Electrical Hall Research Articles

Analytical Evaluation of the Effective Electric Resistivity and Hall Coefficient in the Rectangular and Triangular Checkerboard Composites

Analytical Evaluation of the Effective Electric Resistivity and Hall Coefficient in the Rectangular and Triangular Checkerboard Composites

Transport properties of (AgSbТe2)0.7(PbTe)0.3 thermoelectric compound

Transport properties, namely electrical conductivity, Seebeck and Hall coefficients, and thermal conductivity, were measured from 80 to 560 K. The phase transition at about 410 K, representing the phase transition from α-Ag2Te to β-Ag2Te, influences the electrical transport properties. The temperature dependence of Hall coefficient passes through a maximum ∼200 K and has a negative sign. It is shown that these peculiarities are due to the presence of Ag2Te phase.

Influence of In-induced resonant level on the normal-state and superconducting properties of Sn1.03Te

Normal-state transport properties (2--300 K) of the polycrystalline series ${\mathrm{Sn}}_{1.03\ensuremath{-}\ensuremath{\delta}\ensuremath{-}x}{\mathrm{In}}_{x}\mathrm{Te} (0\ensuremath{\le}x\ensuremath{\le}0.07$; $\ensuremath{\delta}\ensuremath{\le}0.0025$) were investigated by means of electrical resistivity, thermopower, Hall effect, and thermal conductivity measurements. The distortion of the valence-band structure by the In-induced resonant level (RL) has a profound influence on the evolution of the normal-state properties with $x$ and on the emergence of superconductivity evidenced by specific-heat measurements down to 0.35 K. In addition to a nearly 40-fold increase in the residual electrical resistivity ${\ensuremath{\rho}}_{0}$ on going from $x=0.0$ to 0.05, the thermopower $\ensuremath{\alpha}$ shows a nonlinear, complex behavior as a function of both temperature and $x$. While Hall measurements indicate a dominant holelike response across the entire composition and temperature ranges, $\ensuremath{\alpha}$ changes sign below about 100 K and remains negative down to 5 K for $0.0015\ensuremath{\le}x\ensuremath{\le}0.0045$. Additional measurements under magnetic fields ${\ensuremath{\mu}}_{0}H$ of up to 14 T further shows that $\ensuremath{\alpha}({\ensuremath{\mu}}_{0}H)$ gradually shifts towards positive values, suggestive of a dominant holelike contribution to $\ensuremath{\alpha}$. Superconductivity emerges for $x=0.02$ at a critical temperature ${T}_{\mathrm{c}}=0.67$ K, with ${T}_{\mathrm{c}}$ increasing with $x$ to reach 1.73 K for $x=0.07$. The variations in the superconducting parameters with $x$, notably the specific-heat jump at ${T}_{\mathrm{c}}$, confirm the results reported in prior studies and suggests a nontrivial role of the RL on the electron-phonon coupling strength. The striking similarities between this series and the canonical resonant system ${\mathrm{Pb}}_{1\ensuremath{-}x}{\mathrm{Tl}}_{x}\mathrm{Te}$ provide an excellent experimental opportunity to gain a deeper understanding of the close interplay between resonant level, anomalous transport properties, and superconductivity.

Symmetry-preserving boundary of (2+1)D fractional quantum Hall states

We investigate symmetry-preserving gapped boundary of $(2+1)$-dimensional $[(2+1)\mathrm{D}]$ topological phases with global symmetry, which can be either bosonic or fermionic. We develop a general algebraic description for gapped boundary condition for symmetry-enriched or fermionic topological phases, extending the framework of Lagrangian algebra anyon for bosonic phases without symmetry. We then focus on application to the case with U(1) symmetry. We derive new obstructions to symmetry-preserving gapped boundary for U(1)${}^{f}$-symmetric $(2+1)\mathrm{D}$ fermionic topological phases, which are beyond chiral central charge ${c}_{\ensuremath{-}}$ and electric Hall conductivity ${\ensuremath{\sigma}}_{H}$. These obstructions are given by a simple Gauss-Milgram-type formula valid for supermodular category and regarded as a higher version of ${c}_{\ensuremath{-}}$ and ${\ensuremath{\sigma}}_{H}$.

