Semiclassical theory of Hall viscosity

NASA Astrophysics Data System (ADS)

Biswas, Rudro

2014-03-01

Hall viscosity is an intriguing stress response in quantum Hall systems and is predicted to be observable via the conductivity in an inhomogeneous electric field. This has been studied extensively using a range of techniques, such as adiabatic transport, effective field theories, and Kubo formulae. All of these are, however, agnostic as to the distinction between strongly correlated quantum Hall states and non-interacting ones, where the effect arises due to the fundamental non-commuting nature of velocities and orbit positions in a magnetic field. In this talk I shall develop the semiclassical theory of quantized cyclotron orbits drifting in an applied inhomogeneous electric field and use it to provide a clear physical picture of how single particle properties in a magnetic field contribute to the Hall viscosity-dependence of the conductivity.

Spontaneous magnetization and anomalous Hall effect in an emergent Dice lattice

PubMed Central

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

Observation of the quantum Hall effect in δ-doped SrTiO3

PubMed Central

Matsubara, Y.; Takahashi, K. S.; Bahramy, M. S.; Kozuka, Y.; Maryenko, D.; Falson, J.; Tsukazaki, A.; Tokura, Y.; Kawasaki, M.

2016-01-01

The quantum Hall effect is a macroscopic quantum phenomenon in a two-dimensional electron system. The two-dimensional electron system in SrTiO3 has sparked a great deal of interest, mainly because of the strong electron correlation effects expected from the 3d orbitals. Here we report the observation of the quantum Hall effect in a dilute La-doped SrTiO3-two-dimensional electron system, fabricated by metal organic molecular-beam epitaxy. The quantized Hall plateaus are found to be solely stemming from the low Landau levels with even integer-filling factors, ν=4 and 6 without any contribution from odd ν's. For ν=4, the corresponding plateau disappears on decreasing the carrier density. Such peculiar behaviours are proposed to be due to the crossing between the Landau levels originating from the two subbands composed of d orbitals with different effective masses. Our findings pave a way to explore unprecedented quantum phenomena in d-electron systems. PMID:27228903

Quantum Hall resistance standard in graphene devices under relaxed experimental conditions

NASA Astrophysics Data System (ADS)

Ribeiro-Palau, R.; Lafont, F.; Brun-Picard, J.; Kazazis, D.; Michon, A.; Cheynis, F.; Couturaud, O.; Consejo, C.; Jouault, B.; Poirier, W.; Schopfer, F.

2015-11-01

The quantum Hall effect provides a universal standard for electrical resistance that is theoretically based on only the Planck constant h and the electron charge e. Currently, this standard is implemented in GaAs/AlGaAs, but graphene's electronic properties have given hope for a more practical device. Here, we demonstrate that the experimental conditions necessary for the operation of devices made of high-quality graphene grown by chemical vapour deposition on silicon carbide can be extended and significantly relaxed compared with those for state-of-the-art GaAs/AlGaAs devices. In particular, the Hall resistance can be accurately quantized to within 1 × 10-9 over a 10 T wide range of magnetic flux density, down to 3.5 T, at a temperature of up to 10 K or with a current of up to 0.5 mA. This experimental simplification highlights the great potential of graphene in the development of user-friendly and versatile quantum standards that are compatible with broader industrial uses beyond those in national metrology institutes. Furthermore, the measured agreement of the quantized Hall resistance in graphene and GaAs/AlGaAs, with an ultimate uncertainty of 8.2 × 10-11, supports the universality of the quantum Hall effect. This also provides evidence of the relation of the quantized Hall resistance with h and e, which is crucial for the new Système International d'unités to be based on fixing such fundamental constants of nature.

Integer, fractional, and anomalous quantum Hall effects explained with Eyring's rate process theory and free volume concept.

PubMed

Hao, Tian

2017-02-22

The Hall effects, especially the integer, fractional and anomalous quantum Hall effects, have been addressed using Eyring's rate process theory and free volume concept. The basic assumptions are that the conduction process is a common rate controlled "reaction" process that can be described with Eyring's absolute rate process theory; the mobility of electrons should be dependent on the free volume available for conduction electrons. The obtained Hall conductivity is clearly quantized as with prefactors related to both the magnetic flux quantum number and the magnetic quantum number via the azimuthal quantum number, with and without an externally applied magnetic field. This article focuses on two dimensional (2D) systems, but the approaches developed in this article can be extended to 3D systems.

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.

Mini array of quantum Hall devices based on epitaxial graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Novikov, S.; Lebedeva, N.; Hämäläinen, J.

2016-05-07

Series connection of four quantum Hall effect (QHE) devices based on epitaxial graphene films was studied for realization of a quantum resistance standard with an up-scaled value. The tested devices showed quantum Hall plateaux R{sub H,2} at a filling factor v = 2 starting from a relatively low magnetic field (between 4 T and 5 T) when the temperature was 1.5 K. The precision measurements of quantized Hall resistance of four QHE devices connected by triple series connections and external bonding wires were done at B = 7 T and T = 1.5 K using a commercial precision resistance bridge with 50 μA current through the QHE device. The results showed thatmore » the deviation of the quantized Hall resistance of the series connection of four graphene-based QHE devices from the expected value of 4×R{sub H,2} = 2 h/e{sup 2} was smaller than the relative standard uncertainty of the measurement (<1 × 10{sup −7}) limited by the used resistance bridge.« less

Intrinsic quantum anomalous hall effect in a two-dimensional anilato-based lattice.

PubMed

Ni, Xiaojuan; Jiang, Wei; Huang, Huaqing; Jin, Kyung-Hwan; Liu, Feng

2018-06-13

Using first-principles calculations, we predict an intrinsic quantum anomalous Hall (QAH) state in a monolayer anilato-based metal-organic framework M2(C6O4X2)3 (M = Mn and Tc, X = F, Cl, Br and I). The spin-orbit coupling of M d orbitals opens a nontrivial band gap up to 18 meV at the Dirac point. The electron counting rule is used to explain the intrinsic nature of the QAH state. The calculated nonzero Chern number, gapless edge states and quantized Hall conductance all confirm the nontrivial topological properties in the anilato-based lattice. Our findings provide an organic materials platform for the realization of the QAH effect without the need for magnetic and charge doping, which are highly desirable for the development of low-energy-consumption spintronic devices.

Photonic topological boundary pumping as a probe of 4D quantum Hall physics

NASA Astrophysics Data System (ADS)

Zilberberg, Oded; Huang, Sheng; Guglielmon, Jonathan; Wang, Mohan; Chen, Kevin P.; Kraus, Yaacov E.; Rechtsman, Mikael C.

2018-01-01

When a two-dimensional (2D) electron gas is placed in a perpendicular magnetic field, its in-plane transverse conductance becomes quantized; this is known as the quantum Hall effect. It arises from the non-trivial topology of the electronic band structure of the system, where an integer topological invariant (the first Chern number) leads to quantized Hall conductance. It has been shown theoretically that the quantum Hall effect can be generalized to four spatial dimensions, but so far this has not been realized experimentally because experimental systems are limited to three spatial dimensions. Here we use tunable 2D arrays of photonic waveguides to realize a dynamically generated four-dimensional (4D) quantum Hall system experimentally. The inter-waveguide separation in the array is constructed in such a way that the propagation of light through the device samples over momenta in two additional synthetic dimensions, thus realizing a 2D topological pump. As a result, the band structure has 4D topological invariants (known as second Chern numbers) that support a quantized bulk Hall response with 4D symmetry. In a finite-sized system, the 4D topological bulk response is carried by localized edge modes that cross the sample when the synthetic momenta are modulated. We observe this crossing directly through photon pumping of our system from edge to edge and corner to corner. These crossings are equivalent to charge pumping across a 4D system from one three-dimensional hypersurface to the spatially opposite one and from one 2D hyperedge to another. Our results provide a platform for the study of higher-dimensional topological physics.

Photonic topological boundary pumping as a probe of 4D quantum Hall physics.

PubMed

Zilberberg, Oded; Huang, Sheng; Guglielmon, Jonathan; Wang, Mohan; Chen, Kevin P; Kraus, Yaacov E; Rechtsman, Mikael C

2018-01-03

When a two-dimensional (2D) electron gas is placed in a perpendicular magnetic field, its in-plane transverse conductance becomes quantized; this is known as the quantum Hall effect. It arises from the non-trivial topology of the electronic band structure of the system, where an integer topological invariant (the first Chern number) leads to quantized Hall conductance. It has been shown theoretically that the quantum Hall effect can be generalized to four spatial dimensions, but so far this has not been realized experimentally because experimental systems are limited to three spatial dimensions. Here we use tunable 2D arrays of photonic waveguides to realize a dynamically generated four-dimensional (4D) quantum Hall system experimentally. The inter-waveguide separation in the array is constructed in such a way that the propagation of light through the device samples over momenta in two additional synthetic dimensions, thus realizing a 2D topological pump. As a result, the band structure has 4D topological invariants (known as second Chern numbers) that support a quantized bulk Hall response with 4D symmetry. In a finite-sized system, the 4D topological bulk response is carried by localized edge modes that cross the sample when the synthetic momenta are modulated. We observe this crossing directly through photon pumping of our system from edge to edge and corner to corner. These crossings are equivalent to charge pumping across a 4D system from one three-dimensional hypersurface to the spatially opposite one and from one 2D hyperedge to another. Our results provide a platform for the study of higher-dimensional topological physics.

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.

Quantum Hall effect with small numbers of vortices in Bose-Einstein condensates

NASA Astrophysics Data System (ADS)

Byrnes, Tim; Dowling, Jonathan P.

2015-08-01

When vortices are displaced in Bose-Einstein condensates (BECs), the Magnus force gives the system a momentum transverse in the direction to the displacement. We show that BECs in long channels with vortices exhibit a quantization of the current response with respect to the spatial vortex distribution. The quantization originates from the well-known topological property of the phase around a vortex; it is an integer multiple of 2 π . In a way similar to that of the integer quantum Hall effect, the current along the channel is related to this topological phase and can be extracted from two experimentally measurable quantities: the total momentum of the BEC and the spatial distribution. The quantization is in units of m /2 h , where m is the mass of the atoms and h is Planck's constant. We derive an exact vortex momentum-displacement relation for BECs in long channels under general circumstances. Our results present the possibility that the configuration described here can be used as a novel way of measuring the mass of the atoms in the BEC using a topological invariant of the system. If an accurate determination of the plateaus are experimentally possible, this gives the possibility of a topological quantum mass standard and precise determination of the fine structure constant.

Electron-Fluxon Approach to the Quantum Hall Effect

NASA Astrophysics Data System (ADS)

Fujita, Shigeji; Morabito, David; Godoy, Salvador

2001-04-01

Experimental data by Willett et al.(R. Willett et al.), Phys. Rev. Lett. 59, 1776 (1987). show that the Hall resistivity ρ_xy at the extreme low temperatures has plateaus at fractional occupation ratios (2D electron density / fluxon density) ν with odd denominators, where the longitudinal resistivity ρ_xx (nearly) vanishes. The plateau heights are quantized in units of h/e^2. Each plateau is material- and shape-independent and indicates the stability of the superconducting state. The same data show that ρ_xy is linear in B at ν=1/2, where ρ_xx has a small dip, indicating a Fermi-liquid-like state with a different kind of stability. We develop a microscopic theory of the quantum Hall effect in analogy with the theory of the high temperature superconductivity, regarding the fluxon as a quantum particle with half spin and zero mass. Each Landau level, E=(N+1/2)hbar ω_0, ω_0=eB/m, has a great degeneracy. Exchange of a longitudinal phonon can generate an attractive transition between the degenerate states. The same exchange can also pair-create electron-fluxon composites, bosonic and fermionic depending on the number of fluxons. The model accounts for the energy gap at each plateau, ensuring the stability of the superconducting state.

Observation of the Quantum Hall Effect in Confined Films of the Three-Dimensional Dirac Semimetal Cd3 As2

NASA Astrophysics Data System (ADS)

Schumann, Timo; Galletti, Luca; Kealhofer, David A.; Kim, Honggyu; Goyal, Manik; Stemmer, Susanne

2018-01-01

The magnetotransport properties of epitaxial films of Cd3 As2 , a paradigm three-dimensional Dirac semimetal, are investigated. We show that an energy gap opens in the bulk electronic states of sufficiently thin films and, at low temperatures, carriers residing in surface states dominate the electrical transport. The carriers in these states are sufficiently mobile to give rise to a quantized Hall effect. The sharp quantization demonstrates surface transport that is virtually free of parasitic bulk conduction and paves the way for novel quantum transport studies in this class of topological materials. Our results also demonstrate that heterostructuring approaches can be used to study and engineer quantum states in topological semimetals.

Gate-Controlled Transmission of Quantum Hall Edge States in Bilayer Graphene.

PubMed

Li, Jing; Wen, Hua; Watanabe, Kenji; Taniguchi, Takashi; Zhu, Jun

2018-02-02

The edge states of the quantum Hall and fractional quantum Hall effect of a two-dimensional electron gas carry key information of the bulk excitations. Here we demonstrate gate-controlled transmission of edge states in bilayer graphene through a potential barrier with tunable height. The backscattering rate is continuously varied from 0 to close to 1, with fractional quantized values corresponding to the sequential complete backscattering of individual modes. Our experiments demonstrate the feasibility to controllably manipulate edge states in bilayer graphene, thus opening the door to more complex experiments.

Gate-Controlled Transmission of Quantum Hall Edge States in Bilayer Graphene

NASA Astrophysics Data System (ADS)

Li, Jing; Wen, Hua; Watanabe, Kenji; Taniguchi, Takashi; Zhu, Jun

2018-02-01

The edge states of the quantum Hall and fractional quantum Hall effect of a two-dimensional electron gas carry key information of the bulk excitations. Here we demonstrate gate-controlled transmission of edge states in bilayer graphene through a potential barrier with tunable height. The backscattering rate is continuously varied from 0 to close to 1, with fractional quantized values corresponding to the sequential complete backscattering of individual modes. Our experiments demonstrate the feasibility to controllably manipulate edge states in bilayer graphene, thus opening the door to more complex experiments.

Highly-ordered wide bandgap materials for quantized anomalous Hall and magnetoelectric effects

NASA Astrophysics Data System (ADS)

Otrokov, M. M.; Menshchikova, T. V.; Vergniory, M. G.; Rusinov, I. P.; Vyazovskaya, A. Yu; Koroteev, Yu M.; Bihlmayer, G.; Ernst, A.; Echenique, P. M.; Arnau, A.; Chulkov, E. V.

2017-06-01

An interplay of spin-orbit coupling and intrinsic magnetism is known to give rise to the quantum anomalous Hall and topological magnetoelectric effects under certain conditions. Their realization could open access to low power consumption electronics as well as many fundamental phenomena like image magnetic monopoles, Majorana fermions and others. Unfortunately, being realized very recently, these effects are only accessible at extremely low temperatures and the lack of appropriate materials that would enable the temperature increase is a most severe challenge. Here, we propose a novel material platform with unique combination of properties making it perfectly suitable for the realization of both effects at elevated temperatures. The key element of the computational material design is an extension of a topological insulator (TI) surface by a thin film of ferromagnetic insulator, which is both structurally and compositionally compatible with the TI. Following this proposal we suggest a variety of specific systems and discuss their numerous advantages, in particular wide band gaps with the Fermi level located in the gap.

Degradation of GaAs/AlGaAs Quantized Hall Resistors With Alloyed AuGe/Ni Contacts.

PubMed

Lee, Kevin C

1998-01-01

Careful testing over a period of 6 years of a number of GaAs/AlGaAs quantized Hall resistors (QHR) made with alloyed AuGe/Ni contacts, both with and without passivating silicon nitride coatings, has resulted in the identification of important mechanisms responsible for degradation in the performance of the devices as resistance standards. Covering the contacts with a film, such as a low-temperature silicon nitride, that is impervious to humidity and other contaminants in the atmosphere prevents the contacts from degrading. The devices coated with silicon nitride used in this study, however, showed the effects of a conducting path in parallel with the 2-dimensional electron gas (2-DEG) at temperatures above 1.1 K which interferes with their use as resistance standards. Several possible causes of this parallel conduction are evaluated. On the basis of this work, two methods are proposed for protecting QHR devices with alloyed AuGe/Ni contacts from degradation: the heterostructure can be left unpassivated, but the alloyed contacts can be completely covered with a very thick (> 3 μm) coating of gold; or the GaAs cap layer can be carefully etched away after alloying the contacts and prior to depositing a passivating silicon nitride coating over the entire sample. Of the two, the latter is more challenging to effect, but preferable because both the contacts and the heterostructure are protected from corrosion and oxidation.

Spin Hall effects

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

Validation of a quantized-current source with 0.2 ppm uncertainty

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stein, Friederike; Fricke, Lukas, E-mail: lukas.fricke@ptb.de; Scherer, Hansjörg

2015-09-07

We report on high-accuracy measurements of quantized current, sourced by a tunable-barrier single-electron pump at frequencies f up to 1 GHz. The measurements were performed with an ultrastable picoammeter instrument, traceable to the Josephson and quantum Hall effects. Current quantization according to I = ef with e being the elementary charge was confirmed at f = 545 MHz with a total relative uncertainty of 0.2 ppm, improving the state of the art by about a factor of 5. The accuracy of a possible future quantum current standard based on single-electron transport was experimentally validated to be better than the best (indirect) realization of the ampere within themore » present SI.« less

Quantum Hall signatures of dipolar Mahan excitons

NASA Astrophysics Data System (ADS)

Schinner, G. J.; Repp, J.; Kowalik-Seidl, K.; Schubert, E.; Stallhofer, M. P.; Rai, A. K.; Reuter, D.; Wieck, A. D.; Govorov, A. O.; Holleitner, A. W.; Kotthaus, J. P.

2013-01-01

We explore the photoluminescence of spatially indirect, dipolar Mahan excitons in a gated double quantum well diode containing a mesoscopic electrostatic trap for neutral dipolar excitons at low temperatures down to 250 mK and in quantizing magnetic fields. Mahan excitons in the surrounding of the trap, consisting of individual holes interacting with a degenerate two-dimensional electron system confined in one of the quantum wells, exhibit strong quantum Hall signatures at integer filling factors and related anomalies around filling factor ν=(2)/(3),(3)/(5), and (1)/(2), reflecting the formation of composite fermions. Interactions across the trap perimeter are found to influence the energy of the confined neutral dipolar excitons by the presence of the quantum Hall effects in the two-dimensional electron system surrounding the trap.

Position-Momentum Duality and Fractional Quantum Hall Effect in Chern Insulators

DOE PAGES

Claassen, Martin; Lee, Ching-Hua; Thomale, Ronny; ...

2015-06-11

We develop a first quantization description of fractional Chern insulators that is the dual of the conventional fractional quantum Hall (FQH) problem, with the roles of position and momentum interchanged. In this picture, FQH states are described by anisotropic FQH liquids forming in momentum-space Landau levels in a fluctuating magnetic field. The fundamental quantum geometry of the problem emerges from the interplay of single-body and interaction metrics, both of which act as momentum-space duals of the geometrical picture of the anisotropic FQH effect. We then present a novel broad class of ideal Chern insulator lattice models that act as dualsmore » of the isotropic FQH effect. The interacting problem is well-captured by Haldane pseudopotentials and affords a detailed microscopic understanding of the interplay of interactions and non-trivial quantum geometry.« less

Dimensional quantization effects in the thermodynamics of conductive filaments

NASA Astrophysics Data System (ADS)

Niraula, D.; Grice, C. R.; Karpov, V. G.

2018-06-01

We consider the physical effects of dimensional quantization in conductive filaments that underlie operations of some modern electronic devices. We show that, as a result of quantization, a sufficiently thin filament acquires a positive charge. Several applications of this finding include the host material polarization, the stability of filament constrictions, the equilibrium filament radius, polarity in device switching, and quantization of conductance.

Dimensional quantization effects in the thermodynamics of conductive filaments.

PubMed

Niraula, D; Grice, C R; Karpov, V G

2018-06-29

We consider the physical effects of dimensional quantization in conductive filaments that underlie operations of some modern electronic devices. We show that, as a result of quantization, a sufficiently thin filament acquires a positive charge. Several applications of this finding include the host material polarization, the stability of filament constrictions, the equilibrium filament radius, polarity in device switching, and quantization of conductance.

Terahertz spectroscopy on Faraday and Kerr rotations in a quantum anomalous Hall state.

PubMed

Okada, Ken N; Takahashi, Youtarou; Mogi, Masataka; Yoshimi, Ryutaro; Tsukazaki, Atsushi; Takahashi, Kei S; Ogawa, Naoki; Kawasaki, Masashi; Tokura, Yoshinori

2016-07-20

Electrodynamic responses from three-dimensional topological insulators are characterized by the universal magnetoelectric term constituent of the Lagrangian formalism. The quantized magnetoelectric coupling, which is generally referred to as topological magnetoelectric effect, has been predicted to induce exotic phenomena including the universal low-energy magneto-optical effects. Here we report the experimental indication of the topological magnetoelectric effect, which is exemplified by magneto-optical Faraday and Kerr rotations in the quantum anomalous Hall states of magnetic topological insulator surfaces by terahertz magneto-optics. The universal relation composed of the observed Faraday and Kerr rotation angles but not of any material parameters (for example, dielectric constant and magnetic susceptibility) well exhibits the trajectory towards the fine structure constant in the quantized limit.

Terahertz spectroscopy on Faraday and Kerr rotations in a quantum anomalous Hall state

PubMed Central

Okada, Ken N.; Takahashi, Youtarou; Mogi, Masataka; Yoshimi, Ryutaro; Tsukazaki, Atsushi; Takahashi, Kei S.; Ogawa, Naoki; Kawasaki, Masashi; Tokura, Yoshinori

2016-01-01

Electrodynamic responses from three-dimensional topological insulators are characterized by the universal magnetoelectric term constituent of the Lagrangian formalism. The quantized magnetoelectric coupling, which is generally referred to as topological magnetoelectric effect, has been predicted to induce exotic phenomena including the universal low-energy magneto-optical effects. Here we report the experimental indication of the topological magnetoelectric effect, which is exemplified by magneto-optical Faraday and Kerr rotations in the quantum anomalous Hall states of magnetic topological insulator surfaces by terahertz magneto-optics. The universal relation composed of the observed Faraday and Kerr rotation angles but not of any material parameters (for example, dielectric constant and magnetic susceptibility) well exhibits the trajectory towards the fine structure constant in the quantized limit. PMID:27436710

Modeling and analysis of energy quantization effects on single electron inverter performance

NASA Astrophysics Data System (ADS)

Dan, Surya Shankar; Mahapatra, Santanu

2009-08-01

In this paper, for the first time, the effects of energy quantization on single electron transistor (SET) inverter performance are analyzed through analytical modeling and Monte Carlo simulations. It is shown that energy quantization mainly changes the Coulomb blockade region and drain current of SET devices and thus affects the noise margin, power dissipation, and the propagation delay of SET inverter. A new analytical model for the noise margin of SET inverter is proposed which includes the energy quantization effects. Using the noise margin as a metric, the robustness of SET inverter is studied against the effects of energy quantization. A compact expression is developed for a novel parameter quantization threshold which is introduced for the first time in this paper. Quantization threshold explicitly defines the maximum energy quantization that an SET inverter logic circuit can withstand before its noise margin falls below a specified tolerance level. It is found that SET inverter designed with CT:CG=1/3 (where CT and CG are tunnel junction and gate capacitances, respectively) offers maximum robustness against energy quantization.

Topological Hall and Spin Hall Effects in Disordered Skyrmionic Textures

NASA Astrophysics Data System (ADS)

Ndiaye, Papa Birame; Akosa, Collins; Manchon, Aurelien; Spintronics Theory Group Team

We carry out a throughout study of the topological Hall and topological spin Hall effects in disordered skyrmionic systems: the dimensionless (spin) Hall angles are evaluated across the energy band structure in the multiprobe Landauer-Büttiker formalism and their link to the effective magnetic field emerging from the real space topology of the spin texture is highlighted. We discuss these results for an optimal skyrmion size and for various sizes of the sample and found that the adiabatic approximation still holds for large skyrmions as well as for few atomic size-nanoskyrmions. Finally, we test the robustness of the topological signals against disorder strength and show that topological Hall effect is highly sensitive to momentum scattering. This work was supported by the King Abdullah University of Science and Technology (KAUST) through the Award No OSR-CRG URF/1/1693-01 from the Office of Sponsored Research (OSR).

Are quantum spin Hall edge modes more resilient to disorder, sample geometry and inelastic scattering than quantum Hall edge modes?

PubMed

Mani, Arjun; Benjamin, Colin

2016-04-13

On the surface of 2D topological insulators, 1D quantum spin Hall (QSH) edge modes occur with Dirac-like dispersion. Unlike quantum Hall (QH) edge modes, which occur at high magnetic fields in 2D electron gases, the occurrence of QSH edge modes is due to spin-orbit scattering in the bulk of the material. These QSH edge modes are spin-dependent, and chiral-opposite spins move in opposing directions. Electronic spin has a larger decoherence and relaxation time than charge. In view of this, it is expected that QSH edge modes will be more robust to disorder and inelastic scattering than QH edge modes, which are charge-dependent and spin-unpolarized. However, we notice no such advantage accrues in QSH edge modes when subjected to the same degree of contact disorder and/or inelastic scattering in similar setups as QH edge modes. In fact we observe that QSH edge modes are more susceptible to inelastic scattering and contact disorder than QH edge modes. Furthermore, while a single disordered contact has no effect on QH edge modes, it leads to a finite charge Hall current in the case of QSH edge modes, and thus a vanishing of the pure QSH effect. For more than a single disordered contact while QH states continue to remain immune to disorder, QSH edge modes become more susceptible--the Hall resistance for the QSH effect changes sign with increasing disorder. In the case of many disordered contacts with inelastic scattering included, while quantization of Hall edge modes holds, for QSH edge modes a finite charge Hall current still flows. For QSH edge modes in the inelastic scattering regime we distinguish between two cases: with spin-flip and without spin-flip scattering. Finally, while asymmetry in sample geometry can have a deleterious effect in the QSH case, it has no impact in the QH case.

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.

Geometric Defects in Quantum Hall States

NASA Astrophysics Data System (ADS)

Gromov, Andrey

I will describe a geometric analogue of Laughlin quasiholes in fractional quantum Hall (FQH) states. These ``quasiholes'' are generated by an insertion of quantized fluxes of curvature - which can be modeled by branch points of a certain Riemann surface - and, consequently, are related to genons. Unlike quasiholes, the genons are not excitations, but extrinsic defects. Fusion of genons describes the response of an FQH state to a process that changes (effective) topology of the physical space. These defects are abelian for IQH states and non-abelian for FQH states. I will explain how to calculate an electric charge, geometric spin and adiabatic mutual statistics of the these defects. Leo Kadanoff Fellowship.

Probing topology by "heating": Quantized circular dichroism in ultracold atoms.

PubMed

Tran, Duc Thanh; Dauphin, Alexandre; Grushin, Adolfo G; Zoller, Peter; Goldman, Nathan

2017-08-01

We reveal an intriguing manifestation of topology, which appears in the depletion rate of topological states of matter in response to an external drive. This phenomenon is presented by analyzing the response of a generic two-dimensional (2D) Chern insulator subjected to a circular time-periodic perturbation. Because of the system's chiral nature, the depletion rate is shown to depend on the orientation of the circular shake; taking the difference between the rates obtained from two opposite orientations of the drive, and integrating over a proper drive-frequency range, provides a direct measure of the topological Chern number (ν) of the populated band: This "differential integrated rate" is directly related to the strength of the driving field through the quantized coefficient η 0 = ν/ ℏ 2 , where h = 2π ℏ is Planck's constant. Contrary to the integer quantum Hall effect, this quantized response is found to be nonlinear with respect to the strength of the driving field, and it explicitly involves interband transitions. We investigate the possibility of probing this phenomenon in ultracold gases and highlight the crucial role played by edge states in this effect. We extend our results to 3D lattices, establishing a link between depletion rates and the nonlinear photogalvanic effect predicted for Weyl semimetals. The quantized circular dichroism revealed in this work designates depletion rate measurements as a universal probe for topological order in quantum matter.

Surface and 3D Quantum Hall Effects from Engineering of Exceptional Points in Nodal-Line Semimetals

NASA Astrophysics Data System (ADS)

Molina, Rafael A.; González, José

2018-04-01

We show that, under a strong magnetic field, a 3D nodal-line semimetal is driven into a topological insulating phase in which the electronic transport takes place at the surface of the material. When the magnetic field is perpendicular to the nodal ring, the surface states of the semimetal are transmuted into Landau states which correspond to exceptional points, i.e., branch points in the spectrum of a non-Hermitian Hamiltonian which arise upon the extension to complex values of the momentum. The complex structure of the spectrum then allows us to express the number of zero-energy flat bands in terms of a new topological invariant counting the number of exceptional points. When the magnetic field is parallel to the nodal ring, we find that the bulk states are built from the pairing of surfacelike evanescent waves, giving rise to a 3D quantum Hall effect with a flat level of Landau states residing in parallel 2D slices of the 3D material. The Hall conductance is quantized in either case in units of e2/h , leading in the 3D Hall effect to a number of channels growing linearly with the section of the surface and opening the possibility to observe a macroscopic chiral current at the surface of the material.

Tunneling Anomalous and Spin Hall Effects.

PubMed

Matos-Abiague, A; Fabian, J

2015-07-31

We predict, theoretically, the existence of the anomalous Hall effect when a tunneling current flows through a tunnel junction in which only one of the electrodes is magnetic. The interfacial spin-orbit coupling present in the barrier region induces a spin-dependent momentum filtering in the directions perpendicular to the tunneling current, resulting in a skew tunneling even in the absence of impurities. This produces an anomalous Hall conductance and spin Hall currents in the nonmagnetic electrode when a bias voltage is applied across the tunneling heterojunction. If the barrier is composed of a noncentrosymmetric material, the anomalous Hall conductance and spin Hall currents become anisotropic with respect to both the magnetization and crystallographic directions, allowing us to separate this interfacial phenomenon from the bulk anomalous and spin Hall contributions. The proposed effect should be useful for proving and quantifying the interfacial spin-orbit fields in metallic and metal-semiconductor systems.

Origin of the low critical observing temperature of the quantum anomalous Hall effect in V-doped (Bi, Sb) 2Te 3 film

DOE PAGES

Li, W.; Claassen, M.; Chang, Cui -Zu; ...

2016-09-07

The experimental realization of the quantum anomalous Hall (QAH) effect in magnetically-doped (Bi, Sb) 2Te 3 films stands out as a landmark of modern condensed matter physics. However, ultra-low temperatures down to few tens of mK are needed to reach the quantization of Hall resistance, which is two orders of magnitude lower than the ferromagnetic phase transition temperature of the films. Here, we systematically study the band structure of V-doped (Bi, Sb) 2Te 3 thin films by angle-resolved photoemission spectroscopy (ARPES) and show unambiguously that the bulk valence band (BVB) maximum lies higher in energy than the surface state Diracmore » point. Finally, our results demonstrate clear evidence that localization of BVB carriers plays an active role and can account for the temperature discrepancy.« less

Charge carrier coherence and Hall effect in organic semiconductors

DOE PAGES

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

Charge carrier coherence and Hall effect in organic semiconductors.

PubMed

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

PubMed Central

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

Observation of a superfluid Hall effect

PubMed Central

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

Probing topology by “heating”: Quantized circular dichroism in ultracold atoms

PubMed Central

Tran, Duc Thanh; Dauphin, Alexandre; Grushin, Adolfo G.; Zoller, Peter; Goldman, Nathan

2017-01-01

We reveal an intriguing manifestation of topology, which appears in the depletion rate of topological states of matter in response to an external drive. This phenomenon is presented by analyzing the response of a generic two-dimensional (2D) Chern insulator subjected to a circular time-periodic perturbation. Because of the system’s chiral nature, the depletion rate is shown to depend on the orientation of the circular shake; taking the difference between the rates obtained from two opposite orientations of the drive, and integrating over a proper drive-frequency range, provides a direct measure of the topological Chern number (ν) of the populated band: This “differential integrated rate” is directly related to the strength of the driving field through the quantized coefficient η0 = ν/ℏ2, where h = 2π ℏ is Planck’s constant. Contrary to the integer quantum Hall effect, this quantized response is found to be nonlinear with respect to the strength of the driving field, and it explicitly involves interband transitions. We investigate the possibility of probing this phenomenon in ultracold gases and highlight the crucial role played by edge states in this effect. We extend our results to 3D lattices, establishing a link between depletion rates and the nonlinear photogalvanic effect predicted for Weyl semimetals. The quantized circular dichroism revealed in this work designates depletion rate measurements as a universal probe for topological order in quantum matter. PMID:28835930

Hydrodynamic Electron Flow and Hall Viscosity

NASA Astrophysics Data System (ADS)

Scaffidi, Thomas; Nandi, Nabhanila; Schmidt, Burkhard; Mackenzie, Andrew P.; Moore, Joel E.

2017-06-01

In metallic samples of small enough size and sufficiently strong momentum-conserving scattering, the viscosity of the electron gas can become the dominant process governing transport. In this regime, momentum is a long-lived quantity whose evolution is described by an emergent hydrodynamical theory. Furthermore, breaking time-reversal symmetry leads to the appearance of an odd component to the viscosity called the Hall viscosity, which has attracted considerable attention recently due to its quantized nature in gapped systems but still eludes experimental confirmation. Based on microscopic calculations, we discuss how to measure the effects of both the even and odd components of the viscosity using hydrodynamic electronic transport in mesoscopic samples under applied magnetic fields.

Hydrodynamic Electron Flow and Hall Viscosity.

PubMed

Scaffidi, Thomas; Nandi, Nabhanila; Schmidt, Burkhard; Mackenzie, Andrew P; Moore, Joel E

2017-06-02

In metallic samples of small enough size and sufficiently strong momentum-conserving scattering, the viscosity of the electron gas can become the dominant process governing transport. In this regime, momentum is a long-lived quantity whose evolution is described by an emergent hydrodynamical theory. Furthermore, breaking time-reversal symmetry leads to the appearance of an odd component to the viscosity called the Hall viscosity, which has attracted considerable attention recently due to its quantized nature in gapped systems but still eludes experimental confirmation. Based on microscopic calculations, we discuss how to measure the effects of both the even and odd components of the viscosity using hydrodynamic electronic transport in mesoscopic samples under applied magnetic fields.

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.

Reduced Spin Hall Effects from Magnetic Proximity.

DOE PAGES

Zhang, Wei; Jungfleisch, Matthias B.; Jiang, Wanjun; ...

2015-03-26

We investigate temperature-dependent spin pumping and inverse spin Hall effects in thin Pt and Pd in contact with Permalloy. Our experiments show a decrease of the spin Hall effect with decreasing temperature, which is attributed to a temperature-dependent proximity effect. The spin Hall angle decreases from 0.086 at room temperature to 0.042 at 10 K for Pt and is nearly negligible at 10 K for Pd. By first-principle calculations, we show that the spin Hall conductivity indeed reduces by increasing the proximity-induced spin magnetic moments for both Pt and Pd. This work highlights the important role of proximity-induced magnetic orderingmore » to spin Hall phenomena in Pt and Pd.« less

Quantum Hall effect in dual gated BiSbTeSe2 topological insulator

NASA Astrophysics Data System (ADS)

Chong, Su Kong; Han, Kyu Bum; Nagaoka, Akira; Harmer, Jared; Tsuchikawa, Ryuichi; Sparks, Taylor D.; Deshpande, Vikram V.

The discovery of topological insulators (TIs) has expanded the family of Dirac materials and enables the probing of exotic matter such as Majorana fermions and magnetic monopoles. Different from conventional 2D electron gas, 3D TIs exhibit a gapped insulating bulk and gapless topological surface states as a result of the strong spin-orbit coupling. BiSbTeSe2 is also known to be a 3D TI with a large intrinsic bulk gap of about 0.3 eV and a single Dirac cone surface state. The highly bulk insulating BiSbTeSe2 permits surface dominated conduction, which is an ideal system for the study of quantum Hall effect (QHE). Due to the spin-momentum locking, the Dirac fermions at the topological surface states have a degeneracy of one. In the QH regime, the Hall conductance is quantized to (n + 1 / 2) e2 / h , where n is an integer and the factor of half is related to Berry curvature. In this work, we study the QHE 3D TI using a dual gated BiSbTeSe2 device. By tuning the chemical potentials on top and bottom surfaces, integer QHE with Landau filling factors, ν = 0, +/-1, and +/-2 are observed.

Synchronization of spin-transfer torque oscillators by spin pumping, inverse spin Hall, and spin Hall effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elyasi, Mehrdad; Bhatia, Charanjit S.; Yang, Hyunsoo, E-mail: eleyang@nus.edu.sg

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.

Spin Hall Effects in Metallic Antiferromagnets

DOE PAGES

Zhang, Wei; Jungfleisch, Matthias B.; Jiang, Wanjun; ...

2014-11-04

In this paper, we investigate four CuAu-I-type metallic antiferromagnets for their potential as spin current detectors using spin pumping and inverse spin Hall effect. Nontrivial spin Hall effects were observed for FeMn, PdMn, and IrMn while a much higher effect was obtained for PtMn. Using thickness-dependent measurements, we determined the spin diffusion lengths of these materials to be short, on the order of 1 nm. The estimated spin Hall angles of the four materials follow the relationship PtMn > IrMn > PdMn > FeMn, highlighting the correlation between the spin-orbit coupling of nonmagnetic species and the magnitude of the spinmore » Hall effect in their antiferromagnetic alloys. These experiments are compared with first-principles calculations. Finally, engineering the properties of the antiferromagnets as well as their interfaces can pave the way for manipulation of the spin dependent transport properties in antiferromagnet-based spintronics.« less

Master equation for open two-band systems and its applications to Hall conductance

NASA Astrophysics Data System (ADS)

Shen, H. Z.; Zhang, S. S.; Dai, C. M.; Yi, X. X.

2018-02-01

Hall conductivity in the presence of a dephasing environment has recently been investigated with a dissipative term introduced phenomenologically. In this paper, we study the dissipative topological insulator (TI) and its topological transition in the presence of quantized electromagnetic environments. A Lindblad-type equation is derived to determine the dynamics of a two-band system. When the two-band model describes TIs, the environment may be the fluctuations of radiation that surround the TIs. We find the dependence of decay rates in the master equation on Bloch vectors in the two-band system, which leads to a mixing of the band occupations. Hence the environment-induced current is in general not perfectly topological in the presence of coupling to the environment, although deviations are small in the weak limit. As an illustration, we apply the Bloch-vector-dependent master equation to TIs and calculate the Hall conductance of tight-binding electrons in a two-dimensional lattice. The influence of environments on the Hall conductance is presented and discussed. The calculations show that the phase transition points of the TIs are robust against the quantized electromagnetic environment. The results might bridge the gap between quantum optics and topological photonic materials.

Extrinsic spin Hall effect in graphene

NASA Astrophysics Data System (ADS)

Rappoport, Tatiana

The intrinsic spin-orbit coupling in graphene is extremely weak, making it a promising spin conductor for spintronic devices. In addition, many applications also require the generation of spin currents in graphene. Theoretical predictions and recent experimental results suggest one can engineer the spin Hall effect in graphene by greatly enhancing the spin-orbit coupling in the vicinity of an impurity. The extrinsic spin Hall effect then results from the spin-dependent skew scattering of electrons by impurities in the presence of spin-orbit interaction. This effect can be used to efficiently convert charge currents into spin-polarized currents. I will discuss recent experimental results on spin Hall effect in graphene decorated with adatoms and metallic cluster and show that a large spin Hall effect can appear due to skew scattering. While this spin-orbit coupling is small if compared with what it is found in metals, the effect is strongly enhanced in the presence of resonant scattering, giving rise to robust spin Hall angles. I will present our single impurity scattering calculations done with exact partial-wave expansions and complement the analysis with numerical results from a novel real-space implementation of the Kubo formalism for tight-binding Hamiltonians. The author acknowledges the Brazilian agencies CNPq, CAPES, FAPERJ and INCT de Nanoestruturas de Carbono for financial support.

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.

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.

Landau quantization effects on hole-acoustic instability in semiconductor plasmas

NASA Astrophysics Data System (ADS)

Sumera, P.; Rasheed, A.; Jamil, M.; Siddique, M.; Areeb, F.

2017-12-01

The growth rate of the hole acoustic waves (HAWs) exciting in magnetized semiconductor quantum plasma pumped by the electron beam has been investigated. The instability of the waves contains quantum effects including the exchange and correlation potential, Bohm potential, Fermi-degenerate pressure, and the magnetic quantization of semiconductor plasma species. The effects of various plasma parameters, which include relative concentration of plasma particles, beam electron temperature, beam speed, plasma temperature (temperature of electrons/holes), and Landau electron orbital magnetic quantization parameter η, on the growth rate of HAWs, have been discussed. The numerical study of our model of acoustic waves has been applied, as an example, to the GaAs semiconductor exposed to electron beam in the magnetic field environment. An increment in either the concentration of the semiconductor electrons or the speed of beam electrons, in the presence of magnetic quantization of fermion orbital motion, enhances remarkably the growth rate of the HAWs. Although the growth rate of the waves reduces with a rise in the thermal temperature of plasma species, at a particular temperature, we receive a higher instability due to the contribution of magnetic quantization of fermions to it.

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.

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…

A quantized microwave quadrupole insulator with topologically protected corner states

NASA Astrophysics Data System (ADS)

Peterson, Christopher W.; Benalcazar, Wladimir A.; Hughes, Taylor L.; Bahl, Gaurav

2018-03-01

The theory of electric polarization in crystals defines the dipole moment of an insulator in terms of a Berry phase (geometric phase) associated with its electronic ground state. This concept not only solves the long-standing puzzle of how to calculate dipole moments in crystals, but also explains topological band structures in insulators and superconductors, including the quantum anomalous Hall insulator and the quantum spin Hall insulator, as well as quantized adiabatic pumping processes. A recent theoretical study has extended the Berry phase framework to also account for higher electric multipole moments, revealing the existence of higher-order topological phases that have not previously been observed. Here we demonstrate experimentally a member of this predicted class of materials—a quantized quadrupole topological insulator—produced using a gigahertz-frequency reconfigurable microwave circuit. We confirm the non-trivial topological phase using spectroscopic measurements and by identifying corner states that result from the bulk topology. In addition, we test the critical prediction that these corner states are protected by the topology of the bulk, and are not due to surface artefacts, by deforming the edges of the crystal lattice from the topological to the trivial regime. Our results provide conclusive evidence of a unique form of robustness against disorder and deformation, which is characteristic of higher-order topological insulators.

Dynamic State Estimation of Power Systems With Quantization Effects: A Recursive Filter Approach.

