Nonlinear Hall Effect Research Articles

Tunable semimetallic state in compressive-strainedSrIrO3films revealed by transport behavior

Orthorhombic SrIrO3 is a typical spin-orbit-coupling correlated metal that shows diversified physical properties under the external stimuli. Here nonlinear Hall effect and weakly temperature-dependent resistance are observed in a SrIrO3 film epitaxially grown on SrTiO3 substrate. It infers that orthorhombic SrIrO3 is a semimetal oxide. However, linear Hall effect and insensitive-temperature-dependent resistance are observed in SrIrO3 films grown on (La,Sr)(Al,Ta)O3 (LSAT) substrates, suggesting a tunable semimetallic state due to band structure change in SrIrO3 films under different compressive strain. The mechanism of this evolution is explored in detail through strain-state analysis by reciprocal space mapping and electron diffraction, carrier density and mobility calculations, as well as electronic band structure evolution under compressive strain (predicted by tight-binding approximation). It might suggest that the strain-induced band shift leads to the semimetallic tuning in the SrIrO3 film grown on from SrTiO3 to LSAT substrates. Our findings illustrate the tunability of SrIrO3 properties and pave the way to induce novel physical states in SrIrO3 such as the proposed topological insulator state in heterostructures.

Tilted loop currents in cuprate superconductors

The paper briefly surveys theoretical models for the polar Kerr effect (PKE) and time-reversal symmetry breaking in the pseudogap phase of cuprate superconductors. By elimination, the most promising candidate is the tilted loop-current model, obtained from the Simon–Varma model by tilting one triangular loop up and another one down toward the apical oxygens. The model is consistent with the PKE, spin-polarized neutron scattering, and optical anisotropy measurements. Spontaneous currents in this model flow between the in-plane and apical oxygens in such a manner that each oxygen belongs to one current loop. This loop-current pattern is similar to the spin order in the magnetoelectric antiferromagnet Cr2O3, where the PKE is observed experimentally. By analogy, it should be possible to train the PKE sign in the cuprates magnetoelectrically. Several experiments are proposed to confirm the loop-current order: the magnetic-field-induced polarity, the nonlinear anomalous Hall effect, and the second-harmonic generation.

Graphene in proximity to magnetic insulating LaMnO3

Proximity to functional substrates may enhance the coupling between the quantum degrees of freedom and thus develop nontrivial quantum effects in graphene. Here, we demonstrate the successful fabrication of graphene in proximity to atomically flat magnetic insulating LaMnO3 films. The insulating nature of the LaMnO3 films not only ensures the electronic transport only occur in the graphene layers but also allow them to serve as dielectric layers for gating. Transport measurements reveal anomalous behaviors, including asymmetrical longitudinal magnetoresistivity and nonlinear Hall effect. This work may pave a way toward the realization of intriguing quantum phases in graphene.

Quantum and Classical Magnetoresistance in Ambipolar Topological Insulator Transistors with Gate-tunable Bulk and Surface Conduction

Weak antilocalization (WAL) and linear magnetoresistance (LMR) are two most commonly observed magnetoresistance (MR) phenomena in topological insulators (TIs) and often attributed to the Dirac topological surface states (TSS). However, ambiguities exist because these phenomena could also come from bulk states (often carrying significant conduction in many TIs) and are observable even in non-TI materials. Here, we demonstrate back-gated ambipolar TI field-effect transistors in (Bi0.04Sb0.96)2Te3 thin films grown by molecular beam epitaxy on SrTiO3(111), exhibiting a large carrier density tunability (by nearly 2 orders of magnitude) and a metal-insulator transition in the bulk (allowing switching off the bulk conduction). Tuning the Fermi level from bulk band to TSS strongly enhances both the WAL (increasing the number of quantum coherent channels from one to peak around two) and LMR (increasing its slope by up to 10 times). The SS-enhanced LMR is accompanied by a strongly nonlinear Hall effect, suggesting important roles of charge inhomogeneity (and a related classical LMR), although existing models of LMR cannot capture all aspects of our data. Our systematic gate and temperature dependent magnetotransport studies provide deeper insights into the nature of both MR phenomena and reveal differences between bulk and TSS transport in TI related materials.

Field Induced Positional Shift of Bloch Electrons and Its Dynamical Implications

We derive the field correction to the Berry curvature of Bloch electrons, which can be traced back to a positional shift due to the interband mixing induced by external electromagnetic fields. The resulting semiclassical dynamics is accurate to second order in the fields, in the same form as before, provided that the wave packet energy is derived up to the same order. As applications, we discuss the orbital magnetoelectric polarizability and predict nonlinear anomalous Hall effects.

Observation of self-induced optical vortex precession.

We report on the observation of self-induced precession of an optical vortex as a result of the nonlinear interaction between light and liquid crystals. The phenomenon corresponds to an instability for the spin-orbit interaction of light that manifests as a spontaneous axial symmetry breaking, which leads to the orbital motion of the optical vortex around the beam propagation. A nonlinear spin Hall effect of light is experimentally identified, thereby unveiling an original demonstration of spin to extrinsic orbital light angular momentum self-conversion.