Local Time Response of Auroral Electrojet During Magnetically Disturbed Periods: DMSP and CHAMP Coordinated Observations

AbstractBased on 10 years of Defense Meteorological Satellite Program and Challenging Minisatellite Payload coordinated observations, we investigated the local time variation in the response time and strength of the auroral electrojet (AEJ) with respect to the sudden change in solar wind inputs, including merging electric field (Em), substorm, and interplanetary (IP) shock. The daytime (nighttime) AEJ responded several minutes (>30 min) after the key time of Em enhancement. For substorms and IP shocks, the AEJ at all local times showed an instantaneous response. The local time with a westward enhancement of the AEJ was wider during substorms than those during Em enhancement and IP shock. The times when the AEJ or disturbance AEJ attained peaks varied for different disturbances. At IP shock onset, the AEJ in the prenoon and postnoon increased in opposite directions to that in the quiet time. During Em enhancement and IP shock, the duskside AEJ attained a peak faster than the dawnside owing to the more rapid change in the duskside Hall conductance. The relative effects of the convection electric field and Hall conductance on the disturbance AEJ are disclosed at different local times. This study offers insights into the physical mechanisms of local time differences in the response time and strength of AEJ during disturbed periods.

Synthesis and Characterization of Eu2InTe5: A New Layered Multitelluride and Its Thermoelectric Properties

The new layered Eu2InTe5 single crystals are grown via the self flux approach. The single‐crystal X‐ray diffraction analysis reveals that this new material has a crystallographic structure in the tetragonal structure with space group I4/mmm (no. 139) and cell parameters a = b = 4.5981(2) Å, c = 24.302(3) Å. The electrical resistivity and Hall effect measurements demonstrate a “bad metal” with a low charge carrier concentration. The thermoelectric analysis gives the values of the thermopower and the figure of merit at room temperature ≈270 μV K−1 and ≈0.1, respectively, making Eu2InTe5 and its derivatives promising for thermoelectric applications.

Pseudogap Formation in the Nodal-Line Semimetal NaAlGe

NaAlSi and NaAlGe are isostructural and isoelectronic semimetals with topological nodal lines close to the Fermi level. Despite having virtually identical electronic structures, NaAlSi exhibits superconductivity below Tc = 6.8 K, whereas NaAlGe does not. We investigate NaAlGe by measuring its electrical resistivity, Hall effect, magnetic susceptibility, and heat capacity using single crystals. It is revealed that NaAlGe is not a simple semimetal but rather has an unusual ground state with a small pseudogap of ∼100 K close to the Fermi level. We argue that the formation of the pseudogap in NaAlGe is due to an unexpected Fermi surface instability, such as an excitonic instability, as opposed to the electron–phonon instability that leads to the formation of the superconducting gap in NaAlSi.

VENμS: Mission Characteristics, Final Evaluation of the First Phase and Data Production

VENμS (Vegetation and Environment New micro (μ) Satellite) is a micro satellite launched in 2017 by the Israeli Space Agency (ISA) and the French Centre National d’Etudes Spatiales (CNES). VENμS is a research satellite containing two very different devices: an electric Hall effect thruster and a multispectral optical camera. This paper focuses on the multispectral camera. The camera provides images at a resolution of 5 m, with a field of view of 27 km, and the orbit of the satellite was chosen to allow us to revisit of each observed site with constant angles every second day. In November 2020, VENμS ended the first phase of its mission. This phase, called VM01, allowed us to provide about 150 accurate time series over selected scientific sites over almost three years. Extensive work was conducted to calibrate the camera and assess the quality of the products. Not everything worked as planned before launch and a large amount of work was necessary to correct some defects of the camera or to improve the geometric registration of images. This article establishes the image quality VM01 final assessment including the presentation of radiometric and geometric calibration methods, the estimation of instrument performances and their associated temporal stabilities and the monitoring activities. In addition, it highlights the whole mechanism of data programming, reception and production. The end of VM01 phase is not the end of the VENμS mission, and a new phase started on a one-day repeat orbit.

