Transverse Voltage Research Articles

Spinning Randomly in the Hall

Physics The Hall effect occurs when a current running through a conductor is deflected by a perpendicular magnetic field, causing a transverse voltage to develop. In certain semiconductor structures where the motion of the charge carriers is confined to two dimensions, this Hall voltage is quantized. When the parameter of quantization (the so-called filling factor ν) is an integer, the effect can be easily explained through the formation of Landau levels. Fractional filling factors may also occur, requiring a more involved explanation in terms of non-interacting composite fermions. Α state with ν = 5/2 is yet more exotic as it eludes the composite fermion description and was predicted to exhibit a complicated kind of quantum statistics known as non-Abelian, making it especially interesting for quantum computing. However, one of the assumptions of that prediction was that the state was also spin-polarized. Stern et al. test that assumption by measuring the photoluminescence of a GaAs-AlGaAs quantum well and find that the state appears to be spin-unpolarized. Their conclusions agree with those extracted from Raman and tilted-field measurements, prompting further theoretical research into whether a spin-unpolarized state can still support a non-Abelian theory for quantum computing applications. Phys. Rev. Lett. 105 , 96801 (2010).

Influence of the Voltage Applied to the Semiconductor Substrate on Birefringence of Nematic Liquid Crystal

The influence of longitudinal voltage, applied along semiconductor substrate of planar-oriented liquid-crystal cell, on the birefringence of nematic liquid crystal (NLC) has been studied. It is shown that with the fixed value of transverse voltage the application of longitudinal voltage creates an additional possibility to control the electro-optically induced phase shift of light passing through NLC. The dependence of phase shift vs. control voltages is obtained. The results of simulation of the longitudinal voltage influence on the process of NLC reorientation are given. The obtained results can be used for development and fabrication of liquid-crystal phase modulators.

Gigantic transverse voltage induced via off-diagonal thermoelectric effect in CaxCoO2 thin films

Gigantic transverse voltages exceeding several tens volt have been observed in CaxCoO2 thin films with tilted c-axis orientation upon illumination of nanosecond laser pulses. The voltage signals were highly anisotropic within the film surface showing close relation with the c-axis tilt direction. The magnitude and the decay time of the voltage strongly depended on the film thickness. These results confirm that the large laser-induced voltage originates from a phenomenon termed the off-diagonal thermoelectric effect, by which a film out-of-plane temperature gradient leads to generation of a film in-plane voltage.

Stand alone experimental setup for dc transport measurements

Described is a system consisted of Keithley's current source Model 6221 and nanovoltmeter Model 2182A pairs. That pair was developed by Keithley for precise measurements of a sample's one electrical parameter by the dc current-reversal transport technique. Nonstandard synchronization method employed in the presented setup allows assembling several pairs together for low level electrical measurements of a sample's several parameters associated with the same current, thus expanding the applications of these devices. The equipment was tested by simultaneous measurements of such two parameters as transverse magnetoresistance and Hall voltage on the following materials: Si/SiGe, Ge:Mn; HgTe/HgCdTe, and InMnSb.

Magnetic and Magnetoelectric Properties of Particulate (x)PbZr0.53Ti0.47O3–(1−x) Mn0.4Zn0.6Fe2O4 Composites

Magnetic and magnetoelectric properties of particulate (x)PbZr0.53Ti0.47O3–(1−x) Mn0.4Zn0.6Fe2O4 composites, where x is 0; 0.2; 0.4; 0.6; 0.8; and 1.0, have been studied. Measurements of magnetization—magnetic field loops, temperature and field dependences of the differential magnetic susceptibility as well as the transverse magnetoelectric voltage coefficient have shown the profound effect of the composite composition on studied properties.

Anisotropic conductivity of doped graphene due to short-range nonsymmetric scattering

The conductivity of doped graphene is considered taking into account scattering by short-range nonsymmetrical defects, when the longitudinal and transverse components of conductivity tensor appear to be different. The calculations of the anisotropic conductivity tensor are based on the quasiclassical kinetic equation for the case of monopolar transport at low temperatures. The effective longitudinal conductivity and the transverse voltage, which are controlled by orientation of sample and by gate voltage (i.e., doping level), are presented.

