Hall Configuration Research Articles

Spin mixing conductance and spin magnetoresistance of the iridate/manganite interface

We present results on experimental studies of spin current, measured under spin pumping at ferromag-netic resonance in wide frequency band 2-20 GHz for SrIrO3/La0.7Sr0.3MnO3 heterostructures fabricated by RF magnetron sputtering at high temperature. The epitaxial growth of the thin film in heterostructure by a cube-on-cube mechanism was confirmed by XRD and TEM analysis. Taking into account the con-tribution of anisotropic magnetoresistance the spin current was estimated as 1/3 of the total response. We show that both real and imaginary parts of spin mixing conductance are valuable for heterostructures with strong spin-orbit interaction in SrIrO3. Imaginary part of spin mixing conductance was estimated by means of shift of ferromagnetic resonance field of La0.7Sr0.3MnO3 layer in heterostructure. The spin mag-netoresistance was evaluated from angular dependencies of magnetoresistance measured in planar Hall configuration. In order to extract the influence of anisotropic magnetoresistance a La0.7Sr0.3MnO3 film was measured as well. The spin Hall angle for heterostructure was found higher than for interface Pt/ La0.7Sr0.3MnO3.

Longitudinal and transverse frictional drag in graphene/ LaAlO3/SrTiO3 heterostructures

Heterostructures composed of different layered materials provide novel opportunities to investigate the electronic correlations between them. Here we investigate frictional drag between graphene and ${\mathrm{LaAlO}}_{3}/{\mathrm{SrTiO}}_{3}$ (LAO/STO) heterostructures. The LAO/STO layer underneath the graphene is rendered conductive using conductive atomic force microscope (c-AFM) lithography, creating a two-layer system in which the LAO serves as an ultrathin ($<$2 nm) insulating barrier. By sourcing current in both the STO layer and graphene layer, Coulomb drag is studied in a wide range, from an STO superconducting region to a graphene quantum Hall region. Pronounced fluctuations in the frictional drag resistance are observed when the STO is superconducting. A large enhancement of drag resistance is observed when the STO becomes superconducting. Pronounced stripelike oscillations in the frictional drag appear in the quantum Hall region, both along the main channel and the transverse (Hall) configuration. The behavior is consistent with numerical simulations that model energy and momentum transfer from the STO layer to the graphene layer. These help to create a platform for graphene-based metamaterials using the programmable LAO/STO interface.

Simulated acoustic characteristics of stage displacements in a shoebox hall: A case study in Cultural Centre Concert Hall in Taipei

Since Berlin Philharmonic Hall opened in 1963, surround hall configuration has been preferred and used worldwide by architects for its dramatic visual appearance and the proximity to stage. However, according to Beranek’s study, the top three concert halls in the world that have the best acoustics are in shoebox shape. To study the acoustic characteristics of stage displacement in a shoebox hall is the objective of this study. A simplified wired-frame model of Cultural Centre Concert Hall in Taipei is used as an example in this study. It is a stunning performing-arts building as mentioned by Beranek. Its seating capacity is 2077 and it is a shoebox hall. Five different stage displacements along the central axis have been used. The original ceiling configuration is used and moved with each stage displacements. Fixed materials and the relevant absorption coefficients are used in the study as well. Acoustic parameters such as music clarity, lateral refraction, early decay time as well as reverberation time (T30) are simulated. The results showed that for the best proximity, as stage and stage ceiling are moved toward the centre of shoebox hall, the simulated T30 could be increased to approximately 1.7 seconds in 1000 Hz. To meet the original T30 design goal in 2.25 s at 1000 Hz, about 600 m2 of NRC 0.88 acoustic panel were used.

