. The reduced density of states in the superconductor causes a renormalization of the spin Hall angle. We demonstrate that all four of these contributions to the spin Hall conductivity are renormalized in the same way in the superconducting state. In its simplest manifestation, spin swapping transforms a primary spin current into a secondary spin current with swapped current and polarization directions. We find that the spin-swapping coefficient is not explicitly but only implicitly affected by the superconducting gap through the renormalized diffusion coefficients. We discuss experimental consequences for measurements of the (inverse) spin Hall effect and spin swapping in four-terminal geometries. In our geometry, below the superconducting transition temperature, the spin-swapping signal is increased an order of magnitude while changes in the (inverse) spin Hall signal are moderate.
Optical detection of spin Hall effect in metals
NASA Astrophysics Data System (ADS)
van T Erve, Olaf; Hanbicki, Aubrey; Li, Connie; Jonker, Berend
Spin Hall effects in metals have been successfully measured using electrical methods such as nonlocal spin valve transport, ferromagnetic resonance or spin torque transfer experiments. These methods require complex processing techniques and measuring setups. Here we present room temperature measurements of the spin Hall effect in non-magnetic metals such as Pt and β-W using a standard bench top magneto-optic Kerr effect (MOKE) system. With this system, one can readily determine the angular dependence of the induced polarization on the bias current direction. When a bias current is applied, the spin Hall effect causes electrons of opposite spin to be scattered in opposite directions, resulting in a spin accumulation at the surface of the film. The MOKE signal tracks the applied square wave bias current with an amplitude and phase directly related to the spin Hall angle. Using this technique, we show that the spin-Hall angle of β-W is opposite in sign and significantly larger than that of Pt. In addition, we use this technique to detect spin diffusion from β-W into Al thin films, as well as spin diffusion from the topological surface states of Bi2Se3 into Al. We will also show direct modulation of the reflected light up to 100 kHz, using Bi doped Cu samples. This work was supported by internal programs at NRL.
Optical detection of spin Hall effect in metals
Erve, O. M. J. van ‘t Hanbicki, A. T.; McCreary, K. M.; Li, C. H.; Jonker, B. T.
2014-04-28
Optical techniques have been widely used to probe the spin Hall effect in semiconductors. In metals, however, only electrical methods such as nonlocal spin valve transport, ferromagnetic resonance, or spin torque transfer experiments have been successful. These methods require complex processing techniques and measuring setups. We show here that the spin Hall effect can be observed in non-magnetic metals such as Pt and β-W, using a standard bench top magneto-optical Kerr system with very little sample preparation. Applying a square wave current and using Fourier analysis significantly improve our detection level. One can readily determine the angular dependence of the induced polarization on the bias current direction (very difficult to do with voltage detection), the orientation of the spin Hall induced polarization, and the sign of the spin Hall angle. This optical approach is free from the complications of various resistive effects, which can compromise voltage measurements. This opens up the study of spin Hall effect in metals to a variety of spin dynamic and spatial imaging experiments.
The spin Hall effect of light in moving medium
NASA Astrophysics Data System (ADS)
Li, Hehe; Li, Xinzhong; Wang, Jingge
2017-01-01
In this paper, we investigate the spin Hall effect of light in moving inhomogeneous medium using the Gordon metric and the Maxwell’s equations in the gravitational field. Light experiences a moving medium as a gravitational field by means of the Gordon metric. It is shown that the spin Hall effect of light is modified by the motion of medium, and the deflection of the ray trajectory is dependent on the polarization and the motion of the medium. It is interesting that there is no coupling of the spin angular momentum of light and the effective gravitational field when the medium is moving along the direction of the gradient ∇n(r). The results provide a potential method for controlling the spin Hall effect of light in medium.
The onset of MHD nanofluid convection with Hall current effect
NASA Astrophysics Data System (ADS)
Yadav, Dhananjay; Lee, Jinho
2015-08-01
In this paper, the combined effects of Hall current and magnetic field on the onset of convection in an electrically conducting nanofluid layer heated from below is investigated. A physically more realistic boundary condition on the nanoparticle volume fraction is taken i.e. the nanoparticle flux is assumed to be zero rather than prescribing a nanoparticle volume fraction on the rigid impermeable boundaries. The employed model incorporates the effects of Brownian motion and thermophoresis. The resulting eigenvalue problem is solved using the Galerkin method. The results obtained during the analysis are presented graphically for an alumina-water nanofluid. It is observed that the effect of smaller values of the Hall current parameter and the nanoparticle parameters accelerate the onset of convection, while larger values of the Hall current parameter (≥ 15) have no effect on the system stabilities.
Ordinary and anomalous Hall effects of ferromagnetic Mn5Ge3
NASA Astrophysics Data System (ADS)
Zeng, Changgan
2007-03-01
It is well know that in ferromagnetic materials, the Hall effect includes two contributions: the ordinary Hall effect (OHE), which is proportional to the applied magnetic field, and the anomalous Hall effect (AHE), which originates from the magnetization of the material. Although both phenomena have been throughly studied, there are still questions about the origins of both OHE and AHE in ferromagnetic materials with complicated band structures. Using ferromagnetic Mn5Ge3 thin films as an example, we investigate the Hall effect experimentally and theoretically. We have separated the intrinsic and extrinsic contributions to the experimental AHE and calculated the intrinsic anomalous Hall conductivity from the Berry curvature of the Bloch states using first-principles methods. The intrinsic anomalous Hall conductivity depends linearly on the magnetization, which can be understood from the long-wavelength fluctuations of the spin orientation at finite temperatures. The quantitative agreement between theory and experiment is remarkably good, not only near 0 K but also at finite temperatures, up to about 240 K (0.8Tc) [1]. The measured ordinary Hall coefficient is found to change its sign as a function of temperature. From a detailed analysis, which includes magneto-resistance measurements, magnetic characterization, and first-principles calculations, we establish that the sign change of the OHE is mainly caused by the mixing of the AHE with the magneto-resistance and differential susceptibility. This work was done in collaboration with Y. Yao, Di Xiao, Q. Niu, and H.H. Weitering. [1] Changgan Zeng, Yugui Yao, Qian Niu, and Hanno, H. Weitering, Phys. Rev. Lett. 96, 037204 (2006).
Resonant tunneling in fractional Hall effect
NASA Astrophysics Data System (ADS)
Shi, Chuntai; Jain, Jainendra
2006-03-01
We study theoretically the possible transitions of a fractional quantum Hall island surrounded by another fractional quantum Hall state, induced by either the variation of the magnetic field or a backgate voltage, and find a rich set of possibilities in addition to the one considered previously[1],The elementary transitions correspond to the addition or removal of a composite fermion from the edge or the interior of the island; combinations of elementary transitions may occur simultaneously due to electrostatic constraints. Relevance to a recent experiment[2] is considered, which measures the resonant tunneling of composite fermions through their quasi-bound states around such a 2/5 island surrounded by the 1/3 sea. It is shown that the results are consistent with the notion of fractional braiding statistics, but can be explained on the basis of fractional charge alone. We also perform calculations based on microscopic composite fermion wavefunctions of finite systems to test the theoretical considerations. [1]J.K.Jain, S.A.Kivelson, and D.J.Thouless, Phys.Rev.Lett.71, 3003(1993). [2]F.E.Camino, W.Zhou, and V.J.Goldman, Phys.Rev.B 72, 075342(2005).
Composed planar Hall effect sensors with dual-mode operation
NASA Astrophysics Data System (ADS)
Mor, Vladislav; Roy, Debangsu; Schultz, Moty; Klein, Lior
2016-02-01
We present a composed planar Hall effect sensor with two modes of operation: (a) an ON mode where the composed sensor responds to magnetic field excitations similarly to the response of a regular planar Hall effect sensor, and (b) an OFF mode where the response is negligible. The composed planar Hall effect sensor switches from the OFF mode to the ON mode when it is exposed to a magnetic field which exceeds a certain threshold determined by the sensor design. The features of this sensor make it useful as a switch triggered by magnetic field and as a sensing device with memory, as its mode of operation indicates exposure to a magnetic field larger than a certain threshold without the need to be activated during the exposure itself.
Intrinsic Spin Hall Effect in the Two Dimensional Hole Gas
Bernevig, B.Andrei; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.
2010-01-15
We show that two types of spin-orbit coupling in the 2 dimensional hole gas (2DHG), with and without inversion symmetry breaking, contribute to the intrinsic spin Hall effect. Furthermore, the vertex correction due to impurity scattering vanishes in both cases, in sharp contrast to the case of usual Rashba coupling in the electron band. Recently, the spin Hall effect in a hole doped GaAs semiconductor has been observed experimentally by Wunderlich et al. From the fact that the life time broadening is smaller than the spin splitting, and the fact impurity vertex corrections vanish in this system, we argue that the observed spin Hall effect should be in the intrinsic regime.
Plasma Oscillation Characterization of NASA's HERMeS Hall Thruster via High Speed Imaging
NASA Technical Reports Server (NTRS)
Huang, Wensheng; Kamhawi, Hani; Haag, Thomas W.
2016-01-01
The performance and facility effect characterization tests of NASA's 12.5-kW Hall Effect Rocket with Magnetic Shielding had been completed. As a part of these tests, three plasma oscillation characterization studies were performed to help determine operation settings and quantify margins. The studies included the magnetic field strength variation study, background pressure effect study, and cathode flow fraction study. Separate high-speed videos of the thruster including the cathode and of only the cathode were recorded. Breathing mode at 10-15 kHz and cathode gradient-driven mode at 60-75 kHz were observed. An additional high frequency (40-70 kHz) global oscillation mode with sinusoidal probability distribution function was identified.
NASA Astrophysics Data System (ADS)
Tuegel, Thomas I.; Hughes, Taylor L.
2015-10-01
The Hall viscosity describes a nondissipative response to strain in systems with broken time-reversal symmetry. We develop a method for computing the Hall viscosity of lattice systems in strong magnetic fields based on momentum transport, which we compare to the method of momentum polarization used by Tu et al. [Phys. Rev. B 88, 195412 (2013), 10.1103/PhysRevB.88.195412] and Zaletel et al. [Phys. Rev. Lett. 110, 236801 (2013), 10.1103/PhysRevLett.110.236801] for noninteracting systems. We compare the Hall viscosity of square-lattice tight-binding models in magnetic field to the continuum integer quantum Hall effect (IQHE) showing agreement when the magnetic length is much larger than the lattice constant, but deviation as the magnetic field strength increases. We also relate the Hall viscosity of relativistic electrons in magnetic field (the Dirac IQHE) to the conventional IQHE. The Hall viscosity of the lattice Dirac model in magnetic field agrees with the continuum Dirac Hall viscosity when the magnetic length is much larger than the lattice constant. We also show that the Hall viscosity of the lattice model deviates further from the continuum model if the C4 symmetry of the square lattice is broken to C2, but the deviation is again minimized as the magnetic length increases.
The local nature of incompressibility of quantum Hall effect.
Kendirlik, E M; Sirt, S; Kalkan, S B; Ofek, N; Umansky, V; Siddiki, A
2017-01-10
Since the experimental realization of the integer quantum Hall effect in a two-dimensional electron system, the interrelation between the conductance quantization and the topological properties of the system has been investigated. Assuming that the two-dimensional electron system is described by a Bloch Hamiltonian, system is insulating in the bulk of sample throughout the quantum Hall plateau due to a magnetic field induced energy gap. Meanwhile, the system is conducting at the edges resembling a 2+1 dimensional topological insulator without time-reversal symmetry. Here, by our magneto-transport measurements performed on GaAs/AlGaAs high purity Hall bars with two inner contacts we show that incompressible strips formed at the edges result in Hall quantization, even if the bulk is compressible. Consequently, the relationship between the quantum Hall effect and topological bulk insulator breaks for specific field intervals within the plateaus. The measurement of conducting bulk, strongly challenges all existing single-particle theories.
The local nature of incompressibility of quantum Hall effect
NASA Astrophysics Data System (ADS)
Kendirlik, E. M.; Sirt, S.; Kalkan, S. B.; Ofek, N.; Umansky, V.; Siddiki, A.
2017-01-01
Since the experimental realization of the integer quantum Hall effect in a two-dimensional electron system, the interrelation between the conductance quantization and the topological properties of the system has been investigated. Assuming that the two-dimensional electron system is described by a Bloch Hamiltonian, system is insulating in the bulk of sample throughout the quantum Hall plateau due to a magnetic field induced energy gap. Meanwhile, the system is conducting at the edges resembling a 2+1 dimensional topological insulator without time-reversal symmetry. Here, by our magneto-transport measurements performed on GaAs/AlGaAs high purity Hall bars with two inner contacts we show that incompressible strips formed at the edges result in Hall quantization, even if the bulk is compressible. Consequently, the relationship between the quantum Hall effect and topological bulk insulator breaks for specific field intervals within the plateaus. The measurement of conducting bulk, strongly challenges all existing single-particle theories.
The local nature of incompressibility of quantum Hall effect
Kendirlik, E. M.; Sirt, S.; Kalkan, S. B.; Ofek, N.; Umansky, V.; Siddiki, A.
2017-01-01
Since the experimental realization of the integer quantum Hall effect in a two-dimensional electron system, the interrelation between the conductance quantization and the topological properties of the system has been investigated. Assuming that the two-dimensional electron system is described by a Bloch Hamiltonian, system is insulating in the bulk of sample throughout the quantum Hall plateau due to a magnetic field induced energy gap. Meanwhile, the system is conducting at the edges resembling a 2+1 dimensional topological insulator without time-reversal symmetry. Here, by our magneto-transport measurements performed on GaAs/AlGaAs high purity Hall bars with two inner contacts we show that incompressible strips formed at the edges result in Hall quantization, even if the bulk is compressible. Consequently, the relationship between the quantum Hall effect and topological bulk insulator breaks for specific field intervals within the plateaus. The measurement of conducting bulk, strongly challenges all existing single-particle theories. PMID:28071652
The width of the plateaus of the quantum Hall effect
NASA Astrophysics Data System (ADS)
Groshev, Atanas; Scho¨n, Gerd
1994-02-01
We suggest that in high quality samples in the quantum Hall regime the interaction between localized states dominates over disorder effects. It leads to the formation of a Wigner crystal, which melts at a critical value ν c≈0.2 of the filling factor of the localized states. This leads to a finite width of the plateaus of the integer quantum Hall effect Δν=2ν c. This result describes well recent experimental data on single AlGaAs/GaAs heterojunctions (electron and hole gases) and double 2DEG systems.
Complex scattering dynamics and the quantum Hall effects
Trugman, S.A.
1994-12-16
We review both classical and quantum potential scattering in two dimensions in a magnetic field, with applications to the quantum Hall effect. Classical scattering is complex, due to the approach of scattering states to an infinite number of dynamically bound states. Quantum scattering follows the classical behavior rather closely, exhibiting sharp resonances in place of the classical bound states. Extended scatterers provide a quantitative explanation for the breakdown of the QHE at a comparatively small Hall voltage as seen by Kawaji et al., and possibly for noise effects.
Controlling the optical spin Hall effect with light
NASA Astrophysics Data System (ADS)
Lafont, O.; Luk, S. M. H.; Lewandowski, P.; Kwong, N. H.; Leung, P. T.; Galopin, E.; Lemaitre, A.; Tignon, J.; Schumacher, S.; Baudin, E.; Binder, R.
2017-02-01
The optical spin Hall effect is a transport phenomenon of exciton polaritons in semiconductor microcavities, caused by the polaritonic spin-orbit interaction, which leads to the formation of spin textures. The control of the optical spin Hall effect via light injection in a double microcavity is demonstrated. Angular rotations of the polarization pattern up to 22° are observed and compared to a simple theoretical model. The device geometry is responsible for the existence of two polariton branches which allows a robust independent control of the polariton spin and hence the polarization state of the emitted light field, a solution technologically relevant for future spin-optronic devices.
Anomalous Hall Effect in a Feromagnetic Rare-Earth Cobalite
NASA Technical Reports Server (NTRS)
Samoilov, A. V.; Yeh, N. C.; Vasquez, R. P.
1996-01-01
Rare-Earth manganites and cobalites with the perovskite structure have been a subject of great recent interest because their electrical resistance changes significantly when a magnetic field is applied...we have studied the Hall effect in thin film La(sub 0.5)Ca(sub 0.5)CoO(sub 3) material and have obtained convincing evidence fo the so called anomalous Hall effect, typical for magnetic metals...Our results suggest that near the ferromagnetic ordering temperature, the dominant electron scattering mechanism is the spin fluctuation.
Hydromagnetic free convection flow with Hall effect and mass transfer
NASA Astrophysics Data System (ADS)
Sahoo, Prasan Kumar
2016-02-01
The study of magnetohydrodynamics (MHD) deals with the flow of an electrically conducting fluid in the presence of an electromagnetic field, which has many applications in astrophysics, geophysics and engineering. Objective of the present study in this paper is to consider the effect of dissipation and Hall current on the MHD free convection flow with mass transfer in a porous vertical channel. An exact solution of the governing equations is obtained by solving the complex variables. The effect of Hall parameter (m), Hartmann number (M), and Concentration parameter (Sc) on the velocity and temperature of the fluid is studied. Simulation results show that the shear stress of primary and secondary velocity for the lower plate increases with increase in the strength of Hall parameter (m) and decreases with increase in Hartmann number (M) and concentration parameter (Sc).
Thermal Hall Effect of Spin Excitations in a Kagome Magnet.
Hirschberger, Max; Chisnell, Robin; Lee, Young S; Ong, N P
2015-09-04
At low temperatures, the thermal conductivity of spin excitations in a magnetic insulator can exceed that of phonons. However, because they are charge neutral, the spin waves are not expected to display a thermal Hall effect. However, in the kagome lattice, theory predicts that the Berry curvature leads to a thermal Hall conductivity κ(xy). Here we report observation of a large κ(xy) in the kagome magnet Cu(1-3, bdc) which orders magnetically at 1.8 K. The observed κ(xy) undergoes a remarkable sign reversal with changes in temperature or magnetic field, associated with sign alternation of the Chern flux between magnon bands. The close correlation between κ(xy) and κ(xx) firmly precludes a phonon origin for the thermal Hall effect.
Band Collapse and the Quantum Hall Effect in Graphene
Bernevig, B.Andrei; Hughes, Taylor L.; Zhang, Shou-Cheng; Chen, Han-Dong; Wu, Congjun; /Santa Barbara, KITP
2010-03-16
The recent Quantum Hall experiments in graphene have confirmed the theoretically well-understood picture of the quantum Hall (QH) conductance in fermion systems with continuum Dirac spectrum. In this paper we take into account the lattice, and perform an exact diagonalization of the Landau problem on the hexagonal lattice. At very large magnetic fields the Dirac argument fails completely and the Hall conductance, given by the number of edge states present in the gaps of the spectrum, is dominated by lattice effects. As the field is lowered, the experimentally observed situation is recovered through a phenomenon which we call band collapse. As a corollary, for low magnetic field, graphene will exhibit two qualitatively different QHE's: at low filling, the QHE will be dominated by the 'relativistic' Dirac spectrum and the Hall conductance will be odd-integer; above a certain filling, the QHE will be dominated by a non-relativistic spectrum, and the Hall conductance will span all integers, even and odd.
Quantum Hall effect on Riemann surfaces
NASA Astrophysics Data System (ADS)
Tejero Prieto, Carlos
2009-06-01
We study the family of Landau Hamiltonians compatible with a magnetic field on a Riemann surface S by means of Fourier-Mukai and Nahm transforms. Starting from the geometric formulation of adiabatic charge transport on Riemann surfaces, we prove that Hall conductivity is proportional to the intersection product on the first homology group of S and therefore it is quantized. Finally, by using the theory of determinant bundles developed by Bismut, Gillet and Soul, we compute the adiabatic curvature of the spectral bundles defined by the holomorphic Landau levels. We prove that it is given by the polarization of the jacobian variety of the Riemann surface, plus a term depending on the relative analytic torsion.
Quantum anomalous Hall effect in magnetic insulator heterostructure.
Xu, Gang; Wang, Jing; Felser, Claudia; Qi, Xiao-Liang; Zhang, Shou-Cheng
2015-03-11
On the basis of ab initio calculations, we predict that a monolayer of Cr-doped (Bi,Sb)2Te3 and GdI2 heterostructure is a quantum anomalous Hall insulator with a nontrivial band gap up to 38 meV. The principle behind our prediction is that the band inversion between two topologically trivial ferromagnetic insulators can result in a nonzero Chern number, which offers a better way to realize the quantum anomalous Hall state without random magnetic doping. In addition, a simple effective model is presented to describe the basic mechanism of spin polarized band inversion in this system. Moreover, we predict that 3D quantum anomalous Hall insulator could be realized in (Bi2/3Cr1/3)2Te3 /GdI2 superlattice.
Precise quantization of anomalous Hall effect near zero magnetic field
NASA Astrophysics Data System (ADS)
Bestwick, Andrew; Fox, Eli; Kou, Xufeng; Pan, Lei; Wang, Kang; Goldhaber-Gordon, David
2015-03-01
The quantum anomalous Hall effect (QAHE) has recently been of great interest due to its recent experimental realization in thin films of Cr-doped (Bi, Sb)2Te3, a ferromagnetic 3D topological insulator. The presence of ferromagnetic exchange breaks time-reversal symmetry, opening a gap in the surface states, but gives rise to dissipationless chiral conduction at the edge of a magnetized film. Ideally, this leads to vanishing longitudinal resistance and Hall resistance quantized to h /e2 , where h is Planck's constant and e is the electron charge, but perfect quantization has so far proved elusive. Here, we study the QAHE in the limit of zero applied magnetic field, and measure Hall resistance quantized to within one part per 10,000. Deviation from quantization is due primarily to thermally activated carriers, which can be nearly eliminated through adiabatic demagnetization cooling. This result demonstrates an important step toward dissipationless electron transport in technologically relevant conditions.
Cluster multipole theory for anomalous Hall effect in antiferromagnets
NASA Astrophysics Data System (ADS)
Suzuki, M.-T.; Koretsune, T.; Ochi, M.; Arita, R.
2017-03-01
We introduce a cluster extension of multipole moments to discuss the anomalous Hall effect (AHE) in both ferromagnetic (FM) and antiferromagnetic (AFM) states in a unified framework. We first derive general symmetry requirements for the AHE in the presence or absence of the spin-orbit coupling by considering the symmetry of the Berry curvature in k space. The cluster multipole (CMP) moments are then defined to quantify the macroscopic magnetization in noncollinear AFM states as a natural generalization of the magnetization in FM states. We identify the macroscopic CMP order which induces the AHE. The theoretical framework is applied to the noncollinear AFM states of Mn3Ir , for which an AHE was predicted in a first-principles calculation, and Mn3Z (Z =Sn ,Ge ), for which a large AHE was recently discovered experimentally. We further compare the AHE in Mn3Z and bcc Fe in terms of the CMP. We show that the AHE in Mn3Z is characterized by the magnetization of a cluster octupole moment in the same manner as that in bcc Fe characterized by the magnetization of the dipole moment.
The dip effect under integer quantized Hall conditions
NASA Astrophysics Data System (ADS)
Gulebaglan, Sinem Erden; Kalkan, Sirri Batuhan; Sirt, Serkan; Kendirlik, Enver Metin; Siddiki, Afif
2014-03-01
In this work we investigate an unusual transport phenomenon observed in two-dimensional electron gas under integer quantum Hall effect conditions. Our calculations are based on the screening theory, using a semi-analytical model. The transport anomalies are dip and overshoot effects, where the Hall resistance decreases (or increases) unexpectedly at the quantized resistance plateaus intervals. We report on our numerical findings of the dip effect in the Hall resistance, considering GaAs/AlGaAs heterostructures in which we investigated the effect under different experimental conditions. We show that, similar to overshoot, the amplitude of the dip effect is strongly influenced by the edge reconstruction due to electrostatics. It is observed that the steep potential variation close to the physical boundaries of the sample results in narrower incompressible strips, hence, the experimental observation of the dip effect is limited by the properties of these current carrying strips. By performing standard Hall resistance measurements on gate defined narrow samples, we demonstrate that the predictions of the screening theory is in well agreement with our experimental findings.
Quantum anomalous Hall effect in topological insulator memory
Jalil, Mansoor B. A.; Tan, S. G.; Siu, Z. B.
2015-05-07
We theoretically investigate the quantum anomalous Hall effect (QAHE) in a magnetically coupled three-dimensional-topological insulator (3D-TI) system. We apply the generalized spin-orbit coupling Hamiltonian to obtain the Hall conductivity σ{sup xy} of the system. The underlying topology of the QAHE phenomenon is then analyzed to show the quantization of σ{sup xy} and its relation to the Berry phase of the system. Finally, we analyze the feasibility of utilizing σ{sup xy} as a memory read-out in a 3D-TI based memory at finite temperatures, with comparison to known magnetically doped 3D-TIs.
Few-body, hyperspherical treatment of the quantum Hall effect
NASA Astrophysics Data System (ADS)
Wooten, R. E.; Daily, K. M.; Greene, Chris H.
2016-03-01
The quantum Hall effect arises from the quantum behavior of two-dimensional, strongly-interacting electrons exposed to a strong, perpendicular magnetic field [1, 2]. Conventionally treated from a many-body perspective, we instead treat the system from the few-body perspective using collective coordinates and the hyperspherical adiabatic technique developed originally for atomic systems [3]. The grand angular momentum K from K-harmonic few-body theory, is shown to be an approximate good collective quantum number in this system, and is shown to correlate with known fractional quantum Hall (FQH) states at experimentally observed filling factors.
Geometric phase gradient and spin Hall effect of light
NASA Astrophysics Data System (ADS)
Ling, Xiaohui; Zhou, Xinxing; Qiu, Cheng-Wei
2016-10-01
The spin Hall effect (SHE) of light originates from the spin-orbit interaction, which can be explained in terms of two geometric phases: the Rytov-Vladimirskii-Berry phase and the Pancharatnam-Berry phase. Here we present a unified theoretical description of the SHE based on the two types of geometric phase gradients, and observe experimentally the SHE in structured dielectric metasurfaces induced by the PB phase. Unlike the weak real-space spin-Hall shift induced by the SRB phase occurring at interfacial reflection/refraction, the observed SHE occurs in momentum space is large enough to be measured directly.
Inverse spin Hall effect in Pt/(Ga,Mn)As
Nakayama, H.; Chen, L.; Chang, H. W.; Ohno, H.; Matsukura, F.
2015-06-01
We investigate dc voltages under ferromagnetic resonance in a Pt/(Ga,Mn)As bilayer structure. A part of the observed dc voltage is shown to originate from the inverse spin Hall effect. The sign of the inverse spin Hall voltage is the same as that in Py/Pt bilayer structure, even though the stacking order of ferromagnetic and nonmagnetic layers is opposite to each other. The spin mixing conductance at the Pt/(Ga,Mn)As interface is determined to be of the order of 10{sup 19 }m{sup −2}, which is about ten times greater than that of (Ga,Mn)As/p-GaAs.
Effect of Anode Dielectric Coating on Hall Thruster Operation
L. Dorf; Y. Raitses; N.J. Fisch; V. Semenov
2003-10-20
An interesting phenomenon observed in the near-anode region of a Hall thruster is that the anode fall changes from positive to negative upon removal of the dielectric coating, which is produced on the anode surface during the normal course of Hall thruster operation. The anode fall might affect the thruster lifetime and acceleration efficiency. The effect of the anode coating on the anode fall is studied experimentally using both biased and emissive probes. Measurements of discharge current oscillations indicate that thruster operation is more stable with the coated anode.
Sign change of the flux flow hall effect in HTSC
Feigel`man, M.V.; Geshkenbein, V.B.; Larkin, A.I. ||; Vinokur, V.M.
1994-05-01
A novel mechanism for the sign change of the Hall effect in flux flow region is proposed. The difference {delta}n between the electron density at the center of the vortex core and that far outside the vortex causes the additional contribution to the Hall conductivity {delta}{sigma}{sub xy} = {delta}nec/B. This contribution can be bigger than the conventional one inn the dirty case {Delta}(T){tau} < 1. If the electron density inside the core exceeds the electron density outside the core the double sign change may occur as a function of temperature and magnetic field.
Interaction-Driven Spontaneous Quantum Hall Effect on a Kagome Lattice.
Zhu, W; Gong, Shou-Shu; Zeng, Tian-Sheng; Fu, Liang; Sheng, D N
2016-08-26
Topological states of matter have been widely studied as being driven by an external magnetic field, intrinsic spin-orbital coupling, or magnetic doping. Here, we unveil an interaction-driven spontaneous quantum Hall effect (a Chern insulator) emerging in an extended fermion-Hubbard model on a kagome lattice, based on a state-of-the-art density-matrix renormalization group on cylinder geometry and an exact diagonalization in torus geometry. We first demonstrate that the proposed model exhibits an incompressible liquid phase with doublet degenerate ground states as time-reversal partners. The explicit spontaneous time-reversal symmetry breaking is determined by emergent uniform circulating loop currents between nearest neighbors. Importantly, the fingerprint topological nature of the ground state is characterized by quantized Hall conductance. Thus, we identify the liquid phase as a quantum Hall phase, which provides a "proof-of-principle" demonstration of the interaction-driven topological phase in a topologically trivial noninteracting band.
Interaction-Driven Spontaneous Quantum Hall Effect on a Kagome Lattice
NASA Astrophysics Data System (ADS)
Zhu, W.; Gong, Shou-Shu; Zeng, Tian-Sheng; Fu, Liang; Sheng, D. N.
2016-08-01
Topological states of matter have been widely studied as being driven by an external magnetic field, intrinsic spin-orbital coupling, or magnetic doping. Here, we unveil an interaction-driven spontaneous quantum Hall effect (a Chern insulator) emerging in an extended fermion-Hubbard model on a kagome lattice, based on a state-of-the-art density-matrix renormalization group on cylinder geometry and an exact diagonalization in torus geometry. We first demonstrate that the proposed model exhibits an incompressible liquid phase with doublet degenerate ground states as time-reversal partners. The explicit spontaneous time-reversal symmetry breaking is determined by emergent uniform circulating loop currents between nearest neighbors. Importantly, the fingerprint topological nature of the ground state is characterized by quantized Hall conductance. Thus, we identify the liquid phase as a quantum Hall phase, which provides a "proof-of-principle" demonstration of the interaction-driven topological phase in a topologically trivial noninteracting band.
Dynamics of antiferromagnetic skyrmion driven by the spin Hall effect
NASA Astrophysics Data System (ADS)
Jin, Chendong; Song, Chengkun; Wang, Jianbo; Liu, Qingfang
2016-10-01
Magnetic skyrmion moved by the spin-Hall effect is promising for the application of the generation racetrack memories. However, the Magnus force causes a deflected motion of skyrmion, which limits its application. Here, we create an antiferromagnetic skyrmion by injecting a spin-polarized pulse in the nanostripe and investigate the spin Hall effect-induced motion of antiferromagnetic skyrmion by micromagnetic simulations. In contrast to ferromagnetic skyrmion, we find that the antiferromagnetic skyrmion has three evident advantages: (i) the minimum driving current density of antiferromagnetic skyrmion is about two orders smaller than the ferromagnetic skyrmion; (ii) the velocity of the antiferromagnetic skyrmion is about 57 times larger than the ferromagnetic skyrmion driven by the same value of current density; (iii) antiferromagnetic skyrmion can be driven by the spin Hall effect without the influence of Magnus force. In addition, antiferromagnetic skyrmion can move around the pinning sites due to its property of topological protection. Our results present the understanding of antiferromagnetic skyrmion motion driven by the spin Hall effect and may also contribute to the development of antiferromagnetic skyrmion-based racetrack memories.
Hall effect in gallium manganese arsenide-diluted magnetic semiconductors
NASA Astrophysics Data System (ADS)
Ruzmetov, Dmitry A.
A series of GaMnAs samples with various Mn concentrations and thicknesses is extensively studied in this thesis. The influence of annealing on the magnetic, lattice, and electron transport properties of GaMnAs is investigated. X-ray analysis allowed the lattice constants and the strains due to the lattice mismatch between the GaMnAs film and a GaAs substrate for each sample to be determined. Magnetometric measurements confirm the expected anisotropic ferromagnetic characteristics of these semiconductors, and the measured magnetization in hard and easy axis directions indicates that only around 40% of Mn ions contribute to the ferromagnetism. As a result of the study of the electron transport in GaMnAs at high temperatures, we found that the anomalous contribution to the Hall resistivity dominates over the ordinary contribution up to 380 K in our samples. The measured Hall coefficient of metallic samples with low Mn content above the Curie temperature (TC) can be fit with a model that takes into account the ordinary and anomalous contributions to the Hall resistivity. According to our model, the spontaneous Hall coefficient (RS) in our samples is proportional to the square of the longitudinal resistivity above TC, which corresponds to a temperature-independent Hall conductivity, and we checked for one sample that this form of RS holds also at the liquid He temperature. This indicates that the physical mechanism responsible for the anomalous Hall effect (AHE) remains unchanged in the transition from ferromagnetic to paramagnetic phases of the semiconductor. It is found that the temperature dependence of the AHE above TC can be described except for RS(T) with the Curie-Weiss law for the paramagnetic susceptibility with the inclusion of a small, negative, temperature and Mn content independent correction to the susceptibility, which may originate from the diamagnetism of the GaAs matrix. The good agreement between the measured and fitting Hall data suggests that the
The integer quantum hall effect revisited
Michalakis, Spyridon; Hastings, Matthew
2009-01-01
For T - L x L a finite subset of Z{sup 2}, let H{sub o} denote a Hamiltonian on T with periodic boundary conditions and finite range, finite strength intetactions and a unique ground state with a nonvanishing spectral gap. For S {element_of} T, let q{sub s} denote the charge at site s and assume that the total charge Q = {Sigma}{sub s {element_of} T} q{sub s} is conserved. Using the local charge operators q{sub s}, we introduce a boundary magnetic flux in the horizontal and vertical direction and allow the ground state to evolve quasiadiabatically around a square of size one magnetic flux, in flux space. At the end of the evolution we obtain a trivial Berry phase, which we compare, via a method reminiscent of Stokes Theorem. to the Berry phase obtained from an evolution around an exponentially small loop near the origin. As a result, we show, without any averaging assumption, that the Hall conductance is quantized in integer multiples of e{sup 2}/h up to exponentially small corrections of order e{sup -L/{zeta}}, where {zeta}, is a correlation length that depends only on the gap and the range and strength of the interactions.
Nonlinear dynamics induced anomalous Hall effect in topological insulators.
Wang, Guanglei; Xu, Hongya; Lai, Ying-Cheng
2016-01-28
We uncover an alternative mechanism for anomalous Hall effect. In particular, we investigate the magnetisation dynamics of an insulating ferromagnet (FM) deposited on the surface of a three-dimensional topological insulator (TI), subject to an external voltage. The spin-polarised current on the TI surface induces a spin-transfer torque on the magnetisation of the top FM while its dynamics can change the transmission probability of the surface electrons through the exchange coupling and hence the current. We find a host of nonlinear dynamical behaviors including multistability, chaos, and phase synchronisation. Strikingly, a dynamics mediated Hall-like current can arise, which exhibits a nontrivial dependence on the channel conductance. We develop a physical understanding of the mechanism that leads to the anomalous Hall effect. The nonlinear dynamical origin of the effect stipulates that a rich variety of final states exist, implying that the associated Hall current can be controlled to yield desirable behaviors. The phenomenon can find applications in Dirac-material based spintronics.
Nonlinear dynamics induced anomalous Hall effect in topological insulators
NASA Astrophysics Data System (ADS)
Wang, Guanglei; Xu, Hongya; Lai, Ying-Cheng
2016-01-01
We uncover an alternative mechanism for anomalous Hall effect. In particular, we investigate the magnetisation dynamics of an insulating ferromagnet (FM) deposited on the surface of a three-dimensional topological insulator (TI), subject to an external voltage. The spin-polarised current on the TI surface induces a spin-transfer torque on the magnetisation of the top FM while its dynamics can change the transmission probability of the surface electrons through the exchange coupling and hence the current. We find a host of nonlinear dynamical behaviors including multistability, chaos, and phase synchronisation. Strikingly, a dynamics mediated Hall-like current can arise, which exhibits a nontrivial dependence on the channel conductance. We develop a physical understanding of the mechanism that leads to the anomalous Hall effect. The nonlinear dynamical origin of the effect stipulates that a rich variety of final states exist, implying that the associated Hall current can be controlled to yield desirable behaviors. The phenomenon can find applications in Dirac-material based spintronics.
NASA Astrophysics Data System (ADS)
Li, Kai; Liu, Jun; Liu, Weiqiang
2017-01-01
Magnetohydrodynamic (MHD) heat shield system, a novel thermal protection technique in the hypersonic field, has been paid much attention in recent years. In the real flight condition, not only the Lorentz force but also the Hall electric field is induced by the interaction between ionized air post shock and magnetic field. In order to analyze the action mechanisms of the Hall effect, numerical methods of coupling thermochemical nonequilibrium flow field with externally applied magnetic field as well as the induced electric field are constructed and validated. Based on the nonequilibrium model of Hall parameter, numerical simulations of the MHD heat shield system is conducted under two different magnetic induction strengths (B0=0.2 T, 0.5 T) on a reentry capsule forebody. Results show that, the Hall effect is the same under the two magnetic induction strengths when the wall is assumed to be conductive. For this case, with the Hall effect taken into account, the Lorentz force counter stream diminishes a lot and the circumferential component dominates, resulting that the heat flux and shock-off distance approach the case without MHD control. However, for the insulating wall, the Hall effect acts in different ways under these two magnetic induction strengths. For this case, with the Hall effect taken into account, the performance of MHD heat shield system approaches the case neglecting the Hall effect when B0 equals 0.2 T. Such performance becomes worse when B0 equals 0.5 T and the aerothermal environment on the capsule shoulder is even worse than the case without MHD control.
Far-infrared Hall Effect in YBCO films
NASA Astrophysics Data System (ADS)
Grayson, M.; Rigal, L.; Cerne, J.; Schmadel, D. C.; Drew, H. D.; Kung, P.-J.
2001-03-01
In order to gain insight into the so-called "anomalous Hall effect" in Hi Tc superconductors(T.R. Chien, D.A. Brawner, Z.Z. Wang, and N.P. Ong, PRB 43, 6242(1991).) we explore Hall measurements at far-infrared (FIR) frequencies and study the temperature dependence. We separately measure the real and imaginary parts of the magneto-optical response of YBCO thin films to polarized FIR light (15-250 cm-1). The induced rotation of linearly polarized light tells us the real part of the Faraday angle, Re[θ_F(ω)], and the induced dichroism of circularly polarized light tells us Im[θ_F(ω)]. We can then deduce the complex Hall angle without resorting to Kramers-Kronig (K-K) analysis. Since both the Hall angle and the Faraday angle obey sum rules, we can compare to higher frequencies(Cerne, et al., invited talk) and determine additional information about the spectral response at intermediate frequencies. The consistency of these results is verified with K-K analysis.
Generalized Hall effect as a modification of ideal magnetohydrodynamics
Goodman, M.L.
1986-01-01
The generalized Hall effect (GHE) in the generalized Hall model (GHM) is studied as a correction to ideal magnetohydrodynamics (MHD) in the context of how it affects the linear stability of cylindrically symmetric equilibria and how it changes helically symmetric equilibria. The GHM differs from what is usually called the Hall model by including the electron pressure in the electron-momentum equations. This gives the GHM some aspects of a two-fluid model, whereas the Hall model is a one-fluid model. In both cases of cylindrical and helical symmetry, the presence of the electron pressure gradient as part of the GHE gives rise to an electric field tangent to the boundary of the plasma. This introduces an additional boundary condition in the case of a perfectly conducting plasma boundary. In the case of helical symmetry, the equilibrium equations are a generalization of the Grad-Shafranov equation to equilibria with flow and GHE. In the case of cylindrical symmetry, a class of Alfven-wave solutions that do not exist in ideal MHD is obtained and the accumulation point, with respect to large radial wavenumber, of the slow magnetoacoustic wave is shown to be changed from a finite nonzero value in ideal MHD to infinity by the GHE>
Electron Interference in Hall Effect Measurements on GaAs/InAs Core/Shell Nanowires.
Haas, Fabian; Zellekens, Patrick; Lepsa, Mihail; Rieger, Torsten; Grützmacher, Detlev; Lüth, Hans; Schäpers, Thomas
2017-01-11
We present low-temperature magnetotransport measurements on GaAs/InAs core/shell nanowires contacted by regular source-drain leads as well as laterally attached Hall contacts, which only touch parts of the nanowire sidewalls. Low-temperature measurements between source and drain contacts show typical phase coherent effects, such as universal conductance fluctuations in a magnetic field aligned perpendicularly to the nanowire axis as well as Aharonov-Bohm-type oscillations in a parallel aligned magnetic field. However, the signal between the Hall contacts shows a Hall voltage buildup, when the magnetic field is turned perpendicular to the nanowire axis while current is driven through the wire using the source-drain contacts. At low temperatures, the phase coherent effects measured between source and drain leads are superimposed on the Hall voltage, which can be explained by nonlocal probing of large segments of the nanowire. In addition, the Aharonov-Bohm-type oscillations are also observed in the magnetoconductance at magnetic fields aligned parallel to the nanowire axis, using the laterally contacted leads. This measurement geometry hereby directly corresponds to classical Aharonov-Bohm experiments using planar quantum rings. In addition, the Hall voltage is used to characterize the nanowires in terms of charge carrier concentration and mobility, using temperature- and gate-dependent measurements as well as measurements in tilted magnetic fields. The GaAs/InAs core/shell nanowire used in combination with laterally attached contacts is therefore the ideal system to three-dimensionally combine quantum ring experiments using the cross-sectional plane and Hall experiments using the axial nanowire plane.
NASA Astrophysics Data System (ADS)
Kaminou, Yasuhiro; Guo, Xuehan; Inomoto, Michiaki; Ono, Yasushi; Horiuchi, Ritoku
2017-03-01
Hall effects on counter-helicity spheromak merging were investigated by two-dimensional MHD and Hall-MHD simulations of merging two axisymmetric toroidal flux tubes. In Hall-MHD cases, the structure of the reconnection current sheet and reconnection outflow are modified from the MHD case due to the Hall effect. We compared two cases (called "case-O" and "case-I") of counter-helicity merging, which are distinguished by the polarity of toroidal magnetic fluxes. Radial motion of the reconnection X-point is controlled by poloidal electron flow accompanying the toroidal flux of the merging two spheromaks, and this creates a large difference in the current sheet and flow structure between the two cases of the Hall-MHD regime. The radial shift of the reconnection X-point depending on the polarity of toroidal magnetic flux of the spheromaks breaks the symmetry between the two cases. It was also found that there widely exists separation of ion and electron flow which are affected by the modification of the current sheet structure due to the radial shift of the X-point in the downstream side of the merging, and its spatial scale of the distribution of the Hall electric field is larger than the ion skin depth.
Vortices in superconducting films: Statistics and fractional quantum Hall effect
Dziarmaga, J.