PubMed

Hu, Liang; Wang, Zidong; Liu, Xiaohui

2016-08-01

In this paper, a recursive filter algorithm is developed to deal with the state estimation problem for power systems with quantized nonlinear measurements. The measurements from both the remote terminal units and the phasor measurement unit are subject to quantizations described by a logarithmic quantizer. Attention is focused on the design of a recursive filter such that, in the simultaneous presence of nonlinear measurements and quantization effects, an upper bound for the estimation error covariance is guaranteed and subsequently minimized. Instead of using the traditional approximation methods in nonlinear estimation that simply ignore the linearization errors, we treat both the linearization and quantization errors as norm-bounded uncertainties in the algorithm development so as to improve the performance of the estimator. For the power system with such kind of introduced uncertainties, a filter is designed in the framework of robust recursive estimation, and the developed filter algorithm is tested on the IEEE benchmark power system to demonstrate its effectiveness.

Thermally driven anomalous Hall effect transitions in FeRh

NASA Astrophysics Data System (ADS)

Popescu, Adrian; Rodriguez-Lopez, Pablo; Haney, Paul M.; Woods, Lilia M.

2018-04-01

Materials exhibiting controllable magnetic phase transitions are currently in demand for many spintronics applications. Here, we investigate from first principles the electronic structure and intrinsic anomalous Hall, spin Hall, and anomalous Nernst response properties of the FeRh metallic alloy which undergoes a thermally driven antiferromagnetic-to-ferromagnetic phase transition. We show that the energy band structures and underlying Berry curvatures have important signatures in the various Hall effects. Specifically, the suppression of the anomalous Hall and Nernst effects in the antiferromagnetic state and a sign change in the spin Hall conductivity across the transition are found. It is suggested that the FeRh can be used as a spin current detector capable of differentiating the spin Hall effect from other anomalous transverse effects. The implications of this material and its thermally driven phases as a spin current detection scheme are also discussed.

Hall effect of copper nitride thin films

NASA Astrophysics Data System (ADS)

Yue, G. H.; Liu, J. Z.; Li, M.; Yuan, X. M.; Yan, P. X.; Liu, J. L.

2005-08-01

The Hall effect of copper nitride (Cu3N) thin films was investigated in our work. Cu3N films were deposited on glass substrates by radio-frequency (RF) magnetron sputtering at different temperatures using pure copper as the sputtering target. The Hall coefficients of the films are demonstrated to be dependent on the deposition gas flow rate and the measuring temperature. Both the Hall coefficient and resistance of the Cu3N films increase with the nitrogen gas flow rate at room temperature, while the Hall mobility and the carrier density of the films decrease. As the temperature changed from 100 K to 300 K, the Hall coefficient and the resistivity of the films decreased, while the carrier density increased and Hall mobility shows no great change. The energy band gap of the Cu3N films deduced from the curve of the common logarithm of the Hall coefficient against 1/T is 1.17-1.31 eV.

Hydrodynamic Electron Flow and Hall Viscosity

NASA Astrophysics Data System (ADS)

Scaffidi, Thomas; Moll, Philip; Kushwaha, Pallavi; Nandi, Nabhanila; Schmidt, Burkhard; MacKenzie, Andrew; Moore, Joel

In metallic samples of small enough size and sufficiently strong electron-electron scattering, the viscosity of the electron gas can become the dominant process governing transport. In this regime, momentum is a long-lived quantity whose evolution is described by an emergent hydrodynamical theory for which bounds on diffusion were conjectured based on an holographic correspondence. Furthermore, breaking time-reversal symmetry can lead to the appearance of an odd component to the viscosity called the Hall viscosity which has attracted a lot of attention recently due to its quantized nature in gapped systems but still eludes experimental confirmation. Based on microscopic calculations, we discuss how to measure the effects of both the even and odd components of the viscosity using hydrodynamic electronic transport in mesoscopic samples under applied magnetic fields. Gordon and Betty Moore Foundation.

Topological gapped edge states in fractional quantum Hall-superconductor heterostructures

NASA Astrophysics Data System (ADS)

Cook, Ashley; Repellin, Cécile; Regnault, Nicolas; Neupert, Titus

We propose and implement a numerical setup for studying edge states of fractional quantum Hall droplets with a superconducting instability. We focus on a time-reversal symmetric bilayer fractional quantum Hall system of Laughlin ν = 1 / 3 states. The fully gapped edges carry a topological parafermionic degree of freedom that can encode quantum information protected against local perturbations. We numerically simulate such a system using exact diagonalization by restricting the calculation to the Laughlin quasihole subspace. We study the quantization of the total charge on each edge and show that the ground states are permuted by spin flux insertion and the parafermionic Josephson effect, evidencing their topological nature and the Cooper pairing of fractionalized quasiparticles. The full affiliation for Author 3 is: Laboratoire Pierre Aigrain, Ecole Normale Supérieure-PSL Research University, CNRS, Université Pierre et Marie Curie-Sorbonne Universités, Université Paris Diderot-Sorbonne Paris Cité, 24 rue Lhomond, 75231 Paris.

Quantized circular photogalvanic effect in Weyl semimetals

NASA Astrophysics Data System (ADS)

de Juan, Fernando; Grushin, Adolfo G.; Morimoto, Takahiro; Moore, Joel E.

The circular photogalvanic effect (CPGE) is the part of a photocurrent that switches depending on the sense of circular polarization of the incident light. It has been consistently observed in systems without inversion symmetry and depends on non-universal material details. We find that in a class of Weyl semimetals (e.g. SrSi2) and three-dimensional Rashba materials (e.g. doped Te) without inversion and mirror symmetries, the CPGE trace is effectively Quantized in terms of the combination of fundamental constants e3/h2 cɛ0 with no material-dependent parameters. This is so because the CPGE directly measures the topological charge of Weyl points near the Fermi surface, and non-quantized corrections from disorder and additional bands can be small over a significant range of incident frequencies. Moreover, the magnitude of the CPGE induced by a Weyl node is relatively large, which enables the direct detection of the monopole charge with current techniques.

Quantized circular photogalvanic effect in Weyl semimetals

NASA Astrophysics Data System (ADS)

de Juan, Fernando; Grushin, Adolfo G.; Morimoto, Takahiro; Moore, Joel E.

2017-07-01

The circular photogalvanic effect (CPGE) is the part of a photocurrent that switches depending on the sense of circular polarization of the incident light. It has been consistently observed in systems without inversion symmetry and depends on non-universal material details. Here we find that in a class of Weyl semimetals (for example, SrSi2) and three-dimensional Rashba materials (for example, doped Te) without inversion and mirror symmetries, the injection contribution to the CPGE trace is effectively quantized in terms of the fundamental constants e, h, c and with no material-dependent parameters. This is so because the CPGE directly measures the topological charge of Weyl points, and non-quantized corrections from disorder and additional bands can be small over a significant range of incident frequencies. Moreover, the magnitude of the CPGE induced by a Weyl node is relatively large, which enables the direct detection of the monopole charge with current techniques.

Hamiltonian theory of gaps, masses, and polarization in quantum Hall states

NASA Astrophysics Data System (ADS)

Shankar, R.

2001-02-01

In two short papers I had described an extension, to all length scales, of the Hamiltonian theory of composite fermions (CF) that Murthy and I developed for the infrared, and applied it to compute finite-temperature quantities for quantum Hall fractions. I furnish details of the extended theory and apply it to Jain fractions ν=p/(2ps+1). The explicit operator description in terms of the CF allows one to answer quantitative and qualitative issues, some of which cannot even be posed otherwise. I compute activation gaps for several potentials, exhibit their particle-hole symmetry, the profiles of charge density in states with a quasiparticle or hole (all in closed form), and compare to results from trial wave functions and exact diagonalization. The Hartree-Fock approximation is used, since much of the nonperturbative physics is built-in at tree level. I compare the gaps to experiment, and comment on the rough equality of normalized masses near half- and quarter-filling. I compute the critical fields at which the Hall system will jump from one quantized value of polarization to another, and the polarization and relaxation rates for half-filling as a function of temperature and propose a Korringa-like law. After providing some plausibility arguments, I explore the possibility of describing several magnetic phenomena in dirty systems with an effective potential, by extracting a free parameter describing the potential from one data point and then using it to predict all the others from that sample. This works to the accuracy typical of this theory (10-20 %). I explain why the CF behaves like a free particle in some magnetic experiments when it is not, what exactly the CF is made of, what one means by its dipole moment, and how the comparison of theory to experiment must be modified to fit the peculiarities of the quantized Hall problem.

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.

Augmenting Phase Space Quantization to Introduce Additional Physical Effects

NASA Astrophysics Data System (ADS)

Robbins, Matthew P. G.

Quantum mechanics can be done using classical phase space functions and a star product. The state of the system is described by a quasi-probability distribution. A classical system can be quantized in phase space in different ways with different quasi-probability distributions and star products. A transition differential operator relates different phase space quantizations. The objective of this thesis is to introduce additional physical effects into the process of quantization by using the transition operator. As prototypical examples, we first look at the coarse-graining of the Wigner function and the damped simple harmonic oscillator. By generalizing the transition operator and star product to also be functions of the position and momentum, we show that additional physical features beyond damping and coarse-graining can be introduced into a quantum system, including the generalized uncertainty principle of quantum gravity phenomenology, driving forces, and decoherence.

Anomalous Hall effect in calcium-doped lanthanum cobaltite and gadolinium

NASA Astrophysics Data System (ADS)

Baily, Scott Alan

The physical origin of the anomalous (proportional to magnetization) Hall effect is not very well understood. While many theories account for a Hall effect proportional to the magnetization of a material, these theories often predict effects significantly smaller than those found in ferromagnetic materials. An even more significant deficiency of the conventional theories is that they predict an anomalous Hall resistivity that is proportional to a power of the resistivity, and in the absence of a metal insulator transition cannot account for the anomalous Hall effect that peaks near TC. Recent models based on a geometric, or Berry, phase have had a great deal of success describing the anomalous Hall effect in double-exchange systems (e.g., lanthanum manganite and chromium dioxide). In gadolinium, as in double-exchange magnets, the exchange interaction is mediated by the conduction electrons and the anomalous Hall effect may therefore resemble that of CrO2 and other metallic double-exchange ferromagnets. Lanthanum cobaltite is similar to manganite in many ways, but a strong double-exchange interaction is not present. Calcium-doped lanthanum cobaltite films were found to have the largest anomalous Hall effect of any ferromagnetic metal. The primary purpose of this study is to gain insight into the origin of the anomalous Hall effect with the hope that these theories can be extended to account for the effect in other materials. The Hall resistivity, magnetoresistance, and magnetization of a Gadolinium single crystal were measured in fields up to 30 T. Cobaltite films were grown via laser ablation and characterized by a variety of techniques. Hall resistivity, magnetoresistance, magnetization, and magnetothermopower of L 1-xCaxCoO3 samples with 0.15 < x < 0.4 were measured in fields up to 7 T. The Gd results suggest that Berry's phase contributes partially to the Hall effect near TC. Berry's phase theories hold promise for explaining the large anomalous Hall effect in

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.

Fractional charge revealed in computer simulations of resonant tunneling in the fractional quantum Hall regime.

PubMed

Tsiper, E V

2006-08-18

The concept of fractional charge is central to the theory of the fractional quantum Hall effect. Here I use exact diagonalization as well as configuration space renormalization to study finite clusters which are large enough to contain two independent edges. I analyze the conditions of resonant tunneling between the two edges. The "computer experiment" reveals a periodic sequence of resonant tunneling events consistent with the experimentally observed fractional quantization of electric charge in units of e/3 and e/5.

Direct observation of the skyrmion Hall effect

DOE PAGES

Jiang, Wanjun; Zhang, Xichao; Yu, Guoqiang; ...

2016-09-19

The well-known Hall effect describes the transverse deflection of charged particles (electrons/holes) as a result of the Lorentz force. Similarly, it is intriguing to examine if quasi-particles without an electric charge, but with a topological charge, show related transverse motion. Magnetic skyrmions with a well-defined spin texture with a unit topological charge serve as good candidates to test this hypothesis. In spite of the recent progress made on investigating magnetic skyrmions, direct observation of the skyrmion Hall effect has remained elusive. Here, by using a current-induced spin Hall spin torque, we experimentally demonstrate the skyrmion Hall effect, and the resultantmore » skyrmion accumulation, by driving skyrmions from the creep-motion regime (where their dynamics are influenced by pinning defects) into the steady-flow-motion regime. Lastly, the experimental observation of transverse transport of skyrmions due to topological charge may potentially create many exciting opportunities, such as topological selection.« less

Direct observation of the skyrmion Hall effect

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Wanjun; Zhang, Xichao; Yu, Guoqiang

The well-known Hall effect describes the transverse deflection of charged particles (electrons/holes) as a result of the Lorentz force. Similarly, it is intriguing to examine if quasi-particles without an electric charge, but with a topological charge, show related transverse motion. Magnetic skyrmions with a well-defined spin texture with a unit topological charge serve as good candidates to test this hypothesis. In spite of the recent progress made on investigating magnetic skyrmions, direct observation of the skyrmion Hall effect has remained elusive. Here, by using a current-induced spin Hall spin torque, we experimentally demonstrate the skyrmion Hall effect, and the resultantmore » skyrmion accumulation, by driving skyrmions from the creep-motion regime (where their dynamics are influenced by pinning defects) into the steady-flow-motion regime. Lastly, the experimental observation of transverse transport of skyrmions due to topological charge may potentially create many exciting opportunities, such as topological selection.« less

Tunneling Spectroscopy of Quantum Hall States in Bilayer Graphene

NASA Astrophysics Data System (ADS)

Wang, Ke; Harzheim, Achim; Watanabe, Kenji; Taniguchi, Takashi; Kim, Philip

In the quantum Hall (QH) regime, ballistic conducting paths along the physical edges of a sample appear, leading to quantized Hall conductance and vanishing longitudinal magnetoconductance. These QH edge states are often described as ballistic compressible strips separated by insulating incompressible strips, the spatial profiles of which can be crucial in understanding the stability and emergence of interaction driven QH states. In this work, we present tunneling transport between two QH edge states in bilayer graphene. Employing locally gated device structure, we guide and control the separation between the QH edge states in bilayer graphene. Using resonant Landau level tunneling as a spectroscopy tool, we measure the energy gap in bilayer graphene as a function of displacement field and probe the emergence and evolution of incompressible strips.

Spontaneous Hall effect in a chiral p-wave superconductor

NASA Astrophysics Data System (ADS)

Furusaki, Akira; Matsumoto, Masashige; Sigrist, Manfred

2001-08-01

In a chiral superconductor with broken time-reversal symmetry a ``spontaneous Hall effect'' may be observed. We analyze this phenomenon by taking into account the surface properties of a chiral superconductor. We identify two main contributions to the spontaneous Hall effect. One contribution originates from the Bernoulli (or Lorentz) force due to spontaneous currents running along the surfaces of the superconductor. The other contribution has a topological origin and is related to the intrinsic angular momentum of Cooper pairs. The latter can be described in terms of a Chern-Simons-like term in the low-energy field theory of the superconductor and has some similarities with the quantum Hall effect. The spontaneous Hall effect in a chiral superconductor is, however, nonuniversal. Our analysis is based on three approaches to the problem: a self-consistent solution of the Bogoliubov-de Gennes equation, a generalized Ginzburg-Landau theory, and a hydrodynamic formulation. All three methods consistently lead to the same conclusion that the spontaneous Hall resistance of a two-dimensional superconducting Hall bar is of order h/(ekFλ)2, where kF is the Fermi wave vector and λ is the London penetration depth; the Hall resistance is substantially suppressed from a quantum unit of resistance. Experimental issues in measuring this effect are briefly discussed.

Activation energies for the ν=5/2 Fractional Quantum Hall Effect at 10 Tesla

NASA Astrophysics Data System (ADS)

Zhang, Chi; Du, R. R.; Pfeiffer, L. N.; West, K. W.

2010-03-01

We reported on the low-temperature magnetotransport in a high-purity (mobility ˜ 1x10^7cm^2/Vs) modulation-doped GaAs/AlGaAs quantum well with a high electron density (6x10^11 cm-2). A quantized ν=5/2 Hall plateau is observed at B ˜ 10 T, with an activation gap δ5/2˜ 125±10 mK; the plateau can persist up to ˜ 25^o tilt-field. We determined the activation energies δ and quasi-gap energies δ^quasi for the ν=5/2, 7/3, and 8/3 fractional quantum Hall states in tilted-magnetic field (θ). The δ5/2, δ7/3 and the δ5/2^quasi , δ7/3^quasi are found to decrease in θ. We will present the systematic data and discuss their implications on the spin-polarization of ν=5/2 states observed at 10 T.[4pt] [1] R. Willett, Phys. Rev. Lett. 59, 1776 (1987).[0pt] [2] W. Pan et al, Solid State Commun. 119, 641 (2001).

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.

Quantization and fractional quantization of currents in periodically driven stochastic systems. I. Average currents

NASA Astrophysics Data System (ADS)

Chernyak, Vladimir Y.; Klein, John R.; Sinitsyn, Nikolai A.

2012-04-01

This article studies Markovian stochastic motion of a particle on a graph with finite number of nodes and periodically time-dependent transition rates that satisfy the detailed balance condition at any time. We show that under general conditions, the currents in the system on average become quantized or fractionally quantized for adiabatic driving at sufficiently low temperature. We develop the quantitative theory of this quantization and interpret it in terms of topological invariants. By implementing the celebrated Kirchhoff theorem we derive a general and explicit formula for the average generated current that plays a role of an efficient tool for treating the current quantization effects.

An adaptive vector quantization scheme

NASA Technical Reports Server (NTRS)

Cheung, K.-M.

1990-01-01

Vector quantization is known to be an effective compression scheme to achieve a low bit rate so as to minimize communication channel bandwidth and also to reduce digital memory storage while maintaining the necessary fidelity of the data. However, the large number of computations required in vector quantizers has been a handicap in using vector quantization for low-rate source coding. An adaptive vector quantization algorithm is introduced that is inherently suitable for simple hardware implementation because it has a simple architecture. It allows fast encoding and decoding because it requires only addition and subtraction operations.

Prospect of quantum anomalous Hall and quantum spin Hall effect in doped kagome lattice Mott insulators.

PubMed

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.

Hall Effect Spintronics

DTIC Science & Technology

2014-01-01

ferromagnetic films with perpendicular anisotropy were examined, and finally, the magnetoresistance and Hall effect in Manganese- doped Germanium was...interest in ferromagnetic semiconductors. Germanium doped with Mn is particularly interesting Distribution A: Approved for public release...unavoidable, and doped films are strongly inhomogeneous with GexMny, metallic precipitates coexisting with Mn-rich regions and Mn dilute matrix

Intrinsic Spin-Hall Effect in n-Doped Bulk GaAs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bernevig, B.Andrei; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

2010-01-15

We show that the bulk Dresselhauss (k{sup 3}) spin-orbit coupling term leads to an intrinsic spin-Hall effect in n-doped bulk GaAs, but without the appearance of uniform magnetization. The spin-Hall effect in strained and unstrained bulk GaAs has been recently observed experimentally by Kato et. al. [1]. We show that the experimental result is quantitatively consistent with the intrinsic spin-Hall effect due to the Dresselhauss term, when lifetime broadening is taken into account. On the other hand, extrinsic contribution to the spin-Hall effect is several orders of magnitude smaller than the observed effect.

Numerical analysis of Hall effect on the performance of magnetohydrodynamic heat shield system based on nonequilibrium Hall parameter model

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.

Flux and Hall states in ABJM with dynamical flavors

NASA Astrophysics Data System (ADS)

Bea, Yago; Jokela, Niko; Lippert, Matthew; Ramallo, Alfonso V.; Zoakos, Dimitrios

2015-03-01

We study the physics of probe D6-branes with quantized internal worldvolume flux in the ABJM background with unquenched massless flavors. This flux breaks parity in the (2+1)-dimensional gauge theory and allows quantum Hall states. Parity breaking is also explicitly demonstrated via the helicity dependence of the meson spectrum. We obtain general expressions for the conductivities, both in the gapped Minkowski embeddings and in the compressible black hole ones. These conductivities depend on the flux and contain a contribution from the dynamical flavors which can be regarded as an effect of intrinsic disorder due to quantum fluctuations of the fundamentals. We present an explicit, analytic family of supersymmetric solutions with nonzero charge density, electric, and magnetic fields.

Formulation of the relativistic quantum Hall effect and parity anomaly

NASA Astrophysics Data System (ADS)

Yonaga, Kouki; Hasebe, Kazuki; Shibata, Naokazu

2016-06-01

We present a relativistic formulation of the quantum Hall effect on Haldane sphere. An explicit form of the pseudopotential is derived for the relativistic quantum Hall effect with/without mass term. We clarify particular features of the relativistic quantum Hall states with the use of the exact diagonalization study of the pseudopotential Hamiltonian. Physical effects of the mass term to the relativistic quantum Hall states are investigated in detail. The mass term acts as an interpolating parameter between the relativistic and nonrelativistic quantum Hall effects. It is pointed out that the mass term unevenly affects the many-body physics of the positive and negative Landau levels as a manifestation of the "parity anomaly." In particular, we explicitly demonstrate the instability of the Laughlin state of the positive first relativistic Landau level with the reduction of the charge gap.

Hall effect spintronics for gas detection

NASA Astrophysics Data System (ADS)

Gerber, A.; Kopnov, G.; Karpovski, M.

2017-10-01

We present the concept of magnetic gas detection by the extraordinary Hall effect. The technique is compatible with the existing conductometric gas detection technologies and allows the simultaneous measurement of two independent parameters: resistivity and magnetization affected by the target gas. Feasibility of the approach is demonstrated by detecting low concentration hydrogen using thin CoPd films as the sensor material. The Hall effect sensitivity of the optimized samples exceeds 240% per 104 ppm at hydrogen concentrations below 0.5% in the hydrogen/nitrogen atmosphere, which is more than two orders of magnitude higher than the sensitivity of the conductance detection.

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.

Nonlinearity in the effect of an inhomogeneous Hall angle

NASA Astrophysics Data System (ADS)

Koon, Daniel W.

2007-03-01

The differential equation for the electric potential in a conducting material with an inhomogeneous Hall angle is extended to the large-field limit. This equation is solved for a square specimen, using a successive over-relaxation [SOR] technique for matrices of up to 101x101 size, and the Hall weighting function -- the effect of local pointlike perturbations on the measured Hall angle -- is calculated as both the unperturbed Hall angle, θH, and the perturbation, δθH, exceed the linear, small angle limit. Preliminary results show that the Hall angle varies by no more than 5% if both | θH |<1 and | δθH |<1. Thus, previously calculated results for the Hall weighting function can be used for most materials in all but the most extreme magnetic fields.

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…

Observation of anomalous Hall effect in a non-magnetic two-dimensional electron system

PubMed Central

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

Spin-polarized ground state and exact quantization at ν=5/2

NASA Astrophysics Data System (ADS)

Pan, Wei

2002-03-01

The nature of the even-denominator fractional quantum Hall effect at ν=5/2 remains elusive, in particular, its ground state spin-polarization. An earlier, so-called "hollow core" model arrived at a spin-unpolarized wave function. The more recent calculations based on a model of BCS-like pairing of composite fermions, however, suggest that its ground state is spin-polarized. In this talk, I will first review the earlier experiments and then present our recent experimental results showing evidence for a spin-polarized state at ν=5/2. Our ultra-low temperature experiments on a high quality sample established the fully developed FQHE state at ν=5/2 as well as at ν=7/3 and 8/3, manifested by a vanishing R_xx and exact quantization of the Hall plateau. The tilted field experiments showed that the added in-plane magnetic fields not only destroyed the FQHE at ν=5/2, as seen before, but also induced an electrical anisotropy, which is now interpreted as a phase transition from a paired, spin-polarized ν=5/2 state to a stripe phase, not unlike the ones at ν=9/2, 11/2, etc in the N > 1 higher Landau levels. Furthermore, in the experiments on the heterojunction insulated-gate field-effect transistors (HIGFET) at dilution refrigerator temperatures, a strong R_xx minimum and a concomitant developing Hall plateau were observed at ν=5/2 in a magnetic field as high as 12.6 Tesla. This and the subsequent density dependent studies of its energy gap largely rule out a spin-singlet state and point quite convincingly towards a spin-polarized ground state at ν=5/2.

Piezo Voltage Controlled Planar Hall Effect Devices

PubMed Central

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

Piezo Voltage Controlled Planar Hall Effect Devices.

PubMed

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.

Spin Hall Effect in Doped Semiconductor Structures

NASA Astrophysics Data System (ADS)

Tse, Wang-Kong; Das Sarma, S.

2006-02-01

In this Letter we present a microscopic theory of the extrinsic spin Hall effect based on the diagrammatic perturbation theory. Side-jump and skew-scattering contributions are explicitly taken into account to calculate the spin Hall conductivity, and we show that their effects scale as σxySJ/σxySS˜(ℏ/τ)/ɛF, with τ being the transport relaxation time. Motivated by recent experimental work we apply our theory to n- and p-doped 3D and 2D GaAs structures, obtaining σs/σc˜10-3-10-4, where σs(c) is the spin Hall (charge) conductivity, which is in reasonable agreement with the recent experimental results of Kato et al. [Science 306, 1910 (2004)]SCIEAS0036-807510.1126/science.1105514 in n-doped 3D GaAs system.

Spin Hall Effect in Doped Semiconductor Structures

NASA Astrophysics Data System (ADS)

Tse, Wang-Kong; Das Sarma, Sankar

2006-03-01

We present a microscopic theory of the extrinsic spin Hall effect based on the diagrammatic perturbation theory. Side-jump (SJ) and skew-scattering (SS) contributions are explicitly taken into account to calculate the spin Hall conductivity, and we show their effects scale as σxy^SJ/σxy^SS ˜(/τ)/ɛF, where τ being the transport relaxation time. Motivated by recent experimental work we apply our theory to n-doped and p-doped 3D and 2D GaAs structures, obtaining analytical formulas for the SJ and SS contributions. Moreover, the ratio of the spin Hall conductivity to longitudinal conductivity is found as σs/σc˜10-3-10-4, in reasonable agreement with the recent experimental results of Kato et al. [Science 306, 1910 (2004)] in n-doped 3D GaAs system.

Quantizing and sampling considerations in digital phased-locked loops

NASA Technical Reports Server (NTRS)

Hurst, G. T.; Gupta, S. C.

1974-01-01

The quantizer problem is first considered. The conditions under which the uniform white sequence model for the quantizer error is valid are established independent of the sampling rate. An equivalent spectral density is defined for the quantizer error resulting in an effective SNR value. This effective SNR may be used to determine quantized performance from infinitely fine quantized results. Attention is given to sampling rate considerations. Sampling rate characteristics of the digital phase-locked loop (DPLL) structure are investigated for the infinitely fine quantized system. The predicted phase error variance equation is examined as a function of the sampling rate. Simulation results are presented and a method is described which enables the minimum required sampling rate to be determined from the predicted phase error variance equations.

Hall-effect Thruster Channel Surface Properties Investigation (PREPRINT)

DTIC Science & Technology

2011-03-03

Article 3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER Hall-effect Thruster Channel Surface Properties Investigation 5b...13. SUPPLEMENTARY NOTES For publication in the AIAA Journal of Propulsion and Power. 14. ABSTRACT Surface properties of Hall-effect thruster...incorporated into thruster simulations, and these models must account for evolution of channel surface properties due to thruster operation. Results from

Hole mobilities and the effective Hall factor in p-type GaAs

NASA Astrophysics Data System (ADS)

Wenzel, M.; Irmer, G.; Monecke, J.; Siegel, W.

1997-06-01

We prove the effective Hall factor in p-GaAs to be larger than values discussed in the literature up to now. The scattering rates for the relevant scattering mechanisms in p-GaAs have been recalculated after critical testing the existing models. These calculations allow to deduce theoretical drift and theoretical Hall mobilities as functions of temperature which can be compared with measured data. Theoretical Hall factors in the heavy and light hole bands and an effective Hall factor result. The calculated room temperature values of the drift mobility and of the effective Hall factor are 118 cm2/V s and 3.6, respectively. The fitted acoustic deformation potential E1=7.9 eV and the fitted optical coupling constant DK=1.24×1011 eV/m are close to values published before. It is shown that the measured strong dependence of the Hall mobility on the Hall concentration is not mainly caused by scattering by ionized impurities but by the dependence of the effective Hall factor on the hole concentration.

Experiments on Quantum Hall Topological Phases in Ultra Low Temperatures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Du, Rui-Rui

2015-02-14

This project is to cool electrons in semiconductors to extremely low temperatures and to study new states of matter formed by low-dimensional electrons (or holes). At such low temperatures (and with an intense magnetic field), electronic behavior differs completely from ordinary ones observed at room temperatures or regular low temperature. Studies of electrons at such low temperatures would open the door for fundamental discoveries in condensed matter physics. Present studies have been focused on topological phases in the fractional quantum Hall effect in GaAs/AlGaAs semiconductor heterostructures, and the newly discovered (by this group) quantum spin Hall effect in InAs/GaSb materials.more » This project consists of the following components: 1) Development of efficient sample cooling techniques and electron thermometry: Our goal is to reach 1 mK electron temperature and reasonable determination of electron temperature; 2) Experiments at ultra-low temperatures: Our goal is to understand the energy scale of competing quantum phases, by measuring the temperature-dependence of transport features. Focus will be placed on such issues as the energy gap of the 5/2 state, and those of 12/5 (and possible 13/5); resistive signature of instability near 1/2 at ultra-low temperatures; 3) Measurement of the 5/2 gaps in the limit of small or large Zeeman energies: Our goal is to gain physics insight of 5/2 state at limiting experimental parameters, especially those properties concerning the spin polarization; 4) Experiments on tuning the electron-electron interaction in a screened quantum Hall system: Our goal is to gain understanding of the formation of paired fractional quantum Hall state as the interaction pseudo-potential is being modified by a nearby screening electron layer; 5) Experiments on the quantized helical edge states under a strong magnetic field and ultralow temperatures: our goal is to investigate both the bulk and edge states in a quantum spin Hall insulator

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.

Piezo-Hall effect and fundamental piezo-Hall coefficients of single crystal n-type 3C-SiC(100) with low carrier concentration

NASA Astrophysics Data System (ADS)

Qamar, Afzaal; Dao, Dzung Viet; Dinh, Toan; Iacopi, Alan; Walker, Glenn; Phan, Hoang-Phuong; Hold, Leonie; Dimitrijev, Sima

2017-04-01

This article reports the results on the piezo-Hall effect in single crystal n-type 3C-SiC(100) having a low carrier concentration. The effect of the crystallographic orientation on the piezo-Hall effect has been investigated by applying stress to the Hall devices fabricated in different crystallographic directions. Single crystal n-type 3C-SiC(100) and 3C-SiC(111) were grown by low pressure chemical vapor deposition at 1250 °C. Fundamental piezo-Hall coefficients were obtained using the piezo-Hall effect measurements as P11 = (-29 ± 1.3) × 10-11 Pa-1, P12 = (11.06 ± 0.5)× 10-11 Pa-1, and P44 = (-3.4 ± 0.7) × 10-11 Pa-1. It has been observed that the piezo-Hall coefficients of n-type 3C-SiC(100) show a completely different behavior as compared to that of p-type 3C-SiC.

Probing the thermal Hall effect using miniature capacitive strontium titanate thermometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tinsman, Colin; Li, Gang; Asaba, Tomoya

2016-06-27

The thermal Hall effect is the thermal analog of the electrical Hall effect. Rarely observed in normal metals, thermal Hall signals have been argued to be a key property for a number of strongly correlated materials, such as high temperature superconductors, correlated topological insulators, and quantum magnets. The observation of the thermal Hall effect requires precise measurement of temperature in intense magnetic fields. Particularly at low temperature, resistive thermometers have a strong dependence on field, which makes them unsuitable for this purpose. We have created capacitive thermometers which instead measure the dielectric constant of strontium titanate (SrTiO{sub 3}). SrTiO{sub 3}more » approaches a ferroelectric transition, causing its dielectric constant to increase by a few orders of magnitude at low temperature. As a result, these thermometers are very sensitive at low temperature while having very little dependence on the applied magnetic field, making them ideal for thermal Hall measurements. We demonstrate this method by making measurements of the thermal Hall effect in Bismuth in magnetic fields of up to 10 T.« less

Framing anomaly in the effective theory of the fractional quantum Hall effect.

PubMed

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.

Rotating effects on the Landau quantization for an atom with a magnetic quadrupole moment

NASA Astrophysics Data System (ADS)

Fonseca, I. C.; Bakke, K.

2016-01-01

Based on the single particle approximation [Dmitriev et al., Phys. Rev. C 50, 2358 (1994) and C.-C. Chen, Phys. Rev. A 51, 2611 (1995)], the Landau quantization associated with an atom with a magnetic quadrupole moment is introduced, and then, rotating effects on this analogue of the Landau quantization is investigated. It is shown that rotating effects can modify the cyclotron frequency and breaks the degeneracy of the analogue of the Landau levels.

Rotating effects on the Landau quantization for an atom with a magnetic quadrupole moment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fonseca, I. C.; Bakke, K., E-mail: kbakke@fisica.ufpb.br

2016-01-07

Based on the single particle approximation [Dmitriev et al., Phys. Rev. C 50, 2358 (1994) and C.-C. Chen, Phys. Rev. A 51, 2611 (1995)], the Landau quantization associated with an atom with a magnetic quadrupole moment is introduced, and then, rotating effects on this analogue of the Landau quantization is investigated. It is shown that rotating effects can modify the cyclotron frequency and breaks the degeneracy of the analogue of the Landau levels.

Nonlinear dynamics induced anomalous Hall effect in topological insulators

PubMed Central

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. PMID:26819223

Nonlinear dynamics induced anomalous Hall effect in topological insulators.

PubMed

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.

ION ACOUSTIC TURBULENCE, ANOMALOUS TRANSPORT, AND SYSTEM DYNAMICS IN HALL EFFECT THRUSTERS

DTIC Science & Technology

2017-06-30

17394 4 / 13 HALL EFFECT THRUSTERS Hall Effect Thrusters (HET): Traditionally Modeled in R-Z Named for Hall Current in θ Uses Quasi -1D Electron Fluid...HET): Traditionally Modeled in R-Z Named for Hall Current in θ Uses Quasi -1D Electron Fluid Solve Ohm’s Law→ No e−-momentum Zθ Unrolled to YZ...Current in θ Uses Quasi -1D Electron Fluid Solve Ohm’s Law→ No e−-momentum Zθ Unrolled to YZ Electron ExB Drift Unmagnetized Ions Results in Hall Current

Natural inflation from polymer quantization

NASA Astrophysics Data System (ADS)

Ali, Masooma; Seahra, Sanjeev S.

2017-11-01

We study the polymer quantization of a homogeneous massive scalar field in the early Universe using a prescription inequivalent to those previously appearing in the literature. Specifically, we assume a Hilbert space for which the scalar field momentum is well defined but its amplitude is not. This is closer in spirit to the quantization scheme of loop quantum gravity, in which no unique configuration operator exists. We show that in the semiclassical approximation, the main effect of this polymer quantization scheme is to compactify the phase space of chaotic inflation in the field amplitude direction. This gives rise to an effective scalar potential closely resembling that of hybrid natural inflation. Unlike polymer schemes in which the scalar field amplitude is well defined, the semiclassical dynamics involves a past cosmological singularity; i.e., this approach does not mitigate the big bang.

High-Temperature Hall-Effect Apparatus

NASA Technical Reports Server (NTRS)

Wood, C.; Lockwood, R. A.; Chemielewski, A. B.; Parker, J. B.; Zoltan, A.

1985-01-01

Compact furnace minimizes thermal gradients and electrical noise. Semiautomatic Hall-effect apparatus takes measurements on refractory semiconductors at temperatures as high as 1,100 degrees C. Intended especially for use with samples of high conductivity and low chargecarrier mobility that exhibit low signal-to-noise ratios, apparatus carefully constructed to avoid spurious electromagnetic and thermoelectric effects that further degrade measurements.

Higher (odd) dimensional quantum Hall effect and extended dimensional hierarchy

NASA Astrophysics Data System (ADS)

Hasebe, Kazuki

2017-07-01

We demonstrate dimensional ladder of higher dimensional quantum Hall effects by exploiting quantum Hall effects on arbitrary odd dimensional spheres. Non-relativistic and relativistic Landau models are analyzed on S 2 k - 1 in the SO (2 k - 1) monopole background. The total sub-band degeneracy of the odd dimensional lowest Landau level is shown to be equal to the winding number from the base-manifold S 2 k - 1 to the one-dimension higher SO (2 k) gauge group. Based on the chiral Hopf maps, we clarify the underlying quantum Nambu geometry for odd dimensional quantum Hall effect and the resulting quantum geometry is naturally embedded also in one-dimension higher quantum geometry. An origin of such dimensional ladder connecting even and odd dimensional quantum Hall effects is illuminated from a viewpoint of the spectral flow of Atiyah-Patodi-Singer index theorem in differential topology. We also present a BF topological field theory as an effective field theory in which membranes with different dimensions undergo non-trivial linking in odd dimensional space. Finally, an extended version of the dimensional hierarchy for higher dimensional quantum Hall liquids is proposed, and its relationship to quantum anomaly and D-brane physics is discussed.

Giant photonic Hall effect in magnetophotonic crystals.

PubMed

Merzlikin, A M; Vinogradov, A P; Inoue, M; Granovsky, A B

2005-10-01

We have considered a simple, square, two-dimensional (2D) PC built of a magneto-optic matrix with square holes. It is shown that using such a magnetophotonic crystal it is possible to deflect a light beam at very large angles by applying a nonzero external magnetic field. The effect is called the giant photonic Hall effect (GPHE) or the magnetic superprism effect. The GPHE is based on magneto-optical properties, as is the photonic Hall effect [B. A. van Tiggelen and G. L. J. A. Rikken, in, edited by V. M. Shalaev (Springer-Verlag, Berlin, 2002), p. 275]; however GPHE is not caused by asymmetrical light scattering but rather by the influence of an external magnetic field on the photonic band structure.

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.

Quantum Hall effect in graphene with interface-induced spin-orbit coupling

NASA Astrophysics Data System (ADS)

Cysne, Tarik P.; Garcia, Jose H.; Rocha, Alexandre R.; Rappoport, Tatiana G.

2018-02-01

We consider an effective model for graphene with interface-induced spin-orbit coupling and calculate the quantum Hall effect in the low-energy limit. We perform a systematic analysis of the contribution of the different terms of the effective Hamiltonian to the quantum Hall effect (QHE). By analyzing the spin splitting of the quantum Hall states as a function of magnetic field and gate voltage, we obtain different scaling laws that can be used to characterize the spin-orbit coupling in experiments. Furthermore, we employ a real-space quantum transport approach to calculate the quantum Hall conductivity and investigate the robustness of the QHE to disorder introduced by hydrogen impurities. For that purpose, we combine first-principles calculations and a genetic algorithm strategy to obtain a graphene-only Hamiltonian that models the impurity.

The Hall Effect in Hydrided Rare Earth Films

NASA Astrophysics Data System (ADS)

Koon, D. W.; Azofeifa, D. E.; Clark, N.

We describe two new techniques for measuring the Hall effect in capped rare earth films during hydriding. In one, we simultaneously measure resistivity and the Hall coefficient for a rare earth film covered with four different thicknesses of Pd, recovering the charge transport quantities for both materials. In the second technique, we replace Pd with Mn as the covering layer. We will present results from both techniques.

Mixed-state Hall effect of high-T(c) superconductors

NASA Astrophysics Data System (ADS)

Kang, Byeongwon

In this dissertation, we presented the study on the mixed-state Hall effect of high-Tc superconductors (HTSs). In order to understand the mechanisms of the puzzling phenomena in the mixed-state Hall effect of HTSs, the Hall sign anomaly and scaling behavior, Hall measurements are conducted in several HTS thin films. We investigate the mechanism of the sign reversal of the Hall resistivity in Tl-2201 films when the electronic band structure is varied through the underdoped, optimally doped, and overdoped regions. It is found that the Hall sign reversals are an intrinsic property of HTSs and determined by electronic band structure. Although pinning is not found to be the mechanism behind sign reversals, pinning can suppress the appearance of the Hall sign reversal. Therefore, it is concluded that two (or more) sign reversals are a generic behavior of HTSs. From a systematic study of the vortex phase diagram, we discover several new features of the vortex liquid. In the presence of pinning, the vortex-liquid phase can be divided into two regions, a glassy liquid (GL) where vortices remain correlated as manifested in non-Ohmic resistivity, and a regular liquid (RL) where resistivity becomes Ohmic as vortices become uncorrelated. The field dependence of the Hall angle is found to be linear in the RL and nonlinear in the GL. Generally the decoupling line (Hk- T), which is defined as a boundary between the GL and the RL, is lower than the depinning line (Hd-T). As pinning increases the Hk-T may approach the Hd-T, thus vortices are decoupled and depinned nearly simultaneously. For a weak pinning system, on the other hand, the Hk-T and the Hd-T are well separated so that single vortices remain pinned in the region Hk ≤ H ≥ Hd. The behavior of s xy is also investigated in the GL and the RL. In the GL s xy is observed to strongly depend on pinning due to the inter-vortex correlation whereas in the RL s xy is independent of pinning since the pinning effect is scaled out.

Optimal Quantization Scheme for Data-Efficient Target Tracking via UWSNs Using Quantized Measurements.

PubMed

Zhang, Senlin; Chen, Huayan; Liu, Meiqin; Zhang, Qunfei

2017-11-07

Target tracking is one of the broad applications of underwater wireless sensor networks (UWSNs). However, as a result of the temporal and spatial variability of acoustic channels, underwater acoustic communications suffer from an extremely limited bandwidth. In order to reduce network congestion, it is important to shorten the length of the data transmitted from local sensors to the fusion center by quantization. Although quantization can reduce bandwidth cost, it also brings about bad tracking performance as a result of information loss after quantization. To solve this problem, this paper proposes an optimal quantization-based target tracking scheme. It improves the tracking performance of low-bit quantized measurements by minimizing the additional covariance caused by quantization. The simulation demonstrates that our scheme performs much better than the conventional uniform quantization-based target tracking scheme and the increment of the data length affects our scheme only a little. Its tracking performance improves by only 4.4% from 2- to 3-bit, which means our scheme weakly depends on the number of data bits. Moreover, our scheme also weakly depends on the number of participate sensors, and it can work well in sparse sensor networks. In a 6 × 6 × 6 sensor network, compared with 4 × 4 × 4 sensor networks, the number of participant sensors increases by 334.92%, while the tracking accuracy using 1-bit quantized measurements improves by only 50.77%. Overall, our optimal quantization-based target tracking scheme can achieve the pursuit of data-efficiency, which fits the requirements of low-bandwidth UWSNs.