Mathematical modeling of MHD flow and radiative heat transfer past a moving porous rotating disk with Hall effect

PurposeThe present study aims to investigate the effect of radiation on the unsteady magnetohydrodynamic (MHD) flow of a viscous, electrically conducting Newtonian fluid over rotating disk moving upward/downward immersed in a porous medium, considering the Hall effect. The study is motivated by the various applications in the context of solar power technology, electric power generation, Hall accelerators, MHDs generators and other industrial areas when the fluid flow is subjected to the previously mentioned effects such as MHD, Hall effect and thermal radiation.Design/methodology/approachSuitable similarity transformations are employed to reduce the governing nonlinear partial differential equations into the nonlinear ordinary ones. The solutions of the reduced system are numerically obtained using the boundary value problem (BVP) Midrich scheme in Maple. The results are presented graphically for vertical disk movement, magnetic parameter, Hall current, Darcy parameter, thermal radiation and Schmidt number. Skin frictions, mass and heat transfer rates are numerically tabulated.FindingsIt is revealed that the vertical motion of the disk significantly boosts the radial and annular flows. Moreover, the Hall parameter has contrasting effects on velocity profiles for the range of magnetic field but temperature field is oblivious of this behavior. It is observed that heat and mass transfer considerably enhance along vertical disk movement. Also magnetic field, temperature ratio and radiation parameter significantly enhance the temperature field, while reaction rate parameter and Schmidt number decrease the concentration profile. The current model is calibrated in its reduced form to an already published literature with good correlation to ensure the numerical scheme's validity.Originality/valueThis work is original within the best efforts of the authors.

Electrically switchable giant Berry curvature dipole in silicene, germanene and stanene

The anomalous Hall effect in time-reversal symmetry broken systems is underpinned by the concept of Berry curvature in band theory. However, recent experiments reveal that the nonlinear Hall effect (NHE) can be observed in non-magnetic systems without applying an external magnetic field. The emergence of NHE under time-reversal symmetric conditions can be explained in terms of non-vanishing Berry curvature dipole (BCD) arising from inversion symmetry breaking. In this work, we availed realistic tight-binding models, first-principles calculations, and symmetry analyses to explore the combined effect of transverse electric field and strain, which leads to a giant BCD in the elemental buckled honeycomb lattices—silicene, germanene, and stanene. The external electric field breaks the inversion symmetry of these systems, while strain helps to attain an asymmetrical distribution of Berry curvature of a single valley. Furthermore, the topology of the electronic wavefunction switches from the band inverted quantum spin Hall state to normal insulating one at the gapless point. This band gap closing at the critical electric field strength is accompanied by an enhanced Berry curvature and concomitantly a giant BCD at the Fermi level. Our results predict the occurrence of an electrically switchable nonlinear electrical and thermal Hall effect in a new class of elemental systems that can be experimentally verified.

Unusual Electrical and Magnetic Properties in Layered EuZn2As2

AbstractEu‐based compounds often exhibit unusual magnetism, which is critical for nontrivial topological properties seen in materials such as EuCd2As2. The authors investigate the structure and physical properties of EuZn2As2 through measurements of the electrical resistivity, Hall effect, magnetization, and neutron diffraction. Their data show that EuZn2As2 orders antiferromagnetically with an A‐type spin configuration belowTN = 19 K. Surprisingly, there is strong evidence for dominant ferromagnetic fluctuations aboveTN, as reflected by positive Curie–Weiss temperature and extremely large negative magnetoresistance (MR) betweenTNandTfl≈200 K. Furthermore, the angle dependence of the MRabindicates field‐induced spin reorientation from theab‐plane to a direction ≈45° from theabplane. Compared to EuCd2As2, the doubledTNandTflmake EuZn2As2 a better platform for exploring nontrivial magnetic and electronic properties in both magnetic fluctuation (TN < T < Tfl) and ordered (T < TN) regimes.