1996-03-01
We present a derivation of the Berry phase picked up during exchange of parallel vortices. This derivation is based on the Bogolubov{endash}de Gennes formalism. The origin of the Magnus force is also critically reanalyzed. The Magnus force can be interpreted as an interaction with the effective magnetic field. The effective magnetic field may be even of the order 10{sup 6}{ital T}/A. We discuss a possibility of the fractional quantum Hall effect (FQHE) in vortex systems. As the real magnetic field is varied to drive changes in vortex density, the vortex density will prefer to stay at some quantized values. The mere existence of the FQHE does not depend on vortex quantum statistics, although the pattern of the plateaux does. We also discuss how the density of anyonic vortices can lower the effective strengh of the Magnus force, what might be observable in measurements of Hall resistivity. {copyright} {ital 1996 The American Physical Society.}
Quantum Hall effect in graphene decorated with disordered multilayer patches
Nam, Youngwoo; Sun, Jie Lindvall, Niclas; Kireev, Dmitry; Yurgens, August; Jae Yang, Seung; Rae Park, Chong; Woo Park, Yung
2013-12-02
Quantum Hall effect (QHE) is observed in graphene grown by chemical vapour deposition using platinum catalyst. The QHE is even seen in samples which are irregularly decorated with disordered multilayer graphene patches and have very low mobility (<500 cm{sup 2}V{sup −1}s{sup −1}). The effect does not seem to depend on electronic mobility and uniformity of the resulting material, which indicates the robustness of QHE in graphene.
Observation of the fractional quantum Hall effect in an oxide
NASA Astrophysics Data System (ADS)
Tsukazaki, A.; Akasaka, S.; Nakahara, K.; Ohno, Y.; Ohno, H.; Maryenko, D.; Ohtomo, A.; Kawasaki, M.
2010-11-01
The quantum Hall effect arises from the cyclotron motion of charge carriers in two-dimensional systems. However, the ground states related to the integer and fractional quantum Hall effect, respectively, are of entirely different origin. The former can be explained within a single-particle picture; the latter arises from electron correlation effects governed by Coulomb interaction. The prerequisite for the observation of these effects is extremely smooth interfaces of the thin film layers to which the charge carriers are confined. So far, experimental observations of such quantum transport phenomena have been limited to a few material systems based on silicon, III-V compounds and graphene. In ionic materials, the correlation between electrons is expected to be more pronounced than in the conventional heterostructures, owing to a large effective mass of charge carriers. Here we report the observation of the fractional quantum Hall effect in MgZnO/ZnO heterostructures grown by molecular-beam epitaxy, in which the electron mobility exceeds 180,000cm2V-1s-1. Fractional states such as ν=4/3, 5/3 and 8/3 clearly emerge, and the appearance of the ν=2/5 state is indicated. The present study represents a technological advance in oxide electronics that provides opportunities to explore strongly correlated phenomena in quantum transport of dilute carriers.
Observation of the geometric spin Hall effect of light.
Korger, Jan; Aiello, Andrea; Chille, Vanessa; Banzer, Peter; Wittmann, Christoffer; Lindlein, Norbert; Marquardt, Christoph; Leuchs, Gerd
2014-03-21
The spin Hall effect of light (SHEL) is the photonic analogue of the spin Hall effect occurring for charge carriers in solid-state systems. This intriguing phenomenon manifests itself when a light beam refracts at an air-glass interface (conventional SHEL) or when it is projected onto an oblique plane, the latter effect being known as the geometric SHEL. It amounts to a polarization-dependent displacement perpendicular to the plane of incidence. In this work, we experimentally investigate the geometric SHEL for a light beam transmitted across an oblique polarizer. We find that the spatial intensity distribution of the transmitted beam depends on the incident state of polarization and its centroid undergoes a positional displacement exceeding one wavelength. This novel phenomenon is virtually independent from the material properties of the polarizer and, thus, reveals universal features of spin-orbit coupling.
Effect of quantum tunneling on spin Hall magnetoresistance.
Ok, Seulgi; Chen, Wei; Sigrist, Manfred; Manske, Dirk
2017-02-22
We present a formalism that simultaneously incorporates the effect of quantum tunneling and spin diffusion on the spin Hall magnetoresistance observed in normal metal/ferromagnetic insulator bilayers (such as Pt/Y3Fe5O12) and normal metal/ferromagnetic metal bilayers (such as Pt/Co), in which the angle of magnetization influences the magnetoresistance of the normal metal. In the normal metal side the spin diffusion is known to affect the landscape of the spin accumulation caused by spin Hall effect and subsequently the magnetoresistance, while on the ferromagnet side the quantum tunneling effect is detrimental to the interface spin current which also affects the spin accumulation. The influence of generic material properties such as spin diffusion length, layer thickness, interface coupling, and insulating gap can be quantified in a unified manner, and experiments that reveal the quantum feature of the magnetoresistance are suggested.
Effect of quantum tunneling on spin Hall magnetoresistance
NASA Astrophysics Data System (ADS)
Ok, Seulgi; Chen, Wei; Sigrist, Manfred; Manske, Dirk
2017-02-01
We present a formalism that simultaneously incorporates the effect of quantum tunneling and spin diffusion on the spin Hall magnetoresistance observed in normal metal/ferromagnetic insulator bilayers (such as Pt/Y3Fe5O12) and normal metal/ferromagnetic metal bilayers (such as Pt/Co), in which the angle of magnetization influences the magnetoresistance of the normal metal. In the normal metal side the spin diffusion is known to affect the landscape of the spin accumulation caused by spin Hall effect and subsequently the magnetoresistance, while on the ferromagnet side the quantum tunneling effect is detrimental to the interface spin current which also affects the spin accumulation. The influence of generic material properties such as spin diffusion length, layer thickness, interface coupling, and insulating gap can be quantified in a unified manner, and experiments that reveal the quantum feature of the magnetoresistance are suggested.
Development and Characterization of High-Efficiency, High-Specific Impulse Xenon Hall Thrusters
NASA Technical Reports Server (NTRS)
Hofer, Richard R.; Jacobson, David (Technical Monitor)
2004-01-01
This dissertation presents research aimed at extending the efficient operation of 1600 s specific impulse Hall thruster technology to the 2000 to 3000 s range. Motivated by previous industry efforts and mission studies, the aim of this research was to develop and characterize xenon Hall thrusters capable of both high-specific impulse and high-efficiency operation. During the development phase, the laboratory-model NASA 173M Hall thrusters were designed and their performance and plasma characteristics were evaluated. Experiments with the NASA-173M version 1 (v1) validated the plasma lens magnetic field design. Experiments with the NASA 173M version 2 (v2) showed there was a minimum current density and optimum magnetic field topography at which efficiency monotonically increased with voltage. Comparison of the thrusters showed that efficiency can be optimized for specific impulse by varying the plasma lens. During the characterization phase, additional plasma properties of the NASA 173Mv2 were measured and a performance model was derived. Results from the model and experimental data showed how efficient operation at high-specific impulse was enabled through regulation of the electron current with the magnetic field. The electron Hall parameter was approximately constant with voltage, which confirmed efficient operation can be realized only over a limited range of Hall parameters.
Anomalous Hall effect in MnAl/W bilayers: Modification from strong spin Hall effect of W
NASA Astrophysics Data System (ADS)
Meng, K. K.; Miao, J.; Xu, X. G.; Wu, Y.; Zhao, J. H.; Jiang, Y.
2017-04-01
We report systematic measurements of anomalous Hall effect (AHE) in MnAl/W bilayers modified by strong spin Hall effect (SHE) of the heavy metals, in which a single L10-MnAl epitaxial layer reveals obvious orbital two-channel Kondo (2CK) effect. The results are compared with the AHE in MnAl/Cu with weak spin orbit coupling. As increasing the thickness of W, the strong SHE has gradually suppressed the orbital 2CK effect and modified the AHE of MnAl. A scaling involving multiple competing scattering mechanisms has been used to distinguish different contributions to the modified AHE. The direct observation of spin-orbit torque induced magnetization switching confirms that the result is a combination of the AHE of MnAl and SHE of W.
Hall effect in quantum critical charge-cluster glass.
Wu, Jie; Bollinger, Anthony T; Sun, Yujie; Božović, Ivan
2016-04-19
Upon doping, cuprates undergo a quantum phase transition from an insulator to a d-wave superconductor. The nature of this transition and of the insulating state is vividly debated. Here, we study the Hall effect in La2-xSrxCuO4(LSCO) samples doped near the quantum critical point atx∼ 0.06. Dramatic fluctuations in the Hall resistance appear belowTCG∼ 1.5 K and increase as the sample is cooled down further, signaling quantum critical behavior. We explore the doping dependence of this effect in detail, by studying a combinatorial LSCO library in which the Sr content is varied in extremely fine steps,Δx∼ 0.00008. We observe that quantum charge fluctuations wash out when superconductivity emerges but can be restored when the latter is suppressed by applying a magnetic field, showing that the two instabilities compete for the ground state.
Magnonic quantum Hall effect and Wiedemann-Franz law
NASA Astrophysics Data System (ADS)
Nakata, Kouki; Klinovaja, Jelena; Loss, Daniel
2017-03-01
We present a quantum Hall effect of magnons in two-dimensional clean insulating magnets at finite temperature. Through the Aharonov-Casher effect, a magnon moving in an electric field acquires a geometric phase and forms Landau levels in an electric field gradient of sawtooth form. At low temperatures, the lowest energy band being almost flat carries a Chern number associated with a Berry curvature. Appropriately defining the thermal conductance for bosons, we find that the magnon Hall conductances get quantized and show a universal thermomagnetic behavior, i.e., are independent of materials, and obey a Wiedemann-Franz law for magnon transport. We consider magnons with quadratic and linear (Dirac-like) dispersions. Finally, we show that our predictions are within experimental reach for ferromagnets and skyrmion lattices with current device and measurement techniques.
Hall effect in quantum critical charge-cluster glass
Wu, Jie; Bollinger, Anthony T.; Sun, Yujie; Božović, Ivan
2016-01-01
Upon doping, cuprates undergo a quantum phase transition from an insulator to a d-wave superconductor. The nature of this transition and of the insulating state is vividly debated. Here, we study the Hall effect in La2-xSrxCuO4 (LSCO) samples doped near the quantum critical point at x ∼ 0.06. Dramatic fluctuations in the Hall resistance appear below TCG ∼ 1.5 K and increase as the sample is cooled down further, signaling quantum critical behavior. We explore the doping dependence of this effect in detail, by studying a combinatorial LSCO library in which the Sr content is varied in extremely fine steps, Δx ∼ 0.00008. We observe that quantum charge fluctuations wash out when superconductivity emerges but can be restored when the latter is suppressed by applying a magnetic field, showing that the two instabilities compete for the ground state. PMID:27044081
Quasiparticle Aggregation in the Fractional Quantum Hall Effect
DOE R&D Accomplishments Database
Laughlin, R. B.
1984-10-10
Quasiparticles in the Fractional Quantum Hall Effect behave qualitatively like electrons confined to the lowest landau level, and can do everything electrons can do, including condense into second generation Fractional Quantum Hall ground states. I review in this paper the reasoning leading to variational wavefunctions for ground state and quasiparticles in the 1/3 effect. I then show how two-quasiparticle eigenstates are uniquely determined from symmetry, and how this leads in a natural way to variational wavefunctions for composite states which have the correct densities (2/5, 2/7, ...). I show in the process that the boson, anyon and fermion representations for the quasiparticles used by Haldane, Halperin, and me are all equivalent. I demonstrate a simple way to derive Halperin`s multiple-valued quasiparticle wavefunction from the correct single-valued electron wavefunction. (auth)
Precise quantization of anomalous Hall effect near zero magnetic field
Bestwick, A. J.; Fox, E. J.; Kou, Xufeng; Pan, Lei; Wang, Kang L.; Goldhaber-Gordon, D.
2015-05-04
In this study, we report a nearly ideal quantum anomalous Hall effect in a three-dimensional topological insulator thin film with ferromagnetic doping. Near zero applied magnetic field we measure exact quantization in the Hall resistance to within a part per 10,000 and a longitudinal resistivity under 1 Ω per square, with chiral edge transport explicitly confirmed by nonlocal measurements. Deviations from this behavior are found to be caused by thermally activated carriers, as indicated by an Arrhenius law temperature dependence. Using the deviations as a thermometer, we demonstrate an unexpected magnetocaloric effect and use it to reach near-perfect quantization by cooling the sample below the dilution refrigerator base temperature in a process approximating adiabatic demagnetization refrigeration.
Higher-Dimensional Quantum Hall Effect in String Theory
Fabinger, Michal
2002-08-08
We construct a string theory realization of the 4+1d quantum Hall effect recently discovered by Zhang and Hu. The string theory picture contains coincident D4-branes forming an S{sup 4} and having D0-branes (i.e. instantons) in their world-volume. The charged particles are modeled as string ends. Their configuration space approaches in the large n limit a CP{sup 3}, which is an S{sup 2} fibration over S{sup 4}, the extra S{sup 2} being made out of the Chan-Paton degrees of freedom. An alternative matrix theory description involves the fuzzy S{sup 4}. We also find that there is a hierarchy of quantum Hall effects in odd-dimensional spacetimes, generalizing the known cases in 2 + 1d and 4 + 1d.
Nontrivial anomalous Hall effect in ultrathin Pt/permalloy bilayers
NASA Astrophysics Data System (ADS)
Zhang, Yanqing; Shan, Rong
2015-03-01
Anomalous Hall effect of Pt (2.5 nm)/permalloy bilayers with the thickness tPy = 0.6 ~10 nm; Pt/permalloy (2.2 nm) bilayers with the thickness tPt = 1.5 ~10 nm and Pt (2.5 nm)/permalloy (2.2 nm) bilayers with the post-annealing temperature 100 ~500° grown on MgO (001) substrates are investigated. The Pt/permalloy bilayer shows distinguished performance from the single permalloy layer due to the interfacial influence. Effective magnetic anisotropy of the bilayer with tPy <2.2 nm turns to be perpendicular to the film plane and it increases with decreasing measured temperature. More interestingly, the anomalous Hall effect is also greatly enhanced in these Pt/permalloy bilayers, comparing with that in bulk permalloy. The parameters presenting skew scattering, side jump and intrinsic contribution become extremely large, indicating a strong influence of spin orbit coupling coming from Pt/permalloy interface on the anomalous Hall effect.
Extraordinary Hall-effect in colloidal magnetic nanoparticle films
NASA Astrophysics Data System (ADS)
Ben Gur, Leah; Tirosh, Einat; Segal, Amir; Markovich, Gil; Gerber, Alexander
2017-03-01
Colloidal nickel nanoparticles (NPs) coated with polyvinylpyrrolidone (PVP) were synthesized. The nanoparticle dispersions were deposited on substrates and dried under mild heating to form conductive films. The films exhibited very small coercivity, nearly metallic conductivity, and a significant extraordinary Hall effect signal. This method could be useful for preparing simple, printed magnetic field sensors with the advantage of relatively high sensitivity around zero magnetic field, in contrast to magnetoresistive sensors, which have maximal field sensitivity away from zero magnetic field.
Another Nulling Hall-Effect Current-Measuring Circuit
NASA Technical Reports Server (NTRS)
Thibodeau, Phillip E.; Sullender, Craig C.
1993-01-01
Lightweight, low-power circuit provides noncontact measurement of alternating or direct current of many ampheres in main conductor. Advantages of circuit over other nulling Hall-effect current-measuring circuits is stability and accuracy increased by putting both analog-to-digital and digital-to-analog converters in nulling feedback loop. Converters and rest of circuit designed for operation at sampling rate of 100 kHz, but rate changed to alter time or frequency response of circuit.
Dynamical quantum Hall effect in the parameter space.
Gritsev, V; Polkovnikov, A
2012-04-24
Geometric phases in quantum mechanics play an extraordinary role in broadening our understanding of fundamental significance of geometry in nature. One of the best known examples is the Berry phase [M.V. Berry (1984), Proc. Royal. Soc. London A, 392:45], which naturally emerges in quantum adiabatic evolution. So far the applicability and measurements of the Berry phase were mostly limited to systems of weakly interacting quasi-particles, where interference experiments are feasible. Here we show how one can go beyond this limitation and observe the Berry curvature, and hence the Berry phase, in generic systems as a nonadiabatic response of physical observables to the rate of change of an external parameter. These results can be interpreted as a dynamical quantum Hall effect in a parameter space. The conventional quantum Hall effect is a particular example of the general relation if one views the electric field as a rate of change of the vector potential. We illustrate our findings by analyzing the response of interacting spin chains to a rotating magnetic field. We observe the quantization of this response, which we term the rotational quantum Hall effect.
Topological thermal Hall effect in frustrated kagome antiferromagnets
NASA Astrophysics Data System (ADS)
Owerre, S. A.
2017-01-01
In frustrated magnets the Dzyaloshinsky-Moriya interaction (DMI) arising from spin-orbit coupling can induce a magnetic long-range order. Here, we report a theoretical prediction of the thermal Hall effect in frustrated kagome magnets such as KCr3(OH) 6(SO4) 2 and KFe3(OH) 6(SO4)2 . The thermal Hall effects in these materials are induced by scalar spin chirality as opposed to DMI in previous studies. The scalar spin chirality originates from the magnetic-field-induced chiral spin configuration due to noncoplanar spin textures, but in general it can be spontaneously developed as a macroscopic order parameter in chiral quantum spin liquids. Therefore, we infer that there is a possibility of the thermal Hall effect in frustrated kagome magnets such as herbertsmithite ZnCu3(OH) 6Cl2 and the chromium compound Ca10Cr7O28 , although they also show evidence of magnetic long-range order in the presence of applied magnetic field or pressure.
The plasmoid instability and Hall effect during chromospheric magnetic reconnection
NASA Astrophysics Data System (ADS)
Murphy, Nicholas Arnold; Lukin, Vyacheslav
2016-01-01
Magnetic reconnection is a ubiquitous process in the partially ionized solar chromosphere. Recent two-dimensional simulations have shown that the plasmoid instability onsets during partially ionized reconnection [1-4]. We use the plasma-neutral module of the HiFi framework to simulate the nonlinear evolution of the plasmoid instability during symmetric and asymmetric reconnection. These simulations model the plasma and neutrals as separate fluids and include ionization, recombination, charge exchange, thermal conduction, and the Hall effect. The Hall effect leads to the development of significant out-of-plane magnetic fields in the current sheet region in the laminar phase, but we do not observe shortening of the current sheet or significant acceleration of the reconnection rate as a result. After the onset of the plasmoid instability, structure develops on scales comparable to the ion inertial length. We compare simulations of the plasmoid instability with and without the Hall effect to determine its impact on the reconnection process. Finally, we discuss ongoing efforts to connect these simulations with solar observations and laboratory experiments.[1] Leake et al. 2012, ApJ, 760, 109 [2] Leake et al. 2013, PhPl, 20, 062102 [3] Ni et al. 2015, ApJ, 799, 79 [4] Murphy & Lukin 2015, ApJ, 805, 134
Diagnostic Setup for Characterization of Near-Anode Processes in Hall Thrusters
L. Dorf; Y. Raitses; N. J. Fisch
2003-05-29
A diagnostic setup for characterization of the near-anode processes in Hall thrusters was designed and assembled. Experimental results with a single floating probe show that radial probe insertion does not cause perturbations to the discharge and therefore can be used for near-anode measurements.
Diagnostic Setup for Characterization of Near-Anode Processes in Hall Thrusters
L. Dorf; Y. Raitses; N.J. Fisch
2003-09-08
A diagnostic setup for characterization of near-anode processes in Hall-current plasma thrusters consisting of biased and emissive electrostatic probes, high-precision positioning system and low-noise electronic circuitry was developed and tested. Experimental results show that radial probe insertion does not cause perturbations to the discharge and therefore can be used for accurate near-anode measurements.
Quantum Hall effect in epitaxial graphene with permanent magnets
Parmentier, F. D.; Cazimajou, T.; Sekine, Y.; Hibino, H.; Irie, H.; Glattli, D. C.; Kumada, N.; Roulleau, P.
2016-01-01
We have observed the well-kown quantum Hall effect (QHE) in epitaxial graphene grown on silicon carbide (SiC) by using, for the first time, only commercial NdFeB permanent magnets at low temperature. The relatively large and homogeneous magnetic field generated by the magnets, together with the high quality of the epitaxial graphene films, enables the formation of well-developed quantum Hall states at Landau level filling factors v = ±2, commonly observed with superconducting electro-magnets. Furthermore, the chirality of the QHE edge channels can be changed by a top gate. These results demonstrate that basic QHE physics are experimentally accessible in graphene for a fraction of the price of conventional setups using superconducting magnets, which greatly increases the potential of the QHE in graphene for research and applications. PMID:27922114
Quantum Hall effect in epitaxial graphene with permanent magnets.
Parmentier, F D; Cazimajou, T; Sekine, Y; Hibino, H; Irie, H; Glattli, D C; Kumada, N; Roulleau, P
2016-12-06
We have observed the well-kown quantum Hall effect (QHE) in epitaxial graphene grown on silicon carbide (SiC) by using, for the first time, only commercial NdFeB permanent magnets at low temperature. The relatively large and homogeneous magnetic field generated by the magnets, together with the high quality of the epitaxial graphene films, enables the formation of well-developed quantum Hall states at Landau level filling factors v = ±2, commonly observed with superconducting electro-magnets. Furthermore, the chirality of the QHE edge channels can be changed by a top gate. These results demonstrate that basic QHE physics are experimentally accessible in graphene for a fraction of the price of conventional setups using superconducting magnets, which greatly increases the potential of the QHE in graphene for research and applications.
Recent advances in the spin Hall effect of light.
Ling, Xiaohui; Zhou, Xinxing; Huang, Kun; Liu, Yachao; Qiu, Cheng-Wei; Luo, Hailu; Wen, Shuangchun
2017-03-30
The spin Hall effect (SHE) of light, as an analogue of the SHE in electronic systems, is a promising candidate for investigating the SHE in semiconductor spintronics/valleytronics, high-energy physics and condensed matter physics, owing to their similar topological nature in the spin-orbit interaction. The SHE of light exhibits unique potential for exploring the physical properties of nanostructures, such as determining the optical thickness, and the material properties of metallic and magnetic thin films and even atomically thin two-dimensional materials. More importantly, it opens a possible pathway for controlling the spin states of photons and developing next-generation photonic spin Hall devices as a fundamental constituent of the emerging spinoptics. In this review, based on the viewpoint of the geometric phase gradient, we give a detailed presentation of the recent advances in the SHE of light and its applications in precision metrology and future spin-based photonics.
Quantum Hall effect in epitaxial graphene with permanent magnets
NASA Astrophysics Data System (ADS)
Parmentier, F. D.; Cazimajou, T.; Sekine, Y.; Hibino, H.; Irie, H.; Glattli, D. C.; Kumada, N.; Roulleau, P.
2016-12-01
We have observed the well-kown quantum Hall effect (QHE) in epitaxial graphene grown on silicon carbide (SiC) by using, for the first time, only commercial NdFeB permanent magnets at low temperature. The relatively large and homogeneous magnetic field generated by the magnets, together with the high quality of the epitaxial graphene films, enables the formation of well-developed quantum Hall states at Landau level filling factors v = ±2, commonly observed with superconducting electro-magnets. Furthermore, the chirality of the QHE edge channels can be changed by a top gate. These results demonstrate that basic QHE physics are experimentally accessible in graphene for a fraction of the price of conventional setups using superconducting magnets, which greatly increases the potential of the QHE in graphene for research and applications.
Effects of Enhanced Eathode Electron Emission on Hall Thruster Operation
Y. Raitses, A. Smirnov and N. J. Fisch
2009-04-24
Interesting discharge phenomena are observed that have to do with the interaction between the magnetized Hall thruster plasma and the neutralizing cathode. The steadystate parameters of a highly ionized thruster discharge are strongly influenced by the electron supply from the cathode. The enhancement of the cathode electron emission above its self-sustained level affects the discharge current and leads to a dramatic reduction of the plasma divergence and a suppression of large amplitude, low frequency discharge current oscillations usually related to an ionization instability. These effects correlate strongly with the reduction of the voltage drop in the region with the fringing magnetic field between the thruster channel and the cathode. The measured changes of the plasma properties suggest that the electron emission affects the electron cross-field transport in the thruster discharge. These trends are generalized for Hall thrusters of various configurations.
Integer quantum Hall effect of interacting electrons in graphene
NASA Astrophysics Data System (ADS)
Yan, Xin-Zhong; Ting, C. S.
2017-02-01
By taking into account the charge and spin orderings and the exchange interactions between all the Landau levels, we investigate the integer quantum Hall effect of electrons in graphene using the mean-field theory. We find that the fourfold degeneracy of the Landau levels cannot be completely lifted by the Coulomb interactions. In particular, at fillings ν =4 n +2 with n =0 ,1 ,... , there is no splitting between the fourfold degenerated Landau levels. We show that with doping the degenerated lowest empty level can be sequentially filled one by one; the filled level is lower than the empty ones because of the Coulomb-exchange interactions. This result explains the step Δ ν =1 in the quantized Hall conductivity. We present a highly efficient method for dealing with a huge number of the Coulomb couplings between all the Landau levels of the Dirac fermions.
Fractionally charged skyrmions in fractional quantum Hall effect.
Balram, Ajit C; Wurstbauer, U; Wójs, A; Pinczuk, A; Jain, J K
2015-11-26
The fractional quantum Hall effect has inspired searches for exotic emergent topological particles, such as fractionally charged excitations, composite fermions, abelian and nonabelian anyons and Majorana fermions. Fractionally charged skyrmions, which support both topological charge and topological vortex-like spin structure, have also been predicted to occur in the vicinity of 1/3 filling of the lowest Landau level. The fractional skyrmions, however, are anticipated to be exceedingly fragile, suppressed by very small Zeeman energies. Here we show that, slightly away from 1/3 filling, the smallest manifestations of the fractional skyrmion exist in the excitation spectrum for a broad range of Zeeman energies, and appear in resonant inelastic light scattering experiments as well-defined resonances slightly below the long wavelength spin wave mode. The spectroscopy of these exotic bound states serves as a sensitive tool for investigating the residual interaction between composite fermions, responsible for delicate new fractional quantum Hall states in this filling factor region.
Fractionally charged skyrmions in fractional quantum Hall effect
Balram, Ajit C.; Wurstbauer, U.; Wójs, A.; Pinczuk, A.; Jain, J. K.
2015-11-26
The fractional quantum Hall effect has inspired searches for exotic emergent topological particles, such as fractionally charged excitations, composite fermions, abelian and nonabelian anyons and Majorana fermions. Fractionally charged skyrmions, which support both topological charge and topological vortex-like spin structure, have also been predicted to occur in the vicinity of 1/3 filling of the lowest Landau level. The fractional skyrmions, however, are anticipated to be exceedingly fragile, suppressed by very small Zeeman energies. Here we show that, slightly away from 1/3 filling, the smallest manifestations of the fractional skyrmion exist in the excitation spectrum for a broad range of Zeeman energies, and appear in resonant inelastic light scattering experiments as well-defined resonances slightly below the long wavelength spin wave mode. The spectroscopy of these exotic bound states serves as a sensitive tool for investigating the residual interaction between composite fermions, responsible for delicate new fractional quantum Hall states in this filling factor region.
Topological characterization of fractional quantum Hall ground states from microscopic Hamiltonians.
Zaletel, Michael P; Mong, Roger S K; Pollmann, Frank
2013-06-07
We show how to numerically calculate several quantities that characterize topological order starting from a microscopic fractional quantum Hall Hamiltonian. To find the set of degenerate ground states, we employ the infinite density matrix renormalization group method based on the matrix-product state representation of fractional quantum Hall states on an infinite cylinder. To study localized quasiparticles of a chosen topological charge, we use pairs of degenerate ground states as boundary conditions for the infinite density matrix renormalization group. We then show that the wave function obtained on the infinite cylinder geometry can be adapted to a torus of arbitrary modular parameter, which allows us to explicitly calculate the non-Abelian Berry connection associated with the modular T transformation. As a result, the quantum dimensions, topological spins, quasiparticle charges, chiral central charge, and Hall viscosity of the phase can be obtained using data contained entirely in the entanglement spectrum of an infinite cylinder.
The transport mechanism of the integer quantum Hall effect
NASA Astrophysics Data System (ADS)
Hui, Tan; LiMing, W.; Liang, Shi-Dong
2016-11-01
The integer quantum Hall effect (IQHE) is analysed using a mechanism of the electron transport in the form of semi-classic wave packages in this paper. Due to the confinement of the edges of a slab the Landau levels of electrons in a strong magnetic field go up at large wave-vectors to form energy bands. The slopes of the energy bands give the group velocities of electron wave packages and thus contribute to the current. Certain magnetic fields separate the electron transport in the slab into two branches with opposite and large wave vectors, which are localized at the two edges of the slab, respectively. In this case back scattering of electrons is prohibited due to the localization of these two branches. Thus the slab exhibits zero longitudinal resistance and plateaus of Hall resistance. When the Fermi level is sweeping over a Landau level at some magnetic fields, however, the electron waves locate around the central axis of the slab and overlap each other thus back scattering of electrons takes place frequently. Then longitudinal resistance appears and the Hall resistance goes up from one plateau to a new one. This transport mechanism is much clearer and more intuitive than the conventional explanations to the IQHE.
The Microwave Hall Effect Measured Using a Waveguide Tee
NASA Astrophysics Data System (ADS)
Johnson, William; Coppock, Joyce; Anderson, J. Robert
We describe a simple microwave apparatus to measure the Hall effect in semiconductor wafers. This technique does not require contacts on the sample or the use of a resonant cavity. Our method consists of placing a semiconductor wafer into a slot in an X-band (8 - 12 GHz) waveguide series tee, injecting microwave power into the two opposite arms of the tee, and measuring the microwave output at the third arm. A magnetic field is applied perpendicular to the wafer and produces a microwave Hall signal that is linear in the magnetic field and which reverses phase when the magnetic field is reversed. The microwave Hall signal is proportional to the semiconductor mobility, which we compare for calibration purposes with d. c. mobility measurements obtained using the van der Pauw method. We obtain the resistivity by measuring the microwave reflection coefficient of the sample. We determine a calibration constant as a function of the ratio of thickness to skin depth for two and three inch silicon and germanium samples doped with boron or phosphorus. The measured mobilities ranged from 270 to 3000 cm2 / (Vsec)
The microwave Hall effect measured using a waveguide tee
NASA Astrophysics Data System (ADS)
Coppock, J. E.; Anderson, J. R.; Johnson, W. B.
2016-03-01
This paper describes a simple microwave apparatus to measure the Hall effect in semiconductor wafers. The advantage of this technique is that it does not require contacts on the sample or the use of a resonant cavity. Our method consists of placing the semiconductor wafer into a slot cut in an X-band (8-12 GHz) waveguide series tee, injecting microwave power into the two opposite arms of the tee, and measuring the microwave output at the third arm. A magnetic field applied perpendicular to the wafer gives a microwave Hall signal that is linear in the magnetic field and which reverses phase when the magnetic field is reversed. The microwave Hall signal is proportional to the semiconductor mobility, which we compare for calibration purposes with d.c. mobility measurements obtained using the van der Pauw method. We obtain the resistivity by measuring the microwave reflection coefficient of the sample. This paper presents data for silicon and germanium samples doped with boron or phosphorus. The measured mobilities ranged from 270 to 3000 cm2/(V s).
Effects of wall electrodes on Hall effect thruster plasma
Langendorf, S. Walker, M.; Xu, K.
2015-02-15
This paper investigates the physical mechanisms that cause beneficial and detrimental performance effect observed to date in Hall effect thrusters with wall electrodes. It is determined that the wall electrode sheath can reduce ion losses to the wall if positioned near the anode (outside the dense region of the plasma) such that an ion-repelling sheath is able to form. The ability of the wall electrode to form an ion-repelling sheath is inversely proportional to the current drawn—if the wall electrode becomes the dominant sink for the thruster discharge current, increases in wall electrode bias result in increased local plasma potential rather than an ion-repelling sheath. A single-fluid electron flow model gives results that mimic the observed potential structures and the current-sharing fractions between the anode and wall electrodes, showing that potential gradients in the presheath and bulk plasma come at the expense of current draw to the wall electrodes. Secondary electron emission from the wall electrodes (or lack thereof) is inferred to have a larger effect if the electrodes are positioned near the exit plane than if positioned near the anode, due to the difference in energy deposition from the plasma.
High-Resolution ac Measurements of the Hall Effect in Organic Field-Effect Transistors
NASA Astrophysics Data System (ADS)
Chen, Y.; Yi, H. T.; Podzorov, V.
2016-03-01
We describe a high resolving power technique for Hall-effect measurements, efficient in determining Hall mobility and carrier density in organic field-effect transistors and other low-mobility systems. We utilize a small low-frequency ac magnetic field (Brms<0.25 T ) and a phase-sensitive (lock-in) detection of Hall voltage, with the necessary corrections for Faraday induction. This method significantly enhances the signal-to-noise ratio and eliminates the necessity of using high magnetic fields in Hall-effect studies. With the help of this method, we are able to obtain the Hall mobility and carrier density in organic transistors with a mobility as low as μ ˜0.3 cm2 V-1 s-1 by using a compact desktop apparatus and low magnetic fields. We find a good agreement between Hall-effect and electric-field-effect measurements, indicating that, contrary to the common belief, certain organic semiconductors with mobilities below 1 cm2 V-1 s-1 can still exhibit a fully developed, band-semiconductor-like Hall effect, with the Hall mobility and carrier density matching those obtained in longitudinal transistor measurements. This suggests that, even when μ <1 cm2 V-1 s-1 , charges in organic semiconductors can still behave as delocalized coherent carriers. This technique paves the way to ubiquitous Hall-effect studies in a wide range of low-mobility materials and devices, where it is typically very difficult to resolve the Hall effect even in very high dc magnetic fields.
Quantum anomalous Hall effect in stable dumbbell stanene
NASA Astrophysics Data System (ADS)
Zhang, Huisheng; Zhang, Jiayong; Zhao, Bao; Zhou, Tong; Yang, Zhongqin
2016-02-01
Topological property of the dumbbell (DB) stanene, more stable than the stanene with a honeycomb lattice, is investigated by using ab initio methods. The magnetic DB stanene demonstrates an exotic quantum anomalous Hall (QAH) effect due to inversion of the Sn spin-up px,y and spin-down pz states. The QAH gap is found to be opened at Γ point rather than the usual K and K' points, beneficial to observe the effect in experiments. When a 3% tensile strain is applied, a large nontrivial gap (˜50 meV) is achieved. Our results provide another lighthouse for realizing QAH effects in two-dimensional systems.
NASA Astrophysics Data System (ADS)
Zhang, Yang; Sun, Yan; Yang, Hao; Železný, Jakub; Parkin, Stuart P. P.; Felser, Claudia; Yan, Binghai
2017-02-01
We have carried out a comprehensive study of the intrinsic anomalous Hall effect and spin Hall effect of several chiral antiferromagnetic compounds Mn3X (X = Ge, Sn, Ga, Ir, Rh and Pt) by ab initio band structure and Berry phase calculations. These studies reveal large and anisotropic values of both the intrinsic anomalous Hall effect and spin Hall effect. The Mn3X materials exhibit a noncollinear antiferromagnetic order which, to avoid geometrical frustration, forms planes of Mn moments that are arranged in a Kagome-type lattice. With respect to these Kagome planes, we find that both the anomalous Hall conductivity (AHC) and the spin Hall conductivity (SHC) are quite anisotropic for any of these materials. Based on our calculations, we propose how to maximize AHC and SHC for different materials. The band structures and corresponding electron filling, that we show are essential to determine the AHC and SHC, are compared for these different compounds. We point out that Mn3Ga shows a large SHC of about 600 (ℏ /e ) (Ωcm) -1 . Our work provides insights into the realization of strong anomalous Hall effects and spin Hall effects in chiral antiferromagnetic materials.
Non-Contact Thermal Characterization of NASA's HERMeS Hall Thruster
NASA Technical Reports Server (NTRS)
Huang, Wensheng; Kamhawi, Hani; Myers, James L.; Yim, John T.; Neff, Gregory
2015-01-01
The thermal characterization test of NASA's 12.5-kW Hall Effect Rocket with Magnetic Shielding has been completed. This thruster was developed to support a number of potential Solar Electric Propulsion Technology Demonstration Mission concepts, including the Asteroid Redirect Robotic Mission concept. As a part of the preparation for this characterization test, an infrared-based, non-contact thermal imaging system was developed to measure the temperature of various thruster surfaces that are exposed to high voltage or plasma. An in-situ calibration array was incorporated into the setup to improve the accuracy of the temperature measurement. The key design parameters for the calibration array were determined in a separate pilot test. The raw data from the characterization test was analyzed though further work is needed to obtain accurate anode temperatures. Examination of the front pole and discharge channel temperatures showed that the thruster temperature was driven more by discharge voltage than by discharge power. Operation at lower discharge voltages also yielded more uniform temperature distributions than at higher discharge voltages. When operating at high discharge voltage, increasing the magnetic field strength appeared to have made the thermal loading azimuthally more uniform.
Universality and phase diagram in the quantum Hall effect
NASA Astrophysics Data System (ADS)
Wong, Lauren Wai-Wing
We have designed and conducted detailed experiments to explore the following critical, unsolved issues in regarding to the global behavior of the two-dimensional electron gas (2DEG) in the presence of disorder and many-body interaction in the quantum Hall effect (QHE) regime: (1) nature of the quantum Hall liquid-Hall insulator (QHL-HI) phase transition induced by disorder, (2) topological phase diagram and possible existence of a thermodynamically stable "metallic phase" around filling factor nu =1/2, and (3) whether the termination of spin-resolved Landau levels in general a phase transition. First, I present our studies of the disorder-tuned QHL-HI phase transition in both the integer and fractional QHE regimes. We found that the longitudinal resistivity near the critical points shows reflection symmetry and good scaling behavior over a wide range of densities and temperature with the same critical exponent. This supports the notion that quantum phase transitions in the QHE belong to same universality class. Furthermore, the critical conductivities are universal at the transitions. Our approach to investigate the second issue is to map out the phase boundaries corresponding to different QHLs around nu =1/2. We identified a line on which the value of the Hall conductivity equals to 1/2(esp2/h) in the phase diagram; and an another line on which the value of the Hall resistivity equals to 2(h/esp2). We interpreted the later is a result predicted by the composite-fermion theory. The phase boundaries between the HI and the principal QHLs at nu =1 and 1/3 show levitation of the delocalized states of the first Landau levels for electrons and Composite fermions. Our data suggest that there is no true metallic state around nu =1/2. Finally, I present our magnetotransport studies of the spin-resolved integer QHE by changing disorder. For a given Landau level, the difference in filling factors of a pair of spin-split resistivity peaks changes rapidly from one to zero near
Interface engineering of quantum Hall effects in digital transition metal oxide heterostructures.
Xiao, Di; Zhu, Wenguang; Ran, Ying; Nagaosa, Naoto; Okamoto, Satoshi
2011-12-20
Topological insulators are characterized by a non-trivial band topology driven by the spin-orbit coupling. To fully explore the fundamental science and application of topological insulators, material realization is indispensable. Here we predict, based on tight-binding modelling and first-principles calculations, that bilayers of perovskite-type transition-metal oxides grown along the [111] crystallographic axis are potential candidates for two-dimensional topological insulators. The topological band structure of these materials can be fine-tuned by changing dopant ions, substrates and external gate voltages. We predict that LaAuO(3) bilayers have a topologically non-trivial energy gap of about 0.15 eV, which is sufficiently large to realize the quantum spin Hall effect at room temperature. Intriguing phenomena, such as fractional quantum Hall effect, associated with the nearly flat topologically non-trivial bands found in e(g) systems are also discussed.
Interface engineering of quantum Hall effects in digital transition metal oxide heterostructures
Xiao, Di; Zhu, Wenguang; Ran, Ying; Nagaosa, Naoto; Okamoto, Satoshi
2011-01-01
Topological insulators (TIs) are characterized by a non-trivial band topology driven by the spin-orbit coupling. To fully explore the fundamental science and application of TIs, material realization is indispensable. Here we predict, based on tight-binding modeling and first-principles calculations, that bilayers of perovskite-type transition-metal oxides grown along the [111] crystallographic axis are potential candidates for two-dimensional TIs. The topological band structure of these materials can be fine-tuned by changing dopant ions, substrates and external gate voltages. We predict that LaAuO$_3$ bilayers have a topologically non-trivial energy gap of about 0.15~eV, which is sufficiently large to realize the quantum spin Hall effect at room temperature. Intriguing phenomena, such as fractional quantum Hall effect, associated with the nearly flat topologically non-trivial bands found in $e_g$ systems are also discussed.
Spin Hall effect induced by a gravitational field
NASA Astrophysics Data System (ADS)
Dartora, C. A.; Cabrera, G. G.
2010-06-01
The experiment by Collela et al. (1975) [1] evidenced in a striking manner how the gravitational field appears in quantum mechanics. Within the modern framework of gauge theories, one can ascribe such effect as due to gauge fields originated from fundamental symmetries of spacetime: local transformations of the Lorentz-Poincaré group. When this gauge principle is applied to the Dirac equation, we obtain kinematical correlations between the gravitational field and the spin of the particles. The phenomenon is similar to the spin Hall effect found in condensed matter systems, although much smaller in magnitude. Actual measurements may require highly precision interferometric techniques with spin-polarized neutrons.
Orbitronics: the Intrinsic Orbital Hall Effect in p-Doped Silicon
Bernevig, B.Andrei; Hughes, Taylor L.; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.
2010-01-15
The spin Hall effect depends crucially on the intrinsic spin-orbit coupling of the energy band. Because of the smaller spin-orbit coupling in silicon, the spin Hall effect is expected to be much reduced. We show that the electric field in p-doped silicon can induce a dissipationless orbital current in a fashion reminiscent of the spin Hall effect. The vertex correction due to impurity scattering vanishes and the effect is therefore robust against disorder. The orbital Hall effect can lead to the accumulation of local orbital momentum at the edge of the sample, and can be detected by the Kerr effect.
The spin Hall effect as a probe of nonlinear spin fluctuations.
Wei, D H; Niimi, Y; Gu, B; Ziman, T; Maekawa, S; Otani, Y
2012-01-01
The spin Hall effect and its inverse have key roles in spintronic devices as they allow conversion of charge currents to and from spin currents. The conversion efficiency strongly depends on material details, such as the electronic band structure and the nature of impurities. Here we show an anomaly in the inverse spin Hall effect in weak ferromagnetic NiPd alloys near their Curie temperatures with a shape independent of material details, such as Ni concentrations. By extending Kondo's model for the anomalous Hall effect, we explain the observed anomaly as originating from the second-order nonlinear spin fluctuation of Ni moments. This brings to light an essential symmetry difference between the spin Hall effect and the anomalous Hall effect, which reflects the first-order nonlinear fluctuations of local moments. Our finding opens up a new application of the spin Hall effect, by which a minuscule magnetic moment can be detected.
Low temperature hall effect investigation of conducting polymer-carbon nanotubes composite network.
Bahrami, Afarin; Talib, Zainal Abidin; Yunus, Wan Mahmood Mat; Behzad, Kasra; M Abdi, Mahnaz; Din, Fasih Ud
2012-11-14
Polypyrrole (PPy) and polypyrrole-carboxylic functionalized multi wall carbon nanotube composites (PPy/f-MWCNT) were synthesized by in situ chemical oxidative polymerization of pyrrole on the carbon nanotubes (CNTs). The structure of the resulting complex nanotubes was characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The effects of f-MWCNT concentration on the electrical properties of the resulting composites were studied at temperatures between 100 K and 300 K. The Hall mobility and Hall coefficient of PPy and PPy/f-MWCNT composite samples with different concentrations of f-MWCNT were measured using the van der Pauw technique. The mobility decreased slightly with increasing temperature, while the conductivity was dominated by the gradually increasing carrier density.