Anderson Localization from the Berry-Curvature Interchange in Quantum Anomalous Hall Systems

NASA Astrophysics Data System (ADS)

Qiao, Zhenhua; Han, Yulei; Zhang, Lei; Wang, Ke; Deng, Xinzhou; Jiang, Hua; Yang, Shengyuan A.; Wang, Jian; Niu, Qian

2016-07-01

We theoretically investigate the localization mechanism of the quantum anomalous Hall effect (QAHE) in the presence of spin-flip disorders. We show that the QAHE stays quantized at weak disorders, then enters a Berry-curvature mediated metallic phase at moderate disorders, and finally goes into the Anderson insulating phase at strong disorders. From the phase diagram, we find that at the charge neutrality point although the QAHE is most robust against disorders, the corresponding metallic phase is much easier to be localized into the Anderson insulating phase due to the interchange of Berry curvatures carried, respectively, by the conduction and valence bands. In the end, we provide a phenomenological picture related to the topological charges to better understand the underlying physical origin of the QAHE Anderson localization.

BRST quantization of cosmological perturbations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Armendariz-Picon, Cristian; Şengör, Gizem

2016-11-08

BRST quantization is an elegant and powerful method to quantize theories with local symmetries. In this article we study the Hamiltonian BRST quantization of cosmological perturbations in a universe dominated by a scalar field, along with the closely related quantization method of Dirac. We describe how both formalisms apply to perturbations in a time-dependent background, and how expectation values of gauge-invariant operators can be calculated in the in-in formalism. Our analysis focuses mostly on the free theory. By appropriate canonical transformations we simplify and diagonalize the free Hamiltonian. BRST quantization in derivative gauges allows us to dramatically simplify the structuremore » of the propagators, whereas Dirac quantization, which amounts to quantization in synchronous gauge, dispenses with the need to introduce ghosts and preserves the locality of the gauge-fixed action.« less

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.

Berry phase mechanism of the anomalous Hall effect in a disordered two-dimensional magnetic semiconductor structure.

DOE PAGES

Oveshnikov, L. N.; Kulbachinskii, V. A.; Davydov, A. B.; ...

2015-11-24

In this study, the anomalous Hall effect (AHE) arises from the interplay of spin-orbit interactions and ferromagnetic order and is a potentially useful probe of electron spin polarization, especially in nanoscale systems where direct measurement is not feasible. While AHE is rather well-understood in metallic ferromagnets, much less is known about the relevance of different physical mechanisms governing AHE in insulators. As ferromagnetic insulators, but not metals, lend themselves to gatecontrol of electron spin polarization, understanding AHE in the insulating state is valuable from the point of view of spintronic applications. Among the mechanisms proposed in the literature for AHEmore » in insulators, the one related to a geometric (Berry) phase effect has been elusive in past studies. The recent discovery of quantized AHE in magnetically doped topological insulators - essentially a Berry phase effect - provides strong additional motivation to undertake more careful search for geometric phase effects in AHE in the magnetic semiconductors. Here we report our experiments on the temperature and magnetic field dependences of AHE in insulating, strongly-disordered two-dimensional Mn delta-doped semiconductor heterostructures in the hopping regime. In particular, it is shown that at sufficiently low temperatures, the mechanism of AHE related to the Berry phase is favoured.« less

Berry phase mechanism of the anomalous Hall effect in a disordered two-dimensional magnetic semiconductor structure

PubMed Central

Oveshnikov, L. N.; Kulbachinskii, V. A.; Davydov, A. B.; Aronzon, B. A.; Rozhansky, I. V.; Averkiev, N. S.; Kugel, K. I.; Tripathi, V.

2015-01-01

The anomalous Hall effect (AHE) arises from the interplay of spin-orbit interactions and ferromagnetic order and is a potentially useful probe of electron spin polarization, especially in nanoscale systems where direct measurement is not feasible. While AHE is rather well-understood in metallic ferromagnets, much less is known about the relevance of different physical mechanisms governing AHE in insulators. As ferromagnetic insulators, but not metals, lend themselves to gate-control of electron spin polarization, understanding AHE in the insulating state is valuable from the point of view of spintronic applications. Among the mechanisms proposed in the literature for AHE in insulators, the one related to a geometric (Berry) phase effect has been elusive in past studies. The recent discovery of quantized AHE in magnetically doped topological insulators - essentially a Berry phase effect - provides strong additional motivation to undertake more careful search for geometric phase effects in AHE in the magnetic semiconductors. Here we report our experiments on the temperature and magnetic field dependences of AHE in insulating, strongly-disordered two-dimensional Mn delta-doped semiconductor heterostructures in the hopping regime. In particular, it is shown that at sufficiently low temperatures, the mechanism of AHE related to the Berry phase is favoured. PMID:26596472

Valley Hall effect and Nernst effect in strain engineered graphene

NASA Astrophysics Data System (ADS)

Niu, Zhi Ping; Yao, Jian-ming

2018-04-01

We theoretically predict the existence of tunneling valley Hall effect and Nernst effect in the normal/strain/normal graphene junctions, where a strained graphene is sandwiched by two normal graphene electrodes. By applying an electric bias a pure transverse valley Hall current with longitudinal charge current is generated. If the system is driven by a temperature bias, a valley Nernst effect is observed, where a pure transverse valley current without charge current propagates. Furthermore, the transverse valley current can be modulated by the Fermi energy and crystallographic orientation. When the magnetic field is further considered, we obtain a fully valley-polarized current. It is expected these features may be helpful in the design of the controllable valleytronic devices.

Robust vector quantization for noisy channels

NASA Technical Reports Server (NTRS)

Demarca, J. R. B.; Farvardin, N.; Jayant, N. S.; Shoham, Y.

1988-01-01

The paper briefly discusses techniques for making vector quantizers more tolerant to tranmsission errors. Two algorithms are presented for obtaining an efficient binary word assignment to the vector quantizer codewords without increasing the transmission rate. It is shown that about 4.5 dB gain over random assignment can be achieved with these algorithms. It is also proposed to reduce the effects of error propagation in vector-predictive quantizers by appropriately constraining the response of the predictive loop. The constrained system is shown to have about 4 dB of SNR gain over an unconstrained system in a noisy channel, with a small loss of clean-channel performance.

Quantum spin Hall state in monolayer 1T '-WTe 2

DOE PAGES

Tang, Shujie; Zhang, Chaofan; Wong, Dillon; ...

2017-06-26

A quantum spin Hall (QSH) insulator is a novel two-dimensional quantum state of matter that features quantized Hall conductance in the absence of a magnetic field, resulting from topologically protected dissipationless edge states that bridge the energy gap opened by band inversion and strong spin–orbit coupling. By investigating the electronic structure of epitaxially grown monolayer 1T '-WTe 2 using angle-resolved photoemission (ARPES) and first-principles calculations, we observe clear signatures of topological band inversion and bandgap opening, which are the hallmarks of a QSH state. Scanning tunnelling microscopy measurements further confirm the correct crystal structure and the existence of a bulkmore » bandgap, and provide evidence for a modified electronic structure near the edge that is consistent with the expectations for a QSH insulator. Our results establish monolayer 1T '-WTe 2 as a new class of QSH insulator with large band gap in a robust two-dimensional materials family of transition metal dichalcogenides (TMDCs).« less

Quantum spin Hall state in monolayer 1T '-WTe 2

DOE PAGES

Tang, Shujie; Zhang, Chaofan; Wong, Dillon; ...

2017-06-26

A quantum spin Hall (QSH) insulator is a novel two-dimensional quantum state of matter that features quantized Hall conductance in the absence of a magnetic field, resulting from topologically protected dissipationless edge states that bridge the energy gap opened by band inversion and strong spin–orbit coupling. By investigating the electronic structure of epitaxially grown monolayer 1T '-WTe 2 using angle-resolved photoemission (ARPES) and first-principles calculations, we observe clear signatures of topological band inversion and bandgap opening, which are the hallmarks of a QSH state. Scanning tunnelling microscopy measurements further confirm the correct crystal structure and the existence of a bulkmore » bandgap, and provide evidence for a modified electronic structure near the edge that is consistent with the expectations for a QSH insulator. Finally, our results establish monolayer 1T '-WTe 2 as a new class of QSH insulator with large band gap in a robust two-dimensional materials family of transition metal dichalcogenides (TMDCs).« less

Electrical control of the anomalous valley Hall effect in antiferrovalley bilayers

NASA Astrophysics Data System (ADS)

Tong, Wen-Yi; Duan, Chun-Gang

2017-08-01

In analogy to all-electric spintronics, all-electric valleytronics, i.e., valley manipulation via electric means, becomes an exciting new frontier as it may bring revolutions in the field of data storage with ultra-high speed and ultra-low power consumption. The existence of the anomalous valley Hall effect in ferrovalley materials demonstrates the possibility of electrical detection for valley polarization. However, in previously proposed valley-polarized monolayers, the anomalous valley Hall effect is controlled by external magnetic fields. Here, through elaborate structural design, we propose the antiferrovally bilayer as an ideal candidate for realizing all-electric valleytronic devices. Using the minimal k.p model, we show that the energy degeneracy between valley indexes in such system can be lifted by electric approaches. Subsequently, the anomalous valley Hall effect strongly depends on the electric field as well. Taking the bilayer VSe2 as an example, all-electric tuning and detecting of anomalous valley Hall effect is confirmed by density-functional theory calculations, indicating that the valley information in such antiferrovalley bilayer can be reversed by an electric field perpendicular to the plane of the system and easily probed through the sign of the Hall voltage.

Anisotropic anomalous Hall effect in triangular itinerant ferromagnet Fe3GeTe2

NASA Astrophysics Data System (ADS)

Wang, Yihao; Xian, Cong; Wang, Jian; Liu, Bingjie; Ling, Langsheng; Zhang, Lei; Cao, Liang; Qu, Zhe; Xiong, Yimin

2017-10-01

Magnetic frustrated materials are of great interest for their novel spin-dependent transport properties. We report an anisotropic anomalous Hall effect in the triangular itinerant ferromagnet Fe3GeTe2 . When the current flows along the a b plane, Fe3GeTe2 exhibits the conventional anomalous Hall effect below the Curie temperature Tc, which can be depicted by Karplus-Luttinger theory. On the other hand, the topological Hall effect shows up below Tc with current along the c axis. The enhancement of Hall resistivity can be attributed to the chiral effect during the spin-flop process.

Comparing Hall Effect and Field Effect Measurements on the Same Single Nanowire.

PubMed

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 holographic model for the fractional quantum Hall effect

NASA Astrophysics Data System (ADS)

Lippert, Matthew; Meyer, René; Taliotis, Anastasios

2015-01-01

Experimental data for fractional quantum Hall systems can to a large extent be explained by assuming the existence of a Γ0(2) modular symmetry group commuting with the renormalization group flow and hence mapping different phases of two-dimensional electron gases into each other. Based on this insight, we construct a phenomenological holographic model which captures many features of the fractional quantum Hall effect. Using an -invariant Einstein-Maxwell-axio-dilaton theory capturing the important modular transformation properties of quantum Hall physics, we find dyonic diatonic black hole solutions which are gapped and have a Hall conductivity equal to the filling fraction, as expected for quantum Hall states. We also provide several technical results on the general behavior of the gauge field fluctuations around these dyonic dilatonic black hole solutions: we specify a sufficient criterion for IR normalizability of the fluctuations, demonstrate the preservation of the gap under the action, and prove that the singularity of the fluctuation problem in the presence of a magnetic field is an accessory singularity. We finish with a preliminary investigation of the possible IR scaling solutions of our model and some speculations on how they could be important for the observed universality of quantum Hall transitions.

Hall effect at a tunable metal-insulator transition

NASA Astrophysics Data System (ADS)

Teizer, W.; Hellman, F.; Dynes, R. C.

2003-03-01

Using a rotating magnetic field, the Hall effect in three-dimensional amorphous GdxSi1-x has been measured in the critical regime of the metal-insulator transition for a constant total magnetic field. The Hall coefficient R0 is negative, indicating electronlike conductivity, with a magnitude that increases with decreasing conductivity. R0 diverges at the metal-insulator transition, and displays critical behavior with exponent -1 [R0˜(H-HC)-1]. This dependence is interpreted as a linear decrease in the density of mobile carriers n˜R-10˜H-HC, indicative of the dominant influence of interaction effects.

Topological Phase Transitions in the Photonic Spin Hall Effect

DOE PAGES

Kort-Kamp, Wilton Junior de Melo

2017-10-04

The recent synthesis of two-dimensional staggered materials opens up burgeoning opportunities to study optical spin-orbit interactions in semiconducting Dirac-like systems. In this work, we unveil topological phase transitions in the photonic spin Hall effect in the graphene family materials. It is shown that an external static electric field and a high frequency circularly polarized laser allow for active on-demand manipulation of electromagnetic beam shifts. The spin Hall effect of light presents a rich dependence with radiation degrees of freedom, and material properties, and features nontrivial topological properties. Finally, we discover that photonic Hall shifts are sensitive to spin and valleymore » properties of the charge carriers, providing an unprecedented pathway to investigate spintronics and valleytronics in staggered 2D semiconductors.« less

Shot noise generated by graphene p–n junctions in the quantum Hall effect regime

PubMed Central

Kumada, N.; Parmentier, F. D.; Hibino, H.; Glattli, D. C.; Roulleau, P.

2015-01-01

Graphene offers a unique system to investigate transport of Dirac Fermions at p–n junctions. In a magnetic field, combination of quantum Hall physics and the characteristic transport across p–n junctions leads to a fractionally quantized conductance associated with the mixing of electron-like and hole-like modes and their subsequent partitioning. The mixing and partitioning suggest that a p–n junction could be used as an electronic beam splitter. Here we report the shot noise study of the mode-mixing process and demonstrate the crucial role of the p–n junction length. For short p–n junctions, the amplitude of the noise is consistent with an electronic beam-splitter behaviour, whereas, for longer p–n junctions, it is reduced by the energy relaxation. Remarkably, the relaxation length is much larger than typical size of mesoscopic devices, encouraging using graphene for electron quantum optics and quantum information processing. PMID:26337067

Observation of the Zero Hall Plateau in a Quantum Anomalous Hall Insulator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feng, Yang; Feng, Xiao; Ou, Yunbo

We report experimental investigations on the quantum phase transition between the two opposite Hall plateaus of a quantum anomalous Hall insulator. We observe a well-defined plateau with zero Hall conductivity over a range of magnetic field around coercivity when the magnetization reverses. The features of the zero Hall plateau are shown to be closely related to that of the quantum anomalous Hall effect, but its temperature evolution exhibits a significant difference from the network model for a conventional quantum Hall plateau transition. We propose that the chiral edge states residing at the magnetic domain boundaries, which are unique to amore » quantum anomalous Hall insulator, are responsible for the novel features of the zero Hall plateau.« less

Effect of temperature degeneracy and Landau quantization on drift solitary waves and double layers

NASA Astrophysics Data System (ADS)

Shan, Shaukat Ali; Haque, Q.

2018-01-01

The linear and nonlinear drift ion acoustic waves have been investigated in an inhomogeneous, magnetized, dense degenerate, and quantized magnetic field plasma. The linear drift ion acoustic wave propagation along with the nonlinear structures like double layers and solitary waves has been found to be strongly dependent on the drift speed, magnetic field quantization parameter β, and the temperature degeneracy. The graphical illustrations show that the frequency of linear waves and the amplitude of the solitary waves increase with the increase in temperature degeneracy and Landau quantization effect, while the amplitude of the double layers decreases with the increase in η and T. The relevance of the present study is pointed out in the plasma environment of fast ignition inertial confinement fusion, the white dwarf stars, and short pulsed petawatt laser technology.

Vector quantization

NASA Technical Reports Server (NTRS)

Gray, Robert M.

1989-01-01

During the past ten years Vector Quantization (VQ) has developed from a theoretical possibility promised by Shannon's source coding theorems into a powerful and competitive technique for speech and image coding and compression at medium to low bit rates. In this survey, the basic ideas behind the design of vector quantizers are sketched and some comments made on the state-of-the-art and current research efforts.

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.

Nearly associative deformation quantization

NASA Astrophysics Data System (ADS)

Vassilevich, Dmitri; Oliveira, Fernando Martins Costa

2018-04-01

We study several classes of non-associative algebras as possible candidates for deformation quantization in the direction of a Poisson bracket that does not satisfy Jacobi identities. We show that in fact alternative deformation quantization algebras require the Jacobi identities on the Poisson bracket and, under very general assumptions, are associative. At the same time, flexible deformation quantization algebras exist for any Poisson bracket.

Observation of the fractional quantum Hall effect in graphene.

PubMed

Bolotin, Kirill I; Ghahari, Fereshte; Shulman, Michael D; Stormer, Horst L; Kim, Philip

2009-11-12

When electrons are confined in two dimensions and subject to strong magnetic fields, the Coulomb interactions between them can become very strong, leading to the formation of correlated states of matter, such as the fractional quantum Hall liquid. In this strong quantum regime, electrons and magnetic flux quanta bind to form complex composite quasiparticles with fractional electronic charge; these are manifest in transport measurements of the Hall conductivity as rational fractions of the elementary conductance quantum. The experimental discovery of an anomalous integer quantum Hall effect in graphene has enabled the study of a correlated two-dimensional electronic system, in which the interacting electrons behave like massless chiral fermions. However, owing to the prevailing disorder, graphene has so far exhibited only weak signatures of correlated electron phenomena, despite intense experimental and theoretical efforts. Here we report the observation of the fractional quantum Hall effect in ultraclean, suspended graphene. In addition, we show that at low carrier density graphene becomes an insulator with a magnetic-field-tunable energy gap. These newly discovered quantum states offer the opportunity to study correlated Dirac fermions in graphene in the presence of large magnetic fields.

Quantized Majorana conductance

NASA Astrophysics Data System (ADS)

Zhang, Hao; Liu, Chun-Xiao; Gazibegovic, Sasa; Xu, Di; Logan, John A.; Wang, Guanzhong; van Loo, Nick; Bommer, Jouri D. S.; de Moor, Michiel W. A.; Car, Diana; Op Het Veld, Roy L. M.; van Veldhoven, Petrus J.; Koelling, Sebastian; Verheijen, Marcel A.; Pendharkar, Mihir; Pennachio, Daniel J.; Shojaei, Borzoyeh; Lee, Joon Sue; Palmstrøm, Chris J.; Bakkers, Erik P. A. M.; Sarma, S. Das; Kouwenhoven, Leo P.

2018-04-01

Majorana zero-modes—a type of localized quasiparticle—hold great promise for topological quantum computing. Tunnelling spectroscopy in electrical transport is the primary tool for identifying the presence of Majorana zero-modes, for instance as a zero-bias peak in differential conductance. The height of the Majorana zero-bias peak is predicted to be quantized at the universal conductance value of 2e2/h at zero temperature (where e is the charge of an electron and h is the Planck constant), as a direct consequence of the famous Majorana symmetry in which a particle is its own antiparticle. The Majorana symmetry protects the quantization against disorder, interactions and variations in the tunnel coupling. Previous experiments, however, have mostly shown zero-bias peaks much smaller than 2e2/h, with a recent observation of a peak height close to 2e2/h. Here we report a quantized conductance plateau at 2e2/h in the zero-bias conductance measured in indium antimonide semiconductor nanowires covered with an aluminium superconducting shell. The height of our zero-bias peak remains constant despite changing parameters such as the magnetic field and tunnel coupling, indicating that it is a quantized conductance plateau. We distinguish this quantized Majorana peak from possible non-Majorana origins by investigating its robustness to electric and magnetic fields as well as its temperature dependence. The observation of a quantized conductance plateau strongly supports the existence of Majorana zero-modes in the system, consequently paving the way for future braiding experiments that could lead to topological quantum computing.

Quantized Majorana conductance.

PubMed

Zhang, Hao; Liu, Chun-Xiao; Gazibegovic, Sasa; Xu, Di; Logan, John A; Wang, Guanzhong; van Loo, Nick; Bommer, Jouri D S; de Moor, Michiel W A; Car, Diana; Op Het Veld, Roy L M; van Veldhoven, Petrus J; Koelling, Sebastian; Verheijen, Marcel A; Pendharkar, Mihir; Pennachio, Daniel J; Shojaei, Borzoyeh; Lee, Joon Sue; Palmstrøm, Chris J; Bakkers, Erik P A M; Sarma, S Das; Kouwenhoven, Leo P

2018-04-05

Majorana zero-modes-a type of localized quasiparticle-hold great promise for topological quantum computing. Tunnelling spectroscopy in electrical transport is the primary tool for identifying the presence of Majorana zero-modes, for instance as a zero-bias peak in differential conductance. The height of the Majorana zero-bias peak is predicted to be quantized at the universal conductance value of 2e 2 /h at zero temperature (where e is the charge of an electron and h is the Planck constant), as a direct consequence of the famous Majorana symmetry in which a particle is its own antiparticle. The Majorana symmetry protects the quantization against disorder, interactions and variations in the tunnel coupling. Previous experiments, however, have mostly shown zero-bias peaks much smaller than 2e 2 /h, with a recent observation of a peak height close to 2e 2 /h. Here we report a quantized conductance plateau at 2e 2 /h in the zero-bias conductance measured in indium antimonide semiconductor nanowires covered with an aluminium superconducting shell. The height of our zero-bias peak remains constant despite changing parameters such as the magnetic field and tunnel coupling, indicating that it is a quantized conductance plateau. We distinguish this quantized Majorana peak from possible non-Majorana origins by investigating its robustness to electric and magnetic fields as well as its temperature dependence. The observation of a quantized conductance plateau strongly supports the existence of Majorana zero-modes in the system, consequently paving the way for future braiding experiments that could lead to topological quantum computing.

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.

Anderson Localization from the Berry-Curvature Interchange in Quantum Anomalous Hall Systems

NASA Astrophysics Data System (ADS)

Han, Yulei; Qiao, Zhenhua

In this talk, we theoretically investigate the localization mechanism of the quantum anomalous Hall effect (QAHE) in the presence of spin-flip disorders. We show that the QAHE stays quantized at weak disorders, then enters a Berry-curvature mediated metallic phase at moderate disorders, and finally goes into the Anderson insulating phase at strong disorders. From the phase diagram, we find that at the charge neutrality point although the QAHE is most robust against disorders, the corresponding metallic phase is much easier to be localized into the Anderson insulating phase due to the interchange of Berry curvatures carried, respectively, by the conduction and valence bands. In the end, we provide a phenomenological picture related to the topological charges to better understand the underlying physical origin of the QAHE Anderson localization.

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.

Quantum Hall resistance standard in graphene devices under relaxed experimental conditions

NASA Astrophysics Data System (ADS)

Schopfer, F.; Ribeiro-Palau, R.; Lafont, F.; Brun-Picard, J.; Kazazis, D.; Michon, A.; Cheynis, F.; Couturaud, O.; Consejo, C.; Jouault, B.; Poirier, W.

Large-area and high-quality graphene devices synthesized by CVD on SiC are used to develop reliable electrical resistance standards, based on the quantum Hall effect (QHE), with state-of-the-art accuracy of 1x10-9 and under an extended range of experimental conditions of magnetic field (down to 3.5 T), temperature (up to 10 K) or current (up to 0.5 mA). These conditions are much relaxed as compared to what is required by GaAs/AlGaAs standards and will enable to broaden the use of the primary quantum electrical standards to the benefit of Science and Industry for electrical measurements. Furthermore, by comparison of these graphene devices with GaAs/AlGaAs standards, we demonstrate the universality of the QHE within an ultimate uncertainty of 8.2x10-11. This suggests the exact relation of the quantized Hall resistance with the Planck constant and the electron charge, which is crucial for the new SI to be based on fixing such fundamental constants. These results show that graphene realizes its promises and demonstrates its superiority over other materials for a demanding application. Nature Nanotech. 10, 965-971, 2015, Nature Commun. 6, 6806, 2015

Spin precession and spin Hall effect in monolayer graphene/Pt nanostructures

NASA Astrophysics Data System (ADS)

Savero Torres, W.; Sierra, J. F.; Benítez, L. A.; Bonell, F.; Costache, M. V.; Valenzuela, S. O.

2017-12-01

Spin Hall effects have surged as promising phenomena for spin logics operations without ferromagnets. However, the magnitude of the detected electric signals at room temperature in metallic systems has been so far underwhelming. Here, we demonstrate a two-order of magnitude enhancement of the signal in monolayer graphene/Pt devices when compared to their fully metallic counterparts. The enhancement stems in part from efficient spin injection and the large spin resistance of graphene but we also observe 100% spin absorption in Pt and find an unusually large effective spin Hall angle of up to 0.15. The large spin-to-charge conversion allows us to characterise spin precession in graphene under the presence of a magnetic field. Furthermore, by developing an analytical model based on the 1D diffusive spin-transport, we demonstrate that the effective spin-relaxation time in graphene can be accurately determined using the (inverse) spin Hall effect as a means of detection. This is a necessary step to gather full understanding of the consequences of spin absorption in spin Hall devices, which is known to suppress effective spin lifetimes in both metallic and graphene systems.

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.

Deformation of second and third quantization

NASA Astrophysics Data System (ADS)

Faizal, Mir

2015-03-01

In this paper, we will deform the second and third quantized theories by deforming the canonical commutation relations in such a way that they become consistent with the generalized uncertainty principle. Thus, we will first deform the second quantized commutator and obtain a deformed version of the Wheeler-DeWitt equation. Then we will further deform the third quantized theory by deforming the third quantized canonical commutation relation. This way we will obtain a deformed version of the third quantized theory for the multiverse.

Generic superweak chaos induced by Hall effect

NASA Astrophysics Data System (ADS)

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 κ2 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.

Evidence for phonon skew scattering in the spin Hall effect of platinum

NASA Astrophysics Data System (ADS)

Karnad, G. V.; Gorini, C.; Lee, K.; Schulz, T.; Lo Conte, R.; Wells, A. W. J.; Han, D.-S.; Shahbazi, K.; Kim, J.-S.; Moore, T. A.; Swagten, H. J. M.; Eckern, U.; Raimondi, R.; Kläui, M.

2018-03-01

We measure and analyze the effective spin Hall angle of platinum in the low-residual resistivity regime by second-harmonic measurements of the spin-orbit torques for a multilayer of Pt |Co | AlOx . An angular-dependent study of the torques allows us to extract the effective spin Hall angle responsible for the damping-like torque in the system. We observe a strikingly nonmonotonic and reproducible temperature dependence of the torques. This behavior is compatible with recent theoretical predictions which include both intrinsic and extrinsic (impurities and phonons) contributions to the spin Hall effect at finite temperatures.

Low-rate image coding using vector quantization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Makur, A.

1990-01-01

This thesis deals with the development and analysis of a computationally simple vector quantization image compression system for coding monochrome images at low bit rate. Vector quantization has been known to be an effective compression scheme when a low bit rate is desirable, but the intensive computation required in a vector quantization encoder has been a handicap in using it for low rate image coding. The present work shows that, without substantially increasing the coder complexity, it is indeed possible to achieve acceptable picture quality while attaining a high compression ratio. Several modifications to the conventional vector quantization coder aremore » proposed in the thesis. These modifications are shown to offer better subjective quality when compared to the basic coder. Distributed blocks are used instead of spatial blocks to construct the input vectors. A class of input-dependent weighted distortion functions is used to incorporate psychovisual characteristics in the distortion measure. Computationally simple filtering techniques are applied to further improve the decoded image quality. Finally, unique designs of the vector quantization coder using electronic neural networks are described, so that the coding delay is reduced considerably.« less

Tribology of the lubricant quantized sliding state.

PubMed

Castelli, Ivano Eligio; Capozza, Rosario; Vanossi, Andrea; Santoro, Giuseppe E; Manini, Nicola; Tosatti, Erio

2009-11-07

In the framework of Langevin dynamics, we demonstrate clear evidence of the peculiar quantized sliding state, previously found in a simple one-dimensional boundary lubricated model [A. Vanossi et al., Phys. Rev. Lett. 97, 056101 (2006)], for a substantially less idealized two-dimensional description of a confined multilayer solid lubricant under shear. This dynamical state, marked by a nontrivial "quantized" ratio of the averaged lubricant center-of-mass velocity to the externally imposed sliding speed, is recovered, and shown to be robust against the effects of thermal fluctuations, quenched disorder in the confining substrates, and over a wide range of loading forces. The lubricant softness, setting the width of the propagating solitonic structures, is found to play a major role in promoting in-registry commensurate regions beneficial to this quantized sliding. By evaluating the force instantaneously exerted on the top plate, we find that this quantized sliding represents a dynamical "pinned" state, characterized by significantly low values of the kinetic friction. While the quantized sliding occurs due to solitons being driven gently, the transition to ordinary unpinned sliding regimes can involve lubricant melting due to large shear-induced Joule heating, for example at large speed.

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.

Topologies on quantum topoi induced by quantization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nakayama, Kunji

2013-07-15

In the present paper, we consider effects of quantization in a topos approach of quantum theory. A quantum system is assumed to be coded in a quantum topos, by which we mean the topos of presheaves on the context category of commutative subalgebras of a von Neumann algebra of bounded operators on a Hilbert space. A classical system is modeled by a Lie algebra of classical observables. It is shown that a quantization map from the classical observables to self-adjoint operators on the Hilbert space naturally induces geometric morphisms from presheaf topoi related to the classical system to the quantummore » topos. By means of the geometric morphisms, we give Lawvere-Tierney topologies on the quantum topos (and their equivalent Grothendieck topologies on the context category). We show that, among them, there exists a canonical one which we call a quantization topology. We furthermore give an explicit expression of a sheafification functor associated with the quantization topology.« less

Spin wave amplification using the spin Hall effect in permalloy/platinum bilayers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gladii, O.; Henry, Y.; Bailleul, M.

2016-05-16

We investigate the effect of an electrical current on the attenuation length of a 900 nm wavelength spin-wave in a permalloy/Pt bilayer using propagating spin-wave spectroscopy. The modification of the spin-wave relaxation rate is linear in current density, reaching up to 14% for a current density of 2.3 × 10{sup 11} A/m{sup 2} in Pt. This change is attributed to the spin transfer torque induced by the spin Hall effect and corresponds to an effective spin Hall angle of 0.13, which is among the highest values reported so far. The spin Hall effect thus appears as an efficient way of amplifying/attenuating propagating spin waves.

Canonical quantization of classical mechanics in curvilinear coordinates. Invariant quantization procedure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Błaszak, Maciej, E-mail: blaszakm@amu.edu.pl; Domański, Ziemowit, E-mail: ziemowit@amu.edu.pl

In the paper is presented an invariant quantization procedure of classical mechanics on the phase space over flat configuration space. Then, the passage to an operator representation of quantum mechanics in a Hilbert space over configuration space is derived. An explicit form of position and momentum operators as well as their appropriate ordering in arbitrary curvilinear coordinates is demonstrated. Finally, the extension of presented formalism onto non-flat case and related ambiguities of the process of quantization are discussed. -- Highlights: •An invariant quantization procedure of classical mechanics on the phase space over flat configuration space is presented. •The passage tomore » an operator representation of quantum mechanics in a Hilbert space over configuration space is derived. •Explicit form of position and momentum operators and their appropriate ordering in curvilinear coordinates is shown. •The invariant form of Hamiltonian operators quadratic and cubic in momenta is derived. •The extension of presented formalism onto non-flat case and related ambiguities of the quantization process are discussed.« less

Theory of the disordered ν =5/2 quantum thermal Hall state: Emergent symmetry and phase diagram

NASA Astrophysics Data System (ADS)

Lian, Biao; Wang, Juven

2018-04-01

Fractional quantum Hall (FQH) system at Landau level filling fraction ν =5 /2 has long been suggested to be non-Abelian, either Pfaffian (Pf) or antiPfaffian (APf) states by numerical studies, both with quantized Hall conductance σx y=5 e2/2 h . Thermal Hall conductances of the Pf and APf states are quantized at κx y=7 /2 and κx y=3 /2 , respectively, in a proper unit. However, a recent experiment shows the thermal Hall conductance of ν =5 /2 FQH state is κx y=5 /2 . It has been speculated that the system contains random Pf and APf domains driven by disorders, and the neutral chiral Majorana modes on the domain walls may undergo a percolation transition to a κx y=5 /2 phase. In this paper, we do perturbative and nonperturbative analyses on the domain walls between Pf and APf. We show the domain wall theory possesses an emergent SO(4) symmetry at energy scales below a threshold Λ1, which is lowered to an emergent U (1 )×U (1) symmetry at energy scales between Λ1 and a higher value Λ2, and is finally lowered to the composite fermion parity symmetry Z2F above Λ2. Based on the emergent symmetries, we propose a phase diagram of the disordered ν =5 /2 FQH system and show that a κx y=5 /2 phase arises at disorder energy scales Λ >Λ1 . Furthermore, we show the gapped double-semion sector of ND compact domain walls contributes nonlocal topological degeneracy 2ND-1, causing a low-temperature peak in the heat capacity. We implement a nonperturbative method to bootstrap generic topological 1 +1 D domain walls (two-surface defects) applicable to any 2 +1 D non-Abelian topological order. We also identify potentially relevant spin topological quantum field theories (TQFTs) for various ν =5 /2 FQH states in terms of fermionic version of U (1) ±8 Chern-Simons theory ×Z8 -class TQFTs.

Electronic transport in the quantum spin Hall state due to the presence of adatoms in graphene

NASA Astrophysics Data System (ADS)

Lima, Leandro; Lewenkopf, Caio

Heavy adatoms, even at low concentrations, are predicted to turn a graphene sheet into a topological insulator with substantial gap. The adatoms mediate the spin-orbit coupling that is fundamental to the quantum spin Hall effect. The adatoms act as local spin-orbit scatterer inducing hopping processes between distant carbon atoms giving origin to transverse spin currents. Although there are effective models that describe spectral properties of such systems with great detail, quantitative theoretical work for the transport counterpart is still lacking. We developed a multiprobe recursive Green's function technique with spin resolution to analyze the transport properties for large geometries. We use an effective tight-binding Hamiltonian to describe the problem of adatoms randomly placed at the center of the honeycomb hexagons, which is the case for most transition metals. Our choice of current and voltage probes is favorable to experiments since it filters the contribution of only one spin orientation, leading to a quantized spin Hall conductance of e2 / h . We also discuss the electronic propagation in the system by imaging the local density of states and the electronic current densities. The authors acknowledge the Brazilian agencies CNPq, CAPES, FAPERJ and INCT de Nanoestruturas de Carbono for financial support.

Spin-Hall effect in the scattering of structured light from plasmonic nanowire.

PubMed

Sharma, Deepak K; Kumar, Vijay; Vasista, Adarsh B; Chaubey, Shailendra K; Kumar, G V Pavan

2018-06-01

Spin-orbit interactions are subwavelength phenomena that can potentially lead to numerous device-related applications in nanophotonics. Here, we report the spin-Hall effect in the forward scattering of Hermite-Gaussian (HG) and Gaussian beams from a plasmonic nanowire. Asymmetric scattered radiation distribution was observed for circularly polarized beams. Asymmetry in the scattered radiation distribution changes the sign when the polarization handedness inverts. We found a significant enhancement in the spin-Hall effect for a HG beam compared to a Gaussian beam for constant input power. The difference between scattered powers perpendicular to the long axis of the plasmonic nanowire was used to quantify the enhancement. In addition, the nodal line of the HG beam acts as the marker for the spin-Hall shift. Numerical calculations corroborate experimental observations and suggest that the spin flow component of the Poynting vector associated with the circular polarization is responsible for the spin-Hall effect and its enhancement.

Spin-Hall effect in the scattering of structured light from plasmonic nanowire

NASA Astrophysics Data System (ADS)

Sharma, Deepak K.; Kumar, Vijay; Vasista, Adarsh B.; Chaubey, Shailendra K.; Kumar, G. V. Pavan

2018-06-01

Spin-orbit interactions are subwavelength phenomena which can potentially lead to numerous device related applications in nanophotonics. Here, we report Spin-Hall effect in the forward scattering of Hermite-Gaussian and Gaussian beams from a plasmonic nanowire. Asymmetric scattered radiation distribution was observed for circularly polarized beams. Asymmetry in the scattered radiation distribution changes the sign when the polarization handedness inverts. We found a significant enhancement in the Spin-Hall effect for Hermite-Gaussian beam as compared to Gaussian beam for constant input power. The difference between scattered powers perpendicular to the long axis of the plasmonic nanowire was used to quantify the enhancement. In addition to it, nodal line of HG beam acts as the marker for the Spin-Hall shift. Numerical calculations corroborate experimental observations and suggest that the Spin flow component of Poynting vector associated with the circular polarization is responsible for the Spin-Hall effect and its enhancement.

Visibility of wavelet quantization noise

NASA Technical Reports Server (NTRS)

Watson, A. B.; Yang, G. Y.; Solomon, J. A.; Villasenor, J.

1997-01-01

The discrete wavelet transform (DWT) decomposes an image into bands that vary in spatial frequency and orientation. It is widely used for image compression. Measures of the visibility of DWT quantization errors are required to achieve optimal compression. Uniform quantization of a single band of coefficients results in an artifact that we call DWT uniform quantization noise; it is the sum of a lattice of random amplitude basis functions of the corresponding DWT synthesis filter. We measured visual detection thresholds for samples of DWT uniform quantization noise in Y, Cb, and Cr color channels. The spatial frequency of a wavelet is r 2-lambda, where r is display visual resolution in pixels/degree, and lambda is the wavelet level. Thresholds increase rapidly with wavelet spatial frequency. Thresholds also increase from Y to Cr to Cb, and with orientation from lowpass to horizontal/vertical to diagonal. We construct a mathematical model for DWT noise detection thresholds that is a function of level, orientation, and display visual resolution. This allows calculation of a "perceptually lossless" quantization matrix for which all errors are in theory below the visual threshold. The model may also be used as the basis for adaptive quantization schemes.

A hybrid LBG/lattice vector quantizer for high quality image coding

NASA Technical Reports Server (NTRS)

Ramamoorthy, V.; Sayood, K.; Arikan, E. (Editor)

1991-01-01

It is well known that a vector quantizer is an efficient coder offering a good trade-off between quantization distortion and bit rate. The performance of a vector quantizer asymptotically approaches the optimum bound with increasing dimensionality. A vector quantized image suffers from the following types of degradations: (1) edge regions in the coded image contain staircase effects, (2) quasi-constant or slowly varying regions suffer from contouring effects, and (3) textured regions lose details and suffer from granular noise. All three of these degradations are due to the finite size of the code book, the distortion measures used in the design, and due to the finite training procedure involved in the construction of the code book. In this paper, we present an adaptive technique which attempts to ameliorate the edge distortion and contouring effects.

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.

PubMed

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.

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).

The Anomalous Hall Effect and Non-Equilibrium Transport

NASA Astrophysics Data System (ADS)

Ye, Fei

1995-01-01

This thesis contains three relatively independent research areas. In the first part of this thesis, the anomalous Hall effect of amorphous, high-resistance, Fe films (2 -10 monolayers thick) is investigated as a function of temperature. We find a logarithmic temperature dependence of the anomalous Hall resistance similar to the Coulomb anomaly of the resistance but twice its magnitude. The measurements are in excellent agreement with a theoretical calculation and provide us with an independent confirmation of the influence of the enhanced Coulomb interaction in disordered electron systems on transport properties. In the second part of the thesis, the nonequilibrium transport properties of metallic microstructures are studied. An electron beam lithography technique is used in making small structures. The electron temperature and phonon temperature are calculated. It is confirmed that the electron temperatures obtained from both thermometers (weak localization and the Coulomb anomaly) are consistent. It is also found that the phonon temperature in the film is considerably higher than the substrate temperature in the experiments. In addition, the dimensionality of the phonon system in the film is discussed, as well as the phonon escape time. In the third part, the magnetic behavior of V on Au films is studied. Weak localization and the anomalous Hall effect are used to investigate the magnetic properties of sub-mono, mono-, and multilayers of Vanadium on the surface of an Au film. Dilute V atoms possess a strong magnetic moment. For a monolayer the magnetic scattering is reduced by a factor of about 40. This suggests a strongly reduced moment of V compared with the dilute V coverage. From the anomalous Hall effect, it is concluded that the magnetic structure is anti-ferromagnetic; the moment per V atom in multilayers progressively diminishes but is still finite for 16 atomic layers of V. In Appendix A, the nonequilibrium distribution of the phonon system in a metal

Crossover to the anomalous quantum regime in the extrinsic spin Hall effect of graphene

NASA Astrophysics Data System (ADS)

Ferreira, Aires; Milletari, Mirco

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. A.F. gratefully acknowledges the financial support of the Royal Society (U.K.).

Role of helical edge modes in the chiral quantum anomalous Hall state.

PubMed

Mani, Arjun; Benjamin, Colin

2018-01-22

Although indications are that a single chiral quantum anomalous Hall(QAH) edge mode might have been experimentally detected. There have been very many recent experiments which conjecture that a chiral QAH edge mode always materializes along with a pair of quasi-helical quantum spin Hall (QSH) edge modes. In this work we deal with a substantial 'What If?' question- in case the QSH edge modes, from which these QAH edge modes evolve, are not topologically-protected then the QAH edge modes wont be topologically-protected too and thus unfit for use in any applications. Further, as a corollary one can also ask if the topological-protection of QSH edge modes does not carry over during the evolution process to QAH edge modes then again our 'What if?' scenario becomes apparent. The 'how' of the resolution of this 'What if?' conundrum is the main objective of our work. We show in similar set-ups affected by disorder and inelastic scattering, transport via trivial QAH edge mode leads to quantization of Hall resistance and not that via topological QAH edge modes. This perhaps begs a substantial reinterpretation of those experiments which purported to find signatures of chiral(topological) QAH edge modes albeit in conjunction with quasi helical QSH edge modes.

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)

Quantized discrete space oscillators

NASA Technical Reports Server (NTRS)

Uzes, C. A.; Kapuscik, Edward

1993-01-01

A quasi-canonical sequence of finite dimensional quantizations was found which has canonical quantization as its limit. In order to demonstrate its practical utility and its numerical convergence, this formalism is applied to the eigenvalue and 'eigenfunction' problem of several harmonic and anharmonic oscillators.

Hall effect on magnetohydrodynamic instabilities at an elliptic magnetic stagnation line

NASA Astrophysics Data System (ADS)

Spies, Günther O.; Faghihi, Mustafa

1987-06-01

To answer the question whether the Hall effect removes the unphysical feature of ideal magnetohydrodynamics of predicting small wavelength kink instabilities at any elliptic magnetic stagnation line, a normal mode analysis is performed of the motion of an incompressible Hall fluid about cylindrical Z-pinch equilibria with circular cross sections. The eigenvalue loci in the complex frequency plane are derived for the equilibrium with constant current density. Every particular mode becomes stable as the Hall parameter exceeds a critical value. This value, however, depends on the mode such that it increases to infinity as the ideal growth rate decreases to zero, implying that there always remains an infinite number of slowly growing instabilities. Correspondingly, the stability criterion for equilibria with arbitrary current distributions is independent of the Hall parameter.

