Recent magnetotransport studies on uniaxial ferromagnets have reported a cusplike feature in Hall resistivity when the magnetic field is tilted away from the conventional orthogonal direction of the Hall measurement. This feature has often been attributed to the topological Hall effect arising from a non-coplanar spin structure. In this article, we have studied the uniaxial ferromagnet SmMn$_2$Ge$_2$ to demonstrate that this feature is rather a consequence of the nonorthogonal geometry of the Hall measurement and is expected to appear whenever the magnetic field is applied away from the easy axis of magnetization, nonorthogonal to the sample plane. The Hall resistivity, exhibiting this feature, scales with the orthogonal component of the magnetization, indicating that the observed feature is simply a manifestation of the anomalous Hall effect. We explain the origin of this feature based on the evolution of ferromagnetic domains under a nonorthogonal external magnetic field.
We establish a universal theory to understand quasiparticle Hall effects and transverse charge-carrier transport in organic semiconductors. The simulations are applied to organic crystals inspired by rubrene and cover multiple transport regimes. This includes calculations of the intrinsic Hall conductivity in pristine crystals, which are connected with a simple description of semi-classical electron transport that involves the concept of closed electronic orbits in the band structure, which can be easily calculated in density functional theory. Furthermore, this framework is employed to simulate temperature-dependent longitudinal and transverse mobilities in rubrene. These simulations are compared to experimental findings, providing insights into these results by characterizing the non-ideality of the Hall effect due to the influence of vibrational disorder. We finally investigate the conditions for the observation of Shubnikov-de Haas oscillations in the longitudinal resistivity and quantized Hall plateaus in the transverse resistivity. A clear picture why this is not observed in rubrene is developed. These insights into classical and quantum Hall effects and their intermediates in organic semiconductors establish a blueprint for future explorations in similar systems.
Alberto Hijano, Sakineh Vosoughi-nia, F. Sebastián Bergeret
et al.
We extend the Mattis-Bardeen theory for the dynamical response of superconductors to include different types of Hall responses. This is possible thanks to a recent modification of the quasiclassical Usadel equation, which allows for analyzing Hall effects in disordered superconductors and including the precise frequency dependence of such effects. Our results form a basis for analyzing dynamical experiments especially on novel thin-film superconductors, where ordinary Hall and spin Hall effects can both show up.
In a recent work [C. Chevalier, B. M. Wong, Comput. Phys. Commun. ${\bf 274}$, 108299 (2022); arXiv: 2203.05233 [cond-mat.mes-hall]] the interesting and popular problem was considered. Authors attempted to solve the self-consistent Schrödinger-Poisson problem for an effective mass electron in a core-shell semiconductor nanowire. The corresponding MATLAB-based software package was presented. However, an incorrect solution of the Schrödinger equation invalidates the whole result. Here we point out the corresponding error and possible ways to fix it.
Spin-Hall nano-oscillators (SHNOs) are promising spintronic devices to realize current controlled GHz frequency signals in nanoscale devices for neuromorphic computing and creating Ising systems. However, traditional SHNOs -- devices based on transition metals -- have high auto-oscillation threshold currents as well as low quality factors and output powers. Here we demonstrate a new type of hybrid SHNO based on a permalloy (Py) ferromagnetic-metal nanowire and low-damping ferrimagnetic insulator, in the form of epitaxial lithium aluminum ferrite (LAFO) thin films. The superior characteristics of such SHNOs are associated with the excitation of larger spin-precession angles and volumes. We further find that the presence of the ferrimagnetic insulator enhances the auto-oscillation amplitude of spin-wave edge modes, consistent with our micromagnetic modeling. This hybrid SHNO expands spintronic applications, including providing new means of coupling multiple SHNOs for neuromorphic computing and advancing magnonics.
Motivated by recent experiments on the phonon contribution to the thermal Hall effect in the cuprates, we present an analysis of chiral phonon transport. We assume the chiral behavior arises from a non-zero phonon Hall vicosity, which is likely induced by the coupling to electrons. Phonons with a non-zero phonon Hall viscosity have an intrinsic thermal Hall conductivity, but Chen et al. (Phys. Rev. Lett. 124, 167601 (2020)) have argued that a significantly larger thermal Hall conductivity can arise from an extrinsic contribution which is inversely proportional to the density of impurities. We solve the Boltzmann equation for phonon transport and compute the temperature ($T$) dependence of the thermal Hall conductivity originating from skew scattering off point-like impurities. We find that the dominant source for thermal Hall transport is an interference between impurity skew scattering channels with opposite parity. The thermal Hall conductivity $\sim T^{d+2}$ at low $T$ in $d$ dimensions, and has a window of $T$-independent behavior for $T > T_{\rm imp}$, where $T_{\rm imp}$ is determined by the ratio of scattering potentials with opposite parity. We also consider the role of non-specular scattering off the sample boundary, and find that it leads to negligible corrections to thermal Hall transport at low $T$.