Spatially resolved Hall effect measurement in a single semiconductor nanowire.
Storm, Kristian; Halvardsson, Filip; Heurlin, Magnus; Lindgren, David; Gustafsson, Anders; Wu, Phillip M; Monemar, Bo; Samuelson, Lars
2012-11-01
Efficient light-emitting diodes and photovoltaic energy-harvesting devices are expected to play an important role in the continued efforts towards sustainable global power consumption. Semiconductor nanowires are promising candidates as the active components of both light-emitting diodes and photovoltaic cells, primarily due to the added freedom in device design offered by the nanowire geometry. However, for nanowire-based components to move past the proof-of-concept stage and be implemented in production-grade devices, it is necessary to precisely quantify and control fundamental material properties such as doping and carrier mobility. Unfortunately, the nanoscale geometry that makes nanowires interesting for applications also makes them inherently difficult to characterize. Here, we report a method to carry out Hall measurements on single core-shell nanowires. Our technique allows spatially resolved and quantitative determination of the carrier concentration and mobility of the nanowire shell. As Hall measurements have previously been completely unavailable for nanowires, the experimental platform presented here should facilitate the implementation of nanowires in advanced practical devices.
Quantum anomalous Hall effect in magnetic topological insulators
Wang, Jing; Lian, Biao; Zhang, Shou -Cheng
2015-08-25
The search for topologically non-trivial states of matter has become an important goal for condensed matter physics. Here, we give a theoretical introduction to the quantum anomalous Hall (QAH) effect based on magnetic topological insulators in two-dimensions (2D) and three-dimensions (3D). In 2D topological insulators, magnetic order breaks the symmetry between the counter-propagating helical edge states, and as a result, the quantum spin Hall effect can evolve into the QAH effect. In 3D, magnetic order opens up a gap for the topological surface states, and chiral edge state has been predicted to exist on the magnetic domain walls. We present the phase diagram in thin films of a magnetic topological insulator and review the basic mechanism of ferromagnetic order in magnetically doped topological insulators. We also review the recent experimental observation of the QAH effect. Furthermore, we discuss more recent theoretical work on the coexistence of the helical and chiral edge states, multi-channel chiral edge states, the theory of the plateau transition, and the thickness dependence in the QAH effect.
Quantum anomalous Hall effect in magnetic topological insulators
Wang, Jing; Lian, Biao; Zhang, Shou -Cheng
2015-08-25
The search for topologically non-trivial states of matter has become an important goal for condensed matter physics. Here, we give a theoretical introduction to the quantum anomalous Hall (QAH) effect based on magnetic topological insulators in two-dimensions (2D) and three-dimensions (3D). In 2D topological insulators, magnetic order breaks the symmetry between the counter-propagating helical edge states, and as a result, the quantum spin Hall effect can evolve into the QAH effect. In 3D, magnetic order opens up a gap for the topological surface states, and chiral edge state has been predicted to exist on the magnetic domain walls. We presentmore » the phase diagram in thin films of a magnetic topological insulator and review the basic mechanism of ferromagnetic order in magnetically doped topological insulators. We also review the recent experimental observation of the QAH effect. Furthermore, we discuss more recent theoretical work on the coexistence of the helical and chiral edge states, multi-channel chiral edge states, the theory of the plateau transition, and the thickness dependence in the QAH effect.« less
Redundant speed control for brushless Hall effect motor
NASA Technical Reports Server (NTRS)
Nola, F. J. (Inventor)
1973-01-01
A speed control system for a brushless Hall effect device equipped direct current (D.C.) motor is described. Separate windings of the motor are powered by separate speed responsive power sources. A change in speed, upward or downward, because of the failure of a component of one of the power sources results in a corrective signal being generated in the other power source to supply an appropriate power level and polarity to one winding to cause the motor to be corrected in speed.
Unconventional fractional quantum Hall effect in monolayer and bilayer graphene
Jacak, Janusz; Jacak, Lucjan
2016-01-01
The commensurability condition is applied to determine the hierarchy of fractional fillings of Landau levels in monolayer and in bilayer graphene. The filling rates for fractional quantum Hall effect (FQHE) in graphene are found in the first three Landau levels in one-to-one agreement with the experimental data. The presence of even denominator filling fractions in the hierarchy for FQHE in bilayer graphene is explained. Experimentally observed hierarchy of FQHE in the first and second Landau levels in monolayer graphene and in the zeroth Landau level in bilayer graphene is beyond the conventional composite fermion interpretation but fits to the presented nonlocal topology commensurability condition. PMID:27877866
Measurement of spin Hall effect of reflected light.
Qin, Yi; Li, Yan; He, Huanyu; Gong, Qihuang
2009-09-01
We have measured the spin-dependent nanometer-sized displacements of the spin Hall effect of the reflected light from a planar air-glass interface. In the case of the vertical polarization, the displacement is found to increase with the incident angle and subsequently decrease after approximately 48 deg, while in the case of the horizontal polarization, it changes rapidly near the Brewster angle. For a fixed incident angle of 30 deg, the displacement decreases to zero as the polarization angle approaches approximately 39 deg from 0 deg (the horizontal polarization) and then increases in the opposite direction until 90 deg (the vertical polarization).
Quantum spin Hall effect in nanostructures based on cadmium fluoride
Bagraev, N. T.; Guimbitskaya, O. N.; Klyachkin, L. E.; Koudryavtsev, A. A.; Malyarenko, A. M.; Romanov, V. V.; Ryskin, A. I.; Shcheulin, A. S.
2010-10-15
Tunneling current-voltage (I-V) characteristics and temperature dependences of static magnetic susceptibility and specific heat of the CdB{sub x}F{sub 2-x}/p-CdF{sub 2}-QW/CdB{sub x}F{sub 2-x} planar sandwich structures formed on the surface of an n-CdF{sub 2} crystal have been studied in order to identify superconducting properties of the CdB{sub x}F{sub 2-x} {delta} barriers confining the p-type CdF{sub 2} ultranarrow quantum well. Comparative analysis of current-voltage (I-V) characteristics and conductance-voltage dependences (measured at the temperatures, respectively, below and above the critical temperature of superconducting transition) indicates that there is an interrelation between quantization of supercurrent and dimensional quantization of holes in the p-CdF{sub 2} ultranarrow quantum well. It is noteworthy that detection of the Josephson peak of current in each hole subband is accompanied by the appearance of the spectrum of the multiple Andreev reflection (MAR). A high degree of spin polarization of holes in the edge channels along the perimeter of the p-CdF{sub 2} ultranarrow quantum well appears as a result of MAR and makes it possible to identify the quantum spin Hall effect I-V characteristics; this effect becomes pronounced in the case of detection of nonzero conductance at the zero voltage applied to the vertical gate in the Hall geometry of the experiment. Within the energy range of superconducting gap, the I-V characteristics of the spin transistor and quantum spin Hall effect are controlled by the MAR spectrum appearing as the voltage applied to the vertical gate is varied. Beyond the range of the superconducting gap, the observed I-V characteristic of the quantum spin Hall effect is represented by a quantum conductance staircase with a height of the steps equal to e{sub 2}/h; this height is interrelated with the Aharonov-Casher oscillations of longitudinal and depends on the voltage applied to the vertical gate.
High Throughput 600 Watt Hall Effect Thruster for Space Exploration
NASA Technical Reports Server (NTRS)
Szabo, James; Pote, Bruce; Tedrake, Rachel; Paintal, Surjeet; Byrne, Lawrence; Hruby, Vlad; Kamhawi, Hani; Smith, Tim
2016-01-01
A nominal 600-Watt Hall Effect Thruster was developed to propel unmanned space vehicles. Both xenon and iodine compatible versions were demonstrated. With xenon, peak measured thruster efficiency is 46-48% at 600-W, with specific impulse from 1400 s to 1700 s. Evolution of the thruster channel due to ion erosion was predicted through numerical models and calibrated with experimental measurements. Estimated xenon throughput is greater than 100 kg. The thruster is well sized for satellite station keeping and orbit maneuvering, either by itself or within a cluster.
Anomalous Hall effect in the prospective spintronic material Eu1-x Gd x O integrated with Si.
Parfenov, Oleg E; Averyanov, Dmitry V; Tokmachev, Andrey M; Taldenkov, Alexander N; Storchak, Vyacheslav G
2016-06-08
Remarkable properties of EuO make it a versatile spintronic material. Despite numerous experimental and theoretical studies of EuO, little is known about the anomalous Hall effect in this ferromagnet. So far, the effect has not been observed in bulk EuO, though has been detected in EuO films with uncontrolled distribution of defects. In the present work doping is taken under control: epitaxial films of Gd-doped EuO are synthesized integrated with Si using molecular beam epitaxy and characterized with x-ray diffraction and magnetization measurements. Nanoscale transport studies reveal the anomalous Hall effect in the ferromagnetic region for samples with different Gd concentration. The saturated anomalous Hall effect conductivity value of 5.0 S·cm(-1) in Gd-doped EuO is more than an order of magnitude larger than those reported so far for Eu chalcogenides doped with anion vacancies.
Plasma Characterization of Hall Thruster with Active and Passive Segmented Electrodes
Raitses, Y.; Staack, D.; Fisch, N.J.
2002-09-04
Non-emissive electrodes and ceramic spacers placed along the Hall thruster channel are shown to affect the plasma potential distribution and the thruster operation. These effects are associated with physical properties of the electrode material and depend on the electrode configuration, geometry and the magnetic field distribution. An emissive segmented electrode was able to maintain thruster operation by supplying an additional electron flux to sustain the plasma discharge between the anode and cathode neutralizer. These results indicate the possibility of new configurations for segmented electrode Hall thruster.
Large anomalous Hall effect in a half-Heusler antiferromagnet
NASA Astrophysics Data System (ADS)
Suzuki, T.; Chisnell, R.; Devarakonda, A.; Liu, Y.-T.; Feng, W.; Xiao, D.; Lynn, J. W.; Checkelsky, J. G.
2016-12-01
The quantum mechanical (Berry) phase of the electronic wavefunction plays a critical role in the anomalous and spin Hall effects, including their quantized limits. While progress has been made in understanding these effects in ferromagnets, less is known in antiferromagnetic systems. Here we present a study of antiferromagnet GdPtBi, whose electronic structure is similar to that of the topologically non-trivial HgTe (refs ,,), and where the Gd ions offer the possibility to tune the Berry phase via control of the spin texture. We show that this system supports an anomalous Hall angle ΘAH > 0.1, comparable to the largest observed in bulk ferromagnets and significantly larger than in other antiferromagnets. Neutron scattering measurements and electronic structure calculations suggest that this effect originates from avoided crossing or Weyl points that develop near the Fermi level due to a breaking of combined time-reversal and lattice symmetries. Berry phase effects associated with such symmetry breaking have recently been explored in kagome networks; our results extend this to half-Heusler systems with non-trivial band topology. The magnetic textures indicated here may also provide pathways towards realizing the topological insulating and semimetallic states predicted in this material class.
HIGH-FIELD STUDY OF A HALL-EFFECT MICROWAVE CONVERTER
FREQUENCY CONVERTERS, CAVITY RESONATORS, COUPLING CIRCUITS, DIELECTRICS, DIOXIDES, ELECTRIC FIELDS, HALL EFFECT , MAGNETIC FIELDS, MICROWAVE NETWORKS, MICROWAVES, MODEL TESTS, MODULATION, RADIOFREQUENCY POWER, SENSITIVITY, TITANIUM
Krypton charge exchange cross sections for Hall effect thruster models
Hause, Michael L.; Prince, Benjamin D.; Bemish, Raymond J.
2013-04-28
Following discharge from a Hall effect thruster, charge exchange occurs between ions and un-ionized propellant atoms. The low-energy cations produced can disturb operation of onboard instrumentation or the thruster itself. Charge-exchange cross sections for both singly and doubly charged propellant atoms are required to model these interactions. While xenon is the most common propellant currently used in Hall effect thrusters, other propellants are being considered, in particular, krypton. We present here guided-ion beam measurements and comparisons to semiclassical calculations for Kr{sup +} + Kr and Kr{sup 2+} + Kr cross sections. The measurements of symmetric Kr{sup +} + Kr charge exchange are in good agreement with both the calculations including spin-orbit effects and previous measurements. For the symmetric Kr{sup 2+} + Kr reaction, we present cross section measurements for center-of-mass energies between 1 eV and 300 eV, which spans energies not previously examined experimentally. These cross section measurements compare well with a simple one-electron transfer model. Finally, cross sections for the asymmetric Kr{sup 2+} + Kr {yields} Kr{sup +} + Kr{sup +} reaction show an onset near 12 eV, reaching cross sections near constant value of 1.6 A{sup 2} with an exception near 70-80 eV.
Non-invasive Hall current distribution measurement in a Hall effect thruster
NASA Astrophysics Data System (ADS)
Mullins, Carl R.; Farnell, Casey C.; Farnell, Cody C.; Martinez, Rafael A.; Liu, David; Branam, Richard D.; Williams, John D.
2017-01-01
A means is presented to determine the Hall current density distribution in a closed drift thruster by remotely measuring the magnetic field and solving the inverse problem for the current density. The magnetic field was measured by employing an array of eight tunneling magnetoresistive (TMR) sensors capable of milligauss sensitivity when placed in a high background field. The array was positioned just outside the thruster channel on a 1.5 kW Hall thruster equipped with a center-mounted hollow cathode. In the sensor array location, the static magnetic field is approximately 30 G, which is within the linear operating range of the TMR sensors. Furthermore, the induced field at this distance is approximately tens of milligauss, which is within the sensitivity range of the TMR sensors. Because of the nature of the inverse problem, the induced-field measurements do not provide the Hall current density by a simple inversion; however, a Tikhonov regularization of the induced field does provide the current density distributions. These distributions are shown as a function of time in contour plots. The measured ratios between the average Hall current and the average discharge current ranged from 6.1 to 7.3 over a range of operating conditions from 1.3 kW to 2.2 kW. The temporal inverse solution at 1.5 kW exhibited a breathing mode frequency of 24 kHz, which was in agreement with temporal measurements of the discharge current.
Non-invasive Hall current distribution measurement in a Hall effect thruster.
Mullins, Carl R; Farnell, Casey C; Farnell, Cody C; Martinez, Rafael A; Liu, David; Branam, Richard D; Williams, John D
2017-01-01
A means is presented to determine the Hall current density distribution in a closed drift thruster by remotely measuring the magnetic field and solving the inverse problem for the current density. The magnetic field was measured by employing an array of eight tunneling magnetoresistive (TMR) sensors capable of milligauss sensitivity when placed in a high background field. The array was positioned just outside the thruster channel on a 1.5 kW Hall thruster equipped with a center-mounted hollow cathode. In the sensor array location, the static magnetic field is approximately 30 G, which is within the linear operating range of the TMR sensors. Furthermore, the induced field at this distance is approximately tens of milligauss, which is within the sensitivity range of the TMR sensors. Because of the nature of the inverse problem, the induced-field measurements do not provide the Hall current density by a simple inversion; however, a Tikhonov regularization of the induced field does provide the current density distributions. These distributions are shown as a function of time in contour plots. The measured ratios between the average Hall current and the average discharge current ranged from 6.1 to 7.3 over a range of operating conditions from 1.3 kW to 2.2 kW. The temporal inverse solution at 1.5 kW exhibited a breathing mode frequency of 24 kHz, which was in agreement with temporal measurements of the discharge current.
Characterization of Compounds Formed and added on surface of outdoor Seville city hall
NASA Astrophysics Data System (ADS)
Robador, Maria Dolores; Alcalde, Manuel; Arroyo, Fatima; Albardonedo, Antonio; Perez-Rodriguez, Jose Luis
2013-04-01
The building of the City Hall of Seville constitutes one of the samples more important of the architecture plateresque in Andalusia. For centuries the stone façade has suffered different stages of restoration. These treatments joined the effects of the environmental pollution are responsible for formation and deposition of different chemical compounds on the surface of the monuments. This study will supply information of the environmental effects on the rock, and the treatments that have been performed in previous interventions. The petrographic study showed the presence of a carbonate rock of thin grain constituted essentially by bioclastos and fine sand. The study by scanning electron microscopy showed a compact and continuous cover that suggested a polymer layer. The infrared spectroscopy study confirmed presence of acrylic resin. This resin covered sometimes a black crust constituted by alkanes characterized by mass spectrometry. In addition was found nodules constitutes by C, Ca, Fe, Si and Ca. These compounds appeared with gypsum and were attributed to environment contamination produced by combustion. Materials were observed that cover volumetric lagoons for losses of pieces or were used to fix fragments of stones that were free or displaced. The study by X-ray diffraction and infrared spectroscopy confirmed the presence of gypsum. Mortars constituted by calcite (60%) and inert material (40%; mainly quartz, feldspar and mica) were also characterized. In flute of the stone was found a black crust under which appeared a yellowish layer. The portable X-ray fluorescence and X-ray diffraction confirmed the presence of gypsum produced by environmental contamination. Gypsum was also found in the interior of the stone confirming that this mineral has emigrated due the high porosity of the stone. In some zones of the façade was detected some possible wall paintings. Cross-sections were prepared and studied by optical and scanning electron microscopes. A layer of
Spin Hall effects for cold atoms in a light induced gauge potential
Zhu, Shi-Liang; Fu, Hao; Wu, C.-J.; Zhang, S.-C.; Duan, L.-M. /Michigan U., MCTP
2010-03-16
We propose an experimental scheme to observe spin Hall effects with cold atoms in a light induced gauge potential. Under an appropriate configuration, the cold atoms moving in a spatially varying laser field experience an effective spin-dependent gauge potential. Through numerical simulation, we demonstrate that such a gauge field leads to observable spin Hall currents under realistic conditions. We also discuss the quantum spin Hall state in an optical lattice.
2. QUANTUM HALL EFFECT: The problem of Coulomb interactions in the theory of the quantum Hall effect
NASA Astrophysics Data System (ADS)
Baranov, M. A.; Pruisken, A. M. M.; Škoric, B.
2001-10-01
We summarize the main ingredients of a unifying theory for abelian quantum Hall states. This theory combines the Finkel'stein approach to localization and interaction effects with the topological concept of an instanton vacuum as well as Chern-Simons gauge theory. We elaborate on the meaning of a new symmetry (Script F invariance) for systems with an infinitely ranged interaction potential. We address the renormalization of the theory and present the main results in terms of a scaling diagram of the conductances.
Extrinsic spin Hall effect induced by resonant skew scattering in graphene.
Ferreira, Aires; Rappoport, Tatiana G; Cazalilla, Miguel A; Castro Neto, A H
2014-02-14
We show that the extrinsic spin Hall effect can be engineered in monolayer graphene by decoration with small doses of adatoms, molecules, or nanoparticles originating local spin-orbit perturbations. The analysis of the single impurity scattering problem shows that intrinsic and Rashba spin-orbit local couplings enhance the spin Hall effect via skew scattering of charge carriers in the resonant regime. The solution of the transport equations for a random ensemble of spin-orbit impurities reveals that giant spin Hall currents are within the reach of the current state of the art in device fabrication. The spin Hall effect is robust with respect to thermal fluctuations and disorder averaging.
Strong Spin Hall effect in PtMn
NASA Astrophysics Data System (ADS)
Ou, Yongxi; Shi, Shengjie; Ralph, Daniel; Buhrman, Robert
Recent reports indicate that certain metallic antiferromagnets (AFM) can exhibit a significant spin Hall effect. Here we report a large damping-like spin torque efficiency (ξDL) in PtMn/ferromagnet(FM) bilayer structures, determined from both FM-thickness-dependent spin-torque ferromagnetic resonance (ST-FMR), and harmonic response (HR) measurements of layers with perpendicular magnetic anisotropy (PMA). We find that ξDL can vary from <0.1 to >0.15, depending on the thickness of PtMn, the stacking order of the samples, and the choice of the FM material. The field-like spin torque efficiency (ξFL) is also quite variable, 0<|ξFL|<0.5. The large broadening of the ST-FMR linewidth suggests extra spin attenuation at the AFM/FM interface that is possibly due to intermixing. The PtMn/FeCoB/MgO structures that exhibit PMA have a comparatively low switching current density and an unusual asymmetric switching phase diagram. These results indicate that AFM PtMn has significant potential both for advancing the understanding the physics of the spin Hall effect in Pt alloys, and for enabling new spintronics functionality.
Time-reversal-breaking induced quantum spin Hall effect
Luo, Wei; Shao, D. X.; Deng, Ming-Xun; Deng, W. Y.; Sheng, L.
2017-01-01
We show that quantum spin Hall (QSH) effect does not occur in a square lattice model due to cancellation of the intrinsic spin-orbit coupling coming from different hopping paths. However, we show that QSH effect can be induced by the presence of staggered magnetic fluxes alternating directions square by square. When the resulting Peierls phase takes a special value , the system has a composite symmetry ΘΡ− with Θ the time-reversal operator and Ρ− transforming the Peierls phase from γ to γ − , which protects the gapless edge states. Once the phase deviates from , the edge states open a gap, as the composite symmetry is broken. We further investigate the effect of a Zeeman field on the QSH state, and find that the edge states remain gapless for . This indicates that the QSH effect is immune to the magnetic perturbation. PMID:28220858
Time-reversal-breaking induced quantum spin Hall effect
NASA Astrophysics Data System (ADS)
Luo, Wei; Shao, D. X.; Deng, Ming-Xun; Deng, W. Y.; Sheng, L.
2017-02-01
We show that quantum spin Hall (QSH) effect does not occur in a square lattice model due to cancellation of the intrinsic spin-orbit coupling coming from different hopping paths. However, we show that QSH effect can be induced by the presence of staggered magnetic fluxes alternating directions square by square. When the resulting Peierls phase takes a special value , the system has a composite symmetry ΘΡ‑ with Θ the time-reversal operator and Ρ‑ transforming the Peierls phase from γ to γ ‑ , which protects the gapless edge states. Once the phase deviates from , the edge states open a gap, as the composite symmetry is broken. We further investigate the effect of a Zeeman field on the QSH state, and find that the edge states remain gapless for . This indicates that the QSH effect is immune to the magnetic perturbation.
Time-reversal-breaking induced quantum spin Hall effect.
Luo, Wei; Shao, D X; Deng, Ming-Xun; Deng, W Y; Sheng, L
2017-02-21
We show that quantum spin Hall (QSH) effect does not occur in a square lattice model due to cancellation of the intrinsic spin-orbit coupling coming from different hopping paths. However, we show that QSH effect can be induced by the presence of staggered magnetic fluxes alternating directions square by square. When the resulting Peierls phase takes a special value , the system has a composite symmetry ΘΡ- with Θ the time-reversal operator and Ρ- transforming the Peierls phase from γ to γ - , which protects the gapless edge states. Once the phase deviates from , the edge states open a gap, as the composite symmetry is broken. We further investigate the effect of a Zeeman field on the QSH state, and find that the edge states remain gapless for . This indicates that the QSH effect is immune to the magnetic perturbation.
Large extrinsic spin Hall effect in Au-Cu alloys by extensive atomic disorder scattering
NASA Astrophysics Data System (ADS)
Zou, L. K.; Wang, S. H.; Zhang, Y.; Sun, J. R.; Cai, J. W.; Kang, S. S.
2016-01-01
Spin Hall angle, which denotes the conversion efficiency between spin and charge current, is a key parameter in the pure spin current phenomenon. The search for materials with large spin Hall angle is indeed important for scientific interest and potential application in spintronics. Here the large enhanced spin Hall effect (SHE) of Au-Cu alloy is reported by investigating the spin Seebeck effect, spin Hall anomalous Hall effect, and spin Hall magnetoresistance of the Y3F e5O12 (YIG)/A uxC u1 -x hybrid structure over the full composition. At the near equiatomic Au-Cu composition with maximum atomic disorder scattering, the spin Hall angle of the Au-Cu alloy increases by two to three times together with a moderate spin diffusion length in comparison with Au. The longitudinal spin Seebeck voltage and the spin Hall magnetoresistance ratio also increase by two to three times. More importantly, no evidence of anomalous Hall effect is observed in all YIG/Au-Cu samples, in contrast to the cases of other giant SHE materials Pt(Pd), Ta, and W. This behavior makes Au-Cu free from any suspicion of the magnetic proximity effect involved in the hybrid structure, and thus the Au-Cu alloy can be an ideal material for pure spin current study.
Photonic spin Hall effect in metasurfaces: a brief review
NASA Astrophysics Data System (ADS)
Liu, Yachao; Ke, Yougang; Luo, Hailu; Wen, Shuangchun
2017-01-01
The photonic spin Hall effect (SHE) originates from the interplay between the photon-spin (polarization) and the trajectory (extrinsic orbital angular momentum) of light, i.e. the spin-orbit interaction. Metasurfaces, metamaterials with a reduced dimensionality, exhibit exceptional abilities for controlling the spin-orbit interaction and thereby manipulating the photonic SHE. Spin-redirection phase and Pancharatnam-Berry phase are the manifestations of spin-orbit interaction. The former is related to the evolution of the propagation direction and the latter to the manipulation with polarization state. Two distinct forms of splitting based on these two types of geometric phases can be induced by the photonic SHE in metasurfaces: the spin-dependent splitting in position space and in momentum space. The introduction of Pacharatnam-Berry phases, through space-variant polarization manipulations with metasurfaces, enables new approaches for fabricating the spin-Hall devices. Here, we present a short review of photonic SHE in metasurfaces and outline the opportunities in spin photonics.
Pulsed field UCu5 Hall effect and magnetization (I)
Mcdonald, Ross D; Ayala - Valenzuela, Oscar E; Ben, Ueland G; Corneliu, Miclea; Movshovich, R; Tompson, J. D.; Bauer, E; Batista, C. D.; Martin, I
2011-01-14
Prior studies of UCu{sub 5} identified the material as undergoing antiferromagnetic ordering at a temperature of 15 K with a subsequent reduction of the electronic density of states, evident as sharp upturn in resistance, at 1.4 K. High field magnetization measurements indicate a complex temperature-field phase diagram comprising of numerous phases below 15 K up and up to 60 T, with NMR and neutron measurements identifying both simple anitferromagnetic and 4Q-magnetic structures at low fields. The purpose of our investigations is to identify the possibly strong coupling between the itinerant electrons and the local spin structures, such as quantum amplification of the Hall effect due to (field induced) non-colinear spin textures. Comparison with prior literature indicates the sensitivity of the phase stability of the different spin textures to composition and sample preparation. However, the 'simplified' phase diagram of this composition offers the possibility of exploring, anomalous Hall properties arising from a field induced non-colinear spin texture over a wide range of temperatures and magnetic fields.
Hall effect of triplons in a dimerized quantum magnet
NASA Astrophysics Data System (ADS)
Romhányi, Judit; Penc, Karlo; Ganesh, R.
2015-04-01
SrCu2(BO3)2 is the archetypal quantum magnet with a gapped dimer-singlet ground state and triplon excitations. It serves as an excellent realization of the Shastry-Sutherland model, up to small anisotropies arising from Dzyaloshinskii-Moriya interactions. Here we demonstrate that these anisotropies, in fact, give rise to topological character in the triplon band structure. The triplons form a new kind of Dirac cone with three bands touching at a single point, a spin-1 generalization of graphene. An applied magnetic field opens band gaps resulting in topological bands with Chern numbers +/-2. SrCu2(BO3)2 thus provides a magnetic analogue of the integer quantum Hall effect and supports topologically protected edge modes. At a threshold value of the magnetic field set by the Dzyaloshinskii-Moriya interactions, the three triplon bands touch once again in a spin-1 Dirac cone, and lose their topological character. We predict a strong thermal Hall signature in the topological regime.
Hall effect of triplons in a dimerized quantum magnet
NASA Astrophysics Data System (ADS)
Romhanyi, Judit; Penc, Karlo; Ganesh, Ramachandran
2015-03-01
SrCu2(BO3)2 is the archetypal quantum magnet with a gapped dimer-singlet ground state and triplon excitations. It serves as a realization of the Shastry Sutherland model, up to small anisotropies arising from Dzyaloshinskii-Moriya (DM) interactions. We demonstrate that the DM couplings give rise to topological character in the triplon band structure. The triplons form a new kind of a Dirac cone with three bands touching at a single point, a spin-1 generalization of graphene. An applied magnetic field opens band gaps and as a result topological bands with Chern numbers +/- 2 develop. Thus SrCu2(BO3)2 is a magnetic analogue of the integer quantum Hall effect and supports topologically protected edge modes. At a critical value of the magnetic field set by the strength of DM interactions, the three triplon bands touch again in a spin-1 Dirac cone, and lose their topological character. We predict thermal Hall signature in the topological regime.
Fractionally charged skyrmions in fractional quantum Hall effect
Balram, Ajit C.; Wurstbauer, U.; Wójs, A.; ...
2015-11-26
The fractional quantum Hall effect has inspired searches for exotic emergent topological particles, such as fractionally charged excitations, composite fermions, abelian and nonabelian anyons and Majorana fermions. Fractionally charged skyrmions, which support both topological charge and topological vortex-like spin structure, have also been predicted to occur in the vicinity of 1/3 filling of the lowest Landau level. The fractional skyrmions, however, are anticipated to be exceedingly fragile, suppressed by very small Zeeman energies. Here we show that, slightly away from 1/3 filling, the smallest manifestations of the fractional skyrmion exist in the excitation spectrum for a broad range of Zeemanmore » energies, and appear in resonant inelastic light scattering experiments as well-defined resonances slightly below the long wavelength spin wave mode. The spectroscopy of these exotic bound states serves as a sensitive tool for investigating the residual interaction between composite fermions, responsible for delicate new fractional quantum Hall states in this filling factor region.« less
Hall and ion slip effects on peristaltic flow of Jeffrey nanofluid with Joule heating
NASA Astrophysics Data System (ADS)
Hayat, T.; Shafique, Maryam; Tanveer, A.; Alsaedi, A.
2016-06-01
This paper addresses mixed convective peristaltic flow of Jeffrey nanofluid in a channel with complaint walls. The present investigation includes the viscous dissipation, thermal radiation and Joule heating. Hall and ion slip effects are also taken into account. Related problems through long wavelength and low Reynolds number are examined for stream function, temperature and concentration. Impacts of thermal radiation, Hartman number, Brownian motion parameter, thermophoresis, Joule heating, Hall and ion slip parameters are investigated in detail. It is observed that velocity increases and temperature decreases with Hall and ion slip parameters. Further the thermal radiation on temperature has qualitatively similar role to that of Hall and ion slip effects.
Pseudo Magnetic Faraday and Quantum Hall Effect In Oscillating Graphene
NASA Astrophysics Data System (ADS)
Bhagat, Anita; Mullen, Kieran
When a graphene layer is stressed, the strain changes the phase between sites in a tight binding model of the system. This phase can be viewed as a pseudo-magnetic vector potential. The corresponding pseudo-magnetic field has been experimentally verified in static cases. We examine the case of oscillating graphene ribbons and explore two new effects. The first is to investigate an oscillating pseudo-magnetic field that produces a quantum Hall effect: we calculate the I-V characteristic of an oscillating graphene nanoribbon as a function of frequency, and amplitude in both the oscillations and the applied driving voltage. Second, the time dependent pseudo-magnetic field should produce a pseudo-Faraday effect driving electrons in different valleys in opposite directions. In both cases, we make explicit calculations for experiment. This project was supported in part by the US National Science Foundation under Grant DMR-1310407.
High-Field Fractional Quantum Hall Effect in Optical Lattices
Palmer, R.N.; Jaksch, D.
2006-05-12
We consider interacting bosonic atoms in an optical lattice subject to a large simulated magnetic field. We develop a model similar to a bilayer fractional quantum Hall system valid near simple rational numbers of magnetic flux quanta per lattice cell. Then we calculate its ground state, magnetic lengths, fractional fillings, and find unexpected sign changes in the Hall current. Finally we study methods for detecting these novel features via shot noise and Hall current measurements.
Hall and Nernst effects in monolayer MoS2
NASA Astrophysics Data System (ADS)
Zhang, Yun-Hai; Zhang, Ming-Hua
2016-03-01
We study Hall and Nernst transports in monolayer MoS2 based on Green’s function formalism. We have derived analytical results for spin and valley Hall conductivities in the zero temperature and spin and valley Nernst conductivities in the low temperature. We found that tuning of the band gap and spin-orbit splitting can drive system transition from spin Hall insulator (SHI) to valley Hall insulator (VHI). When the system is subjected to a temperature gradient, the spin and valley Nernst conductivities are dependent on Berry curvature.
Spin Hall effect of light in photon tunneling
Luo Hailu; Wen Shuangchun; Shu Weixing; Fan Dianyuan
2010-10-15
We resolve the breakdown of angular momentum conservation on two-dimensional photon tunneling by considering the spin Hall effect (SHE) of light. This effect manifests itself as polarization-dependent transverse shifts of the field centroid when a classic wave packet tunnels through a prism-air-prism barrier. For the left or the right circularly polarized component, the transverse shift can be modulated by altering the refractive index gradient associated with the two prisms. We find that the SHE in conventional beam refraction can be evidently enhanced via photon tunneling mechanism. The transverse spatial shift is governed by the total angular momentum conservation law, while the transverse angular shift is governed by the total linear momentum conservation law. These findings open the possibility for developing new nanophotonic devices and can be extrapolated to other physical systems.
Thermoelectric effects in quantum Hall systems beyond linear response
NASA Astrophysics Data System (ADS)
López, Rosa; Hwang, Sun-Yong; Sánchez, David
2014-12-01
We consider a quantum Hall system with an antidot acting as a energy dependent scatterer. In the purely charge case, we find deviations from the Wiedemann-Franz law that take place in the nonlinear regime of transport. We also discuss Peltier effects beyond linear response and describe both effects using magnetic-field asymmetric transport coefficients. For the spin case such as that arising along the helical edge states of a two-dimensional topological insulator, we investigate the generation of spin currents as a result of applied voltage and temperature differences in samples attached to ferromagnetic leads. We find that in the parallel configuration the spin current can be tuned with the leads' polarization even in the linear regime of transport. In contrast, for antiparallel magnetizations the spin currents has a strict nonlinear dependence on the the applied fields.
Heterodyne Hall effect in a two-dimensional electron gas
NASA Astrophysics Data System (ADS)
Oka, Takashi; Bucciantini, Leda
2016-10-01
We study the hitherto unaddressed phenomenon of the quantum Hall effect with a magnetic and electric field oscillating in time with resonant frequencies. This phenomenon highlights an example of a heterodyne device with the magnetic field acting as a driving force, and it is analyzed in detail in its classical and quantum versions using Floquet theory. A bulk current flowing perpendicularly to the applied electric field is found, with a frequency shifted by integer multiples of the driving frequency. When the ratio of the cyclotron and driving frequency takes special values, the electron's classical trajectory forms a loop and the effective mass diverges, while in the quantum case we find an analog of the Landau quantization. A possible realization using metamaterial plasmonics is discussed.
Investigating dissipation in the quantum anomalous Hall effect
NASA Astrophysics Data System (ADS)
Fox, Eli; Bestwick, Andrew; Goldhaber-Gordon, David; Feng, Yang; Ou, Yunbo; He, Ke; Wang, Yayu; Xue, Qi-Kun; Kou, Xufeng; Pan, Lei; Wang, Kang
In the quantum anomalous Hall effect, a magnetic exchange gap in a 3D topological insulator gives rise to dissipationless chiral edge states. Though the effect has recently been realized in a family of ferromagnetically-doped (Bi,Sb)2Te3 topological insulator thin films, experiments to date have found non-vanishing longitudinal resistance, contrary to initial theoretical expectations. Proposed sources of this dissipation include extra gapless or activated quasi-helical edge states, thermally activated 2D conduction, and variable-range hopping. Here, we discuss transport measurements of Corbino disk and non-local geometries to identify the mechanism of non-ideal behavior. This work supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award No. 19-7503.
Perturbation analysis of ionization oscillations in Hall effect thrusters
Hara, Kentaro Sekerak, Michael J.; Boyd, Iain D.; Gallimore, Alec D.
2014-12-15
A perturbation analysis of ionization oscillations, which cause low frequency oscillations of the discharge plasma, in Hall effect thrusters is presented including the electron energy equation in addition to heavy-species transport. Excitation and stabilization of such oscillations, often called the breathing mode, are discussed in terms of the growth rate obtained from the linear perturbation equations of the discharge plasma. The instability induced from the ionization occurs only when the perturbation in the electron energy is included while the neutral atom flow contributes to the damping of the oscillation. Effects of the electron energy loss mechanisms such as wall heat loss, inelastic collisions, and convective heat flux are discussed. It is shown that the ionization oscillations can be damped when the electron transport is reduced and the electron temperature increases so that the energy loss to the wall stabilizes the ionization instability.
Influence of disorder on anomalous Hall effect for Heusler compounds
NASA Astrophysics Data System (ADS)
Vilanova Vidal, E.; Schneider, H.; Jakob, G.
2011-05-01
The anomalous Hall effect (AHE) is a long known but still not fully understood transport effect. Most theory papers focus on the influence of one particular contribution to the AHE. Actual measured experimental data, however, often are not in accord with idealized assumptions. In this work we discuss the data analysis for materials with low residual resistivity ratios. As prototypical materials we study half metallic Heusler compounds. Here the influence of defects and disorder is apparent in a material with a complex topology of the Fermi surface. Using films of different degree of disorder, we show how different scattering mechanisms can be separated. For Co2FeSi0.6Al0.4 and Co2FeGa0.5Ge0.5 the AHE induced by B2-type disorder and temperature-dependent scattering is positive, while DO3-type disorder and possible intrinsic contributions possess a negative sign.
Deformed Calogero-Sutherland model and fractional quantum Hall effect
NASA Astrophysics Data System (ADS)
Atai, Farrokh; Langmann, Edwin
2017-01-01
The deformed Calogero-Sutherland (CS) model is a quantum integrable system with arbitrary numbers of two types of particles and reducing to the standard CS model in special cases. We show that a known collective field description of the CS model, which is based on conformal field theory (CFT), is actually a collective field description of the deformed CS model. This provides a natural application of the deformed CS model in Wen's effective field theory of the fractional quantum Hall effect (FQHE), with the two kinds of particles corresponding to electrons and quasi-hole excitations. In particular, we use known mathematical results about super-Jack polynomials to obtain simple explicit formulas for the orthonormal CFT basis proposed by van Elburg and Schoutens in the context of the FQHE.
NASA Astrophysics Data System (ADS)
Ji, Wei-xiao; Zhang, Chang-wen; Ding, Meng; Zhang, Bao-min; Li, Ping; Li, Feng; Ren, Miao-juan; Wang, Pei-ji; Zhang, Run-wu; Hu, Shu-jun; Yan, Shi-shen
2016-08-01
Bismuth (Bi) has attracted a great deal of attention for its strongest spin-orbit coupling (SOC) strength among main group elements. Although quantum anomalous Hall (QAH) state is predicted in half-hydrogenated Bi honeycomb monolayers Bi2H, the experimental results are still missing. Halogen atoms (X = F, Cl and Br) were also frequently used as modifications, but Bi2X films show a frustrating metallic character that masks the QAH effects. Here, first-principle calculations are performed to predict the full-cyanided bismuthene (Bi2(CN)2) as 2D topological insulator supporting quantum spin Hall state with a record large gap up to 1.10 eV, and more importantly, half-cyanogen saturated bismuthene (Bi2(CN)) as a Chern insulator supporting a valley-polarized QAH state, with a Curie temperature to be 164 K, as well as a large gap reaching 0.348 eV which could be further tuned by bi-axial strain and SOC strength. Our findings provide an appropriate and flexible material family candidate for spintronic and valleytronic devices.
Observation of anomalous Hall effect in a non-magnetic two-dimensional electron system
Maryenko, D.; Mishchenko, A. S.; Bahramy, M. S.; Ernst, A.; Falson, J.; Kozuka, Y.; Tsukazaki, A.; Nagaosa, N.; Kawasaki, M.
2017-01-01
Anomalous Hall effect, a manifestation of Hall effect occurring in systems without time-reversal symmetry, has been mostly observed in ferromagnetically ordered materials. However, its realization in high-mobility two-dimensional electron system remains elusive, as the incorporation of magnetic moments deteriorates the device performance compared to non-doped structure. Here we observe systematic emergence of anomalous Hall effect in various MgZnO/ZnO heterostructures that exhibit quantum Hall effect. At low temperatures, our nominally non-magnetic heterostructures display an anomalous Hall effect response similar to that of a clean ferromagnetic metal, while keeping a large anomalous Hall effect angle θAHE≈20°. Such a behaviour is consistent with Giovannini–Kondo model in which the anomalous Hall effect arises from the skew scattering of electrons by localized paramagnetic centres. Our study unveils a new aspect of many-body interactions in two-dimensional electron systems and shows how the anomalous Hall effect can emerge in a non-magnetic system. PMID:28300133
Thickness Dependence of the Quantum Anomalous Hall Effect in Magnetic Topological Insulator Films.
Feng, Xiao; Feng, Yang; Wang, Jing; Ou, Yunbo; Hao, Zhenqi; Liu, Chang; Zhang, Zuocheng; Zhang, Liguo; Lin, Chaojing; Liao, Jian; Li, Yongqing; Wang, Li-Li; Ji, Shuai-Hua; Chen, Xi; Ma, Xucun; Zhang, Shou-Cheng; Wang, Yayu; He, Ke; Xue, Qi-Kun
2016-08-01
The evolution of the quantum anomalous Hall effect with the thickness of Cr-doped (Bi,Sb)2 Te3 magnetic topological insulator films is studied, revealing how the effect is caused by the interplay of the surface states, band-bending, and ferromagnetic exchange energy. Homogeneity in ferromagnetism is found to be the key to high-temperature quantum anomalous Hall material.
Observation of anomalous Hall effect in a non-magnetic two-dimensional electron system
NASA Astrophysics Data System (ADS)
Maryenko, D.; Mishchenko, A. S.; Bahramy, M. S.; Ernst, A.; Falson, J.; Kozuka, Y.; Tsukazaki, A.; Nagaosa, N.; Kawasaki, M.
2017-03-01
Anomalous Hall effect, a manifestation of Hall effect occurring in systems without time-reversal symmetry, has been mostly observed in ferromagnetically ordered materials. However, its realization in high-mobility two-dimensional electron system remains elusive, as the incorporation of magnetic moments deteriorates the device performance compared to non-doped structure. Here we observe systematic emergence of anomalous Hall effect in various MgZnO/ZnO heterostructures that exhibit quantum Hall effect. At low temperatures, our nominally non-magnetic heterostructures display an anomalous Hall effect response similar to that of a clean ferromagnetic metal, while keeping a large anomalous Hall effect angle θAHE~20°. Such a behaviour is consistent with Giovannini-Kondo model in which the anomalous Hall effect arises from the skew scattering of electrons by localized paramagnetic centres. Our study unveils a new aspect of many-body interactions in two-dimensional electron systems and shows how the anomalous Hall effect can emerge in a non-magnetic system.
Evaluation of the Hall-effect sensor for determination of eyelid closure in vivo.
