Transverse Transport Properties Research Articles

Giant anomalous transverse transport properties of Co-doped two-dimensional Fe3GaTe2

Giant anomalous transverse transport properties of Co-doped two-dimensional Fe3GaTe2

Experimental investigation of intrinsic mechanism dominated anomalous Hall effect in hexagonal alloys Fe3-xMnxGe (x = 0.05, 0.1, 0.5)

Iron alloys are among the most fundamental and extensively studied alloys, particularly in recent years with the advancements in spintronics. The anomalous Hall effect based on intrinsic Berry curvature has sparked a significant research interest in magnetic materials. In this experimental study, we quantitatively elucidated the AHE mechanism in Fe3-xMnxGe (x = 0.05, 0.1, 0.5) alloy using the Tian-Ye-Jin model. It is found that the intrinsic mechanism associated with the band structure dominates the anomalous Hall effect of alloys, akin to the parent compound Fe3Ge. In addition, the total and separated intrinsic anomalous Hall conductivity decrease with the increase of doping level. The percentage of anomalous Hall conductivity in total anomalous Hall conductivity increases with increasing temperature and decreasing doping level. The percentage of intrinsic contribution was significantly higher than extrinsic contribution, confirming the intrinsic mechanism dominated anomalous Hall effect. This study provides a reference for tailoring transverse transport properties through doping.

Amplification of ferromagnetic and transverse transport properties during monolayer-to-bilayer transition in MnSe2: A first-principle study

Transverse anomalous transport properties are highly beneficial for spintronics applications compared with conventional longitudinal transport properties behaviors. Thus, we explore the thickness-dependent anomalous transverse transport properties of mono- and bilayer two-dimensional MnSe2. Both structures have ferromagnetic ground states with half metallicity. The monolayer structure has a perpendicular magnetic anisotropy of 2.51 meV, and this is increased to 3.57 meV in the bilayer. We find a Curie temperature of 221 K in monolayer MnSe2, and it reaches 286 K in the bilayer MnSe2. Despite a relatively small anomalous Hall conductivity (AHC) in the monolayer (−30 S/cm), it is substantially enhanced to −402 S/cm in the bilayer. Due to this enhancement of the AHC, the bilayer MnSe2 displays a large anomalous thermal Hall conductivity −0.10 W/K.m at 100 K and is further enhanced to −0.2 W/K.m at 200 K. Overall, our study may suggest that the 2D MnSe2 can be utilized for potential spintronics applications.

Numerical model for transverse current transport in multi-filament twisting strands under uniform axial strain

This paper establishes a three-dimensional finite element model for multi-filament twisting strands. The model studies the changes in its transverse transport properties by applying uniform axial loads. The electro-mechanical coupling relation of superconducting filaments is established by the scaling law and n-power relation. When the average strain of the filaments is between 0.1% and 0.2%, the equivalent conductivity of filaments almost decreases linearly by 67.7% with respect to that for zero-strain. Meanwhile, the contact resistance Rc increases quadratically with the strain, the value of Rc=3.9×10-15Ωm2 is calculated at strain 0.2% and n=6, and reaches the same order of magnitude as the previous work. As n increases from 6 to 10, the contact resistance increases sharply by 104 order of magnitude in unit of Ω·m2. It is indicated that the contact resistance is sensitive to the n value. By gradually increasing the number of filaments in a strand model, the average potential difference decreases in a nearly linear manner, and the minimum value of 9.9×10-11V is found for the strand of 36 filaments at 0.2% strain. It suggests that filaments improve the capacity of transverse transport. Besides, the average transverse current density of the strand is suppressed by the strain, its value decreasing from 800A/m2 at zero strain to 570A/m2 at 0.2% strain. It is shown that its capability to carry transverse current is declined under strain.