Askar A. Iliasov, Mikhail I. Katsnelson, Shengjun Yuan
We calculate the Hall conductivity of a Sierpinski carpet using Kubo-Bastin formula. The quantization of Hall conductivity disappears when we increase the depth of the fractal. The Hall conductivity is no more proportional to the Chern number. Nevertheless, these quantities behave in a similar way showing some reminiscence of a topological nature of the Hall conductivity. We also study numerically the bulk-edge correspondence and find that the edge states become less manifested when the depth of Sierpinski carpet is increased.
Hall viscosity, also known as the Lorentz shear modulus, has been proposed as a topological property of a quantum Hall fluid. Using a recent formulation of the composite fermion theory on the torus, we evaluate the Hall viscosities for a large number of fractional quantum Hall states at filling factors of the form $ν=n/(2pn\pm 1)$, where $n$ and $p$ are integers, from the explicit wave functions for these states. The calculated Hall viscosities $η^A$ agree with the expression $η^A=(\hbar/4) {\cal S}ρ$, where $ρ$ is the density and ${\cal S}=2p\pm n$ is the "shift" in the spherical geometry. We discuss the role of modular invariance of the wave functions, of the center-of-mass momentum, and also of the lowest-Landau-level projection. Finally, we show that the Hall viscosity for $ν={n\over 2pn+1}$ may be derived analytically from the microscopic wave functions, provided that the overall normalization factor satisfies a certain behavior in the thermodynamic limit. This derivation should be applicable to a class of states in the parton construction, which are products of integer quantum Hall states with magnetic fields pointing in the same direction.
It is known that the Shubnikov--de Haas oscillations can be observed in the Hall resistivity, although their amplitude is much weaker than the amplitude of the diagonal resistivity oscillations. Employing a model of two-dimensional massive Dirac fermions that exhibits anomalous Hall effect, we demonstrate that the amplitude of the Shubnikov--de Haas oscillations of the anomalous Hall conductivity is the same as that of the diagonal conductivity. We argue that the oscillations of the anomalous Hall conductivity can be observed by studying the valley Hall effect in graphene superlattices and the spin Hall effect in the low-buckled Dirac materials.
We derive a generalized set of Ward identities that captures the effects of topological charge on Hall transport. The Ward identities follow from the 2+1 dimensional momentum algebra, which includes a central extension proportional to the topological charge density. In the presence of topological objects like Skyrmions, we observe that the central term leads to a direct relation between the thermal Hall conductivity and the topological charge density. We extend this relation to incorporate the effects of a magnetic field and an electric current. The topological charge density produces a distinct signature in the electric Hall conductivity, which is identified in existing experimental data, and yields further novel predictions. For insulating materials with translation invariance, the Hall viscosity can be directly determined from the Skyrmion density and the thermal Hall conductivity to be measured as a function of momentum.
We calculate a topological invariant, whose value would coincide with the Chern number in case of integer quantum Hall effect, for fractional quantum Hall states. In case of Abelian fractional quantum Hall states, this invariant is shown to be equal to the trace of the K-matrix. In case of non-Abelian fractional quantum Hall states, this invariant can be calculated on a case by case basis from the conformal field theory describing these states. This invariant can be used, for example, to distinguish between different fractional Hall states numerically even though, as a single number, it cannot uniquely label distinct states.
The quantum Hall transition is one of the simplest and most studied quantum phase transitions. Nevertheless, the experimental observation of a new phase in this regime, the quantum Hall insulator, still remains a puzzle since the first report more than a decade ago, as it is in contradiction with all theoretical studies based on microscopically coherent quantum calculations. In this work we introduce into the coherent quantum theory a new ingredient - rare incoherent events, in a controlled manner. Using both direct numerical solutions and real-space renormalization, we demonstrate that these decoherence events stabilize the elusive quantum Hall insulator phase, which becomes even more stable with increasing temperature and voltage bias, in agreement with experiments.