Hamiel, S R; Bleicher, J N; Tubach, M R; Cronan, J C
1995-07-01
A small device to detect eyelid closure was designed on the basis of a Hall-effect sensor. Accurate sensing of normal eyelid closure is required to develop a prosthetic eyelid closure device for patients with paralyzed orbicularis oculi muscles. In this study, six rabbits had the sensors surgically implanted. A Hall-effect sensor, a small device that measures magnetic fields, was implanted in the inferior eyelid near the ciliary margin. An opposing magnet was implanted in the upper eyelid. Thus, as the eyelid closes, the output of the Hall-effect sensor will increase. This output voltage was monitored weekly. During the first 5 weeks the output of the Hall-effect sensor decreased slightly but then reached a steady state for the duration of the experiment. This study suggests that the Hall-effect sensor could be used to detect normal eyelid closure in an implantable facial reanimation device.
Magnetic bilayer-skyrmions without skyrmion Hall effect.
Zhang, Xichao; Zhou, Yan; Ezawa, Motohiko
2016-01-19
Magnetic skyrmions might be used as information carriers in future advanced memories, logic gates and computing devices. However, there exists an obstacle known as the skyrmion Hall effect (SkHE), that is, the skyrmion trajectories bend away from the driving current direction due to the Magnus force. Consequently, the skyrmions in constricted geometries may be destroyed by touching the sample edges. Here we theoretically propose that the SkHE can be suppressed in the antiferromagnetically exchange-coupled bilayer system, since the Magnus forces in the top and bottom layers are exactly cancelled. We show that such a pair of SkHE-free magnetic skyrmions can be nucleated and be driven by the current-induced torque. Our proposal provides a promising means to move magnetic skyrmions in a perfectly straight trajectory in ultra-dense devices with ultra-fast processing speed.
Fractional quantum Hall effect in HgTe quantum wells
NASA Astrophysics Data System (ADS)
Wang, Jianhui
2016-02-01
We study the possibility of fractional quantum Hall effects in HgTe quantum wells using exact diagonalization. Our results show that Laughlin states, the Moore-Read state, and the Read-Rezayi Z3 state can all be supported. However, near the level crossing point (of the single-particle spectrum) the gap can be destroyed by Landau level mixing, and the Moore-Read state and the Read-Rezayi state dominate over their respective competing states only for wide wells. For smaller well widths the Moore-Read state crosses over to the composite fermion Fermi sea, while the Read-Rezayi state loses its dominance over the hierarchy state.
Microbeads detection using spin-valve planar Hall effect sensors.
Volmer, M; Avram, M
2012-09-01
In this paper we present a micromagnetic approach to describe the detection of magnetic nanobeads using planar Hall effect sensors. The magnetic beads polarized by a dc magnetic field generate a field, which can affect the magnetization state of spin-valve sensor, leading in principle, to a detectable signal. For magnetic nanobeads we assumed a superparamagnetic behaviour. Three detection geometries are discussed and some specific behaviours were highlighted by micromagnetic simulations. We found that when the polarising field is applied parallel with the sensor surface a very weak signal can be obtained. This is because at working fields, for which the magnetic nanobeads are magnetised, the sensor saturates. We identified other setups that can overcome this shortcoming and deliver a net signal.
Hall Current Effects in Mean-Field Dynamo Theory
NASA Astrophysics Data System (ADS)
Lingam, Manasvi; Bhattacharjee, Amitava
2016-09-01
The role of the Hall term on large-scale dynamo action is investigated by means of the first-order smoothing approximation. It is shown that the standard α coefficient is altered, and is zero when a specific double Beltrami state is attained, in contrast to the Alfvénic state for magnetohydrodynamical dynamos. The β coefficient is no longer positive definite, and thereby enables dynamo action even if α-quenching were to operate. The similarities and differences with the (magnetic) shear-current effect are pointed out, and a mechanism that may be potentially responsible for β \\lt 0 is advanced. The results are compared against previous studies, and their astrophysical relevance is also highlighted.
Robustness of topological Hall effect of nontrivial spin textures
NASA Astrophysics Data System (ADS)
Jalil, Mansoor B. A.; Tan, Seng Ghee
2014-05-01
We analyze the topological Hall conductivity (THC) of topologically nontrivial spin textures like magnetic vortices and skyrmions and investigate its possible application in the readback for magnetic memory based on those spin textures. Under adiabatic conditions, such spin textures would theoretically yield quantized THC values, which are related to topological invariants such as the winding number and polarity, and as such are insensitive to fluctuations and smooth deformations. However, in a practical setting, the finite size of spin texture elements and the influence of edges may cause them to deviate from their ideal configurations. We calculate the degree of robustness of the THC output in practical magnetic memories in the presence of edge and finite size effects.
Rotational spin Hall effect in a uniaxial crystal
NASA Astrophysics Data System (ADS)
Fadeyeva, Tatyana A.; Alexeyev, Constantine N.; Rubass, Alexander F.; Ivanov, Maksym O.; Zinov'ev, Alexey O.; Konovalenko, Victor L.; Volyar, Alexander V.
2012-04-01
We have considered the propagation process of the phase-matched array of singular beams through a uniaxial crystal. We have revealed that local beams in the array are rotated when propagating. However the right and left rotations are unequal. There are at least two processes responsible for the array rotation: the interference of local beams and the spatial depolarization. The interference takes place in the vortex birth and annihilation events forming the symmetrical part of the rotation. The depolarization process contributes to the asymmetry of the rotation that is called the rotational spin Hall effect. It can be brought to light due to the difference between the envelopes of the dependences of the angular displacement on the inclination angle of the local beams or the crystal length reaching the value some angular degree. The direction of the additional array rotation is exclusively defined by the handedness of the circular polarization in the initial beam array.
Rotational spin Hall effect in a uniaxial crystal.
Fadeyeva, Tatyana A; Alexeyev, Constantine N; Rubass, Alexander F; Ivanov, Maksym O; Zinov'ev, Alexey O; Konovalenko, Victor L; Volyar, Alexander V
2012-04-01
We have considered the propagation process of the phase-matched array of singular beams through a uniaxial crystal. We have revealed that local beams in the array are rotated when propagating. However the right and left rotations are unequal. There are at least two processes responsible for the array rotation: the interference of local beams and the spatial depolarization. The interference takes place in the vortex birth and annihilation events forming the symmetrical part of the rotation. The depolarization process contributes to the asymmetry of the rotation that is called the rotational spin Hall effect. It can be brought to light due to the difference between the envelopes of the dependences of the angular displacement on the inclination angle of the local beams or the crystal length reaching the value of some angular degree. The direction of the additional array rotation is exclusively defined by the handedness of the circular polarization in the initial beam array.
Magnetic bilayer-skyrmions without skyrmion Hall effect
Zhang, Xichao; Zhou, Yan; Ezawa, Motohiko
2016-01-01
Magnetic skyrmions might be used as information carriers in future advanced memories, logic gates and computing devices. However, there exists an obstacle known as the skyrmion Hall effect (SkHE), that is, the skyrmion trajectories bend away from the driving current direction due to the Magnus force. Consequently, the skyrmions in constricted geometries may be destroyed by touching the sample edges. Here we theoretically propose that the SkHE can be suppressed in the antiferromagnetically exchange-coupled bilayer system, since the Magnus forces in the top and bottom layers are exactly cancelled. We show that such a pair of SkHE-free magnetic skyrmions can be nucleated and be driven by the current-induced torque. Our proposal provides a promising means to move magnetic skyrmions in a perfectly straight trajectory in ultra-dense devices with ultra-fast processing speed. PMID:26782905
Measuring cervical dilatation in human parturition using the Hall effect.
Kriewall, T J; Work, B A
1977-01-01
An instrument was developed to continuously measure cervical dilatation in human labor. The instrument utilizes a small magnetic field source, which is attached to one edge of the cervix while a magnetic field sensor is attached to the diametrically opposite edge of the cervix. The sensor, using two Hall generators, measures orthogonal components of the field to minimize the effects of angular orientation between the source and sensor. The instrument's characteristics indicate that it can measure dilation throughout the range of 1-10 cm, but because its clinical reliability is consistent from only 1-7 cm, the equipment needs to be improved in the ways outlined in the text. This measurement, especially when analyzed with the continous measurement of intrauterine pressure, can provide the obstetrician with new insight into the physiology of labor.
Inverse spin Hall effect in a complex ferromagnetic oxide heterostructure
Wahler, Martin; Homonnay, Nico; Richter, Tim; Müller, Alexander; Eisenschmidt, Christian; Fuhrmann, Bodo; Schmidt, Georg
2016-01-01
We present spin pumping and inverse spin Hall effect (ISHE) in an epitaxial complex oxide heterostructure. Ferromagnetic La0.7Sr0.3MnO3 (LSMO) is used as a source of spin pumping while the spin sink exhibiting the ISHE consists of SrRuO3 (SRO). SRO is a ferromagnetic oxide with metallic conductivity, however, with a Curie temperature (TC) of 155 K, thus well below room temperature. This choice allows to perform the experiment above and below TC of the SRO and to demonstrate that SRO not only shows an ISHE of a magnitude comparable to Pt (though with opposite sign) in its non magnetic state but also exhibits a finite ISHE even 50 K below TC. PMID:27346793
Magnetic bilayer-skyrmions without skyrmion Hall effect
NASA Astrophysics Data System (ADS)
Zhang, Xichao; Zhou, Yan; Ezawa, Motohiko
2016-01-01
Magnetic skyrmions might be used as information carriers in future advanced memories, logic gates and computing devices. However, there exists an obstacle known as the skyrmion Hall effect (SkHE), that is, the skyrmion trajectories bend away from the driving current direction due to the Magnus force. Consequently, the skyrmions in constricted geometries may be destroyed by touching the sample edges. Here we theoretically propose that the SkHE can be suppressed in the antiferromagnetically exchange-coupled bilayer system, since the Magnus forces in the top and bottom layers are exactly cancelled. We show that such a pair of SkHE-free magnetic skyrmions can be nucleated and be driven by the current-induced torque. Our proposal provides a promising means to move magnetic skyrmions in a perfectly straight trajectory in ultra-dense devices with ultra-fast processing speed.
Hall Effect Thruster Plume Contamination and Erosion Study
NASA Technical Reports Server (NTRS)
Jaworske, Donald A.
2000-01-01
The objective of the Hall effect thruster plume contamination and erosion study was to evaluate the impact of a xenon ion plume on various samples placed in the vicinity of a Hall effect thruster for a continuous 100 hour exposure. NASA Glenn Research Center was responsible for the pre- and post-test evaluation of three sample types placed around the thruster: solar cell cover glass, RTV silicone, and Kapton(R). Mass and profilometer), were used to identify the degree of deposition and/or erosion on the solar cell cover glass, RTV silicone, and Kapton@ samples. Transmittance, reflectance, solar absorptance, and room temperature emittance were used to identify the degree of performance degradation of the solar cell cover glass samples alone. Auger spectroscopy was used to identify the chemical constituents found on the surface of the exposed solar cell cover glass samples. Chemical analysis indicated some boron nitride contamination on the samples, from boron nitride insulators used in the body of the thruster. However, erosion outweighted contamination. All samples exhibited some degree of erosion. with the most erosion occurring near the centerline of the plume and the least occurring at the +/- 90 deg positions. For the solar cell cover glass samples, erosion progressed through the antireflective coating and into the microsheet glass itself. Erosion occurred in the solar cell cover glass, RTV silicone and Kapton(R) at different rates. All optical properties changed with the degree of erosion, with solar absorptance and room temperature emittance increasing with erosion. The transmittance of some samples decreased while the reflectance of some samples increased and others decreased. All results are consistent with an energetic plume of xenon ions serving as a source for erosion.
Quantum anomalous Hall effect in stanene on a nonmagnetic substrate
NASA Astrophysics Data System (ADS)
Zhang, Huisheng; Zhou, Tong; Zhang, Jiayong; Zhao, Bao; Yao, Yugui; Yang, Zhongqin
2016-12-01
Since the quantum anomalous Hall (QAH) effect was realized in magnetic topological insulators, research on the effect has become a hot topic. The very harsh realizing requirements of the effect in experiments, however, hinder its practical applications. Based on ab initio methods, we find that nonmagnetic Pb I2 films are ideal substrates for the two-dimensional honeycomb stanene. The QAH effect with a pretty large band gap (up to 90 meV) can be achieved in the functionalized stanene /Pb I2 heterostructure. Despite van der Waals interactions in the heterostructure, band inversions are found to be happening between Sn (s and px ,y ) and Pb (px ,y) orbitals, playing a key role in determining the nontrivial topology and the large band gap of the system. Having no magnetic atoms is imperative to triggering the QAH effect. A very stable rudimentary device having QAH effects is proposed based on the Sn /Pb I2 heterostructure. Our results demonstrate that QAH effects can be easily realized in the Sn /Pb I2 heterostructures in experiments.
Crossover to the anomalous quantum regime in the extrinsic spin Hall effect of graphene
NASA Astrophysics Data System (ADS)
Milletarı, Mirco; Ferreira, Aires
2016-11-01
Recent reports of spin-orbit coupling enhancement in chemically modified graphene have opened doors to studies of the spin Hall effect with massless chiral fermions. Here, we theoretically investigate the interaction and impurity density dependence of the extrinsic spin Hall effect in spin-orbit coupled graphene. We present a nonperturbative quantum diagrammatic calculation of the spin Hall response function in the strong-coupling regime that incorporates skew scattering and anomalous impurity density-independent contributions on equal footing. The spin Hall conductivity dependence on Fermi energy and electron-impurity interaction strength reveals the existence of experimentally accessible regions where anomalous quantum processes dominate. Our findings suggest that spin-orbit-coupled graphene is an ideal model system for probing the competition between semiclassical and bona fide quantum scattering mechanisms underlying the spin Hall effect.
Tuning the spin Hall effect of Pt from the moderately dirty to the superclean regime
NASA Astrophysics Data System (ADS)
Sagasta, Edurne; Omori, Yasutomo; Isasa, Miren; Gradhand, Martin; Hueso, Luis E.; Niimi, Yasuhiro; Otani, YoshiChika; Casanova, Fèlix
2016-08-01
We systematically measure and analyze the spin diffusion length and the spin Hall effect in Pt with a wide range of conductivities using the spin absorption method in lateral spin valve devices. We observe a linear relation between the spin diffusion length and the conductivity, evidencing that the spin relaxation in Pt is governed by the Elliott-Yafet mechanism. We find a single intrinsic spin Hall conductivity (σSHint=1600 ±150 Ω-1c m-1) for Pt in the full range studied which is in good agreement with theory. We have obtained the crossover between the moderately dirty and the superclean scaling regimes of the spin Hall effect by tuning the conductivity. This is equivalent to that obtained for the anomalous Hall effect. Our results explain the spread of the spin Hall angle values in the literature and find a route to maximize this important parameter.
Edge states and integer quantum Hall effect in topological insulator thin films.
Zhang, Song-Bo; Lu, Hai-Zhou; Shen, Shun-Qing
2015-08-25
The integer quantum Hall effect is a topological state of quantum matter in two dimensions, and has recently been observed in three-dimensional topological insulator thin films. Here we study the Landau levels and edge states of surface Dirac fermions in topological insulators under strong magnetic field. We examine the formation of the quantum plateaux of the Hall conductance and find two different patterns, in one pattern the filling number covers all integers while only odd integers in the other. We focus on the quantum plateau closest to zero energy and demonstrate the breakdown of the quantum spin Hall effect resulting from structure inversion asymmetry. The phase diagrams of the quantum Hall states are presented as functions of magnetic field, gate voltage and chemical potential. This work establishes an intuitive picture of the edge states to understand the integer quantum Hall effect for Dirac electrons in topological insulator thin films.
Effective Field Theory of Fractional Quantized Hall Nematics
Mulligan, Michael; Nayak, Chetan; Kachru, Shamit; /Stanford U., Phys. Dept. /SLAC
2012-06-06
We present a Landau-Ginzburg theory for a fractional quantized Hall nematic state and the transition to it from an isotropic fractional quantum Hall state. This justifies Lifshitz-Chern-Simons theory - which is shown to be its dual - on a more microscopic basis and enables us to compute a ground state wave function in the symmetry-broken phase. In such a state of matter, the Hall resistance remains quantized while the longitudinal DC resistivity due to thermally-excited quasiparticles is anisotropic. We interpret recent experiments at Landau level filling factor {nu} = 7/3 in terms of our theory.
Magnetic Topological Insulators and Quantum Anomalous Hall Effect
NASA Astrophysics Data System (ADS)
Kou, Xufeng
The engineering of topological surface states is a key to realize applicable devices based on topological insulators (TIs). Among various proposals, introducing magnetic impurities into TIs has been proven to be an effective way to open a surface gap and integrate additional ferromagnetism with the original topological order. In this Dissertation, we study both the intrinsic electrical and magnetic properties of the magnetic TI thin films grown by molecular beam epitaxy. By doping transition element Cr into the host tetradymite-type V-VI semiconductors, we achieve robust ferromagnetic order with a strong perpendicular magnetic anisotropy. With additional top-gating capability, we realize the electric-field-controlled ferromagnetism in the magnetic TI systems, and demonstrate such magneto-electric effects can be effectively manipulated, depending on the interplays between the band topology, magnetic exchange coupling, and structural engineering. Most significantly, we report the observation of quantum anomalous Hall effect (QAHE) in the Cr-doped (BiSb)2Te3 samples where dissipationless chiral edge conduction is realized in the macroscopic millimeter-size devices without the presence of any external magnetic field, and the stability of the quantized Hall conductance of e2/h is well-maintained as the film thickness varies across the 2D hybridization limit. With additional quantum confinement, we discover the metal-to-insulator switching between two opposite QAHE states, and reveal the universal QAHE phase diagram in the thin magnetic TI samples. In addition to the uniform magnetic TIs, we further investigate the TI/Cr-doped TI bilayer structures prepared by the modulation-doped growth method. By controlling the magnetic interaction profile, we observe the Dirac hole-mediated ferromagnetism and develop an effective way to manipulate its strength. Besides, the giant spin-orbit torque in such magnetic TI-based heterostructures enables us to demonstrate the current
Magnon Hall effect without Dzyaloshinskii-Moriya interaction.
Owerre, S A
2017-01-25
Topological magnon bands and magnon Hall effect in insulating collinear ferromagnets are induced by the Dzyaloshinskii-Moriya interaction (DMI) even at zero magnetic field. In the geometrically frustrated star lattice, a coplanar/noncollinear [Formula: see text] magnetic ordering may be present due to spin frustration. This magnetic structure, however, does not exhibit topological magnon effects even with DMI in contrast to collinear ferromagnets. We show that a magnetic field applied perpendicular to the star plane induces a non-coplanar spin configuration with nonzero spin scalar chirality, which provides topological effects without the need of DMI. The non-coplanar spin texture originates from the topology of the spin configurations and does not need the presence of DMI or magnetic ordering, which suggests that this phenomenon may be present in the chiral spin liquid phases of frustrated magnetic systems. We propose that these anomalous topological magnon effects can be accessible in polymeric iron (III) acetate-a star-lattice antiferromagnet with both spin frustration and long-range magnetic ordering.
Magnon Hall effect without Dzyaloshinskii-Moriya interaction
NASA Astrophysics Data System (ADS)
Owerre, S. A.
2017-01-01
Topological magnon bands and magnon Hall effect in insulating collinear ferromagnets are induced by the Dzyaloshinskii-Moriya interaction (DMI) even at zero magnetic field. In the geometrically frustrated star lattice, a coplanar/noncollinear \\mathbf{q}=0 magnetic ordering may be present due to spin frustration. This magnetic structure, however, does not exhibit topological magnon effects even with DMI in contrast to collinear ferromagnets. We show that a magnetic field applied perpendicular to the star plane induces a non-coplanar spin configuration with nonzero spin scalar chirality, which provides topological effects without the need of DMI. The non-coplanar spin texture originates from the topology of the spin configurations and does not need the presence of DMI or magnetic ordering, which suggests that this phenomenon may be present in the chiral spin liquid phases of frustrated magnetic systems. We propose that these anomalous topological magnon effects can be accessible in polymeric iron (III) acetate—a star-lattice antiferromagnet with both spin frustration and long-range magnetic ordering.
Size effects and Hall-Petch relation in polycrystalline cobalt
NASA Astrophysics Data System (ADS)
Fleurier, Gwendoline; Hug, Eric; Martinez, Mayerling; Dubos, Pierre-Antoine; Keller, Clément
2015-02-01
The mechanical behaviour of polycrystalline hexagonal close-packed cobalt was investigated over a large range of grain size d in order to examine the occurrence of size effects. Crystallographic texture and amount of face centred cubic allotropic phase were maintained unchanged thanks to appropriate heat treatment procedures. The Hall-Petch (HP) relation exhibits two distinct behaviours from the very beginning of plastic strain levels. The conventional HP law is fulfilled for a number of grains across the thickness t higher than a critical value (t/d)c = 14. For t/d lower than (t/d)c, a multicrystalline regime is evidenced highlighting a strong reduction in flow stress. The high value of (t/d)c is related to the low-stacking fault energy of cobalt in the basal plane. The size effect is predominant in the first work hardening stage where slip mechanisms and stacking faults predominate. In the second stage, driven by mechanical twinning processes, this effect is less sensitive. Finally, the size effect could also affect the end of the elastic stage, in link with nonlinear elasticity mechanisms.
Zhang, Wei; Jungfleisch, Matthias B.; Freimuth, Frank; Jiang, Wanjun; Sklenar, Joseph; Pearson, John E.; Ketterson, John B.; Mokrousov, Yuri; Hoffmann, Axel
2015-10-06
We investigate spin-orbit torques of metallic CuAu-I-type antiferromagnets using spin-torque ferromagnetic resonance tuned by a dc-bias current. The observed spin torques predominantly arise from diffusive transport of spin current generated by the spin Hall effect. We find a growth-orientation dependence of the spin torques by studying epitaxial samples, which may be correlated to the anisotropy of the spin Hall effect. The observed anisotropy is consistent with first-principles calculations on the intrinsic spin Hall effect. Our work suggests large tunable spin-orbit effects in magnetically-ordered materials.
Near-Surface Plasma Characterization of the 12.5-kW NASA TDU1 Hall Thruster
NASA Technical Reports Server (NTRS)
Shastry, Rohit; Huang, Wensheng; Kamhawi, Hani
2015-01-01
To advance the state-of-the-art in Hall thruster technology, NASA is developing a 12.5-kW, high-specific-impulse, high-throughput thruster for the Solar Electric Propulsion Technology Demonstration Mission. In order to meet the demanding lifetime requirements of potential missions such as the Asteroid Redirect Robotic Mission, magnetic shielding was incorporated into the thruster design. Two units of the resulting thruster, called the Hall Effect Rocket with Magnetic Shielding (HERMeS), were fabricated and are presently being characterized. The first of these units, designated the Technology Development Unit 1 (TDU1), has undergone extensive performance and thermal characterization at NASA Glenn Research Center. A preliminary lifetime assessment was conducted by characterizing the degree of magnetic shielding within the thruster. This characterization was accomplished by placing eight flush-mounted Langmuir probes within each discharge channel wall and measuring the local plasma potential and electron temperature at various axial locations. Measured properties indicate a high degree of magnetic shielding across the throttle table, with plasma potential variations along each channel wall being less than or equal to 5 eV and electron temperatures being maintained at less than or equal to 5 eV, even at 800 V discharge voltage near the thruster exit plane. These properties indicate that ion impact energies within the HERMeS will not exceed 26 eV, which is below the expected sputtering threshold energy for boron nitride. Parametric studies that varied the facility backpressure and magnetic field strength at 300 V, 9.4 kW, illustrate that the plasma potential and electron temperature are insensitive to these parameters, with shielding being maintained at facility pressures 3X higher and magnetic field strengths 2.5X higher than nominal conditions. Overall, the preliminary lifetime assessment indicates a high degree of shielding within the HERMeS TDU1, effectively
NASA Astrophysics Data System (ADS)
El Hadri, M. S.; Pirro, P.; Lambert, C.-H.; Bergeard, N.; Petit-Watelot, S.; Hehn, M.; Malinowski, G.; Montaigne, F.; Quessab, Y.; Medapalli, R.; Fullerton, E. E.; Mangin, S.
2016-02-01
We present an experimental study of all-optical helicity-dependent switching (AO-HDS) of ferromagnetic Pt/Co/Pt heterostructures with perpendicular magnetic anisotropy. The sample is patterned into a Hall cross and the AO-HDS is measured via the anomalous Hall effect. This all-electrical probing of the magnetization during AO-HDS enables a statistical quantification of the switching ratio for different laser parameters, such as the threshold power to achieve AO-HDS and the exposure time needed to reach complete switching at a given laser power. We find that the AO-HDS is a cumulative process, a certain number of optical pulses is needed to obtain a full and reproducible helicity-dependent switching. The deterministic switching of the ferromagnetic Pt/Co/Pt Hall cross provides a full "opto-spintronic device," where the remanent magnetization can be all-optically and reproducibly written and erased without the need of an external magnetic field.
Tunnelling anomalous and planar Hall effects (Conference Presentation)
NASA Astrophysics Data System (ADS)
Matos-Abiague, Alex; Scharf, Benedikt; Han, Jong E.; Hankiewicz, Ewelina M.; Zutic, Igor
2016-10-01
We theoretically show how the interplay between spin-orbit coupling (SOC) and magnetism can result in a finite tunneling Hall conductance, transverse to the applied bias. For two-dimensional tunnel junctions with a ferromagnetic lead and magnetization perpendicular to the current flow, the detected anomalous Hall voltage can be used to extract information not only about the spin polarization but also about the strength of the interfacial SOC. In contrast, a tunneling current across a ferromagnetic barrier on the surface of a three-dimensional topological insulator (TI) can induce a planar Hall response even when the magnetization is oriented along the current flow[1]. The tunneling nature of the states contributing to the planar Hall conductance can be switched from the ordinary to the Klein regimes by the electrostatic control of the barrier strength. This allows for an enhancement of the transverse response and a giant Hall angle, with the tunneling planar Hall conductance exceeding the longitudinal component. Despite the simplicity of a single ferromagnetic region, the TI/ferromagnet system exhibits a variety of functionalities. In addition to a spin-valve operation for magnetic sensing and storing information, positive, negative, and negative differential conductances can be tuned by properly adjusting the barrier potential and/or varying the magnetization direction. Such different resistive behaviors in the same system are attractive for potential applications in reconfigurable spintronic devices. [1] B. Scharf, A. Matos-Abiague, J. E. Han, E. M. Hankiewicz, and I. Zutic, arXiv:1601.01009 (2016).
Configuration interaction matrix elements for the quantum Hall effect
NASA Astrophysics Data System (ADS)
Wooten, Rachel; Macek, Joseph
2015-03-01
In the spherical model of the quantum Hall system, the two-body matrix elements and pseudopotentials can be found analytically in terms of a general scalar pair interaction potential by expressing the pair interaction as a weighted sum over Legendre polynomials. For non-infinite systems, only a finite set of terms in the potential expansion contribute to the interactions; the contributing terms define an effective spatial potential for the system. The connection between the effective spatial potential and the pseudopotential is one-to-one for finite systems, and any completely defined model pseudopotential can be analytically inverted to give a unique corresponding spatial potential. This technique of inverting the pseudopotential to derive effective spatial potentials may be of use for developing accurate model spatial potentials for quantum Monte Carlo simulations. We demonstrate the technique and the corresponding spatial potentials for a few example model pseudopotentials. Supported by Office of Basic Energy Sciences, U.S. DOE, Grant DE-FG02-02ER15283 to the University of Tennessee.
Self-Impedance-Matched Hall-Effect Gyrators and Circulators
NASA Astrophysics Data System (ADS)
Bosco, S.; Haupt, F.; DiVincenzo, D. P.
2017-02-01
We present a model study of an alternative implementation of a two-port Hall-effect microwave gyrator. Our setup involves three electrodes, one of which acts as a common ground for the others. Based on the capacitive-coupling model of Viola and DiVincenzo, we analyze the performance of the device and we predict that ideal gyration can be achieved at specific frequencies. Interestingly, the impedance of the three-terminal gyrator can be made arbitrarily small for certain coupling strengths, so that no auxiliary impedance matching is required. Although the bandwidth of the device shrinks as the impedance decreases, it can be improved by reducing the magnetic field; it can be realistically increased up to 150 MHz at 50 Ω by working at the filling factor ν =10 . We also examine the effects of the parasitic capacitive coupling between electrodes and we find that, although, in general, they strongly influence the response of device, their effect is negligible at low impedance. Finally, we analyze an interferometric implementation of a circulator, which incorporates the gyrator in a Mach-Zender-like construction. Perfect circulation in both directions can be achieved, depending on frequency and on the details of the interferometer.
Perceptual significance of seat-dip effect related direct sound coloration in concert halls.
Tahvanainen, Henna; Haapaniemi, Aki; Lokki, Tapio
2017-03-01
In concert halls, the spectrum of direct sound (here 0 to 15 ms) is influenced by the seat-dip effect that causes selective low frequency attenuation. The seat-dip effect has been considered to be detrimental to the acoustic quality of halls, yet there is little evidence about the perceptual significance of the effect. This paper studies the discrimination and preference of seat-dip effect related changes in the direct sound, with realistic auralization of multichannel anechoic orchestra recordings in halls measured with the loudspeaker orchestra. Comparisons are made with a free-field direct sound and direct sound magnitude changes typically associated with the seat-dip effect. Overall, the differences were not significantly audible, except with a subgroup of participants in one out of four halls, and two out of three comparisons. Furthermore, participants' preference for the uncolored direct sound was significant in the halls with less reflected energy, but non-significant in the halls with more reflected energy. The results imply that for most seats in adequately reverberant halls, typical seat-dip effect related coloration in the direct sound can be perceptually negligible.
Sandhu, Adarsh; Kumagai, Yoshimichi; Lapicki, Adam; Sakamoto, Satoshi; Abe, Masanori; Handa, Hiroshi
2007-04-15
Detection of magnetically labeled biomolecules using micro-Hall biosensors is a promising method for monitoring biomolecular recognition processes. The measurement efficiency of standard systems is limited by the time taken for magnetic beads to reach the sensing area of the Hall devices. Here, micro-current lines were integrated with Hall effect structures to manipulate the position of magnetic beads via field gradients generated by localized currents flowing in the current lines. Beads were accumulated onto the sensor surface within seconds of passing currents through the current lines. Real-time detection of magnetic beads using current lines integrated with Hall biosensors was achieved. These results are promising in establishing Hall biosensor platforms as efficient and inexpensive means of monitoring biomolecular reactions for medical applications.
Framing anomaly in the effective theory of the fractional quantum Hall effect.
Gromov, Andrey; Cho, Gil Young; You, Yizhi; Abanov, Alexander G; Fradkin, Eduardo
2015-01-09
We consider the geometric part of the effective action for the fractional quantum Hall effect (FQHE). It is shown that accounting for the framing anomaly of the quantum Chern-Simons theory is essential to obtain the correct gravitational linear response functions. In the lowest order in gradients, the linear response generating functional includes Chern-Simons, Wen-Zee, and gravitational Chern-Simons terms. The latter term has a contribution from the framing anomaly which fixes the value of thermal Hall conductivity and contributes to the Hall viscosity of the FQH states on a sphere. We also discuss the effects of the framing anomaly on linear responses for non-Abelian FQH states.
Large anomalous Hall effect in a non-collinear antiferromagnet at room temperature.
Nakatsuji, Satoru; Kiyohara, Naoki; Higo, Tomoya
2015-11-12
In ferromagnetic conductors, an electric current may induce a transverse voltage drop in zero applied magnetic field: this anomalous Hall effect is observed to be proportional to magnetization, and thus is not usually seen in antiferromagnets in zero field. Recent developments in theory and experiment have provided a framework for understanding the anomalous Hall effect using Berry-phase concepts, and this perspective has led to predictions that, under certain conditions, a large anomalous Hall effect may appear in spin liquids and antiferromagnets without net spin magnetization. Although such a spontaneous Hall effect has now been observed in a spin liquid state, a zero-field anomalous Hall effect has hitherto not been reported for antiferromagnets. Here we report empirical evidence for a large anomalous Hall effect in an antiferromagnet that has vanishingly small magnetization. In particular, we find that Mn3Sn, an antiferromagnet that has a non-collinear 120-degree spin order, exhibits a large anomalous Hall conductivity of around 20 per ohm per centimetre at room temperature and more than 100 per ohm per centimetre at low temperatures, reaching the same order of magnitude as in ferromagnetic metals. Notably, the chiral antiferromagnetic state has a very weak and soft ferromagnetic moment of about 0.002 Bohr magnetons per Mn atom (refs 10, 12), allowing us to switch the sign of the Hall effect with a small magnetic field of around a few hundred oersted. This soft response of the large anomalous Hall effect could be useful for various applications including spintronics--for example, to develop a memory device that produces almost no perturbing stray fields.
Hall effects on the steady structure of the rotational layer at the dayside magnetopause
Westerberg, Lars G.; Aakerstedt, Hans O.
2007-10-15
The influence of the Hall term in the generalized Ohm's law on the large-scale plasma flow during conditions of ongoing magnetic reconnection at the dayside magnetopause (MP) is investigated. Of special interest is the plasma flow behavior during the transition of the MP transition layer as the Hall effect grows in proportion to the viscous-resistive effects. The governing equations are solved approximately by an ordinary perturbation expansion in orders of large Reynolds and Lundqvist numbers. It is shown that the flow pattern is strongly dependent on the magnitude of the Hall parameter; as it approaches zero, the viscous-resistive solution is obtained, while for an ordering of the same magnitude as the resistivity/viscosity, the Hall effect begins to affect the flow structure severely. For an increasing value on the Hall parameter, oscillations are brought into the system, an effect that is enhanced with the magnitude of the Hall parameter. Furthermore, it is shown that as the Hall effect begins to dominate, the transition layer thickens.
Topological edge states and fractional quantum Hall effect from umklapp scattering.
Klinovaja, Jelena; Loss, Daniel
2013-11-08
We study anisotropic lattice strips in the presence of a magnetic field in the quantum Hall effect regime. At specific magnetic fields, causing resonant umklapp scattering, the system is gapped in the bulk and supports chiral edge states in close analogy to topological insulators. In electron gases with stripes, these gaps result in plateaus for the Hall conductivity exactly at the known fillings n/m (both positive integers and m odd) for the integer and fractional quantum Hall effect. For double strips, we find topological phase transitions with phases that support midgap edge states with flat dispersion. The topological effects predicted here could be tested directly in optical lattices.
Quantum anomalous Hall effect in ferromagnetic transition metal halides
NASA Astrophysics Data System (ADS)
Huang, Chengxi; Zhou, Jian; Wu, Haiping; Deng, Kaiming; Jena, Puru; Kan, Erjun
2017-01-01
The quantum anomalous Hall (QAH) effect is a novel topological spintronic phenomenon arising from inherent magnetization and spin-orbit coupling. Various theoretical and experimental efforts have been devoted in search of intrinsic QAH insulators. However, up to now, it has only been observed in Cr or V doped (Bi,Sb ) 2T e3 film in experiments with very low working temperature. Based on the successful synthesis of transition metal halides, we use first-principles calculations to predict that the Ru I3 monolayer is an intrinsic ferromagnetic QAH insulator with a topologically nontrivial global band gap of 11 meV. This topologically nontrivial band gap at the Fermi level is due to its crystal symmetry, thus the QAH effect is robust. Its Curie temperature, estimated to be ˜360 K using Monte Carlo simulation, is above room temperature and higher than most two-dimensional ferromagnetic thin films. The inclusion of Hubbard U in the Ru-d electrons does not affect this result. We also discuss the manipulation of its exchange energy and nontrivial band gap by applying in-plane strain. Our work adds an experimentally feasible member to the QAH insulator family, which is expected to have broad applications in nanoelectronics and spintronics.
Edge states and integer quantum Hall effect in topological insulator thin films
NASA Astrophysics Data System (ADS)
Zhang, Song-Bo; Lu, Hai-Zhou; Shen, Shun-Qing
The integer quantum Hall effect is a topological state of quantum matter in two dimensions, and has recently been observed in three-dimensional topological insulator thin films. In this report, I will talk about the Landau levels and edge states of surface Dirac fermions in topological insulators under a strong magnetic field. We examine the formation of the quantum plateaux of the Hall conductance and find two different patterns, in one pattern the filling number covers all integers while only odd integers in the other. We focus on the quantum plateau closest to zero energy and demonstrate the breakdown of the quantum spin Hall effect as a result of the interplay of magnetic field and structure inversion asymmetry. We also reveal that the edge states exist only for the integer Hall conductance while no edge-state solution can be found for the ''half-integer'' Hall conductance. The addition of top and bottom surface Dirac fermions always form well-defined edge states, and gives an integer quantum Hall effect. This work establishes an intuitive picture of the edge states to understand the integer quantum Hall effect for Dirac electrons in topological insulator thin films.
Comparative study on the performance of five different Hall effect devices.
Paun, Maria-Alexandra; Sallese, Jean-Michel; Kayal, Maher
2013-02-05
Five different Hall Effect sensors were modeled and their performance evaluated using a three dimensional simulator. The physical structure of the implemented sensors reproduces a certain technological fabrication process. Hall voltage, absolute, current-related, voltage-related and power-related sensitivities were obtained for each sensor. The effect of artificial offset was also investigated for cross-like structures. The simulation procedure guides the designer in choosing the Hall cell optimum shape, dimensions and device polarization conditions that would allow the highest performance.
Numerical study of inhomogeneity effects on Hall measurements of graphene films
NASA Astrophysics Data System (ADS)
Lee, Kangmu; Asbeck, Peter
2015-04-01
This paper presents a two-dimensional model calculation of inhomogeneous graphene films which incorporates a random distribution of dopants (leading to electron and hole puddles) for analysis of Hall measurements. The model predicts significant effects of inhomogeneity on the Hall coefficient, which can lead to an underestimate of carrier mobility. We investigate the effect of parameters including size of puddles, local charge density deviation, and device sizes. The inhomogeneity of epitaxial graphene generated by steps and terraces of SiC substrates is also discussed. The simulation results quantify possible statistical errors in Hall mobility measurements, Dirac point estimation and non-uniformity of scaled devices over wafers.
Numerical simulation of the Hall effect in magnetized accretion disks with the Pluto code
NASA Astrophysics Data System (ADS)
Nakhaei, Mohammad; Safaei, Ghasem; Abbassi, Shahram
2014-01-01
We investigate the Hall effect in a standard magnetized accretion disk which is accompanied by dissipation due to viscosity and magnetic resistivity. By considering an initial magnetic field, using the PLUTO code, we perform a numerical magnetohydrodynamic simulation in order to study the effect of Hall diffusion on the physical structure of the disk. Current density and temperature of the disk are significantly modified by Hall diffusion, but the global structure of the disk is not substantially affected. The changes in the current densities and temperature of the disk lead to a modification in the disk luminosity and radiation.
Strong Intrinsic Spin Hall Effect in the TaAs Family of Weyl Semimetals.
Sun, Yan; Zhang, Yang; Felser, Claudia; Yan, Binghai
2016-09-30
Since their discovery, topological insulators are expected to be ideal spintronic materials owing to the spin currents carried by surface states with spin-momentum locking. However, the bulk doping problem remains an obstacle that hinders such an application. In this work, we predict that a newly discovered family of topological materials, the Weyl semimetals, exhibits a large intrinsic spin Hall effect that can be utilized to generate and detect spin currents. Our ab initio calculations reveal a large spin Hall conductivity in the TaAs family of Weyl materials. Considering the low charge conductivity of semimetals, Weyl semimetals are believed to present a larger spin Hall angle (the ratio of the spin Hall conductivity over the charge conductivity) than that of conventional spin Hall systems such as the 4d and 5d transition metals. The spin Hall effect originates intrinsically from the bulk band structure of Weyl semimetals, which exhibit a large Berry curvature and spin-orbit coupling, so the bulk carrier problem in the topological insulators is naturally avoided. Our work not only paves the way for employing Weyl semimetals in spintronics, but also proposes a new guideline for searching for the spin Hall effect in various topological materials.
Strong Intrinsic Spin Hall Effect in the TaAs Family of Weyl Semimetals
NASA Astrophysics Data System (ADS)
Sun, Yan; Zhang, Yang; Felser, Claudia; Yan, Binghai
2016-09-01
Since their discovery, topological insulators are expected to be ideal spintronic materials owing to the spin currents carried by surface states with spin-momentum locking. However, the bulk doping problem remains an obstacle that hinders such an application. In this work, we predict that a newly discovered family of topological materials, the Weyl semimetals, exhibits a large intrinsic spin Hall effect that can be utilized to generate and detect spin currents. Our ab initio calculations reveal a large spin Hall conductivity in the TaAs family of Weyl materials. Considering the low charge conductivity of semimetals, Weyl semimetals are believed to present a larger spin Hall angle (the ratio of the spin Hall conductivity over the charge conductivity) than that of conventional spin Hall systems such as the 4 d and 5 d transition metals. The spin Hall effect originates intrinsically from the bulk band structure of Weyl semimetals, which exhibit a large Berry curvature and spin-orbit coupling, so the bulk carrier problem in the topological insulators is naturally avoided. Our work not only paves the way for employing Weyl semimetals in spintronics, but also proposes a new guideline for searching for the spin Hall effect in various topological materials.
Concepts of ferrovalley material and anomalous valley Hall effect.
Tong, Wen-Yi; Gong, Shi-Jing; Wan, Xiangang; Duan, Chun-Gang
2016-12-16
Valleytronics rooted in the valley degree of freedom is of both theoretical and technological importance as it offers additional opportunities for information storage, as well as electronic, magnetic and optical switches. In analogy to ferroelectric materials with spontaneous charge polarization, or ferromagnetic materials with spontaneous spin polarization, here we introduce a new member of ferroic family, that is, a ferrovalley material with spontaneous valley polarization. Combining a two-band k·p model with first-principles calculations, we show that 2H-VSe2 monolayer, where the spin-orbit coupling coexists with the intrinsic exchange interaction of transition-metal d electrons, is such a room-temperature ferrovalley material. We further predict that such system could demonstrate many distinctive properties, for example, chirality-dependent optical band gap and, more interestingly, anomalous valley Hall effect. On account of the latter, functional devices based on ferrovalley materials, such as valley-based nonvolatile random access memory and valley filter, are contemplated for valleytronic applications.
Hall effect in charged conducting ferroelectric domain walls.
Campbell, M P; McConville, J P V; McQuaid, R G P; Prabhakaran, D; Kumar, A; Gregg, J M
2016-12-12
Enhanced conductivity at specific domain walls in ferroelectrics is now an established phenomenon. Surprisingly, however, little is known about the most fundamental aspects of conduction. Carrier types, densities and mobilities have not been determined and transport mechanisms are still a matter of guesswork. Here we demonstrate that intermittent-contact atomic force microscopy (AFM) can detect the Hall effect in conducting domain walls. Studying YbMnO3 single crystals, we have confirmed that p-type conduction occurs in tail-to-tail charged domain walls. By calibration of the AFM signal, an upper estimate of ∼1 × 10(16) cm(-3) is calculated for the mobile carrier density in the wall, around four orders of magnitude below that required for complete screening of the polar discontinuity. A carrier mobility of∼50 cm(2)V(-1)s(-1) is calculated, about an order of magnitude below equivalent carrier mobilities in p-type silicon, but sufficiently high to preclude carrier-lattice coupling associated with small polarons.