Field-induced multiple quantum phase transitions in the antiferromagnetic Kondo-lattice compound CeRhAl4Si2

We report a comprehensive phase diagram of the antiferromagnetic Kondo-lattice compound ${\mathrm{CeRhAl}}_{4}{\mathrm{Si}}_{2}$ down to 0.3 K by investigating electrical resistivity, magnetoresistivity, and Hall resistivity under the magnetic field along the $c$ axis. At zero field, ${\mathrm{CeRhAl}}_{4}{\mathrm{Si}}_{2}$ undergoes two successive antiferromagnetic transitions at ${T}_{\mathrm{N}1}=14.2\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and ${T}_{\mathrm{N}2}=8.4\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, respectively. Upon applying magnetic field, the first-order transition of ${T}_{\mathrm{N}2}$ is continuously suppressed at the critical field of 5.5 T. On the other hand, the smooth suppression of the second-order transition of ${T}_{\mathrm{N}1}$ terminates at a tricritical point of 6.6 T and 4.7 K, followed by a first-order transition line and an additional phase transition line, which are monotonically suppressed at 6.7 and 7.2 T, respectively, implying the field-induced multiple quantum phase transitions. Particularly, in the paramagnetic region before the Fermi liquid behavior is fully developed, a quantum critical phase with non-Fermi liquid behavior is revealed, indicating a potential spin liquid state that was predicted from the global quantum phase diagram. These results suggest that ${\mathrm{CeRhAl}}_{4}{\mathrm{Si}}_{2}$ is a promising candidate to study a quantum phase transition that occurs in electronic systems with high degree of frustration.

Vacancy induced anomalies in the electrical transport properties of Ag-doped Zn1−xCdxSb (x = 0.375) solid solutions

Zinc antimonide (ZnSb) and its solid solution with CdSb are well-known p-type thermoelectric materials. Electrical transport properties of doped ZnSb exhibit certain anomalies: (a) non-monotonic changes in the electrical properties with temperature and (b) occurrence of a reversible hysteresis loop in electrical transport data when thermally cycled. The objective of this study was to investigate the underlying cause of these behaviors. Ag-doped compositions of (Zn0.625Cd0.375)1−δAgδSb (δ = 0, 0.02, and 0.04) solid solutions have been prepared by melt-synthesis—rapid compaction—annealing process. Measurement of the electrical conductivity (σ), Seebeck coefficient (S), and Hall coefficient (RH) (room temperature to 673 K) displayed the characteristic hysteresis behavior on thermal cycling along with the unusual rise in the charge carrier concentration (n) around 500 K. Aside from that, it was found that cooling rates dramatically influence room temperature properties. Analysis of synchrotron-based x-ray diffraction data by Rietveld refinement indicates that Ag-doping results in the formation of Zn vacancies [Vzn]. Also, a sharp drop in the concentration of Zn vacancies, [Vzn] around 550 K was observed and could be correlated with the changes in n values. This correlation between changes in [Vzn] and n has been used to explain the observed electrical anomalies, which are a consequence of the repeated annihilation and creation of Zn vacancies with temperature changes.

Максимальная прыжковая электропроводность на постоянном токе по водородоподобным примесям в полупроводниках

A quasi-classical model for calculating DC (direct current) electrical conductivity in crystalline semiconductors with hydrogen-like impurities is developed at the transition from band conduction to impurity hopping conduction with decreasing temperature. This transition from the minimum band conductivity to the maximum hopping conductivity via impurities has the form of a characteristic ``kink'' in the temperature dependence of the electrical resistivity. The idea of the calculation is to preliminarily determine the transition temperature Tj using the standard approach within the framework of the two-band model. The shift of the top of the v-band (the bottom of the c-band) into the depth of the band gap due to the formation of a quasi-continuous band of allowed energy values from the excited states of acceptors (donors) is taken into account. This leads to a decrease in the value of a thermal ionization energy of the main shallow impurities due to a decrease in the maximum localization radius of a hole on an acceptor (an electron on a donor) with increasing impurity concentration. The values of the observed maximum hopping conductivity and drift hopping mobility corresponding to the temperature Tj are calculated. The numerical calculation within the framework of the proposed model is consistent with the known experimental data on the electrical conductivity and Hall coefficient of moderately compensated p-Ge crystals doped by neutron transmutation and non-intentionally compensated metallurgically doped n-Ge, as well as n- and p-Si crystals on the insulator side of the Mott insulator–metal concentration phase transition.