Magnetotransport as a diagnostic of spin reorientation: Kagome ferromagnet as a case study

While in most ferro or antiferromagnetic materials there is a unique crystallographic direction, including crystallographically equivalent directions, in which the moments like to point due to spin-orbit coupling, in some, the direction of the spin reorients as a function of a certain physical parameter such as temperature, pressure etc. Fe3Sn2 is a kagome ferromagnet with an onset of ferromagnetism below 650 K, and undergoes a spin reorientation near 150 K. While it is known that the moments in Fe3Sn2 point perpendicular to the kagome plane at high temperatures and parallel to the kagome plane at low temperatures, how the distribution of the magnetic domains in the two different spin orientations evolve throughout the spin reorientation is not well known. Furthermore, while there have been various reports on the magnetotransport properties in the Hall configuration, the angular dependence of magnetoresistance has not been studied so far. In this paper, we have examined the spin reorientation by using anisotropic magnetoresistivity in detail, exploiting the dependence of the resistivity on the direction between magnetization and applied current. We are able to determine the distribution of the magnetic domains as a function of temperature between 360 K to 2 K and the reorientation transition to peak at 120 K. We discover that both out of plane and in plane phases coexist at temperatures around the spin reorientation, indicative of a first order transition. Although the volume of the magnetic domains in the different phases sharply changes at the spin reorientation transition, the electronic structure for a specific magnetization is not influenced by the spin reorientation. In contrast, we observe an electronic transition around 40 K, hitherto unreported, and reflected in both the zero-field resistivity and anisotropic resistivity.

Direct patterning of nitrogen-doped chemical vapor deposited graphene-based microstructures for charge carrier measurements employing femtosecond laser ablation

Chemical vapor deposited nitrogen-doped graphene, transferred onto a SiO2/Si substrate, was selectively patterned by femtosecond laser ablation for the formation of the topology dedicated to charge carrier measurements. Ultrashort 1030 nm wavelength Yb:KGW fs-laser pulses of 22 μJ energy,14 mJ cm−2 fluence, 96% pulse overlap, and a scanning speed of 100 mm s−1, were found to be the optimum regime for the high throughput microstructure ablation in graphene, without surface damage of the substrate in the employed fs-laser micromachining workstation. Optical scanning electron and atomic force microscopy, as well as Raman spectroscopy, were applied to clarify the intensive fs-laser light irradiation effects on graphene and the substrate, and to also verify the quality of the graphene removal. Measurements of magnetotransport properties of the fs-laser ablated nitrogen-doped graphene microstructure in the Hall configuration enabled the determination of the type, as well as concentration of charge carriers in a wide range of temperatures.

Measurement of the Hall effect at nanoscale with three probes.

The Hall effect and its varieties such as quantum, anomalous, and spin Hall effects provide indispensable tools for the characterization of electronic and magnetic properties of materials, metrology, and spintronics. The conventional four-probe Hall configuration is generally not amenable to measurements at nanoscale due to current shunting by the Hall electrodes. We demonstrate that Hall measurements on the nanoscale can be facilitated by the three-probe Hall configuration that avoids the shunting problem. We illustrate the efficiency of the proposed approach with anomalous Hall effect-based measurements of individual activation events during domain wall motion in magnetic films with perpendicular anisotropy.

Robust topological surface transport with weak localization bulk channels in polycrystalline Bi2Te3 films

Bi2Te3 polycrystalline topological insulator films have provided an attractive material platform to investigate topological insulator properties and created new opportunities for novel magneto-electronic device applications. In order to confirm that Bi2Te3 polycrystalline film has a robust topological surface state, and whether such surface Dirac fermions can be protected from localization in transport, we performed a systematic transport measurement and analysis based on a Sn-doped Bi2Te3 polycrystalline film with Hall configuration electrodes. We demonstrated that the electron–electron interaction effect is very strong, which can help realize an insulating ground state. The surface state of the film always exhibits stable weak anti-localization features despite the presence of many structural defects and non-magnetic doping, and the Hall resistance can present a significant nonlinear dependence on magnetic fields. These two characteristics provide significant experimental evidence that the polycrystalline film has a robust topological surface state, and that such surface electrons cannot be localized. Owing to the lack of topological protection, the weak anti-localization transport of bulk electrons cannot be guaranteed, and weak localization behavior may appear in the bulk channels. These results verify that robust topological surface transport in topological insulator polycrystalline films can be accompanied by weak localization bulk channels.

