scholarly journals Баллистическое течение двумерных электронов в магнитном поле

2021 ◽  
Vol 55 (7) ◽  
pp. 566
Author(s):  
А.Н. Афанасьев ◽  
П.С. Алексеев ◽  
А.А. Грешнов ◽  
М.А. Семина
Keyword(s):  
Magnetic Fields ◽  
Ballistic Transport ◽  
Ballistic Regime ◽  
Electron Collisions ◽  
Viscosity Effect ◽  
Small Density ◽  
Longitudinal Resistance ◽  
Analytical Formulas ◽  
Sample Width ◽  
Theoretical Results

In conductors with a very small density of defects, electrons at low temperatures collide predominantly with a sample edges. Therefore, the ballistic regime of charge and heat transport is realized. The application of a perpendicular magnetic field substantially modifies the character of ballistic transport. For the case of two-dimensional (2D) electrons in the magnetic fields corresponding to the diameter of the cyclotron trajectories smaller than the sample width a hydrodynamic transport regime is formed. In the latter regime, the flow is mainly controlled by rare electron–electron collisions, which determine the viscosity effect. In this work, we study the ballistic flow of 2D electrons in long samples in magnetic fields up to the critical field of the transition to the hydrodynamic regime. From solution of the kinetic equation, we obtain analytical formulas for the profiles of the current density and the Hall electric field far and near the ballistic-hydrodynamic transition as well as for the longitudinal and Hall resistances in these ranges. Our theoretical results, apparently, describe the observed longitudinal resistance of pure graphene samples in the diapason of magnetic fields below the ballistic-hydrodynamic transition.

scholarly journals Collisions in Strong Magnetic Fields

1987 ◽  
Vol 40 (1) ◽  
pp. 89 ◽  
Author(s):  
Michelle C Storey ◽  
DB Melrose
Keyword(s):  
Magnetic Fields ◽  
Cross Sections ◽  
Primary Source ◽  
Superstrong Magnetic Field ◽  
Electron Collisions ◽  
Proton Collisions ◽  
X Ray ◽  
Cyclotron Emission ◽  
Final Electron ◽  
Collision Processes

Exact cross sections for electron-electron collisions and electron-proton collisions in a superstrong magnetic field are derived using the QED formalism developed by Melrose and Parle. The results are compared with those of Langer who used a different QED formalism. The intended application is to collision processes in the accretion columns above neutron stars where magnetic fields of order 109 T are thought to be present. The particular case of electrons initially in their ground states, with one final electron in an excited state is described in detail; this process is thought to be the primary source of photons in X-ray pulsars, through subsequent cyclotron emission.

scholarly journals Restoration of superconductivity in high magnetic fields in UTe2

2020 ◽  
Vol 34 (32) ◽  
pp. 2030007
Author(s):  
Andrei G. Lebed
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Superconducting State ◽  
Critical Magnetic Field ◽  
High Magnetic Fields ◽  
Two Dimensional ◽  
Upper Critical Magnetic Field ◽  
Reentrant Superconductivity ◽  
Theoretical Results ◽  
General Method

It was theoretically predicted more than 20 years ago [A. G. Lebed and K. Yamaji, Phys. Rev. Lett. 80, 2697 (1998)], that a triplet quasi-two-dimensional (Q2D) superconductor could restore its superconducting state in parallel magnetic fields, which are higher than its upper critical magnetic field, [Formula: see text]. It is very likely that, recently, such phenomenon has been experimentally discovered in the Q2D superconductor UTe2 by Nicholas Butch, Sheng Ran, and their colleagues and has been confirmed by Japanese–French team. We review our previous theoretical results using such a general method that it describes the reentrant superconductivity in the abovementioned compound and will hopefully describes the similar phenomena, which can be discovered in other Q2D superconductors.