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.

Carrier coherence and high-resolution Hall effect measurements in organic semiconductors.

NASA Astrophysics Data System (ADS)

Podzorov, Vitaly

Charge conduction in organic semiconductors frequently occurs in a regime at the borderline between a band-like coherent motion of delocalazied carriers in extended states and an incoherent hopping through localized states. Many intrinsic factors are competing for defining the dominant transport mechanism, including the strength of intermolecular interactions represented by the transfer integrals, carrier self-localization due to formation of polarons, electron-phonon coupling, scattering and off-diagonal thermal disorder (see, e.g.,). Depending on the interplay between these processes, either band-like or hopping charge transport realizes. Besides these intrinsic factors, a significant role in practical devices is played by the static disorder (chemical impurities and structural defects) that leads to carrier trapping at various energies and time scales. In most of these cases, the charge carrier mobility in OFETs is rather small (0.1 - 20 cm2V-1s-1)),and in order to carefully and accurately characterize it,Hall effect measurements are necessary. Conventional Hall measurements are extremely challenging in systems with such low mobilities. Here,we present a novel Hall measurement technique that can be carried out in low magnetic fields with an amazing sensitivity,much greater than that attained in conventional Hall measurements. We apply this method to mobility measurements in a variety of OFETs with mobility as low as 0.3 cm2V-1s-1 and reveal various peculiarities of Hall effect in low-mobility systems. By taking advantage of this powerful new experimental capability, we have understood several ``mysteries'' of Hall effect observed by various groups in OFETs over the last decade. The work was financially supported by NSF DMR-1506609, and Ministry of Education and Science of the Russian Federation in the framework of Increase Competitiveness Program of NUST «MISiS» (No. K3-2016-004), decree dated 16th of March 2013, N 211.

Quantum Computing and Second Quantization

DOE PAGES

Makaruk, Hanna Ewa

2017-02-10

Quantum computers are by their nature many particle quantum systems. Both the many-particle arrangement and being quantum are necessary for the existence of the entangled states, which are responsible for the parallelism of the quantum computers. Second quantization is a very important approximate method of describing such systems. This lecture will present the general idea of the second quantization, and discuss shortly some of the most important formulations of second quantization.

Quantum Computing and Second Quantization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Makaruk, Hanna Ewa

Quantum computers are by their nature many particle quantum systems. Both the many-particle arrangement and being quantum are necessary for the existence of the entangled states, which are responsible for the parallelism of the quantum computers. Second quantization is a very important approximate method of describing such systems. This lecture will present the general idea of the second quantization, and discuss shortly some of the most important formulations of second quantization.

Hall-effect arc protector

DOEpatents

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.

Hall-effect arc protector

DOEpatents

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.

ADHM and the 4d quantum Hall effect

NASA Astrophysics Data System (ADS)

Barns-Graham, Alec; Dorey, Nick; Lohitsiri, Nakarin; Tong, David; Turner, Carl

2018-04-01

Yang-Mills instantons are solitonic particles in d = 4 + 1 dimensional gauge theories. We construct and analyse the quantum Hall states that arise when these particles are restricted to the lowest Landau level. We describe the ground state wavefunctions for both Abelian and non-Abelian quantum Hall states. Although our model is purely bosonic, we show that the excitations of this 4d quantum Hall state are governed by the Nekrasov partition function of a certain five dimensional supersymmetric gauge theory with Chern-Simons term. The partition function can also be interpreted as a variant of the Hilbert series of the instanton moduli space, counting holomorphic sections rather than holomorphic functions. It is known that the Hilbert series of the instanton moduli space can be rewritten using mirror symmetry of 3d gauge theories in terms of Coulomb branch variables. We generalise this approach to include the effect of a five dimensional Chern-Simons term. We demonstrate that the resulting Coulomb branch formula coincides with the corresponding Higgs branch Molien integral which, in turn, reproduces the standard formula for the Nekrasov partition function.

Magnetic mirror effect in a cylindrical Hall thruster

NASA Astrophysics Data System (ADS)

Jiang, Yiwei; Tang, Haibin; Ren, Junxue; Li, Min; Cao, Jinbin

2018-01-01

For cylindrical Hall thrusters, the magnetic field geometry is totally different from that in conventional Hall thrusters. In this study, we investigate the magnetic mirror effect in a fully cylindrical Hall thruster by changing the number of iron rings (0-5), which surround the discharge channel wall. The plasma properties inside the discharge channel and plume area are simulated with a self-developed PIC-MCC code. The numerical results show significant influence of magnetic geometry on the electron confinement. With the number of rings increasing above three, the near-wall electron density gap is reduced, indicating the suppression of neutral gas leakage. The electron temperature inside the discharge channel reaches its peak (38.4 eV) when the magnetic mirror is strongest. It is also found that the thruster performance has strong relations with the magnetic mirror as the propellant utilisation efficiency reaches the maximum (1.18) at the biggest magnetic mirror ratio. Also, the optimal magnetic mirror improves the multi-charged ion dynamics, including the ion production and propellant utilisation efficiency.

Inverse spin Hall effect in a closed loop circuit

DOE Office of Scientific and Technical Information (OSTI.GOV)

Omori, Y.; Auvray, F.; Wakamura, T.

We present measurements of inverse spin Hall effects (ISHEs), in which the conversion of a spin current into a charge current via the ISHE is detected not as a voltage in a standard open circuit but directly as the charge current generated in a closed loop. The method is applied to the ISHEs of Bi-doped Cu and Pt. The derived expression of ISHE for the loop structure can relate the charge current flowing into the loop to the spin Hall angle of the SHE material and the resistance of the loop.

Effect of signal intensity and camera quantization on laser speckle contrast analysis

PubMed Central

Song, Lipei; Elson, Daniel S.

2012-01-01

Laser speckle contrast analysis (LASCA) is limited to being a qualitative method for the measurement of blood flow and tissue perfusion as it is sensitive to the measurement configuration. The signal intensity is one of the parameters that can affect the contrast values due to the quantization of the signals by the camera and analog-to-digital converter (ADC). In this paper we deduce the theoretical relationship between signal intensity and contrast values based on the probability density function (PDF) of the speckle pattern and simplify it to a rational function. A simple method to correct this contrast error is suggested. The experimental results demonstrate that this relationship can effectively compensate the bias in contrast values induced by the quantized signal intensity and correct for bias induced by signal intensity variations across the field of view. PMID:23304650

BFV approach to geometric quantization

NASA Astrophysics Data System (ADS)

Fradkin, E. S.; Linetsky, V. Ya.

1994-12-01

A gauge-invariant approach to geometric quantization is developed. It yields a complete quantum description for dynamical systems with non-trivial geometry and topology of the phase space. The method is a global version of the gauge-invariant approach to quantization of second-class constraints developed by Batalin, Fradkin and Fradkina (BFF). Physical quantum states and quantum observables are respectively described by covariantly constant sections of the Fock bundle and the bundle of hermitian operators over the phase space with a flat connection defined by the nilpotent BVF-BRST operator. Perturbative calculation of the first non-trivial quantum correction to the Poisson brackets leads to the Chevalley cocycle known in deformation quantization. Consistency conditions lead to a topological quantization condition with metaplectic anomaly.

Effects of Ionospheric Hall Polarization on Magnetospheric Configurations and Dynamics in Global MHD Simulation

NASA Astrophysics Data System (ADS)

Nakamizo, A.; Yoshikawa, A.; Tanaka, T.

2017-12-01

We investigate how the M-I coupling and boundary conditions affects the results of global simulations of the magnetosphere. More specifically, we examine the effects of ionospheric Hall polarization on magnetospheric convection and dynamics by using an MHD code developed by Tanaka et al. [2010]. This study is motivated by the recently proposed idea that the ionospheric convection is modified by the ionospheric polarization [Yoshikawa et al., 2013]. We perform simulations for the following pairs of Hall conductance and IMF-By; Hall conductance set by αH = 2, 3.5, 5, and uniform distribution (1.0 [S] everywhere), where RH is the ratio of Hall to Pedersen conductance, and IMF-By of positive, negative, and zero. The results are summarized as follows. (a) Large-scale structure: In the cases of uniform Hall conductance, the magnetosphere is completely symmetric under the zero IMF-By. In the cases of non-uniform Hall conductance, the magnetosphere shows asymmetries globally even under the zero IMF-By. Asymmetries become severe for larger αH. The results indicate that ionospheric Hall polarization is one of the important factors to determine the global structure. (b) Formation of NENL: The location becomes closer to the earth and timing becomes earlier for larger RH. The difference is considered to be related to the combined effects of field lines twisting due to ionospheric Hall polarization and M-I energy/current closures. (c) Near-earth convection: In the cases of non-uniform Hall conductance, an inflection structure is formed around premidnight sector on equatorial plane inside 10 RE. Considering that the region 2 FAC is not sufficiently generated in MHD models, the structure corresponds to a convection reversal often shown in the RCM. Previous studies regard the structure as the Harang Reversal in the magnetosphere. In the cases of uniform Hall conductance, by contrast, such structure is not formed, indicating that the Harang Reversal may not be formed without the

Large anomalous Hall effect driven by a nonvanishing Berry curvature in the noncolinear antiferromagnet Mn3Ge.

PubMed

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.

Simplifying Nanowire Hall Effect Characterization by Using a Three-Probe Device Design.

PubMed

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.

Floquet Engineering of Optical Solenoids and Quantized Charge Pumping along Tailored Paths in Two-Dimensional Chern Insulators

NASA Astrophysics Data System (ADS)

Wang, Botao; Ünal, F. Nur; Eckardt, André

2018-06-01

The insertion of a local magnetic flux, as the one created by a thin solenoid, plays an important role in gedanken experiments of quantum Hall physics. By combining Floquet engineering of artificial magnetic fields with the ability of single-site addressing in quantum gas microscopes, we propose a scheme for the realization of such local solenoid-type magnetic fields in optical lattices. We show that it can be employed to manipulate and probe elementary excitations of a topological Chern insulator. This includes quantized adiabatic charge pumping along tailored paths inside the bulk, as well as the controlled population of edge modes.

Chiral Majorana fermion modes in a quantum anomalous Hall insulator–superconductor structure

DOE PAGES

He, Qing Lin; Pan, Lei; Stern, Alexander L.; ...

2017-07-21

Majorana fermion is a hypothetical particle that is its own antiparticle. We report transport measurements that suggest the existence of one-dimensional chiral Majorana fermion modes in the hybrid system of a quantum anomalous Hall insulator thin film coupled with a superconductor. As the external magnetic field is swept, half-integer quantized conductance plateaus are observed at the locations of magnetization reversals, giving a distinct signature of the Majorana fermion modes. This transport signature is reproducible over many magnetic field sweeps and appears at different temperatures. This finding may open up an avenue to control Majorana fermions for implementing robust topological quantummore » computing.« less

Deformation quantization of fermi fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Galaviz, I.; Garcia-Compean, H.; Departamento de Fisica, Centro de Investigacion y de Estudios Avanzados del IPN, P.O. Box 14-740, 07000 Mexico, D.F.

2008-04-15

Deformation quantization for any Grassmann scalar free field is described via the Weyl-Wigner-Moyal formalism. The Stratonovich-Weyl quantizer, the Moyal *-product and the Wigner functional are obtained by extending the formalism proposed recently in [I. Galaviz, H. Garcia-Compean, M. Przanowski, F.J. Turrubiates, Weyl-Wigner-Moyal Formalism for Fermi Classical Systems, arXiv:hep-th/0612245] to the fermionic systems of infinite number of degrees of freedom. In particular, this formalism is applied to quantize the Dirac free field. It is observed that the use of suitable oscillator variables facilitates considerably the procedure. The Stratonovich-Weyl quantizer, the Moyal *-product, the Wigner functional, the normal ordering operator, and finally,more » the Dirac propagator have been found with the use of these variables.« less

Can Hall effect trigger Kelvin-Helmholtz instability in sub-Alfvénic flows?

NASA Astrophysics Data System (ADS)

Pandey, B. P.

2018-05-01

In the Hall magnetohydrodynamics, the onset condition of the Kelvin-Helmholtz instability is solely determined by the Hall effect and is independent of the nature of shear flows. In addition, the physical mechanism behind the super- and sub-Alfvénic flows becoming unstable is quite different: the high-frequency right circularly polarized whistler becomes unstable in the super-Alfvénic flows whereas low-frequency, left circularly polarized ion-cyclotron wave becomes unstable in the presence of sub-Alfvénic shear flows. The growth rate of the Kelvin-Helmholtz instability in the super-Alfvénic case is higher than the corresponding ideal magnetohydrodynamic rate. In the sub-Alfvénic case, the Hall effect opens up a new, hitherto inaccessible (to the magnetohydrodynamics) channel through which the partially or fully ionized fluid can become Kelvin-Helmholtz unstable. The instability growth rate in this case is smaller than the super-Alfvénic case owing to the smaller free shear energy content of the flow. When the Hall term is somewhat smaller than the advection term in the induction equation, the Hall effect is also responsible for the appearance of a new overstable mode whose growth rate is smaller than the purely growing Kelvin-Helmholtz mode. On the other hand, when the Hall diffusion dominates the advection term, the growth rate of the instability depends only on the Alfvén -Mach number and is independent of the Hall diffusion coefficient. Further, the growth rate in this case linearly increases with the Alfvén frequency with smaller slope for sub-Alfvénic flows.

MnSi nanostructures obtained from epitaxially grown thin films: magnetotransport and Hall effect

NASA Astrophysics Data System (ADS)

Schroeter, D.; Steinki, N.; Schilling, M.; Fernández Scarioni, A.; Krzysteczko, P.; Dziomba, T.; Schumacher, H. W.; Menzel, D.; Süllow, S.

2018-06-01

We present a comparative study of the (magneto)transport properties, including Hall effect, of bulk, epitaxially grown thin film and nanostructured MnSi. In order to set our results in relation to published data we extensively characterize our materials, this way establishing a comparatively good sample quality. Our analysis reveals that in particular for thin film and nanostructured material, there are extrinsic and intrinsic contributions to the electronic transport properties, which by modeling the data we separate out. Finally, we discuss our Hall effect data of nanostructured MnSi under consideration of the extrinsic contributions and with respect to the question of the detection of a topological Hall effect in a skyrmionic lattice.

Anomalous Nernst and Hall effects in magnetized platinum and palladium

NASA Astrophysics Data System (ADS)

Guo, G. Y.; Niu, Q.; Nagaosa, N.

2014-06-01

We study the anomalous Nernst effect (ANE) and anomalous Hall effect (AHE) in proximity-induced ferromagnetic palladium and platinum which is widely used in spintronics, within the Berry phase formalism based on the relativistic band-structure calculations. We find that both the anomalous Hall (σxyA) and Nernst (αxyA) conductivities can be related to the spin Hall conductivity (σxyS) and band exchange splitting (Δex) by relations σxyA=ΔexeℏσxyS(EF)' and αxyA=-π23kB2TΔexℏσxys(μ )'', respectively. In particular, these relations would predict that the σxyA in the magnetized Pt (Pd) would be positive (negative) since the σxyS(EF)' is positive (negative). Furthermore, both σxyA and αxyA are approximately proportional to the induced spin magnetic moment (ms) because the Δex is a linear function of ms. Using the reported ms in the magnetized Pt and Pd, we predict that the intrinsic anomalous Nernst conductivity (ANC) in the magnetic platinum and palladium would be gigantic, being up to ten times larger than, e.g., iron, while the intrinsic anomalous Hall conductivity (AHC) would also be significant.

Conductance Quantization in Resistive Random Access Memory

NASA Astrophysics Data System (ADS)

Li, Yang; Long, Shibing; Liu, Yang; Hu, Chen; Teng, Jiao; Liu, Qi; Lv, Hangbing; Suñé, Jordi; Liu, Ming

2015-10-01

The intrinsic scaling-down ability, simple metal-insulator-metal (MIM) sandwich structure, excellent performances, and complementary metal-oxide-semiconductor (CMOS) technology-compatible fabrication processes make resistive random access memory (RRAM) one of the most promising candidates for the next-generation memory. The RRAM device also exhibits rich electrical, thermal, magnetic, and optical effects, in close correlation with the abundant resistive switching (RS) materials, metal-oxide interface, and multiple RS mechanisms including the formation/rupture of nanoscale to atomic-sized conductive filament (CF) incorporated in RS layer. Conductance quantization effect has been observed in the atomic-sized CF in RRAM, which provides a good opportunity to deeply investigate the RS mechanism in mesoscopic dimension. In this review paper, the operating principles of RRAM are introduced first, followed by the summarization of the basic conductance quantization phenomenon in RRAM and the related RS mechanisms, device structures, and material system. Then, we discuss the theory and modeling of quantum transport in RRAM. Finally, we present the opportunities and challenges in quantized RRAM devices and our views on the future prospects.

Conductance Quantization in Resistive Random Access Memory.

PubMed

Li, Yang; Long, Shibing; Liu, Yang; Hu, Chen; Teng, Jiao; Liu, Qi; Lv, Hangbing; Suñé, Jordi; Liu, Ming

2015-12-01

The intrinsic scaling-down ability, simple metal-insulator-metal (MIM) sandwich structure, excellent performances, and complementary metal-oxide-semiconductor (CMOS) technology-compatible fabrication processes make resistive random access memory (RRAM) one of the most promising candidates for the next-generation memory. The RRAM device also exhibits rich electrical, thermal, magnetic, and optical effects, in close correlation with the abundant resistive switching (RS) materials, metal-oxide interface, and multiple RS mechanisms including the formation/rupture of nanoscale to atomic-sized conductive filament (CF) incorporated in RS layer. Conductance quantization effect has been observed in the atomic-sized CF in RRAM, which provides a good opportunity to deeply investigate the RS mechanism in mesoscopic dimension. In this review paper, the operating principles of RRAM are introduced first, followed by the summarization of the basic conductance quantization phenomenon in RRAM and the related RS mechanisms, device structures, and material system. Then, we discuss the theory and modeling of quantum transport in RRAM. Finally, we present the opportunities and challenges in quantized RRAM devices and our views on the future prospects.

Hall effect in quantum critical charge-cluster glass

PubMed Central

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

Hall effect in quantum critical charge-cluster glass.

PubMed

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.

Termination of the spin-resolved integer quantum Hall effect

NASA Astrophysics Data System (ADS)

Wong, L. W.; Jiang, H. W.; Palm, E.; Schaff, W. J.

1997-03-01

We report a magnetotransport study of the termination of the spin-resolved integer quantum Hall effect by controlled disorder in a gated GaAs/AlxGa1-xAs heterostructure. We have found that, for a given Nth Landau level, the difference in filling factors of a pair of spin-split resistivity peaks δνN=\\|νN↑-νN↓\\| changes rapidly from one to zero near a critical density nc. Scaling analysis shows that δνN collapses onto a single curve independent of N when plotted against the parameter (n-nc)/nc for five Landau levels. The effect of increasing the Zeeman energy is also examined by tilting the direction of magnetic field relative to the plane of the two-dimensional electron gas. Our experiment suggests the termination of the spin-resolved quantum Hall effect is a phase transition.

Spontaneous Hall effects in the electron system at the SmTiO3/EuTiO3 interface

NASA Astrophysics Data System (ADS)

Ahadi, Kaveh; Kim, Honggyu; Stemmer, Susanne

2018-05-01

Magnetotransport and magnetism of epitaxial SmTiO3/EuTiO3 heterostructures grown by molecular beam epitaxy are investigated. It is shown that the polar discontinuity at the interface introduces ˜3.9 × 1014 cm-2 carriers into the EuTiO3. The itinerant carriers exhibit two distinct contributions to the spontaneous Hall effect. The anomalous Hall effect appears despite a very small magnetization, indicating a non-collinear spin structure, and the second contribution resembles a topological Hall effect. Qualitative differences exist in the temperature dependence of both Hall effects when compared to uniformly doped EuTiO3. In particular, the topological Hall effect contribution appears at higher temperatures and the anomalous Hall effect shows a sign change with temperature. The results suggest that interfaces can be used to tune topological phenomena in itinerant magnetic systems.

A review of the quantum Hall effects in MgZnO/ZnO heterostructures

NASA Astrophysics Data System (ADS)

Falson, Joseph; Kawasaki, Masashi

2018-05-01

This review visits recent experimental efforts on high mobility two-dimensional electron systems (2DES) hosted at the Mg x Zn1-x O/ZnO heterointerface. We begin with the growth of these samples, and highlight the key characteristics of ozone-assisted molecular beam epitaxy required for their production. The transport characteristics of these structures are found to rival that of traditional semiconductor material systems, as signified by the high electron mobility (μ > 1000 000 cm2 Vs‑1) and rich quantum Hall features. Owing to a large effective mass and small dielectric constant, interaction effects are an order of magnitude stronger in comparison with the well studied GaAs-based 2DES. The strong correlation physics results in robust Fermi-liquid renormalization of the effective mass and spin susceptibility of carriers, which in turn dictates the parameter space for the quantum Hall effect. Finally, we explore the quantum Hall effect with a particular emphasis on the spin degree of freedom of carriers, and how their large spin splitting allows control of the ground states encountered at ultra-low temperatures within the fractional quantum Hall regime. We discuss in detail the physics of even-denominator fractional quantum Hall states, whose observation and underlying character remain elusive and exotic.

Hall effect in the coma of 67P/Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Huang, Z.; Tóth, G.; Gombosi, T. I.; Jia, X.; Combi, M. R.; Hansen, K. C.; Fougere, N.; Shou, Y.; Tenishev, V.; Altwegg, K.; Rubin, M.

2018-04-01

Magnetohydrodynamics simulations have been carried out in studying the solar wind and cometary plasma interactions for decades. Various plasma boundaries have been simulated and compared well with observations for comet 1P/Halley. The Rosetta mission, which studies comet 67P/Churyumov-Gerasimenko, challenges our understanding of the solar wind and comet interactions. The Rosetta Plasma Consortium observed regions of very weak magnetic field outside the predicted diamagnetic cavity. In this paper, we simulate the inner coma with the Hall magnetohydrodynamics equations and show that the Hall effect is important in the inner coma environment. The magnetic field topology becomes complex and magnetic reconnection occurs on the dayside when the Hall effect is taken into account. The magnetic reconnection on the dayside can generate weak magnetic field regions outside the global diamagnetic cavity, which may explain the Rosetta Plasma Consortium observations. We conclude that the substantial change in the inner coma environment is due to the fact that the ion inertial length (or gyro radius) is not much smaller than the size of the diamagnetic cavity.

Anomalous Hall effect in ZrTe5

NASA Astrophysics Data System (ADS)

Liang, Tian; Lin, Jingjing; Gibson, Quinn; Kushwaha, Satya; Liu, Minhao; Wang, Wudi; Xiong, Hongyu; Sobota, Jonathan A.; Hashimoto, Makoto; Kirchmann, Patrick S.; Shen, Zhi-Xun; Cava, R. J.; Ong, N. P.

2018-05-01

Research in topological matter has expanded to include the Dirac and Weyl semimetals1-10, which feature three-dimensional Dirac states protected by symmetry. Zirconium pentatelluride has been of recent interest as a potential Dirac or Weyl semimetal material. Here, we report the results of experiments performed by in situ three-dimensional double-axis rotation to extract the full 4π solid angular dependence of the transport properties. A clear anomalous Hall effect is detected in every sample studied, with no magnetic ordering observed in the system to the experimental sensitivity of torque magnetometry. Large anomalous Hall signals develop when the magnetic field is rotated in the plane of the stacked quasi-two-dimensional layers, with the values vanishing above about 60 K, where the negative longitudinal magnetoresistance also disappears. This suggests a close relation in their origins, which we attribute to the Berry curvature generated by the Weyl nodes.

Quantum anomalous Hall effect in magnetic topological insulators

DOE PAGES

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

Hall effect mobility for SiC MOSFETs with increasing dose of nitrogen implantation into channel region

NASA Astrophysics Data System (ADS)

Noguchi, Munetaka; Iwamatsu, Toshiaki; Amishiro, Hiroyuki; Watanabe, Hiroshi; Kita, Koji; Yamakawa, Satoshi

2018-04-01

The Hall effect mobility (μHall) of the Si-face 4H-SiC metal–oxide–semiconductor field effect transistor (MOSFET) with a nitrogen (N)-implanted channel region was investigated by increasing the N dose. The μHall in the channel region was systematically examined regarding channel structures, that is, the surface and buried channels. It was experimentally demonstrated that increasing the N dose results in an improvement in μHall in the channel region due to the formation of the buried channel. However, further increase in N dose was found to decrease the μHall in the channel region, owing to the decrease in the electron mobility in the N-implanted bulk region.

Perceptual Optimization of DCT Color Quantization Matrices

NASA Technical Reports Server (NTRS)

Watson, Andrew B.; Statler, Irving C. (Technical Monitor)

1994-01-01

Many image compression schemes employ a block Discrete Cosine Transform (DCT) and uniform quantization. Acceptable rate/distortion performance depends upon proper design of the quantization matrix. In previous work, we showed how to use a model of the visibility of DCT basis functions to design quantization matrices for arbitrary display resolutions and color spaces. Subsequently, we showed how to optimize greyscale quantization matrices for individual images, for optimal rate/perceptual distortion performance. Here we describe extensions of this optimization algorithm to color images.

Hall effect in quantum critical charge-cluster glass

DOE PAGES

Bozovic, Ivan; Wu, Jie; Bollinger, Anthony T.; ...

2016-04-04

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 La 2-xSr xCuO 4 (LSCO) samples doped near the quantum critical point at x ≈ 0.06. Dramatic fluctuations in the Hall resistance appear below T CG ≈ 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 variedmore » in extremely fine steps, Δx ≈ 0.00008. Furthermore, 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.« less

Noncommutative gerbes and deformation quantization

NASA Astrophysics Data System (ADS)

Aschieri, Paolo; Baković, Igor; Jurčo, Branislav; Schupp, Peter

2010-11-01

We define noncommutative gerbes using the language of star products. Quantized twisted Poisson structures are discussed as an explicit realization in the sense of deformation quantization. Our motivation is the noncommutative description of D-branes in the presence of topologically non-trivial background fields.

Robert B. Laughlin and the Fractional Quantum Hall Effect

Science.gov Websites

dropdown arrow Site Map A-Z Index Menu Synopsis Robert B. Laughlin and the Fractional Quantum Hall Effect Tsui discovered the effect. In 1983, Laughlin, then at the Lawrence Livermore National Laboratory , provided the theoretical explanation of the effect in terms of fractionally charged particles. It was a

A visual detection model for DCT coefficient quantization

NASA Technical Reports Server (NTRS)

Ahumada, Albert J., Jr.; Watson, Andrew B.

1994-01-01

The discrete cosine transform (DCT) is widely used in image compression and is part of the JPEG and MPEG compression standards. The degree of compression and the amount of distortion in the decompressed image are controlled by the quantization of the transform coefficients. The standards do not specify how the DCT coefficients should be quantized. One approach is to set the quantization level for each coefficient so that the quantization error is near the threshold of visibility. Results from previous work are combined to form the current best detection model for DCT coefficient quantization noise. This model predicts sensitivity as a function of display parameters, enabling quantization matrices to be designed for display situations varying in luminance, veiling light, and spatial frequency related conditions (pixel size, viewing distance, and aspect ratio). It also allows arbitrary color space directions for the representation of color. A model-based method of optimizing the quantization matrix for an individual image was developed. The model described above provides visual thresholds for each DCT frequency. These thresholds are adjusted within each block for visual light adaptation and contrast masking. For given quantization matrix, the DCT quantization errors are scaled by the adjusted thresholds to yield perceptual errors. These errors are pooled nonlinearly over the image to yield total perceptual error. With this model one may estimate the quantization matrix for a particular image that yields minimum bit rate for a given total perceptual error, or minimum perceptual error for a given bit rate. Custom matrices for a number of images show clear improvement over image-independent matrices. Custom matrices are compatible with the JPEG standard, which requires transmission of the quantization matrix.

Spin Hall effect originated from fractal surface

NASA Astrophysics Data System (ADS)

Hajzadeh, I.; Mohseni, S. M.; Movahed, S. M. S.; Jafari, G. R.

2018-05-01

The spin Hall effect (SHE) has shown promising impact in the field of spintronics and magnonics from fundamental and practical points of view. This effect originates from several mechanisms of spin scatterers based on spin–orbit coupling (SOC) and also can be manipulated through the surface roughness. Here, the effect of correlated surface roughness on the SHE in metallic thin films with small SOC is investigated theoretically. Toward this, the self-affine fractal surface in the framework of the Born approximation is exploited. The surface roughness is described by the k-correlation model and is characterized by the roughness exponent H , the in-plane correlation length ξ and the rms roughness amplitude δ. It is found that the spin Hall angle in metallic thin film increases by two orders of magnitude when H decreases from H  =  1 to H  =  0. In addition, the source of SHE for surface roughness with Gaussian profile distribution function is found to be mainly the side jump scattering while that with a non-Gaussian profile suggests both of the side jump and skew scatterings are present. Our achievements address how details of the surface roughness profile can adjust the SHE in non-heavy metals.

Quantization of an electromagnetic field in two-dimensional photonic structures based on the scattering matrix formalism ( S-quantization)

NASA Astrophysics Data System (ADS)

Ivanov, K. A.; Nikolaev, V. V.; Gubaydullin, A. R.; Kaliteevski, M. A.

2017-10-01

Based on the scattering matrix formalism, we have developed a method of quantization of an electromagnetic field in two-dimensional photonic nanostructures ( S-quantization in the two-dimensional case). In this method, the fields at the boundaries of the quantization box are expanded into a Fourier series and are related with each other by the scattering matrix of the system, which is the product of matrices describing the propagation of plane waves in empty regions of the quantization box and the scattering matrix of the photonic structure (or an arbitrary inhomogeneity). The quantization condition (similarly to the onedimensional case) is formulated as follows: the eigenvalues of the scattering matrix are equal to unity, which corresponds to the fact that the set of waves that are incident on the structure (components of the expansion into the Fourier series) is equal to the set of waves that travel away from the structure (outgoing waves). The coefficients of the matrix of scattering through the inhomogeneous structure have been calculated using the following procedure: the structure is divided into parallel layers such that the permittivity in each layer varies only along the axis that is perpendicular to the layers. Using the Fourier transform, the Maxwell equations have been written in the form of a matrix that relates the Fourier components of the electric field at the boundaries of neighboring layers. The product of these matrices is the transfer matrix in the basis of the Fourier components of the electric field. Represented in a block form, it is composed by matrices that contain the reflection and transmission coefficients for the Fourier components of the field, which, in turn, constitute the scattering matrix. The developed method considerably simplifies the calculation scheme for the analysis of the behavior of the electromagnetic field in structures with a two-dimensional inhomogeneity. In addition, this method makes it possible to obviate

Quantum Nonlinear Hall Effect Induced by Berry Curvature Dipole in Time-Reversal Invariant Materials.

PubMed

Sodemann, Inti; Fu, Liang

2015-11-20

It is well known that a nonvanishing Hall conductivity requires broken time-reversal symmetry. However, in this work, we demonstrate that Hall-like currents can occur in second-order response to external electric fields in a wide class of time-reversal invariant and inversion breaking materials, at both zero and twice the driving frequency. This nonlinear Hall effect has a quantum origin arising 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. The nonlinear Hall coefficient is a rank-two pseudotensor, whose form is determined by point group symmetry. We discus optimal conditions to observe this effect and propose candidate two- and three-dimensional materials, including topological crystalline insulators, transition metal dichalcogenides, and Weyl semimetals.

Conductivity predictions for the 5/2 fractional quantum Hall state using the composite fermion superconductor model

NASA Astrophysics Data System (ADS)

Foster, Kerwin Crayton

The fractional quantum Hall effect (FQHE) occurs when a two-dimensional electron gas is placed in a strong magnetic field at low temperatures. When this effect occurs the Hall resistance, RH, defined to be the Hall voltage divided by the current, is quantized, with RH = (1/nu)h/ e2 where nu = p/q is the Landau level filling fraction; and p and q are relatively prime integers. For almost all observed FQHE states, q is odd with one notable exception: the nu = 5/2 FQHE state. Understanding the nature of this incompressible even-denominator state is one of the central questions in the theory of the FQHE and is the subject of this Dissertation. We use a powerful theoretical tool for studying the FQHE: composite fermion theory. Composite fermions can be viewed as electrons bound to an even number of magnetic flux quanta. Jain has shown that the FQHE for electrons can be viewed as an integer quantum Hall effect (p = 1) for composite fermions. More recently, Halperin, Lee and Read developed a successful theory of the compressible nu = 1/2 state using composite fermions. There is now compelling theoretical evidence that the 5/2 state is a so-called Moore-Read state---a state which can be viewed as a spin-polarized p-wave superconductor of composite fermions. We have developed a semi-phenomenological description of this state by modifying the Halperin-Lee-Read theory, adding a p-wave pairing interaction between composite fermions by hand. The electromagnetic response functions for the resulting superconducting state of composite fermions are then calculated. We show that these response functions exhibit the expected BCS 'coherence factor' effects, such as the Hebel-Slichter peak. Using the composite fermion response functions, we then calculate the corresponding electronic response functions using Chern-Simons theory. We find that in the electronic response, the most striking coherence factor effects (e.g., the Hebel-Slichter peak) are strongly suppressed. However, the low

Full Spectrum Conversion Using Traveling Pulse Wave Quantization

DTIC Science & Technology

2017-03-01

Full Spectrum Conversion Using Traveling Pulse Wave Quantization Michael S. Kappes Mikko E. Waltari IQ-Analog Corporation San Diego, California...temporal-domain quantization technique called Traveling Pulse Wave Quantization (TPWQ). Full spectrum conversion is defined as the complete...pulse width measurements that are continuously generated hence the name “traveling” pulse wave quantization. Our TPWQ-based ADC is composed of a

Anomalous Hall effect in ZrTe 5

DOE PAGES

Liang, Tian; Lin, Jingjing; Gibson, Quinn; ...

2018-03-19

Research in topological matter has expanded to include the Dirac and Weyl semimetals which feature three-dimensional Dirac states protected by symmetry. Zirconium pentatelluride has been of recent interest as a potential Dirac or Weyl semimetal material. Here, we report the results of experiments performed by in situ three-dimensional double-axis rotation to extract the full 4π solid angular dependence of the transport properties. A clear anomalous Hall effect is detected in every sample studied, with no magnetic ordering observed in the system to the experimental sensitivity of torque magnetometry. Large anomalous Hall signals develop when the magnetic field is rotated inmore » the plane of the stacked quasi-two-dimensional layers, with the values vanishing above about 60 K, where the negative longitudinal magnetoresistance also disappears. Finally, this suggests a close relation in their origins, which we attribute to the Berry curvature generated by the Weyl nodes.« less

Anomalous Hall effect in ZrTe 5

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liang, Tian; Lin, Jingjing; Gibson, Quinn

Research in topological matter has expanded to include the Dirac and Weyl semimetals which feature three-dimensional Dirac states protected by symmetry. Zirconium pentatelluride has been of recent interest as a potential Dirac or Weyl semimetal material. Here, we report the results of experiments performed by in situ three-dimensional double-axis rotation to extract the full 4π solid angular dependence of the transport properties. A clear anomalous Hall effect is detected in every sample studied, with no magnetic ordering observed in the system to the experimental sensitivity of torque magnetometry. Large anomalous Hall signals develop when the magnetic field is rotated inmore » the plane of the stacked quasi-two-dimensional layers, with the values vanishing above about 60 K, where the negative longitudinal magnetoresistance also disappears. Finally, this suggests a close relation in their origins, which we attribute to the Berry curvature generated by the Weyl nodes.« less

Admittance measurements in the quantum Hall effect regime

NASA Astrophysics Data System (ADS)

Hernández, C.; Consejo, C.; Chaubet, C.

2014-11-01

In this work we present an admittance study of a two-dimensional electron gas (2DEG) in the quantum Hall effect (QHE) regime. We have studied several Hall bars in different contacts configurations in the frequency range 100 Hz-1 MHz. Our interpretation is based on the Landauer-Büttiker theory and takes into account both the capacitance and the topology of the coaxial cables which are connected to the sample holder. We show that we always observe losses through the capacitive impedance of the coaxial cables, except in the two contacts configuration in which the cable capacitance does not influence the admittance measurement of the sample. In this case, we measure the electrochemical capacitance of the 2DEG and show its dependence with the filling factor ν.

Anomalous Hall effect in epitaxial permalloy thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Y. Q.; Sun, N. Y.; Shan, R.

2013-10-28

Anomalous Hall effect (AHE) of epitaxial permalloy thin films grown on MgO (001) substrates is investigated. The longitudinal conductivity independent term (i.e., the sum of intrinsic and side-jump contributions) of the anomalous Hall conductivity (AHC) is found to be much smaller than those of Fe and Ni films. Band theoretical calculations of the intrinsic AHC as a function of the number of valence electrons (band filling) indicate that the AHC of the permalloy is in the vicinity of sign change, thus resulting in the smallness of the intrinsic AHC. The contribution of the phonon scattering is found to be comparablemore » to that of the impurity scattering. This work suggests that the permalloy films are ideal systems to understand the AHE mechanisms induced by impurity scattering.« less

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).

Automated High-Temperature Hall-Effect Apparatus

NASA Technical Reports Server (NTRS)

Parker, James B.; Zoltan, Leslie D.

1992-01-01

Automated apparatus takes Hall-effect measurements of specimens of thermoelectric materials at temperatures from ambient to 1,200 K using computer control to obtain better resolution of data and more data points about three times as fast as before. Four-probe electrical-resistance measurements taken in 12 electrical and 2 magnetic orientations to characterize specimens at each temperature. Computer acquires data, and controls apparatus via three feedback loops: one for temperature, one for magnetic field, and one for electrical-potential data.

Geometrical Description of fractional quantum Hall quasiparticles

NASA Astrophysics Data System (ADS)

Park, Yeje; Yang, Bo; Haldane, F. D. M.

2012-02-01

We examine a description of fractional quantum Hall quasiparticles and quasiholes suggested by a recent geometrical approach (F. D. M. Haldane, Phys. Rev. Lett. 108, 116801 (2011)) to FQH systems, where the local excess electric charge density in the incompressible state is given by a topologically-quantized ``guiding-center spin'' times the Gaussian curvature of a ``guiding-center metric tensor'' that characterizes the local shape of the correlation hole around electrons in the fluid. We use a phenomenological energy function with two ingredients: the shear distortion energy of area-preserving distortions of the fluid, and a local (short-range) approximation to the Coulomb energy of the fluctuation of charge density associated with the Gaussian curvature. Quasiparticles and quasiholes of the 1/3 Laughlin state are modeled as ``punctures'' in the incompressible fluid which then relax by geometric distortion which generates Gaussian curvature, giving rise to the charge-density profile around the topological excitation.

Interaction-induced interference in the integer quantum Hall effect

NASA Astrophysics Data System (ADS)

Sivan, I.; Bhattacharyya, R.; Choi, H. K.; Heiblum, M.; Feldman, D. E.; Mahalu, D.; Umansky, V.

2018-03-01

In recent interference experiments with an electronic Fabry-Pérot interferometer (FPI), implemented in the integer quantum Hall effect regime, a flux periodicity of h /2 e was observed at bulk fillings νB>2.5 . The halved periodicity was accompanied by an interfering charge e*=2 e , determined by shot-noise measurements. Here, we present measurements demonstrating that, counterintuitively, the coherence and the interference periodicity of the interfering chiral edge channel are solely determined by the coherence and the enclosed flux of the adjacent edge channel. Our results elucidate the important role of the latter and suggest that a neutral chiral edge mode plays a crucial role in the pairing phenomenon. Our findings reveal that the observed pairing of electrons is not a curious isolated phenomenon, but one of many manifestations of unexpected edge physics in the quantum Hall effect regime.

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.

Coherent state quantization of quaternions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muraleetharan, B., E-mail: bbmuraleetharan@jfn.ac.lk, E-mail: santhar@gmail.com; Thirulogasanthar, K., E-mail: bbmuraleetharan@jfn.ac.lk, E-mail: santhar@gmail.com

Parallel to the quantization of the complex plane, using the canonical coherent states of a right quaternionic Hilbert space, quaternion field of quaternionic quantum mechanics is quantized. Associated upper symbols, lower symbols, and related quantities are analyzed. Quaternionic version of the harmonic oscillator and Weyl-Heisenberg algebra are also obtained.

Pseudo-Hall Effect in Graphite on Paper Based Four Terminal Devices for Stress Sensing Applications

NASA Astrophysics Data System (ADS)

Qamar, Afzaal; Sarwar, Tuba; Dinh, Toan; Foisal, A. R. M.; Phan, Hoang-Phuong; Viet Dao, Dzung

2017-04-01

A cost effective and easy to fabricate stress sensor based on pseudo-Hall effect in Graphite on Paper (GOP) has been presented in this article. The four terminal devices were developed by pencil drawing with hand on to the paper substrate. The stress was applied to the paper containing four terminal devices with the input current applied at two terminals and the offset voltage observed at other two terminals called pseudo-Hall effect. The GOP stress sensor showed significant response to the applied stress which was smooth and linear. These results showed that the pseudo-Hall effect in GOP based four terminal devices can be used for cost effective, flexible and easy to make stress, strain or force sensors.

BFV quantization on hermitian symmetric spaces

NASA Astrophysics Data System (ADS)

Fradkin, E. S.; Linetsky, V. Ya.

1995-02-01

Gauge-invariant BFV approach to geometric quantization is applied to the case of hermitian symmetric spaces G/ H. In particular, gauge invariant quantization on the Lobachevski plane and sphere is carried out. Due to the presence of symmetry, master equations for the first-class constraints, quantum observables and physical quantum states are exactly solvable. BFV-BRST operator defines a flat G-connection in the Fock bundle over G/ H. Physical quantum states are covariantly constant sections with respect to this connection and are shown to coincide with the generalized coherent states for the group G. Vacuum expectation values of the quantum observables commuting with the quantum first-class constraints reduce to the covariant symbols of Berezin. The gauge-invariant approach to quantization on symplectic manifolds synthesizes geometric, deformation and Berezin quantization approaches.

Interfacial scattering effect on anisotropic magnetoresistance and anomalous Hall effect in Ta/Fe multilayers

NASA Astrophysics Data System (ADS)

Zhang, Qiang; Zhang, Junwei; Zhao, Yuelei; Wen, Yan; Li, Peng; Zhang, Senfu; He, Xin; Zhang, Junli; Zhang, Xixiang

2018-05-01

The effect of interfacial scattering on anisotropic magnetoresistance (AMR) and anomalous Hall effect (AHE) was studied in the (Ta12/n/Fe36/n) n multilayers, where the numbers give the thickness in nanometer and n is an integer from 1 to 12. The multilayer structure has been confirmed by the XRR spectra and STEM images of cross-sections. The magneto-transport properties were measured by four-point probe method in Hall bar shaped samples in the temperature range of 5 - 300 K. The AMR increases with n, which could be ascribed to the interfacial spin-orbit scattering. At 5 K, the longitudinal resistivity (ρxx) increases by 6.4 times and the anomalous Hall resistivity (ρAHE) increases by 49.4 times from n =1 to n =12, indicative of the interfacial scattering effect. The skew-scattering, side-jump and intrinsic contributions to the AHE were separated successfully. As n increases from 1 to 12, the intrinsic contribution decreases because of the decaying crystallinity or finite size effect and the intrinsic contribution dominated the AHE for all samples. The side jump changes from negative to positive because the interfacial scattering and intralayer scattering in Fe layers both contribute to side jump in the AHE but with opposite sign.

