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We study elastic electron scattering and localization by ubiquitous isotopic disorder in one-dimensional systems appearing due to interaction with phonon modes localized at isotope impurities. By using a tight-binding model with intersite hopping matrix element dependent on the interatomic distance, we find mass-dependent backscattering probability by single and pairs of isotopic impurities. For the pairs, in addition to the mass, the distance between the isotopes plays the critical role. Single impurities effectively attract electrons and can produce localized weakly bound electron states. In the presence of disorder, the electron free path at positive energies becomes finite and the corresponding Anderson localization at the spatial scale greatly exceeding the distance between the impurities becomes possible., Comment: 11 figues

The influence of the reduced mass on the results of the approximation by the Morse function of the ground electronic state term potential U(r) of hydrogen molecule nH2 for seven symmetrical isotopologues n = 1-7 is investigated. For each isotopologue, two alternative model solutions of the Schroedinger equation are obtained, namely, M1(r) and M2(r) functions, which differ by the selection of the primary fitting parameters in the Morse approximation. The U(r) - M(r) functions are shown to clearly visualize the differences between the shapes of the potential at its approximation. The concept of systematic deviation of Morse functions from the real potential is introduced. This deviation is always present in the approximation of simple terms, for which U(r) curve lies between M1(r) and M2(r) without crossings. In case of nH2, for M1(r) the systematic monotonous deviation increases, reaching 1700-2770 cm-1 (for 7H2-1H2) at the level of the asymptote. For M2(r) the systematic deviation decreases at larger distances: it is dome-shaped with a maximum of ca. 1500 cm-1 in the upper part of the term, after which it falls to zero. The M2(r) curves for different isotopologues diverge by less than 20 cm-1. There are also anomalies, where M1(r) and M2(r) cross U(r), called "Herzberg anomaly". For example, at around r = 1.08 A the U(r) - M2(r) function shows anomalous negative values ranging from -125 cm-1 (for 1H2) to -142 cm-1 (for 7H2). The diagnostic value of Herzberg anomaly and anharmonicities for various isotopologues is discussed.

This article continues the series of works by the authors on the approximation of the electronic terms of diatomic molecules by the Morse formula, which is the simplest anharmonic approximation of the real term U(r). Depending on the choice of parameters, the approximation has two alternative solutions M1(r) and M2(r), with different patterns of deviations from the real term and its vibrational structure. The difference {\delta}(r)=U(r)-M(r) quantitatively shows the changes in the shape of the terms during approximation. We introduced an empirical anharmonicity function -2{\omega}_e x(v), which characterizes the positions of vibrational levels in the potential well; it demonstrates the distortion of the vibrational structure of the term U(r) during the approximation. Based on the data from literature, the functions {\delta}(r) and -2{\omega}_e x(v) were constructed for more than 20 molecules. Here we present a group of simple terms with minimal deviations from the Morse shape.

The process $e^+e^- \to \omega\pi^0 \to \pi^+\pi^-\pi^0\pi^0$ is studied in the center-of-mass energy region $1.05-2.00$ GeV using data with an integral luminosity of about 35 pb$^{-1}$ collected with the SND detector at the VEPP-2000 $e^+e^-$ collider. In the energy range under study, the value of the measured Born cross section varies from 0.7 to 18 nb. The statistical uncertainty of the cross section is $2-23$%, while the systematic uncertainty is in the range of $3.0-14.2$%. The results are consistent with previous measurements but have better accuracy., Comment: 13 pages, 11 figures

The $e^+e^-\to\eta\gamma$ cross section is measured in the center-of-mass energy range from 1.07 to 2.00 GeV in the decay channel $\eta\to 3\pi^0$, $\pi^0\to\gamma\gamma$. The data set with an integrated luminosity of 242 pb$^{-1}$ accumulated in the experiment with the SND detector at the VEPP-2000 $e^+e^-$ collider is analyzed., Comment: 12 pages, 3 figures