Vibration Response Analysis of MRE Cantilever Sandwich Beam under Non-Homogeneous Magnetic Fields

2013 ◽  
Vol 303-306 ◽  
pp. 49-52 ◽  
Author(s):  
Ming Long ◽  
Guo Liang Hu ◽  
Shao Long Wang
Keyword(s):  
Magnetic Fields ◽  
Natural Frequency ◽  
Vibration Isolation ◽  
Sandwich Beam ◽  
Rolling Stock ◽  
Transverse Motion ◽  
Response Analysis ◽  
Ansys Software ◽  
Motion Equations ◽  
Theoretical Results

A three layer sandwich beam with an aluminum face sheet and a magnetorheological elastomer (MRE) core was fabricated. The transverse motion equations of MRE cantilever sandwich beam under non-homogeneous magnetic fields were derived with the fine Mead-Markus model, and the first natural frequency of the beam were calculated. Meanwhile, the first natural frequency of the beam was also simulated using ANSYS software. The numerical simulations accorded with theoretical results in general. The results are expected to provide guidance to develop broadband vibration isolation devices for railways and rolling stock.

scholarly journals Cross sections of electron collisions with noble gases atoms

2021 ◽  
pp. 11-16
Author(s):  
Rusudan Golyatina ◽  
Sergei Maiorov
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Noble Gas ◽  
Empirical Formulas ◽  
Electron Collisions ◽  
Wide Range ◽  
Analytical Formulas ◽  
The Cross ◽  
Approximation Coefficients ◽  
Ionization Cross Sections

Consideration is given to the analysis of data on the cross sections of elastic and inelastic col-lisions of electrons with noble gas atoms. The transport (diffusion) cross section, the excita-tion and ionization cross sections are studied. For the selected sets of experimental and theo-retical data, optimal analytical formulas are found and approximation coefficients are select-ed for them. The obtained semi-empirical formulas allow us to reproduce the cross section values in a wide range of collision energies from 0.001 to 10000 eV with an accuracy of sev-eral percent.

scholarly journals Valley-polarized domain wall magnons in 2D ferromagnetic bilayers

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Doried Ghader
Keyword(s):  
Domain Wall ◽  
Domain Walls ◽  
Ballistic Transport ◽  
The Other ◽  
Polarized Electrons ◽  
Technological Field ◽  
Electrostatic Doping ◽  
Layer Stacking ◽  
Theoretical Results ◽  
Moriya Interaction

Abstract Valleytronics is a pioneering technological field relying on the valley degree of freedom to achieve novel electronic functionalities. Topological valley-polarized electrons confined to domain walls in bilayer graphene were extensively studied in view of their potentials in valleytronics. Here, we study the magnonic version of domain wall excitations in 2D honeycomb ferromagnetic bilayers (FBL) with collinear order. In particular, we explore the implications of Dzyaloshinskii-Moriya interaction (DMI) and electrostatic doping (ED) on the existence and characteristics of 1D magnons confined to layer stacking domain walls in FBL. The coexistence of DMI and ED is found to enrich the topology in FBL, yet the corresponding domain wall magnons do not carry a well-defined valley index. On the other hand, we show that layer stacking domain walls in DMI-free FBL constitute 1D channels for ballistic transport of topological valley-polarized magnons. Our theoretical results raise hope towards magnon valleytronic devices based on atomically thin topological magnetic materials.

scholarly journals Synchrotron Radiation in Periodic Magnetic Fields of FEL Undulators—Theoretical Analysis for Experiments

Symmetry ◽  
2020 ◽  
Vol 12 (8) ◽  
pp. 1258 ◽  
Author(s):  
Konstantin Zhukovsky
Keyword(s):  
Synchrotron Radiation ◽  
Magnetic Fields ◽  
Free Electron ◽  
Magnetic Components ◽  
Radiation Properties ◽  
Power Evolution ◽  
Periodic Components ◽  
Theoretical Results ◽  
Harmonic Power ◽  
Even Harmonics

A theoretical study of the synchrotron radiation (SR) from electrons in periodic magnetic fields with non-periodic magnetic components is presented. It is applied to several free electron lasers (FELs) accounting for the real characteristics of their electron beams: finite sizes, energy spread, divergence etc. All the losses and off-axis effects are accounted analytically. Exact expressions for the harmonic radiation in multiperiodic magnetic fields with non-periodic components and off-axis effects are given in terms of the generalized Bessel and Airy-type functions. Their analytical forms clearly distinguish all contributions in each polarization of the undulator radiation (UR). The application to FELs is demonstrated with the help of the analytical model for FEL harmonic power evolution, which accounts for all major losses and has been verified with the results of well documented FEL experiments. The analysis of the off-axis effects for the odd and even harmonics is performed for SPRING8 Angstrom Compact free-electron LAser (SACLA) and Pohang Accelerator Laboratory (PAL-XFEL). The modelling describes theoretically the power levels of odd and even harmonics and the spectral line width and shape. The obtained theoretical results agree well with the available data for FEL experiments; where no data exist, we predict and explain the FEL radiation properties. The proposed theoretical approach is applicable to practically any FEL.