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

Effective anomalous Hall coefficient in an ultrathin Co layer sandwiched by Pt layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Peng; Wu, Di; Jiang, Zhengsheng

2014-02-14

Anomalous Hall effect in Co/Pt multilayer is important to study the effect of interface with strong spin-orbit coupling. However, the shunting effect of the layers in such system and the circuit in the plane perpendicular to the injected current were overlooked in most works and thus, anomalous Hall coefficient in Co/Pt multilayer has not been determined accurately. Considering the shunting effect and the equivalent circuit, we show that the effective anomalous Hall coefficient of a 0.5 nm thick Co layer sandwiched by Pt layers R{sub S} is 0.29 ± 0.01 μΩ cm/T at the zero temperature limit and increases to about 0.73 μΩ cm/T at the temperaturemore » of 300 K. R{sub S} is one order larger than that in bulk Co film, indicating the large contribution of the Co/Pt interface. R{sub S} increases with the resistivity of Co as well as a resistivity independent contribution of −0.23 ± 0.01 μΩ cm/T. The equivalent anomalous Hall current in the Co layer has a maximum of 1.1% of the injected transverse current in the Co layer around the temperature of 80 K.« less

A visual detection model for DCT coefficient quantization

NASA Technical Reports Server (NTRS)

Ahumada, Albert J., Jr.; Peterson, Heidi A.

1993-01-01

The discrete cosine transform (DCT) is widely used in image compression, and is part of the JPEG and MPEG compression standards. The degree of compression, and the amount of distortion in the decompressed image are determined by the quantization of the transform coefficients. The standards do not specify how the DCT coefficients should be quantized. Our approach is to set the quantization level for each coefficient so that the quantization error is at the threshold of visibility. Here we combine results from our previous work to form our current best detection model for DCT coefficient quantization noise. This model predicts sensitivity as a function of display parameters, enabling quantization matrices to be designed for display situations varying in luminance, veiling light, and spatial frequency related conditions (pixel size, viewing distance, and aspect ratio). It also allows arbitrary color space directions for the representation of color.

Controlling charge quantization with quantum fluctuations.

PubMed

Jezouin, S; Iftikhar, Z; Anthore, A; Parmentier, F D; Gennser, U; Cavanna, A; Ouerghi, A; Levkivskyi, I P; Idrisov, E; Sukhorukov, E V; Glazman, L I; Pierre, F

2016-08-04

In 1909, Millikan showed that the charge of electrically isolated systems is quantized in units of the elementary electron charge e. Today, the persistence of charge quantization in small, weakly connected conductors allows for circuits in which single electrons are manipulated, with applications in, for example, metrology, detectors and thermometry. However, as the connection strength is increased, the discreteness of charge is progressively reduced by quantum fluctuations. Here we report the full quantum control and characterization of charge quantization. By using semiconductor-based tunable elemental conduction channels to connect a micrometre-scale metallic island to a circuit, we explore the complete evolution of charge quantization while scanning the entire range of connection strengths, from a very weak (tunnel) to a perfect (ballistic) contact. We observe, when approaching the ballistic limit, that charge quantization is destroyed by quantum fluctuations, and scales as the square root of the residual probability for an electron to be reflected across the quantum channel; this scaling also applies beyond the different regimes of connection strength currently accessible to theory. At increased temperatures, the thermal fluctuations result in an exponential suppression of charge quantization and in a universal square-root scaling, valid for all connection strengths, in agreement with expectations. Besides being pertinent for the improvement of single-electron circuits and their applications, and for the metal-semiconductor hybrids relevant to topological quantum computing, knowledge of the quantum laws of electricity will be essential for the quantum engineering of future nanoelectronic devices.

Large anomalous Hall effect in a non-collinear antiferromagnet Mn3Sn at room temperature

NASA Astrophysics Data System (ADS)

Higo, Tomoya; Kiyohara, Naoki; Nakatsuji, Satoru

Recent development in theoretical and experimental studies 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. In this talk, we will present experimental results showing that the antiferromagnet Mn3Sn, which has a non-collinear 120-degree spin order, exhibits a large anomalous Hall effect. The magnitude of the Hall conductivity is ~ 20 Ω-1 cm-1 at room temperature and > 100 Ω-1 cm-1 at low temperatures. We found that a main component of the Hall signal, which is nearly independent of a magnetic field and magnetization, can change the sign with the reversal of a small applied field, corresponding to the rotation of the staggered moments of the non-collinear antiferromagnetic spin order which carries a very small net moment of a few of mμB. Supported by PRESTO, JST, and Grants-in-Aid for Program for Advancing Strategic International Networks to Accelerate the Circulation of Talented Researchers (No. R2604) and Scientific Research on Innovative Areas (15H05882 and 15H05883) from JSPS.

Scaling relation of the anomalous Hall effect in (Ga,Mn)As

NASA Astrophysics Data System (ADS)

Glunk, M.; Daeubler, J.; Schoch, W.; Sauer, R.; Limmer, W.

2009-09-01

We present magnetotransport studies performed on an extended set of (Ga,Mn)As samples at 4.2 K with longitudinal conductivities σxx ranging from the low-conductivity to the high-conductivity regime. The anomalous Hall conductivity σxy(AH) is extracted from the measured longitudinal and Hall resistivities. A transition from σxy(AH)=20Ω-1cm-1 due to the Berry phase effect in the high-conductivity regime to a scaling relation σxy(AH)∝σxx1.6 for low-conductivity samples is observed. This scaling relation is consistent with a recently developed unified theory of the anomalous Hall effect in the framework of the Keldysh formalism. It turns out to be independent of crystallographic orientation, growth conditions, Mn concentration, and strain, and can therefore be considered universal for low-conductivity (Ga,Mn)As. The relation plays a crucial role when deriving values of the hole concentration from magnetotransport measurements in low-conductivity (Ga,Mn)As. In addition, the hole diffusion constants for the high-conductivity samples are determined from the measured longitudinal conductivities.

The microwave Hall effect measured using a waveguide tee

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coppock, J. E.; Anderson, J. R.; Johnson, W. B.

2016-03-14

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 phasemore » 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 cm{sup 2}/(V s).« less

Classical Hall Effect without Magnetic Field

NASA Astrophysics Data System (ADS)

Schade, Nicholas; Tao, Chiao-Yu; Schuster, David; Nagel, Sidney

We show that the sign and density of charge carriers in a material can be obtained without the presence of a magnetic field. This effect, analogous to the classical Hall effect, is due solely to the geometry of the current-carrying wire. When current flows, surface charges along the wire create small electric fields that direct the current to follow the path of the conductor. In a curved wire, the charge carriers must experience a centripetal force, which arises from an electric field perpendicular to the drift velocity. This electric field produces a potential difference between the sides of the wire that depends on the sign and density of the charge carriers. We experimentally investigate circuits made from superconductors or graphene to find evidence for this effect.

Subband Image Coding with Jointly Optimized Quantizers

NASA Technical Reports Server (NTRS)

Kossentini, Faouzi; Chung, Wilson C.; Smith Mark J. T.

1995-01-01

An iterative design algorithm for the joint design of complexity- and entropy-constrained subband quantizers and associated entropy coders is proposed. Unlike conventional subband design algorithms, the proposed algorithm does not require the use of various bit allocation algorithms. Multistage residual quantizers are employed here because they provide greater control of the complexity-performance tradeoffs, and also because they allow efficient and effective high-order statistical modeling. The resulting subband coder exploits statistical dependencies within subbands, across subbands, and across stages, mainly through complexity-constrained high-order entropy coding. Experimental results demonstrate that the complexity-rate-distortion performance of the new subband coder is exceptional.

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.

On the Dequantization of Fedosov's Deformation Quantization

NASA Astrophysics Data System (ADS)

Karabegov, Alexander V.

2003-08-01

To each natural deformation quantization on a Poisson manifold M we associate a Poisson morphism from the formal neighborhood of the zero section of the cotangent bundle to M to the formal neighborhood of the diagonal of the product M x M~, where M~ is a copy of M with the opposite Poisson structure. We call it dequantization of the natural deformation quantization. Then we "dequantize" Fedosov's quantization.

Topological Hall Effect from Strong to Weak Coupling

NASA Astrophysics Data System (ADS)

Nakazawa, Kazuki; Bibes, Manuel; Kohno, Hiroshi

2018-03-01

The topological Hall effect (THE) of electrons coupled to a noncoplanar spin texture has been studied so far for the strong- and weak-coupling regimes separately; the former in terms of the Berry phase and the latter by perturbation theory. In this letter, we present a unified treatment in terms of spin gauge field by considering not only the adiabatic (Berry phase) component of the gauge field but also the nonadiabatic component. While only the adiabatic contribution is important in the strong-coupling regime, it is completely canceled by a part of the nonadiabatic contribution in the weak-coupling regime, where the THE is governed by the remaining nonadiabatic terms. We found a new weak-coupling region that cannot be accessed by a simple perturbation theory, where the Hall conductivity is proportional to M, with 2M being the exchange splitting of the electron spectrum.

Generalized noise terms for the quantized fluctuational electrodynamics

NASA Astrophysics Data System (ADS)

Partanen, Mikko; Häyrynen, Teppo; Tulkki, Jukka; Oksanen, Jani

2017-03-01

The quantization of optical fields in vacuum has been known for decades, but extending the field quantization to lossy and dispersive media in nonequilibrium conditions has proven to be complicated due to the position-dependent electric and magnetic responses of the media. In fact, consistent position-dependent quantum models for the photon number in resonant structures have only been formulated very recently and only for dielectric media. Here we present a general position-dependent quantized fluctuational electrodynamics (QFED) formalism that extends the consistent field quantization to describe the photon number also in the presence of magnetic field-matter interactions. It is shown that the magnetic fluctuations provide an additional degree of freedom in media where the magnetic coupling to the field is prominent. Therefore, the field quantization requires an additional independent noise operator that is commuting with the conventional bosonic noise operator describing the polarization current fluctuations in dielectric media. In addition to allowing the detailed description of field fluctuations, our methods provide practical tools for modeling optical energy transfer and the formation of thermal balance in general dielectric and magnetic nanodevices. We use QFED to investigate the magnetic properties of microcavity systems to demonstrate an example geometry in which it is possible to probe fields arising from the electric and magnetic source terms. We show that, as a consequence of the magnetic Purcell effect, the tuning of the position of an emitter layer placed inside a vacuum cavity can make the emissivity of a magnetic emitter to exceed the emissivity of a corresponding electric emitter.

Driving and detecting ferromagnetic resonance in insulators with the spin Hall effect

DOE PAGES

Sklenar, Joseph; Zhang, Wei; Jungfleisch, Matthias B.; ...

2015-11-06

We demonstrate the generation and detection of spin-torque ferromagnetic resonance in Pt/Y 3Fe 5O 12 (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 currentmore » through the inverse spin Hall effect. The voltage is measured with applied magnetic field directions that range in-plane to nearly perpendicular. In conclusion, 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.« less

A recursive technique for adaptive vector quantization

NASA Technical Reports Server (NTRS)

Lindsay, Robert A.

1989-01-01

Vector Quantization (VQ) is fast becoming an accepted, if not preferred method for image compression. The VQ performs well when compressing all types of imagery including Video, Electro-Optical (EO), Infrared (IR), Synthetic Aperture Radar (SAR), Multi-Spectral (MS), and digital map data. The only requirement is to change the codebook to switch the compressor from one image sensor to another. There are several approaches for designing codebooks for a vector quantizer. Adaptive Vector Quantization is a procedure that simultaneously designs codebooks as the data is being encoded or quantized. This is done by computing the centroid as a recursive moving average where the centroids move after every vector is encoded. When computing the centroid of a fixed set of vectors the resultant centroid is identical to the previous centroid calculation. This method of centroid calculation can be easily combined with VQ encoding techniques. The defined quantizer changes after every encoded vector by recursively updating the centroid of minimum distance which is the selected by the encoder. Since the quantizer is changing definition or states after every encoded vector, the decoder must now receive updates to the codebook. This is done as side information by multiplexing bits into the compressed source data.

Spin Hall effects in metallic antiferromagnets – perspectives for future spin-orbitronics

DOE PAGES

Sklenar, Joseph; Zhang, Wei; Jungfleisch, Matthias B.; ...

2016-03-07

In this paper, we investigate angular dependent spin-orbit torques from the spin Hall effect in a metallic antiferromagnet using the spin-torque ferromagnetic resonance technique. The large spin Hall effect exists in PtMn, a prototypical CuAu-I-type metallic antiferromagnet. By applying epitaxial growth, we previously reported an appreciable difference in spin-orbit torques for c- and a-axis orientated samples, implying anisotropic effects in magnetically ordered materials. In this work we demonstrate through bipolar-magnetic-field experiments a small but noticeable asymmetric behavior in the spin-transfer-torque that appears as a hysteresis effect. Finally, we also suggest that metallic antiferromagnets may be good candidates for the investigationmore » of various unidirectional effects related to novel spin-orbitronics phenomena.« less

Nondestructive hall coefficient measurements using ACPD techniques

NASA Astrophysics Data System (ADS)

Velicheti, Dheeraj; Nagy, Peter B.; Hassan, Waled

2018-04-01

Hall coefficient measurements offer great opportunities as well as major challenges for nondestructive materials characterization. The Hall effect is produced by the magnetic Lorentz force acting on moving charge carriers in the presence of an applied magnetic field. The magnetic perturbation gives rise to a Hall current that is normal to the conduction current but does not directly perturb the electric potential distribution. Therefore, Hall coefficient measurements usually exploit the so-called transverse galvanomagnetic potential drop effect that arises when the Hall current is intercepted by the boundaries of the specimen and thereby produce a measurable potential drop. In contrast, no Hall potential is produced in a large plate in the presence of a uniform normal field at quasi-static low frequencies. In other words, conventional Hall coefficient measurements are inherently destructive since they require cutting the material under tests. This study investigated the feasibility of using alternating current potential drop (ACPD) techniques for nondestructive Hall coefficient measurements in plates. Specifically, the directional four-point square-electrode configuration is investigated with superimposed external magnetic field. Two methods are suggested to make Hall coefficient measurements in large plates without destructive machining. At low frequencies, constraining the bias magnetic field can replace constraining the dimensions of the specimen, which is inherently destructive. For example, when a cylindrical permanent magnet is used to provide the bias magnetic field, the peak Hall voltage is produced when the diameter of the magnet is equal to the diagonal of the square ACPD probe. Although this method is less effective than cutting the specimen to a finite size, the loss of sensitivity is less than one order of magnitude even at very low frequencies. In contrast, at sufficiently high inspection frequencies the magnetic field of the Hall current induces a

Approaching quantum anomalous Hall effect in proximity-coupled YIG/graphene/h-BN sandwich structure

NASA Astrophysics Data System (ADS)

Tang, Chi; Cheng, Bin; Aldosary, Mohammed; Wang, Zhiyong; Jiang, Zilong; Watanabe, K.; Taniguchi, T.; Bockrath, Marc; Shi, Jing

2018-02-01

Quantum anomalous Hall state is expected to emerge in Dirac electron systems such as graphene under both sufficiently strong exchange and spin-orbit interactions. In pristine graphene, neither interaction exists; however, both interactions can be acquired by coupling graphene to a magnetic insulator as revealed by the anomalous Hall effect. Here, we show enhanced magnetic proximity coupling by sandwiching graphene between a ferrimagnetic insulator yttrium iron garnet (YIG) and hexagonal-boron nitride (h-BN) which also serves as a top gate dielectric. By sweeping the top-gate voltage, we observe Fermi level-dependent anomalous Hall conductance. As the Dirac point is approached from both electron and hole sides, the anomalous Hall conductance reaches ¼ of the quantum anomalous Hall conductance 2e2/h. The exchange coupling strength is determined to be as high as 27 meV from the transition temperature of the induced magnetic phase. YIG/graphene/h-BN is an excellent heterostructure for demonstrating proximity-induced interactions in two-dimensional electron systems.

Robust emergence of a topological Hall effect in MnGa/heavy metal bilayers

NASA Astrophysics Data System (ADS)

Meng, K. K.; Zhao, X. P.; Liu, P. F.; Liu, Q.; Wu, Y.; Li, Z. P.; Chen, J. K.; Miao, J.; Xu, X. G.; Zhao, J. H.; Jiang, Y.

2018-02-01

We have investigated the topological Hall effect (THE) in MnGa/Pt and MnGa/Ta bilayers induced by the inter- facial Dzyaloshinskii-Moriya interaction (DMI). By varying the growth parameters, we can modulate the domain wall energy, and the largest THE signals are found when the domain wall energy is the smallest. The large topological portion of the Hall signal from the total Hall signal has been extracted in the whole temperature range from 5 to 300 K. These results open up the exploration of the DMI induced magnetic behavior based on the bulk perpendicular magnetic anisotropy materials for fundamental physics and magnetic storage technologies.

Hall effects on peristaltic flow of couple stress fluid in a vertical asymmetric channel

NASA Astrophysics Data System (ADS)

Maninaga Kumar, P.; Kavitha, A.; Saravana, R.

2017-11-01

The influence of Hall effect on peristaltic transport of a couple stress fluid in a vertical asymmetric channel is examined. The problem is solved under the assumptions of low Reynolds number and long wavelength. The velocity, temperature and concentration are obtained by using analytical solutions. Effect of Hall parameter, couple stress fluid parameter, Froude number, Hartmann number and the phase difference on the pumping characteristics, temperature and concentration are discussed graphically.

Resonant spin Hall effect in two dimensional electron gas

NASA Astrophysics Data System (ADS)

Shen, Shun-Qing

2005-03-01

Remarkable phenomena have been observed in 2DEG over last two decades, most notably, the discovery of integer and fractional quantum Hall effect. The study of spin transport provides a good opportunity to explore spin physics in two-dimensional electron gas (2DEG) with spin-orbit coupling and other interaction. It is already known that the spin-orbit coupling leads to a zero-field spin splitting, and competes with the Zeeman spin splitting if the system is subjected to a magnetic field perpendicular to the plane of 2DEG. The result can be detected as beating of the Shubnikov-de Haas oscillation. Very recently the speaker and his collaborators studied transport properties of a two-dimensional electron system with Rashba spin-orbit coupling in a perpendicular magnetic field. The spin-orbit coupling competes with the Zeeman splitting to generate additional degeneracies between different Landau levels at certain magnetic fields. It is predicted theoretically that this degeneracy, if occurring at the Fermi level, gives rise to a resonant spin Hall conductance, whose height is divergent as 1/T and whose weight is divergent as -lnT at low temperatures. The charge Hall conductance changes by 2e^2/h instead of e^2/h as the magnetic field changes through the resonant point. The speaker will address the resonance condition, symmetries in the spin-orbit coupling, the singularity of magnetic susceptibility, nonlinear electric field effect, the edge effect and the disorder effect due to impurities. This work was supported by the Research Grants Council of Hong Kong under Grant No.: HKU 7088/01P. *S. Q. Shen, M. Ma, X. C. Xie, and F. C. Zhang, Phys. Rev. Lett. 92, 256603 (2004) *S. Q. Shen, Y. J. Bao, M. Ma, X. C. Xie, and F. C. Zhang, cond-mat/0410169

Topological phase transitions and quantum Hall effect in the graphene family

NASA Astrophysics Data System (ADS)

Ledwith, P.; Kort-Kamp, W. J. M.; Dalvit, D. A. R.

2018-04-01

Monolayer staggered materials of the graphene family present intrinsic spin-orbit coupling and can be driven through several topological phase transitions using external circularly polarized lasers and static electric or magnetic fields. We show how topological features arising from photoinduced phase transitions and the magnetic-field-induced quantum Hall effect coexist in these materials and simultaneously impact their Hall conductivity through their corresponding charge Chern numbers. We also show that the spectral response of the longitudinal conductivity contains signatures of the various phase-transition boundaries, that the transverse conductivity encodes information about the topology of the band structure, and that both present resonant peaks which can be unequivocally associated with one of the four inequivalent Dirac cones present in these materials. This complex optoelectronic response can be probed with straightforward Faraday rotation experiments, allowing the study of the crossroads between quantum Hall physics, spintronics, and valleytronics.

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

Chiral topological superconductor and half-integer conductance plateau from quantum anomalous Hall plateau transition

DOE PAGES

Wang, Jing; Zhou, Quan; Lian, Biao; ...

2015-08-31

Here, we propose to realize a two-dimensional chiral topological superconducting (TSC) state from the quantum anomalous Hall plateau transition in a magnetic topological insulator thin film through the proximity effect to a conventional s -wave superconductor. This state has a full pairing gap in the bulk and a single chiral Majorana mode at the edge. The optimal condition for realizing such chiral TSC is to have inequivalent superconducting pairing amplitudes on top and bottom surfaces of the doped magnetic topological insulator. We further propose several transport experiments to detect the chiral TSC. One unique signature is that the conductance willmore » be quantized into a half-integer plateau at the coercive field in this hybrid system. In particular, with the point contact formed by a superconducting junction, the conductance oscillates between e 2 /2h and e2 /h with the frequency determined by the voltage across the junction. We close by discussing the feasibility of these experimental proposals.« less

Chiral topological superconductor and half-integer conductance plateau from quantum anomalous Hall plateau transition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jing; Zhou, Quan; Lian, Biao

Here, we propose to realize a two-dimensional chiral topological superconducting (TSC) state from the quantum anomalous Hall plateau transition in a magnetic topological insulator thin film through the proximity effect to a conventional s -wave superconductor. This state has a full pairing gap in the bulk and a single chiral Majorana mode at the edge. The optimal condition for realizing such chiral TSC is to have inequivalent superconducting pairing amplitudes on top and bottom surfaces of the doped magnetic topological insulator. We further propose several transport experiments to detect the chiral TSC. One unique signature is that the conductance willmore » be quantized into a half-integer plateau at the coercive field in this hybrid system. In particular, with the point contact formed by a superconducting junction, the conductance oscillates between e 2 /2h and e2 /h with the frequency determined by the voltage across the junction. We close by discussing the feasibility of these experimental proposals.« less

Reversed Hall effect and plasma conductivity in the presence of charged impurities

NASA Astrophysics Data System (ADS)

Yaroshenko, V. V.; Lühr, H.

2018-01-01

The Hall conductivity of magnetized plasma can be strongly suppressed by the contribution of negatively charged particulates (referred further as "dust"). Once the charge density accumulated by the dust exceeds a certain threshold, the Hall component becomes negative, providing a reversal in the Hall current. Such an effect is unique for dust-loaded plasmas, and it can hardly be achieved in electronegative plasmas. Further growth of the dust density leads to an increase in both the absolute value of the Hall and Pedersen conductivities, while the field-aligned component is decreased. These modifications enhance the role of transverse electric currents and reduce the anisotropy of a magnetized plasma when loaded with charged impurities. The findings provide an important basis for studying the generation of electric currents and transport phenomena in magnetized plasma systems containing small charged particulates. They can be relevant for a wide range of applications from naturally occurring space plasmas in planetary magnetospheres and astrophysical objects to laboratory dusty plasmas (Magnetized Dusty Plasma Experiment) and to technological and fusion plasmas.

Quantized kernel least mean square algorithm.

PubMed

Chen, Badong; Zhao, Songlin; Zhu, Pingping; Príncipe, José C

2012-01-01

In this paper, we propose a quantization approach, as an alternative of sparsification, to curb the growth of the radial basis function structure in kernel adaptive filtering. The basic idea behind this method is to quantize and hence compress the input (or feature) space. Different from sparsification, the new approach uses the "redundant" data to update the coefficient of the closest center. In particular, a quantized kernel least mean square (QKLMS) algorithm is developed, which is based on a simple online vector quantization method. The analytical study of the mean square convergence has been carried out. The energy conservation relation for QKLMS is established, and on this basis we arrive at a sufficient condition for mean square convergence, and a lower and upper bound on the theoretical value of the steady-state excess mean square error. Static function estimation and short-term chaotic time-series prediction examples are presented to demonstrate the excellent performance.

Effects of Hall current and electrical resistivity on the stability of gravitating anisotropic quantum plasma

NASA Astrophysics Data System (ADS)

Bhakta, S.; Prajapati, R. P.

2018-02-01

The effects of Hall current and finite electrical resistivity are studied on the stability of uniformly rotating and self-gravitating anisotropic quantum plasma. The generalized Ohm's law modified by Hall current and electrical resistivity is used along with the quantum magnetohydrodynamic fluid equations. The general dispersion relation is derived using normal mode analysis and discussed in the parallel and perpendicular propagations. In the parallel propagation, the Jeans instability criterion, expression of critical Jeans wavenumber, and Jeans length are found to be independent of non-ideal effects and uniform rotation but in perpendicular propagation only rotation affects the Jeans instability criterion. The unstable gravitating mode modified by Bohm potential and the stable Alfven mode modified by non-ideal effects are obtained separately. The criterion of firehose instability remains unaffected due to the presence of non-ideal effects. In the perpendicular propagation, finite electrical resistivity and quantum pressure anisotropy modify the dispersion relation, whereas no effect of Hall current was observed in the dispersion characteristics. The Hall current, finite electrical resistivity, rotation, and quantum corrections stabilize the growth rate. The stability of the dynamical system is analyzed using the Routh-Hurwitz criterion.

Quantization of Non-Lagrangian Systems

NASA Astrophysics Data System (ADS)

Kochan, Denis

A novel method for quantization of non-Lagrangian (open) systems is proposed. It is argued that the essential object, which provides both classical and quantum evolution, is a certain canonical two-form defined in extended velocity space. In this setting classical dynamics is recovered from the stringy-type variational principle, which employs umbilical surfaces instead of histories of the system. Quantization is then accomplished in accordance with the introduced variational principle. The path integral for the transition probability amplitude (propagator) is rearranged to a surface functional integral. In the standard case of closed (Lagrangian) systems the presented method reduces to the standard Feynman's approach. The inverse problem of the calculus of variation, the problem of quantization ambiguity and the quantum mechanics in the presence of friction are analyzed in detail.

Quantum Hall effect in epitaxial graphene with permanent magnets.

PubMed

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.

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.

Fractionally charged skyrmions in fractional quantum Hall effect

DOE PAGES

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

Anomalous Hall effect scaling in ferromagnetic thin films

NASA Astrophysics Data System (ADS)

Grigoryan, Vahram L.; Xiao, Jiang; Wang, Xuhui; Xia, Ke

2017-10-01

We propose a scaling law for anomalous Hall effect in ferromagnetic thin films. Our approach distinguishes multiple scattering sources, namely, bulk impurity, phonon for Hall resistivity, and most importantly the rough surface contribution to longitudinal resistivity. In stark contrast to earlier laws that rely on temperature- and thickness-dependent fitting coefficients, this scaling law fits the recent experimental data excellently with constant parameters that are independent of temperature and film thickness, strongly indicating that this law captures the underlying physical processes. Based on a few data points, this scaling law can even fit all experimental data in full temperature and thickness range. We apply this law to interpret the experimental data for Fe, Co, and Ni and conclude that (i) the phonon-induced skew scattering is unimportant as expected; (ii) contribution from the impurity-induced skew scattering is negative; (iii) the intrinsic (extrinsic) mechanism dominates in Fe (Co), and both the extrinsic and intrinsic contributions are important in Ni.

Fractionally charged skyrmions in fractional quantum Hall effect

PubMed Central

Balram, Ajit C.; Wurstbauer, U.; Wójs, A.; Pinczuk, A.; Jain, J. K.

2015-01-01

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. PMID:26608906

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.

Quasiparticle-mediated spin Hall effect in a superconductor.

PubMed

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.

Topological phase transitions and quantum Hall effect in the graphene family

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ledwith, Patrick John; Kort-Kamp, Wilton Junior de Melo; Dalvit, Diego Alejandro Roberto

Monolayer staggered materials of the graphene family present intrinsic spin-orbit coupling and can be driven through several topological phase transitions using external circularly polarized lasers and static electric or magnetic fields. We show how topological features arising from photoinduced phase transitions and the magnetic-field-induced quantum Hall effect coexist in these materials and simultaneously impact their Hall conductivity through their corresponding charge Chern numbers. We also show that the spectral response of the longitudinal conductivity contains signatures of the various phase-transition boundaries, that the transverse conductivity encodes information about the topology of the band structure, and that both present resonant peaksmore » which can be unequivocally associated with one of the four inequivalent Dirac cones present in these materials. As a result, this complex optoelectronic response can be probed with straightforward Faraday rotation experiments, allowing the study of the crossroads between quantum Hall physics, spintronics, and valleytronics.« less

Engineering the quantum anomalous Hall effect in graphene with uniaxial strains

DOE Office of Scientific and Technical Information (OSTI.GOV)

Diniz, G. S., E-mail: ginetom@gmail.com; Guassi, M. R.; Qu, F.

2013-12-28

We theoretically investigate the manipulation of the quantum anomalous Hall effect (QAHE) in graphene by means of the uniaxial strain. The values of Chern number and Hall conductance demonstrate that the strained graphene in presence of Rashba spin-orbit coupling and exchange field, for vanishing intrinsic spin-orbit coupling, possesses non-trivial topological phase, which is robust against the direction and modulus of the strain. Besides, we also find that the interplay between Rashba and intrinsic spin-orbit couplings results in a topological phase transition in the strained graphene. Remarkably, as the strain strength is increased beyond approximately 7%, the critical parameters of themore » exchange field for triggering the quantum anomalous Hall phase transition show distinct behaviors—decrease (increase) for strains along zigzag (armchair) direction. Our findings open up a new platform for manipulation of the QAHE by an experimentally accessible strain deformation of the graphene structure, with promising application on novel quantum electronic devices with high efficiency.« less

Topological phase transitions and quantum Hall effect in the graphene family

DOE PAGES

Ledwith, Patrick John; Kort-Kamp, Wilton Junior de Melo; Dalvit, Diego Alejandro Roberto

2018-04-15

Monolayer staggered materials of the graphene family present intrinsic spin-orbit coupling and can be driven through several topological phase transitions using external circularly polarized lasers and static electric or magnetic fields. We show how topological features arising from photoinduced phase transitions and the magnetic-field-induced quantum Hall effect coexist in these materials and simultaneously impact their Hall conductivity through their corresponding charge Chern numbers. We also show that the spectral response of the longitudinal conductivity contains signatures of the various phase-transition boundaries, that the transverse conductivity encodes information about the topology of the band structure, and that both present resonant peaksmore » which can be unequivocally associated with one of the four inequivalent Dirac cones present in these materials. As a result, this complex optoelectronic response can be probed with straightforward Faraday rotation experiments, allowing the study of the crossroads between quantum Hall physics, spintronics, and valleytronics.« less

Robust fault tolerant control based on sliding mode method for uncertain linear systems with quantization.

PubMed

Hao, Li-Ying; Yang, Guang-Hong

2013-09-01

This paper is concerned with the problem of robust fault-tolerant compensation control problem for uncertain linear systems subject to both state and input signal quantization. By incorporating novel matrix full-rank factorization technique with sliding surface design successfully, the total failure of certain actuators can be coped with, under a special actuator redundancy assumption. In order to compensate for quantization errors, an adjustment range of quantization sensitivity for a dynamic uniform quantizer is given through the flexible choices of design parameters. Comparing with the existing results, the derived inequality condition leads to the fault tolerance ability stronger and much wider scope of applicability. With a static adjustment policy of quantization sensitivity, an adaptive sliding mode controller is then designed to maintain the sliding mode, where the gain of the nonlinear unit vector term is updated automatically to compensate for the effects of actuator faults, quantization errors, exogenous disturbances and parameter uncertainties without the need for a fault detection and isolation (FDI) mechanism. Finally, the effectiveness of the proposed design method is illustrated via a model of a rocket fairing structural-acoustic. Copyright © 2013 ISA. Published by Elsevier Ltd. All rights reserved.

Pseudo-Kähler Quantization on Flag Manifolds

NASA Astrophysics Data System (ADS)

Karabegov, Alexander V.

A unified approach to geometric, symbol and deformation quantizations on a generalized flag manifold endowed with an invariant pseudo-Kähler structure is proposed. In particular cases we arrive at Berezin's quantization via covariant and contravariant symbols.

Anomalous Hall resistance in bilayer quantum Hall systems

NASA Astrophysics Data System (ADS)

Ezawa, Z. F.; Suzuki, S.; Tsitsishvili, G.

2007-07-01

We present a microscopic theory of the Hall current in the bilayer quantum Hall system on the basis of noncommutative geometry. By analyzing the Heisenberg equation of motion and the continuity equation of charge, we demonstrate the emergence of the phase current in a system where the interlayer phase coherence develops spontaneously. The phase current arranges itself to minimize the total energy of the system, as it induces certain anomalous behaviors in the Hall current in the counterflow geometry and also in the drag experiment. They explain the recent experimental data for anomalous Hall resistances due to Kellogg [Phys. Rev. Lett. 88, 126804 (2002); 93, 036801 (2004)] and Tutuc [Phys. Rev. Lett. 93, 036802 (2004)] at ν=1 .

5. View of Community Hall, first floor interior, entrance hall ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

5. View of Community Hall, first floor interior, entrance hall on east side of building, facing southeast. Ticket booth center foreground, stairway to auditorium right foreground. - Community Hall, Rainier Avenue & View Drive, Port Gamble, Kitsap County, WA

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.

Quantum Hall effect in ac driven graphene: From the half-integer to the integer case

NASA Astrophysics Data System (ADS)

Ding, Kai-He; Lim, Lih-King; Su, Gang; Weng, Zheng-Yu

2018-01-01

We theoretically study the quantum Hall effect (QHE) in graphene with an ac electric field. Based on the tight-binding model, the structure of the half-integer Hall plateaus at σxy=±(n +1 /2 ) 4 e2/h (n is an integer) gets qualitatively changed with the addition of new integer Hall plateaus at σxy=±n (4 e2/h ) starting from the edges of the band center regime towards the band center with an increasing ac field. Beyond a critical field strength, a Hall plateau with σxy=0 can be realized at the band center, hence fully restoring a conventional integer QHE with particle-hole symmetry. Within a low-energy Hamiltonian for Dirac cones merging, we show a very good agreement with the tight-binding calculations for the Hall plateau transitions. We also obtain the band structure for driven graphene ribbons to provide a further understanding on the appearance of the new Hall plateaus, showing a trivial insulator behavior for the σxy=0 state. In the presence of disorder, we numerically study the disorder-induced destruction of the quantum Hall states in a finite driven sample and find that qualitative features known in the undriven disordered case are maintained.

Quantization of Electromagnetic Fields in Cavities

NASA Technical Reports Server (NTRS)

Kakazu, Kiyotaka; Oshiro, Kazunori

1996-01-01

A quantization procedure for the electromagnetic field in a rectangular cavity with perfect conductor walls is presented, where a decomposition formula of the field plays an essential role. All vector mode functions are obtained by using the decomposition. After expanding the field in terms of the vector mode functions, we get the quantized electromagnetic Hamiltonian.

Simultaneous fault detection and control design for switched systems with two quantized signals.

PubMed

Li, Jian; Park, Ju H; Ye, Dan

2017-01-01

The problem of simultaneous fault detection and control design for switched systems with two quantized signals is presented in this paper. Dynamic quantizers are employed, respectively, before the output is passed to fault detector, and before the control input is transmitted to the switched system. Taking the quantized errors into account, the robust performance for this kind of system is given. Furthermore, sufficient conditions for the existence of fault detector/controller are presented in the framework of linear matrix inequalities, and fault detector/controller gains and the supremum of quantizer range are derived by a convex optimized method. Finally, two illustrative examples demonstrate the effectiveness of the proposed method. Copyright © 2016 ISA. Published by Elsevier Ltd. All rights reserved.

Quantization of gauge fields, graph polynomials and graph homology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kreimer, Dirk, E-mail: kreimer@physik.hu-berlin.de; Sars, Matthias; Suijlekom, Walter D. van

2013-09-15

We review quantization of gauge fields using algebraic properties of 3-regular graphs. We derive the Feynman integrand at n loops for a non-abelian gauge theory quantized in a covariant gauge from scalar integrands for connected 3-regular graphs, obtained from the two Symanzik polynomials. The transition to the full gauge theory amplitude is obtained by the use of a third, new, graph polynomial, the corolla polynomial. This implies effectively a covariant quantization without ghosts, where all the relevant signs of the ghost sector are incorporated in a double complex furnished by the corolla polynomial–we call it cycle homology–and by graph homology.more » -- Highlights: •We derive gauge theory Feynman from scalar field theory with 3-valent vertices. •We clarify the role of graph homology and cycle homology. •We use parametric renormalization and the new corolla polynomial.« less

Spin-Hall effect and emergent antiferromagnetic phase transition in n-Si

NASA Astrophysics Data System (ADS)

Lou, Paul C.; Kumar, Sandeep

2018-04-01

Spin current experiences minimal dephasing and scattering in Si due to small spin-orbit coupling and spin-lattice interactions is the primary source of spin relaxation. We hypothesize that if the specimen dimension is of the same order as the spin diffusion length then spin polarization will lead to non-equilibrium spin accumulation and emergent phase transition. In n-Si, spin diffusion length has been reported up to 6 μm. The spin accumulation in Si will modify the thermal transport behavior of Si, which can be detected with thermal characterization. In this study, we report observation of spin-Hall effect and emergent antiferromagnetic phase transition behavior using magneto-electro-thermal transport characterization. The freestanding Pd (1 nm)/Ni80Fe20 (75 nm)/MgO (1 nm)/n-Si (2 μm) thin film specimen exhibits a magnetic field dependent thermal transport and spin-Hall magnetoresistance behavior attributed to Rashba effect. An emergent phase transition is discovered using self-heating 3ω method, which shows a diverging behavior at 270 K as a function of temperature similar to a second order phase transition. We propose that spin-Hall effect leads to the spin accumulation and resulting emergent antiferromagnetic phase transition. We propose that the length scale for Rashba effect can be equal to the spin diffusion length and two-dimensional electron gas is not essential for it. The emergent antiferromagnetic phase transition is attributed to the site inversion asymmetry in diamond cubic Si lattice.

Noise fluctuations and drive dependence of the skyrmion Hall effect in disordered systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reichhardt, Charles; Olson Reichhardt, Cynthia Jane

Using a particle-based simulation model, we show that quenched disorder creates a drive-dependent skyrmion Hall effect as measured by the change in the ratiomore » $$R={V}_{\\perp }/{V}_{| | }$$ of the skyrmion velocity perpendicular (V ⊥) and parallel ($${V}_{| | }$$) to an external drive. R is zero at depinning and increases linearly with increasing drive, in agreement with recent experimental observations. At sufficiently high drives where the skyrmions enter a free flow regime, R saturates to the disorder-free limit. In addition, this behavior is robust for a wide range of disorder strengths and intrinsic Hall angle values, and occurs whenever plastic flow is present. For systems with small intrinsic Hall angles, we find that the Hall angle increases linearly with external drive, as also observed in experiment. In the weak pinning regime where the skyrmion lattice depins elastically, R is nonlinear and the net direction of the skyrmion lattice motion can rotate as a function of external drive. We show that the changes in the skyrmion Hall effect correlate with changes in the power spectrum of the skyrmion velocity noise fluctuations. The plastic flow regime is associated with $1/f$ noise, while in the regime in which R has saturated, the noise is white with a weak narrow band signal, and the noise power drops by several orders of magnitude. Finally, at low drives, the velocity noise in the perpendicular and parallel directions is of the same order of magnitude, while at intermediate drives the perpendicular noise fluctuations are much larger.« less

Noise fluctuations and drive dependence of the skyrmion Hall effect in disordered systems

DOE PAGES

Reichhardt, Charles; Olson Reichhardt, Cynthia Jane

2016-09-29

Using a particle-based simulation model, we show that quenched disorder creates a drive-dependent skyrmion Hall effect as measured by the change in the ratiomore » $$R={V}_{\\perp }/{V}_{| | }$$ of the skyrmion velocity perpendicular (V ⊥) and parallel ($${V}_{| | }$$) to an external drive. R is zero at depinning and increases linearly with increasing drive, in agreement with recent experimental observations. At sufficiently high drives where the skyrmions enter a free flow regime, R saturates to the disorder-free limit. In addition, this behavior is robust for a wide range of disorder strengths and intrinsic Hall angle values, and occurs whenever plastic flow is present. For systems with small intrinsic Hall angles, we find that the Hall angle increases linearly with external drive, as also observed in experiment. In the weak pinning regime where the skyrmion lattice depins elastically, R is nonlinear and the net direction of the skyrmion lattice motion can rotate as a function of external drive. We show that the changes in the skyrmion Hall effect correlate with changes in the power spectrum of the skyrmion velocity noise fluctuations. The plastic flow regime is associated with $1/f$ noise, while in the regime in which R has saturated, the noise is white with a weak narrow band signal, and the noise power drops by several orders of magnitude. Finally, at low drives, the velocity noise in the perpendicular and parallel directions is of the same order of magnitude, while at intermediate drives the perpendicular noise fluctuations are much larger.« less

Covariant Conservation Laws and the Spin Hall Effect in Dirac-Rashba Systems

NASA Astrophysics Data System (ADS)

Milletarı, Mirco; Offidani, Manuel; Ferreira, Aires; Raimondi, Roberto

2017-12-01

We present a theoretical analysis of two-dimensional Dirac-Rashba systems in the presence of disorder and external perturbations. We unveil a set of exact symmetry relations (Ward identities) that impose strong constraints on the spin dynamics of Dirac fermions subject to proximity-induced interactions. This allows us to demonstrate that an arbitrary dilute concentration of scalar impurities results in the total suppression of nonequilibrium spin Hall currents when only Rashba spin-orbit coupling is present. Remarkably, a finite spin Hall conductivity is restored when the minimal Dirac-Rashba model is supplemented with a spin-valley interaction. The Ward identities provide a systematic way to predict the emergence of the spin Hall effect in a wider class of Dirac-Rashba systems of experimental relevance and represent an important benchmark for testing the validity of numerical methodologies.

Pt thickness dependence of spin Hall effect switching of in-plane magnetized CoFeB free layers studied by differential planar Hall effect

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.

Valley-chiral quantum Hall state in graphene superlattice structure

NASA Astrophysics Data System (ADS)

Tian, H. Y.; Tao, W. W.; Wang, J.; Cui, Y. H.; Xu, N.; Huang, B. B.; Luo, G. X.; Hao, Y. H.