Deflection of suspended graphene by a transverse electric field

We investigate the electromechanical response of doubly clamped graphene nanoribbons to a transverse gate voltage. An analytical model is developed to predict the field-induced deformation of graphene nanoribbons as a function of field intensity and graphene geometry. This model is validated through atomistic simulations using the combination of a constitutive charge-dipole model and a pseudochemical many-body potential. As a newly observed effect of electric polarization, this field-induced deflection allows the graphene to oscillate at its natural frequency, which is found to decrease dramatically with increasing graphene size.

Hall anomaly in CNT-doped Y-123 high temperature superconductor

Abstract In order to study the Hall effect in pure and CNT-doped Y-123 polycrystalline samples, we have measured the longitudinal and transverse voltages at different magnetic field (0 − 9 T) in the normal and vortex states. In the normal state, the Hall coefficient is positive and decreases with increasing temperature, and can be approximately fitted to R H = a + bT −1 . We have found a sign reversal in the pure sample for the magnetic field of about 3 T, and double sign reversal of the Hall coefficient in the 0.7 wt% CNT-doped sample at about 3 and 5 T. The Hall resistivity in our samples depends on the pinning.

Quantifying Spin Hall Angles from Spin Pumping: Experiments and Theory

Spin Hall effects intermix spin and charge currents even in nonmagnetic materials and, therefore, ultimately may allow the use of spin transport without the need for ferromagnets. We show how spin Hall effects can be quantified by integrating Ni{80}Fe{20}|normal metal (N) bilayers into a coplanar waveguide. A dc spin current in N can be generated by spin pumping in a controllable way by ferromagnetic resonance. The transverse dc voltage detected along the Ni{80}Fe{20}|N has contributions from both the anisotropic magnetoresistance and the spin Hall effect, which can be distinguished by their symmetries. We developed a theory that accounts for both. In this way, we determine the spin Hall angle quantitatively for Pt, Au, and Mo. This approach can readily be adapted to any conducting material with even very small spin Hall angles.

Base-By-Base Ratcheting of Single Stranded DNA through a Solid-State Nanopore

The benefits of low-cost, high-throughput human genome sequencing to medical science has inspired recent experimental work focused on DNA translocation through solid-state nanopores. Given that microelectronic fabrication methods permit the integration of nano-electronics devices to sense each DNA base, the genetic code (DNA sequence) could be read out during translocation by measurement of transverse electrical current, voltage signal, ionic current or hydrogen-bond mediated tunneling signal generated by each base in turn. However, DNA translocation inside a solid nanopore remains poorly controlled and DNA moves too rapidly to be detected at the desired single-base resolution. Here we show using realistic atomistic modeling that the recently proposed DNA transistor can achieve single-base control. These simulation results and a simple theoretical model inspired by the numerical studies demonstrate that when pulled by an optical tweezer as in a single molecule experiment or driven by a biasing electric field as in a high-throughput screening mode, the DNA transistor allows single stranded DNA to transits a nanopore in a stick-slip or thermal ratchet-like fashion, i.e. DNA alternatively stops and advances quickly one nucleotide spacing. During a stick state, a DNA base could be positioned before a sensor for an accurate read-out. We expect that the DNA transistor could be utilized in conjunction with a nanopore-based DNA sensing technology to achieve the goal of fast and cheap DNA sequencing.