Quasiparticle-mediated spin Hall effect in a superconductor
NASA Astrophysics Data System (ADS)
Wakamura, Taro
Superconductivity often brings novel phenomena to spintronics. According to theoretical predictions, superconductivity may enhance the spin Hall effect (SHE) due to the increase in the resistance of superconducting quasiparticles which mediate spin transport in superconductors. In this work, we show a first experimental observation of quasiparticle-mediated SHE in a superconducting NbN, which exhibits an enormous enhancement below the superconducting critical temperature (TC = 10 K). We fabricated a lateral device structure composed of Py (NiFe) and NbN wires bridged by a nonmagnetic Cu wire. A pure spin current is generated in the Cu bridge by a spin injection current (I) between the Py and the Cu, and absorbed into the NbN wire. The absorbed spin currents are converted into charge currents via the inverse SHE, thereby generating the inverse SH voltage (VISHE) . When NbN is in the normal state at 20 K (>TC) , inverse SH signals ΔRISHE (RISHE ≡VISHE / I) are independent of I. However, at 3 K (
Emergence and mechanism in the fractional quantum Hall effect
NASA Astrophysics Data System (ADS)
Bain, Jonathan
2016-11-01
For some authors, an adequate notion of emergence must include an account of a mechanism by means of which emergent behavior is realized. This appeal to mechanism is problematic in the case of the fractional quantum Hall effect (FQHE). There is a consensus among physicists that the FQHE exhibits emergent phenomena, but there are at least four alternative explanations of the latter that, arguably, appeal to ontologically distinct mechanisms, both at the microphysics level and at the level of general organizing principles. In light of this underdetermination of mechanism, one is faced with the following options: (I) deny that emergence is present in the FQHE; (II) argue for the priority of one mechanistic explanation over the others; or (III) temper the desire for a mechanism-centric account of emergence. I will argue that there are good reasons to reject (I) and (II) and accept (III). In particular, I will suggest that a law-centric account of emergence does just fine in explaining the emergent phenomena associated with the FQHE.
Spin Hall effects in metallic multilayers (Conference Presentation)
NASA Astrophysics Data System (ADS)
Woltersdorf, Georg; Wei, Dahai H.; Obstbaum, Martin; Back, Christian H.; Decker, Martin
2016-10-01
We study the direct as well as the inverse SHE. In the case of the direct SHE a dc charge current is applied in the plane of a ferromagnet/normal metal layer stack and the SHE creates a spin polarization at the surface of the normal metal leading to the injection of a spin current into the ferromagnet. This spin current is absorbed in the ferromagnet and causes a spin transfer torque. Using time and spatially resolved Kerr microscopy we measure the transferred spin momentum and compute the spin Hall angle. In a second set of experiments using identical samples pure spin currents are injected by the spin pumping effect from the ferromagnet into the normal metal. The spin current injected by spin pumping has a large ac component transverse to the static magnetization direction and a very small dc component parallel to the magnetization direction. The inverse SHE converts these spin current into charge current. The corresponding inverse SHE voltages induced by spin pumping at ferromagnetic resonance are measured in permalloy/platinum and permalloy/gold multilayers in various excitation geometries and as a function of frequency in order to separate the contributions of anisotropic magnetoresistance and SHE. In addition, we present experimental evidence for the ac component of inverse SHE voltages generated by spin pumping.
Concepts of ferrovalley material and anomalous valley Hall effect
Tong, Wen-Yi; Gong, Shi-Jing; Wan, Xiangang; Duan, Chun-Gang
2016-01-01
Valleytronics rooted in the valley degree of freedom is of both theoretical and technological importance as it offers additional opportunities for information storage, as well as electronic, magnetic and optical switches. In analogy to ferroelectric materials with spontaneous charge polarization, or ferromagnetic materials with spontaneous spin polarization, here we introduce a new member of ferroic family, that is, a ferrovalley material with spontaneous valley polarization. Combining a two-band k·p model with first-principles calculations, we show that 2H-VSe2 monolayer, where the spin–orbit coupling coexists with the intrinsic exchange interaction of transition-metal d electrons, is such a room-temperature ferrovalley material. We further predict that such system could demonstrate many distinctive properties, for example, chirality-dependent optical band gap and, more interestingly, anomalous valley Hall effect. On account of the latter, functional devices based on ferrovalley materials, such as valley-based nonvolatile random access memory and valley filter, are contemplated for valleytronic applications. PMID:27982088
Quantum transport in graphene Hall bars: Effects of vacancy disorder
NASA Astrophysics Data System (ADS)
Petrović, M. D.; Peeters, F. M.
2016-12-01
Using the tight-binding model, we investigate the influence of vacancy disorder on electrical transport in graphene Hall bars in the presence of quantizing magnetic fields. Disorder, induced by a random distribution of monovacancies, breaks the graphene sublattice symmetry and creates states localized on the vacancies. These states are observable in the bend resistance, as well as in the total DOS. Their energy is proportional to the square root of the magnetic field, while their localization length is proportional to the cyclotron radius. At the energies of these localized states, the electron current flows around the monovacancies and, as we show, it can follow unexpected paths depending on the particular arrangement of vacancies. We study how these localized states change with the vacancy concentration, and what are the effects of including the next-nearest-neighbor hopping term. Our results are also compared with the situation when double vacancies are present in the system. Double vacancies also induce localized states, but their energy and magnetic field dependencies are different. Their localization energy scales linearly with the magnetic field, and their localization length appears not to depend on the field strength.
Hall effect in charged conducting ferroelectric domain walls
Campbell, M. P.; McConville, J.P.V.; McQuaid, R.G.P.; Prabhakaran, D.; Kumar, A.; Gregg, J. M.
2016-01-01
Enhanced conductivity at specific domain walls in ferroelectrics is now an established phenomenon. Surprisingly, however, little is known about the most fundamental aspects of conduction. Carrier types, densities and mobilities have not been determined and transport mechanisms are still a matter of guesswork. Here we demonstrate that intermittent-contact atomic force microscopy (AFM) can detect the Hall effect in conducting domain walls. Studying YbMnO3 single crystals, we have confirmed that p-type conduction occurs in tail-to-tail charged domain walls. By calibration of the AFM signal, an upper estimate of ∼1 × 1016 cm−3 is calculated for the mobile carrier density in the wall, around four orders of magnitude below that required for complete screening of the polar discontinuity. A carrier mobility of∼50 cm2V−1s−1 is calculated, about an order of magnitude below equivalent carrier mobilities in p-type silicon, but sufficiently high to preclude carrier-lattice coupling associated with small polarons. PMID:27941794
Does the Hall Effect Solve the Flux Pileup Saturation Problem?
NASA Technical Reports Server (NTRS)
Dorelli, John C.
2010-01-01
It is well known that magnetic flux pileup can significantly speed up the rate of magnetic reconnection in high Lundquist number resistive MHD,allowing reconnection to proceed at a rate which is insensitive to the plasma resistivity over a wide range of Lundquist number. Hence, pileup is a possible solution to the Sweet-Parker time scale problem. Unfortunately, pileup tends to saturate above a critical value of the Lundquist number, S_c, where the value ofS_c depends on initial and boundary conditions, with Sweet-Parker scaling returning above S_c. It has been argued (see Dorelli and Bim [2003] and Dorelli [2003]) that the Hall effect can allow flux pileup to saturate (when the scale of the current sheet approaches ion inertial scale, di) before the reconnection rate begins to stall. However, the resulting saturated reconnection rate, while insensitive to the plasma resistivity, was found to depend strongly on the di. In this presentation, we revisit the problem of magnetic island coalescence (which is a well known example of flux pileup reconnection), addressing the dependence of the maximum coalescence rate on the ratio of di in the "large island" limit in which the following inequality is always satisfied: l_eta di lambda, where I_eta is the resistive diffusion length and lambda is the island wavelength.
Concepts of ferrovalley material and anomalous valley Hall effect
NASA Astrophysics Data System (ADS)
Tong, Wen-Yi; Gong, Shi-Jing; Wan, Xiangang; Duan, Chun-Gang
2016-12-01
Valleytronics rooted in the valley degree of freedom is of both theoretical and technological importance as it offers additional opportunities for information storage, as well as electronic, magnetic and optical switches. In analogy to ferroelectric materials with spontaneous charge polarization, or ferromagnetic materials with spontaneous spin polarization, here we introduce a new member of ferroic family, that is, a ferrovalley material with spontaneous valley polarization. Combining a two-band k.p model with first-principles calculations, we show that 2H-VSe2 monolayer, where the spin-orbit coupling coexists with the intrinsic exchange interaction of transition-metal d electrons, is such a room-temperature ferrovalley material. We further predict that such system could demonstrate many distinctive properties, for example, chirality-dependent optical band gap and, more interestingly, anomalous valley Hall effect. On account of the latter, functional devices based on ferrovalley materials, such as valley-based nonvolatile random access memory and valley filter, are contemplated for valleytronic applications.
Observation of orbital resonance Hall effect in (TMTSF)2ClO4.
Kobayashi, Kaya; Satsukawa, H; Yamada, J; Terashima, T; Uji, S
2014-03-21
We report the observation of a Hall effect driven by orbital resonance in the quasi-1-dimensional (q1D) organic conductor (TMTSF)2ClO4. Although a conventional Hall effect is not expected in this class of materials due to their reduced dimensionality, we observed a prominent Hall response at certain orientations of the magnetic field B corresponding to lattice vectors of the constituent molecular chains, known as the magic angles (MAs). We show that this Hall effect can be understood as the response of conducting planes generated by an effective locking of the orbital motion of the charge carriers to the MA driven by an electron-trajectory resonance. This phenomenon supports a class of theories describing the rich behavior of MA phenomena in q1D materials based on altered dimensionality. Furthermore, we observed that the effective carrier density of the conducting planes is exponentially suppressed in large B, which indicates possible density wave formation.
Quantum Anomalous Hall Effect in Low-buckled Honeycomb Lattice with In-plane Magnetization
NASA Astrophysics Data System (ADS)
Ren, Yafei; Pan, Hui; Yang, Fei; Li, Xin; Qiao, Zhenhua; Zhenhua Qiao's Group Team; Hui Pan's Group Team
With out-of-plane magnetization, the quantum anomalous Hall effect has been extensively studied in quantum wells and two-dimensional atomic crystal layers. Here, we investigate the possibility of realizing quantum anomalous Hall effect (QAHE) in honeycomb lattices with in-plane magnetization. We show that the QAHE can only occur in low-buckled honeycomb lattice where both intrinsic and intrinsic Rashba spin-orbit coupling appear spontaneously. The extrinsic Rashba spin-orbit coupling is detrimental to this phase. In contrast to the out-of-plane magnetization induced QAHE, the QAHE from in-plane magnetization is achieved in the vicinity of the time reversal symmetric momenta at M points rather than Dirac points. In monolayer case, the QAHE can be characterized by Chern number = +/- 1 whereas additional phases with Chern number = +/- 2 appear in chiral stacked bilayer system. The Chern number strongly depends on the orientation of the magnetization. The bilayer system also provides additional tunability via out-of-plane electric field, which can reduce the critical magnetization strength required to induce QAHE. It can also lead to topological phase transitions from = +/- 2 to +/- 1 and finally to 0 Equal contribution from Yafei Ren and Hui Pan.
Large local Hall effect in pin-hole dominated multigraphene spin-valves.
Muduli, P K; Barzola-Quiquia, J; Dusari, S; Ballestar, A; Bern, F; Böhlmann, W; Esquinazi, P
2013-01-11
We report local and non-local measurements in pin-hole dominated mesoscopic multigraphene spin-valves. Local spin-valve measurements show spurious switching behavior in resistance during magnetic field sweeping similar to the signal observed due to spin injection into multigraphene. The switching behavior has been explained in terms of a local Hall effect due to a thickness irregularity of the tunnel barrier. The local Hall effect appears due to a large local magnetostatic field produced near the roughness in the AlO(x) tunnel barrier. In our samples the resistance change due to the local Hall effect remains negligibly small above 75 K. A strong local Hall effect might hinder spin injection into multigraphene, resulting in no spin signal in non-local measurements.
Investigation of magnetic proximity effect in Ta/YIG bilayer Hall bar structure
Yang, Yumeng; Wu, Baolei; Wu, Yihong; Yao, Kui; Shannigrahi, Santiranjan; Zong, Baoyu
2014-05-07
In this work, the investigation of magnetic proximity effect was extended to Ta which has been reported to have a negative spin Hall angle. Magnetoresistance (MR) and Hall measurements for in-plane and out-of-plane applied magnetic field sweeps were carried out at room temperature. The size of the MR ratio observed (∼10{sup −5}) and its magnetization direction dependence are similar to that reported in Pt/yttrium iron garnet, both of which can be explained by the spin Hall magnetoresistance theory. Additionally, a flip of magnetoresistance polarity is observed at 4 K in the temperature dependent measurements, which can be explained by the magnetic proximity effect induced anisotropic magnetoresistance at low temperature. Our findings suggest that both magnetic proximity effect and spin Hall magnetoresistance have contribution to the recently observed unconventional magnetoresistance effect.
High Performance Power Module for Hall Effect Thrusters
NASA Technical Reports Server (NTRS)
Pinero, Luis R.; Peterson, Peter Y.; Bowers, Glen E.
2002-01-01
Previous efforts to develop power electronics for Hall thruster systems have targeted the 1 to 5 kW power range and an output voltage of approximately 300 V. New Hall thrusters are being developed for higher power, higher specific impulse, and multi-mode operation. These thrusters require up to 50 kW of power and a discharge voltage in excess of 600 V. Modular power supplies can process more power with higher efficiency at the expense of complexity. A 1 kW discharge power module was designed, built and integrated with a Hall thruster. The breadboard module has a power conversion efficiency in excess of 96 percent and weighs only 0.765 kg. This module will be used to develop a kW, multi-kW, and high voltage power processors.
Non-Contact Thermal Characterization of NASA's HERMeS Hall Thruster
NASA Technical Reports Server (NTRS)
Huang, Wensheng; Kamhawi, Hani; Meyers, James L.; Yim, John T.; Neff, Gregory
2015-01-01
The Thermal Characterization Test of NASAs 12.5-kW Hall thruster is being completed. This thruster is being developed to support of a number of potential Solar Electric Propulsion Technology Demonstration Mission concepts, including the Asteroid Redirect Robotic Mission concept. As a part of this test, an infrared-based, non-contact thermal imaging system was developed to measure Hall thruster surfaces that are exposed to high voltage or harsh environment. To increase the accuracy of the measurement, a calibration array was implemented, and a pilot test was performed to determine key design parameters for the calibration array. The raw data is analyzed in conjunction with a simplified thermal model of the channel to account for reflection. The reduced data will be used to refine the thruster thermal model, which is critical to the verification of the thruster thermal specifications. The present paper will give an overview of the decision process that led to identification of the need for a non-contact temperature diagnostic, the development of said diagnostic, the measurement results, and the simplified thermal model of the channel.
Gauge potential formulations of the spin Hall effect in graphene
NASA Astrophysics Data System (ADS)
Dayi, Ömer F.; Yunt, Elif
2011-06-01
Two different gauge potential methods are engaged to calculate explicitly the spin Hall conductivity in graphene. The graphene Hamiltonian with spin-orbit interaction is expressed in terms of kinematic momenta by introducing a gauge potential. A formulation of the spin Hall conductivity is established by requiring that the time evolution of this kinematic momentum vector vanishes. We then calculated the conductivity employing the Berry gauge fields. We show that both of the gauge fields can be deduced from the pure gauge field arising from the Foldy-Wouthuysen transformations.
NASA Astrophysics Data System (ADS)
Yu, H. L.; Jiang, C.; Zhai, Z. Y.
2017-01-01
We investigate numerically the integer quantum Hall effect in a three-band triangular-lattice model. The three bands own the Chern number C=2,-1,-1, respectively. The lowest topological flat band carrying Chern number C=2, which leads to the Hall plateau σH = 2 (e2 / h) . This Hall plateau is sensitive to the disorder scattering and is rapidly destroyed by the weak disorder. Further increasing the strength of disorder, the gap of density of states always disappears before the vanishing of the corresponding Hall plateau. The scaling behavior of quantum phase transition between an insulator and a quantum Hall plateau is studied. We find that the insulator-plateau transition becomes sharper with increasing the size of system. Due to the different of edge states, the critical energy Ec1 gradually shifts to the center of Hall plateau while Ec2 is unaffected with increasing the disorder strength.
Hall effect sensors embedded within two-pole toothless stator assembly
NASA Technical Reports Server (NTRS)
Denk, Joseph (Inventor); Grant, Richard J. (Inventor)
1994-01-01
A two-pole toothless PM machine employs Hall effect sensors to indicate the position of the machine's rotor relative to power windings in the machine's stator. The Hall effect sensors are located in the main magnetic air gap underneath the power windings. The main magnetic air gap is defined by an outer magnetic surface of the rotor and an inner surface of the stator's flux collector ring.
Giant spin-Hall effect induced by the Zeeman interaction in graphene.
Abanin, D A; Gorbachev, R V; Novoselov, K S; Geim, A K; Levitov, L S
2011-08-26
We propose a new approach to generate and detect spin currents in graphene, based on a large spin-Hall response arising near the neutrality point in the presence of an external magnetic field. Spin currents result from the imbalance of the Hall resistivity for the spin-up and spin-down carriers induced by the Zeeman interaction, and do not involve a spin-orbit interaction. Large values of the spin-Hall response achievable in moderate magnetic fields produced by on-chip sources, and up to room temperature, make the effect viable for spintronics applications.
Electrical detection of magnetic domain walls by inverse and direct spin Hall effect
NASA Astrophysics Data System (ADS)
Pham, V. T.; Zahnd, G.; Marty, A.; Savero Torres, W.; Jamet, M.; Noël, P.; Vila, L.; Attané, J. P.
2016-11-01
Domain wall (DW) detection is a prerequisite to perform current-induced DW motion. In this letter, we demonstrate a detection method, based on the ability for a ferromagnetic nanowire, in which a DW is pinned, to inject or detect a pure spin current. The device consists of such a ferromagnetic nanowire in contact with an orthogonal spin Hall effect (SHE) nanowire. When a current flows along the ferromagnetic nanowire, and provided a DW is pinned, the pure spin current is transformed into a transverse voltage by inverse spin Hall effect (ISHE). In the reciprocal configuration, the pure spin current created by the direct SHE, generates a transverse voltage along the ferromagnetic wire. Finite element method (FEM) simulations allow estimating the Pt spin Hall angle (SHA) (7.5 ± 0.5%). This technique provides an electrical way to study the DW motion, a device akin to the ferromagnetic/spin Hall effect bilayers typically used for spin-orbit torques experiments.
Ferromagnetic/Nonmagnetic Nanostructures for the Electrical Measurement of the Spin Hall Effect.
Pham, Van Tuong; Vila, Laurent; Zahnd, Gilles; Marty, Alain; Savero-Torres, Williams; Jamet, Matthieu; Attané, Jean-Philippe
2016-11-09
Spin-orbitronics is based on the ability of spin-orbit interactions to achieve the conversion between charge currents and pure spin currents. As the precise evaluation of the conversion efficiency becomes a crucial issue, the need for straightforward ways to observe this conversion has emerged as one of the main challenges in spintronics. Here, we propose a simple device, akin to the ferromagnetic/nonmagnetic bilayers used in most spin-orbit torques experiments, and consisting of a spin Hall effect wire connected to two transverse ferromagnetic electrodes. We show that this system allows probing electrically the direct and inverse conversion in a spin Hall effect system and measuring both the spin Hall angle and the spin diffusion length. By applying this method to several spin Hall effect materials (Pt, Pd, Au, Ta, W), we show that it represents a promising tool for the metrology of spin-orbit materials.
Hall effect and magnetoresistivity in the ternary molybdenum sulfides
NASA Technical Reports Server (NTRS)
Woollam, J. A.; Haugland, E. J.; Alterovitz, S. A.
1978-01-01
The Hall coefficient and magnetoresistance of sputtered films of Cu(x)Mo6S8 and PbMo6S8 have been measured, as well as the magnetoresistance in sintered samples of the same materials. Assuming a single band model, net carrier densities and mean mobilities are determined
Hysteresis in the anomalous Hall effect of MnAs thin films
NASA Astrophysics Data System (ADS)
Jaeckel, Felix T.; Stintz, Andreas; El-Emawy, Abdel-Rahman A.; Malloy, Kevin J.
2008-03-01
We report detailed measurements of the Hall effect in MBE-grown MnAs thin films on (001)-GaAs as a function of temperature. Hysteresis of the Hall resistivity is observed for temperatures between 300 and 355 K. Non-linear behavior of the Hall resistivity persists up to 390 K. The appearance of hysteresis at low temperatures can be explained by the emergence of stable, out-of-plane domains due to the shape anisotropy of the contracting α-phase. However, the persistence of the hysteresis and the anomalous Hall effect at temperatures significantly above 318 K is not consistent with the complete transformation of the α-phase and introduces new questions about the magnetic properties of the β-phase.
Metallization and Hall-effect of Mg{sub 2}Ge under high pressure
Li, Yuqiang; Gao, Yang; Han, Yonghao Liu, Cailong; Peng, Gang; Ke, Feng; Gao, Chunxiao; Wang, Qinglin; Ma, Yanzhang
2015-10-05
The electrical transport properties of Mg{sub 2}Ge under high pressure were studied with the in situ temperature-dependent resistivity and Hall-effect measurements. The theoretically predicted metallization of Mg{sub 2}Ge was definitely found around 7.4 GPa by the temperature-dependent resistivity measurement. Other two pressure-induced structural phase transitions were also reflected by the measurements. Hall-effect measurement showed that the dominant charge carrier in the metallic Mg{sub 2}Ge was hole, indicating the “bad metal” nature of Mg{sub 2}Ge. The Hall mobility and charge carrier concentration results pointed out that the electrical transport behavior in the antifluorite phase was controlled by the increase quantity of drifting electrons under high pressure, but in both anticotunnite and Ni{sub 2}In-type phases it was governed by the Hall mobility.
Berry curvature induced nonlinear Hall effect in time-reversal invariant materials
NASA Astrophysics Data System (ADS)
Sodemann, Inti; Fu, Liang
2015-03-01
It is well-known that a non-vanishing Hall conductivity requires time-reversal symmetry breaking. However, in this work, we demonstrate that a Hall-like transverse current can occur in second-order response to an external electric field in a wide class of time-reversal invariant and inversion breaking materials. This nonlinear Hall effect arises from the dipole moment of the Berry curvature in momentum space, which generates a net anomalous velocity when the system is in a current-carrying state. We show that the nonlinear Hall coefficient is a rank-two pseudo-tensor, whose form is determined by point group symmetry. We will describe the optimal conditions and candidate materials to observe this effect. IS is supported by the Pappalardo Fellowship in Physics. LF is supported by DOE Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-SC0010526.
Understanding the physics of a possible non-Abelian fractional quantum hall effect state.
Pan, Wei; Crawford, Matthew; Tallakulam, Madhu; Ross, Anthony Joseph, III
2010-10-01
We wish to present in this report experimental results from a one-year Senior Council Tier-1 LDRD project that focused on understanding the physics of a possible non-Abelian fractional quantum Hall effect state. We first give a general introduction to the quantum Hall effect, and then present the experimental results on the edge-state transport in a special fractional quantum Hall effect state at Landau level filling {nu} = 5/2 - a possible non-Abelian quantum Hall state. This state has been at the center of current basic research due to its potential applications in fault-resistant topological quantum computation. We will also describe the semiconductor 'Hall-bar' devices we used in this project. Electron physics in low dimensional systems has been one of the most exciting fields in condensed matter physics for many years. This is especially true of quantum Hall effect (QHE) physics, which has seen its intellectual wealth applied in and has influenced many seemingly unrelated fields, such as the black hole physics, where a fractional QHE-like phase has been identified. Two Nobel prizes have been awarded for discoveries of quantum Hall effects: in 1985 to von Klitzing for the discovery of integer QHE, and in 1998 to Tsui, Stormer, and Laughlin for the discovery of fractional QHE. Today, QH physics remains one of the most vibrant research fields, and many unexpected novel quantum states continue to be discovered and to surprise us, such as utilizing an exotic, non-Abelian FQHE state at {nu} = 5/2 for fault resistant topological computation. Below we give a briefly introduction of the quantum Hall physics.
The Quantum Spin Hall Effect: Theory and Experiment
Konig, Markus; Buhmann, Hartmut; Molenkamp, Laurens W.; Hughes, Taylor L.; Liu, Chao-Xing; Qi, Xiao-Liang; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.
2010-03-19
The search for topologically non-trivial states of matter has become an important goal for condensed matter physics. Recently, a new class of topological insulators has been proposed. These topological insulators have an insulating gap in the bulk, but have topologically protected edge states due to the time reversal symmetry. In two dimensions the helical edge states give rise to the quantum spin Hall (QSH) effect, in the absence of any external magnetic field. Here we review a recent theory which predicts that the QSH state can be realized in HgTe/CdTe semiconductor quantum wells. By varying the thickness of the quantum well, the band structure changes from a normal to an 'inverted' type at a critical thickness d{sub c}. We present an analytical solution of the helical edge states and explicitly demonstrate their topological stability. We also review the recent experimental observation of the QSH state in HgTe/(Hg,Cd)Te quantum wells. We review both the fabrication of the sample and the experimental setup. For thin quantum wells with well width d{sub QW} < 6.3 nm, the insulating regime shows the conventional behavior of vanishingly small conductance at low temperature. However, for thicker quantum wells (d{sub QW} > 6.3 nm), the nominally insulating regime shows a plateau of residual conductance close to 2e{sup 2}/h. The residual conductance is independent of the sample width, indicating that it is caused by edge states. Furthermore, the residual conductance is destroyed by a small external magnetic field. The quantum phase transition at the critical thickness, d{sub c} = 6.3 nm, is also independently determined from the occurrence of a magnetic field induced insulator to metal transition.
Giant planar Hall effect in epitaxial (Ga,Mn)as devices.
Tang, H X; Kawakami, R K; Awschalom, D D; Roukes, M L
2003-03-14
Large Hall resistance jumps are observed in microdevices patterned from epitaxial (Ga,Mn)As layers when subjected to a swept, in-plane magnetic field. This giant planar Hall effect is 4 orders of magnitude greater than previously observed in metallic ferromagnets. This enables extremely sensitive measurements of the angle-dependent magnetic properties of (Ga,Mn)As. The magnetic anisotropy fields deduced from these measurements are compared with theoretical predictions.
Temperature-dependent nonlinear Hall effect in macroscopic Si-MOS antidot array
NASA Astrophysics Data System (ADS)
Kuntsevich, A. Yu.; Shupletsov, A. V.; Nunuparov, M. S.
2016-05-01
By measuring magnetoresistance and the Hall effect in a classically moderate perpendicular magnetic field in a Si-MOSFET-type macroscopic antidot array, we found a nonlinear with field, temperature- and density-dependent Hall resistivity. We argue that this nonlinearity originates from low mobility shells of the antidots with a strong temperature dependence of the resistivity and suggest a qualitative explanation of the phenomenon.
Spin cloud induced around an elastic scatterer by the intrinsic spin hall effect.
Mal'shukov, A G; Chu, C S
2006-08-18
Similar to the Landauer electric dipole created around an impurity by the electric current, a spin polarized cloud of electrons can be induced by the intrinsic spin Hall effect near a spin independent elastic scatterer. It is shown that in the ballistic range around the impurity, such a cloud appears in the case of Rashba spin-orbit interaction, even though the bulk spin Hall current is absent.
Zhou, Jian; Sun, Qiang; Wang, Qian; Kawazoe, Yoshiyuki; Jena, Puru
2016-06-07
Exploring a two-dimensional intrinsic quantum spin Hall state with a large band gap as well as an anomalous Hall state in realizable materials is one of the most fundamental and important goals for future applications in spintronics, valleytronics, and quantum computing. Here, by combining first-principles calculations with a tight-binding model, we predict that Sb or Bi can epitaxially grow on a stable and ferromagnetic MnO2 thin film substrate, forming a flat honeycomb sheet. The flatness of Sb or Bi provides an opportunity for the existence of Dirac points in the Brillouin zone, with its position effectively tuned by surface hydrogenation. The Dirac points in spin up and spin down channels split due to the proximity effects induced by MnO2. In the presence of both intrinsic and Rashba spin-orbit coupling, we find two band gaps exhibiting a large band gap quantum spin Hall state and a nearly quantized anomalous Hall state which can be tuned by adjusting the Fermi level. Our findings provide an efficient way to realize both quantized intrinsic spin Hall conductivity and anomalous Hall conductivity in a single material.
Quantum anomalous Hall effect in magnetically doped InAs/GaSb quantum wells.
Wang, Qing-Ze; Liu, Xin; Zhang, Hai-Jun; Samarth, Nitin; Zhang, Shou-Cheng; Liu, Chao-Xing
2014-10-03
The quantum anomalous Hall effect has recently been observed experimentally in thin films of Cr-doped (Bi,Sb)(2)Te(3) at a low temperature (∼ 30 mK). In this work, we propose realizing the quantum anomalous Hall effect in more conventional diluted magnetic semiconductors with magnetically doped InAs/GaSb type-II quantum wells. Based on a four-band model, we find an enhancement of the Curie temperature of ferromagnetism due to band edge singularities in the inverted regime of InAs/GaSb quantum wells. Below the Curie temperature, the quantum anomalous Hall effect is confirmed by the direct calculation of Hall conductance. The parameter regime for the quantum anomalous Hall phase is identified based on the eight-band Kane model. The high sample quality and strong exchange coupling make magnetically doped InAs/GaSb quantum wells good candidates for realizing the quantum anomalous Hall insulator at a high temperature.
Anomalous Hall effect sensors based on magnetic element doped topological insulator thin films
NASA Astrophysics Data System (ADS)
Ni, Yan; Zhang, Zhen; Nlebedim, Ikenna; Jiles, David
Anomalous Hall effect (AHE) is recently discovered in magnetic element doped topological insulators (TIs), which promises low power consumption highly efficient spintronics and electronics. This discovery broaden the family of Hall effect (HE) sensors. In this work, both HE and AHE sensor based on Mn and Cr doped Bi2Te3 TI thin films will be systematically studied. The influence of Mn concentration on sensitivity of MnxBi2-xTe3 HE sensors will be discussed. The Hall sensitivity increase 8 times caused by quantum AHE will be reported. AHE senor based on Cr-doped Bi2Te3 TI thin films will also be studied and compared with Mn doped Bi2Te3 AHE sensor. The influence of thickness on sensitivity of CrxBi2-xTe3 AHE sensors will be discussed. Ultrahigh Hall sensitivity is obtained in Cr doped Bi2Te3. The largest Hall sensitivity can reach 2620 Ω/T in sensor which is almost twice higher than that of the normal semiconductor HE sensor. Our work indicates that magnetic element doped topological insulator with AHE are good candidates for ultra-sensitive Hall effect sensors.
Edge waves in plates with resonators: an elastic analogue of the quantum valley Hall effect
NASA Astrophysics Data System (ADS)
Pal, Raj Kumar; Ruzzene, Massimo
2017-02-01
We investigate elastic periodic structures characterized by topologically nontrivial bandgaps supporting backscattering suppressed edge waves. These edge waves are topologically protected and are obtained by breaking inversion symmetry within the unit cell. Examples for discrete one and two-dimensional lattices elucidate the concept and illustrate parallels with the quantum valley Hall effect. The concept is implemented on an elastic plate featuring an array of resonators arranged according to a hexagonal topology. The resulting continuous structures have non-trivial bandgaps supporting edge waves at the interface between two media with different topological invariants. The topological properties of the considered configurations are predicted by unit cell and finite strip dispersion analyses. Numerical simulations demonstrate edge wave propagation for excitation at frequencies belonging to the bulk bandgaps. The considered plate configurations define a framework for the implementation of topological concepts on continuous elastic structures of potential engineering relevance.
Electronic Transport and Quantum Hall Effect in Bipolar Graphene p-n-p Junctions
NASA Astrophysics Data System (ADS)
Özyilmaz, Barbaros; Jarillo-Herrero, Pablo; Efetov, Dmitri; Abanin, Dmitry A.; Levitov, Leonid S.; Kim, Philip
2007-10-01
We have developed a device fabrication process to pattern graphene into nanostructures of arbitrary shape and control their electronic properties using local electrostatic gates. Electronic transport measurements have been used to characterize locally gated bipolar graphene p-n-p junctions. We observe a series of fractional quantum Hall conductance plateaus at high magnetic fields as the local charge density is varied in the p and n regions. These fractional plateaus, originating from chiral edge states equilibration at the p-n interfaces, exhibit sensitivity to interedge backscattering which is found to be strong for some of the plateaus and much weaker for other plateaus. We use this effect to explore the role of backscattering and estimate disorder strength in our graphene devices.
Effect of Background Pressure on the Plasma Oscillation Characteristics of the HiVHAc Hall Thruster
NASA Technical Reports Server (NTRS)
Huang, Wensheng; Kamhawi, Hani; Lobbia, Robert B.; Brown, Daniel L.
2014-01-01
During a component compatibility test of the NASA HiVHAc Hall thruster, a number of plasma diagnostics were implemented to study the effect of varying facility background pressure on thruster operation. These diagnostics characterized the thruster performance, the plume, and the plasma oscillations in the thruster. Thruster performance and plume characteristics as functions of background pressure were previously published. This paper focuses on changes in the plasma oscillation characteristics with changing background pressure. The diagnostics used to study plasma oscillations include a high-speed camera and a set of high-speed Langmuir probes. The results show a rise in the oscillation frequency of the "breathing" mode with rising background pressure, which is hypothesized to be due to a shortening acceleration/ionization zone. An attempt is made to apply a simplified ingestion model to the data. The combined results are used to estimate the maximum acceptable background pressure for performance and wear testing.
Spin Hall Effect and Origins of Nonlocal Resistance in Adatom-Decorated Graphene.
Van Tuan, D; Marmolejo-Tejada, J M; Waintal, X; Nikolić, B K; Valenzuela, S O; Roche, S
2016-10-21
Recent experiments reporting an unexpectedly large spin Hall effect (SHE) in graphene decorated with adatoms have raised a fierce controversy. We apply numerically exact Kubo and Landauer-Büttiker formulas to realistic models of gold-decorated disordered graphene (including adatom clustering) to obtain the spin Hall conductivity and spin Hall angle, as well as the nonlocal resistance as a quantity accessible to experiments. Large spin Hall angles of ∼0.1 are obtained at zero temperature, but their dependence on adatom clustering differs from the predictions of semiclassical transport theories. Furthermore, we find multiple background contributions to the nonlocal resistance, some of which are unrelated to the SHE or any other spin-dependent origin, as well as a strong suppression of the SHE at room temperature. This motivates us to design a multiterminal graphene geometry which suppresses these background contributions and could, therefore, quantify the upper limit for spin-current generation in two-dimensional materials.
Robust fractional quantum Hall effect in the N=2 Landau level in bilayer graphene.
Diankov, Georgi; Liang, Chi-Te; Amet, François; Gallagher, Patrick; Lee, Menyoung; Bestwick, Andrew J; Tharratt, Kevin; Coniglio, William; Jaroszynski, Jan; Watanabe, Kenji; Taniguchi, Takashi; Goldhaber-Gordon, David
2016-12-21
The fractional quantum Hall effect is a canonical example of electron-electron interactions producing new ground states in many-body systems. Most fractional quantum Hall studies have focussed on the lowest Landau level, whose fractional states are successfully explained by the composite fermion model. In the widely studied GaAs-based system, the composite fermion picture is thought to become unstable for the N≥2 Landau level, where competing many-body phases have been observed. Here we report magneto-resistance measurements of fractional quantum Hall states in the N=2 Landau level (filling factors 4<|ν|<8) in bilayer graphene. In contrast with recent observations of particle-hole asymmetry in the N=0/N=1 Landau levels of bilayer graphene, the fractional quantum Hall states we observe in the N=2 Landau level obey particle-hole symmetry within the fully symmetry-broken Landau level. Possible alternative ground states other than the composite fermions are discussed.
Robust fractional quantum Hall effect in the N=2 Landau level in bilayer graphene
NASA Astrophysics Data System (ADS)
Diankov, Georgi; Liang, Chi-Te; Amet, François; Gallagher, Patrick; Lee, Menyoung; Bestwick, Andrew J.; Tharratt, Kevin; Coniglio, William; Jaroszynski, Jan; Watanabe, Kenji; Taniguchi, Takashi; Goldhaber-Gordon, David
2016-12-01
The fractional quantum Hall effect is a canonical example of electron-electron interactions producing new ground states in many-body systems. Most fractional quantum Hall studies have focussed on the lowest Landau level, whose fractional states are successfully explained by the composite fermion model. In the widely studied GaAs-based system, the composite fermion picture is thought to become unstable for the N≥2 Landau level, where competing many-body phases have been observed. Here we report magneto-resistance measurements of fractional quantum Hall states in the N=2 Landau level (filling factors 4<|ν|<8) in bilayer graphene. In contrast with recent observations of particle-hole asymmetry in the N=0/N=1 Landau levels of bilayer graphene, the fractional quantum Hall states we observe in the N=2 Landau level obey particle-hole symmetry within the fully symmetry-broken Landau level. Possible alternative ground states other than the composite fermions are discussed.
Doping and Hall effect in SrTiO3
NASA Astrophysics Data System (ADS)
Stemmer, Susanne
2015-03-01
Electron-doped SrTiO3 has generated renewed interest because of reports of coexisting magnetism and superconductivity, and of superconducting transitions at extremely low carrier densities. In this talk, we will present new insights into doping and its electronic structure obtained using very high quality SrTiO3 films grown by molecular beam epitaxy. We discuss the arrangements and imaging of individual La dopant atoms and clusters using quantitative scanning transmission electron microscopy. We present studies of the temperature dependence of the Hall coefficient, Hall mobility, and of Shubnikov-de Haas oscillations. We will particularly discuss the significance of the regime in which the resistance follows a T2 temperature-dependence over a wide range of temperatures and doping. This work was performed in collaboration with Evgeny Mikheev, Adam Kajdos, Jinwoo Hwang, Jack Zhang, and Jim Allen.
Bilayer-induced asymmetric quantum Hall effect in epitaxial graphene
NASA Astrophysics Data System (ADS)
Iagallo, Andrea; Tanabe, Shinichi; Roddaro, Stefano; Takamura, Makoto; Sekine, Yoshiaki; Hibino, Hiroki; Miseikis, Vaidotas; Coletti, Camilla; Piazza, Vincenzo; Beltram, Fabio; Heun, Stefan
2015-05-01
The transport properties of epitaxial graphene on SiC(0001) at quantizing magnetic fields are investigated. Devices patterned perpendicularly to SiC terraces clearly exhibit bilayer inclusions distributed along the substrate step edges. We show that the transport properties in the quantum Hall regime are heavily affected by the presence of bilayer inclusions, and observe a significant departure from the conventional quantum Hall characteristics. In particular, we observe anomalous values of the quantized resistance and a peculiar asymmetry with magnetic field which was not observed before for graphene on SiC. A quantitative model involving enhanced inter-channel scattering mediated by the presence of bilayer inclusions is presented that successfully explains the observed symmetry properties.
Quantum Hall Effect in Bernal-stacked tetralayer graphene
NASA Astrophysics Data System (ADS)
Shi, Yanmeng; Che, Shi; Espiritu, Timothy; Pi, Ziqi; Taniguchi, Takashi; Watanabe, Kenji; Lau, Chun Ning
Bernal-stacked few layer graphene is of particular interest due to its unique tunable band structure. Here we study the electric transport of Bernal-stack tetralayer graphene that are encapsulated by boron nitride sheets. The device shows a clear Landau fan with multiple Landau level crossing features. We will present the dependence of its quantum Hall properties on electric and magnetic fields, and compare with theoretical calculations.
Josephson effect without superconductivity: realization in quantum Hall bilayers.
Fogler, M M; Wilczek, F
2001-02-26
We show that a quantum Hall bilayer with the total filling nu = 1 should exhibit a dynamical regime similar to the flux flow in large Josephson junctions. This analogy may explain a conspicuous peak in the interlayer tunneling conductance [Phys. Rev. Lett. 84, 5808 (2000)]. The flux flow is likely to be spatiotemporally chaotic at low-bias voltage, which will manifest itself through broadband noise. The peak position can be controlled by an in-plane magnetic field.
A general method to measure the Hall effect in nanowires: examples of FeS2 and MnSi.
DeGrave, John P; Liang, Dong; Jin, Song
2013-06-12
We present a general methodology for measuring the Hall effect on nanostructures with one-dimensional (1D) nanowire morphology. Relying only on typical e-beam lithography, the methodology developed herein utilizes an angled electrode evaporation technique so that the nanowire itself is a shadow mask and an intimate sidewall contact can be formed for the Hall electrodes. A six-contact electrode scheme with offset transverse contacts is utilized that allows monitoring of both the longitudinal resistivity and the Hall resistivity which is extracted from the raw voltage from the transverse electrodes using an antisymmetrization procedure. Our method does not require the use of a highly engineered lithographic process to produce directly opposing Hall electrodes with a very small gap. Hall effect measurements on semiconducting iron pyrite (FeS2) nanowire devices are validated by comparing to Hall effect measurements in the conventional Hall geometry using FeS2 plate devices. This Hall effect measurement is further extended to MnSi nanowires, and the distinct anomalous Hall effect signature is identified for the first time in chiral magnetic MnSi nanowires, a significant step toward identifying the topological Hall effect due to skyrmions in chiral magnetic nanowires.
Anomalous Hall effect studies on Tb-Fe thin films
NASA Astrophysics Data System (ADS)
Rajasekhar, P.; Deepak Kumar, K.; Markandeyulu, G.
2016-08-01
Tbx Fe100-x (with x=11, 25, 31 and 44) thin films were prepared with the substrates kept at a temperature of 300 °C and the Hall resistivities and electrical resistivities were investigated in the temperature range 25-300 K. The sign of Hall resistivity is found to change from positive for x=31 to negative for x=44 film at temperatures 25 K and 300 K, reflecting the compensation of Tb and Fe magnetic moments between these two compositions. Perpendicular magnetic anisotropy was observed in the films of x=25 and 31 at 25 K as well as at 300 K. The Hall resistivity is seen to increase for the films of x=11 and 31 with increasing temperature, while it decreases for the films of x=25 and 44 with increasing temperature. The temperature coefficients of electrical resistivities of these films are seen to be positive. The presence of perpendicular magnetic anisotropy (refers to magnetic anisotropy, in this paper) in the temperature range 25-300 K in Tb25Fe75 and Tb31Fe69 and their metallic nature are indicators that the Tb-Fe films deposited at higher temperatures are more suitable for magneto optic data storage applications than their amorphous counterparts, due to the stability of the former.
Sekine, Akihiko; Nomura, Kentaro
2016-03-04
We search for dynamical magnetoelectric phenomena in three-dimensional correlated systems with spin-orbit coupling. We focus on the antiferromagnetic insulator phases where the dynamical axion field is realized by the fluctuation of the antiferromagnetic order parameter. It is shown that the dynamical chiral magnetic effect, an alternating current generation by magnetic fields, emerges due to such time dependences of the order parameter as antiferromagnetic resonance. It is also shown that the anomalous Hall effect arises due to such spatial variations of the order parameter as antiferromagnetic domain walls. Our study indicates that spin excitations in antiferromagnetic insulators with spin-orbit coupling can result in nontrivial charge responses. Moreover, observing the chiral magnetic effect and anomalous Hall effect in our system is equivalent to detecting the dynamical axion field in condensed matter.