Recent progress in fabricating high-quality conductors with small densities of defects has initiated the studies of the viscous electron fluid and has motivated the search for the evidences of the hydrodynamic regime of electron transport. In this work we come up with the spin imaging technique allowing us to attest to the emergence of electron hydrodynamic flows. Based on numerical calculations we demonstrate that the injected electron spin density is inhomogeneous across the channel when the viscous electron fluid forms the Poiseuille flow. We also argue that the Hanle curves at different positions across the channel acquire relative phase shifts resulting from the variation of the electron drift velocity in inhomogeneous hydrodynamic flows. The studied effects can be employed to evidence and study the viscous electron fluid non-invasively., Comment: 5 pages, 4 figures

We present the results of an experimental study of multiple scattering of positively charged high energy particles in bent samples of monocrystalline silicon. This work confirms the recently discovered effect of a strong reduction in the rms multiple scattering angle of particles channeled in the silicon (111) plane. The effect is observed in the plane orthogonal to the bending plane. We show in detail the influence of angular constraints on the magnitude of the effect. Comparison of the multiple scattering process at different energies indicates a violation of the law of inverse proportionality of the rms angle of channeled particles with energy. By increasing the statistics, we have improved the results of multiple scattering measurements for particles moving, but not channeled, in silicon crystals., Comment: arXiv admin note: text overlap with arXiv:1910.00250 minor fixes

The recent rise of material platforms combining magnetism and two-dimensionality of mobile carriers reveals a diverse spectrum of spin-orbit phenomena and stimulates its ongoing theoretical discussions. In this work we use the density matrix approach to provide a unified description of subtle microscopic effects governing the electron gas spin behavior in the clean limit upon electric perturbations in two-dimensional magnets with strong spin-orbit coupling. We discuss that an inhomogeneity of electrostatic potential generally leads to the electron gas spin tilting with the subsequent formation of equilibrium skyrmion-like spin textures and demonstrate that several microscopic mechanisms of 2DEG spin response are equally important for this effect. We analyze the dynamics of 2DEG spin upon an oscillating electric field with a specific focus on the emergent electric dipole spin resonance. We address the resonant enhancement of magneto-optical phenomena from the spin precession equation perspective and discuss it in terms of the resonant spin generation. We also clarify the connection of both static and dynamic spin phenomena arising in response to a scalar perturbation with the electronic band Berry curvature., Comment: 22 article pages, 5 appendix pages, 5 figures

The topological Hall effect is used extensively to study chiral spin textures in various materials. However, the factors controlling its magnitude in technologically-relevant thin films remain uncertain. Using variable temperature magnetotransport and real-space magnetic imaging in a series of Ir/Fe/Co/Pt heterostructures, here we report that the chiral spin fluctuations at the phase boundary between isolated skyrmions and a disordered skyrmion lattice result in a power-law enhancement of the topological Hall resistivity by up to three orders of magnitude. Our work reveals the dominant role of skyrmion stability and configuration in determining the magnitude of the topological Hall effect., Comment: 10 pages, 3 figures

Memory effects can have a profound impact on the resistivity of semiconductor systems, resulting in giant negative magnetoresistance and MIRO phenomena. This work opens the discussion of the memory effects in 3D conducting systems featured by the presence of the extended one-dimensional defects, such as screw dislocations or static charge stripes. We demonstrate that accounting for the memory effect, that is the capture of electrons on collisionless spiral trajectories winding around extended defects, leads to the strong negative magnetoresistance in case when the external magnetic field direction becomes parallel to the defects axis. This effect gives rise to a significant magnetoresistance anisotropy already for an isotropic Fermi surface and no spin-orbit effects. The proposed resistivity feature can be used to detect one-dimensional scattering defects in these systems.

The UA9 setup, installed in the Super Proton Synchrotron (SPS) at CERN, was exploited for a proof of principle of the double-crystal scenario, proposed to measure the electric and the magnetic moments of short-lived baryons in a high-energy hadron collider, such as the Large Hadron Collider (LHC). Linear and angular actuators were used to position the crystals and establish the required beam configuration. Timepix detectors and high-sensitivity Beam Loss Monitors were exploited to observe the deflected beams. Linear and angular scans allowed exploring the particle interactions with the two crystals and recording their efficiency. The measured values of the beam trajectories, profiles and of the channeling efficiency agree with the results of a Monte-Carlo simulation., Comment: 25 pages, 13 figures