Interfacial pH-gradient induced micro-capillary filling with the aid of transverse electrodes arrays in presence of electrical double layer effects

In the present work, we outline the design and analysis of a micro-capillary filling mechanism through the aid of interfacial pH gradients (and hence interfacial tension gradients) generated by employing arrays of transverse electrodes inducing step changes in voltages, in a natural buffer system that requires low power and no synthetic ampholytes. The capillary transport is modulated by a dynamic and non-trivial coupling between the interfacial tension and viscous resistances, as a consequence of the underlying intermolecular interactions. The competing effects of the driving and the retarding forces effectively determine the displacement, velocity and acceleration characteristics of the capillary front, in a dynamically evolving manner. A comprehensive theoretical model of capillary dynamics is developed here to address these issues in details, thereby revealing the combined influence of the interfacial electrochemistry and the applied transverse voltages, as guided by the pertinent fundamental thermodynamic principles governed by free energy considerations and the physico-chemical phenomena over interfacial scales. Non-trivial implications of the pH-gradient driven micro-capillary transport are aptly emphasized, so as to offer significant physical insights on the adopted strategy as a guiding principle for facilitating capillary filling processes by inducing a modulation in the effective interfacial energy. Particular implications on the capillary filling time are also pinpointed, revealing the effectiveness of the adopted design strategy. Finally, a universal scaling relationship of the capillary filling time as a function of the pertinent operating parameters is derived, so as to provide a generalized guideline for implementing the design scheme. A non-dimensional parameter, depending simultaneously on the inter-electrode pitch and the transverse voltage, is identified, which may be kept to a minimal limit within the other operating constraints of the chosen system, towards minimizing the capillary filling time.

Nernst effect and dimensionality in the quantum limit

Nernst effect, the transverse voltage generated by a longitudinal thermal gradient in presence of magnetic field has recently emerged as a very sensitive, yet poorly understood, probe of electron organization in solids. Here we report on an experiment on graphite, a macroscopic stack of graphene layers, which establishes a fundamental link between dimensionality of an electronic system and its Nernst response. In sharp contrast with single-layer graphene, the Nernst signal sharply peaks whenever a Landau level meets the Fermi level. This points to the degrees of freedom provided by finite interlayer coupling as a source of enhanced thermoelectric response in the vicinity of the quantum limit. Since Landau quantization slices a three-dimensional Fermi surface, each intersection of a Landau level with the Fermi level modifies the Fermi surface topology. According to our results, the most prominent signature of such a topological phase transition emerges in the transverse thermoelectric response.

Transverse Photovoltage Induced by Circularly Polarized Light

We discovered that when circularly polarized light is obliquely incident on a two-dimensional metallic photonic crystal slab, electrical voltage is induced perpendicular to the incident plane. The sign of the signal is reversed by changing the sense of polarization or incident angle. The origin of this transverse photoinduced voltage is explained in terms of the force proportional to the light intensity induced by the asymmetry, which is brought about by the angular momentum of the incident light, along with the modification of local near-surface electromagnetic fields in the slab and field enhancement due to surface plasmon resonance.

Microchip free flow planar reversed phase electrochromatography with monolithic stationary phase

In this study, microchip free flow planar RP electrochromatography (microFF-PRPEC) was developed by in situ polymerization of monolithic materials in microchamber, and successfully applied for the separation of dyes and proteins. Poly(butyle methyacrylate-co-ethylene dimethacrylate) was prepared by UV-initiated polymerization in a glass microchamber (42 mm long, 23 mm wide, and 28 microm deep). A mixture of 1-propanol, 1,4-butanediol, and water was chosen as porogens, and 1.2% (wt%) 2-acrylamide-2-methyl-propanesulfonic acid (AMPS) was added into the polymerization solution to generate EOF. With 30% v/v ACN-15 mM Tris-HCl as the mobile phase, rhodamine B and methyl green were separated from each other with 400 V transverse voltage applied, and resolution as high as 4.6 was obtained, much higher than that obtained by microFFE under optimal conditions. Furthermore, microFF-PRPEC was also successfully applied into the separation of lysozyme and ribonuclease B, and resolution as high as 9.4 was obtained. All these results demonstrate that microFF-RPPEC might have great potential in the microscale continuous preparation of samples with improved resolution compared to microFFE.