Analysis of Structural Characteristics of Underground Cavern Group by Simulating All Cavern Excavation

The traditional Three‐dimensional (3D) model for stability analysis of a large underground cavern group only includes the main powerhouse, the main transformer chamber, the tailrace surge tank, the main electrical wire hall, and part of the diversion tunnel and tailwater tunnel. Other caverns excavation are not taken into consideration, which is inconsistent with the actual project. In this study, a 3D Finite Element Method (FEM) model, including all the cavities, and a 3D simplified model containing only part of the cavities were established based on the actual underground cavern group project. We study the structural characteristics of the cavern group during excavation via 3D nonlinear FEM. At the same time, three numerical calculation schemes are designed for comparison. The results show that the simulated distributions of the stress field, deformation field, and plastic zone of the two numerical models are similar, but the magnitudes of the 3D FEM model, which considers all caverns are generally higher than the simplified model. The difference between the two simulated horizontal displacements of the main powerhouse reaches 53.72%. Therefore, from the perspective of engineering safety and actual construction, it is advisable to adopt the 3D FEM model, including all the cavities, when conducting a simulation analysis of the underground cavern group.

Maximum hopping direct current conductivity via hydrogen-like impurities in semiconductors

A quasi-classical model for calculating DC (direct current) electrical conductivity in crystalline semiconductors with hydrogen-like impurities is developed at the transition from band conduction to impurity hopping conduction with decreasing temperature. This transition from the minimum band conductivity to the maximum hopping conductivity via impurities has the form of a characteristic "kink" in the temperature dependence of the electrical resistivity. The idea of the calculation is to preliminarily determine the transition temperature Tj using the standard approach within the framework of the two-band model. The shift of the top of the v-band (the bottom of the c-band) into the depth of the band gap due to the formation of a quasi-continuous band of allowed energy values from the excited states of acceptors (donors) is taken into account. This leads to a decrease in the value of a thermal ionization energy of the majority shallow impurities due to a decrease in the maximum localization radius of a hole on an acceptor (an electron on a donor) with increasing impurity concentration. The values of the observed maximum hopping conductivity and drift hopping mobility corresponding to the temperature Tj are calculated. The numerical calculation within the framework of the proposed model is consistent with the known experimental data on the electrical conductivity and Hall coefficient of moderately compensated p-Ge crystals doped by neutron transmutation and non-intentionally compensated metallurgically doped n-Ge, as well as n- and p-Si crystals on the insulator side of the Mott insulator--metal concentration phase transition. Keywords: bulk crystals of germanium and silicon, hydrogen-like acceptors and donors, holes and electrons, band and hopping motion of charge carriers.

Quasi-1D electronic transport and isotropic phonon transport in the Zintl Ca5In2Sb6

Crystals with anisotropic thermoelectric transport coefficients can yield a high figure-of-merit along the direction with the highest electronic mobility, provided the Seebeck coefficient and thermal conductivity are relatively isotropic. In this study, we combine experiment and theory to investigate the anisotropic properties of the quasi-1D Zintl phase Ca5In2Sb6. Ca5In2Sb6 is predicted by ab initio calculations to have extremely anisotropic p-type electrical conductivity and power factor, arising from light effective mass parallel to its ladder-like polyanionic chains. In contrast, the Seebeck coefficient and lattice thermal conductivity are predicted to be relatively isotropic. The latter is evidenced by the nearly isotropic computed speed of sound tensor and experimentally obtained thermal expansion coefficients. In order to characterize the anisotropic electrical conductivity, Ca5In2Sb6 single crystals were grown from an In–Sb rich molten flux and measured both parallel and perpendicular to the polyanionic chains. Due to the small crystal cross-sections, measurements perpendicular to the growth direction demanded a novel photolithography methodology whereby micro-ribbons were extracted using focused ion beam milling, and processed using laser photolithography to deposit contacts for electrical resistivity and Hall coefficient measurements. The conductivity parallel to the growth direction was found to be nearly 20x higher than the perpendicular direction, in agreement with our theoretical predictions. This study represents one of the first experimental confirmations of highly anisotropic electrical conductivity in Zintl thermoelectrics.