Anisotropic thermal and electrical conductivities of individual polyacrylonitrile-based carbon fibers

Understanding the anisotropy of thermal and electrical properties of carbon fibers is important for many applications, but transverse transport properties are difficult to measure. We apply time-domain thermoreflectance (TDTR) mapping to determine spatial variations in the transverse thermal conductivity for different radial positions for two polyacrylonitrile (PAN)-based carbon fibers, the IM7 and AS4 fibers. Single-point TDTR measurements determine the longitudinal and transverse thermal conductivities of the carbon fibers. The transverse and longitudinal electrical resistivities of the AS4 fibers are determined by the van der Pauw method and four-point method, respectively. The transverse thermal conductivity of IM7 fibers is approximately uniform (2.0 W/m-K) at different radial positions. In contrast, the transverse thermal conductivity of the core (3.0 W/m-K) in AS4 fibers is higher than the shell (2.4 W/m-K). The longitudinal thermal conductivity of IM7 fibers is 7.5 W/m-K and the value of AS4 fibers is 6.9 W/m-K. The transverse electrical resistivity of AS4 fibers is 6.3 × 10−5 Ωm and the longitudinal electrical resistivity is 1.5 × 10−5 Ωm; the electrical resistivities of IM7 fibers were reported previously. Both the thermal and electrical measurements indicate a larger anisotropy of the IM7 fiber than the AS4 fiber.

Controlling the electronic bands of a 2D semiconductor by force microscopy

In this work, we investigate the transverse transport properties of few-layers MoS2 using a Conductive Atomic Force Microscopy based technique. We find that the system changes between a low-force regime, characterized by a nearly-ideal contact between the MoS2 flake and the substrate, and a high-force regime, for which this contact starts to become highly non-ideal. We propose a 3-diode model that effectively describes the current-voltage characteristics of few-layers MoS2. From this model, we estimate how fast the energy gaps of two-dimensional MoS2 materials change as a function of the applied force. From our analysis, we estimate that MoS2-Au Schottky barrier heights change at the rate of 0.21, 0.23, and 0.78 meV nN−1 for the few-layers, three-layers, and two-layers MoS2, respectively. Our work opens up new possibilities of investigating and controlling the electronic properties of 2D semiconducting materials.

Giant anomalous Nernst effect in the Co2MnAl1−xSix Heusler alloy induced by Fermi level tuning and atomic ordering

Co2MnAl has been predicted to have Weyl points near Fermi level which is expected to give rise to exotic transverse transport properties such as large anomalous Hall(AHE) and Nernst effects(ANE) due to large Berry curvature. In this study, the effect of Fermi level position and atomic ordering on AHE and ANE in Co2MnAl1-xSix were studied systematically. The Co2MnAl film keeps B2-disordred structure regardless of annealing temperature, which results in much smaller anomalous Hall conductivity sigma_xy and transverse Peltier coefficient sigma_xy than those calculated for L21-ordered Co2MnAl. Our newly performed calculation of sigma_xy with taking B2 disordering into account well reproduces experimental result, thus it was concluded that Berry curvature originating from Weyl points is largely reduced by B2 disordering. It was also revealed Al substitution with Si shifts the position of Fermi level and improves the L21-atomic ordering largely, leading to strong enhancement of sigma_xy, which also agreed with our theoretical calculation. The highest thermopower of ANE of 6.1uV, which is comparable to the recent reports for Co2MnGa, was observed for Co2MnAl0.63Si0.37 because of dominant contribution of sigma_xy. This study clearly shows the importance of both Fermi level tuning and high atomic ordering for obtaining the effect of topological feature in Co-based Heusler alloys on transverse transport properties.

Semiclassical theory of anomalous transport in type-II topological Weyl semimetals

Weyl semimetals possess low energy excitations which act as monopoles of Berry curvature in momentum space. These emergent monopoles are at the heart of the extensive novel transport properties that Weyl semimetals exhibit. The singular nature of the Berry curvature around the nodal points in Weyl semimetals allows for the possibility of large anomalous transport coefficients in zero applied magnetic field. Recently a new class, termed type-II Weyl semimetals, has been demonstrated in a variety of materials, where the Weyl nodes are tilted. We present here a study of anomalous transport in this new class of Weyl semimetals. We find that the parameter governing the tilt of these type-II Weyl points is intimately related to the zero field transverse transport properties. We also find that the temperature dependence of the chemical potential plays an important role in determining how the transport coefficients can effectively probe the Berry curvature of the type-II Weyl points. We also discuss the experimental implications of our work for time-reversal breaking type-II Weyl semimetals.