Effects of Hall electric fields on the saturation of forced antiparallel magnetic field merging
NASA Astrophysics Data System (ADS)
Dorelli, John C.
2003-08-01
The role of Hall electric fields in flux pile-up antiparallel magnetic field merging is addressed. Analytical solutions of the resistive Hall magnetohydrodynamics (Hall-MHD) equations are obtained, describing stagnation point flows in a thin current sheet. The stagnation point flow solutions explain a number of interesting effects observed in two-dimensional resistive Hall-MHD simulations of forced magnetic reconnection. In particular, when Hall electric fields are important within the current sheet, less pile-up of magnetic energy is required upstream of the current sheet to support a given reconnection electric field. Fast electron flows transport magnetic flux into the diffusion layer without requiring a compensating drop in plasma pressure upstream of the current sheet. The maximum flux pile-up merging rate allowed by the external plasma pressure becomes independent of the Lundquist number, scaling like the square root of the ratio of the ion inertial length to the spatial scale of the stagnation point flow. Thus, Hall electric fields provide a possible solution to the problem of flux pile-up saturation in two-dimensional, resistive MHD models of forced magnetic reconnection.
Doping dependent nonlinear Hall effect in SmFeAsO(1-x)F(x).
Riggs, Scott C; McDonald, R D; Kemper, J B; Stegen, Z; Boebinger, G S; Balakirev, F F; Kohama, Y; Migliori, A; Chen, H; Liu, R H; Chen, X H
2009-10-14
We report the Hall resistivity, ρ(xy), of polycrystalline SmFeAsO(1-x)F(x) for four different fluorine concentrations from the onset of superconductivity through the collapse of the structural phase transition. For the two more highly doped samples, ρ(xy) is linear in magnetic field up to 50 T with only weak temperature dependence, reminiscent of a simple Fermi liquid. For the lightly doped samples with x<0.15, we find a low temperature regime characterized as ρ(xy)(H) being both nonlinear in magnetic field and strongly temperature-dependent even though the Hall angle is small. The onset temperature for this nonlinear regime is in the vicinity of the structural phase (SPT)/magnetic ordering (MO) transitions. The temperature dependence of the Hall resistivity is consistent with a thermal activation of carriers across an energy gap. The evolution of the energy gap with doping is reported.
NASA Astrophysics Data System (ADS)
Deng, Ming-Xun; Luo, Wei; Deng, W. Y.; Chen, M. N.; Sheng, L.; Xing, D. Y.
2016-12-01
We investigate the anomalous Hall effect (AHE) on the surface of a topological insulator induced by a finite concentration of magnetic impurities, and find topologically nontrivial and trivial mechanisms simultaneously contributing to the Hall conductivity. In the topologically nontrivial mechanism, the impurities gap the surface spectrum and result in a half-integer quantized intrinsic Hall conductivity in units e2/h , while in the topologically trivial mechanism, the half-integer quantized plateau is modified by impurity-induced localized states via a gap-filling process. The nonmagnetic charge potential itself, though participating in the gap-filling process, cannot induce the AHE. In the presence of a finite magnetic potential, the charge potential would destroy the symmetric distribution of the Hall conductivity by redistributing the localized levels. More interestingly, the sign of the Hall conductivity is tunable by changing the strength of the charge potential.
Hall Effect on Thermal Instability of Viscoelastic Dusty Fluid in Porous Medium
NASA Astrophysics Data System (ADS)
Singh, M.; Gupta, R. K.
2013-08-01
The effect of Hall currents and suspended dusty particles on the hydromagnetic stability of a compressible, electrically conducting Rivlin-Ericksen elastico viscous fluid in a porous medium is considered. Following the linearized stability theory and normal mode analysis the dispersion relation is obtained. For the case of stationary convection, Hall currents and suspended particles are found to have destabilizing effects whereas compressibility and magnetic field have stabilizing effects on the system. The medium permeability, however, has stabilizing and destabilizing effects on thermal instability in contrast to its destabilizing effect in the absence of the magnetic field. The critical Rayleigh numbers and the wave numbers of the associated disturbances for the onset of instability as stationary convection are obtained and the behavior of various parameters on critical thermal Rayleigh numbers are depicted graphically. The magnetic field, Hall currents and viscoelasticity parameter are found to introduce oscillatory modes in the systems, which did not exist in the absence of these parameters
NASA Astrophysics Data System (ADS)
Meng, K. K.; Miao, J.; Xu, X. G.; Wu, Y.; Zhao, X. P.; Zhao, J. H.; Jiang, Y.
2016-12-01
We report systematic measurements of anomalous Hall effect (AHE) and spin-orbit torques (SOTs) in MnGa/IrMn films, in which a single L 10-MnGa epitaxial layer reveals obvious orbital two-channel Kondo (2CK) effect. As increasing the thickness of the antiferromagnet IrMn, the strong spin Hall effect (SHE) has gradually suppressed the orbital 2CK effect and modified the AHE of MnGa. A scaling involving multiple competing scattering mechanisms has been used to distinguish different contributions to the modified AHE. Finally, the sizeable SOT in the MnGa/IrMn films induced by the strong SHE of IrMn have been investigated. The IrMn layer also supplies an in-plane exchange bias field and enables nearly field-free magnetization reversal.
Extraordinary Hall effect in Kondo-type systems: Contributions from anomalous velocity
NASA Astrophysics Data System (ADS)
Levy, P. M.
1988-10-01
Kondo systems exhibit a relatively large extraordinary Hall effect which is due to asymmetric resonant scattering of conduction electrons. Theories based on the skew scattering mechanism account for data at high temperatures T>TK (the Kondo temperature) but are unable to explain the very-low-temperature variation of the Hall constant observed in heavy-fermion compounds. Aside from the ordinary Hall effect, caused by the Lorentz force and skew scattering (which makes the scattering probability antisymmetric with respect to interchange of scattering vectors), there exists an additional contribution to the Hall effect known as the anomalous-velocity contribution. This contribution is due to a change in the expression for the current operator in the presence of spin-orbit forces. We derive an expression for the anomalous velocity in terms of the T matrices describing conduction-electron scattering; it is not limited to weak spin-orbit scattering as were previous results. We use the Anderson model of local moments in metals to write this scattering in terms of the mixing interaction between local and conduction electrons, and the local state's Green's function. The transverse Hall current due to anomalous velocity is determined and evaluated in two limits. At high temperature, we use the weak-coupling form of the local state's Green's function; at T=0 K a phase-shift analysis is used, and we rely on the Friedel-Langreth sum rule to give us the phase shift at the Fermi surface. At high temperatures we find that the contribution from anomalous velocity to the Hall constant is quite small compared to that from skew scattering. On the contrary, at low temperatures the anomalous velocity makes the dominant contribution to the Hall constant in Kondo systems.
NASA Astrophysics Data System (ADS)
Morawetz, K.
2015-12-01
The coupled kinetic equation for density and spin Wigner functions is derived including spin-orbit coupling, electric and magnetic fields, and self-consistent Hartree mean fields suited for SU(2) transport. The interactions are assumed to be with scalar and magnetic impurities as well as scalar and spin-flip potentials among the particles. The spin-orbit interaction is used in a form suitable for solid state physics with Rashba or Dresselhaus coupling, graphene, extrinsic spin-orbit coupling, and effective nuclear matter coupling. The deficiencies of the two-fluid model are worked out consisting of the appearance of an effective in-medium spin precession. The stationary solution of all these systems shows a band splitting controlled by an effective medium-dependent Zeeman field. The self-consistent precession direction is discussed and a cancellation of linear spin-orbit coupling at zero temperature is reported. The precession of spin around this effective direction caused by spin-orbit coupling leads to anomalous charge and spin currents in an electric field. Anomalous Hall conductivity is shown to consist of the known results obtained from the Kubo formula or Berry phases and a symmetric part interpreted as an inverse Hall effect. Analogously the spin-Hall and inverse spin-Hall effects of spin currents are discussed which are present even without magnetic fields showing a spin accumulation triggered by currents. The analytical dynamical expressions for zero temperature are derived and discussed in dependence on the magnetic field and effective magnetizations. The anomalous Hall and spin-Hall effect changes sign at higher than a critical frequency dependent on the relaxation time.
A novel NO2 gas sensor based on Hall effect operating at room temperature
NASA Astrophysics Data System (ADS)
Lin, J. Y.; Xie, W. M.; He, X. L.; Wang, H. C.
2016-09-01
Tungsten trioxide nanoparticles were obtained by a simple thermal oxidation approach. The structural and morphological properties of these nanoparticles are investigated using XRD, SEM and TEM. A WO3 thick film was deposited on the four Au electrodes to be a WO3 Hall effect sensor. The sensor was tested between magnetic field in a plastic test chamber. Room-temperature nitrogen dioxide sensing characteristics of Hall effect sensor were studied for various concentration levels of nitrogen dioxide at dry air and humidity conditions. A typical room-temperature response of 3.27 was achieved at 40 ppm of NO2 with a response and recovery times of 36 and 45 s, respectively. NO2 gas sensing mechanism of Hall effect sensor was also studied. The room-temperature operation, with the low deposition cost of the sensor, suggests suitability for developing a low-power cost-effective nitrogen dioxide sensor.
Quantum anomalous Hall effect and tunable topological states in 3d transition metals doped silicene.
Zhang, Xiao-Long; Liu, Lan-Feng; Liu, Wu-Ming
2013-10-09
Silicene is an intriguing 2D topological material which is closely analogous to graphene but with stronger spin orbit coupling effect and natural compatibility with current silicon-based electronics industry. Here we demonstrate that silicene decorated with certain 3d transition metals (Vanadium) can sustain a stable quantum anomalous Hall effect using both analytical model and first-principles Wannier interpolation. We also predict the quantum valley Hall effect and electrically tunable topological states could be realized in certain transition metal doped silicene where the energy band inversion occurs. Our findings provide new scheme for the realization of quantum anomalous Hall effect and platform for electrically controllable topological states which are highly desirable for future nanoelectronics and spintronics application.
Hall effect on MHD flow and heat transfer over a stretching sheet with variable thickness
NASA Astrophysics Data System (ADS)
Prasad, K. V.; Vajravelu, K.; Vaidya, Hanumesh
2016-07-01
We investigate the MHD flow and heat transfer of an electrically conducting fluid over a stretching sheet with variable thickness. The wall temperature and the wall velocity are assumed to vary. The effects of external magnetic field along the sheet and the Hall currents are considered. The governing equations are solved numerically using an implicit finite difference scheme. The obtained numerical results are compared with the available results in the literature for some special cases and the results are found to be in very good agreement. The effects of the physical parameters on the velocity and temperature fields are presented graphically and analyzed. The effect of the Hall current gives rise to a cross flow. Moreover, the Hall current and the magnetic field have strong effect on the flow and heat transfer characteristics, i.e., shear stress and the Nusselt number.
Hall current effects in the Lewis magnetohydrodynamic generator
NASA Technical Reports Server (NTRS)
Nichols, L. D.; Sovie, R. J.
1972-01-01
Data obtained in a magnetohydrodynamic generator are compared with theoretical values calculated by using the Dzung theory. The generator was operated with cesium-seeded argon as the working fluid. The gas temperature varied from 1800 to 2100 K, the gas pressure from 19 to 22 N/sq cm, the Mach number from 0.3 to 0.5, and the magnetic field strength from 0.2 to 1.6 T. The analysis indicates that there is incomplete seed vaporization and that Hall current shorting paths (through the working fluid to ground at both the entrance and exit of the channel) limit generator performance.
Low-temperature Hall effect in bismuth chalcogenides thin films
NASA Astrophysics Data System (ADS)
Kuntsevich, A. Yu.; Gabdullin, A. A.; Prudkogliad, V. A.; Selivanov, Yu. G.; Chizhevskii, E. G.; Pudalov, V. M.
2016-12-01
Bismuth chalcogenides are the most studied 3D topological insulators. As a rule, at low temperatures, thin films of these materials demonstrate positive magnetoresistance due to weak antilocalization. Weak antilocalization should lead to resistivity decrease at low temperatures; in experiments, however, resistivity grows as temperature decreases. From transport measurements for several thin films (with various carrier density, thickness, and carrier mobility), and by using a purely phenomenological approach, with no microscopic theory, we show that the low-temperature growth of the resistivity is accompanied by growth of the Hall coefficient, in agreement with the diffusive electron-electron interaction correction mechanism. Our data reasonably explain the low-temperature resistivity upturn.
Modeling of graphene Hall effect sensors for microbead detection
NASA Astrophysics Data System (ADS)
Manzin, A.; Simonetto, E.; Amato, G.; Panchal, V.; Kazakova, O.
2015-05-01
This paper deals with the modeling of sensitivity of epitaxial graphene Hall bars, from sub-micrometer to micrometer size, to the stray field generated by a magnetic microbead. To demonstrate experiment feasibility, the model is first validated by comparison to measurement results, considering an ac-dc detection scheme. Then, a comprehensive numerical analysis is performed to investigate signal detriment caused by sensor material heterogeneities, saturation of bead magnetization at high fields, increment of bead distance from sensor surface, and device width increase.
NASA Astrophysics Data System (ADS)
Isogami, Shinji; Tsunoda, Masakiyo
2016-04-01
In this study, the output DC electric voltage (V out) generated by a Pt-capped Fe4N bilayer film (Fe4N/Pt) under ferromagnetic resonance conditions at room temperature was assessed. The contributions from the inverse spin-Hall effect (ISHE), the planar-Hall effect (PHE) and the anomalous-Hall effect (AHE) were separated from the output voltage by analysis of V out values determined at varying external field polar angles. The results showed that the polarity of the ISHE (V ISHE) component of V out was opposite to that of the PHE (V PHE). As a result, the magnitude of the intrinsic V ISHE was beyond V out by as much as the magnitude of V PHE. The X-ray diffraction structural analysis revealed the polycrystal of the Fe4N/Pt with (001) orientation, which might be one of the possible mechanisms for enhanced intrinsic V ISHE.
Effective-field-theory model for the fractional quantum Hall effect
NASA Technical Reports Server (NTRS)
Zhang, S. C.; Hansson, T. H.; Kivelson, S.
1989-01-01
Starting directly from the microscopic Hamiltonian, a field-theory model is derived for the fractional quantum Hall effect. By considering an approximate coarse-grained version of the same model, a Landau-Ginzburg theory similar to that of Girvin (1986) is constructed. The partition function of the model exhibits cusps as a function of density. It is shown that the collective density fluctuations are massive.
Coriolis effect and spin Hall effect of light in an inhomogeneous chiral medium.
Zhang, Yongliang; Shi, Lina; Xie, Changqing
2016-07-01
We theoretically investigate the spin Hall effect of spinning light in an inhomogeneous chiral medium. The Hamiltonian equations of the photon are analytically obtained within eikonal approximation in the noninertial orthogonal frame. Besides the usual spin curvature coupling, the chiral parameter enters the Hamiltonian as a spin-torsion-like interaction. We reveal that both terms have parallel geometric origins as the Coriolis terms of Maxwell's equations in nontrivial frames.
Effects of Landau level mixing on the fractional quantum Hall effect in monolayer graphene.
Peterson, Michael R; Nayak, Chetan
2014-08-22
We report results of exact diagonalization studies of the spin- and valley-polarized fractional quantum Hall effect in the N = 0 and N = 1 Landau levels in graphene. We use an effective model that incorporates Landau level mixing to lowest order in the parameter κ = ((e(2)/εℓ)/(ħv(F)/ℓ)) = (e(2)/εv(F)ħ), which is magnetic field independent and can only be varied through the choice of substrate. We find Landau level mixing effects are negligible in the N = 0 Landau level for κ ≲ 2. In fact, the lowest Landau level projected Coulomb Hamiltonian is a better approximation to the real Hamiltonian for graphene than it is for semiconductor based quantum wells. Consequently, the principal fractional quantum Hall states are expected in the N = 0 Landau level over this range of κ. In the N = 1 Landau level, fractional quantum Hall states are expected for a smaller range of κ and Landau level mixing strongly breaks particle-hole symmetry, producing qualitatively different results compared to the N = 0 Landau level. At half filling of the N = 1 Landau level, we predict the anti-Pfaffian state will occur for κ ∼ 0.25-0.75.
NASA Astrophysics Data System (ADS)
Socratous, Josephine; Watanabe, Shun; Banger, Kulbinder K.; Warwick, Christopher N.; Branquinho, Rita; Barquinha, Pedro; Martins, Rodrigo; Fortunato, Elvira; Sirringhaus, Henning
2017-01-01
Despite the success of exploiting the properties of amorphous oxide semiconductors for device applications, the charge transport in these materials is still not clearly understood. The observation of a definite Hall voltage suggests that electron transport in the conduction band is free-electron-like. However, the temperature dependence of the Hall and field-effect mobilities cannot be explained using a simple bandlike model. Here, we perform gated Hall effect measurements in field-effect transistors, which allow us to make two independent estimates of the charge carrier concentration and determine the Hall factor providing information on the energy dependence of the relaxation time. We demonstrate that the Hall factor in a range of sputtered and solution-processed quaternary amorphous oxides, such as a-InGaZnO, is close to two, while in ternary oxides, such as InZnO, it is near unity. This suggests that quaternary elements like Ga act as strong ionized impurity scattering centers in these materials.
The spin Hall effect in single-crystalline gold thin films
NASA Astrophysics Data System (ADS)
Tian, Dai; Chen, Caigan; Wang, Hua; Jin, Xiaofeng
2016-10-01
The spin Hall effect has been investigated in 10-nm-thick epitaxial Au (001) single crystal films via H-pattern devices, whose minimum characteristic dimension is about 40 nm. By improving the film quality and optimizing the in-plane geometry parameters of the devices, we explicitly extract the spin Hall effect contribution from the ballistic and bypass contribution which were previously reported to be dominating the non-local voltage. Furthermore, we calculate a lower limit of the spin Hall angle of 0.08 at room temperature. Our results indicate that the giant spin Hall effect in Au thin films is dominated not by the interior defects scattering, but by the surface scattering. Besides, our results also provide an additional experimental method to determine the magnitude of spin Hall angle unambiguously. Project supported by the National Basic Research Program of China (Grant Nos. 2015CB921400 and 2011CB921802) and the National Natural Science Foundation of China (Grant Nos. 11374057, 11434003, and 11421404).
Unusual spin Hall effect of a light beam in chiral metamaterials
Wang Hailei; Zhang Xiangdong
2011-05-15
We present a solution to the problem of reflection and refraction of a polarized Gaussian beam at the interface between the transparent medium and the chiral metamaterials. Some unusual spin Hall effects of reflected and transmitted light have been found. It is shown that the spin-dependent displacements of the reflected beam centroid can not only reach several tens of wavelengths at certain incident angles; the reversed effect for the transmitted beams can also be realized by tuning the chiral parameters. These findings provide an alternative pathway for controlling the spin Hall effects of light and thereby open up the possibility for developing new nanophotonic devices.
Including Landau level mixing in numerical studies of the quantum Hall effect
NASA Astrophysics Data System (ADS)
Wooten, R. E.; Macek, J. H.; Quinn, J. J.
2013-10-01
Landau level mixing should influence the quantum Hall effect for all but the strongest applied magnetic fields. However, the effects of Landau level mixing have proven difficult to model theoretically. We propose a simple method for examining the effects of Landau level mixing on electron pairs for intermediate magnetic fields by incorporating multiple Landau levels into the pseudopotentials on the Haldane sphere.
Geometric Effect on Quantum Anomalous Hall State in Magnetic Topological Insulator
NASA Astrophysics Data System (ADS)
Xing, Yanxia
An intriguing observation on the quantum anomalous Hall (QAH) effect in a magnetic topological insulator (MTI) is the dissipative edge states. With the aid of non-equilibrium Green's functions,the QAH effect in an MTI with a three dimensional effective tight-binding model is studied.We predict that due to geometric structure in the third dimension z,the unideal contact between terminal leads and central scattering region induces the backscattering in the central Hall bar,as the function of split gates. Such backscattering leads to a nonzero longitudinal resistance and quantized Hall resistance, which would explain the dissipative edge states in experiments.A further numerical simulation prove above prediction as well.These results are rewarding on future experimental observations and transport calculations based on first principe.
Split-quaternionic Hopf map, quantum Hall effect, and twistor theory
Hasebe, Kazuki
2010-02-15
Introducing a noncompact version of the Hopf map, we demonstrate remarkable close relations between quantum Hall effect and twistor theory. We first construct quantum Hall effect on a hyperboloid based on the noncompact 2nd Hopf map of split-quaternions. We analyze a hyperbolic one-particle mechanics, and explore many-body problem, where a many-body ground state wave function and membrane-like excitations are derived explicitly. In the lowest Landau level, the symmetry is enhanced from SO(3,2) to the SU(2,2) conformal symmetry. We point out that the quantum Hall effect naturally realizes the philosophy of twistor theory. In particular, emergence mechanism of fuzzy space-time is discussed somehow in detail.
Topological Hubbard model and its high-temperature quantum Hall effect.
Neupert, Titus; Santos, Luiz; Ryu, Shinsei; Chamon, Claudio; Mudry, Christopher
2012-01-27
The quintessential two-dimensional lattice model that describes the competition between the kinetic energy of electrons and their short-range repulsive interactions is the repulsive Hubbard model. We study a time-reversal symmetric variant of the repulsive Hubbard model defined on a planar lattice: Whereas the interaction is unchanged, any fully occupied band supports a quantized spin Hall effect. We show that at 1/2 filling of this band, the ground state develops spontaneously and simultaneously Ising ferromagnetic long-range order and a quantized charge Hall effect when the interaction is sufficiently strong. We ponder on the possible practical applications, beyond metrology, that the quantized charge Hall effect might have if it could be realized at high temperatures and without external magnetic fields in strongly correlated materials.
Parity effect of bipolar quantum Hall edge transport around graphene antidots
Matsuo, Sadashige; Nakaharai, Shu; Komatsu, Katsuyoshi; Tsukagoshi, Kazuhito; Moriyama, Takahiro; Ono, Teruo; Kobayashi, Kensuke
2015-01-01
Parity effect, which means that even-odd property of an integer physical parameter results in an essential difference, ubiquitously appears and enables us to grasp its physical essence as the microscopic mechanism is less significant in coarse graining. Here we report a new parity effect of quantum Hall edge transport in graphene antidot devices with pn junctions (PNJs). We found and experimentally verified that the bipolar quantum Hall edge transport is drastically affected by the parity of the number of PNJs. This parity effect is universal in bipolar quantum Hall edge transport of not only graphene but also massless Dirac electron systems. These results offer a promising way to design electron interferometers in graphene. PMID:26122468
Quantum Hall effect in semiconductor systems with quantum dots and antidots
Beltukov, Ya. M.; Greshnov, A. A.
2015-04-15
The integer quantum Hall effect in systems of semiconductor quantum dots and antidots is studied theoretically as a factor of temperature. It is established that the conditions for carrier localization in quantum-dot systems favor the observation of the quantum Hall effect at higher temperatures than in quantum-well systems. The obtained numerical results show that the fundamental plateau corresponding to the transition between the ground and first excited Landau levels can be retained up to a temperature of T ∼ 50 K, which is an order of magnitude higher than in the case of quantum wells. Implementation of the quantum Hall effect at such temperatures requires quantum-dot systems with controllable characteristics, including the optimal size and concentration and moderate geometrical and composition fluctuations. In addition, ordered arrangement is desirable, hence quantum antidots are preferable.
Perpendicular magnetic anisotropy in Co2MnGa and its anomalous Hall effect
NASA Astrophysics Data System (ADS)
Ludbrook, B. M.; Ruck, B. J.; Granville, S.
2017-02-01
We report perpendicular magnetic anisotropy in the ferromagnetic Heusler alloy Co2MnGa in a MgO/Co2MnGa/Pd trilayer stack for Co2MnGa thicknesses up to 3.5 nm. There is a thickness- and temperature-dependent spin reorientation transition from perpendicular to in-plane magnetic anisotropy, which we study through the anomalous Hall effect. From the temperature dependence of the anomalous Hall effect, we observe the expected scaling of ρx y A H E with ρxx, suggesting that the intrinsic and side-jump mechanisms are largely responsible for the anomalous Hall effect in this material.
Erkaev, N. V.; Semenov, V. S.; Biernat, H. K.
2010-06-15
Hall magnetohydrodynamic model is investigated for current sheet flapping oscillations, which implies a gradient of the normal magnetic field component. For the initial undisturbed current sheet structure, the normal magnetic field component is assumed to have a weak linear variation. The profile of the electric current velocity is described by hyperbolic functions with a maximum at the center of the current sheet. In the framework of this model, eigenfrequencies are calculated as functions of the wave number for the ''kink'' and ''sausage'' flapping wave modes. Because of the Hall effects, the flapping eigenfrequency is larger for the waves propagating along the electric current, and it is smaller for the opposite wave propagation with respect to the current. The asymmetry of the flapping wave propagation, caused by Hall effects, is pronounced stronger for thinner current sheets. This is due to the Doppler effect related to the electric current velocity.
Exotic emergent phenomena in the fractional quantum Hall effect
NASA Astrophysics Data System (ADS)
Coimbatore Balram, Ajit
When two-dimensional electron systems are subjected to a perpendicular magnetic field, they exhibit the marvelous phenomenon known as the fractional quantum Hall effect (FQHE). This arises as a result of the formation of composite fermions (CFs), which are bound states of electrons and an even number of vortices. The FQHE of electrons is understood as arising from the integer QHE (IQHE) of CFs. Alongside superconductivity, Bose-Einstein condensation and spin-liquids, the CF quantum fluid provides a model system for understanding strongly correlated systems and their collective behavior. Although it has been more than three decades since the experimental discovery of FQHE, the field continues to produce profound insights and pose interesting problems some of which have been addressed in this thesis. A major unanswered question in the field of FQHE is the mechanism of FQHE for the 1/3 state in the second Landau level (7/3 state). Numerical studies of this state have brought out the following puzzle: exact diagonalization studies suggest that the ground state and excitations of 1/3 state in the second Landau level are different from its counterpart in the lowest Landau level (LLL), while entanglement spectra of the two states point to the fact that they fall in the same universality class. Using methods from CF theory we show that the excitations of the 7/3 FQHE lie in the same universality class as those of the 1/3 state but are strongly modified due to screening by CF excitons, thereby settling the above discrepancy. Armed with the exciton calculation, we illustrate that by imposing certain exclusion rules for CF excitons one can build the full spectrum of FQHE in the lowest Landau level. Equipped with the techniques to calculate the spectra of FQHE systems, we carry out an extensive study of FQHE of multi-component CFs (systems possessing degrees of freedom for eg: valley and spin degeneracy), which is applicable to FQHE in systems such as graphene, AlAs and Ga
Experimental comparison of ring and diamond shaped planar Hall effect bridge magnetic field sensors
NASA Astrophysics Data System (ADS)
Henriksen, Anders Dahl; Rizzi, Giovanni; Hansen, Mikkel Fougt
2015-09-01
Planar Hall effect magnetic field sensors with ring and diamond shaped geometries are experimentally compared with respect to their magnetic field sensitivity and total signal variation. Theoretically, diamond shaped sensors are predicted to be 41% more sensitive than corresponding ring shaped sensors for negligible shape anisotropy. To experimentally validate this, we have fabricated both sensor geometries in the exchange-biased stack Ni80Fe20(tFM)/Cu(tCu)/Mn80Ir20(10 nm) with tFM=10 , 20, and 30 nm and tCu=0 , 0.3, and 0.6 nm. Sensors from each stack were characterized by external magnetic field sweeps, which were analyzed in terms of a single domain model. The total signal variation of the diamond sensors was generally found to be about 40% higher than that for the ring sensors in agreement with theoretical predictions. However, for the low-field sensitivity, the corresponding improvement varied from 0% to 35% where the largest improvement was observed for sensor stacks with comparatively strong exchange bias. This is explained by the ring sensors being less affected by shape anisotropy than the diamond sensors. To study the effect of shape anisotropy, we also characterized sensors that were surrounded by the magnetic stack with a small gap of 3 μm. These sensors were found to be less affected by shape anisotropy and thus showed higher low-field sensitivities.
Hall effect control of magnetotail dawn-dusk asymmetry: A three-dimensional global hybrid simulation
NASA Astrophysics Data System (ADS)
Lu, San; Lin, Y.; Angelopoulos, V.; Artemyev, A. V.; Pritchett, P. L.; Lu, Quanming; Wang, X. Y.
2016-12-01
Magnetotail reconnection and related phenomena (e.g., flux ropes, dipolarizing flux bundles, flow bursts, and particle injections) occur more frequently on the duskside than on the dawnside. Because this asymmetry can directly result in dawn-dusk asymmetric space weather effects, uncovering its physical origin is important for better understanding, modeling, and prediction of the space weather phenomena. However, the cause of this pervasive asymmetry is unclear. Using three-dimensional global hybrid simulations, we demonstrate that the Hall physics in the magnetotail current sheet is responsible for the asymmetry. The current sheet thins progressively under enhanced global convection; when its thickness reaches ion kinetic scales, some ions are decoupled from the magnetized electrons (the Hall effect). The resultant Hall electric field Ez is directed toward the neutral plane. The Hall effect is stronger (grows faster) on the duskside; i.e., more ions become unmagnetized there and do not comove with the magnetized dawnward Ez × Bx drifting electrons, thus creating a larger additional cross-tail current intensity jy (in addition to the diamagnetic current) on the duskside, compared to the dawnside. The stronger Hall effect strength on the duskside is controlled by the higher ion temperature, thinner current sheet, and smaller normal magnetic field Bz there. These asymmetric current sheet properties are in turn controlled by two competing processes that correspond to the Hall effect: (1) the dawnward E × B drift of the magnetic flux and magnetized ions and electrons and (2) the transient motion of the unmagnetized ions which do not execute E × B drift.
Spontaneous magnetization and anomalous Hall effect in an emergent Dice lattice.
Dutta, Omjyoti; Przysiężna, Anna; Zakrzewski, Jakub
2015-06-09
Ultracold atoms in optical lattices serve as a tool to model different physical phenomena appearing originally in condensed matter. To study magnetic phenomena one needs to engineer synthetic fields as atoms are neutral. Appropriately shaped optical potentials force atoms to mimic charged particles moving in a given field. We present the realization of artificial gauge fields for the observation of anomalous Hall effect. Two species of attractively interacting ultracold fermions are considered to be trapped in a shaken two dimensional triangular lattice. A combination of interaction induced tunneling and shaking can result in an emergent Dice lattice. In such a lattice the staggered synthetic magnetic flux appears and it can be controlled with external parameters. The obtained synthetic fields are non-Abelian. Depending on the tuning of the staggered flux we can obtain either anomalous Hall effect or its quantized version. Our results are reminiscent of Anomalous Hall conductivity in spin-orbit coupled ferromagnets.
Quantum Hall effect in black phosphorus two-dimensional electron system.
Li, Likai; Yang, Fangyuan; Ye, Guo Jun; Zhang, Zuocheng; Zhu, Zengwei; Lou, Wenkai; Zhou, Xiaoying; Li, Liang; Watanabe, Kenji; Taniguchi, Takashi; Chang, Kai; Wang, Yayu; Chen, Xian Hui; Zhang, Yuanbo
2016-07-01
The development of new, high-quality functional materials has been at the forefront of condensed-matter research. The recent advent of two-dimensional black phosphorus has greatly enriched the materials base of two-dimensional electron systems (2DESs). Here, we report the observation of the integer quantum Hall effect in a high-quality black phosphorus 2DES. The high quality is achieved by embedding the black phosphorus 2DES in a van der Waals heterostructure close to a graphite back gate; the graphite gate screens the impurity potential in the 2DES and brings the carrier Hall mobility up to 6,000 cm(2) V(-1) s(-1). The exceptional mobility enabled us to observe the quantum Hall effect and to gain important information on the energetics of the spin-split Landau levels in black phosphorus. Our results set the stage for further study on quantum transport and device application in the ultrahigh mobility regime.
NASA Astrophysics Data System (ADS)
Bagrov, Andrey A.; Principi, Alessandro; Katsnelson, Mikhail I.
2017-03-01
We address the question of the stability of the fractional quantum Hall effect in the presence of pseudomagnetic disorder generated by mechanical deformations of a graphene sheet. Neglecting the potential disorder and taking into account only strain-induced random pseudomagnetic fields, it is possible to write down a Laughlin-like trial ground-state wave function explicitly. Exploiting the Laughlin plasma analogy, we demonstrate that in the case of fluctuating pseudomagnetic fluxes of a relatively small amplitude, the fractional quantum Hall effect is always stable upon the deformations. By contrast, in the case of bubble-induced pseudomagnetic fields in graphene on a substrate (a small number of large fluxes) the disorder can be strong enough to cause a glass transition in the corresponding classical Coulomb plasma, resulting in the destruction of the fractional quantum Hall regime and in a quantum phase transition to a nonergodic state of the lowest Landau level.
Driving and detecting ferromagnetic resonance in insulators with the spin Hall effect.
Sklenar, Joseph; Zhang, Wei; Jungfleisch, Matthias B.; Jiang, Wanjun; Chang, Houchen; Pearson, John E.; Wu, Mingzhong; Ketterson, John B.; Hoffmann, Axel
2015-11-06
We demonstrate the generation and detection of spin-torque ferromagnetic resonance in Pt/Y3Fe5O12 (YIG) bilayers. A unique attribute of this system is that the spin Hall effect lies at the heart of both the generation and detection processes and no charge current is passing through the insulating magnetic layer. When the YIG undergoes resonance, a dc voltage is detected longitudinally along the Pt that can be described by two components. One is the mixing of the spin Hall magnetoresistance with the microwave current. The other results from spin pumping into the Pt being converted to a dc current through the inverse spin Hall effect. The voltage is measured with applied magnetic field directions that range in-plane to nearly perpendicular. We find that for magnetic fields that are mostly out-of-plane, an imaginary component of the spin mixing conductance is required to model our data.
Effects of magnetic field and Hall current to the blood velocity and LDL transfer
NASA Astrophysics Data System (ADS)
Abdullah, I.; Naser, N.; Talib, A. H.; Mahali, S.
2015-09-01
The magnetic field and Hall current effects have been considered on blood velocity and concentration of low-density lipoprotein (LDL). It is important to observe those effects to the flowing blood in a stenosed artery. The analysis from the obtained results may be useful to some clinical procedures, such as MRI, where the radiologists may have more information in the investigations before cardiac operations could be done. In this study, the uniform magnetic field and Hall current are applied to the Newtonian blood flow through an artery having a cosine-shaped stenosis. The governing equations are coupled with mass transfer and solved employing a finite difference Marker and Cell (MAC) method with an appropriate initial and boundary conditions. The graphical results of velocity profiles and LDL concentration are presented in this paper and the results show that the velocity increases and concentration decreases as Hall parameter increased.
Second Landau level fractional quantum Hall effects in the Corbino geometry
NASA Astrophysics Data System (ADS)
Schmidt, B. A.; Bennaceur, K.; Bilodeau, S.; Gervais, G.; Pfeiffer, L. N.; West, K. W.
2015-09-01
For certain measurements, the Corbino geometry has a distinct advantage over the Hall and van der Pauw geometries, in that it provides a direct probe of the bulk 2DEG without complications due to edge effects. This may be important in enabling detection of the non-Abelian entropy of the 5/2 fractional quantum Hall state via bulk thermodynamic measurements. We report the successful fabrication and measurement of a Corbino-geometry sample in an ultra-high mobility GaAs heterostructure, with a focus on transport in the second and higher Landau levels. In particular, we report activation energy gaps of fractional quantum Hall states, with all edge effects ruled out, and extrapolate σ0 from the Arrhenius fits. Our results show that activated transport in the second Landau level remains poorly understood. The development of this Corbino device opens the possibility to study the bulk of the 5/2 state using techniques not possible in other geometries.
Spontaneous magnetization and anomalous Hall effect in an emergent Dice lattice
Dutta, Omjyoti; Przysiężna, Anna; Zakrzewski, Jakub
2015-01-01
Ultracold atoms in optical lattices serve as a tool to model different physical phenomena appearing originally in condensed matter. To study magnetic phenomena one needs to engineer synthetic fields as atoms are neutral. Appropriately shaped optical potentials force atoms to mimic charged particles moving in a given field. We present the realization of artificial gauge fields for the observation of anomalous Hall effect. Two species of attractively interacting ultracold fermions are considered to be trapped in a shaken two dimensional triangular lattice. A combination of interaction induced tunneling and shaking can result in an emergent Dice lattice. In such a lattice the staggered synthetic magnetic flux appears and it can be controlled with external parameters. The obtained synthetic fields are non-Abelian. Depending on the tuning of the staggered flux we can obtain either anomalous Hall effect or its quantized version. Our results are reminiscent of Anomalous Hall conductivity in spin-orbit coupled ferromagnets. PMID:26057635
Experimental Observation of the Inverse Spin Hall Effect at Room Temperature
Liu, Baoli; Shi, Junren; Wang, Wenxin; Zhao, Hongming; Li, Dafang; Zhang, Shoucheng; Xue, Qikun; Chen, Dongmin; /Beijing, Inst. Phys.
2010-03-16
We observe the inverse spin Hall effect in a two-dimensional electron gas confined in Al-GaAs/InGaAs quantum wells. Specifically, they find that an inhomogeneous spin density induced by the optical injection gives rise to an electric current transverse to both the spin polarization and its gradient. The spin Hall conductivity can be inferred from such a measurement through the Einstein relation and the onsager relation, and is found to have the order of magnitude of 0.5(e{sup 2}/h). The observation is made at the room temperature and in samples with macroscopic sizes, suggesting that the inverse spin Hall effects is a robust macroscopic transport phenomenon.
A novel method of including Landau level mixing in numerical studies of the quantum Hall effect
Wooten, Rachel; Quinn, John; Macek, Joseph
2013-12-04
Landau level mixing should influence the quantum Hall effect for all except the strongest applied magnetic fields. We propose a simple method for examining the effects of Landau level mixing by incorporating multiple Landau levels into the Haldane pseudopotentials through exact numerical diagonalization. Some of the resulting pseudopotentials for the lowest and first excited Landau levels will be presented.
A novel method of including Landau level mixing in numerical studies of the quantum Hall effect
NASA Astrophysics Data System (ADS)
Wooten, Rachel; Quinn, John; Macek, Joseph
2013-12-01
Landau level mixing should influence the quantum Hall effect for all except the strongest applied magnetic fields. We propose a simple method for examining the effects of Landau level mixing by incorporating multiple Landau levels into the Haldane pseudopotentials through exact numerical diagonalization. Some of the resulting pseudopotentials for the lowest and first excited Landau levels will be presented.
The Anomalous Hall effect in MnSi and FexTaS2
NASA Astrophysics Data System (ADS)
Lee, Minhyea
2007-03-01
In a high-purity ferromagnet with long carrier lifetime τ, e.g. MnSi, the ordinary Hall conductivity σH^N can dominate the intrinsic Anomalous Hall effect (AHE) conductivity σH^A. We show that the large magnetoresistance provides a way to separate accurately the two Hall currents. Below TC, we find that the AHE conductivity is strictly proportional to the magnetization M, viz. σH^A = SHM with a parameter SH that is independent of both temperature T and field H. This implies that σH^A is strictly independent of τ. In the layered, hard ferromagnet FexTaS2, the large coercivity leads to abrupt reversals of M when it switches. We show that this provides an accurate way to separate σH^A from σH^N. Again, σH^A is independent of T from 5 to 50 K. We compare the observed constancy at low T with theories for the AHE. We also describe a Hall anomaly recently observed in MnSi under pressure. This anomaly appears to arise from strong sensitivity of the Hall current to the spin texture, possibly reflecting its finite chirality. The dependence of the anomaly to T and H will be reported. **This work is done in collaboration with Y. Onose, J. G. Checkelsky, E. Morosan, R. J. Cava, Y. Tokura and N. P. Ong.
Disorder Effect on Chiral Edge Modes and Anomalous Hall Conductance in Weyl Semimetals
NASA Astrophysics Data System (ADS)
Takane, Yositake
2016-12-01
Typical Weyl semimetals host chiral surface states and hence show an anomalous Hall response. Although a Weyl semimetal phase is known to be robust against weak disorder, the effect of disorder on chiral states has not been fully clarified so far. We study the behavior of such chiral states in the presence of disorder and its consequences on an anomalous Hall response, focusing on a thin slab of Weyl semimetal with chiral surface states along its edge. It is shown that weak disorder does not disrupt chiral edge states but crucially affects them owing to the renormalization of a mass parameter: the number of chiral edge states changes depending on the strength of disorder. It is also shown that the Hall conductance is quantized when the Fermi level is located near Weyl nodes within a finite-size gap. This quantization of the Hall conductance collapses once the strength of disorder exceeds a critical value, suggesting that it serves as a probe to distinguish a Weyl semimetal phase from a diffusive anomalous Hall metal phase.
NASA Astrophysics Data System (ADS)
Mihajlović, G.; Mosendz, O.; Wan, L.; Smith, N.; Choi, Y.; Wang, Y.; Katine, J. A.
2016-11-01
We introduce a differential planar Hall effect method that enables the experimental study of spin orbit torque switching of in-plane magnetized free layers in a simple Hall bar device geometry. Using this method, we study the Pt thickness dependence of switching currents and show that they decrease monotonically down to the minimum experimental thickness of ˜5 nm, while the critical current and power densities are very weakly thickness dependent, exhibiting the minimum values of Jc0 = 1.1 × 108 A/cm2 and ρJc0 2=0.6 ×1012 W/cm 3 at this minimum thickness. Our results suggest that a significant reduction of the critical parameters could be achieved by optimizing the free layer magnetics, which makes this technology a viable candidate for fast, high endurance and low-error rate applications such as cache memories.
Quantum Hall effect on top and bottom surface states of topological insulator (Bi1-xSbx)2Te3 films.
Yoshimi, R; Tsukazaki, A; Kozuka, Y; Falson, J; Takahashi, K S; Checkelsky, J G; Nagaosa, N; Kawasaki, M; Tokura, Y
2015-04-14
The three-dimensional topological insulator is a novel state of matter characterized by two-dimensional metallic Dirac states on its surface. To verify the topological nature of the surface states, Bi-based chalcogenides such as Bi2Se3, Bi2Te3, Sb2Te3 and their combined/mixed compounds have been intensively studied. Here, we report the realization of the quantum Hall effect on the surface Dirac states in (Bi1-xSbx)2Te3 films. With electrostatic gate-tuning of the Fermi level in the bulk band gap under magnetic fields, the quantum Hall states with filling factor ±1 are resolved. Furthermore, the appearance of a quantum Hall plateau at filling factor zero reflects a pseudo-spin Hall insulator state when the Fermi level is tuned in between the energy levels of the non-degenerate top and bottom surface Dirac points. The observation of the quantum Hall effect in three-dimensional topological insulator films may pave a way toward topological insulator-based electronics.
Puddle-Induced Resistance Oscillations in the Breakdown of the Graphene Quantum Hall Effect
NASA Astrophysics Data System (ADS)
Yang, M.; Couturaud, O.; Desrat, W.; Consejo, C.; Kazazis, D.; Yakimova, R.; Syväjärvi, M.; Goiran, M.; Béard, J.; Frings, P.; Pierre, M.; Cresti, A.; Escoffier, W.; Jouault, B.