Investigating the thermoelectric power generation performance of ZnCuO: A p-type mixed-metal oxide system

Thermoelectric power generation performance of ZnCuO nanostructures is enhanced by varying the concentration of Cu atoms. This is tested by growing samples of ZnCuO by simple hydrothermal route at different Cu concentrations (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5). The X-ray diffraction (XRD) pattern shows the formation of mixed-metal oxide phases of ZnO and CuO, while the increase in Cu concentration results in generation of more stable CuO phases. Raman spectroscopy measurement is performed for all synthesized samples, which supports the XRD results. For the thermoelectric and electric conductivity behavior, Seebeck coefficient and Hall measurements are performed for all samples. Data suggest an improvement in Seebeck coefficient from 32 to 73 μV°C−1 with the increase of Cu concentration in the host crystal. Electrical conductivity data also show a similar increasing trend (19–36 Scm−1) resulting in a high power-factor value of 1.12 × 10−5 Wm−1K−2 for the sample with highest Cu concentration. This enhanced thermoelectric performance with increasing concentration of Cu atoms is due to the improvement of carrier mobility. The mobility of carriers is thought to increase because of the emergence of mixed composite phases, as verified by XRD and Raman spectroscopy measurements.

Preparation and Characterization of Nanosized Substituted Perovskite Compounds with Orthorhombic Structure

In this work, five substituted perovskite such as (Gd0.9Sr0.1) Mn0.8Co0.2O3, Tb0.8Sr0.2FeO3, Gd0.6Sr0.4RuO3, SrCe0.95Y0.05O3, and Mn0.6Co0.4SnO3 were synthesized by tartrate and hydroxide precursor method. The resulting samples were characterized by inductively coupled plasma spectroscopy, energy dispersive X-ray analysis, infrared spectroscopy, thermal analysis, X-ray powder diffraction, transmission electron microscope (TEM), selected field of electron diffraction (SAED), d.c. electrical conductivity, Hall effect, dielectric measurements, and low-temperature magnetization measurements. The X-ray diffraction pattern for all compounds was indicated the formation of single-phase perovskite with orthorhombic structure except Tb0.8Sr0.2FeO3 and Mn0.6Co0.4SnO3 perovskite. These compounds showed a cubic and rhombohedral structure, respectively. The lattice parameter and the unit cell volume slightly decreased as ionic radii decrease in agreement with the lanthanide contraction. The average size of cation ˂ RA ˃, mismatch factor (σ2), and tolerance factor (t) gives the combined effects of disorder and inhomogeneity in these compounds. The average particle size determined from TEM was in the range of 22 to 77 nm for all compounds. The temperature dependence of electrical conductivity for all compounds showed a definite break in 500 K to 610 K. except the Gd0.6Sr0.4RuO3 compound, which corresponds to semiconducting behavior. While the Gd0.6Sr0.4RuO3 sample shows a metallic-like semiconductor. The thermoelectric power and Hall effect measurements for all compounds were n-type semiconductivity except the SrCe0.95Y0.05O3 compound. It showed p-type semiconductivity. The frequency dependence of the dielectric constant and dielectric loss in these substituted perovskites were discussed using the Maxwell-Wagner model. Magnetic studies showed that the thermo-magnetic irreversibility for all compounds.

Effects of strain, disorder, and Coulomb screening on free-carrier mobility in doped cadmium oxide

The interplay of stress, disorder, and Coulomb screening dictating the mobility of doped cadmium oxide (CdO) is examined using Raman spectroscopy to identify the mechanisms driving dopant incorporation and scattering within this emerging infrared optical material. Specifically, multi-wavelength Raman and UV-vis spectroscopies are combined with electrical Hall measurements on a series of yttrium (X = Y) and indium (X = In) doped X:CdO thin-films. Hall measurements confirm n-type doping and establish carrier concentrations and mobilities. Spectral fitting along the low-frequency Raman combination bands, especially the TA+TO(X) mode, reveals that the evolution of strain and disorder within the lattice as a function of dopant concentration is strongly correlated with mobility. Coupling between the electronic and lattice environments was examined through analysis of first- and second-order longitudinal–optical phonon–plasmon coupled modes that monotonically decrease in energy and asymmetrically broaden with increasing dopant concentration. By fitting these trends to an impurity-induced Fröhlich model for the Raman scattering intensity, exciton–phonon and exciton–impurity coupling factors are quantified. These coupling factors indicate a continual decrease in the amount of ionized impurity scattering with increasing dopant concentration and are not as well correlated with mobility. This shows that lattice strain and disorder are the primary determining factors for mobility in donor-doped CdO. In aggregate, the study confirms previously postulated defect equilibrium arguments for dopant incorporation in CdO while at the same time identifying paths for its further refinement.