2016-05-01

We theoretically investigate the quantum Hall effect in a graphene superlattice (GS) system, in which the two valleys of graphene are coupled together. In the presence of a perpendicular magnetic field, an ordinary quantum Hall effect is found with the sequence σxy=ν e^2/h(ν=0,+/-1,+/-2,\\cdots) . At the zeroth Hall platform, a valley-chiral Hall state stemming from the single K or K' valley is found and it is localized only on one sample boundary contributing to the longitudinal conductance but not to the Hall conductivity. Our findings may shed light on the graphene-based valleytronics applications.

Chiral Majorana fermion modes in a quantum anomalous Hall insulator-superconductor structure.

PubMed

He, Qing Lin; Pan, Lei; Stern, Alexander L; Burks, Edward C; Che, Xiaoyu; Yin, Gen; Wang, Jing; Lian, Biao; Zhou, Quan; Choi, Eun Sang; Murata, Koichi; Kou, Xufeng; Chen, Zhijie; Nie, Tianxiao; Shao, Qiming; Fan, Yabin; Zhang, Shou-Cheng; Liu, Kai; Xia, Jing; Wang, Kang L

2017-07-21

Majorana fermion is a hypothetical particle that is its own antiparticle. We report transport measurements that suggest the existence of one-dimensional chiral Majorana fermion modes in the hybrid system of a quantum anomalous Hall insulator thin film coupled with a superconductor. As the external magnetic field is swept, half-integer quantized conductance plateaus are observed at the locations of magnetization reversals, giving a distinct signature of the Majorana fermion modes. This transport signature is reproducible over many magnetic field sweeps and appears at different temperatures. This finding may open up an avenue to control Majorana fermions for implementing robust topological quantum computing. Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

What do you measure when you measure the Hall effect?

NASA Astrophysics Data System (ADS)

Koon, D. W.; Knickerbocker, C. J.

1993-02-01

A formalism for calculating the sensitivity of Hall measurements to local inhomogeneities of the sample material or the magnetic field is developed. This Hall weighting function g(x,y) is calculated for various placements of current and voltage probes on square and circular laminar samples. Unlike the resistivity weighting function, it is nonnegative throughout the entire sample, provided all probes lie at the edge of the sample. Singularities arise in the Hall weighting function near the current and voltage probes except in the case where these probes are located at the corners of a square. Implications of the results for cross, clover, and bridge samples, and the implications of our results for metal-insulator transition and quantum Hall studies are discussed.

Image Coding Based on Address Vector Quantization.

NASA Astrophysics Data System (ADS)

Feng, Yushu

Image coding is finding increased application in teleconferencing, archiving, and remote sensing. This thesis investigates the potential of Vector Quantization (VQ), a relatively new source coding technique, for compression of monochromatic and color images. Extensions of the Vector Quantization technique to the Address Vector Quantization method have been investigated. In Vector Quantization, the image data to be encoded are first processed to yield a set of vectors. A codeword from the codebook which best matches the input image vector is then selected. Compression is achieved by replacing the image vector with the index of the code-word which produced the best match, the index is sent to the channel. Reconstruction of the image is done by using a table lookup technique, where the label is simply used as an address for a table containing the representative vectors. A code-book of representative vectors (codewords) is generated using an iterative clustering algorithm such as K-means, or the generalized Lloyd algorithm. A review of different Vector Quantization techniques are given in chapter 1. Chapter 2 gives an overview of codebook design methods including the Kohonen neural network to design codebook. During the encoding process, the correlation of the address is considered and Address Vector Quantization is developed for color image and monochrome image coding. Address VQ which includes static and dynamic processes is introduced in chapter 3. In order to overcome the problems in Hierarchical VQ, Multi-layer Address Vector Quantization is proposed in chapter 4. This approach gives the same performance as that of the normal VQ scheme but the bit rate is about 1/2 to 1/3 as that of the normal VQ method. In chapter 5, a Dynamic Finite State VQ based on a probability transition matrix to select the best subcodebook to encode the image is developed. In chapter 6, a new adaptive vector quantization scheme, suitable for color video coding, called "A Self -Organizing

Quantization of simple parametrized systems

NASA Astrophysics Data System (ADS)

Ruffini, G.

2005-11-01

I study the canonical formulation and quantization of some simple parametrized systems, including the non-relativistic parametrized particle and the relativistic parametrized particle. Using Dirac's formalism I construct for each case the classical reduced phase space and study the dependence on the gauge fixing used. Two separate features of these systems can make this construction difficult: the actions are not invariant at the boundaries, and the constraints may have disconnected solution spaces. The relativistic particle is affected by both, while the non-relativistic particle displays only by the first. Analyzing the role of canonical transformations in the reduced phase space, I show that a change of gauge fixing is equivalent to a canonical transformation. In the relativistic case, quantization of one branch of the constraint at the time is applied and I analyze the electromagenetic backgrounds in which it is possible to quantize simultaneously both branches and still obtain a covariant unitary quantum theory. To preserve unitarity and space-time covariance, second quantization is needed unless there is no electric field. I motivate a definition of the inner product in all these cases and derive the Klein-Gordon inner product for the relativistic case. I construct phase space path integral representations for amplitudes for the BFV and the Faddeev path integrals, from which the path integrals in coordinate space (Faddeev-Popov and geometric path integrals) are derived.

Gravitational surface Hamiltonian and entropy quantization

NASA Astrophysics Data System (ADS)

Bakshi, Ashish; Majhi, Bibhas Ranjan; Samanta, Saurav

2017-02-01

The surface Hamiltonian corresponding to the surface part of a gravitational action has xp structure where p is conjugate momentum of x. Moreover, it leads to TS on the horizon of a black hole. Here T and S are temperature and entropy of the horizon. Imposing the hermiticity condition we quantize this Hamiltonian. This leads to an equidistant spectrum of its eigenvalues. Using this we show that the entropy of the horizon is quantized. This analysis holds for any order of Lanczos-Lovelock gravity. For general relativity, the area spectrum is consistent with Bekenstein's observation. This provides a more robust confirmation of this earlier result as the calculation is based on the direct quantization of the Hamiltonian in the sense of usual quantum mechanics.

Safety halls--an evaluation.

PubMed

Nyberg, Anders; Gregersen, Nils Petter; Nolén, Sixten; Engström, Inger

2005-01-01

In most countries, drivers licensing systems usually include teaching some aspects of using safety equipment (e.g., airbags and seat belts). However, there is now evidence worldwide that such education is inadequate, as indicated by, for example, the overrepresentation of young drivers who do not use seat belts. A randomized controlled study was conducted in Sweden to evaluate the effects of visiting a facility known as a "safety hall" in combination with the mandatory skid training. The results were assessed to determine the effects of the knowledge and attitudes of learner drivers in the following subjects: airbags, securing loads, seat belts, sitting posture, speed, and tires. An experimental group and a control group comprising 658 and 668 learners, respectively, answered identical questionnaires on three different occasions (pretest, posttest 1, and posttest 2). The results show that, for most of the topics considered, knowledge and attitudes in both groups were better at posttest 2 than at the pretest, and in general, the best knowledge and attitudes were found in the experimental group. The combined safety/skid training seems to have had the greatest effect on seat belts and loads. The findings also indicate that the safety halls can be further improved to achieve an even better effect. The use of safety halls has improved the knowledge and attitudes of learner drivers concerning several important areas related to traffic safety. Since knowledge and attitudes are important predictors of behavior, implementing safety halls can be expected to lead to improvements, especially regarding the use of safety belts and securing loads.

Performance of a Cylindrical Hall-Effect Thruster Using Permanent Magnets

NASA Technical Reports Server (NTRS)

Polzin, Kurt A.; Raitses, Y.; Merino, E.; Fisch, N. J.

2009-01-01

While annular Hall thrusters can operate at high efficiency at kW power levels, it is difficult to construct one that operates over a broad envelope from 1 kW down to 100 W while maintaining an efficiency of 45-55%. Scaling to low power while holding the main dimensionless parameters constant requires a decrease in the thruster channel size and an increase in the magnetic field strength. Increasing the magnetic field becomes technically challenging since the field can saturate the miniaturized inner components of the magnetic circuit and scaling down the magnetic circuit leaves very little room for magnetic pole pieces and heat shields. In addition, the central magnetic pole piece defining the interior wall of the annular channel can experience excessive heat loads in a miniaturized Hall thruster, with the temperature eventually exceeding the Curie temperature of the material and in extreme circumstances leading to accelerated erosion of the channel wall. An alternative approach is to employ a cylindrical Hall thruster (CHT) geometry. Laboratory model CHTs have operated at power levels ranging from 50 W up to 1 kW. These thrusters exhibit performance characteristics that are comparable to conventional, annular Hall thrusters of similar size. Compared to the annular Hall thruster, the CHTs insulator surface area to discharge chamber volume ratio is lower. Consequently, there is the potential for reduced wall losses in the channel of a CHT, and any reduction in wall losses should translate into lower channel heating rates and reduced erosion, making the CHT geometry promising for low-power applications. This potential for high performance in the low-power regime has served as the impetus for research and development efforts aimed at understanding and improving CHT performance. Recently, a 2.6 cm channel diameter permanent magnet CHT (shown in Fig. 1) was tested. This thruster has the promise of reduced power consumption over previous CHT iterations that employed

Spin-orbit torque induced magnetic vortex polarity reversal utilizing spin-Hall effect

NASA Astrophysics Data System (ADS)

Li, Cheng; Cai, Li; Liu, Baojun; Yang, Xiaokuo; Cui, Huanqing; Wang, Sen; Wei, Bo

2018-05-01

We propose an effective magnetic vortex polarity reversal scheme that makes use of spin-orbit torque introduced by spin-Hall effect in heavy-metal/ferromagnet multilayers structure, which can result in subnanosecond polarity reversal without endangering the structural stability. Micromagnetic simulations are performed to investigate the spin-Hall effect driven dynamics evolution of magnetic vortex. The mechanism of magnetic vortex polarity reversal is uncovered by a quantitative analysis of exchange energy density, magnetostatic energy density, and their total energy density. The simulation results indicate that the magnetic vortex polarity is reversed through the nucleation-annihilation process of topological vortex-antivortex pair. This scheme is an attractive option for ultra-fast magnetic vortex polarity reversal, which can be used as the guidelines for the choice of polarity reversal scheme in vortex-based random access memory.

Spin injection and detection via the anomalous spin Hall effect of a ferromagnetic metal

NASA Astrophysics Data System (ADS)

Das, K. S.; Schoemaker, W. Y.; van Wees, B. J.; Vera-Marun, I. J.

2017-12-01

We report a spin injection and detection mechanism via the anomalous Hall effect in a ferromagnetic metal. The anomalous spin Hall effect (ASHE) refers to the transverse spin current generated within the ferromagnet. We utilize the ASHE and its reciprocal effect to electrically inject and detect magnons in a magnetic insulator (yttrium iron garnet) in a nonlocal geometry. Our experiments reveal that permalloy has a comparable spin injection and detection efficiency to that of platinum, owing to the ASHE. We also demonstrate the tunability of the ASHE via the orientation of the permalloy magnetization, thus creating possibilities for spintronic applications.

Polymer-Fourier quantization of the scalar field revisited

NASA Astrophysics Data System (ADS)

Garcia-Chung, Angel; Vergara, J. David

2016-10-01

The polymer quantization of the Fourier modes of the real scalar field is studied within algebraic scheme. We replace the positive linear functional of the standard Poincaré invariant quantization by a singular one. This singular positive linear functional is constructed as mimicking the singular limit of the complex structure of the Poincaré invariant Fock quantization. The resulting symmetry group of such polymer quantization is the subgroup SDiff(ℝ4) which is a subgroup of Diff(ℝ4) formed by spatial volume preserving diffeomorphisms. In consequence, this yields an entirely different irreducible representation of the canonical commutation relations, nonunitary equivalent to the standard Fock representation. We also compared the Poincaré invariant Fock vacuum with the polymer Fourier vacuum.

Video data compression using artificial neural network differential vector quantization

NASA Technical Reports Server (NTRS)

Krishnamurthy, Ashok K.; Bibyk, Steven B.; Ahalt, Stanley C.

1991-01-01

An artificial neural network vector quantizer is developed for use in data compression applications such as Digital Video. Differential Vector Quantization is used to preserve edge features, and a new adaptive algorithm, known as Frequency-Sensitive Competitive Learning, is used to develop the vector quantizer codebook. To develop real time performance, a custom Very Large Scale Integration Application Specific Integrated Circuit (VLSI ASIC) is being developed to realize the associative memory functions needed in the vector quantization algorithm. By using vector quantization, the need for Huffman coding can be eliminated, resulting in superior performance against channel bit errors than methods that use variable length codes.

Instabilities caused by floating-point arithmetic quantization.

NASA Technical Reports Server (NTRS)

Phillips, C. L.

1972-01-01

It is shown that an otherwise stable digital control system can be made unstable by signal quantization when the controller operates on floating-point arithmetic. Sufficient conditions of instability are determined, and an example of loss of stability is treated when only one quantizer is operated.

Effect of magnetic quantization on ion acoustic waves ultra-relativistic dense plasma

NASA Astrophysics Data System (ADS)

Javed, Asif; Rasheed, A.; Jamil, M.; Siddique, M.; Tsintsadze, N. L.

2017-11-01

In this paper, we have studied the influence of magnetic quantization of orbital motion of the electrons on the profile of linear and nonlinear ion-acoustic waves, which are propagating in the ultra-relativistic dense magneto quantum plasmas. We have employed both Thomas Fermi and Quantum Magneto Hydrodynamic models (along with the Poisson equation) of quantum plasmas. To investigate the large amplitude nonlinear structure of the acoustic wave, Sagdeev-Pseudo-Potential approach has been adopted. The numerical analysis of the linear dispersion relation and the nonlinear acoustic waves has been presented by drawing their graphs that highlight the effects of plasma parameters on these waves in both the linear and the nonlinear regimes. It has been noticed that only supersonic ion acoustic solitary waves can be excited in the above mentioned quantum plasma even when the value of the critical Mach number is less than unity. Both width and depth of Sagdeev potential reduces on increasing the magnetic quantization parameter η. Whereas the amplitude of the ion acoustic soliton reduces on increasing η, its width appears to be directly proportional to η. The present work would be helpful to understand the excitation of nonlinear ion-acoustic waves in the dense astrophysical environments such as magnetars and in intense-laser plasma interactions.

Quantization ambiguities and bounds on geometric scalars in anisotropic loop quantum cosmology

NASA Astrophysics Data System (ADS)

Singh, Parampreet; Wilson-Ewing, Edward

2014-02-01

We study quantization ambiguities in loop quantum cosmology that arise for space-times with non-zero spatial curvature and anisotropies. Motivated by lessons from different possible loop quantizations of the closed Friedmann-Lemaître-Robertson-Walker cosmology, we find that using open holonomies of the extrinsic curvature, which due to gauge-fixing can be treated as a connection, leads to the same quantum geometry effects that are found in spatially flat cosmologies. More specifically, in contrast to the quantization based on open holonomies of the Ashtekar-Barbero connection, the expansion and shear scalars in the effective theories of the Bianchi type II and Bianchi type IX models have upper bounds, and these are in exact agreement with the bounds found in the effective theories of the Friedmann-Lemaître-Robertson-Walker and Bianchi type I models in loop quantum cosmology. We also comment on some ambiguities present in the definition of inverse triad operators and their role.

Quantization improves stabilization of dynamical systems with delayed feedback

NASA Astrophysics Data System (ADS)

Stepan, Gabor; Milton, John G.; Insperger, Tamas

2017-11-01

We show that an unstable scalar dynamical system with time-delayed feedback can be stabilized by quantizing the feedback. The discrete time model corresponds to a previously unrecognized case of the microchaotic map in which the fixed point is both locally and globally repelling. In the continuous-time model, stabilization by quantization is possible when the fixed point in the absence of feedback is an unstable node, and in the presence of feedback, it is an unstable focus (spiral). The results are illustrated with numerical simulation of the unstable Hayes equation. The solutions of the quantized Hayes equation take the form of oscillations in which the amplitude is a function of the size of the quantization step. If the quantization step is sufficiently small, the amplitude of the oscillations can be small enough to practically approximate the dynamics around a stable fixed point.

Large thermal Hall effect in a frustrated pyrochlore magnet

NASA Astrophysics Data System (ADS)

Hirschberger, Max; Krizan, Jason; Cava, Robert J.; Ong, N. Phuan

2015-03-01

In frustrated magnetism, the nature of the ground state and its elementary excitations are a matter of considerable debate. We present a detailed study of the full thermal conductivity tensor κij, including the Righi-Leduc (or thermal Hall) effect, in single crystals of the frustrated quantum spin-ice pyrochlore Tb2Ti2O7. The off-diagonal response κxy / T is large in this insulating material, despite the absence of itinerant electrons experiencing the Lorentz force. Our experiments over the temperature range of 0 . 8 - 200 K and in fields up to 14 T reveal a remarkable phenomenology: A sizeable field-linear Hall effect κxy / T is observed below 100 K, and its slope with respect to magnetic field increases strongly as we cool the sample. We observe significant curvature in the field dependence of κxy / T below 15 K. At the lowest temperatures, both κxx / T and the initial slope limB-->0 [κxy / TB ] are constant in temperature, behavior reminiscent of fermionic heat conduction in dirty metals. Experimental methods and verification of the intrinsic nature of the effect will be discussed. R.J.C. and N.P.O. are supported by a MURI Grant (ARO W911NF-12-1-0461) and by the US National Science Foundation (Grant Number DMR 0819860).

Interaction driven quantum Hall effect in artificially stacked graphene bilayers

PubMed Central

Iqbal, Muhammad Zahir; Iqbal, Muhammad Waqas; Siddique, Salma; Khan, Muhammad Farooq; Ramay, Shahid Mahmood; Nam, Jungtae; Kim, Keun Soo; Eom, Jonghwa

2016-01-01

The honeycomb lattice structure of graphene gives rise to its exceptional electronic properties of linear dispersion relation and its chiral nature of charge carriers. The exceptional electronic properties of graphene stem from linear dispersion relation and chiral nature of charge carries, originating from its honeycomb lattice structure. Here, we address the quantum Hall effect in artificially stacked graphene bilayers and single layer graphene grown by chemical vapor deposition. The quantum Hall plateaus started to appear more than 3 T and became clearer at higher magnetic fields up to 9 T. Shubnikov-de Hass oscillations were manifestly observed in graphene bilayers texture. These unusual plateaus may have been due to the layers interaction in artificially stacked graphene bilayers. Our study initiates the understanding of interactions between artificially stacked graphene layers. PMID:27098387

Interaction driven quantum Hall effect in artificially stacked graphene bilayers.

PubMed

Iqbal, Muhammad Zahir; Iqbal, Muhammad Waqas; Siddique, Salma; Khan, Muhammad Farooq; Ramay, Shahid Mahmood; Nam, Jungtae; Kim, Keun Soo; Eom, Jonghwa

2016-04-21

The honeycomb lattice structure of graphene gives rise to its exceptional electronic properties of linear dispersion relation and its chiral nature of charge carriers. The exceptional electronic properties of graphene stem from linear dispersion relation and chiral nature of charge carries, originating from its honeycomb lattice structure. Here, we address the quantum Hall effect in artificially stacked graphene bilayers and single layer graphene grown by chemical vapor deposition. The quantum Hall plateaus started to appear more than 3 T and became clearer at higher magnetic fields up to 9 T. Shubnikov-de Hass oscillations were manifestly observed in graphene bilayers texture. These unusual plateaus may have been due to the layers interaction in artificially stacked graphene bilayers. Our study initiates the understanding of interactions between artificially stacked graphene layers.

A Generic Theory of the Integer Quantum Hall Effect

NASA Astrophysics Data System (ADS)

Shen, Yu

The integer quantum Hall effect (IQHE) is usually modeled by a Galilean or rotationally invariant Hamiltonian. These are not generic symmetries for electrons moving in a crystal background and can potentially confuse non-topological quantities with topological ones and identify otherwise distinct geometrical properties. In this thesis we present a generic theory for the IQHE. First we show that a generic guiding-center coherent state, defined by a natural metric in each Landau level, has the form of an antiholomorphic function times a Gaussian factor. Then by numerically solving the eigenproblem for a quartic Hamiltonian and finding the roots of the antiholomorphic part we are able to define a topological spin sn = n + 1/2 where n is the number of central roots that are enclosed by the semiclassical orbit. We derive a generic formula for the Hall viscosity in the absence of rotational symmetry and show that the previous interpretation of the scalar Hall viscosity as the "intrinsic orbital angular momentum" breaks down since the concept of angular momentum requires the presence of rotational symmetry. We also calculate generic electromagnetic responses and differentiate between universal terms that are diagonal with respect to Landau level index and non-universal terms that depend on inter-Landau-level mixing. We conclude that the generic theory offers a fundamental definition for the topological spin and reveals finer structure in the geometrical properties of the IQHE.

Assessment of bilayer silicene to probe as quantum spin and valley Hall effect

NASA Astrophysics Data System (ADS)

Rehman, Majeed Ur; Qiao, Zhenhua

2018-02-01

Silicene takes precedence over graphene due to its buckling type structure and strong spin orbit coupling. Motivated by these properties, we study the silicene bilayer in the presence of applied perpendicular electric field and intrinsic spin orbit coupling to probe as quantum spin/valley Hall effect. Using analytical approach, we calculate the spin Chern-number of bilayer silicene and then compare it with monolayer silicene. We reveal that bilayer silicene hosts double spin Chern-number as compared to single layer silicene and therefore accordingly has twice as many edge states in contrast to single layer silicene. In addition, we investigate the combined effect of intrinsic spin orbit coupling and the external electric field, we find that bilayer silicene, likewise single layer silicene, goes through a phase transitions from a quantum spin Hall state to a quantum valley Hall state when the strength of the applied electric field exceeds the intrinsic spin orbit coupling strength. We believe that the results and outcomes obtained for bilayer silicene are experimentally more accessible as compared to bilayer graphene, because of strong SO coupling in bilayer silicene.

Gauge fixing and BFV quantization

NASA Astrophysics Data System (ADS)

Rogers, Alice

2000-01-01

Non-singularity conditions are established for the Batalin-Fradkin-Vilkovisky (BFV) gauge-fixing fermion which are sufficient for it to lead to the correct path integral for a theory with constraints canonically quantized in the BFV approach. The conditions ensure that the anticommutator of this fermion with the BRST charge regularizes the path integral by regularizing the trace over non-physical states in each ghost sector. The results are applied to the quantization of a system which has a Gribov problem, using a non-standard form of the gauge-fixing fermion.

Fine structure constant and quantized optical transparency of plasmonic nanoarrays.

PubMed

Kravets, V G; Schedin, F; Grigorenko, A N

2012-01-24

Optics is renowned for displaying quantum phenomena. Indeed, studies of emission and absorption lines, the photoelectric effect and blackbody radiation helped to build the foundations of quantum mechanics. Nevertheless, it came as a surprise that the visible transparency of suspended graphene is determined solely by the fine structure constant, as this kind of universality had been previously reserved only for quantized resistance and flux quanta in superconductors. Here we describe a plasmonic system in which relative optical transparency is determined solely by the fine structure constant. The system consists of a regular array of gold nanoparticles fabricated on a thin metallic sublayer. We show that its relative transparency can be quantized in the near-infrared, which we attribute to the quantized contact resistance between the nanoparticles and the metallic sublayer. Our results open new possibilities in the exploration of universal dynamic conductance in plasmonic nanooptics.

Thermal field theory and generalized light front quantization

NASA Astrophysics Data System (ADS)

Weldon, H. Arthur

2003-04-01

The dependence of thermal field theory on the surface of quantization and on the velocity of the heat bath is investigated by working in general coordinates that are arbitrary linear combinations of the Minkowski coordinates. In the general coordinates the metric tensor gμν¯ is nondiagonal. The Kubo-Martin-Schwinger condition requires periodicity in thermal correlation functions when the temporal variable changes by an amount -i/(T(g00¯)). Light-front quantization fails since g00¯=0; however, various related quantizations are possible.

Anomalous Hall effect assisted by interfacial chemical reaction in perpendicular Co/Pt multilayers

NASA Astrophysics Data System (ADS)

Liu, Qian; Jiang, Shaolong; Teng, Jiao

2018-05-01

To uncover the underlying mechanism of Mg effect on the improved anomalous Hall effect (AHE) of perpendicular [Pt/Co]3/Mg/HfO2 multilayers, the X-ray photoelectron spectroscopy analysis has been carried out. It is found that Mg interlayer at the Co/HfO2 interface could prevent the Co oxidation to some extent via interfacial chemical reaction. As a result, A large anomalous Hall resistivity (ρAH) is obtained in perpendicular [Pt/Co]3/Mg/HfO2 multilayers, with a maximum ρAH of 3.02 μΩ cm, which is 59% larger than that in Co/Pt multilayers without Mg insertion. This effective modification of the AHE based on interfacial chemical reaction provides a promising pathway for spintronic applications.

Intrinsic superspin Hall current

NASA Astrophysics Data System (ADS)

Linder, Jacob; Amundsen, Morten; Risinggârd, Vetle

2017-09-01

We discover an intrinsic superspin Hall current: an injected charge supercurrent in a Josephson junction containing heavy normal metals and a ferromagnet generates a transverse spin supercurrent. There is no accompanying dissipation of energy, in contrast to the conventional spin Hall effect. The physical origin of the effect is an antisymmetric spin density induced among transverse modes ky near the interface of the superconductor arising due to the coexistence of p -wave and conventional s -wave superconducting correlations with a belonging phase mismatch. Our predictions can be tested in hybrid structures including thin heavy metal layers combined with strong ferromagnets and ordinary s -wave superconductors.

Faraday Probe Analysis, Part 2: Evaluation of Facility Effects on Ion Migration in a Hall Thruster Plume (Preprint)

DTIC Science & Technology

2010-02-24

A nested Faraday probe was designed and fabricated to assess facility effects in a systematic study of ion migration in a Hall thruster plume...Current density distributions were studied at 8, 12, 16, and 20 thruster diameters downstream of the Hall thruster exit plane with four probe configurations...measurements are a significant improvement for comparisons with numerical simulations and investigations of Hall thruster performance.

Probabilistic distance-based quantizer design for distributed estimation

NASA Astrophysics Data System (ADS)

Kim, Yoon Hak

2016-12-01

We consider an iterative design of independently operating local quantizers at nodes that should cooperate without interaction to achieve application objectives for distributed estimation systems. We suggest as a new cost function a probabilistic distance between the posterior distribution and its quantized one expressed as the Kullback Leibler (KL) divergence. We first present the analysis that minimizing the KL divergence in the cyclic generalized Lloyd design framework is equivalent to maximizing the logarithmic quantized posterior distribution on the average which can be further computationally reduced in our iterative design. We propose an iterative design algorithm that seeks to maximize the simplified version of the posterior quantized distribution and discuss that our algorithm converges to a global optimum due to the convexity of the cost function and generates the most informative quantized measurements. We also provide an independent encoding technique that enables minimization of the cost function and can be efficiently simplified for a practical use of power-constrained nodes. We finally demonstrate through extensive experiments an obvious advantage of improved estimation performance as compared with the typical designs and the novel design techniques previously published.

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.

Relational symplectic groupoid quantization for constant poisson structures

NASA Astrophysics Data System (ADS)

Cattaneo, Alberto S.; Moshayedi, Nima; Wernli, Konstantin

2017-09-01

As a detailed application of the BV-BFV formalism for the quantization of field theories on manifolds with boundary, this note describes a quantization of the relational symplectic groupoid for a constant Poisson structure. The presence of mixed boundary conditions and the globalization of results are also addressed. In particular, the paper includes an extension to space-times with boundary of some formal geometry considerations in the BV-BFV formalism, and specifically introduces into the BV-BFV framework a "differential" version of the classical and quantum master equations. The quantization constructed in this paper induces Kontsevich's deformation quantization on the underlying Poisson manifold, i.e., the Moyal product, which is known in full details. This allows focussing on the BV-BFV technology and testing it. For the inexperienced reader, this is also a practical and reasonably simple way to learn it.

Quantization Distortion in Block Transform-Compressed Data

NASA Technical Reports Server (NTRS)

Boden, A. F.

1995-01-01

The popular JPEG image compression standard is an example of a block transform-based compression scheme; the image is systematically subdivided into block that are individually transformed, quantized, and encoded. The compression is achieved by quantizing the transformed data, reducing the data entropy and thus facilitating efficient encoding. A generic block transform model is introduced.

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.

Instant-Form and Light-Front Quantization of Field Theories

NASA Astrophysics Data System (ADS)

Kulshreshtha, Usha; Kulshreshtha, Daya Shankar; Vary, James

2018-05-01

In this work we consider the instant-form and light-front quantization of some field theories. As an example, we consider a class of gauged non-linear sigma models with different regularizations. In particular, we present the path integral quantization of the gauged non-linear sigma model in the Faddeevian regularization. We also make a comparision of the possible differences in the instant-form and light-front quantization at appropriate places.

Spectral Analysis of Non-ideal MRI Modes: The Effect of Hall Diffusion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mohandas, Gopakumar; Pessah, Martin E., E-mail: gopakumar@nbi.ku.dk, E-mail: mpessah@nbi.ku.dk

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 themore » 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.« less

Hall effect in Ce/sub 1-x/Y/sub x/Pd/sub 3/ mixed-valence alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fert, A.; Pureur, P.; Hamzic, A.

Mixed-valence and Kondo lattice systems exhibit large anomalous Hall coefficients with a striking change of sign at low temperature in several systems (CePd/sub 3/, CeCu/sub 6/,..., etc.). We have studied the Hall effect of Ce/sub 1-x/Y/sub x/Pd/sub 3/, in which the substitution of small amounts of Y for Ce prevents the development of coherence at low temperature. We find that the Hall coefficient does not change its sign at low temperature and can be well understood in the one-impurity model of Ramakrishnan, Coleman, and Anderson. We infer that the change of sign observed in CePd/sub 3/ is an effect ofmore » coherence.« less

Gauge Physics of Spin Hall Effect

PubMed Central

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

A programmable quantum current standard from the Josephson and the quantum Hall effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Poirier, W., E-mail: wilfrid.poirier@lne.fr; Lafont, F.; Djordjevic, S.

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.

Universe creation from the third-quantized vacuum

DOE Office of Scientific and Technical Information (OSTI.GOV)

McGuigan, M.

1989-04-15

Third quantization leads to a Hilbert space containing a third-quantized vacuum in which no universes are present as well as multiuniverse states. We consider the possibility of universe creation for the special case where the universe emerges in a no-particle state. The probability of such a creation is computed from both the path-integral and operator formalisms.

Universe creation from the third-quantized vacuum

NASA Astrophysics Data System (ADS)

McGuigan, Michael

1989-04-01

Third quantization leads to a Hilbert space containing a third-quantized vacuum in which no universes are present as well as multiuniverse states. We consider the possibility of universe creation for the special case where the universe emerges in a no-particle state. The probability of such a creation is computed from both the path-integral and operator formalisms.

Concert hall acoustics

NASA Astrophysics Data System (ADS)

Schroeder, Manfred

2004-05-01

I will review some work at Bell Laboratories on artificial reverberation and concert hall acoustics including Philharmonic Hall (Lincoln Center for the Performing Arts, New York). I will also touch on sound diffusion by number-theoretic surfaces and the measurement of reverberation time using the music as played in the hall as a ``test'' signal.

Silicon-based microfabricated tin oxide gas sensor incorporating use of Hall effect measurement

NASA Astrophysics Data System (ADS)

Hammond, Joseph Wilson

2000-10-01

Characterization of a microfabricated sol-gel derived nano-particle tin oxide thin film on a silicon substrate, through simultaneous measurement of conductivity, Hall mobility and electron density, had not been accomplished before this study. Conductivity is a function of carrier density and Hall mobility. Therefore, a full understanding of the sensing mechanism of tin oxide requires knowledge of the sensor conductivity, electron density and Hall mobility. A tin oxide thin film (1100A thick), derived by the sol-gel method, was deposited on a Si/SiO2 substrate by means of spin coating method. The sol-gel method produces films of porous interconnected nano-sized particles and is relatively inexpensive and easy to produce compared to existing methods of tin oxide thin film deposition. A goal of this study was to determine the compatibility of sol-gel derived tin oxide thin films with silicon based microfabrication procedures. It was determined that conductivity sensitivity is strongly dependant on electron density level and shows very weak dependence on Hall mobility. Lack of Hall mobility sensitivity to H2 concentration suggests that conduction is grain control limited. In this regime, in which the grain size (D) is less than twice the characteristic Debye length (LD), a change in reducing gas concentration results in a nearly simultaneous change in carrier density throughout the entire grain, while the Hall mobility remains unchanged. The sensor calcined at 500°C and operated at 250°C showed maximum conductivity sensitivity to H2 in air. The sensor exhibited a high conductivity sensitivity of 10.6 to 100ppm H2 in air with response time of (˜1) minute and recovery time of (˜4) minutes. Images of the thin film surface, obtained by SEM, were used to study the effects of calcination temperature and operating conditions on the tin oxide structure. Sensitivity decreased as average grain size increased from 7.7nm to 14.7nm, with increasing calcination temperature from

Pseudospectral Model for Hybrid PIC Hall-effect Thruster Simulation

DTIC Science & Technology

2015-07-01

and Fernandez6 (hybrid- PIC ). This work follows the example of Lam and Fernandez but substitutes a spectral description in the azimuthal direction to...Paper 3. DATES COVERED (From - To) July 2015-July 2015 4. TITLE AND SUBTITLE Pseudospectral model for hybrid PIC Hall-effect thruster simulationect...of a pseudospectral azimuthal-axial hybrid- PIC HET code which is designed to explicitly resolve and filter azimuthal fluctuations in the

Effect of azimuthal diversion rail on an ATON-type Hall thruster

NASA Astrophysics Data System (ADS)

Xu, Zhang; Liqiu, Wei; Liang, Han; Yongjie, Ding; Daren, Yu

2017-03-01

A newly designed azimuthal diversion rail (ADR) is studied and used to enhance the ionization process in an ATON-type Hall thruster. The diversion rail efficiently reduces the neutral flow axial velocity, and hence, increases the resistance time of atoms in the discharge channel of the Hall thruster. Thrust performances, in terms of thrust, anode efficiency and ion beam divergence, are found to be improved because of the application of the diversion rail, especially at low mass flow rate conditions. Experiment results reveal that the ADR increases the mass utilization under insufficient mass flow rate operating conditions. The design of the ADR broadens the efficient operating range of Hall thrusters and has significant contribution to multi-mode Hall thruster development.

Landau quantization of Dirac fermions in graphene and its multilayers

NASA Astrophysics Data System (ADS)

Yin, Long-Jing; Bai, Ke-Ke; Wang, Wen-Xiao; Li, Si-Yu; Zhang, Yu; He, Lin

2017-08-01

When electrons are confined in a two-dimensional (2D) system, typical quantum-mechanical phenomena such as Landau quantization can be detected. Graphene systems, including the single atomic layer and few-layer stacked crystals, are ideal 2D materials for studying a variety of quantum-mechanical problems. In this article, we review the experimental progress in the unusual Landau quantized behaviors of Dirac fermions in monolayer and multilayer graphene by using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Through STS measurement of the strong magnetic fields, distinct Landau-level spectra and rich level-splitting phenomena are observed in different graphene layers. These unique properties provide an effective method for identifying the number of layers, as well as the stacking orders, and investigating the fundamentally physical phenomena of graphene. Moreover, in the presence of a strain and charged defects, the Landau quantization of graphene can be significantly modified, leading to unusual spectroscopic and electronic properties.

Anomalous Hall effect in semiconductor quantum wells in proximity to chiral p -wave superconductors

NASA Astrophysics Data System (ADS)

Yang, F.; Yu, T.; Wu, M. W.

2018-05-01

By using the gauge-invariant optical Bloch equation, we perform a microscopic kinetic investigation on the anomalous Hall effect in chiral p -wave superconducting states. Specifically, the intrinsic anomalous Hall conductivity in the absence of the magnetic field is zero as a consequence of Galilean invariance in our description. As for the extrinsic channel, a finite anomalous Hall current is obtained from the impurity scattering with the optically excited normal quasiparticle current even at zero temperature. From our kinetic description, it can be clearly seen that the excited normal quasiparticle current is due to an induced center-of-mass momentum of Cooper pairs through the acceleration driven by ac electric field. For the induced anomalous Hall current, we show that the conventional skew-scattering channel in the linear response makes the dominant contribution in the strong impurity interaction. In this case, our kinetic description as a supplementary viewpoint mostly confirms the results of Kubo formalism in the literature. Nevertheless, in the weak impurity interaction, this skew-scattering channel becomes marginal and we reveal that an induction channel from the Born contribution dominates the anomalous Hall current. This channel, which has long been overlooked in the literature, is due to the particle-hole asymmetry by nonlinear optical excitation. Finally, we study the case in the chiral p -wave superconducting state with a transverse conical magnetization, which breaks the Galilean invariance. In this situation, the intrinsic anomalous Hall conductivity is no longer zero. Comparison of this intrinsic channel with the extrinsic one from impurity scattering is addressed.

Quantization error of CCD cameras and their influence on phase calculation in fringe pattern analysis.

PubMed

Skydan, Oleksandr A; Lilley, Francis; Lalor, Michael J; Burton, David R

2003-09-10

We present an investigation into the phase errors that occur in fringe pattern analysis that are caused by quantization effects. When acquisition devices with a limited value of camera bit depth are used, there are a limited number of quantization levels available to record the signal. This may adversely affect the recorded signal and adds a potential source of instrumental error to the measurement system. Quantization effects also determine the accuracy that may be achieved by acquisition devices in a measurement system. We used the Fourier fringe analysis measurement technique. However, the principles can be applied equally well for other phase measuring techniques to yield a phase error distribution that is caused by the camera bit depth.

Entropy-aware projected Landweber reconstruction for quantized block compressive sensing of aerial imagery

NASA Astrophysics Data System (ADS)

Liu, Hao; Li, Kangda; Wang, Bing; Tang, Hainie; Gong, Xiaohui

2017-01-01

A quantized block compressive sensing (QBCS) framework, which incorporates the universal measurement, quantization/inverse quantization, entropy coder/decoder, and iterative projected Landweber reconstruction, is summarized. Under the QBCS framework, this paper presents an improved reconstruction algorithm for aerial imagery, QBCS, with entropy-aware projected Landweber (QBCS-EPL), which leverages the full-image sparse transform without Wiener filter and an entropy-aware thresholding model for wavelet-domain image denoising. Through analyzing the functional relation between the soft-thresholding factors and entropy-based bitrates for different quantization methods, the proposed model can effectively remove wavelet-domain noise of bivariate shrinkage and achieve better image reconstruction quality. For the overall performance of QBCS reconstruction, experimental results demonstrate that the proposed QBCS-EPL algorithm significantly outperforms several existing algorithms. With the experiment-driven methodology, the QBCS-EPL algorithm can obtain better reconstruction quality at a relatively moderate computational cost, which makes it more desirable for aerial imagery applications.

Fractional quantum Hall effect in strained graphene: Stability of Laughlin states in disordered pseudomagnetic fields

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.

Magnetotransport properties of 8-Pmmn borophene: effects of Hall field and strain.

PubMed

Islam, S K Firoz

2018-07-11

The polymorph of 8-Pmmn borophene is an anisotropic Dirac material with tilted Dirac cones at two valleys. The tilting of the Dirac cones at two valleys are in opposite directions, which manifests itself via the valley dependent Landau levels in presence of an in-plane electric field (Hall field). The valley dependent Landau levels cause valley polarized magnetotransport properties in presence of the Hall field, which is in contrast to the monolayer graphene with isotropic non-tilted Dirac cones. The longitudinal conductivity and Hall conductivity are evaluated by using linear response theory in low temperature regime. An analytical approximate form of the longitudinal conductivity is also obtained. It is observed that the tilting of the Dirac cones amplifies the frequency of the longitudinal conductivity oscillation (Shubnikov-de Haas). On the other hand, the Hall conductivity exhibits graphene-like plateaus except the appearance of valley dependent steps which are purely attributed to the Hall field induced lifting of the valley degeneracy in the Landau levels. Finally we look into the different cases when the Hall field is applied to the strained borophene and find that valley dependency is fully dominated by strain rather than Hall field. Another noticeable point is that if the real magnetic field is replaced by the strain induced pseudo magnetic field then the electric field looses its ability to cause valley polarized transport.

Floating-point system quantization errors in digital control systems

NASA Technical Reports Server (NTRS)

Phillips, C. L.

1973-01-01

The results are reported of research into the effects on system operation of signal quantization in a digital control system. The investigation considered digital controllers (filters) operating in floating-point arithmetic in either open-loop or closed-loop systems. An error analysis technique is developed, and is implemented by a digital computer program that is based on a digital simulation of the system. As an output the program gives the programing form required for minimum system quantization errors (either maximum of rms errors), and the maximum and rms errors that appear in the system output for a given bit configuration. The program can be integrated into existing digital simulations of a system.

Quantum Hall effect breakdown in two-dimensional hole gases

NASA Astrophysics Data System (ADS)

Eaves, L.; Stoddart, S. T.; Wirtz, R.; Neumann, A. C.; Gallagher, B. L.; Main, P. C.; Henini, M.

2000-02-01

The breakdown of dissipationless current flow in the quantum Hall effect is studied for a two-dimensional hole gas at filling factors i=1 and 2. At high currents, the magnetoresistance curves at breakdown exhibit a series of steps accompanied by hysteresis and intermittent noise. These are compared with similar data for electron systems and are discussed in terms of a hydrodynamic model involving inter-Landau level scattering at the sample edge.

Fast large-scale object retrieval with binary quantization

NASA Astrophysics Data System (ADS)

Zhou, Shifu; Zeng, Dan; Shen, Wei; Zhang, Zhijiang; Tian, Qi

2015-11-01

The objective of large-scale object retrieval systems is to search for images that contain the target object in an image database. Where state-of-the-art approaches rely on global image representations to conduct searches, we consider many boxes per image as candidates to search locally in a picture. In this paper, a feature quantization algorithm called binary quantization is proposed. In binary quantization, a scale-invariant feature transform (SIFT) feature is quantized into a descriptive and discriminative bit-vector, which allows itself to adapt to the classic inverted file structure for box indexing. The inverted file, which stores the bit-vector and box ID where the SIFT feature is located inside, is compact and can be loaded into the main memory for efficient box indexing. We evaluate our approach on available object retrieval datasets. Experimental results demonstrate that the proposed approach is fast and achieves excellent search quality. Therefore, the proposed approach is an improvement over state-of-the-art approaches for object retrieval.