Fractional quantum Hall effect revisited

The topology-based explanation of the fractional quantum Hall effect (FQHE) is summarized. The cyclotron braid subgroups crucial for this approach are introduced in order to identify the origin of the Laughlin correlations in 2D (two-dimensional) Hall systems. Flux-tubes and vortices for composite fermions in their standard constructions are explained in terms of cyclotron braids. The derivation of the hierarchy of the FQHE is proposed by mapping onto the integer effect within the topology-based approach. The experimental observations of the FQHE supporting the cyclotron braid picture are reviewed with a special attention paid to recent experiments with a suspended graphene. The triggering role of a carrier mobility for organization of the fractional state in Hall configuration is emphasized. The prerequisites for the FQHE are indicated including topological conditions substantially increasing the previously accepted set of physical necessities. The explanation of numerical studies by exact diagonalizations of the fractional Chern insulator states is formulated in terms of the topology condition applied to the Berry field flux quantization. Some new ideas withz regard to the synthetic fractional states in the optical lattices are also formulated.

Spin valve effect of the interfacial spin accumulation in yttrium iron garnet/platinum bilayers

We report the spin valve effect in yttrium iron garnet/platinum (YIG/Pt) bilayers. The spin Hall effect (SHE) generates spin accumulation at the YIG/Pt interface and can be opened/closed by magnetization switching in the electrical insulator YIG. The interfacial spin accumulation was measured in both YIG/Pt and YIG/Cu/Pt structures using a planar Hall configuration. The spin valve effect remained, even after a 2 nm thick Cu layer was inserted between the YIG and Pt layers, which aimed to exclude the induced magnetization at the YIG/Pt interface. The transverse Hall voltage and switching field were dependent on the applied charge current density. The origin of this behavior can be explained by the SHE induced torque exerted on the domain wall, caused by the transfer of the spin angular momentum from the spin-polarized current to the YIG magnetic moment.

Generation of a fully valley-polarized current in bulk graphene

The generation of a fully valley-polarized current (FVPC) in bulk graphene is a fundamental goal in valleytronics. To this end, we investigate valley-dependent transport through a strained graphene modulated by a finite magnetic superlattice. It is found that this device allows a coexistence of insulating transmission gap of one valley and metallic resonant band of the other. Accordingly, a substantial bulk FVPC appears in a wide range of edge orientation and temperature, which can be effectively tuned by structural parameters. A valley-resolved Hall configuration is designed to measure the valley polarization degree of the filtered current.

Optimization design of grading ring and electrical field analysis of 800 kV UHVDC Wall wall bushing

This paper has analyzed the reason for the flashover of a typical 800 kV converting transformer bushing. The finite element method is applied to calculate the electric field and potential distribution along HV bushing as well as optimize the design of grading rings for the 800 kV UHVDC bushing. The three-dimensional (3D) model of 800kV bushing with valve hall configuration is established using ANSYS software. According to the calculation of electric field and potential distribution along the bushing without any grading ring, the joint of flange and shed and sheath has higher field intensity, and the electric field is rather unevenly distributed. Afterwards, this paper presents a method of adding a grading ring to the flange side in order to reduce the field intensity around the surface of shed & sheath. This method also optimizes the location and the configuration parameters of the grading ring, with an aim to limit the maximal electric field intensity around the metal fitting and the grading ring and obtain the optimal design of grading ring. Finally, it is verified by the 3D model that the maximal field intensity around the surface of flange, shed and sheath, and the grading ring is controlled within acceptable range, and the optimized design can be applied to the ±800 kV UHVDC power station project to reduce the occurrence probability of flashover of UHVDC bushing.

Landau–Zener tunnelling in 2D periodic structures in the presence of a gauge field: I. Tunnelling rates

We study the interband Landau–Zener tunnelling of a quantum particle in the Hall configuration, i.e., in the presence of gauge field (for example, magnetic field for a charged particle) and in-plane potential field (electric field for a charged particle) normal to the lattice plane. The interband tunnelling is induced by the potential field and for the vanishing gauge field is described by the common Landau–Zener theory. We generalize this theory for a nonzero gauge field. The depletion rates of low-energy bands are calculated by using a semi-analytical method of the truncated Floquet matrix.