In this paper we argue that the electron skew-scattering on paramagnetic impurities in non-magnetic systems, such as bulk semiconductors, possesses a remarkable fingerprint allowing to differentiate it directly from other microscopic mechanisms of the emergent Hall response. We demonstrate theoretically that the exchange interaction between the impurity magnetic moment and mobile electrons leads to the emergence of an electric Hall current persisting even at zero electron spin polarization. We describe two microscopic mechanisms behind this effect, namely the exchange interaction assisted skew-scattering and the conversion of the SHE induced transverse spin current to the charge one owing to the difference between the spin-up and spin-down conductivities. We propose an essentially all-electric scheme based on a spin-injection ferromagnetic-semiconductor device which allows one to reveal the effect of paramagnetic impurities on the Hall phenomena via the detection of the spin polarization independent terms in the Hall voltage.

We discuss in details the electron scattering pattern on skyrmion-like magnetic textures in two-dimensional geometry. The special attention is focused on analyzing the scattering asymmetry, which is a precursor of the topological Hall effect. We present analytical results valid for the limiting regimes of strong and weak coupling, we also describe the numerical scheme that gives access to the exact solution of the scattering problem. Based on the numerical computations we investigate the properties of the asymmetric scattering for an arbitrary magnitude of the interaction strength and the topology of a magnetic texture. We analyze in details the conditions when the topological charge of a magnetic texture is indeed essential for the appearance of the Hall response. We also describe how the electron scattering asymmetry is modified due to an additional short-range impurity located inside a magnetic skyrmion., Comment: 28 pages, 6 figures

The theoretical study considers chiral spin texture induced in a 2D electron gas (2DEG) by magnetic skyrmions. We calculate the electron gas spin density as a linear response to the exchange interaction between the 2DEG and the magnetization field of a magnetic skyrmion. Two physically distinct regimes occur. When the size of the skyrmion is larger than the inverse Fermi wavevector $k_F^{-1}$, the spin density response follows the magnetization profile of the skyrmion. In the opposite case of a small skyrmion the emerging spin structure of 2DEG has a characteristic size of $k_F^{-1}$ and the response becomes non-local, it can be viewed as chiral Friedel oscillations. At that, the emerging spin structure of the oscillations appears to be more complex than that of the skyrmion itself., Comment: 6 pages, 7 figures

In this paper, we discuss an experimental layout for the two-crystals scenario at the Super Proton Synchrotron (SPS) accelerator. The research focuses on a fixed target setup at the circulating machine in a frame of the Physics Beyond Colliders (PBC) project at CERN. The UA9 experiment at the SPS serves as a testbench for the proof of concept, which is planning to be projected onto the Large Hadron Collider (LHC) scale. The presented in the text configuration was used for the quantitative characterization of the deflected particle beam by a pair of bent silicon crystals. For the first time in the double-crystal configuration, a particle deflection efficiency by the second crystal of $0.188 \pm 3 \cdot 10^{-5}$ and $0.179 \pm 0.013$ was measured on the accelerator by means of the Timepix detector and Beam Loss Monitor (BLM) respectively. In this setup, a wide range angular scan allowed a possibility to \textit{in situ} investigate different crystal working regimes (channeling, volume reflection, etc.), and to measure a bent crystal torsion., Comment: 6 pages, 8 figures. To be submitted to PLB

In this work we manifest that an electrostatic disorder in conducting systems with broken time reversal symmetry universally leads to a chiral ordering of the electron gas giving rise to skyrmion-like textures in spatial distribution of the electron spin density. We describe a microscopic mechanism underlying the formation of the equilibrium chiral spin textures in two-dimensional systems with spin-orbit interaction and exchange spin splitting. We have obtained analytical expressions for spin-density response functions and have analyzed both local and non-local spin response to electrostatic perturbations for systems with parabolic-like and Dirac electron spectra. With the proposed theory we come up with a concept of controlling spin chirality by electrical means., Comment: 6 Pages, 4 Figures, Supplementary materials 4 Pages