Prediction-guided quantization for video tone mapping

NASA Astrophysics Data System (ADS)

Le Dauphin, Agnès.; Boitard, Ronan; Thoreau, Dominique; Olivier, Yannick; Francois, Edouard; LeLéannec, Fabrice

2014-09-01

Tone Mapping Operators (TMOs) compress High Dynamic Range (HDR) content to address Low Dynamic Range (LDR) displays. However, before reaching the end-user, this tone mapped content is usually compressed for broadcasting or storage purposes. Any TMO includes a quantization step to convert floating point values to integer ones. In this work, we propose to adapt this quantization, in the loop of an encoder, to reduce the entropy of the tone mapped video content. Our technique provides an appropriate quantization for each mode of both the Intra and Inter-prediction that is performed in the loop of a block-based encoder. The mode that minimizes a rate-distortion criterion uses its associated quantization to provide integer values for the rest of the encoding process. The method has been implemented in HEVC and was tested over two different scenarios: the compression of tone mapped LDR video content (using the HM10.0) and the compression of perceptually encoded HDR content (HM14.0). Results show an average bit-rate reduction under the same PSNR for all the sequences and TMO considered of 20.3% and 27.3% for tone mapped content and 2.4% and 2.7% for HDR content.

A free-trailing vane flow direction indicator employing a linear output Hall effect transducer

NASA Technical Reports Server (NTRS)

Zell, Peter T.; Mcmahon, Robert D.

1988-01-01

The Hall effect vane (HEV) was developed to measure flow angularity in the NASA 40-by-80-foot and 80-by-120-foot wind tunnels. This indicator is capable of sensing flow direction at air speeds from 5 to 300 knots and over a + or - 40 deg angle range with a resolution of 0.1 deg. A free-trailing vane configuration employing a linear output Hall effect transducer as a shaft angle resolver was used. The current configuration of the HEV is designed primarily for wind tunnel calibration testing; however, other potential applications include atmospheric, flight or ground research testing. The HEV met initial design requirements.

Hall effect in a moving liquid

NASA Astrophysics Data System (ADS)

Di Lieto, Alberto; Giuliano, Alessia; Maccarrone, Francesco; Paffuti, Giampiero

2012-01-01

A simple experiment, suitable for performing in an undergraduate physics laboratory, illustrates electromagnetic induction through the water entering into a cylindrical rubber tube by detecting the voltage developed across the tube in the direction transverse both to the flow velocity and to the magnetic field. The apparatus is a very simple example of an electromagnetic flowmeter, a device which is commonly used both in industrial and physiological techniques. The phenomenology observed is similar to that of the Hall effect in the absence of an electric current in the direction of motion of the carriers. The experimental results show a dependence on the intensity of the magnetic field and on the carrier velocity, in good agreement with the theory. Discussion of the system, based on classical electromagnetism, indicates that the effect depends only on the flow rate, and is independent both of the velocity profile and of the electrical conductivity of the medium.

Quantization of Simple Parametrized Systems

NASA Astrophysics Data System (ADS)

Ruffini, Giulio

1995-01-01

I study the canonical formulation and quantization of some simple parametrized systems using Dirac's formalism and the Becchi-Rouet-Stora-Tyutin (BRST) extended phase space method. These systems include the parametrized particle and minisuperspace. Using Dirac's formalism I first analyze for each case the construction of the classical reduced phase space. There are two separate features of these systems that may make this construction difficult: (a) Because of the boundary conditions used, the actions are not gauge invariant at the boundaries. (b) The constraints may have a disconnected solution space. The relativistic particle and minisuperspace have such complicated constraints, while the non-relativistic particle displays only the first feature. I first show that a change of gauge fixing is equivalent to a canonical transformation in the reduced phase space, thus resolving the problems associated with the first feature above. Then I consider the quantization of these systems using several approaches: Dirac's method, Dirac-Fock quantization, and the BRST formalism. In the cases of the relativistic particle and minisuperspace I consider first the quantization of one branch of the constraint at the time and then discuss the backgrounds in which it is possible to quantize simultaneously both branches. I motivate and define the inner product, and obtain, for example, the Klein-Gordon inner product for the relativistic case. Then I show how to construct phase space path integral representations for amplitudes in these approaches--the Batalin-Fradkin-Vilkovisky (BFV) and the Faddeev path integrals --from which one can then derive the path integrals in coordinate space--the Faddeev-Popov path integral and the geometric path integral. In particular I establish the connection between the Hilbert space representation and the range of the lapse in the path integrals. I also examine the class of paths that contribute in the path integrals and how they affect space

Berezin-Toeplitz quantization and naturally defined star products for Kähler manifolds

NASA Astrophysics Data System (ADS)

Schlichenmaier, Martin

2018-04-01

For compact quantizable Kähler manifolds the Berezin-Toeplitz quantization schemes, both operator and deformation quantization (star product) are reviewed. The treatment includes Berezin's covariant symbols and the Berezin transform. The general compact quantizable case was done by Bordemann-Meinrenken-Schlichenmaier, Schlichenmaier, and Karabegov-Schlichenmaier. For star products on Kähler manifolds, separation of variables, or equivalently star product of (anti-) Wick type, is a crucial property. As canonically defined star products the Berezin-Toeplitz, Berezin, and the geometric quantization are treated. It turns out that all three are equivalent, but different.

Subband directional vector quantization in radiological image compression

NASA Astrophysics Data System (ADS)

Akrout, Nabil M.; Diab, Chaouki; Prost, Remy; Goutte, Robert; Amiel, Michel

1992-05-01

The aim of this paper is to propose a new scheme for image compression. The method is very efficient for images which have directional edges such as the tree-like structure of the coronary vessels in digital angiograms. This method involves two steps. First, the original image is decomposed at different resolution levels using a pyramidal subband decomposition scheme. For decomposition/reconstruction of the image, free of aliasing and boundary errors, we use an ideal band-pass filter bank implemented in the Discrete Cosine Transform domain (DCT). Second, the high-frequency subbands are vector quantized using a multiresolution codebook with vertical and horizontal codewords which take into account the edge orientation of each subband. The proposed method reduces the blocking effect encountered at low bit rates in conventional vector quantization.

Supporting Dynamic Quantization for High-Dimensional Data Analytics.

PubMed

Guzun, Gheorghi; Canahuate, Guadalupe

2017-05-01

Similarity searches are at the heart of exploratory data analysis tasks. Distance metrics are typically used to characterize the similarity between data objects represented as feature vectors. However, when the dimensionality of the data increases and the number of features is large, traditional distance metrics fail to distinguish between the closest and furthest data points. Localized distance functions have been proposed as an alternative to traditional distance metrics. These functions only consider dimensions close to query to compute the distance/similarity. Furthermore, in order to enable interactive explorations of high-dimensional data, indexing support for ad-hoc queries is needed. In this work we set up to investigate whether bit-sliced indices can be used for exploratory analytics such as similarity searches and data clustering for high-dimensional big-data. We also propose a novel dynamic quantization called Query dependent Equi-Depth (QED) quantization and show its effectiveness on characterizing high-dimensional similarity. When applying QED we observe improvements in kNN classification accuracy over traditional distance functions. Gheorghi Guzun and Guadalupe Canahuate. 2017. Supporting Dynamic Quantization for High-Dimensional Data Analytics. In Proceedings of Ex-ploreDB'17, Chicago, IL, USA, May 14-19, 2017, 6 pages. https://doi.org/http://dx.doi.org/10.1145/3077331.3077336.

Equivalence of Einstein and Jordan frames in quantized anisotropic cosmological models

NASA Astrophysics Data System (ADS)

Pandey, Sachin; Pal, Sridip; Banerjee, Narayan

2018-06-01

The present work shows that the mathematical equivalence of the Jordan frame and its conformally transformed version, the Einstein frame, so as far as Brans-Dicke theory is concerned, survives a quantization of cosmological models, arising as solutions to the Brans-Dicke theory. We work with the Wheeler-deWitt quantization scheme and take up quite a few anisotropic cosmological models as examples. We effectively show that the transformation from the Jordan to the Einstein frame is a canonical one and hence two frames furnish equivalent description of same physical scenario.

Group Γ (2) and the fractional quantum Hall effect

NASA Astrophysics Data System (ADS)

Georgelin, Yvon; Wallet, Jean-Christophe

1997-02-01

We analyze the action of the inhomogeneous modular group Γ (2) on the three cusps of its principal fundamental domain in the Poincaré half plane. From this, we obtain an exhaustive classification of the fractional quantum Hall numbers. This classification, in which the integer and the fractional states appear on an equal level, is somehow similar to the one given by Jain. We also present some resulting remarks concerning direct phase transitions between the different quantum Hall states.

Experimental evidences of a large extrinsic spin Hall effect in AuW alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laczkowski, P.; Rojas-Sánchez, J.-C.; INAC/SP2M, CEA-Université Joseph Fourier, F-38054 Grenoble

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.

Low temperature hall effect investigation of conducting polymer-carbon nanotubes composite network.

PubMed

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.

Magnon Hall effect without Dzyaloshinskii-Moriya interaction.

PubMed

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.

Image-adapted visually weighted quantization matrices for digital image compression

NASA Technical Reports Server (NTRS)

Watson, Andrew B. (Inventor)

1994-01-01

A method for performing image compression that eliminates redundant and invisible image components is presented. The image compression uses a Discrete Cosine Transform (DCT) and each DCT coefficient yielded by the transform is quantized by an entry in a quantization matrix which determines the perceived image quality and the bit rate of the image being compressed. The present invention adapts or customizes the quantization matrix to the image being compressed. The quantization matrix comprises visual masking by luminance and contrast techniques and by an error pooling technique all resulting in a minimum perceptual error for any given bit rate, or minimum bit rate for a given perceptual error.

Effects of macroscopic inhomogeneities on resistive and Hall measurements on crosses, cloverleafs, and bars

NASA Astrophysics Data System (ADS)

Koon, D. W.; Knickerbocker, C. J.

1996-12-01

The effect of macroscopic inhomogeneities on resistivity and Hall angle measurements is studied by calculating weighting functions (the relative effect of perturbations in a local transport property on the measured global average for the object) for cross, cloverleaf, and bar-shaped geometries. The ``sweet spot,'' the region in the center of the object that the measurement effectively samples, is smaller for crosses and cloverleafs than for the circles and squares already studied, and smaller for the cloverleaf than for the corresponding cross. Resistivity measurements for crosses and cloverleafs suffer from singularities and negative weighting, which can be eliminated by averaging two independent resistance measurements, as done in the van der Pauw technique. Resistivity and Hall measurements made on sufficiently narrow bars are shown to effectively sample only the region directly between the voltage probes.

Design and Testing of a Hall Effect Thruster with Additively Manufactured Components

NASA Astrophysics Data System (ADS)

Hopping, Ethan

The UAH-78AM is a low-power Hall effect thruster developed at the University of Alabama in Huntsville to study the application of low-cost additive manufacturing in the design and fabrication of Hall thrusters. The goal of this project is to assess the feasibility of using unconventional materials to produce a low-cost functioning Hall effect thruster and consider how additive manufacturing can expand the design space and provide other benefits. The thruster features channel walls and a propellant distributor that were manufactured using 3D printing with a variety of materials including ABS, ULTEM, and glazed ceramic. A version of the thruster was tested at NASA Glenn Research Center to obtain performance metrics and to validate the ability of the thruster to produce thrust and sustain a discharge. The design of the thruster and the transient performance measurements are presented here. Measured thrust ranged from 17.2 mN to 30.4 mN over a discharge power of 280 W to 520 W with an anode Isp range of 870 s to 1450 s. Temperature limitations of materials used for the channel walls and propellant distributor limit the ability to run the thruster at thermal steady-state. While the current thruster design is not yet ready for continuous operation, revisions to the device that could enable longer duration tests are discussed.

Hall effect analysis in irradiated silicon samples with different resistivities

NASA Astrophysics Data System (ADS)

Borchi, E.; Bruzzi, M.; Dezillie, B.; Lazanu, S.; Li, Z.; Pirollo, S.

1999-08-01

The changes induced by neutron irradiation in n- and p-type silicon samples with starting resistivities from 10 /spl Omega/-cm up to 30 k/spl Omega/-cm, grown using different techniques, as float-zone (FZ), Czochralski (CZ) and epitaxial, have been analyzed by Van der Pauw and Hall effect measurements. Increasing the fluence, each set of samples evolves toward a quasi-intrinsic p-type material. This behavior has been explained in the frame of a two-level model, that considers the introduction during irradiation of mainly two defects. A deep acceptor and a deep donor, probably related to the divacancy and to the C/sub i/O/sub i/ complex, are placed in the upper and lower half of the forbidden gap, respectively. This simple model explains quantitatively the data on resistivity and Hall coefficient of each set of samples up to the fluence of /spl ap/10/sup 14/ n/cm/sup 2/.

Deficiency of the bulk spin Hall effect model for spin-orbit torques in magnetic-insulator/heavy-metal heterostructures

NASA Astrophysics Data System (ADS)

Li, Junxue; Yu, Guoqiang; Tang, Chi; Liu, Yizhou; Shi, Zhong; Liu, Yawen; Navabi, Aryan; Aldosary, Mohammed; Shao, Qiming; Wang, Kang L.; Lake, Roger; Shi, Jing

2017-06-01

Electrical currents in a magnetic-insulator/heavy-metal heterostructure can induce two simultaneous effects, namely, spin Hall magnetoresistance (SMR) on the heavy-metal side and spin-orbit torques (SOTs) on the magnetic-insulator side. Within the framework of a pure spin current model based on the bulk spin Hall effect (SHE), the ratio of the spin Hall-induced anomalous Hall effect (SH-AHE) to SMR should be equal to the ratio of the fieldlike torque (FLT) to the dampinglike torque (DLT). We perform a quantitative study of SMR, SH-AHE, and SOTs in a series of thulium iron garnet/platinum or T m3F e5O12/Pt heterostructures with different T m3F e5O12 thicknesses, where T m3F e5O12 is a ferrimagnetic insulator with perpendicular magnetic anisotropy. We find the ratio between the measured effective fields of FLT and DLT is at least two times larger than the ratio of the SH-AHE to SMR. In addition, the bulk SHE model grossly underestimates the spin-torque efficiency of FLT. Our results reveal deficiencies of the bulk SHE model and also address the importance of interfacial effects such as the Rashba and magnetic proximity effects in magnetic-insulator/heavy-metal heterostructures.

Hall thruster with grooved walls

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li Hong; Ning Zhongxi; Yu Daren

2013-02-28

Axial-oriented and azimuthal-distributed grooves are formed on channel walls of a Hall thruster after the engine undergoes a long-term operation. Existing studies have demonstrated the relation between the grooves and the near-wall physics, such as sheath and electron near-wall transport. The idea to optimize the thruster performance with such grooves was also proposed. Therefore, this paper is devoted to explore the effects of wall grooves on the discharge characteristics of a Hall thruster. With experimental measurements, the variations on electron conductivity, ionization distribution, and integrated performance are obtained. The involved physical mechanisms are then analyzed and discussed. The findings helpmore » to not only better understand the working principle of Hall thruster discharge but also establish a physical fundamental for the subsequent optimization with artificial grooves.« less

Hall effects on hydromagnetic free convection flow along a porous flat plate with mass transfer

NASA Astrophysics Data System (ADS)

Hossain, M. A.; Rashid, R. I. M. A.

1987-01-01

Effect of Hall current on the unsteady free convection flow of a viscous incompressible and electrically conducting fluid, in presence of foreign gases (such as H2, CO2, H2O, NH3), along an infinite vertical porous flat plate subjected to a transpiration velocity inversely proportional to the square-root of time is investigated in the presence of a uniform transverse magnetic field. The results are discussed with the effects of the parameters Gc (the Grashof number for mass transfer), m (the Hall parameter) and Sc (the Schmidt number) for Pr = 0.71, which represents air.

Hierarchically clustered adaptive quantization CMAC and its learning convergence.

PubMed

Teddy, S D; Lai, E M K; Quek, C

2007-11-01

The cerebellar model articulation controller (CMAC) neural network (NN) is a well-established computational model of the human cerebellum. Nevertheless, there are two major drawbacks associated with the uniform quantization scheme of the CMAC network. They are the following: (1) a constant output resolution associated with the entire input space and (2) the generalization-accuracy dilemma. Moreover, the size of the CMAC network is an exponential function of the number of inputs. Depending on the characteristics of the training data, only a small percentage of the entire set of CMAC memory cells is utilized. Therefore, the efficient utilization of the CMAC memory is a crucial issue. One approach is to quantize the input space nonuniformly. For existing nonuniformly quantized CMAC systems, there is a tradeoff between memory efficiency and computational complexity. Inspired by the underlying organizational mechanism of the human brain, this paper presents a novel CMAC architecture named hierarchically clustered adaptive quantization CMAC (HCAQ-CMAC). HCAQ-CMAC employs hierarchical clustering for the nonuniform quantization of the input space to identify significant input segments and subsequently allocating more memory cells to these regions. The stability of the HCAQ-CMAC network is theoretically guaranteed by the proof of its learning convergence. The performance of the proposed network is subsequently benchmarked against the original CMAC network, as well as two other existing CMAC variants on two real-life applications, namely, automated control of car maneuver and modeling of the human blood glucose dynamics. The experimental results have demonstrated that the HCAQ-CMAC network offers an efficient memory allocation scheme and improves the generalization and accuracy of the network output to achieve better or comparable performances with smaller memory usages. Index Terms-Cerebellar model articulation controller (CMAC), hierarchical clustering, hierarchically

From Weyl to Born-Jordan quantization: The Schrödinger representation revisited

NASA Astrophysics Data System (ADS)

de Gosson, Maurice A.

2016-03-01

The ordering problem has been one of the long standing and much discussed questions in quantum mechanics from its very beginning. Nowadays, there is more or less a consensus among physicists that the right prescription is Weyl's rule, which is closely related to the Moyal-Wigner phase space formalism. We propose in this report an alternative approach by replacing Weyl quantization with the less well-known Born-Jordan quantization. This choice is actually natural if we want the Heisenberg and Schrödinger pictures of quantum mechanics to be mathematically equivalent. It turns out that, in addition, Born-Jordan quantization can be recovered from Feynman's path integral approach provided that one used short-time propagators arising from correct formulas for the short-time action, as observed by Makri and Miller. These observations lead to a slightly different quantum mechanics, exhibiting some unexpected features, and this without affecting the main existing theory; for instance quantizations of physical Hamiltonian functions are the same as in the Weyl correspondence. The differences are in fact of a more subtle nature; for instance, the quantum observables will not correspond in a one-to-one fashion to classical ones, and the dequantization of a Born-Jordan quantum operator is less straightforward than that of the corresponding Weyl operator. The use of Born-Jordan quantization moreover solves the "angular momentum dilemma", which already puzzled L. Pauling. Born-Jordan quantization has been known for some time (but not fully exploited) by mathematicians working in time-frequency analysis and signal analysis, but ignored by physicists. One of the aims of this report is to collect and synthesize these sporadic discussions, while analyzing the conceptual differences with Weyl quantization, which is also reviewed in detail. Another striking feature is that the Born-Jordan formalism leads to a redefinition of phase space quantum mechanics, where the usual Wigner

Quantization noise in digital speech. M.S. Thesis- Houston Univ.

NASA Technical Reports Server (NTRS)

Schmidt, O. L.

1972-01-01

The amount of quantization noise generated in a digital-to-analog converter is dependent on the number of bits or quantization levels used to digitize the analog signal in the analog-to-digital converter. The minimum number of quantization levels and the minimum sample rate were derived for a digital voice channel. A sample rate of 6000 samples per second and lowpass filters with a 3 db cutoff of 2400 Hz are required for 100 percent sentence intelligibility. Consonant sounds are the first speech components to be degraded by quantization noise. A compression amplifier can be used to increase the weighting of the consonant sound amplitudes in the analog-to-digital converter. An expansion network must be installed at the output of the digital-to-analog converter to restore the original weighting of the consonant sounds. This technique results in 100 percent sentence intelligibility for a sample rate of 5000 samples per second, eight quantization levels, and lowpass filters with a 3 db cutoff of 2000 Hz.

Quantization and Superselection Sectors I:. Transformation Group C*-ALGEBRAS

NASA Astrophysics Data System (ADS)

Landsman, N. P.

Quantization is defined as the act of assigning an appropriate C*-algebra { A} to a given configuration space Q, along with a prescription mapping self-adjoint elements of { A} into physically interpretable observables. This procedure is adopted to solve the problem of quantizing a particle moving on a homogeneous locally compact configuration space Q=G/H. Here { A} is chosen to be the transformation group C*-algebra corresponding to the canonical action of G on Q. The structure of these algebras and their representations are examined in some detail. Inequivalent quantizations are identified with inequivalent irreducible representations of the C*-algebra corresponding to the system, hence with its superselection sectors. Introducing the concept of a pre-Hamiltonian, we construct a large class of G-invariant time-evolutions on these algebras, and find the Hamiltonians implementing these time-evolutions in each irreducible representation of { A}. “Topological” terms in the Hamiltonian (or the corresponding action) turn out to be representation-dependent, and are automatically induced by the quantization procedure. Known “topological” charge quantization or periodicity conditions are then identically satisfied as a consequence of the representation theory of { A}.

The spin-Hall effect and spin-orbit torques in epitaxial Co2FeAl/platinum bilayers

NASA Astrophysics Data System (ADS)

Peterson, T. A.; Liu, C.; McFadden, T.; Palmstrøm, C. J.; Crowell, P. A.

We have performed magnetoresistance measurements on epitaxially grown Co2FeAl/platinum (CFA/Pt) ultrathin ferromagnet/heavy metal bilayers to study the spin-Hall effect in Pt and the accompanying spin-orbit torque (SOT) exerted on the magnetic CFA layer. Specifically, we measure the spin-Hall magnetoresistance in the Pt layer by changing the orientation of the CFA magnetization with respect to the spin current orientation created in the Pt, and we determine the SOT efficiency using a second-harmonic detection technique. Because the latter of the two measurements is proportional to the spin-Hall ratio θSHE while the former is proportional to θSHE2, we are able to extract the bare Pt spin-Hall ratio with no assumptions about the CFA/Pt interface spin mixing conductance. Furthermore, by varying the Pt thickness we show that the results are consistent with resistivity-independent spin-Hall conductivity. Finally, the two measurements in combination allow us to infer a spin-mixing conductance at the CFA/Pt interface of 2 +/- 1 ×1015Ω-1m-2 . The combination of spin-Hall magnetoresistance and SOT measurements allows for a determination of the spin-mixing conductance using only low-frequency transport techniques. This work was supported by STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA.

Interface engineering of quantum Hall effects in digital transition metal oxide heterostructures.

PubMed

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.

Establishment of a Hall Thruster Cluster

DTIC Science & Technology

2004-02-01

DURIP funds were used to develop a Hall thruster cluster test facility centered around the University of Michigan Large Vacuum Test Facility and a 2x2 cluster of BUSEK 600 W BHT-600 Hall thrusters. This capability will facilitate our three-year program to address the issue of high-power CDT operation and to provide insight on how chamber effects influence CDT engine/cluster characteristics.

Effect of IrMn inserted layer on anomalous-Hall resistance and spin-Hall magnetoresistance in Pt/IrMn/YIG heterostructures

NASA Astrophysics Data System (ADS)

Shang, T.; Yang, H. L.; Zhan, Q. F.; Zuo, Z. H.; Xie, Y. L.; Liu, L. P.; Zhang, S. L.; Zhang, Y.; Li, H. H.; Wang, B. M.; Wu, Y. H.; Zhang, S.; Li, Run-Wei

2016-10-01

We report an investigation of anomalous-Hall resistance (AHR) and spin-Hall magnetoresistance (SMR) in Pt/Ir20Mn80/Y3Fe5O12 (Pt/IrMn/YIG) heterostructures. The AHR of Pt/IrMn/YIG heterostructures with an antiferromagnetic inserted layer is dramatically enhanced as compared to that of the Pt/YIG bilayer. The temperature dependent AHR behavior is nontrivial, while the IrMn thickness dependent AHR displays a peak at an IrMn thickness of 3 nm. The observed SMR in the temperature range of 10-300 K indicates that the spin current generated in the Pt layer can penetrate the IrMn layer (≤3 nm) to interact with the ferromagnetic YIG layer. The lack of conventional anisotropic magnetoresistance (AMR) implies that the insertion of the IrMn layer between Pt and YIG could efficiently suppress the magnetic proximity effect (MPE) on induced Pt moments by YIG.

Magnetic resonance image compression using scalar-vector quantization

NASA Astrophysics Data System (ADS)

Mohsenian, Nader; Shahri, Homayoun

1995-12-01

A new coding scheme based on the scalar-vector quantizer (SVQ) is developed for compression of medical images. SVQ is a fixed-rate encoder and its rate-distortion performance is close to that of optimal entropy-constrained scalar quantizers (ECSQs) for memoryless sources. The use of a fixed-rate quantizer is expected to eliminate some of the complexity issues of using variable-length scalar quantizers. When transmission of images over noisy channels is considered, our coding scheme does not suffer from error propagation which is typical of coding schemes which use variable-length codes. For a set of magnetic resonance (MR) images, coding results obtained from SVQ and ECSQ at low bit-rates are indistinguishable. Furthermore, our encoded images are perceptually indistinguishable from the original, when displayed on a monitor. This makes our SVQ based coder an attractive compression scheme for picture archiving and communication systems (PACS), currently under consideration for an all digital radiology environment in hospitals, where reliable transmission, storage, and high fidelity reconstruction of images are desired.

Can one ADM quantize relativistic bosonicstrings and membranes?

NASA Astrophysics Data System (ADS)

Moncrief, Vincent

2006-04-01

The standard methods for quantizing relativistic strings diverge significantly from the Dirac-Wheeler-DeWitt program for quantization of generally covariant systems and one wonders whether the latter could be successfully implemented as an alternative to the former. As a first step in this direction, we consider the possibility of quantizing strings (and also relativistic membranes) via a partially gauge-fixed ADM (Arnowitt, Deser and Misner) formulation of the reduced field equations for these systems. By exploiting some (Euclidean signature) Hamilton-Jacobi techniques that Mike Ryan and I had developed previously for the quantization of Bianchi IX cosmological models, I show how to construct Diff( S 1)-invariant (or Diff(Σ)-invariant in the case of membranes) ground state wave functionals for the cases of co-dimension one strings and membranes embedded in Minkowski spacetime. I also show that the reduced Hamiltonian density operators for these systems weakly commute when applied to physical (i.e. Diff( S 1) or Diff(Σ)-invariant) states. While many open questions remain, these preliminary results seem to encourage further research along the same lines.

Towards Reduced Wall Effect Hall Plasma Accelerators

DTIC Science & Technology

2007-07-01

Unpublished Conference Presentations E. Fernandez, N. Borelli , M. Cappelli, N. Gascon, "Investigation of Fluctuation-Induced Electron Transport in Hall...International Electric Propulsion Conference, Princeton University, October 31 November 4, 2005. 38. E. Fernandez, N. Borelli , M. Cappelli, N. Gascon

Nonequilibrium Hall Response After a Topological Quench

NASA Astrophysics Data System (ADS)

Unal, F. Nur; Mueller, Erich; Oktel, M. O.

2017-04-01

We theoretically study the Hall response of a lattice system following a quench where the topology of a filled band is suddenly changed. In the limit where the physics is dominated by a single Dirac cone, we find that the change in the Hall conductivity is two-thirds of the quantum of conductivity. We explore this universal behavior in the Haldane model, and discuss cold-atom experiments for its observation. Beyond linear response, the Hall effect crosses over from fractional to integer values. We investigate finite-size effects, and the role of the harmonic confinement. Furthermore, we explore the magnetic field quenches in ladders formed in synthetic dimensions. This work is supported by TUBITAK, NSFPHY-1508300, ARO-MURI W9111NF-14-1-0003.

Coriolis effect in optics: unified geometric phase and spin-Hall effect.

PubMed

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.

Numerical Study of Current Driven Instabilities and Anomalous Electron Transport in Hall-effect Thrusters

NASA Astrophysics Data System (ADS)

Tran, Jonathan

Plasma turbulence and the resulting anomalous electron transport due to azimuthal current driven instabilities in Hall-effect thrusters is a promising candidate for developing predictive models for the observed anomalous transport. A theory for anomalous electron transport and current driven instabilities has been recently studied by [Lafluer et al., 2016a]. Due to the extreme cost of fully resolving the Debye length and plasma frequency, hybrid plasma simulations utilizing kinetic ions and quasi-steady state fluid electrons have long been the principle workhorse methodology for Hall-effect thruster modeling. Using a reduced dimension particle in cell simulation implemented in the Thermophysics Universal Research Framework developed by the Air Force Research Lab, we show collective electron-wave scattering due to large amplitude azimuthal fluctuations of the electric field and the plasma density. These high-frequency and short wavelength fluctuations can lead to an effective cross-field mobility many orders of magnitude larger than what is expected from classical electron-neutral momentum collisions in the low neutral density regime. We further adapt the previous study by [Lampe et al., 1971] and [Stringer, 1964] for related current driven instabilities to electric propulsion relevant mass ratios and conditions. Finally, we conduct a preliminary study of resolving this instability with a modified hybrid simulation with the hope of integration with established hybrid Hall-effect thruster simulations.

Magnetic field evolution in white dwarfs: The hall effect and complexity of the field

NASA Technical Reports Server (NTRS)

Muslimov, A. G.; Van Horn, H. M.; Wood, M. A.

1995-01-01

We calculate the evolution of the magnetic fields in white dwarfs, taking into account the Hall effect. Because this effect depends nonlinearly upon the magnetic field strength B, the time dependences of the various multipole field components are coupled. The evolution of the field is thus significantly more complicated than has been indicated by previous investigations. Our calculations employ recent white dwarf evolutionary sequences computed for stars with masses 0.4, 0.6, 0.8, and 1.0 solar mass. We show that in the presence of a strong (up to approximately 10(exp 9) G) internal toroidal magnetic field; the evolution of even the lowest order poloidal modes can be substantially changed by the Hall effect. As an example, we compute the evolution of an initially weak quadrupole component, which we take arbitrarily to be approximately 0.1%-1% of the strength of a dominant dipole field. We find that coupling provided by the Hall effect can produce growth of the ratio of the quadrupole to the dipole component of the surface value of the magnetic field strength by more than a factor of 10 over the 10(exp 9) to 10(exp 10) year cooling lifetime of the white dwarf. Some consequences of these results for the process of magnetic-field evolution in white dwarfs are briefly discussed.

Real-space and reciprocal-space Berry phases in the Hall effect of Mn(1-x)Fe(x)Si.

PubMed

Franz, C; Freimuth, F; Bauer, A; Ritz, R; Schnarr, C; Duvinage, C; Adams, T; Blügel, S; Rosch, A; Mokrousov, Y; Pfleiderer, C

2014-05-09

We report an experimental and computational study of the Hall effect in Mn(1-x)Fe(x)Si, as complemented by measurements in Mn(1-x)Co(x)Si, when helimagnetic order is suppressed under substitutional doping. For small x the anomalous Hall effect (AHE) and the topological Hall effect (THE) change sign. Under larger doping the AHE remains small and consistent with the magnetization, while the THE grows by over a factor of 10. Both the sign and the magnitude of the AHE and the THE are in excellent agreement with calculations based on density functional theory. Our study provides the long-sought material-specific microscopic justification that, while the AHE is due to the reciprocal-space Berry curvature, the THE originates in real-space Berry phases.

Exact quantization of Einstein-Rosen waves coupled to massless scalar matter.

PubMed

Barbero G, J Fernando; Garay, Iñaki; Villaseñor, Eduardo J S

2005-07-29

We show in this Letter that gravity coupled to a massless scalar field with full cylindrical symmetry can be exactly quantized by an extension of the techniques used in the quantization of Einstein-Rosen waves. This system provides a useful test bed to discuss a number of issues in quantum general relativity, such as the emergence of the classical metric, microcausality, and large quantum gravity effects. It may also provide an appropriate framework to study gravitational critical phenomena from a quantum point of view, issues related to black hole evaporation, and the consistent definition of test fields and particles in quantum gravity.

Resonant Hall effect under generation of a self-sustaining mode of spin current in nonmagnetic bipolar conductors with identical characters between holes and electrons

NASA Astrophysics Data System (ADS)

Sakai, Masamichi; Takao, Hiraku; Matsunaga, Tomoyoshi; Nishimagi, Makoto; Iizasa, Keitaro; Sakuraba, Takahito; Higuchi, Koji; Kitajima, Akira; Hasegawa, Shigehiko; Nakamura, Osamu; Kurokawa, Yuichiro; Awano, Hiroyuki

2018-03-01

We have proposed an enhancement mechanism of the Hall effect, the signal of which is amplified due to the generation of a sustaining mode of spin current. Our analytic derivations of the Hall resistivity revealed the conditions indispensable for the observation of the effect: (i) the presence of the transverse component of an effective electric field due to spin splitting in chemical potential in addition to the longitudinal component; (ii) the simultaneous presence of holes and electrons each having approximately the same characteristics; (iii) spin-polarized current injection from magnetized electrodes; (iv) the boundary condition for the transverse current (J c, y = 0). The model proposed in this study was experimentally verified by using van der Pauw-type Hall devices consisting of the nonmagnetic bipolar conductor YH x (x ≃ 2) and TbFeCo electrodes. Replacing Au electrodes with TbFeCo electrodes alters the Hall resistivity from the ordinary Hall effect to the anomalous Hall-like effect with an enhancement factor of approximately 50 at 4 T. We interpreted the enhancement phenomenon in terms of the present model.

Coriolis effect and spin Hall effect of light in an inhomogeneous chiral medium.

PubMed

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.

Diagnostics Systems for Permanent Hall Thrusters Development

NASA Astrophysics Data System (ADS)

Ferreira, Jose Leonardo; Soares Ferreira, Ivan; Santos, Jean; Miranda, Rodrigo; Possa, M. Gabriela

This work describes the development of Permanent Magnet Hall Effect Plasma Thruster (PHALL) and its diagnostic systems at The Plasma Physics Laboratory of University of Brasilia. The project consists on the construction and characterization of plasma propulsion engines based on the Hall Effect. Electric thrusters have been employed in over 220 successful space missions. Two types stand out: the Hall-Effect Thruster (HET) and the Gridded Ion Engine (GIE). The first, which we deal with in this project, has the advantage of greater simplicity of operation, a smaller weight for the propulsion subsystem and a longer shelf life. It can operate in two configurations: magnetic layer and anode layer, the difference between the two lying in the positioning of the anode inside the plasma channel. A Hall-Effect Thruster-HET is a type of plasma thruster in which the propellant gas is ionized and accelerated by a magneto hydrodynamic effect combined with electrostatic ion acceleration. So the essential operating principle of the HET is that it uses a J x B force and an electrostatic potential to accelerate ions up to high speeds. In a HET, the attractive negative charge is provided by electrons at the open end of the Thruster instead of a grid, as in the case of the electrostatic ion thrusters. A strong radial magnetic field is used to hold the electrons in place, with the combination of the magnetic field and the electrostatic potential force generating a fast circulating electron current, the Hall current, around the axis of the Thruster, mainly composed by drifting electrons in an ion plasma background. Only a slow axial drift towards the anode occurs. The main attractive features of the Hall-Effect Thruster are its simple design and operating principles. Most of the Hall-Effect Thrusters use electromagnet coils to produce the main magnetic field responsible for plasma generation and acceleration. In this paper we present a different new concept, a Permanent Magnet Hall-Effect

Differential calculus on quantized simple lie groups

NASA Astrophysics Data System (ADS)

Jurčo, Branislav

1991-07-01

Differential calculi, generalizations of Woronowicz's four-dimensional calculus on SU q (2), are introduced for quantized classical simple Lie groups in a constructive way. For this purpose, the approach of Faddeev and his collaborators to quantum groups was used. An equivalence of Woronowicz's enveloping algebra generated by the dual space to the left-invariant differential forms and the corresponding quantized universal enveloping algebra, is obtained for our differential calculi. Real forms for q ∈ ℝ are also discussed.

Integral Sliding Mode Fault-Tolerant Control for Uncertain Linear Systems Over Networks With Signals Quantization.

PubMed

Hao, Li-Ying; Park, Ju H; Ye, Dan

2017-09-01

In this paper, a new robust fault-tolerant compensation control method for uncertain linear systems over networks is proposed, where only quantized signals are assumed to be available. This approach is based on the integral sliding mode (ISM) method where two kinds of integral sliding surfaces are constructed. One is the continuous-state-dependent surface with the aim of sliding mode stability analysis and the other is the quantization-state-dependent surface, which is used for ISM controller design. A scheme that combines the adaptive ISM controller and quantization parameter adjustment strategy is then proposed. Through utilizing H ∞ control analytical technique, once the system is in the sliding mode, the nature of performing disturbance attenuation and fault tolerance from the initial time can be found without requiring any fault information. Finally, the effectiveness of our proposed ISM control fault-tolerant schemes against quantization errors is demonstrated in the simulation.

Facility Focus: Residence Halls.

ERIC Educational Resources Information Center

College Planning & Management, 2002

2002-01-01

Describes residence halls seeking to meet needs beyond traditional mass housing for the 18- to 22-year-old students: Whittemore Hall at the Tuck School of Business at Dartmouth College (for older students); Small Group Housing at Washington University (grouping students with common interests); and the renovation of the residence hall at Boston's…

Astronaut Hall of Fame

NASA Image and Video Library

2018-04-21

Scott D. Altman, second from left, is inducted into the Astronaut Hall of Fame (AHOF) during a ceremony inside the Space Shuttle Atlantis attraction at NASA's Kennedy Space Center Visitor Complex in Florida. At far left, Hall of Famer Curt Brown, board chairman, Astronaut Scholarship Foundation (ASF), inducts Altman into the Hall of Fame Class of 2018. At right is Hall of Famer John Grunsfeld, who spoke on Altman's behalf during the ceremony. At far right is Thomas D. Jones, Ph.D., who also was inducted into the AHOF Class of 2018. Inductees into the Hall of Fame are selected by a committee of Hall of Fame astronauts, former NASA officials, flight directors, historians and journalists. The process is administered by the Astronaut Scholarship Foundation. To be eligible, an astronaut must have made his or her first flight at least 17 years before the induction. Candidates must be a U.S. citizen and a NASA-trained commander, pilot or mission specialist who has orbited the earth at least once. Including Altman and Jones, 97 astronauts have been inducted into the AHOF.

Astronaut Hall of Fame

NASA Image and Video Library

2018-04-21

Thomas D. Jones, Ph.D., in the center, is inducted into the Astronaut Hall of Fame (AHOF) during a ceremony inside the Space Shuttle Atlantis attraction at NASA’s Kennedy Space Center Visitor Complex in Florida. At left, Hall of Famer Curt Brown, board chairman, Astronaut Scholarship Foundation (ASF), inducts Jones into the Hall of Fame Class of 2018. At right is Hall of Famer Storey Musgrave, who spoke on Jones behalf during the ceremony. Also inducted was retired astronaut Scott D. Altman. Inductees into the Hall of Fame are selected by a committee of Hall of Fame astronauts, former NASA officials, flight directors, historians and journalists. The process is administered by the Astronaut Scholarship Foundation. To be eligible, an astronaut must have made his or her first flight at least 17 years before the induction. Candidates must be a U.S. citizen and a NASA-trained commander, pilot or mission specialist who has orbited the earth at least once. Including Altman and Jones, 97 astronauts have been inducted into the AHOF.

Oxidized Mn:Ge magnetic semiconductor: Observation of anomalous Hall effect and large magnetoresistance

NASA Astrophysics Data System (ADS)

Duc Dung, Dang; Choi, Jiyoun; Feng, Wuwei; Cao Khang, Nguyen; Cho, Sunglae

2018-03-01

We report on the structural and magneto-transport properties of the as-grown and oxidized Mn:Ge magnetic semiconductors. Based on X-ray diffraction and X-ray photoelectron spectroscopy results, the samples annealed at 650 and 700 °C became fully oxidized and the chemical binding energies of Mn was found to be Mn3O4. Thus, the system became Mn3O4 clusters embedded in Ge1-yOy. The as-grown sample showed positive linear Hall effect and negligible negative magnetoresistance (MR), which trend remained for the sample annealed up to 550 °C. Interestingly, for the samples annealed at above 650 °C, we observed the anomalous Hall effect around 45 K and the giant positive MR, which are respectively 59.2% and 78.5% at 7 kOe annealed at 650 °C and 700 °C.

NASA's 2004 Hall Thruster Program

NASA Technical Reports Server (NTRS)

Jacobson, David T.; Manzella, David H.; Hofer, Richard R.; Peterson, Peter Y.

2004-01-01

An overview of NASA's Hall thruster research and development tasks conducted during fiscal year 2004 is presented. These tasks focus on: raising the technology readiness level of high power Hall thrusters, developing a moderate-power/ moderate specific impulse Hall thruster, demonstrating high-power/high specific impulse Hall thruster operation, and addressing the fundamental technical challenges of emerging Hall thruster concepts. Programmatic background information, technical accomplishments and out year plans for each program element performed under the sponsorship of the In-Space Transportation Program, Project Prometheus, and the Energetics Project are provided.

Two-component quantum Hall effects in topological flat bands

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zeng, Tian-Sheng; Zhu, Wei; Sheng, D. N.

2017-03-27

Here in this paper, we study quantum Hall states for two-component particles (hardcore bosons and fermions) loading in topological lattice models. By tuning the interplay of interspecies and intraspecies interactions, we demonstrate that two-component fractional quantum Hall states emerge at certain fractional filling factors ν = 1/2 for fermions (ν = 2/3 for bosons) in the lowest Chern band, classified by features from ground states including the unique Chern number matrix (inverse of the K matrix), the fractional charge and spin pumpings, and two parallel propagating edge modes. Moreover, we also apply our strategy to two-component fermions at integer fillingmore » factor ν = 2 , where a possible topological Neel antiferromagnetic phase is under intense debate very recently. For the typical π -flux checkerboard lattice, by tuning the onsite Hubbard repulsion, we establish a first-order phase transition directly from a two-component fermionic ν = 2 quantum Hall state at weak interaction to a topologically trivial antiferromagnetic insulator at strong interaction, and therefore exclude the possibility of an intermediate topological phase for our system.« less

Inverse spin Hall and spin rectification effects in NiFe/FeMn exchange-biased thin films

NASA Astrophysics Data System (ADS)

Garcia, W. J. S.; Seeger, R. L.; da Silva, R. B.; Harres, A.

2017-11-01

Materials presenting high spin-orbit coupling are able to convert spin currents in charge currents. The phenomenon, known as inverse spin Hall effect, promises to revolutionize spintronic technology enabling the electrical detection of spin currents. It has been observed in a variety of systems, usually non-magnetic metals. We study the voltage emerging in exchange biased Ta/NiFe/FeMn/Ta thin films near the ferromagnetic resonance. Measured signals are related to both inverse spin Hall and spin rectification effects, and two distinct protocols were employed to separate their contributions.The curve shift due to the exchange bias effect may enable high frequency applications without an external applied magnetic field.