Berry-phase-mediated topological thermoelectric transport in gapped single and bilayer graphene

We consider the anomalous thermoelectric transport in gapped single and bilayer graphene where the gap may be due to broken inversion symmetry. In the presence of the gap, nontrivial Berry phase effects can be shown to mediate a transverse thermoelectric voltage in response to an applied temperature gradient even in the absence of a perpendicular magnetic field. This spontaneous anomalous Nernst effect is nonzero for nonuniform chemical potential in the two inequivalent valleys in the graphene band structure. Conversely, the Nernst response can be used to create a valley-index polarization between the two transverse sample edges as in the analogous valley Hall effect.

Dual-mode magnetoelectric effect in laminate composite of Terfenol-D alloy and PMN–PT transformer with double output ports

The magnetoelectric effect of a laminate composite made by sandwiching a Rosen-type Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) single crystal transformer between two length-magnetized magnetostrictive Tb0.3Dy0.7Fe1.92 (Terfenol-D) alloy plates has been investigated. An additional giant sharp longitudinal–longitudinal (L–L) mode resonant magnetoelectric voltage coefficient of 15.6 V Oe−1 due to the transformer voltage gain effect was observed besides the longitudinal–transverse (L–T) mode magnetoelectric voltage coefficient of 4.0 V Oe−1. Moreover, our novel dual-mode (L–L and L–T) laminate can provide two independent output ports, which makes the composite a promising material for multifunctional application in magnetic sensors and magnetoelectric transducers.

Frequency doubling and memory effects in the spin Hall effect

We predict that when an alternating voltage is applied to a semiconducting system with inhomogeneous electron density in the direction perpendicular to main current flow, the spin Hall effect results in a transverse voltage containing a double-frequency component. We also demonstrate that there is a phase shift between applied and transverse-voltage oscillations, related to the general memristive behavior of semiconductor spintronic systems. A different method to achieve frequency doubling based on the inverse spin Hall effect is also discussed.

Nonlinear two-dimensional frequency- and temperature-dependent vortex dynamics in a tilted washboard pinning potential

The Langevin equation for a two-dimensional nonlinear guided vortex motion in a tilted cosine pinning potential in the presence of an ac current is exactly solved in terms of a matrix continued fraction at arbitrary value of the Hall effect. The influence of an ac current of arbitrary amplitude and frequency on the dc and ac magnetoresistivity tensors is theoretically considered. Experimental realization of this model in thin-film geometry opens up a possibility for a variety of experimental studies of directed motion of vortices under [dc + ac)- driving simply by measuring longitudinal and transverse voltages.

Transverse voltage in superconductors at zero applied magnetic field

A systematic study of the transverse voltage at zero magnetic field in the superconducting state is reported. The effects of warming rate, temperature, applied magnetic field, and electrical current on the transversal resistance ( R XY) of polycrystalline superconducting sample are taken into account. At zero magnetic field two peaks are observed in R XY( T) curves which are related to the double superconducting transition in the R XX( T) component. In the superconducting ( R XX = zero) and normal states no transverse voltage has been detected at zero magnetic field as expected. The results are discussed within the framework of the motion of Abrikosov and Josephson vortices and anti-vortices. A new scaling relation between transverse and longitudinal components given by R XY ∼ d R XX/d T has been confirmed.

Generation of terahertz radiation by a moving bunch of nonequilibrium electron-hole plasma

We report on properties of coherent radiation from nonequilibrium electron-hole $(e\text{\ensuremath{-}}h)$ plasma bunch excited by an ultrashort laser pulse crossing a semiconducting slab subject to transverse bias voltage. Self-consisted calculations of nonequilibrium Boltzmann and Maxwell equations have established the fundamental role of uniformly moving bunch of $e\text{\ensuremath{-}}h$ plasma in coherent generation of terahertz radiation. We have shown that predicted properties crucially depend on the physics of dissipation mechanisms, current configurations, and relative traveling velocities of $e\text{\ensuremath{-}}h$ plasma bunch and terahertz radiation pulse. It has distinguished two major regimes of terahertz emission, single pulse emission, and firing twinned pulses at the moments of creation and extinction of moving bunch of $e\text{\ensuremath{-}}h$ plasma related to the front and rare boundaries of semiconducting slab, respectively. The results of developed theory are applied to enhance the performance of photoconductive terahertz emitters.