Landau–Zener tunnelling in 2D periodic structures in the presence of a gauge field: II. Electric breakdown

We analyse dynamics of a quantum particle in a square lattice in the Hall configuration beyond the single-band approximation. For vanishing gauge (magnetic) field this dynamics is defined by the inter-band Landau–Zener tunnelling, which is responsible for the phenomenon known as the electric breakdown. We show that in the presence of a gauge field this phenomenon is absent, at least, in its common sense. Instead, the Landau–Zener tunnelling leads to the appearance of a finite current which flows in the direction orthogonal to the vector of a potential (electric) field.

Driven Harper model

We analyze the driven Harper model, which appears in the problem of tight-binding electrons in the Hall configuration (normal to the lattice plane magnetic field plus in-plane electric field). The presence of an electric field extends the celebrated Harper model, which is parametrized by the Peierls phase, into the driven Harper model, which is additionally parametrized by two Bloch frequencies, associated with the two components of the electric field. We show that the eigenstates of the driven Harper model are either extended or localized, depending on the commensurability of the Bloch frequencies. This results holds for both rational and irrational values of the Peierls phase. In the case of incommensurate Bloch frequencies we provide an estimate for the wave-function localization length.

Study of diffusion of wave packets in a square lattice under external fields along the discrete nonlinear Schrödinger equation

Abstract The object of the present work is to analyze the effect of nonlinearity on wave packet propagation in a square lattice subject to a magnetic and an electric field in the Hall configuration, by using the Discrete Nonlinear Schrodinger Equation (DNLSE). In previous works we have shown that without the nonlinear term, the presence of the magnetic field induces the formation of vortices that remain stationary, while a wave packet is introduced in the system. As for the effect of an applied electric field, it was shown that the vortices propagate in a direction perpendicular to the electric field, similar behavior as presented in the classical treatment, we provide a quantum mechanics explanation for that. We have performed the calculations considering first the action of the magnetic field as well as the nonlinearity. The results indicate that for low values of the nonlinear parameter U the vortices remain stationary while preserving the form. For greater values of the parameter the picture gets distorted, the more so, the greater the nonlinearity. As for the inclusion of the electric field, we note that for small U, the wave packet propagates perpendicular to the applied field, until for greater values of U the wave gets partially localized in a definite region of the lattice. That is, for strong nonlinearity the wave packet gets partially trapped, while the tail of it can propagate through the lattice. Note that this tail propagation is responsible for the over-diffusion for long times of the wave packet under the action of an electric field. We have produced short films that show clearly the time evolution of the wave packet, which can add to the understanding of the dynamics.

조선후기 한양의 상류주택과 비교를 통한 낙선재의 건축특성 연구

Nakseonjae in Changdeokgung Palace was established at The King Hunjong's 13rd year (1847), the mid-19th century. It was constructed for own rests of King Hunjong and the residence of Kyungbin (king's concubines), and is showing features of upper-class houses from several points such as rustic architectural types by getting out of authoritative aspects as king's shelter space within the palace, block and floor distribution that separated spaces for men and women, simplicity in structures and styles, and non-colorful painting etc. This study aims at tracing on which architectural types did the upper-class houses within Hanyang (modern Seoul) at late Joseon Dynasty have and what was characteristics of Nakseonjae. The resemblance between Nakseonjae and the upper-class houses was very little differences from scale aspects, and floor plan shapes of Anchae (women's quarters) and Sarangchae (men's quarters) were followed basic common styles. Also, resemblance could be confirmed in the structural styles too. Characteristics of Nakseonjae are showing apparent differences from clearance compositions such as hall configuration etc. Nakseonjae was king's dwelling place, and spaces for house's collateral functions such as kitchen, stable, and warehouse etc together with shrine were unnecessary, and such places were substituted into servants' quarters for assisting the Royal family. In detailed structural styles, column's size was larger 3cm or more than the upper-class houses, and its height was higher to the degree of 30~60cm. Besides, formality as king's shelter space was raised more in decorating aspects, and Nakseonjae was implemented by getting architectural influences from Qing Dynasty of China. This study induced features of Hanyang's upper-class houses at the 19th century by supplementing distribution and space configurations at existing cases of Seoul and Gyeonggi area together with house diagrams having been collected by Gaokdohyung (site and floor plan) of Jangseogak Library, and confirmed resemblances and differences with Nakseonjae, that is, features of Nakseonjae. Through the result, this study judges a fact that architecture of Nakseonjae seemed to be affected from conveniences of upper-class houses within Hanseong, and also architectural styles and distribution types of Nakseonje would give influences to the upper-class houses.