2016-12-01
We report on the stability of the quantum Hall plateau in wide Hall bars made from a chemically gated graphene film grown on SiC. The ν =2 quantized plateau appears from fields B ≃5 T and persists up to B ≃80 T . At high current density, in the breakdown regime, the longitudinal resistance oscillates with a 1 /B periodicity and an anomalous phase, which we relate to the presence of additional electron reservoirs. The high field experimental data suggest that these reservoirs induce a continuous increase of the carrier density up to the highest available magnetic field, thus enlarging the quantum plateaus. These in-plane inhomogeneities, in the form of high carrier density graphene pockets, modulate the quantum Hall effect breakdown and decrease the breakdown current.
Puddle-Induced Resistance Oscillations in the Breakdown of the Graphene Quantum Hall Effect.
Yang, M; Couturaud, O; Desrat, W; Consejo, C; Kazazis, D; Yakimova, R; Syväjärvi, M; Goiran, M; Béard, J; Frings, P; Pierre, M; Cresti, A; Escoffier, W; Jouault, B
2016-12-02
We report on the stability of the quantum Hall plateau in wide Hall bars made from a chemically gated graphene film grown on SiC. The ν=2 quantized plateau appears from fields B≃5 T and persists up to B≃80 T. At high current density, in the breakdown regime, the longitudinal resistance oscillates with a 1/B periodicity and an anomalous phase, which we relate to the presence of additional electron reservoirs. The high field experimental data suggest that these reservoirs induce a continuous increase of the carrier density up to the highest available magnetic field, thus enlarging the quantum plateaus. These in-plane inhomogeneities, in the form of high carrier density graphene pockets, modulate the quantum Hall effect breakdown and decrease the breakdown current.
Fractional quantum Hall effect at Landau level filling ν = 4/11
Pan, W.; Baldwin, K. W.; West, K. W.; Pfeiffer, L. N.; Tsui, D. C.
2015-01-09
In this study, we report low temperature electronic transport results on the fractional quantum Hall effect of composite fermions at Landau level filling ν = 4/11 in a very high mobility and low density sample. Measurements were carried out at temperatures down to 15mK, where an activated magnetoresistance R_{xx} and a quantized Hall resistance R_{xy}, within 1% of the expected value of h/(4/11)e^{2}, were observed. The temperature dependence of the R_{xx} minimum at 4/11 yields an activation energy gap of ~ 7 mK. Developing Hall plateaus were also observed at the neighboring states at ν = 3/8 and 5/13.
Devil's Staircase Phase Diagram of the Fractional Quantum Hall Effect in the Thin-Torus Limit.
Rotondo, Pietro; Molinari, Luca Guido; Ratti, Piergiorgio; Gherardi, Marco
2016-06-24
After more than three decades, the fractional quantum Hall effect still poses challenges to contemporary physics. Recent experiments point toward a fractal scenario for the Hall resistivity as a function of the magnetic field. Here, we consider the so-called thin-torus limit of the Hamiltonian describing interacting electrons in a strong magnetic field, restricted to the lowest Landau level, and we show that it can be mapped onto a one-dimensional lattice gas with repulsive interactions, with the magnetic field playing the role of the chemical potential. The statistical mechanics of such models leads us to interpret the sequence of Hall plateaux as a fractal phase diagram whose landscape shows a qualitative agreement with experiments.
Devil's Staircase Phase Diagram of the Fractional Quantum Hall Effect in the Thin-Torus Limit
NASA Astrophysics Data System (ADS)
Rotondo, Pietro; Molinari, Luca Guido; Ratti, Piergiorgio; Gherardi, Marco
2016-06-01
After more than three decades, the fractional quantum Hall effect still poses challenges to contemporary physics. Recent experiments point toward a fractal scenario for the Hall resistivity as a function of the magnetic field. Here, we consider the so-called thin-torus limit of the Hamiltonian describing interacting electrons in a strong magnetic field, restricted to the lowest Landau level, and we show that it can be mapped onto a one-dimensional lattice gas with repulsive interactions, with the magnetic field playing the role of the chemical potential. The statistical mechanics of such models leads us to interpret the sequence of Hall plateaux as a fractal phase diagram whose landscape shows a qualitative agreement with experiments.
Axial Hall effect and universality of holographic Weyl semi-metals
NASA Astrophysics Data System (ADS)
Copetti, Christian; Fernández-Pendás, Jorge; Landsteiner, Karl
2017-02-01
The holographic Weyl semimetal is a model of a strongly coupled topological semi-metal. A topological quantum phase transition separates a topological phase with non-vanishing anomalous Hall conductivity from a trivial state. We investigate how this phase transition depends on the parameters of the scalar potential (mass and quartic self coupling) finding that the quantum phase transition persists for a large region in parameter space. We then compute the axial Hall conductivity. The algebraic structure of the axial anomaly predicts it to be 1/3 of the electric Hall conductivity. We find that this holds once a non-trivial renormalization effect on the external axial gauge fields is taken into account. Finally we show that the phase transition also occurs in a top-down model based on a consistent truncation of type IIB supergravity.
Korhonen, T
1991-03-01
A Hall effect device was constructed for a measurement of head movements in three spatial dimensions during classical conditioning experiments in cats. A Hall sensor was used to detect movements of a magnetic fragment floating in a small (15 x 15 mm) cube. The magnetic fragment was kept in the centre of the sealed cube with a thin coil spring which was filled with thin oil for damping excessive afteroscillations. A comparison of this device to a commercial accelerometer showed that the accuracy of the Hall device is sufficient for the movement recordings and that the device is sensitive also to slowly accelerating movements. The construction is compact and can be easily mounted, for example, on the head stage of a freely moving animal.
Fractional quantum Hall effect at Landau level filling ν = 4/11
Pan, W.; Baldwin, K. W.; West, K. W.; ...
2015-01-09
In this study, we report low temperature electronic transport results on the fractional quantum Hall effect of composite fermions at Landau level filling ν = 4/11 in a very high mobility and low density sample. Measurements were carried out at temperatures down to 15mK, where an activated magnetoresistance Rxx and a quantized Hall resistance Rxy, within 1% of the expected value of h/(4/11)e2, were observed. The temperature dependence of the Rxx minimum at 4/11 yields an activation energy gap of ~ 7 mK. Developing Hall plateaus were also observed at the neighboring states at ν = 3/8 and 5/13.
Composite-Particles (Boson, Fermion) Theory of Fractional Quantum Hall Effect
NASA Astrophysics Data System (ADS)
Fujita, Shigeji; Suzuki, Akira; Ho, Hung-Cheuk
2017-02-01
A theory is developed for fractional quantum Hall effect in terms of composite (c)-bosons (fermions) without useing Laughlin's results about the fractional charge. Here the c-particle (fermion, boson) is defined as a bound composite fermion (boson) containing a conduction electron and an even (odd) number of fluxons (elementary magnetic fluxes). The Bose-condensed c-bosons, each containing an electron and an odd number m of fluxons at the filling factor ν=1/ m is shown to generate the Hall conductivity plateau value m e 2/ h, where the density of c-particles, n_{φ }^{(m)}, either bosonic or fermionic, with m fluxons is given by n_{φ }^{(m)}=ne/m, n e = electron density. The only assumption is that any c-fermion carries a charge magnitude equal to the electron charge e. The quantum Hall state is shown to be more stable at ν=1/3 than at ν=1.
Hall Effects on Mhd Flow Past an Accelerated Plate with Heat Transfer
NASA Astrophysics Data System (ADS)
Sundarnath, J. K.; Muthucumarswamy, R.
2015-02-01
Hall current and rotation on an MHD flow past an accelerated horizontal plate relative to a rotating fluid, in the presence of heat transfer has been analyzed. The effects of the Hall parameter, Hartmann number, rotation parameter (non-dimensional angular velocity), Grashof's number and Prandtl number on axial and transverse velocity profiles are presented graphically. It is found that with the increase in the Hartmann number, the axial and transverse velocity components increase in a direction opposite to that of obtained by increasing the Hall parameter and rotation parameter. Also, when Ω=M2m /(1 + m2 ) , it is observed that the transverse velocity component vanishes and axial velocity attains a maximum value.
A unified theory of quantum Hall effect and high temperature superconductivity
NASA Astrophysics Data System (ADS)
Fujita, Shigeji; Suzuki, Akira
2014-03-01
The quantum Hall effect (QHE) and high temperature superconductivity (HTSC) have remarkable common features. They occur only in two-dimensional (2D) solids. The critical temperature Tc of some HTSC exceeds 160K while the room temperature QHE is observed in graphene. The cause of both QHE and HTSC is the phonon exchange attraction. We develop a theoretical model for the QHE in terms of the composite bosons (fermions), each containing an electron and an odd (even) number of fluxons (magnetic flux quanta). The composite particles (boson, fermion) are bound by the phonon exchange attraction. If the Bose-Einstein condensation (BEC) of the composite (c)- bosons occurs, then the system exhibits zero resistivity and the associated Hall conductivity plateau. The Hall conductivity is calculated rigorously without averaging. The mystery of the fractional charge carried by the c-bosons is resolved in our model.
3d Transition Metal Adsorption Induced the valley-polarized Anomalous Hall Effect in Germanene
Zhou, P.; Sun, L. Z.
2016-01-01
Based on DFT + U and Berry curvature calculations, we study the electronic structures and topological properties of 3d transition metal (TM) atom (from Ti to Co) adsorbed germanene (TM-germanene). We find that valley-polarized anomalous Hall effect (VAHE) can be realized in germanene by adsorbing Cr, Mn, or Co atoms on its surface. A finite valley Hall voltage can be easily detected in their nanoribbon, which is important for valleytronics devices. Moreover, different valley-polarized current and even reversible valley Hall voltage can be archived by shifting the Fermi energy of the systems. Such versatile features of the systems show potential in next generation electronics devices. PMID:27312176
Song, Zhigang; Quhe, Ruge; Liu, Shunquan; Li, Yan; Feng, Ji; Yang, Yingchang; Lu, Jing; Yang, Jinbo
2015-09-11
In this Letter, a tunable valley polarization is investigated for honeycomb systems with broken inversion symmetry such as transition-metal dichalcogenide MX2 (M = Mo, W; X = S, Se) monolayers through elliptical pumping. Compared to circular pumping, elliptical pumping is a more universal and effective method to create coherent valley polarization. When two valleys of MX2 monolayers are doped or polarized, a novel anomalous Hall effect (called valley orbital magnetic moment Hall effect) is predicted. Valley orbital magnetic moment Hall effect can generate an orbital magnetic moment current without the accompaniment of a charge current, which opens a new avenue for exploration of valleytronics and orbitronics. Valley orbital magnetic moment Hall effect is expected to overshadow spin Hall effect and is tunable under elliptical pumping.
Knight, S; Schöche, S; Darakchieva, V; Kühne, P; Carlin, J-F; Grandjean, N; Herzinger, C M; Schubert, M; Hofmann, T
2015-06-15
The effect of a tunable, externally coupled Fabry-Perot cavity to resonantly enhance the optical Hall effect signatures at terahertz frequencies produced by a traditional Drude-like two-dimensional electron gas is shown and discussed in this Letter. As a result, the detection of optical Hall effect signatures at conveniently obtainable magnetic fields, for example, by neodymium permanent magnets, is demonstrated. An AlInN/GaN-based high-electron mobility transistor structure grown on a sapphire substrate is used for the experiment. The optical Hall effect signatures and their dispersions, which are governed by the frequency and the reflectance minima and maxima of the externally coupled Fabry-Perot cavity, are presented and discussed. Tuning the externally coupled Fabry-Perot cavity strongly modifies the optical Hall effect signatures, which provides a new degree of freedom for optical Hall effect experiments in addition to frequency, angle of incidence, and magnetic field direction and strength.
Song, Zhigang; Quhe, Ruge; Liu, Shunquan; Li, Yan; Feng, Ji; Yang, Yingchang; Lu, Jing; Yang, Jinbo
2015-01-01
In this Letter, a tunable valley polarization is investigated for honeycomb systems with broken inversion symmetry such as transition-metal dichalcogenide MX2 (M = Mo, W; X = S, Se) monolayers through elliptical pumping. Compared to circular pumping, elliptical pumping is a more universal and effective method to create coherent valley polarization. When two valleys of MX2 monolayers are doped or polarized, a novel anomalous Hall effect (called valley orbital magnetic moment Hall effect) is predicted. Valley orbital magnetic moment Hall effect can generate an orbital magnetic moment current without the accompaniment of a charge current, which opens a new avenue for exploration of valleytronics and orbitronics. Valley orbital magnetic moment Hall effect is expected to overshadow spin Hall effect and is tunable under elliptical pumping. PMID:26358835
NASA Astrophysics Data System (ADS)
Miwa, R. H.; Kagimura, R.; Lima, Matheus P.; Fazzio, A.
2015-05-01
We have performed an ab initio theoretical study of the energetic stability and the electronic properties of pristine and hydrogen-adsorbed grain boundaries (GBs) in silicene. We find that GBs in silicene present lower formation energy when compared with their counterparts in graphene. Removing the inversion symmetry, by applying an external electric field perpendicular to the silicene sheet, we verify the formation of valley-indexed metallic states lying along the GBs, characterizing the quantum valley Hall effect (QVHE). Here, we find the maintenance of the QVHE upon the presence of disordered and asymmetric geometries along the GBs. Those metallic states are suppressed upon the adsorption of H adatoms along the GBs. The H adatoms promote an unbalance on the electronic occupation of the unsaturated π electrons beside the hydrogenated GB rows, giving rise to (i) a net magnetic moment on the Si atoms along the edge sites of the hydrogenated GBs and (ii) an electronic band structure characterized by spin-polarized valley states protected against backscattering processes.
Electrical detection of coherent spin precession using the ballistic intrinsic spin Hall effect.
Choi, Won Young; Kim, Hyung-jun; Chang, Joonyeon; Han, Suk Hee; Koo, Hyun Cheol; Johnson, Mark
2015-08-01
The spin-orbit interaction in two-dimensional electron systems provides an exceptionally rich area of research. Coherent spin precession in a Rashba effective magnetic field in the channel of a spin field-effect transistor and the spin Hall effect are the two most compelling topics in this area. Here, we combine these effects to provide a direct demonstration of the ballistic intrinsic spin Hall effect and to demonstrate a technique for an all-electric measurement of the Datta-Das conductance oscillation, that is, the oscillation in the source-drain conductance due to spin precession. Our hybrid device has a ferromagnet electrode as a spin injector and a spin Hall detector. Results from multiple devices with different channel lengths map out two full wavelengths of the Datta-Das oscillation. We also use the original Datta-Das technique with a single device of fixed length and measure the channel conductance as the gate voltage is varied. Our experiments show that the ballistic spin Hall effect can be used for efficient injection or detection of spin polarized electrons, thereby enabling the development of an integrated spin transistor.
Electrical detection of coherent spin precession using the ballistic intrinsic spin Hall effect
NASA Astrophysics Data System (ADS)
Choi, Won Young; Kim, Hyung-Jun; Chang, Joonyeon; Han, Suk Hee; Koo, Hyun Cheol; Johnson, Mark
2015-08-01
The spin-orbit interaction in two-dimensional electron systems provides an exceptionally rich area of research. Coherent spin precession in a Rashba effective magnetic field in the channel of a spin field-effect transistor and the spin Hall effect are the two most compelling topics in this area. Here, we combine these effects to provide a direct demonstration of the ballistic intrinsic spin Hall effect and to demonstrate a technique for an all-electric measurement of the Datta-Das conductance oscillation, that is, the oscillation in the source-drain conductance due to spin precession. Our hybrid device has a ferromagnet electrode as a spin injector and a spin Hall detector. Results from multiple devices with different channel lengths map out two full wavelengths of the Datta-Das oscillation. We also use the original Datta-Das technique with a single device of fixed length and measure the channel conductance as the gate voltage is varied. Our experiments show that the ballistic spin Hall effect can be used for efficient injection or detection of spin polarized electrons, thereby enabling the development of an integrated spin transistor.
Hall effect on a Merging Formation Process of a Field-Reversed Configuration
NASA Astrophysics Data System (ADS)
Kaminou, Yasuhiro; Guo, Xuehan; Inomoto, Michiaki; Ono, Yasushi; Horiuchi, Ritoku
2015-11-01
Counter-helicity spheromak merging is one of the formation methods of a Field-Reversed Configuration (FRC). In counter-helicity spheromak merging, two spheromaks with opposing toroidal fields merge together, through magnetic reconnection events and relax into a FRC, which has no or little toroidal field. This process contains magnetic reconnection and a relaxation phenomena, and the Hall effect has some essential effects on these process because the X-point in the magnetic reconnection or the O-point of the FRC has no or little magnetic field. However, the Hall effect as both global and local effect on counter-helicity spheromak merging has not been elucidated. In this poster, we conducted 2D/3D Hall-MHD simulations and experiments of counter-helicity spheromak merging. We find that the Hall effect enhances the reconnection rate, and reduces the generation of toroidal sheared-flow. The suppression of the ``slingshot effect'' affects the relaxation process. We will discuss details in the poster.
NASA Astrophysics Data System (ADS)
Ziman, Timothy; Gu, Bo; Maekawa, Sadamichi
2017-01-01
The spin Hall effect is affected by the Coulomb interaction as well as spin-spin correlations in metals. Here we examine the enhancement in the effect caused by resonant skew scattering induced by electron correlations. For single-impurity scattering, local Coulomb correlations may significantly change the observed spin Hall angle. There may be additional effects because of the special atomic environment close to a surface — extra degeneracies compared to the bulk, enhanced correlations that move the relative d- or f-levels, and interference effects coming from the lower local dimension. Our results may explain the very large spin Hall angle observed in CuBi alloys. We discuss the impact on the spin Hall effect from cooperative effects, firstly in an itinerant ferromagnet where there is an anomaly near the Curie temperature originating from high-order spin fluctuations. The second case considered is a metallic spin glass, where exchange via slowly fluctuating magnetic moments may lead to the precession of an injected spin current. This decreases the net spin-charge conversion from skew scattering at temperatures below a value three or four times the freezing temperature.
Magnon transport in noncollinear spin textures: Anisotropies and topological magnon Hall effects
NASA Astrophysics Data System (ADS)
Mook, Alexander; Göbel, Börge; Henk, Jürgen; Mertig, Ingrid
2017-01-01
We analyze signatures of noncollinear spin textures in the magnon transport of both spin and heat by means of atomistic spin dynamics. The influence of the spin texture is demonstrated for a spin spiral and for a skyrmion lattice on a frustrated antiferromagnet. Spin spirals show an anisotropy in the longitudinal transport, whereas skyrmion lattices exhibit transverse transport, which is interpreted in terms of topology and establishes skyrmion-induced versions of magnon Hall effects. The conductivities depend sensitively on the spiral pitch and on the skyrmion size; we predict magnon Hall angles as large as 60%.
Analogue of the quantum Hall effect for neutral particles with magnetic dipole moment
NASA Astrophysics Data System (ADS)
Ribeiro, L. R.; Passos, E.; Furtado, C.; Sergeenkov, S.
2017-03-01
In this paper we investigate a possibility for the existence of an analog of the Quantum Hall Effect for neutral particles with a permanent magnetic moment μ in the presence of crossed inhomogeneous magnetic and electric fields. We predict the appearance of Hall conductivity σH = (e2 / h) ν (μ) with the Landau filling factor ν (μ) ∝μ2. The estimates of the model parameters suggest quite an optimistic possibility to experimentally verify this prediction in optically trapped clouds of atomic BEC.
Hysteretic magnetoresistance and unconventional anomalous Hall effect in the frustrated magnet TmB4
NASA Astrophysics Data System (ADS)
Sunku, Sai Swaroop; Kong, Tai; Ito, Toshimitsu; Canfield, Paul C.; Shastry, B. Sriram; Sengupta, Pinaki; Panagopoulos, Christos
2016-05-01
We study TmB4, a frustrated magnet on the Archimedean Shastry-Sutherland lattice, through magnetization and transport experiments. The lack of anisotropy in resistivity shows that TmB4 is an electronically three-dimensional system. The magnetoresistance (MR) is hysteretic at low temperature even though a corresponding hysteresis in magnetization is absent. The Hall resistivity shows unconventional anomalous Hall effect (AHE) and is linear above saturation despite a large MR. We propose that complex structures at magnetic domain walls may be responsible for the hysteretic MR and may also lead to the AHE.
Spin Hall effect-controlled magnetization dynamics in NiMnSb
Dürrenfeld, P. Ranjbar, M.; Gerhard, F.; Gould, C.; Molenkamp, L. W.; Åkerman, J.
2015-05-07
We investigate the influence of a spin current generated from a platinum layer on the ferromagnetic resonance (FMR) properties of an adjacent ferromagnetic layer composed of the halfmetallic half-Heusler material NiMnSb. Spin Hall nano-oscillator devices are fabricated, and the technique of spin torque FMR is used to locally study the magnetic properties as in-plane anisotropies and resonance fields. A change in the FMR linewidth, in accordance with the additional spin torque produced by the spin Hall effect, is present for an applied dc current. For sufficiently large currents, this should yield auto-oscillations, which however are not achievable in the present device geometry.
Spin-torque switching of a nano-magnet using giant spin hall effect
Penumatcha, Ashish V. Das, Suprem R.; Chen, Zhihong; Appenzeller, Joerg
2015-10-15
The Giant Spin Hall Effect(GSHE) in metals with high spin-orbit coupling is an efficient way to convert charge currents to spin currents, making it well-suited for writing information into magnets in non-volatile magnetic memory as well as spin-logic devices. We demonstrate the switching of an in-plane CoFeB magnet using a combination of GSHE and an external magnetic field. The magnetic field dependence of the critical current is used to estimate the spin hall angle with the help of a thermal activation model for spin-transfer torque switching of a nanomagnet.
Hysteretic magnetoresistance and unconventional anomalous Hall effect in the frustrated magnet TmB4
NASA Astrophysics Data System (ADS)
Sunku, Sai Swaroop; Kong, Tai; Ito, Toshimitsu; Canfield, Paul C.; Shastry, B. Sriram; Sengupta, Pinaki; Panagopoulos, Christos
We study TmB4, a frustrated magnet on the Archimedean Shastry-Sutherland lattice, through magnetization and transport experiments. The lack of anisotropy in resistivity shows that TmB4 is an electronically three-dimensional system. The magnetoresistance (MR) is hysteretic at low-temperature even though a corresponding hysteresis in magnetization is absent. The Hall resistivity shows unconventional anomalous Hall effect (AHE) and is linear above saturation despite a large MR. We suggest that both hysteretic MR and AHE arise from the formation of complex non-coplanar structures at magnetic domain walls. Current address: Department of Applied Physics and Applied Mathematics, Columbia University.
Charge-density-wave stripe state in fractional quantum spin Hall effects
NASA Astrophysics Data System (ADS)
Li, Wei; Chen, Yan
2016-02-01
By means of finite-size exact diagonalization, we theoretically study the effect of an inter-spin interaction in a fractional quantum spin Hall system, and demonstrate that the charge-density-wave stripe state can be realized in a fractional quantum spin Hall system by tuning the strength of an inter-spin interaction, which clarifies the nature of the puzzling mysterious phase emerging in previous studies. The experimental realization of such exotic quantum state as well as its evolution in optical lattices are also discussed. These results may provide insights into the future studies of fractional topological insulators.
Experimental evidences of a large extrinsic spin Hall effect in AuW alloy
Laczkowski, P.; Rojas-Sánchez, J.-C.
2014-04-07
We report an experimental study of a gold-tungsten alloy (7 at. % W concentration in Au host) displaying remarkable properties for spintronics applications using both magneto-transport in lateral spin valve devices and spin-pumping with inverse spin Hall effect experiments. A very large spin Hall angle of about 10% is consistently found using both techniques with the reliable spin diffusion length of 2 nm estimated by the spin sink experiments in the lateral spin valves. With its chemical stability, high resistivity, and small induced damping, this AuW alloy may find applications in the nearest future.
Effects of ionization distribution on plasma beam focusing characteristics in Hall thrusters
NASA Astrophysics Data System (ADS)
Ning, Zhongxi; Liu, Hui; Yu, Daren; Zhou, Zhongxiang
2011-11-01
The relationship between ionization distribution and divergence of plasma beam in a Hall thruster is investigated using spectrum and probe methods. Experimental results indicate that the shift of ionization region towards the exit of channel causes the reduction of accelerating field and the enhancement of electron thermal pressure effect, which result in further deviation of equipotential lines to magnetic field lines and further increase in divergence of plasma beam. It is, therefore, suggested that to put the ionization region deep inside the channel and separate it from the acceleration region at the design, and development stage is helpful to improve the plasma beam focusing characteristics of a Hall thruster.
A programmable quantum current standard from the Josephson and the quantum Hall effects
Poirier, W. Lafont, F.; Djordjevic, S.; Schopfer, F.; Devoille, L.
2014-01-28
We propose a way to realize a programmable quantum current standard (PQCS) from the Josephson voltage standard and the quantum Hall resistance standard (QHR) exploiting the multiple connection technique provided by the quantum Hall effect (QHE) and the exactness of the cryogenic current comparator. The PQCS could lead to breakthroughs in electrical metrology like the realization of a programmable quantum current source, a quantum ampere-meter, and a simplified closure of the quantum metrological triangle. Moreover, very accurate universality tests of the QHE could be performed by comparing PQCS based on different QHRs.
Effects of ionization distribution on plasma beam focusing characteristics in Hall thrusters
Ning Zhongxi; Liu Hui; Yu Daren; Zhou Zhongxiang
2011-11-28
The relationship between ionization distribution and divergence of plasma beam in a Hall thruster is investigated using spectrum and probe methods. Experimental results indicate that the shift of ionization region towards the exit of channel causes the reduction of accelerating field and the enhancement of electron thermal pressure effect, which result in further deviation of equipotential lines to magnetic field lines and further increase in divergence of plasma beam. It is, therefore, suggested that to put the ionization region deep inside the channel and separate it from the acceleration region at the design, and development stage is helpful to improve the plasma beam focusing characteristics of a Hall thruster.
Hysteretic magnetoresistance and unconventional anomalous Hall effect in the frustrated magnet TmB4
Sunku, Sai Swaroop; Kong, Tai; Ito, Toshimitsu; ...
2016-05-11
We study TmB4, a frustrated magnet on the Archimedean Shastry-Sutherland lattice, through magnetization and transport experiments. The lack of anisotropy in resistivity shows that TmB4 is an electronically three-dimensional system. The magnetoresistance (MR) is hysteretic at low temperature even though a corresponding hysteresis in magnetization is absent. The Hall resistivity shows unconventional anomalous Hall effect (AHE) and is linear above saturation despite a large MR. In conclusion, we propose that complex structures at magnetic domain walls may be responsible for the hysteretic MR and may also lead to the AHE.
NASA Astrophysics Data System (ADS)
Matsuno, Genki; Omori, Yukiko; Eguchi, Takaaki; Kobayashi, Akito
2016-09-01
The topological domain wall and valley Hall effect are theoretically investigated in the molecular conductor α-(BEDT-TTF)2I3. By using the mean-field theory in an extended Hubbard model, it is demonstrated under a cylinder boundary condition that a domain wall emerges in the charge ordered phase, and exhibits a topological nature near the phase transition to the massless Dirac Fermion phase. The topological nature is well characterized by the Berry curvature, which has opposite signs in two charge ordered phases divided by the domain wall, and gives rise to the valley Hall conductivity with opposite signs, enabling these phases to be distinguished. It is also found that the valley Hall conductivity in the tilted Dirac cones exhibits a characteristic double-peak structure as a function of chemical potential using the semi classical formalism.
Dirac Circles and Quantum Hall Effect in 3D Inversion-Symmetric Crystals
NASA Astrophysics Data System (ADS)
Wieder, Benjamin J.; Kim, Youngkuk; Kane, C. L.
2015-03-01
In the presence of inversion and time-reversal symmetries, materials with weak spin-orbit coupling may host topologically protected Dirac line nodes. A band inversion transition in these systems can produce a line node which closes on itself and forms a protected Dirac circle. The surfaces parallel to this circle host zero-energy puddles in momentum space which are flat if the inverting bands have the same effective mass. In cases with differing effective masses, the surface modes disperse, but the bulk Dirac circle remains gapless. Adding an external magnetic field perpendicular to this circle creates surface Landau levels, whose number can be controlled by tuning the field strength. When a new level is created or destroyed, the bulk becomes gapless and the zero-temperature bulk conductivity displays a sharp peak. The sequence of conductivity peaks describes an unusual manifestation of the integer quantum hall effect. We characterize surface and bulk transport as a function of magnetic field strength and in the presence of disorder.
Disorder effects in the quantum Hall effect of graphene p-n junctions
NASA Astrophysics Data System (ADS)
Li, Jian; Shen, Shun-Qing
2008-11-01
The quantum Hall effect in graphene p-n junctions is studied numerically with emphasis on the effect of disorder at the interface of two adjacent regions. Conductance plateaus are found to be attached to the intensity of the disorder and are accompanied by universal conductance fluctuations in the bipolar regime, which is in good agreement with theoretical predictions of the random matrix theory on quantum chaotic cavities. The calculated Fano factors can be used in an experimental identification of the underlying transport character.
Power Reduction of the Air-Breathing Hall-Effect Thruster
NASA Astrophysics Data System (ADS)
Kim, Sungrae
Electric propulsion system is spotlighted as the next generation space propulsion system due to its benefits; one of them is specific impulse. While there are a lot of types in electric propulsion system, Hall-Effect Thruster, one of electric propulsion system, has higher thrust-to-power ratio and requires fewer power supplies for operation in comparison to other electric propulsion systems, which means it is optimal for long space voyage. The usual propellant for Hall-Effect Thruster is Xenon and it is used to be stored in the tank, which may increase the weight of the thruster. Therefore, one theory that uses the ambient air as a propellant has been proposed and it is introduced as Air-Breathing Hall-Effect Thruster. Referring to the analysis on Air-Breathing Hall-Effect Thruster, the goal of this paper is to reduce the power of the thruster so that it can be applied to real mission such as satellite orbit adjustment. To reduce the power of the thruster, two assumptions are considered. First one is changing the altitude for the operation, while another one is assuming the alpha value that is electron density to ambient air density. With assumptions above, the analysis was done and the results are represented. The power could be decreased to 10s˜1000s with the assumptions. However, some parameters that do not satisfy the expectation, which would be the question for future work, and it will be introduced at the end of the thesis.
Non-commutative geometry in higher dimensional quantum hall effect as A-class topological insulator
NASA Astrophysics Data System (ADS)
Hasebe, K.
2014-09-01
We clarify relations between the higher dimensional quantum Hall effect and A-class topological insulator. In particular, we elucidate physical implications of the higher dimensional non-commutative geometry in the context of A-class topological insulator. This presentation is based on arXiv:1403.5066.
Numerical study of influence of hydrogen backflow on krypton Hall effect thruster plasma focusing
NASA Astrophysics Data System (ADS)
Yan, Shilin; Ding, Yongjie; Wei, Liqiu; Hu, Yanlin; Li, Jie; Ning, Zhongxi; Yu, Daren
2017-03-01
The influence of backflow hydrogen on plasma plume focusing of a krypton Hall effect thruster is studied via a numerical simulation method. Theoretical analysis indicates that hydrogen participates in the plasma discharge process, changes the potential and ionization distribution in the thruster discharge cavity, and finally affects the plume focusing within a vacuum vessel.
A syringe injection rate detector employing a dual Hall-effect sensor configuration.
Mukherjee, Biswarup; George, Boby; Sivaprakasam, Mohanasankar
2013-01-01
Injection of fluids in the body using needle syringes is a standard clinical practice. The rate of injection can have various pathological effects on the body such as the pain perceived or in case of anesthesia, the amount of akinesia attained. Hence, a training system with a modified syringe employing a simple measurement scheme where a trainee can observe and practice the rate of injection prior to administering on actual human subjects, can be of great value towards reduction of complications in real life situations. In this paper, we develop a system for measurement of syringe injection rate with two Hall-effect sensors. Ring magnets attached to the body of the syringe along with the dual Hall-effect sensor configuration help in determining the position of the piston with respect to the syringe body. The two Hall-sensors are arranged in a differential configuration such that a linear relationship is obtained between the volume of liquid in the syringe (in ml) and the Hall-effect sensor output voltages. A prototype developed validated the measurement scheme. The rate of injection was displayed in real-time with a LabVIEW based Virtual Instrument. The error was within acceptable limits illustrating its efficacy for practical training purposes.
ERIC Educational Resources Information Center
Boekeloo, Bradley O.; Bush, Elizabeth N.; Novik, Melinda G.
2009-01-01
Objective: The authors examined the secondhand effects among college freshmen of others' alcohol use and related student characteristics, and perceptions about residence hallmates. Participants: The authors surveyed 509 incoming freshmen residing in predominantly freshman residence halls. Methods: The authors administered a Web-based survey 2…
NASA Astrophysics Data System (ADS)
Taniguchi, Tomohiro
2016-11-01
A theoretical formulation of magnetoresistance effect in a metallic ferromagnetic/nonmagnetic bilayer originated from the charge-spin conversion by the anomalous Hall effect is presented. Analytical expressions of the longitudinal and transverse resistivities in both nonmagnet and ferromagnet are obtained by solving the spin diffusion equation. The magnetoresistance generated from charge-spin conversion purely caused by the anomalous Hall effect in the ferromagnet is found to be proportional to the square of the spin polarizations in the ferromagnet and has fixed sign. We also find additional magnetoresistances in both nonmagnet and ferromagnet arising from the mixing of the spin Hall and anomalous Hall effects. The sign of this mixing resistance depends on those of the spin Hall angle in the nonmagnet and the spin polarizations of the ferromagnet.
Magnetoresistance, electrical conductivity, and Hall effect of glassy carbon
Baker, D.F.
1983-02-01
These properties of glassy carbon heat treated for three hours between 1200 and 2700/sup 0/C were measured from 3 to 300/sup 0/K in magnetic fields up to 5 tesla. The magnetoresistance was generally negative and saturated with reciprocal temperature, but still increased as a function of magnetic field. The maximum negative magnetoresistance measured was 2.2% for 2700/sup 0/C material. Several models based on the negative magnetoresistance being proportional to the square of the magnetic moment were attempted; the best fit was obtained for the simplest model combining Curie and Pauli paramagnetism for heat treatments above 1600/sup 0/C. Positive magnetoresistance was found only in less than 1600/sup 0/C treated glassy carbon. The electrical conductivity, of the order of 200 (ohm-cm)/sup -1/ at room temperature, can be empirically written as sigma = A + Bexp(-CT/sup -1/4) - DT/sup -1/2. The Hall coefficient was independent of magnetic field, insensitive to temperature, but was a strong function of heat treatment temperature, crossing over from negative to positive at about 1700/sup 0/C and ranging from -0.048 to 0.126 cm/sup 3//coul. The idea of one-dimensional filaments in glassy carbon suggested by the electrical conductivity is compatible with the present consensus view of the microstructure.
From quantum confinement to quantum Hall effect in graphene nanostructures
NASA Astrophysics Data System (ADS)
Guimarães, M. H. D.; Shevtsov, O.; Waintal, X.; van Wees, B. J.
2012-02-01
We study the evolution of the two-terminal conductance plateaus with a magnetic field for armchair graphene nanoribbons (GNRs) and graphene nanoconstrictions (GNCs). For GNRs, the conductance plateaus of (2e2)/(h) at zero magnetic field evolve smoothly to the quantum Hall regime, where the plateaus in conductance at even multiples of (2e2)/(h) disappear. It is shown that the relation between the energy and magnetic field does not follow the same behavior as in “bulk” graphene, reflecting the different electronic structure of a GNR. For the nanoconstrictions we show that the conductance plateaus do not have the same sharp behavior in zero magnetic field as in a GNR, which reflects the presence of backscattering in such structures. Our results show good agreement with recent experiments on high-quality graphene nanoconstrictions. The behavior with the magnetic field for a GNC shows some resemblance to the one for a GNR but now depends also on the length of the constriction. By analyzing the evolution of the conductance plateaus in the presence of the magnetic field we can obtain the width of the structures studied and show that this is a powerful experimental technique in the study of the electronic and structural properties of narrow structures.
Quantum anomalous Hall effect in time-reversal-symmetry breaking topological insulators
NASA Astrophysics Data System (ADS)
Chang, Cui-Zu; Li, Mingda
2016-03-01
The quantum anomalous Hall effect (QAHE), the last member of Hall family, was predicted to exhibit quantized Hall conductivity {σyx}=\\frac{{{e}2}}{h} without any external magnetic field. The QAHE shares a similar physical phenomenon with the integer quantum Hall effect (QHE), whereas its physical origin relies on the intrinsic topological inverted band structure and ferromagnetism. Since the QAHE does not require external energy input in the form of magnetic field, it is believed that this effect has unique potential for applications in future electronic devices with low-power consumption. More recently, the QAHE has been experimentally observed in thin films of the time-reversal symmetry breaking ferromagnetic (FM) topological insulators (TI), Cr- and V- doped (Bi,Sb)2Te3. In this topical review, we review the history of TI based QAHE, the route to the experimental observation of the QAHE in the above two systems, the current status of the research of the QAHE, and finally the prospects for future studies.
Quantum anomalous Hall effect in time-reversal-symmetry breaking topological insulators.
Chang, Cui-Zu; Li, Mingda
2016-03-31
The quantum anomalous Hall effect (QAHE), the last member of Hall family, was predicted to exhibit quantized Hall conductivity σ(yx) = e2/h without any external magnetic field. The QAHE shares a similar physical phenomenon with the integer quantum Hall effect (QHE), whereas its physical origin relies on the intrinsic topological inverted band structure and ferromagnetism. Since the QAHE does not require external energy input in the form of magnetic field, it is believed that this effect has unique potential for applications in future electronic devices with low-power consumption. More recently, the QAHE has been experimentally observed in thin films of the time-reversal symmetry breaking ferromagnetic (FM) topological insulators (TI), Cr- and V- doped (Bi,Sb)2Te3. In this topical review, we review the history of TI based QAHE, the route to the experimental observation of the QAHE in the above two systems, the current status of the research of the QAHE, and finally the prospects for future studies.
Spin Hall effect and Landau spectrum of Dirac electrons in bismuth
NASA Astrophysics Data System (ADS)
Fuseya, Yuki
2015-03-01
Bismuth has played an important role in solid-state physics. Many key phenomena were first discovered in bismuth, such as diamagnetism, Seebeck, Nernst, Shubnikov-de Haas, and de Haas-van Alphen effects. These phenomena result from particular electronic states of bismuth. The strong spin-orbit interaction (~ 1.5eV) causes strong spin-dependent interband couplings resulting in an anomalous spin magnetic moment. We investigate the spin Hall effect and the angular dependent Landau spectrum of bismuth paying special attention to the effect of the anomalous spin magnetic moment. It is shown that the spin Hall insulator is possible and there is a fundamental relationship between the spin Hall conductivity and orbital diamagnetism in the insulating state of the Dirac electrons. Based on this theoretical finding, the magnitude of spin Hall conductivity is estimated for bismuth by that of orbital susceptibility. The magnitude of spin Hall conductivity turns out to be as large as 104Ω-1 cm-1, which is about 100 times larger than that of Pt. It is also shown that the ratio of the Zeeman splitting to the cyclotron energy, which reflects the effect of crystalline spin-orbit interaction, for holes at the T-point can be larger than 1.0 (the maximum of previous theories) and exhibit strong angular dependence, which gives a possible solution to the long-standing mystery of holes at the T-point. In collaboration with Masao Ogata, Hidetoshi Fukuyama, Zengwei Zhu, Benoît Fauqué, Woun Kang, and Kamran Behnia. Supported by JSPS (KAKENHI 24244053, 25870231, and 13428660).
Prediction of near-room-temperature quantum anomalous Hall effect on honeycomb materials.
Wu, Shu-Chun; Shan, Guangcun; Yan, Binghai
2014-12-19
Recently, the long-sough quantum anomalous Hall effect was realized in a magnetic topological insulator. However, the requirement of an extremely low temperature (approximately 30 mK) hinders realistic applications. Based on ab initio band structure calculations, we propose a quantum anomalous Hall platform with a large energy gap of 0.34 and 0.06 eV on honeycomb lattices comprised of Sn and Ge, respectively. The ferromagnetic (FM) order forms in one sublattice of the honeycomb structure by controlling the surface functionalization rather than dilute magnetic doping, which is expected to be visualized by spin polarized STM in experiment. Strong coupling between the inherent quantum spin Hall state and ferromagnetism results in considerable exchange splitting and, consequently, an FM insulator with a large energy gap. The estimated mean-field Curie temperature is 243 and 509 K for Sn and Ge lattices, respectively. The large energy gap and high Curie temperature indicate the feasibility of the quantum anomalous Hall effect in the near-room-temperature and even room-temperature regions.
Electrical control of the valley Hall effect in bilayer MoS2 transistors.
Lee, Jieun; Mak, Kin Fai; Shan, Jie
2016-05-01
The valley degree of freedom of electrons in solids has been proposed as a new type of information carrier, beyond the electron charge and spin. The potential of two-dimensional semiconductor transition metal dichalcogenides in valley-based electronic and optoelectronic applications has recently been illustrated through experimental demonstrations of the optical orientation of the valley polarization and of the valley Hall effect in monolayer MoS2. However, the valley Hall conductivity in monolayer MoS2, a non-centrosymmetric crystal, cannot be easily tuned, which presents a challenge for the development of valley-based applications. Here, we show that the valley Hall effect in bilayer MoS2 transistors can be controlled with a gate voltage. The gate applies an electric field perpendicular to the plane of the material, breaking the inversion symmetry present in bilayer MoS2. The valley polarization induced by the longitudinal electrical current was imaged with Kerr rotation microscopy. The polarization was found to be present only near the edges of the device channel with opposite sign for the two edges, and was out-of-plane and strongly dependent on the gate voltage. Our observations are consistent with symmetry-dependent Berry curvature and valley Hall conductivity in bilayer MoS2.
Unconventional topological Hall effect in skyrmion crystals caused by the topology of the lattice
NASA Astrophysics Data System (ADS)
Göbel, Börge; Mook, Alexander; Henk, Jürgen; Mertig, Ingrid
2017-03-01
The hallmark of a skyrmion crystal (SkX) is the topological Hall effect (THE). In this article we predict and explain an unconventional behavior of the topological Hall conductivity in SkXs. In simple terms, the spin texture of the skyrmions causes an inhomogeneous emergent magnetic field whose associated Lorentz force acts on the electrons. By making the emergent field homogeneous, the THE is mapped onto the quantum Hall effect (QHE). Consequently, each electronic band of the SkX is assigned to a Landau level. This correspondence of THE and QHE allows us to explain the unconventional behavior of the THE of electrons in SkXs. For example, a skyrmion crystal on a triangular lattice exhibits a quantized topological Hall conductivity with steps of 2 .e2/h below and with steps of 1 .e2/h above the van Hove singularity. On top of this, the conductivity shows a prominent sign change at the van Hove singularity. These unconventional features are deeply connected to the topology of the structural lattice.