Transmutation of Skyrmions to Half-Solitons Driven by the Nonlinear Optical Spin Hall Effect

We show that the spin domains, generated in the linear optical spin Hall effect by the analog of spin-orbit interaction for exciton polaritons, are associated with the formation of a Skyrmion lattice. In the nonlinear regime, the spin anisotropy of the polariton-polariton interactions results in a spatial compression of the domains and in a transmutation of the Skyrmions into oblique half-solitons. This phase transition is associated with both the focusing of the spin currents and the emergence of a strongly anisotropic emission pattern.

Nonlinear Anomalous Hall Effect and Negative Magnetoresistance in a System with Random Rashba Field

We predict two spin-dependent transport phenomena in two-dimensional electron systems, which are induced by a spatially fluctuating Rashba spin-orbit interaction. When the electron gas is magnetized, the random Rashba interaction leads to the anomalous Hall effect. An example of such a system is a narrow-gap magnetic semiconductor-based symmetric quantum well. We show that the anomalous Hall conductivity reveals a strongly nonlinear dependence on the magnetization, decreasing exponentially at large spin density. We also show that electron scattering from a fluctuating Rashba field in a two-dimensional nonmagnetic electron system leads to a negative magnetoresistance arising solely due to spin-dependent effects.

Nonlinear Optical Spin Hall Effect and Long-Range Spin Transport in Polariton Lasers

We report on the experimental observation of the nonlinear analogue of the optical spin Hall effect under highly nonresonant circularly polarized excitation of an exciton-polariton condensate in a GaAs/AlGaAs microcavity. The circularly polarized polariton condensates propagate over macroscopic distances, while the collective condensate spins coherently precess around an effective magnetic field in the sample plane performing up to four complete revolutions.

OptimizingBi2−xSbxTe3−ySeysolid solutions to approach the intrinsic topological insulator regime

To optimize the bulk-insulating behavior in the topological insulator materials having a tetradymite structure, we have synthesized and have characterized single-crystal samples of ${\mathrm{Bi}}_{2\text{\ensuremath{-}}x}{\mathrm{Sb}}_{x}{\mathrm{Te}}_{3\text{\ensuremath{-}}y}{\mathrm{Se}}_{y}$ solid solution at various compositions. We have elucidated that there are a series of intrinsic compositions where the acceptors and donors compensate each other and present a maximal bulk-insulating behavior. At such compositions, the resistivity can become as large as several $\ensuremath{\Omega}$ cm at low temperatures, and one can infer the role of the surface-transport channel in the nonlinear Hall effect. In particular, the composition of ${\mathrm{Bi}}_{1.5}{\mathrm{Sb}}_{0.5}{\mathrm{Te}}_{1.7}{\mathrm{Se}}_{1.3}$ achieves the lowest bulk carrier density and appears to be best suited for surface-transport studies.

Nonlinear spin Hall effect in GaAs (110) quantum wells

We consider stationary spin current in a (110)-oriented GaAs-based symmetric quantum well due to a nonlinear response to an external periodic electric field. The model assumed includes the Dresselhaus spin-orbit interaction and the random Rashba spin-orbit coupling. The Dresselhaus term is uniform in the quantum well plane and gives rise to spin splitting of the electron band. The external electric field of frequency $\omega$ - in the presence of random Rashba coupling -- leads to virtual spin-flip transitions between spin subbands, generating stationary pure spin current proportional to the square of the field amplitude.

Nonlinear Hall Effect as a Signature of Electronic Phase Separation in the Semimetallic FerromagnetEuB6

This work reports a study of the nonlinear Hall effect (HE) in the semimetallic ferromagnet EuB(6). A distinct switch in its Hall resistivity slope is observed in the paramagnetic phase, which occurs at a single critical magnetization over a wide temperature range. The observation is interpreted as the point of percolation for entities of a more conducting and magnetically ordered phase in a less ordered background. With an increasing applied magnetic field, the conducting regions either increase in number or expand beyond the percolation limit, hence increasing the global conductivity and effective carrier density. An empirical two-component model provides excellent scaling and a quantitative fit to the HE data and may be applicable to other correlated electron systems.

Nonlinear Hall effect in a quasi-two-dimensional electron system

The nonlinear electron transport in GaAs double quantum wells with two occupied size-quantization levels has been studied at a temperature of 4.2 K in the magnetic fields B < 1 T. It has been found that a sinusoidal electric current Iac induces the generation of higher harmonics of both longitudinal Vxx(B) and Hall Vxy(B) voltages in the quasi-two-dimensional electron system under consideration. The Hall voltage oscillating in the magnetic field has been shown to appear in the electron system with two occupied size-quantization levels in the presence of microwave radiation and dc electric current Idc. The experimental data indicate the independent contributions of the diagonal and off-diagonal components of the conductivity tensor to the nonlinear magnetotransport at high filling factors.