Transverse transport properties of a charged drop in an electric field

Transport properties of a charged droplet of weakly interacting particles in transverse electric field are investigated. Nonequilibrium, time-dependent distribution function which describes a process of the droplet transverse evolution with constant entropy in the field is calculated. With the help of this distribution function, shear viscosity coefficients in the transverse plane are calculated as well. They are found to be dependent on the ratio of the potential energy of the droplet in the electric field to the kinetic energy of the droplet; for weakly interacting particles, this parameter is small. Additionally, these coefficients are time-dependent and change during the hydrodynamical state of the droplet's expansion. Applicability of the results to the description of initial states of quark–gluon plasma (QGP) obtained in high-energy interactions of nuclei is also discussed.

Microwave transport approach to the coherence of interchain hopping in (TMTSF) PF

We report a microwave study of the longitudinal and transverse transport properties of the quasi-one-dimensional organic conductor (TMTSF)$_2$PF$_6$ in its normal phase. The contactless technique have provided a direct measurement of the temperature profile of the resistivity along the {\bf b'} direction and in magnetic fields up to 14 T. A characteristic energy scale ($T_x \sim 40 K$) has been observed which delimits a transient regime from an insulating to a metallic behavior. This anomalous profile is discussed in terms of the onset of coherent transport properties along the {\bf b'} direction below 40 K. This is also supported by the observation of a finite longitudinal and transverse magnetoresitances only below 40 K, indicative of a two-dimensional regime. Below $T_x$, however, strong deviations with respect to a Fermi liquid behavior are evidenced.

Current–Voltage Characteristics of Porous Silicon Made from A P/N Junction Structure

ABSTRACTWe have made studies on the TRANSVERSE transport properties of the porous Si made from a novel P/N junction structure. The structures of porous Si were examined for various electrochemical etching conditions and they were correlated with the electrical data. The junciton was fabricated by shallow diffusion, with porous Si formed perpendicular to the junction and between two indium ohmic contacts. This structure confines currents to the direction parallel to the surface. Distinct feature on I–V curves have been observed, including sudden rise of currents and the existence of negative differential resistances (NDR). The characteristics appeared stable and depended on the polarity of bias. Suggestions are made that the porous Si could be composed of microcrystals, and feasibility of carrier transport through quantum boxes responsible for the electrical behaviors are discussed.

Optical investigation of the electrical anisotropy of (SN)x single crystals

AbstractPolarized reflectance spectra of (SN)x single crystals are investigated in the range from 0.15 to 4 eV. For light polarized parallel to the polymeric chains the Drude behaviour found previously is confirmed. The optical properties perpendicular to the chains, however, are explained by a modified Maxwell‐Garnett model. This model takes into account the fibrous structure of (SN)x crystals and allows to separate the intrinsic and extrinsic transverse transport properties.

Electrical conductivity of tetrathiofulvalinium tetracyanoquinodimethan (TTF) (TCNQ)

The temperature dependence of the dc electrical conductivity of tetrathiofulvalinium tetracyanoquinodimethan (TTF)(TCNQ) measured along the crystallographic $a$, $b$, and ${c}^{*}$ axes and the corresponding anisotropies $\frac{{\ensuremath{\sigma}}_{\ensuremath{\parallel}}^{b}}{{\ensuremath{\sigma}}_{\ensuremath{\perp}}^{a}}$ and $\frac{{\ensuremath{\sigma}}_{\ensuremath{\parallel}}^{b}}{{\ensuremath{\sigma}}_{\ensuremath{\perp}}^{{c}^{*}}}$ are reported. Standard four-probe measurements are supplemented by applying the technique of Montgomery to the question of inhomogeneous currents in this anisotropic conductor. We have observed that the intrinsic anisotropy contains two maxima which provide a direct internal method for unambiguously testing the validity of four-probe measurements of the conductivity along the principal conducting $b$ axis. The transverse transport properties are diffusive and yield an electrical anisotropy greater than 500 at room temperature which increases to greater than ${10}^{4}$ near 58 K. The extreme sensitivity of this one-dimensional metal to crystalline imperfections is experimentally demonstrated through temperature cycling studies. The dc results confirm (TTF)(TCNQ) is a one-dimensional metal exhibiting a strongly temperature-dependent $b$-axis conductivity that reaches maximum values exceeding ${10}^{5}$ ${(\mathrm{\ensuremath{\Omega}}\phantom{\rule{0ex}{0ex}}\mathrm{c}\mathrm{m})}^{\ensuremath{-}}$. These data are taken as confirming evidence that above 58 K the metallic state exhibits strong electron correlations associated with a many-body collective state in which the conductivity can greatly exceed the limitations of single-particle scattering.