scholarly journals Minibands in twisted bilayer graphene probed by magnetic focusing

2020 ◽  
Vol 6 (16) ◽  
pp. eaay7838 ◽  
Author(s):  
A. I. Berdyugin ◽  
B. Tsim ◽  
P. Kumaravadivel ◽  
S. G. Xu ◽  
A. Ceferino ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Magnetic Fields ◽  
Long Range ◽  
Electron Scattering ◽  
Low Temperatures ◽  
Ballistic Transport ◽  
Bilayer Graphene ◽  
Degree Of Freedom ◽  
Magnetic Focusing ◽  
Twisted Bilayer Graphene

Magnetic fields force ballistic electrons injected from a narrow contact to move along skipping orbits and form caustics. This leads to pronounced resistance peaks at nearby voltage probes as electrons are effectively focused inside them, a phenomenon known as magnetic focusing. This can be used not only for the demonstration of ballistic transport but also to study the electronic structure of metals. Here, we use magnetic focusing to probe narrowbands in graphene bilayers twisted at ~2°. Their minibands are found to support long-range ballistic transport limited at low temperatures by intrinsic electron-electron scattering. A voltage bias between the layers causes strong minivalley splitting and allows selective focusing for different minivalleys, which is of interest for using this degree of freedom in frequently discussed valleytronics.

scholarly journals Evolution of magnetic fields in the IGM: kinetic MHD turbulence

2008 ◽  
Vol 4 (S259) ◽  
pp. 563-564
Author(s):  
Reinaldo S. de Lima ◽  
E. M. de Gouveia Dal Pino ◽  
A. Lazarian ◽  
D. Falceta-Gonçalves
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Larmor Frequency ◽  
Local Magnetic Field ◽  
Magnetic Fluctuations ◽  
Mhd Turbulence ◽  
Mhd Simulations ◽  
Small Density ◽  
Forced Turbulence ◽  
Ion Collision

AbstractIn this work, we present 3D MHD simulations of non-helical, forced turbulence, with an anisotropic thermal pressure with respect to the orientation of the local magnetic field. Such anisotropy arises when the plasma is weakly collisional, i.e., when the Larmor frequency is much greater than the ion-ion collision frequency. In this Kinetic MHD regime (KMHD), there are instabilities that give rise to fast growing magnetic fluctuations in the smallest scales. The plasma that fills the intergalactic and intracluster media has small density (n ~ 10−3cm−3), hence the effects of these instabilities could be important in the turbulent amplification of the magnetic fields there. In order to study the KMHD turbulence, we have performed 3D numerical simulations employing a godunov-MHD code (e.g., Kowal, Lazarian & Beresnyak 2007; Falceta-Gonçalves, Lazarian & Kowal 2008). The power spectrum of the velocity and magnetic fields were calculated for two cases: when there is a pre-existing mean magnetic field, and when there is only an initial weak magnetic field.

scholarly journals Magnetic field of complex helical conductors

2013 ◽  
Vol 62 (4) ◽  
pp. 533-540 ◽  
Author(s):  
Krzysztof Budnik ◽  
Wojciech Machczyński
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Electric Power ◽  
Electromagnetic Compatibility ◽  
Complex Geometry ◽  
Phase Distribution ◽  
Low Frequency ◽  
Software Tool ◽  
Helical Structure ◽  
Analytical Formulas

Abstract Transmission of the electric power is accompanied with generation of low - frequency electromagnetic fields. Electromagnetic compatibility studies require that the fields from sources of electric power be well known. Unfortunately, many of these sources are not defined to the desired degree of accuracy. This applies e.g. to the case of the twisted-wire pair used in telephone communication; already practiced is twisting of insulated high-voltage three phase power cables and single-phase distribution cables as well. The paper presents a theoretical study of the calculation of magnetic fields in vicinity of conductors having helical structure. For the helical conductor with finite length the method is based on the Biot-Savart law. Since the lay-out of the cables is much more similar to a broken line than to strait line, in the paper the magnetic flux densities produced by helical conductor of complex geometry are also derived. The analytical formulas for calculating the 3D magnetic field can be used by a software tool to model the magnetic fields generated by e.g. twisted wires, helical coils, etc.

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