Hall effects and sub-grid-scale modeling in magnetohydrodynamic turbulence simulations
NASA Astrophysics Data System (ADS)
Miura, Hideaki; Araki, Keisuke; Hamba, Fujihiro
2016-07-01
Effects of the Hall term on short-wave components of magnetohydrodynamic turbulence and sub-grid-scale modeling of the effects are studied. Direct numerical simulations of homogeneous magnetohydrodynamic turbulence with and without the Hall term are carried out. The Hall term excites short-wave components in the magnetic field, demanding a high numerical resolution to resolve the scales smaller than the ion skin depth. A k 7 / 3-like scaling-law in the magnetic energy spectrum associated with the excitation of the short-wave components is clearly shown by the use of both an isotropic spectrum and a one-dimensional spectrum. It is also shown that the introduction of the Hall term can cause a structural transition in the vorticity field from tubes to sheets. In order to overcome a strong demand on high-resolution in space and time and to enable quicker computations, large eddy simulations with a Smagorinsky-type sub-grid-scale model are carried out. It is shown that our large eddy simulations successfully reproduce not only the energy spectrum but also tubular vortex structures, reducing the computational cost considerably.
NASA Astrophysics Data System (ADS)
Yue, Z.; Raikh, M. E.
2016-09-01
The Quantum anomalous Hall (QAH) effect in the films with nontrivial band structure accompanies the ferromagnetic transition in the system of magnetic dopants. Experimentally, the QAH transition manifests itself as a jump in the dependence of longitudinal resistivity on a weak external magnetic field. Microscopically, this jump originates from the emergence of a chiral edge mode on one side of the ferromagnetic transition. We study analytically the effect of an extended confinement on the structure of the edge modes. We employ the simplest model of the extended confinement in the form of a potential step next to the hard wall. It is shown that, unlike the conventional quantum Hall effect, where all edge channels are chiral, in the QAH effect, a complex structure of the boundary leads to nonchiral edge modes which are present on both sides of the ferromagnetic transition. Wave functions of nonchiral modes are different above and below the transition: on the "topological" side, where the chiral edge mode is supported, nonchiral modes are "repelled" from the boundary; i.e., they are much less localized than on the "trivial" side. Thus, the disorder-induced scattering into these modes will boost the extension of the chiral edge mode. The prime experimental manifestation of nonchiral modes is that, by contributing to longitudinal resistance, they smear the QAH transition.
Performance Characterization of the Air Force Transformational Satellite 12 kW Hall Thruster
NASA Technical Reports Server (NTRS)
Kamhawi, Hani; Haag, Thomas W.; Smith, Timothy; Herman, Daniel; Huang, Wensheng; Shastry, Rohit; Peterson, Peter; Mathers, Alex
2013-01-01
The STMD GCD ISP project is tasked with developing, maturing, and testing enabling human exploration propulsion requirements and potential designs for advanced high-energy, in-space propulsion systems to support deep-space human exploration and reduce travel time between Earth's orbit and future destinations for human activity. High-power Hall propulsion systems have been identified as enabling technologies and have been the focus of the activities at NASA Glenn-In-house effort to evaluate performance and interrogate operation of NASA designed and manufactured Hall thrusters. Evaluate existing high TRL EP devices that may be suitable for implementation in SEP TDM.
NASA Astrophysics Data System (ADS)
Huang, Chun-Feng; Tsai, I.-H.
It is well-established how the quantum interference induces strong localization leading to quantum Hall effect at high enough magnetic fields. Decreasing the magnetic fields, however, the localization strength can be reduced and the semiclassical magneto-oscillations following Shubnikov-de Haas formula appear in most quantum Hall systems. To understand the transport properties as the localization strength becomes weak, our team has investigated the magneto-resistance in some quantum Hall systems at low magnetic fields. Under the semiclassical transport, the crossing points in Hall plateaus showed Landau-band quantization and microwave-induced heating demonstrated the band-edge equivalence important to Landau-level addition transformation. We note that such equivalence is consistent with the edge universality based on the random matrices of Wigner type, and the Landau-band quantization can be explained by considering geometric phase effects. From our study, some quantum Hall features can survive as the semiclassical transport reveals the insufficient localization.
Interplay of Rashba effect and spin Hall effect in perpendicular Pt/Co/MgO magnetic multilayers
NASA Astrophysics Data System (ADS)
Yun-Chi, Zhao; Guang, Yang; Bo-Wen, Dong; Shou-Guo, Wang; Chao, Wang; Young, Sun; Jing-Yan, Zhang; Guang-Hua, Yu
2016-07-01
The interplay of the Rashba effect and the spin Hall effect originating from current induced spin-orbit coupling was investigated in the as-deposited and annealed Pt/Co/MgO stacks with perpendicular magnetic anisotropy. The above two effects were analyzed based on Hall measurements under external magnetic fields longitudinal and vertical to dc current, respectively. The coercive field as a function of dc current in vertical mode with only the Rashba effect involved decreases due to thermal annealing. Meanwhile, spin orbit torques calculated from Hall resistance with only the spin Hall effect involved in the longitudinal mode decrease in the annealed sample. The experimental results prove that the bottom Pt/Co interface rather than the Co/MgO top one plays a more critical role in both Rashba effect and spin Hall effect. Project supported by the National Basic Research Program of China (Grant No. 2015CB921401), the National Natural Science Foundation of China (Grant Nos. 51331002, 51371027, 51431009, 51471183, and 11274371), the National Instrumentation Program of China (Grant No. 2012YQ120048), and the Instrument Development Program of Chinese Academy of Sciences (Grant No. YZ201345).
Characteristics and transport effects of the electron drift instability in Hall-effect thrusters
NASA Astrophysics Data System (ADS)
Lafleur, T.; Baalrud, S. D.; Chabert, P.
2017-02-01
The large electron {E}× {B} drift (relative to the ions) in the azimuthal direction of Hall-effect thrusters is well known to excite a strong instability. In a recent paper (Lafleur et al 2016 Phys. Plasmas 23 053503) we demonstrated that this instability leads to an enhanced electron–ion friction force that increases the electron cross-field mobility to levels similar to those seen experimentally. Here we extend this work by considering in detail the onset criteria for the formation of this instability (both in xenon, and other propellants of interest), and identify a number of important characteristics that it displays within Hall-effect thrusters (HETs): including the appearance of an additional non-dimensionalized scaling parameter (the instability growth-to-convection ratio), which controls the instability evolution and amplitude. We also investigate the effect that the instability has on electron and ion heating in HETs, and show that it leads to an ion rotation in the azimuthal direction that is in agreement with that seen experimentally.
Nayak, Ajaya K; Fischer, Julia Erika; Sun, Yan; Yan, Binghai; Karel, Julie; Komarek, Alexander C; Shekhar, Chandra; Kumar, Nitesh; Schnelle, Walter; Kübler, Jürgen; Felser, Claudia; Parkin, Stuart S P
2016-04-01
It is well established that the anomalous Hall effect displayed by a ferromagnet scales with its magnetization. Therefore, an antiferromagnet that has no net magnetization should exhibit no anomalous Hall effect. We show that the noncolinear triangular antiferromagnet Mn3Ge exhibits a large anomalous Hall effect comparable to that of ferromagnetic metals; the magnitude of the anomalous conductivity is ~500 (ohm·cm)(-1) at 2 K and ~50 (ohm·cm)(-1) at room temperature. The angular dependence of the anomalous Hall effect measurements confirms that the small residual in-plane magnetic moment has no role in the observed effect except to control the chirality of the spin triangular structure. Our theoretical calculations demonstrate that the large anomalous Hall effect in Mn3Ge originates from a nonvanishing Berry curvature that arises from the chiral spin structure, and that also results in a large spin Hall effect of 1100 (ħ/e) (ohm·cm)(-1), comparable to that of platinum. The present results pave the way toward the realization of room temperature antiferromagnetic spintronics and spin Hall effect-based data storage devices.
Hall and gyro-viscous effects to the Rayleigh-Taylor instability in a 2D slab
NASA Astrophysics Data System (ADS)
Goto, Ryosuke; Miura, Hideaki; Ito, Atsushi; Sato, Masahiko; Hatori, Tomotoharu
2013-10-01
Small scale effects such as the Finite Larmor Radius (FLR) effect and the Hall term which are ignored in the single-fluid MHD model can be important for the growth of the high wave number unstable modes such as the ballooning instability. Here we consider a simple Rayleigh-Taylor (R-T) instability in a 2D slab, and study the effect of the Hall term and the FLR effect to the R-T instability. The FLR effect is modeled as the gyro-viscous tensor. It is shown that the linear growth rate of the high wave number modes are reduced by the FLR effect and increased by the Hall term. However, when the Hall term and the FLR effect are added simultaneously, high wave number modes are strongly reduced. We will compare results of linear stability analysis to those of nonlinear simulations, and study some aspects of nonlinear growth under the effect of the FLR and the Hall terms by the use of an appropriate index such as the mixing width. In the Hall case, mixing width is slightly increased compared with MHD case. However growth rate reduces when the Hall term and the gyro-viscosity are added simultaneously, mixing width reaches comparable level with MHD case.
NASA Astrophysics Data System (ADS)
Zhou, Jian; Jena, Puru
2017-02-01
While most of the two-dimensional (2D) topological crystalline insulators (TCIs) belong to group IV-VI narrow-band-gap semiconductors in a square lattice, in the present work we predict a TCI family based on transition metal intercalated compounds in a hexagonal lattice. First-principles calculations combined with a substrate-fixed globally optimal structural search technique show that a layer of Os prefers a uniform distribution between two graphene sheets. Band dispersion calculations reveal a Dirac point and a Dirac nodal ring near the Fermi level. The Dirac point is ascribed to the hybridization of e2 and e2* orbitals, and the Dirac ring is formed due to dispersion of s and e1* orbitals. Upon inclusion of spin-orbit coupling, these Dirac states open topologically nontrivial local band gaps, which are characterized by nonzero mirror Chern numbers. The quantum spin Hall effect is also observed by integrating the spin Berry curvature in the Brillouin zone. In contrast to the 2D group IV-VI TCIs whose band inversions at X and Y points are "locked" by C4 rotation symmetry, here the relative energy of two local band gaps can be manipulated by in-plane biaxial strains. Some other similar intercalation compounds are also shown to be topologically nontrivial. Our work extends the 2D TCI family into a hexagonal lattice composed of transition metals.
Interplay of flux guiding and Hall effect in Nb films with nanogrooves
NASA Astrophysics Data System (ADS)
Dobrovolskiy, O. V.; Hanefeld, M.; Zörb, M.; Huth, M.; Shklovskij, V. A.
2016-06-01
The interplay between vortex guiding and the Hall effect in superconducting Nb films with periodically arranged nanogrooves is studied via four-probe measurements in standard and Hall configurations and accompanying theoretical modeling. The nanogrooves are milled by focused ion beam and induce a symmetric pinning potential of the washboard type. The resistivity tensor of the films is determined in the limit of small current densities at temperatures close to the critical temperature for the fundamental matching configuration of the vortex lattice with respect to the pinning nanolandscape. The angle between the current direction with respect to the grooves is set at seven fixed values between 0° and 90°. A sign change is observed in the temperature dependence of the Hall resistivity {ρ }\\perp - of as-grown films in a narrow temperature range near T c . By contrast, for all nanopatterned films {ρ }\\perp - is non-zero in a broader temperature range below T c , allowing us to discriminate between two contributions in {ρ }\\perp -, namely one contribution originating from the guided vortex motion and the other one caused by the Hall anomaly just as in as-grown Nb films. All four measured resistivity components are successfully fitted to analytical expressions derived within the framework of a stochastic model of competing isotropic and anisotropic pinning. This provides evidence of the model validity for the description of the resistive response of superconductor thin films with washboard pinning nanolandscapes.
Gated Hall Effect Measurements on Selectively grown InGaAs Nanowires.
Lindelöw, Fredrik Gustav; Zota, Cezar; Lind, Erik
2017-02-23
InGaAs nanowires is one of the promising material systems of replacing silicon in future CMOS transistors, due to its high electron mobility, in combination with the excellent electrostatic control from the tri-gate geometry. In this article, we report on gated Hall measurements on single and multiple In0.85Ga0.15As nanowires, selectively grown in a Hall bridge geometry with nanowire widths down to 50 nm and thicknesses of 10 nm. The gated nanowires can be used as junctionless transistors, which allows for a simplified device processing as no regrowth of contact layer or ion implantation is needed, which is especially beneficial as transistor dimensions are scaled down. The analysis shows that the InGaAs layer has a carrier concentration above 10^19 cm^-3, with a Hall carrier mobility of around 1000 cm^2V^-1s^-1. The gated Hall measurements reveal an increased carrier concentration as a function of applied gate voltage, with an increasing mobility for narrow nanowires but no significant effect on larger nanowires.
Effects of an Internally-Mounted Cathode on Hall Thruster Plume Properties
NASA Technical Reports Server (NTRS)
Hofer, Richard R.; Johnson, Lee K.; Goebel, Dan M.; Fitzgerald, Dennis J.
2006-01-01
The effects of cathode position on the plume properties of an 8 kW BHT-8000 Busek Hall thruster are discussed. Experiments were conducted at the Jet Propulsion Laboratory (JPL) in a vacuum chamber suitable for the development and qualification of high-power Hall thrusters. Multi-mode Hall thruster operation was demonstrated at operating conditions ranging from 200-500 V discharge voltage, 10-40 A discharge current, and 2-8 kW discharge power. Reductions in plume divergence and increased near-field plume symmetries were found to result from the use of an internally-mounted cathode instead of the traditional externally-mounted configuration. High-current hollow cathodes developed at JPL utilizing lanthanum hexaboride (LaB6) emitters were also demonstrated. Discharge currents up to 100 A were achieved with the cathode operating alone and up to 40 A during operation with the Hall thruster. LaB6 cathodes were investigated because of their potential to reduce overall system cost and risk due to less stringent xenon purity and handling requirements.
O the Generalized Hall Effect as a Modification of Ideal Magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Goodman, Michael Lee
The generalized Hall effect (GHE) in the generalized Hall model (GHM) is studied as a correction to ideal magnetohydrodynamics (MHD) in the context of how it affects the linear stability of cylindrically symmetric equilibria and how it changes helically symmetric equilibria. The GHM differs from what is usually called the Hall model by including the electron pressure in the electron momentum equation. This gives the GHM some aspects of a two fluid model whereas the Hall model is a one fluid model. In both cases of cyclindrical and helical symmetry the presence of the electron pressure gradient as part of the GHE gives rise to an electric field tangent to the boundary of the plasma. This introduces an additional boundary condition in the case of a perfectly conducting plasma boundary. In the case of helical symmetry the equilibrium equations are a generalization of the Grad-Schafranov equation to equilibria with flow and GHE. The classification of these partial differential equations is independent of the component of the ion fluid velocity parallel to the helical direction which may allow for transonic or supersonic flows which are governed by elliptic equations. In the case of cylindrical symmetry a class of Alfven wave solutions that do not exist in ideal MHD is obtained and the accumulation point, with respect to large radial wavenumber, of the slow magnetoacoustic wave is shown to be changed from a finite nonzero value in ideal MHD to infinity by the GHE.
HYBRID AND HALL-MHD SIMULATIONS OF COLLISIONLESS RECONNECTION: EFFECTS OF PLASMA PRESSURE TENSOR
L. YIN; D. WINSKE; ET AL
2001-05-01
In this study we performed two-dimensional hybrid (particle ions, massless fluid electrons) and Hall-MHD simulations of collisionless reconnection in a thin current sheet. Both calculations include the full electron pressure tensor (instead of a localized resistivity) in the generalized Ohm's law to initiate reconnection, and in both an initial perturbation to the Harris equilibrium is applied. First, electron dynamics from the two calculations are compared, and we find overall agreement between the two calculations in both the reconnection rate and the global configuration. To address the issue of how kinetic treatment for the ions affects the reconnection dynamics, we compared the fluid-ion dynamics from the Hall-MHD calculation to the particle-ion dynamics obtained from the hybrid simulation. The comparison demonstrates that off-diagonal elements of the ion pressure tensor are important in correctly modeling the ion out-of-plane momentum transport from the X point. It is that these effects can be modeled efficiently using a particle Hall-MHD simulation method in which particle ions used in a predictor/corrector to implement the ion gyro-radius corrections. We also investigate the micro- macro-scale coupling in the magnetotail dynamics by using a new integrated approach in which particle Hall-MHD calculations are embedded inside a MHD simulation. Initial results of the simulation concerning current sheet thinning and reconnection dynamics are discussed.
Robust fractional quantum Hall effect in the N=2 Landau level in bilayer graphene
Diankov, Georgi; Liang, Chi-Te; Amet, François; Gallagher, Patrick; Lee, Menyoung; Bestwick, Andrew J.; Tharratt, Kevin; Coniglio, William; Jaroszynski, Jan; Watanabe, Kenji; Taniguchi, Takashi; Goldhaber-Gordon, David
2016-01-01
The fractional quantum Hall effect is a canonical example of electron–electron interactions producing new ground states in many-body systems. Most fractional quantum Hall studies have focussed on the lowest Landau level, whose fractional states are successfully explained by the composite fermion model. In the widely studied GaAs-based system, the composite fermion picture is thought to become unstable for the N≥2 Landau level, where competing many-body phases have been observed. Here we report magneto-resistance measurements of fractional quantum Hall states in the N=2 Landau level (filling factors 4<|ν|<8) in bilayer graphene. In contrast with recent observations of particle–hole asymmetry in the N=0/N=1 Landau levels of bilayer graphene, the fractional quantum Hall states we observe in the N=2 Landau level obey particle–hole symmetry within the fully symmetry-broken Landau level. Possible alternative ground states other than the composite fermions are discussed. PMID:28000663
Nayak, Ajaya K.; Fischer, Julia Erika; Sun, Yan; Yan, Binghai; Karel, Julie; Komarek, Alexander C.; Shekhar, Chandra; Kumar, Nitesh; Schnelle, Walter; Kübler, Jürgen; Felser, Claudia; Parkin, Stuart S. P.
2016-01-01
It is well established that the anomalous Hall effect displayed by a ferromagnet scales with its magnetization. Therefore, an antiferromagnet that has no net magnetization should exhibit no anomalous Hall effect. We show that the noncolinear triangular antiferromagnet Mn3Ge exhibits a large anomalous Hall effect comparable to that of ferromagnetic metals; the magnitude of the anomalous conductivity is ~500 (ohm·cm)−1 at 2 K and ~50 (ohm·cm)−1 at room temperature. The angular dependence of the anomalous Hall effect measurements confirms that the small residual in-plane magnetic moment has no role in the observed effect except to control the chirality of the spin triangular structure. Our theoretical calculations demonstrate that the large anomalous Hall effect in Mn3Ge originates from a nonvanishing Berry curvature that arises from the chiral spin structure, and that also results in a large spin Hall effect of 1100 (ħ/e) (ohm·cm)−1, comparable to that of platinum. The present results pave the way toward the realization of room temperature antiferromagnetic spintronics and spin Hall effect–based data storage devices. PMID:27152355
The Hall-Petch effect as a manifestation of the general size effect
NASA Astrophysics Data System (ADS)
Li, Y.; Bushby, A. J.; Dunstan, D. J.
2016-06-01
The experimental evidence for the Hall-Petch dependence of strength on the inverse square-root of grain size is reviewed critically. Both the classic data and more recent results are considered. While the data are traditionally fitted to the inverse square-root dependence, they also fit well to many other functions, both power law and non-power law. There have been difficulties, recognized for half-a-century, in the inverse square-root expression. It is now explained as an artefact of faulty data analysis. A Bayesian meta-analysis shows that the data strongly support the simple inverse or lnd/d expressions. Since these expressions derive from underlying theory, they are also more readily explicable. It is concluded that the Hall-Petch effect is not to be explained by the variety of theories found in the literature, but is a manifestation of, or to be underlain by the general size effect observed throughout micromechanics, owing to the inverse relationship between the stress required and the space available for dislocation sources to operate.
Determination of the Pt spin diffusion length by spin-pumping and spin Hall effect
Zhang, Wei; Pearson, John E.; Hoffmann, Axel; Vlaminck, Vincent; Divan, Ralu; Bader, Samuel D.
2013-12-09
The spin diffusion length of Pt at room temperature and at 8 K is experimentally determined via spin pumping and spin Hall effect in permalloy/Pt bilayers. Voltages generated during excitation of ferromagnetic resonance from the inverse spin Hall effect and anisotropic magnetoresistance effect were investigated with a broadband approach. Varying the Pt layer thickness gives rise to an evolution of the voltage line shape due to the superposition of the above two effects. By studying the ratio of the two voltage components with the Pt layer thickness, the spin diffusion length of Pt can be directly extracted. We obtain a spin diffusion length of ∼1.2 nm at room temperature and ∼1.6 nm at 8 K.
Influence of complex disorder on skew-scattering Hall effects in L 10 -ordered FePt alloy
NASA Astrophysics Data System (ADS)
Zimmermann, Bernd; Long, Nguyen H.; Mavropoulos, Phivos; Blügel, Stefan; Mokrousov, Yuriy
2016-08-01
We show by first-principles calculations that the skew-scattering anomalous Hall and spin Hall angles of L 10 -ordered FePt drastically depend on different types of disorder. A different sign of the anomalous Hall angle is obtained when slightly deviating from the stoichiometric ratio towards the Fe-rich side as compared to the Pt-rich side. For stoichiometric samples, short-range ordering of defects has a profound effect on the Hall angles and can change them by a factor of 2 as compared to the case of uncorrelated disorder. This might explain the vast range of anomalous Hall angles measured in experiments, which undergo different preparation procedures and thus might differ in their crystallographic quality.
Observation of inverse spin Hall effect in ferromagnetic FePt alloys using spin Seebeck effect
Seki, Takeshi Takanashi, Koki; Uchida, Ken-ichi; Kikkawa, Takashi; Qiu, Zhiyong; Saitoh, Eiji
2015-08-31
We experimentally observed the inverse spin Hall effect (ISHE) of ferromagnetic FePt alloys. Spin Seebeck effect due to the temperature gradient generated the spin current (J{sub s}) in the FePt|Y{sub 3}Fe{sub 5}O{sub 12} (YIG) structure, and J{sub s} was injected from YIG to FePt and converted to the charge current through ISHE of FePt. The significant difference in magnetization switching fields for FePt and YIG led to the clear separation of the voltage of ISHE from that of anomalous Nernst effect in FePt. We also investigated the effect of ordering of FePt crystal structure on the magnitude of ISHE voltage in FePt.
Observation of inverse spin Hall effect in ferromagnetic FePt alloys using spin Seebeck effect
NASA Astrophysics Data System (ADS)
Seki, Takeshi; Uchida, Ken-ichi; Kikkawa, Takashi; Qiu, Zhiyong; Saitoh, Eiji; Takanashi, Koki
2015-08-01
We experimentally observed the inverse spin Hall effect (ISHE) of ferromagnetic FePt alloys. Spin Seebeck effect due to the temperature gradient generated the spin current (Js) in the FePt|Y3Fe5O12 (YIG) structure, and Js was injected from YIG to FePt and converted to the charge current through ISHE of FePt. The significant difference in magnetization switching fields for FePt and YIG led to the clear separation of the voltage of ISHE from that of anomalous Nernst effect in FePt. We also investigated the effect of ordering of FePt crystal structure on the magnitude of ISHE voltage in FePt.
Reprint of : Effect of incoherent scattering on three-terminal quantum Hall thermoelectrics
NASA Astrophysics Data System (ADS)
Sánchez, Rafael; Sothmann, Björn; Jordan, Andrew N.
2016-08-01
A three-terminal conductor presents peculiar thermoelectric and thermal properties in the quantum Hall regime: it can behave as a symmetric rectifier and as an ideal thermal diode. These properties rely on the coherent propagation along chiral edge channels. We investigate the effect of breaking the coherent propagation by the introduction of a probe terminal. It is shown that chiral effects not only survive the presence of incoherence but they can even improve the thermoelectric performance in the totally incoherent regime.
NASA Astrophysics Data System (ADS)
Hui, Hoi-Yin; Sau, Jay D.
2017-01-01
Time-reversal invariance places strong constraints on the properties of the quantum spin Hall edge. One such restriction is the inevitability of dissipation in a Josephson junction between two superconductors formed on such an edge without the presence of interaction. Interactions and spin-conservation breaking are key ingredients for the realization of the dissipationless ac Josephson effect on such quantum spin Hall edges. We present a simple quantum impurity model that allows us to create a dissipationless fractional Josephson effect on a quantum spin Hall edge. We then use this model to substantiate a general argument that shows that any such nondissipative Josephson effect must necessarily be 8 π periodic.
NASA Astrophysics Data System (ADS)
Liu, Cheng; Liu, Ji-Gou; Zhang, Quan
2015-02-01
The paper presents a novel method to reduce the zero offset in Hall-Effect based magnetic measurement with single power supply. This method consists of a coarse zero compensation and a fine zero adjustment afterwards. By using the proposed method the zero output offset of Hall Effect sensors under using single power supply can be controlled within 0.2%. This method can be applied to all Hall Effect sensors with analog output and other similar sensors, which are powered with a single voltage or current source.
Geometrical optics of beams with vortices: Berry phase and orbital angular momentum Hall effect.
Bliokh, Konstantin Yu
2006-07-28
We consider propagation of a paraxial beam carrying the spin angular momentum (polarization) and intrinsic orbital angular momentum (IOAM) in a smoothly inhomogeneous isotropic medium. It is shown that the presence of IOAM can dramatically enhance and rearrange the topological phenomena that previously were considered solely in connection to the polarization of transverse waves. In particular, the appearance of a new type of Berry phase that describes the parallel transport of the beam structure along a curved ray is predicted. We derive the ray equations demonstrating the splitting of beams with different values of IOAM. This is the orbital angular momentum Hall effect, which resembles the Magnus effect for optical vortices. Unlike the spin Hall effect of photons, it can be much larger in magnitude and is inherent to waves of any nature. Experimental means to detect the phenomena are discussed.
Quasiparticle-mediated spin Hall effect in a superconductor.
Wakamura, T; Akaike, H; Omori, Y; Niimi, Y; Takahashi, S; Fujimaki, A; Maekawa, S; Otani, Y
2015-07-01
In some materials the competition between superconductivity and magnetism brings about a variety of unique phenomena such as the coexistence of superconductivity and magnetism in heavy-fermion superconductors or spin-triplet supercurrent in ferromagnetic Josephson junctions. Recent observations of spin-charge separation in a lateral spin valve with a superconductor evidence that these remarkable properties are applicable to spintronics, although there are still few works exploring this possibility. Here, we report the experimental observation of the quasiparticle-mediated spin Hall effect in a superconductor, NbN. This compound exhibits the inverse spin Hall (ISH) effect even below the superconducting transition temperature. Surprisingly, the ISH signal increases by more than 2,000 times compared with that in the normal state with a decrease of the injected spin current. The effect disappears when the distance between the voltage probes becomes larger than the charge imbalance length, corroborating that the huge ISH signals measured are mediated by quasiparticles.
Sheath oscillation characteristics and effect on near-wall conduction in a krypton Hall thruster
Zhang, Fengkui Kong, Lingyi; Li, Chenliang; Yang, Haiwei; Li, Wei
2014-11-15
Despite its affordability, the krypton Hall-effect thruster in applications always had problems in regard to performance. The reason for this degradation is studied from the perspective of the near-wall conductivity of electrons. Using the particle-in-cell method, the sheath oscillation characteristics and its effect on near-wall conduction are compared in the krypton and xenon Hall-effect thrusters both with wall material composed of BNSiO{sub 2}. Comparing these two thrusters, the sheath in the krypton-plasma thruster will oscillate at low electron temperatures. The near-wall conduction current is only produced by collisions between electrons and wall, thereby causing a deficiency in the channel current. The sheath displays spatial oscillations only at high electron temperature; electrons are then reflected to produce the non-oscillation conduction current needed for the krypton-plasma thruster. However, it is accompanied with intensified oscillations.
Geometrical Optics of Beams with Vortices: Berry Phase and Orbital Angular Momentum Hall Effect
Bliokh, Konstantin Yu.
2006-07-28
We consider propagation of a paraxial beam carrying the spin angular momentum (polarization) and intrinsic orbital angular momentum (IOAM) in a smoothly inhomogeneous isotropic medium. It is shown that the presence of IOAM can dramatically enhance and rearrange the topological phenomena that previously were considered solely in connection to the polarization of transverse waves. In particular, the appearance of a new type of Berry phase that describes the parallel transport of the beam structure along a curved ray is predicted. We derive the ray equations demonstrating the splitting of beams with different values of IOAM. This is the orbital angular momentum Hall effect, which resembles the Magnus effect for optical vortices. Unlike the spin Hall effect of photons, it can be much larger in magnitude and is inherent to waves of any nature. Experimental means to detect the phenomena are discussed.
Electron Inertia Effects in Hall-Driven Magnetic Field Penetration in Electron-Magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Richardson, Andrew; Angus, Justin; Swanekamp, Stephen; Schumer, Joseph; Ottinger, Paul
2015-11-01
Magnetic field penetration in electron-magnetohydrodynamics (EMHD) can be driven by density gradients through the Hall term. Here we describe the effect of electron inertia on simplified one- and two- dimensional models of a magnetic front. Nonlinear effects due to inertia cause the 1D model to develop peaked solitary waves, while in 2D a shear-driven Kelvin-Helholtz like instability causes the front to break into a series of vortices which propagate into the plasma. The combination of these two effects means that in 2D, Hall driven magnetic field penetration will typically happen in the form of complex vortex-dominated penetration, rather than as a transversely-smooth shock front. This work was supported by the Naval Research Laboratory Base Program.
Spintronic Oscillator Based on Spin-Current Feedback Using the Spin Hall Effect
NASA Astrophysics Data System (ADS)
Bhuktare, Swapnil; Singh, Hanuman; Bose, Arnab; Tulapurkar, Ashwin. A.
2017-01-01
We propose a radio-frequency nano-oscillator based on feedback of spin current into a magnetic tunnel junction (MTJ) with an in-plane magnetized pinned layer and an out-of-plane magnetized free layer. The MTJ is connected to a "feedback" strip of a material like tungsten with a giant spin Hall effect. On passing a dc current through the MTJ, the thermal fluctuations of its free layer produce an oscillatory voltage across itself owing to the magnetoresistance effect. This oscillatory voltage drives an oscillatory current into the tungsten strip which converts this charge current into spin current via the spin Hall effect and feeds it back to the MTJ. We show that this feedback can amplify the fluctuations further and drive the free layer into periodic precessional states. We also propose a way of implementing spin-current feedback by using a nanomagnet coupled to the free layer of the MTJ by dipolar magnetic field.
NASA Astrophysics Data System (ADS)
Zhou, X.; Ma, L.; Shi, Z.; Fan, W. J.; Zheng, Jian-Guo; Evans, R. F. L.; Zhou, S. M.
2015-08-01
We study the anomalous Hall-like effect (AHLE) and the effective anisotropic magnetoresistance (EAMR) in antiferromagnetic γ -IrMn3/Y3Fe5O12(YIG ) and Pt/YIG heterostructures. For γ -IrMn3/YIG , the EAMR and the AHLE resistivity change sign with temperature due to the competition between the spin Hall magnetoresistance (SMR) and the magnetic proximity effect (MPE) induced by the interfacial antiferromagnetic uncompensated magnetic moment. In contrast, for Pt/YIG, the AHLE resistivity changes sign with temperature whereas no sign change is observed in the EAMR. This is because the MPE and the SMR play a dominant role in the AHLE and the EAMR, respectively. As different types of galvanomagnetic properties, the AHLE and the EAMR have proved vital in disentangling the MPE and the SMR in metal/insulating-ferromagnet heterostructures.
Coriolis effect in optics: unified geometric phase and spin-Hall effect.
Bliokh, Konstantin Y; Gorodetski, Yuri; Kleiner, Vladimir; Hasman, Erez
2008-07-18
We examine the spin-orbit coupling effects that appear when a wave carrying intrinsic angular momentum interacts with a medium. The Berry phase is shown to be a manifestation of the Coriolis effect in a noninertial reference frame attached to the wave. In the most general case, when both the direction of propagation and the state of the wave are varied, the phase is given by a simple expression that unifies the spin redirection Berry phase and the Pancharatnam-Berry phase. The theory is supported by the experiment demonstrating the spin-orbit coupling of electromagnetic waves via a surface plasmon nanostructure. The measurements verify the unified geometric phase, demonstrated by the observed polarization-dependent shift (spin-Hall effect) of the waves.
Spectral Analysis of Non-ideal MRI Modes: The Effect of Hall Diffusion
NASA Astrophysics Data System (ADS)
Mohandas, Gopakumar; Pessah, Martin E.
2017-03-01
The effect of magnetic field diffusion on the stability of accretion disks is a problem that has attracted considerable interest of late. In particular, the Hall effect has the potential to bring about remarkable changes in the dynamical behavior of disks that are without parallel. In this paper, we conduct a systematic examination of the linear eigenmodes in a weakly magnetized differentially rotating gas with a special focus on Hall diffusion. We first develop a geometrical representation of the eigenmodes and provide a detailed quantitative description of the polarization properties of the oscillatory modes under the combined influence of the Coriolis and Hall effects. We also analyze the effects of magnetic diffusion on the structure of the unstable modes and derive analytical expressions for the kinetic and magnetic stresses and energy densities associated with the non-ideal magnetorotational instability (MRI). Our analysis explicitly demonstrates that, if the dissipative effects are relatively weak, the kinetic stresses and energies make up the dominant contribution to the total stress and energy density when the equilibrium angular momentum and magnetic field vectors are anti-parallel. This is in sharp contrast to what is observed in the case of the ideal or dissipative MRI. We conduct shearing box simulations and find very good agreement with the results derived from linear theory. Because the modes under consideration are also exact solutions of the nonlinear equations, the unconventional nature of the kinetic and magnetic stresses may have significant implications for the nonlinear evolution in some regions of protoplanetary disks.
Field effect vs. Hall mobility in back-gated multilayered InSe FETs
NASA Astrophysics Data System (ADS)
Sucharitakul, Sukrit; Goble, Nicholas; Rajesh Kumar, U.; Sankar, Raman; Chou, Fang Cheng; Chen, Yit-Tsong; Gao, Xuan
2015-03-01
2D graphene-like materials, not only are interesting for their exotic transport behavior but also, hold promises for their mechanical robustness and many possibilities in miniaturization. As one material belonging to this category, InSe is not only a promising candidate for optoelectronic devices but also has potential for ultrathin field effect transistor (FET) with high mobility transport. Recent investigation showed that exfoliated InSe FET device on PMMA substrate can yield field effect mobility as high as 1000 cm2/Vs at room temperature. In this work, various substrates such as PMMA, bare SiO2, passivated SiO2, and Si3N4 were used to fabricate InSe FET devices. Through back gating and Hall measurement, the devices' field effect mobility and intrinsic Hall mobility were extracted at various temperatures to study the dielectric effect on the material's intrinsic transport behavior. Overall trend of the devices' mobility was found to increase as the temperature is reduced due to reduced phonon scattering. The sample's field effect and Hall mobilities over the range of 77-300K fall in the range of 0.5-2.0 × 103 cm2/Vs, better than the transition metal-dichalcogenides. X.P.A.G. acknowledges NSF CAREER Award (Grant Number DMR-1151534).
Northey, G W; Oliver, M L; Rittenhouse, D M
2006-01-01
Biomechanics studies often require the analysis of position and orientation. Although a variety of transducer and camera systems can be utilized, a common inexpensive alternative is the Hall effect sensor. Hall effect sensors have been used extensively for one-dimensional position analysis but their non-linear behavior and cross-talk effects make them difficult to calibrate for effective and accurate two- and three-dimensional position and orientation analysis. The aim of this study was to develop and calibrate a displacement measurement system for a hydraulic-actuation joystick used for repetitive motion analysis of heavy equipment operators. The system utilizes an array of four Hall effect sensors that are all active during any joystick movement. This built-in redundancy allows the calibration to utilize fully connected feed forward neural networks in conjunction with a Microscribe 3D digitizer. A fully connected feed forward neural network with one hidden layer containing five neurons was developed. Results indicate that the ability of the neural network to accurately predict the x, y and z coordinates of the joystick handle was good with r(2) values of 0.98 and higher. The calibration technique was found to be equally as accurate when used on data collected 5 days after the initial calibration, indicating the system is robust and stable enough to not require calibration every time the joystick is used. This calibration system allowed an infinite number of joystick orientations and positions to be found within the range of joystick motion.
Minimal Model of Spin-Transfer Torque and Spin Pumping Caused by the Spin Hall Effect.
Chen, Wei; Sigrist, Manfred; Sinova, Jairo; Manske, Dirk
2015-11-20
In the normal-metal-ferromagnetic-insulator bilayer (such as Pt/Y_{3}Fe_{5}O_{12}) and the normal-metal-ferromagnetic-metal-oxide trilayer (such as Pt/Co/AlO_{x}) where spin injection and ejection are achieved by the spin Hall effect in the normal metal, we propose a minimal model based on quantum tunneling of spins to explain the spin-transfer torque and spin pumping caused by the spin Hall effect. The ratio of their dampinglike to fieldlike component depends on the tunneling wave function that is strongly influenced by generic material properties such as interface s-d coupling, insulating gap, and layer thickness, yet the spin relaxation plays a minor role. The quantified result renders our minimal model an inexpensive tool for searching for appropriate materials.
Silicon Carbide (SiC) Power Processing Unit (PPU) for Hall Effect Thrusters
NASA Technical Reports Server (NTRS)
Reese, Bradley
2015-01-01
Arkansas Power Electronics International (APEI), Inc., is developing a high-efficiency, radiation-hardened 3.8-kW SiC power supply for the PPU of Hall effect thrusters. This project specifically targets the design of a PPU for the high-voltage Hall accelerator (HiVHAC) thruster, with target specifications of 80- to 160-V input, 200- to 700-V/5A output, efficiency greater than 96 percent, and peak power density in excess of 2.5 kW/kg. The PPU under development uses SiC junction field-effect transistor power switches, components that APEI, Inc., has irradiated under total ionizing dose conditions to greater than 3 MRad with little to no change in device performance.
Enhanced spin Hall effect by electron correlations in CuBi alloys
Gu, Bo Xu, Zhuo; Mori, Michiyasu; Maekawa, Sadamichi; Ziman, Timothy
2015-05-07
A recent experiment in CuBi alloys obtained a large spin Hall angle (SHA) of −0.24 (Niimi et al., Phys. Rev. Lett. 109, 156602 (2012)). We find that the SHA can be dramatically enhanced by Bi impurities close to the Cu surface. The mechanisms of this enhancement are two-fold. One is that the localized impurity state on surface has a decreased hybridization and combined with Coulomb correlation effect. The other comes from the low-dimensional state of conduction electrons on surface, which results in a further enhancement of skew scattering by impurities. Furthermore, we note that a discrepancy in sign of SHA between the experiment and previous theories is simply caused by different definitions of SHA. This re-establishes skew scattering as the essential mechanism underlying the spin Hall effect in CuBi alloys.
NASA Astrophysics Data System (ADS)
Yomo, Shusuke; Tozer, Stanley
2013-03-01
The Hall effect was successfully measured for a single crystal of high temperature superconductor in a Moissanite-anvil clamp cell up to 5 GPa, with proper arrangement of lead wires and a sample. Zylon gasket, good in electrical insulation, worked well up to 5 GPa. The 30-40 % increase of the clamped pressure was observed during cooling to below 60 K. The appreciable pressure effect of the a-b plane Hall coefficient was observed and negative for La2 - x Srx CuO4 with x = 0.090. The result is discussed with those for sintered samples and those studied with a different pressurizing method. Thanks are due to Visiting Scientist Program, NHMFL, and NNSA grant DE-FG52-03NA00066.
The formation of anomalous Hall effect depending on W atoms in ZnO thin films
NASA Astrophysics Data System (ADS)
Can, Musa Mutlu; Shah, S. Ismat; Fırat, Tezer
2014-06-01
This article investigates the effects of intrinsic point defects and extrinsic W atoms on magneto electrical properties in the ZnO lattice. The analyses were accomplished for ∼0.5% W including ZnO thin films, grown using a radio frequency (RF) magnetron sputtering system. The polarized spin current dependent magnetic formation was investigated by longitudinal and transverse magneto electrical measurements in a temperature range of 5 K to 300 K. The positive magneto resistivity (PMR) ratios reached 28.8%, 12.7%, and 17.6% at 5 K for thin films, having different post-deposition annealing conditions as a consequence of ionic W dependent defects in the lattice. Furthermore, an anomalous Hall effect, originating from polarized spin currents, was understood from the split in Hall resistance versus magnetic field (Rxy(H)) curves for the thin film with high amount of Zn2+ and W6+ ionic defects.
Realization of tunable spin-dependent splitting in intrinsic photonic spin Hall effect
Ling, Xiaohui; Yi, Xunong; Zhou, Xinxing; Liu, Yachao; Shu, Weixing; Wen, Shuangchun; Luo, Hailu
2014-10-13
We report the realization of tunable spin-dependent splitting in intrinsic photonic spin Hall effect. By breaking the rotational symmetry of a cylindrical vector beam, the intrinsic vortex phases that the two spin components of the vector beam carries, which is similar to the geometric Pancharatnam-Berry phase, are no longer continuous in the azimuthal direction, and leads to observation of spin accumulation at the opposite edge of the beam. Due to the inherent nature of the phase and independency of light-matter interaction, the observed photonic spin Hall effect is intrinsic. Modulating the topological charge of the vector beam, the spin-dependent splitting can be enhanced and the direction of spin accumulation is switchable. Our findings may provide a possible route for generation and manipulation of spin-polarized photons, and enables spin-based photonics applications.
NASA Astrophysics Data System (ADS)
Munoz, F.; Collado, H. P. Ojeda; Usaj, Gonzalo; Sofo, Jorge O.; Balseiro, C. A.
2016-06-01
The electronic structure of bilayer graphene under pressure develops very interesting features with an enhancement of the trigonal warping and a splitting of the parabolic touching bands at the K point of the reciprocal space into four Dirac cones, one at K and three along the T symmetry lines. As pressure is increased, these cones separate in reciprocal space and in energy, breaking the electron-hole symmetry. Due to their energy separation, their opposite Berry curvature can be observed in valley Hall effect experiments and in the structure of the Landau levels. Based on the electronic structure obtained by density functional theory, we develop a low energy Hamiltonian that describes the effects of pressure on measurable quantities such as the Hall conductivity and the Landau levels of the system.
Effect of electron temperature anisotropy on near-wall conductivity in Hall thrusters
Zhang, Fengkui E-mail: yudaren@hit.edu.cn; Kong, Lingyi; Zhang, Xueyi; Li, Wei; Yu, Daren E-mail: yudaren@hit.edu.cn
2014-06-15
The electron velocity distribution in Hall thrusters is anisotropic, which not only makes the sheath oscillate in time, but also causes the sheath to oscillate in space under the condition of low electron temperatures. The spatial oscillation sheath has a significant effect on near-wall transport current. In this Letter, the method of particle-in-cell (2D + 3 V) was adopted to simulate the effect of anisotropic electron temperatures on near-wall conductivity in a Hall thruster. Results show that the electron-wall collision frequency is within the same order in magnitude for both anisotropic and isotropic electron temperatures. The near-wall transport current produced by collisions between the electrons and the walls is much smaller than experimental measurements. However, under the condition of anisotropic electron temperatures, the non-collision transport current produced by slow electrons which reflected by the spatial oscillation sheath is much larger and closes to measurements.