Theory of interference-induced quantum corrections to conductivity is developed for two dimensional systems with chiral spin textures including skyrmions. The effect of exchange interaction between electrons and spin textures on weak localization of electronic waves is studied. The spin dephasing rates are calculated as functions of the spin texture size. The anomalous magnetoresistance is shown to be governed by the size and magnetization spatial distribution of the spin textures. The effect of average magnetization-induced spin splitting on weak localization is analyzed. The sign-alternating weak-antilocalization magnetoresistance is demonstrated for skyrmion crystals. We argue that analysis of the low-field magnetoresistance serves as an independent tool for an experimental detection of chiral spin textures and, in particular, skyrmions., Comment: 6 pages, 4 Figures

We present a consistent theory of the topological Hall effect (THE) in 2D magnetic systems with disordered array of chiral spin textures, such as magnetic skyrmions. We focus on the scattering regime when the mean-free path of itinerant electrons exceeds the spin texture size, and THE arises from the asymmetric carrier scattering on individual chiral spin textures. We calculate the resistivity tensor on the basis of the Boltzmann kinetic equation taking into account the asymmetric scattering on skyrmions via the collision integral. Our theory describes both the adiabatic regime, when THE arises from a spin Hall effect and the non-adiabatic scattering when THE is due to purely charge transverse currents. We analyze the dependence of THE resistivity on a chiral spin texture structure,as well as on material parameters. We discuss the crossover between spin and charge regimes of THE driven by the increase of skyrmion size, the features of THE due to the variation of the Fermi energy, and the exchange interaction strength; we comment on the sign and magnitude of THE, Comment: 11 pages, 8 figures

We consider topological Hall effect (THE) in thin ferromagnetic films due to electron scattering on magnetic skyrmions in the presence of the relatively strong external magnetic field. We account for the effect of the magnetic field on a skyrmion structure and describe the hallmarks of THE differentiating it from ordinary and anomalous Hall effects. We have found that, although in typical ferromagnets the variation of magnetic field in the range 1-5 T substantially affects the skyrmion size, THE changes rather weakly remaining quite robust. Therefore, the magnitude of THE is primarily determined by the skyrmions sheet density $n_{sk}$, being comparable to the magnitude of the ordinary Hall effect (OHE) at $n_{sk}=10^{11}$ cm$^{-2}$. The sign of THE is opposite to that of OHE for skyrmions with positive vorticity, while for antiskyrmions the signs are the same., Comment: 6 pages, 4 figures

In this letter we develop the theory of Hall effect driven by non-collinear magnetic textures (topological Hall effect - THE) in diluted magnetic semiconductors (DMS). We show that a carrier spin-orbit interaction induces a chiral magnetic ordering inside a bound magnetic polaron (BMP). The inner structure of non-collinear BMP is controlled by the type of spin-orbit coupling, allowing to create skyrmion- (Rashba) or antiskyrmion-like (Dresselhaus) configurations. The asymmetric scattering of itinerant carriers on polarons leads to the Hall signal which exists in weak external magnetic fields and low temperatures. We point out that DMS-based systems allow one to investigate experimentally the dependence of THE both on a carrier spin polarization and on a non-collinear magnetic texture shape., Comment: 5 pages, 2 figures, 1 table and supplementary materials

We propose a new theory of the topological Hall effect (THE) in systems with chiral magnetization vortices such as magnetic skyrmions. We solve the problem of electron scattering on a magnetic skyrmion exactly, for an arbitrary strength of exchange interaction and the skyrmion size. We report the existence of different regimes of THE and resolve the apparent contradiction between the adiabatic Berry phase theoretical approach and the perturbation theory for THE. We traced how the topological charge Hall effect transforms into the spin Hall effect upon varying the exchange interaction strength or the skyrmion size. This transformation has a nontrivial character: it is accompanied by an oscillating behavior of both charge and spin Hall currents. This hallmark of THE allows one to differentiate the chirality driven contribution to Hall response in the experiments., Comment: 13 pages, 10 figures

We present a theory of electron scattring on a magnetic skyrmion for the case when exchange interaction is moderate so that adiabatic approximation and Berry phase approach is not applicable. The theory explains the appearance of a topological Hall current in the systems with magnetic skyrmions, of a special importance its applicability to dilute magnetic semiconductors with a weak exchange interaction., Comment: 4 pages, 2 figures