Hall effect and fine structures in magnetic reconnection with high plasma {beta}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jin, S.P.; Yang, H.A.; Wang, X.G.

2005-04-15

Magnetic reconnection with various plasma {beta} (the ratio of plasma pressure to the magnetic pressure) is studied numerically using a 2.5 dimensional Hall magnetohydrodynamics (MHD) code developed from a multistep implicit scheme. The initial state of the Hall MHD simulation is an equilibrium Harris sheet with L{sub c}=0.5d{sub i} (where L{sub c} is the half-width of the equilibrium current layer and d{sub i} is the ion inertial length) and a zero guide field (i.e., B{sub y0}=0 at t=0). Driven by a constant boundary inflow a quasisteady fast reconnection occurs in the plasma with a low uniform resistivity. The out-of-plane magneticmore » field component B{sub y} is then spontaneously generated and its quadrupolar structure is shown around the X point. It is demonstrated by the comparing studies that the reconnection dynamics is controlled by the Hall effect and the effect of scalar electron pressure gradient is negligible in the generalized Ohm's law. It is also found that the openness of the magnetic separatrix angle and associated quadrupolar B{sub y} structure is enlarged as {beta} increases. When {beta}>2.0 fine structures of B{sub y} contours with reversed sign emerge. The numerical results indicate that the variations in electron velocity V{sub e} are greater than those in ion velocity V{sub i} and the decoupling of electron and ion occurs in larger scale lengths than d{sub i} as {beta} increases. Clearly, the reserve current, which is associated with the relative motion between electrons and ions, generates the fine structures of B{sub y} contours in the outflow region. Then the corresponding profile of B{sub y} component exhibits a static whistler wave signature. Enhanced wave activities observed during a Cluster crossing of the high-{beta} exterior cusp region [Y. Khotyaintsev, A. Vaivads, Y. Ogawa, B. Popielawska, M. Andre, S. Buchert, P. Decreau, B. Lavraud, and H. Reme, Ann. Geophys. 22, 2403 (2004)] might be related to the Hall effects of magnetic

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bestwick, A. J.; Fox, E. J.; Kou, Xufeng

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 bymore » cooling the sample below the dilution refrigerator base temperature in a process approximating adiabatic demagnetization refrigeration.« less

2-Step scalar deadzone quantization for bitplane image coding.

PubMed

Auli-Llinas, Francesc

2013-12-01

Modern lossy image coding systems generate a quality progressive codestream that, truncated at increasing rates, produces an image with decreasing distortion. Quality progressivity is commonly provided by an embedded quantizer that employs uniform scalar deadzone quantization (USDQ) together with a bitplane coding strategy. This paper introduces a 2-step scalar deadzone quantization (2SDQ) scheme that achieves same coding performance as that of USDQ while reducing the coding passes and the emitted symbols of the bitplane coding engine. This serves to reduce the computational costs of the codec and/or to code high dynamic range images. The main insights behind 2SDQ are the use of two quantization step sizes that approximate wavelet coefficients with more or less precision depending on their density, and a rate-distortion optimization technique that adjusts the distortion decreases produced when coding 2SDQ indexes. The integration of 2SDQ in current codecs is straightforward. The applicability and efficiency of 2SDQ are demonstrated within the framework of JPEG2000.

Third Quantization and Quantum Universes

NASA Astrophysics Data System (ADS)

Kim, Sang Pyo

2014-01-01

We study the third quantization of the Friedmann-Robertson-Walker cosmology with N-minimal massless fields. The third quantized Hamiltonian for the Wheeler-DeWitt equation in the minisuperspace consists of infinite number of intrinsic time-dependent, decoupled oscillators. The Hamiltonian has a pair of invariant operators for each universe with conserved momenta of the fields that play a role of the annihilation and the creation operators and that construct various quantum states for the universe. The closed universe exhibits an interesting feature of transitions from stable states to tachyonic states depending on the conserved momenta of the fields. In the classical forbidden unstable regime, the quantum states have googolplex growing position and conjugate momentum dispersions, which defy any measurements of the position of the universe.

Quantization selection in the high-throughput H.264/AVC encoder based on the RD

NASA Astrophysics Data System (ADS)

Pastuszak, Grzegorz

2013-10-01

In the hardware video encoder, the quantization is responsible for quality losses. On the other hand, it allows the reduction of bit rates to the target one. If the mode selection is based on the rate-distortion criterion, the quantization can also be adjusted to obtain better compression efficiency. Particularly, the use of Lagrangian function with a given multiplier enables the encoder to select the most suitable quantization step determined by the quantization parameter QP. Moreover, the quantization offset added before discarding the fraction value after quantization can be adjusted. In order to select the best quantization parameter and offset in real time, the HD/SD encoder should be implemented in the hardware. In particular, the hardware architecture should embed the transformation and quantization modules able to process the same residuals many times. In this work, such an architecture is used. Experimental results show what improvements in terms of compression efficiency are achievable for Intra coding.

Hysteretic magnetoresistance and unconventional anomalous Hall effect in the frustrated magnet TmB 4

DOE PAGES

Sunku, Sai Swaroop; Kong, Tai; Ito, Toshimitsu; ...

2016-05-11

We study TmB 4, 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.

Group theoretical quantization of isotropic loop cosmology

NASA Astrophysics Data System (ADS)

Livine, Etera R.; Martín-Benito, Mercedes

2012-06-01

We achieve a group theoretical quantization of the flat Friedmann-Robertson-Walker model coupled to a massless scalar field adopting the improved dynamics of loop quantum cosmology. Deparemetrizing the system using the scalar field as internal time, we first identify a complete set of phase space observables whose Poisson algebra is isomorphic to the su(1,1) Lie algebra. It is generated by the volume observable and the Hamiltonian. These observables describe faithfully the regularized phase space underlying the loop quantization: they account for the polymerization of the variable conjugate to the volume and for the existence of a kinematical nonvanishing minimum volume. Since the Hamiltonian is an element in the su(1,1) Lie algebra, the dynamics is now implemented as SU(1, 1) transformations. At the quantum level, the system is quantized as a timelike irreducible representation of the group SU(1, 1). These representations are labeled by a half-integer spin, which gives the minimal volume. They provide superselection sectors without quantization anomalies and no factor ordering ambiguity arises when representing the Hamiltonian. We then explicitly construct SU(1, 1) coherent states to study the quantum evolution. They not only provide semiclassical states but truly dynamical coherent states. Their use further clarifies the nature of the bounce that resolves the big bang singularity.

Quantum hall ferromagnets

NASA Astrophysics Data System (ADS)

Kumar, Akshay

We study several quantum phases that are related to the quantum Hall effect. Our initial focus is on a pair of quantum Hall ferromagnets where the quantum Hall ordering occurs simultaneously with a spontaneous breaking of an internal symmetry associated with a semiconductor valley index. In our first example ---AlAs heterostructures--- we study domain wall structure, role of random-field disorder and dipole moment physics. Then in the second example ---Si(111)--- we show that symmetry breaking near several integer filling fractions involves a combination of selection by thermal fluctuations known as "order by disorder" and a selection by the energetics of Skyrme lattices induced by moving away from the commensurate fillings, a mechanism we term "order by doping". We also study ground state of such systems near filling factor one in the absence of valley Zeeman energy. We show that even though the lowest energy charged excitations are charge one skyrmions, the lowest energy skyrmion lattice has charge > 1 per unit cell. We then broaden our discussion to include lattice systems having multiple Chern number bands. We find analogs of quantum Hall ferromagnets in the menagerie of fractional Chern insulator phases. Unlike in the AlAs system, here the domain walls come naturally with gapped electronic excitations. We close with a result involving only topology: we show that ABC stacked multilayer graphene placed on boron nitride substrate has flat bands with non-zero local Berry curvature but zero Chern number. This allows access to an interaction dominated system with a non-trivial quantum distance metric but without the extra complication of a non-zero Chern number.

Covariant effective action for a Galilean invariant quantum Hall system

NASA Astrophysics Data System (ADS)

Geracie, Michael; Prabhu, Kartik; Roberts, Matthew M.

2016-09-01

We construct effective field theories for gapped quantum Hall systems coupled to background geometries with local Galilean invariance i.e. Bargmann spacetimes. Along with an electromagnetic field, these backgrounds include the effects of curved Galilean spacetimes, including torsion and a gravitational field, allowing us to study charge, energy, stress and mass currents within a unified framework. A shift symmetry specific to single constituent theories constraints the effective action to couple to an effective background gauge field and spin connection that is solved for by a self-consistent equation, providing a manifestly covariant extension of Hoyos and Son's improvement terms to arbitrary order in m.

Covariant effective action for a Galilean invariant quantum Hall system

DOE PAGES

Geracie, Michael; Prabhu, Kartik; Roberts, Matthew M.

2016-09-16

Here, we construct effective field theories for gapped quantum Hall systems coupled to background geometries with local Galilean invariance i.e. Bargmann spacetimes. Along with an electromagnetic field, these backgrounds include the effects of curved Galilean spacetimes, including torsion and a gravitational field, allowing us to study charge, energy, stress and mass currents within a unified framework. A shift symmetry specific to single constituent theories constraints the effective action to couple to an effective background gauge field and spin connection that is solved for by a self-consistent equation, providing a manifestly covariant extension of Hoyos and Son’s improvement terms to arbitrarymore » order in m.« less

Geometrical optics of beams with vortices: Berry phase and orbital angular momentum Hall effect.

PubMed

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.

Magnon Hall effect on the Lieb lattice.

PubMed

Cao, Xiaodong; Chen, Kai; He, Dahai

2015-04-29

Ferromagnetic insulators without inversion symmetry may show magnon Hall effect (MHE) in the presence of a temperature gradient due to the existence of Dzyaloshinskii-Moriya interaction (DMI). In this theoretical study, we investigate MHE on a lattice with inversion symmetry, namely the Lieb lattice, where the DMI is introduced by adding an external electric field. We show the nontrivial topology of this model by examining the existence of edge states and computing the topological phase diagram characterized by the Chern numbers of different bands. Together with the topological phase diagram, we can further determine the sign and magnitude of the transverse thermal conductivity. The impact of the flat band possessed by this model on the thermal conductivity is discussed by computing the Berry curvature analytically.

Model predictive control of non-linear systems over networks with data quantization and packet loss.

PubMed

Yu, Jimin; Nan, Liangsheng; Tang, Xiaoming; Wang, Ping

2015-11-01

This paper studies the approach of model predictive control (MPC) for the non-linear systems under networked environment where both data quantization and packet loss may occur. The non-linear controlled plant in the networked control system (NCS) is represented by a Tagaki-Sugeno (T-S) model. The sensed data and control signal are quantized in both links and described as sector bound uncertainties by applying sector bound approach. Then, the quantized data are transmitted in the communication networks and may suffer from the effect of packet losses, which are modeled as Bernoulli process. A fuzzy predictive controller which guarantees the stability of the closed-loop system is obtained by solving a set of linear matrix inequalities (LMIs). A numerical example is given to illustrate the effectiveness of the proposed method. Copyright © 2015 ISA. Published by Elsevier Ltd. All rights reserved.

Theoretical study of spin Hall effect in conjugated Organic semiconductors

NASA Astrophysics Data System (ADS)

Mahani, M. R.; Delin, A.

The spin Hall effect (SHE), a direct conversion between electronic and spin currents, is a rapidly growing branch of spintronics. The study of SHE in conjugated polymers has gained momentum recently due to the weak spin-orbit couplings and hyperfine interactions in these materials. Our calculations of SHE based on the recent work, are the result of the misalignment of pi-orbitals in triads consisting of three molecules. In disordered organics, where the electronic conduction is through hopping of the electrons among randomly oriented molecules, instead of identifying a hopping triad to represent the entire system, we numerically solve the master equations for electrical and spin hall conductivities by summing the contributions from all triads in a sufficiently large system. The interference between the direct and indirect hoppings in these triads leads to SHE proportional to the orientation vector of molecule at the first order of spin-orbit coupling. Hence, our results show, the degree of molecular alignment as well as the strength of the spin-orbit coupling can be used to control the SHE in organics.

Uniform quantized electron gas

NASA Astrophysics Data System (ADS)

Høye, Johan S.; Lomba, Enrique

2016-10-01

In this work we study the correlation energy of the quantized electron gas of uniform density at temperature T  =  0. To do so we utilize methods from classical statistical mechanics. The basis for this is the Feynman path integral for the partition function of quantized systems. With this representation the quantum mechanical problem can be interpreted as, and is equivalent to, a classical polymer problem in four dimensions where the fourth dimension is imaginary time. Thus methods, results, and properties obtained in the statistical mechanics of classical fluids can be utilized. From this viewpoint we recover the well known RPA (random phase approximation). Then to improve it we modify the RPA by requiring the corresponding correlation function to be such that electrons with equal spins can not be on the same position. Numerical evaluations are compared with well known results of a standard parameterization of Monte Carlo correlation energies.

Magnesium Hall Thruster

NASA Technical Reports Server (NTRS)

Szabo, James J.

2015-01-01

This Phase II project is developing a magnesium (Mg) Hall effect thruster system that would open the door for in situ resource utilization (ISRU)-based solar system exploration. Magnesium is light and easy to ionize. For a Mars- Earth transfer, the propellant mass savings with respect to a xenon Hall effect thruster (HET) system are enormous. Magnesium also can be combusted in a rocket with carbon dioxide (CO2) or water (H2O), enabling a multimode propulsion system with propellant sharing and ISRU. In the near term, CO2 and H2O would be collected in situ on Mars or the moon. In the far term, Mg itself would be collected from Martian and lunar regolith. In Phase I, an integrated, medium-power (1- to 3-kW) Mg HET system was developed and tested. Controlled, steady operation at constant voltage and power was demonstrated. Preliminary measurements indicate a specific impulse (Isp) greater than 4,000 s was achieved at a discharge potential of 400 V. The feasibility of delivering fluidized Mg powder to a medium- or high-power thruster also was demonstrated. Phase II of the project evaluated the performance of an integrated, highpower Mg Hall thruster system in a relevant space environment. Researchers improved the medium power thruster system and characterized it in detail. Researchers also designed and built a high-power (8- to 20-kW) Mg HET. A fluidized powder feed system supporting the high-power thruster was built and delivered to Busek Company, Inc.

Density-Dependent Quantized Least Squares Support Vector Machine for Large Data Sets.

PubMed

Nan, Shengyu; Sun, Lei; Chen, Badong; Lin, Zhiping; Toh, Kar-Ann

2017-01-01

Based on the knowledge that input data distribution is important for learning, a data density-dependent quantization scheme (DQS) is proposed for sparse input data representation. The usefulness of the representation scheme is demonstrated by using it as a data preprocessing unit attached to the well-known least squares support vector machine (LS-SVM) for application on big data sets. Essentially, the proposed DQS adopts a single shrinkage threshold to obtain a simple quantization scheme, which adapts its outputs to input data density. With this quantization scheme, a large data set is quantized to a small subset where considerable sample size reduction is generally obtained. In particular, the sample size reduction can save significant computational cost when using the quantized subset for feature approximation via the Nyström method. Based on the quantized subset, the approximated features are incorporated into LS-SVM to develop a data density-dependent quantized LS-SVM (DQLS-SVM), where an analytic solution is obtained in the primal solution space. The developed DQLS-SVM is evaluated on synthetic and benchmark data with particular emphasis on large data sets. Extensive experimental results show that the learning machine incorporating DQS attains not only high computational efficiency but also good generalization performance.

Optimum Design Rules for CMOS Hall Sensors

PubMed Central

Crescentini, Marco; Biondi, Michele; Romani, Aldo; Tartagni, Marco; Sangiorgi, Enrico

2017-01-01

This manuscript analyzes the effects of design parameters, such as aspect ratio, doping concentration and bias, on the performance of a general CMOS Hall sensor, with insight on current-related sensitivity, power consumption, and bandwidth. The article focuses on rectangular-shaped Hall probes since this is the most general geometry leading to shape-independent results. The devices are analyzed by means of 3D-TCAD simulations embedding galvanomagnetic transport model, which takes into account the Lorentz force acting on carriers due to a magnetic field. Simulation results define a set of trade-offs and design rules that can be used by electronic designers to conceive their own Hall probes. PMID:28375191

Optimum Design Rules for CMOS Hall Sensors.

PubMed

Crescentini, Marco; Biondi, Michele; Romani, Aldo; Tartagni, Marco; Sangiorgi, Enrico

2017-04-04

This manuscript analyzes the effects of design parameters, such as aspect ratio, doping concentration and bias, on the performance of a general CMOS Hall sensor, with insight on current-related sensitivity, power consumption, and bandwidth. The article focuses on rectangular-shaped Hall probes since this is the most general geometry leading to shape-independent results. The devices are analyzed by means of 3D-TCAD simulations embedding galvanomagnetic transport model, which takes into account the Lorentz force acting on carriers due to a magnetic field. Simulation results define a set of trade-offs and design rules that can be used by electronic designers to conceive their own Hall probes.

Spin Hall and Nernst effects of Weyl magnons

NASA Astrophysics Data System (ADS)

Zyuzin, Vladimir A.; Kovalev, Alexey A.

2018-05-01

In this paper, we present a simple model of a three-dimensional insulating magnetic structure which represents a magnonic analog of the layered electronic system described by A. A. Burkov and L. Balents [Phys. Rev. Lett. 107, 127205 (2011), 10.1103/PhysRevLett.107.127205]. In particular, our model realizes Weyl magnons as well as surface states with a Dirac spectrum. In this model, the Dzyaloshinskii-Moriya interaction is responsible for the separation of opposite Weyl points in momentum space. We calculate the intrinsic (due to the Berry curvature) transport properties of Weyl and so-called anomalous Hall effect magnons. The results are compared with fermionic analogs.

First Observation of a Hall Effect in a Dusty Plasma: A Charged Granular Flow with Relevance to Planetary Rings

NASA Astrophysics Data System (ADS)

Eiskowitz, Skylar; Ballew, Nolan; Rojas, Rubén; Lathrop, Daniel

2017-11-01

The particles in Saturn's rings exhibit complex dynamic behavior. They experience solar radiation pressure, electromagnetic forces, and granular collisions. To investigate the possibility of the Hall Effect in the dusty plasma that comprise Saturn's rings, we have built an experiment that demonstrates the Hall Effect in granular matter. We focus on the Hall Effect because the rings' grains become collisionally charged and experience Saturn's dipolar magnetic field and Lorentz forces as they orbit. The experimental setup includes a closed ring-like track where granular matter is forced to circulate driven by compressed air. The structure sits between two electromagnets so that a portion of the track experiences up to a 0.2 T magnetic field. We vary the strength of the field and the speed of the particles. We report the voltage differences between two conducting plates on opposite sides of the track. If Saturn's rings do experience the Hall Effect, the inside and outside of the rings will develop a charge separation that can lead to a radial electric field and various phenomena including orbital effects due to the additional electric forces. Observational evidence from Cassini suggests that Saturn's rings exhibit lighting, supporting the notion that they are electrically charged. TREND REU program sponsored by the National Science Foundation.

Adaptive robust fault tolerant control design for a class of nonlinear uncertain MIMO systems with quantization.

PubMed

Ao, Wei; Song, Yongdong; Wen, Changyun

2017-05-01

In this paper, we investigate the adaptive control problem for a class of nonlinear uncertain MIMO systems with actuator faults and quantization effects. Under some mild conditions, an adaptive robust fault-tolerant control is developed to compensate the affects of uncertainties, actuator failures and errors caused by quantization, and a range of the parameters for these quantizers is established. Furthermore, a Lyapunov-like approach is adopted to demonstrate that the ultimately uniformly bounded output tracking error is guaranteed by the controller, and the signals of the closed-loop system are ensured to be bounded, even in the presence of at most m-q actuators stuck or outage. Finally, numerical simulations are provided to verify and illustrate the effectiveness of the proposed adaptive schemes. Copyright © 2017 ISA. Published by Elsevier Ltd. All rights reserved.

BFV-BRST quantization of two-dimensional supergravity

NASA Astrophysics Data System (ADS)

Fujiwara, T.; Igarashi, Y.; Kuriki, R.; Tabei, T.

1996-01-01

Two-dimensional supergravity theory is quantized as an anomalous gauge theory. In the Batalin-Fradkin (BF) formalism, the anomaly-canceling super-Liouville fields are introduced to identify the original second-class constrained system with a gauge-fixed version of a first-class system. The BFV-BRST quantization applies to formulate the theory in the most general class of gauges. A local effective action constructed in the configuration space contains two super-Liouville actions; one is a noncovariant but local functional written only in terms of two-dimensional supergravity fields, and the other contains the super-Liouville fields canceling the super-Weyl anomaly. Auxiliary fields for the Liouville and the gravity supermultiplets are introduced to make the BRST algebra close off-shell. Inclusion of them turns out to be essentially important especially in the super-light-cone gauge fixing, where the supercurvature equations (∂3-g++=∂2-χ++=0) are obtained as a result of BRST invariance of the theory. Our approach reveals the origin of the OSp(1,2) current algebra symmetry in a transparent manner.

Electronic quantization in dielectric nanolaminates

NASA Astrophysics Data System (ADS)

Willemsen, T.; Geerke, P.; Jupé, M.; Gallais, L.; Ristau, D.

2016-12-01

The scientific background in the field of the laser induced damage processes in optical coatings has been significantly extended during the last decades. Especially for the ultra-short pulse regime a clear correlation between the electronic material parameters and the laser damage threshold could be demonstrated. In the present study, the quantization in nanolaminates is investigated to gain a deeper insight into the behavior of the blue shift of the bandgap in specific coating materials as well as to find approximations for the effective mass of the electrons. The theoretical predictions are correlated to the measurements.

Precision Tests of a Quantum Hall Effect Device DC Equivalent Circuit Using Double-Series and Triple-Series Connections

PubMed Central

Jeffery, A.; Elmquist, R. E.; Cage, M. E.

1995-01-01

Precision tests verify the dc equivalent circuit used by Ricketts and Kemeny to describe a quantum Hall effect device in terms of electrical circuit elements. The tests employ the use of cryogenic current comparators and the double-series and triple-series connection techniques of Delahaye. Verification of the dc equivalent circuit in double-series and triple-series connections is a necessary step in developing the ac quantum Hall effect as an intrinsic standard of resistance. PMID:29151768

Giant spin Hall effect in graphene grown by chemical vapour deposition

NASA Astrophysics Data System (ADS)

Balakrishnan, Jayakumar; Koon, Gavin Kok Wai; Avsar, Ahmet; Ho, Yuda; Lee, Jong Hak; Jaiswal, Manu; Baeck, Seung-Jae; Ahn, Jong-Hyun; Ferreira, Aires; Cazalilla, Miguel A.; Neto, Antonio H. Castro; Özyilmaz, Barbaros

2014-09-01

Advances in large-area graphene synthesis via chemical vapour deposition on metals like copper were instrumental in the demonstration of graphene-based novel, wafer-scale electronic circuits and proof-of-concept applications such as flexible touch panels. Here, we show that graphene grown by chemical vapour deposition on copper is equally promising for spintronics applications. In contrast to natural graphene, our experiments demonstrate that chemically synthesized graphene has a strong spin-orbit coupling as high as 20 meV giving rise to a giant spin Hall effect. The exceptionally large spin Hall angle ~0.2 provides an important step towards graphene-based spintronics devices within existing complementary metal-oxide-semiconductor technology. Our microscopic model shows that unavoidable residual copper adatom clusters act as local spin-orbit scatterers and, in the resonant scattering limit, induce transverse spin currents with enhanced skew-scattering contribution. Our findings are confirmed independently by introducing metallic adatoms-copper, silver and gold on exfoliated graphene samples.

Superfield quantization

NASA Astrophysics Data System (ADS)

Batalin, I. A.; Bering, K.; Damgaard, P. H.

1998-03-01

We present a superfield formulation of the quantization program for theories with first-class constraints. An exact operator formulation is given, and we show how to set up a phase-space path integral entirely in terms of superfields. BRST transformations and canonical transformations enter on equal footing, and they allow us to establish a superspace analog of the BFV theorem. We also present a formal derivation of the Lagrangian superfield analogue of the field-antifield formalism by an integration over half of the phase-space variables.

Copenhagen's single system premise prevents a unified view of integer and fractional quantum hall effect

NASA Astrophysics Data System (ADS)

Post, Evert Jan

1999-05-01

This essay presents conclusive evidence of the impermissibility of Copenhagen's single system interpretation of the Schroedinger process. The latter needs to be viewed as a tool exclusively describing phase and orientation randomized ensembles and is not be used for isolated single systems. Asymptotic closeness of single system and ensemble behavior and the rare nature of true single system manifestations have prevented a definitive identification of this Copenhagen deficiency over the past three quarter century. Quantum uncertainty so becomes a basic trade mark of phase and orientation disordered ensembles. The ensuing void of usable single system tools opens a new inquiry for tools without statistical connotations. Three, in part already known, period integrals here identified as flux, charge and action counters emerge as diffeo-4 invariant tools fully compatible with the demands of the general theory of relativity. The discovery of the quantum Hall effect has been instrumental in forcing a distinction between ensemble disorder as in the normal Hall effect versus ensemble order in the plateau states. Since the order of the latter permits a view of the plateau states as a macro- or meso-scopic single system, the period integral description applies, yielding a straightforward unified description of integer and fractional quantum Hall effects.

Quantum Hall Effect near the Charge Neutrality Point in a Two-Dimensional Electron-Hole System

NASA Astrophysics Data System (ADS)

Gusev, G. M.; Olshanetsky, E. B.; Kvon, Z. D.; Mikhailov, N. N.; Dvoretsky, S. A.; Portal, J. C.

2010-04-01

We study the transport properties of HgTe-based quantum wells containing simultaneously electrons and holes in a magnetic field B. At the charge neutrality point (CNP) with nearly equal electron and hole densities, the resistance is found to increase very strongly with B while the Hall resistivity turns to zero. This behavior results in a wide plateau in the Hall conductivity σxy≈0 and in a minimum of diagonal conductivity σxx at ν=νp-νn=0, where νn and νp are the electron and hole Landau level filling factors. We suggest that the transport at the CNP point is determined by electron-hole “snake states” propagating along the ν=0 lines. Our observations are qualitatively similar to the quantum Hall effect in graphene as well as to the transport in a random magnetic field with a zero mean value.

Sheath oscillation characteristics and effect on near-wall conduction in a krypton Hall thruster

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Fengkui, E-mail: fengkuizhang@163.com; Kong, Lingyi; Li, Chenliang

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.more » 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.« less

Iodine Plasma Species Measurements in a Hall Effect Thruster Plume

DTIC Science & Technology

2013-04-01

direction f = species fraction 0g = gravitational constant at Earth’s surface, 9.81 m/s 2 I = current, subscripts b for beam, c for cathode, d for...Hall effect thruster uses crossed electric and magnetic fields to generate and accelerate ions. The gas in the discharge is partially ionized, although...early 1960s.10 Ions are weakly magnetized and most are accelerated directly out of the channel, forming the ion beam. The bulk of the cathode

4D Sommerfeld quantization of the complex extended charge

NASA Astrophysics Data System (ADS)

Bulyzhenkov, Igor E.

2017-12-01

Gravitational fields and accelerations cannot change quantized magnetic flux in closed line contours due to flat 3D section of curved 4D space-time-matter. The relativistic Bohr-Sommerfeld quantization of the imaginary charge reveals an electric analog of the Compton length, which can introduce quantitatively the fine structure constant and the Plank length.

Enhanced thermoelectric response in the fractional quantum Hall effect

NASA Astrophysics Data System (ADS)

Roura-Bas, Pablo; Arrachea, Liliana; Fradkin, Eduardo

2018-02-01

We study the linear thermoelectric response of a quantum dot embedded in a constriction of a quantum Hall bar with fractional filling factors ν =1 /m within Laughlin series. We calculate the figure of merit Z T for the maximum efficiency at a fixed temperature difference. We find a significant enhancement of this quantity in the fractional filling in relation to the integer-filling case, which is a direct consequence of the fractionalization of the electron in the fractional quantum Hall state. We present simple theoretical expressions for the Onsager coefficients at low temperatures, which explicitly show that Z T and the Seebeck coefficient increase with m .

The shear-Hall instability in newborn neutron stars

NASA Astrophysics Data System (ADS)

Kondić, T.; Rüdiger, G.; Hollerbach, R.

2011-11-01

Aims: In the first few minutes of a newborn neutron star's life the Hall effect and differential rotation may both be important. We demonstrate that these two ingredients are sufficient for generating a "shear-Hall instability" and for studying its excitation conditions, growth rates, and characteristic magnetic field patterns. Methods: We numerically solve the induction equation in a spherical shell, with a kinematically prescribed differential rotation profile Ω(s), where s is the cylindrical radius. The Hall term is linearized about an imposed uniform axial field. The linear stability of individual azimuthal modes, both axisymmetric and non-axisymmetric, is then investigated. Results: For the shear-Hall instability to occur, the axial field must be parallel to the rotation axis if Ω(s) decreases outward, whereas if Ω(s) increases outward it must be anti-parallel. The instability draws its energy from the differential rotation, and occurs on the short rotational timescale rather than on the much longer Hall timescale. It operates most efficiently if the Hall time is comparable to the diffusion time. Depending on the precise field strengths B0, either axisymmetric or non-axisymmetric modes may be the most unstable. Conclusions: Even if the differential rotation in newborn neutron stars is quenched within minutes, the shear-Hall instability may nevertheless amplify any seed magnetic fields by many orders of magnitude.

Quantized Chiral Magnetic Current from Reconnections of Magnetic Flux.

PubMed

Hirono, Yuji; Kharzeev, Dmitri E; Yin, Yi

2016-10-21

We introduce a new mechanism for the chiral magnetic effect that does not require an initial chirality imbalance. The chiral magnetic current is generated by reconnections of magnetic flux that change the magnetic helicity of the system. The resulting current is entirely determined by the change of magnetic helicity, and it is quantized.

Dissipation and quantization for composite systems

NASA Astrophysics Data System (ADS)

Blasone, Massimo; Jizba, Petr; Scardigli, Fabio; Vitiello, Giuseppe

2009-11-01

In the framework of 't Hooft's quantization proposal, we show how to obtain from the composite system of two classical Bateman's oscillators a quantum isotonic oscillator. In a specific range of parameters, such a system can be interpreted as a particle in an effective magnetic field, interacting through a spin-orbit interaction term. In the limit of a large separation from the interaction region one can describe the system in terms of two irreducible elementary subsystems which correspond to two independent quantum harmonic oscillators.

't Hooft Quantization for Interacting Systems

NASA Astrophysics Data System (ADS)

Jizba, Petr; Scardigli, Fabio; Blasone, Massimo; Vitiello, Giuseppe

2012-02-01

In the framework of 't Hooft's "deterministic quantization" proposal, we show how to obtain from a composite system of two classical Bateman's oscillators a quantum isotonic oscillator. In a specific range of parameters, such a system can be also interpreted as a particle in an effective magnetic field, interacting through a spin-orbit interaction term. In the limit of a large separation from the interaction region, the system can be described in terms of two irreducible elementary subsystems, corresponding to two independent quantum harmonic oscillators.

Hall-Effect Measurements Probing the Degree of Charge-Carrier Delocalization in Solution-Processed Crystalline Molecular Semiconductors

NASA Astrophysics Data System (ADS)

Chang, Jui-Fen; Sakanoue, Tomo; Olivier, Yoann; Uemura, Takafumi; Dufourg-Madec, Marie-Beatrice; Yeates, Stephen G.; Cornil, Jérôme; Takeya, Jun; Troisi, Alessandro; Sirringhaus, Henning

2011-08-01

Intramolecular structure and intermolecular packing in crystalline molecular semiconductors should have profound effects on the charge-carrier wave function, but simple drift mobility measurements are not very sensitive to this. Here we show that differences in the Hall resistance of two soluble pentacene derivatives can be explained with different degrees of carrier delocalization being limited by thermal lattice fluctuations. A combination of Hall measurements, optical spectroscopy, and theoretical simulations provides a powerful probe of structure-property relationships at a molecular level.

Chiral transport along magnetic domain walls in the quantum anomalous Hall effect

DOE PAGES

Rosen, Ilan T.; Fox, Eli J.; Kou, Xufeng; ...

2017-12-01

The recent prediction, and subsequent discovery, of the quantum anomalous Hall (QAH) effect in thin films of the three-dimensional ferromagnetic topological insulator (MTI) (Crmore » $$_y$$Bi$$_x$$Sb$$_{1-x-y}$$)$$_2$$Te$$_3$$ has opened new possibilities for chiral-edge-state-based devices in zero external magnetic field. Like the $$\

Time-Symmetric Quantization in Spacetimes with Event Horizons

NASA Astrophysics Data System (ADS)

Kobakhidze, Archil; Rodd, Nicholas

2013-08-01

The standard quantization formalism in spacetimes with event horizons implies a non-unitary evolution of quantum states, as initial pure states may evolve into thermal states. This phenomenon is behind the famous black hole information loss paradox which provoked long-standing debates on the compatibility of quantum mechanics and gravity. In this paper we demonstrate that within an alternative time-symmetric quantization formalism thermal radiation is absent and states evolve unitarily in spacetimes with event horizons. We also discuss the theoretical consistency of the proposed formalism. We explicitly demonstrate that the theory preserves the microcausality condition and suggest a "reinterpretation postulate" to resolve other apparent pathologies associated with negative energy states. Accordingly as there is a consistent alternative, we argue that choosing to use time-asymmetric quantization is a necessary condition for the black hole information loss paradox.

Large anomalous Hall effect in Pt interfaced with perpendicular anisotropy ferrimagnetic insulator

NASA Astrophysics Data System (ADS)

Tang, Chi; Sellappan, Pathikumar; Liu, Yawen; Garay, Javier; Shi, Jing; Shines Team

We demonstrate the strain induced perpendicular magnetic anisotropy (PMA) in a ferrimagnetic insulator (FMI), Tm3Fe5O12 (TIG) and the first observation of large anomalous Hall effect (AHE) in TIG/Pt bilayers. Atomically flat TIG films were deposited by a laser molecular beam epitaxy system on (111)-orientated substituted gadolinium gallium garnet substrates. The strength of PMA could be effectively tuned by controlling the oxygen pressure during deposition. Sharp squared anomalous Hall hysteresis loops were observed in bilayers of TIG/Pt over a range of thicknesses of Pt, with the maximum AHE conductivity reaching 1 S/cm at room temperature. The AHE vanishes when a 5 nm Cu layer was inserted between Pt and TIG, strongly indicating the proximity-induced ferromagnetism in Pt. The large AHE in the bilayer structures demonstrates a potential use of PMA-FMI related heterostructures in spintronics. This work was supported as part of the SHINES, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # SC0012670.

Generalized radiation-field quantization method and the Petermann excess-noise factor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, Y.-J.; Siegman, A.E.; E.L. Ginzton Laboratory, Stanford University, Stanford, California 94305

2003-10-01

We propose a generalized radiation-field quantization formalism, where quantization does not have to be referenced to a set of power-orthogonal eigenmodes as conventionally required. This formalism can be used to directly quantize the true system eigenmodes, which can be non-power-orthogonal due to the open nature of the system or the gain/loss medium involved in the system. We apply this generalized field quantization to the laser linewidth problem, in particular, lasers with non-power-orthogonal oscillation modes, and derive the excess-noise factor in a fully quantum-mechanical framework. We also show that, despite the excess-noise factor for oscillating modes, the total spatially averaged decaymore » rate for the laser atoms remains unchanged.« less

6D fractional quantum Hall effect

NASA Astrophysics Data System (ADS)

Heckman, Jonathan J.; Tizzano, Luigi

2018-05-01

We present a 6D generalization of the fractional quantum Hall effect involving membranes coupled to a three-form potential in the presence of a large background four-form flux. The low energy physics is governed by a bulk 7D topological field theory of abelian three-form potentials with a single derivative Chern-Simons-like action coupled to a 6D anti-chiral theory of Euclidean effective strings. We derive the fractional conductivity, and explain how continued fractions which figure prominently in the classification of 6D superconformal field theories correspond to a hierarchy of excited states. Using methods from conformal field theory we also compute the analog of the Laughlin wavefunction. Compactification of the 7D theory provides a uniform perspective on various lower-dimensional gapped systems coupled to boundary degrees of freedom. We also show that a supersymmetric version of the 7D theory embeds in M-theory, and can be decoupled from gravity. Encouraged by this, we present a conjecture in which IIB string theory is an edge mode of a 10 + 2-dimensional bulk topological theory, thus placing all twelve dimensions of F-theory on a physical footing.

Topological approach to quantum Hall effects and its important applications: higher Landau levels, graphene and its bilayer

NASA Astrophysics Data System (ADS)

Jacak, Janusz; Łydżba, Patrycja; Jacak, Lucjan

2017-05-01

In this paper the topological approach to quantum Hall effects is carefully described. Commensurability conditions together with proposed generators of a system braid group are employed to establish the fractional quantum Hall effect hierarchies of conventional semiconductors, monolayer and bilayer graphene structures. Obtained filling factors are compared with experimental data and a very good agreement is achieved. Preliminary constructions of ground-state wave functions in the lowest Landau level are put forward. Furthermore, this work explains why pyramids of fillings from higher bands are not counterparts of the well-known composite-fermion hierarchy - it provides with the cause for an intriguing robustness of ν = 7/3 , 8/3 and 5/2 states (also in graphene). The argumentation why paired states can be developed in two-subband systems (wide quantum wells) only when the Fermi energy lies in the first Landau level is specified. Finally, the paper also clarifies how an additional surface in bilayer systems contributes to an observation of the fractional quantum Hall effect near half-filling, ν = 1/2 .

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.

Hall viscosity and electromagnetic response of electrons in graphene

NASA Astrophysics Data System (ADS)

Sherafati, Mohammad; Principi, Alessandro; Vignale, Giovanni

The Hall viscosity is a dissipationless component of the viscosity tensor of an electron liquid with broken time- reversal symmetry, such as a two-dimensional electron gas (2DEG) in the quantum Hall state. Similar to the Hall conductivity, the Hall viscosity is an anomalous transport coefficient; however, while the former is connected with the current response, the latter stems from the stress response to a geometric deformation. For a Galilean-invariant system such as 2DEG, the current density is indeed the generator of the geometric deformation: therefore a connection between the Hall connectivity and viscosity is expected and by now well established. In the case of graphene, a non-Galilean-invariant system, the existence of such a connection is far from obvious, as the current operator is essentially different from the momentum operator. In this talk, I will first present our results of the geometric Hall viscosity of electrons in single-layer graphene. Then, from the expansion of the nonlocal Hall conductivity for small wave vectors, I demonstrate that, in spite of the lack of Galilean invariance, an effective mass can be defined such that the relationship between the Hall conductivity and the viscosity retains the form it has in Galilean-invariant systems, not only for a large number of occupied Landau levels, but also, with very high accuracy, for the undoped system.

Quantized Algebra I Texts

ERIC Educational Resources Information Center

DeBuvitz, William

2014-01-01

I am a volunteer reader at the Princeton unit of "Learning Ally" (formerly "Recording for the Blind & Dyslexic") and I recently discovered that high school students are introduced to the concept of quantization well before they take chemistry and physics. For the past few months I have been reading onto computer files a…

The uniform quantized electron gas revisited

NASA Astrophysics Data System (ADS)

Lomba, Enrique; Høye, Johan S.

2017-11-01

In this article we continue and extend our recent work on the correlation energy of the quantized electron gas of uniform density at temperature T=0 . As before, we utilize the methods, properties, and results obtained by means of classical statistical mechanics. These were extended to quantized systems via the Feynman path integral formalism. The latter translates the quantum problem into a classical polymer problem in four dimensions. Again, the well known RPA (random phase approximation) is recovered as a basic result which we then modify and improve upon. Here we analyze the condition of thermodynamic self-consistency. Our numerical calculations exhibit a remarkable agreement with well known results of a standard parameterization of Monte Carlo correlation energies.

Ensemble Density Functional Approach to the Quantum Hall Effect

NASA Astrophysics Data System (ADS)

Heinonen, O.

1997-03-01

The fractional quantum Hall effect (FQHE) occurs in a two-dimensional electron gas of density n when a strong magnetic field perpendicular to the plane of the electron gas takes on certain strengths B(n). At these magnetic field strengths the system is incompressible, i.e., there is a finite cost in energy for creating charge density fluctuations in the bulk. Even so the boundary of the electron gas supports gapless modes of density waves. The bulk energy gap arises because of the strong electron-electron interactions. There are very good models for infinite homogeneous systems and for the gapless excitations of the boundary of the electron gas. But in order to explain experiments on quantum Hall systems, including Hall bars and quantum dots, new approaches are needed which can accurately describe inhomogeneous systems, including Landau level mixing and the spin degree of freedom. One possibility is an ensemble density functional theory approach that we have developed.(O. Heinonen, M.I. Lubin, and M.D. Johnson, Phys. Rev. Lett. 75), 4110 (1995)(O. Heinonen, M.I. Lubin, and M.D. Johnson, Int. J. Quant. Chem, December 1996) We have applied this to study edge reconstructions of spin-polarized quantum dots. The results for a six-electron test case are in excellent agreement with numerical diagonalizations. For larger systems, compressible and incompressible strips appear as the magnetic field is increased from the region in which a dot forms a compact so-called maximum density droplet. We have recently included spin degree of freedom to study the stability of a maximum density droplet, and charge-spin textures in inhomogeneous systems. As an example, when the Zeeman coupling is decreased, we find that the maximum density droplet develops a spin-structured edge instability. This implies that the spin degree of freedom may play a significant role in the study of edge modes at low or moderate magnetic fields.

Current-Nonlinear Hall Effect and Spin-Orbit Torque Magnetization Switching in a Magnetic Topological Insulator

NASA Astrophysics Data System (ADS)

Yasuda, K.; Tsukazaki, A.; Yoshimi, R.; Kondou, K.; Takahashi, K. S.; Otani, Y.; Kawasaki, M.; Tokura, Y.

2017-09-01

The current-nonlinear Hall effect or second harmonic Hall voltage is widely used as one of the methods for estimating charge-spin conversion efficiency, which is attributed to the magnetization oscillation by spin-orbit torque (SOT). Here, we argue the second harmonic Hall voltage under a large in-plane magnetic field with an in-plane magnetization configuration in magnetic-nonmagnetic topological insulator (TI) heterostructures, Crx (Bi1 -ySby )2 -xTe3 /(Bi1 -ySby )2Te3 , where it is clearly shown that the large second harmonic voltage is governed not by SOT but mainly by asymmetric magnon scattering without macroscopic magnetization oscillation. Thus, this method does not allow an accurate estimation of charge-spin conversion efficiency in TI. Instead, the SOT contribution is exemplified by current pulse induced nonvolatile magnetization switching, which is realized with a current density of 2.5 ×1010 A m-2 , showing its potential as a spintronic material.