The (guiding-center) "Hall viscosity" is a fundamental tensor property of incompressible ``Hall fluids'' exhibiting the fractional quantum Hall effect; it determines the stress induced by a non-uniform electric field, and the intrinsic dipole moment on (unreconstructed) edges. It is characterized by a rational number and an intrinsic metric tensor that defines distances on an ``incompressibility lengthscale''. These properties do not require rotational invariance in the 2D plane. The sign of the guiding-center Hall viscosity distinguishes particle fluids from hole fluids, and its magnitude provides a lower bound to the coefficient of the $O(q^4)$ small-q limit of the guiding center structure factor, a fundamental measure of incompressibility. This bound becomes an equality for conformally-invariant model wavefunctions such as Laughlin or Moore-Read states.
Abstract Mutations in mes-2, mes-3, mes-4, and mes-6 result in maternal-effect sterility: hermaphrodite offspring of mes/mes mothers are sterile because of underproliferation and death of the germ cells, as well as an absence of gametes. Mutant germ cells do not undergo programmed cell death, but instead undergo a necrotic-type death, and their general poor health apparently prevents surviving germ cells from forming gametes. Male offspring of mes mothers display a significantly less severe germline phenotype than their hermaphrodite siblings, and males are often fertile. This differential response of hermaphrodite and male offspring to the absence of mes+ product is a result of their different X chromosome compositions; regardless of their sexual phenotype, XX worms display a more severe germline phenotype than XO worms, and XXX worms display the most severe phenotype. The sensitivity of the mutant phenotype to chromosome dosage, along with the similarity of two MES proteins to chromatin-associated regulators of gene expression in Drosophila, suggest that the essential role of the mes genes is in control of gene expression in the germline. An additional, nonessential role of the mes genes in the soma is suggested by the surprising finding that mutations in the mes genes, like mutations in dosage compensation genes, feminize animals whose male sexual identity is somewhat ambiguous. We hypothesize that the mes genes encode maternally supplied regulators of chromatin structure and gene expression in the germline and perhaps in somatic cells of the early embryo, and that at least some of their targets are on the X chromosomes.
AbstractTl pentafluoroorthotellurate (I) prepared from TlF and teflic acid HOTeF5 in toluene reacts with mesitylene (II) to produce the teflate‐bridged di(η6‐mesitylene)Tl dimer (III).
Straipsnyje glaustai apžvelgiama ir kritiškai įvertinama Lietuvos ekonomikos mokslo būklė - praeities, dabarties ir ateities raidos tendencijos - pasaulio ekonominės minties plėtros ir globalizacijos iššūkių “žmogiškajam kapitalui” kontekste. Teigiama, kad ekonomikos mokslo potencialo požiūriu Lietuva vis dar deja, tebėra visiškai nekonkurencinga pasaulinėje mokslo rinkoje, kartu mėginama paaiškinti šią padėtį lėmusius ir tebelemiančius veiksnius. Aptariant padėtį ir ją lėmusius veiksnius svarstoma, kaip būtų galima spręsti Lietuvos ekonomikos mokslą kamuojančias problemas.
We discuss the comment by Zarand and Zawadowski (cond-mat/0009283) on our preprint cond-mat/0007430 where it has been shown that the strong coupling regime for the two-channel Kondo model of two level system can be never realized for any realistic microscopic description. The authors of the comment state that the Kondo temperature can be substantially increased due to electron-hole asymmetry. Here we show by direct calculation that the electron-hole asymmetry does not enter the leading logarithmic approximation. Consequently, we disagree with the aforementioned comment.
We study the properties of the "spin quantum Hall fluid" - a novel spin phase with quantized spin Hall conductance that is potentially realizable in superconducting systems with unconventional pairing symmetry. A simple realization is provided by a $d_{x^2-y^2} + id_{xy}$ superconductor which we argue has a dimensionless spin Hall conductance equal to two. A theory of the edge states of the $d_{x^2-y^2}+id_{xy}$ superconductor is developed. The properties of the transition to a phase with vanishing spin Hall conductance induced by disorder are considered. We construct a description of this transition in terms of a supersymmetric spin chain, and use it to numerically determine universal properties of the transition. We discuss various possible experimental probes of this quantum Hall physics.
A new kind of charge-Hall effect is shown. Unlike in the usual Hall effect, the driving force in the longitudinal direction is a spin force, which may originate from the gradient of a Zeeman field or a spin-dependent chemical potential. The transverse force is provided by a Berry curvature in a mixed position-momentum space. We can establish an Onsager relation between this effect and the spin-Hall effect provided the spin current in the latter is modified by a torque dipole contribution. This remarkable relation leads to new ways for experimental detection of spin accumulation predicted by the spin Hall effect.