Magnetotransport and magnetic properties of β-FeSi2single crystals

Magnetotransport and magnetic properties have been measured for β-FeSi2 single crystals from 4.2 to 300 K using a pulsed magnet, a superconducting magnet, and a SQUID magnetometer. Nonlinear Hall effect followed by a normal Hall effect was observed, involving a hysteresis effect at low temperature. The signs of normal Hall coefficients changed from positive to negative ones at around 180 K. The magnetization curves above 180 K are well explained by considering the superparamagnetism. Below 150 K we found that the aggregates of Fe atoms exhibit an inter-aggregate ferromagnetic interaction. At low temperature we also found that the cohesive forces obtained from the ρH-B curves are larger than those from the M-Bcurves. This discrepancy was discussed qualitatively by a proposed model.

Regularization of the Alfvén singularity by the Hall effect

An ideal magnetohydrodynamics (MHD) equilibrium is described by a system of rather complicated singular differential equations when a flow is included. The so-called Alfvén singularity occurs at the place where the Doppler-shifted Alfvén velocity vanishes. It is due to the vanishing of the highest-order derivative in the differential equation. The Hall effect, working as a singular perturbation to the ideal MHD system, yields a new branch of regular solutions that can smoothly connect two regions separated by the Alfvén singularity. The thickness of the transition layer is of the order of the ion skin depth, the intrinsic length scale brought about by the singular perturbation. The regularization mechanism of the nonlinear Hall effect is not as simple as that of the diffusion effect producing an entropy (viscosity) solution in a viscous fluid. The Hall effect removes the restriction binding the magnetic and flow characteristics, and creates the new branch of regularized solutions. One-dimensional analysis loses sight of this new branch of equilibria.

Nonlinear Hall effect for materials with weak thermoelectric power coefficients: preliminary comparisons between theoretical results of the thermodynamic field theory and experimental data.

This paper forms a part of a series of manuscripts which we intend to submit for publication in the near future, aiming to test the validity of the thermodynamic field theory (TFT), previously formulated, comparing the theoretical results with experimental data. In this particular case, we shall analyze the Hall effect. As known, when a magnetic field is applied at right angles to the direction of an electric current or a thermal gradient, galvano- and thermomagnetic effects appear in the material. In this paper, we shall show that if we study these effects in nonlinear regime, the TFT foresees an interesting effect: the nonlinear Hall effect. This prediction is herein submitted to experimental verifications. In this paper, we shall analyze this effect studying materials with weak thermoelectric power coefficients. We shall show the agreement between the theoretical predictions of the TFT and experiments. Experimental curves related to the nonlinear Hall effect allow us to determine the order of magnitude of the constant chi introduced in the TFT.

Thermodynamic field theory with applications

AbstractThermodynamic field theory (TFT) allows us to deal with thermodynamic systems submitted even to strong nonequilibrium conditions. The theory formulated in this article enables us to find field equations whose solutions give the generalized relations between the thermodynamic forces and their conjugate flows. It will be shown that evolution of thermodynamic systems is well described in Weyl's space. In the particular case in which the thermodynamic forces and conjugate flows are linked only through a symmetric tensor (the metric tensor), the resulting geometry is Riemannian geometry. When Weyl's space is even‐dimensional, the thermodynamic space introduced in this study becomes a differentiable symplectic manifold. As an example of application, the thermoelectric effect and the unimolecular triangular chemical reaction are analyzed in great detail. The Field–Körös–Noyes model shows the theoretical treatment of a more complex chemical example. Theoretical analysis of materials simultaneously submitted to magnetic fields and electric currents can be found in previous articles. In this case, TFT foresees a new effect: the nonlinear Hall effect. The agreement between the theoretical predictions and experiments is discussed. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004

Nonlinear Hall effect in a time-periodic electric field and related phenomena

A motion of neutral and charged particles located nearby a metal surface under joint action of time-periodic electric field $E(t)$ directed normally to the surface and permanent magnetic field H directed along the surface has been considered. It has been shown that due to a nonlinearity of the system there exists a directed transport of the particles perpendicularly to both magnetic and electric fields with velocity which is proportional to ${E}^{2}H.$ The velocity has been evaluated for charged (ions, electrons, etc.) and neutral (atoms, molecules, nanosize clusters, etc.) particles adsorbed on a metal surface. Corresponding surface electric current has been found as a function of a frequency of the electric field and material parameters. It has been noted that the similar phenomena appear in a bulk of electrically inhomogeneous media.

Nonlinear Hall Effect on Metal Surfaces in a Periodic Electric Field

A theory of nonlinear Hall effect arising in the metal surface layer as a result of the application of an alternating electric field is given. Expressions for the Hall current are derived.

Linear and nonlinear Hall effect in the spin-density wave phase of (TMTSF) 2AsF6

Measurements of the Hall effect at low electric fields in the metallic and spin-density wave (SDW) phases in (TMTSF) 2 AsF 6 shows that the scattering of single particles is strongly reduced in the SDW phase. This is attributed to a strong electron-electron scattering present in the metallic phase and absent in the SDW phase. Above the depinning threshold field for the nonlinear SDW conductivity the Hall voltage is a reliable measure of the quasiparticle current. This current is reduced above the depinning threshold because of the backflow of quasiparticles due to the interaction with the moving SDW. At 4.2 K the backflow coefficient is comparable to what is observed in CDW systems