Wave packets in graphene under external fields: Vortices formation

In this work we analyzed the time propagation of wave packets on a sheet of graphene under the action of external magnetic and electric fields in the Hall configuration. The treatment given in this work to the problem of particle propagation in graphene is based on the tight-binding model, not requiring to consider the linear approximation of the band structure around point K in the Brillouin zone. So, our calculation is able to describe the behavior of the particle in more general cases, not only the case of low lying excited states, the so-called massless Dirac electrons. Evaluating the time evolution of the wave function we assume as an initial state a Gaussian with a given velocity. We have considered the symmetric gauge for the vector potential. For specific cases one is able to show a very interesting effect such as the apparition of vortices, i.e., the initial wave is split into components each one of these forming vortices that remain stationaries as time goes. Moreover, for a packet with a wave vector near point K in the Brillouin zone, one is able to show the presence of the effect of zitterbewegung, that is, a trembling motion of the centroid of the wave packet. The inclusion of a dc electric field in the plane of the graphene lattice displaces the vortices in a direction perpendicular to the field.

The Rhetoric of Ableism

This essay argues that rhetoric is both the means by which ableist culture perpetuates itself and the basis of successful strategies for challenging its practices. Public demonstrations, countercultural performances, autobiography, transformative histories, and critiques of ableist films and novels all apply rhetorical solutions to the problem of ableism. The study employs Kenneth Burke's theory of identification and Stuart Hall's configuration of ideology to uncover those commonplace "languages of practical thought" that generate and sustain ableist perspectives and ideas. Focusing on the rhetoric of ableism at the level of the warrants used to interpret disability, this article closely examines the way Aristotle's Generation of Animals relies on the equivocation "normal is natural."

A “Globalized” Studio Environment: Configuring Reflexive Spatial Agendas

De territorialization - a concept of territory where social, economic, and political space are not necessarily geographical has developed from the radical alterations brought about by rapid globalization. For the first time in history, cultural spaces are developing that have no tangible connection to geographical places. Conventional learning structures, teaching methods, and course content make it difficult for these educational institutions to operate effectively in this climate. To prosper, they must make decisions expeditiously and the development of new programs must take place quickly, seamlessly, and continuously. More importantly, with the changes demanded by these processes, the classroom must truly become a global entity. In this paper, an argument is proposed that though the forces of globalization have radically changed our conception and use of space, its material manifestation is as important now more then ever to those training to be architects and designers. However, the old lecture hall and studio configuration must make way for a new type of reflexive space that allows disciplinary boundaries to become blurred and more flexible. If this occurs, universities might again become bastions of critical thought illustrating possible types of alternative spaces and temporalities within our personal and communal lives. By cultivating spaces built on the imperatives of diversity and simultaneity, the monistic onslaught of the global network culture could be translated into a multitude of spaces and temporalities that add richness to the necessary social, political, and cultural aspects of our lives. Within architectural discourse, this call is doubly important because this type of individual will most affect the virtual/material interfaces that are become increasingly common as the effects of economic and technological transformations are felt on a global scale.

Magneto-ballistic effects in non-centrosymmetric GaAs/AlGaAs cross junctions

Magneto-ballistic transport is studied in a mesoscopic four-terminal junction with broken symmetry in the classical ballistic transport regime. Depending on the measurement configuration the device acts as a non-centrosymmetric Hall junction or a ballistic rectifier. In Hall configuration the absolute value of the Hall voltage depends on the current polarity. This nonlinearity is attributed to a current-polarity-dependent feeding of ballistic electrons into the Hall probes. A centrosymmetric reference sample shows the well-known linear Hall characteristic. In rectifier configuration the rectified inertial-ballistic signal is superimposed by the Hall component. The inertial-ballistic component is maintained in perpendicular magnetic fields exceeding B = 400 mT .