Strong Magnetic Field Parallel Research Articles

Angular momentum of radiation from a charge drifting along a cylindrical channel in a magnetic field

The angular momentum of radiation related to the passage of relativistic particles in a cylindrical channel is studied theoretically. To enhance the angular momentum of radiation, it is proposed to place the channel in a strong magnetic field parallel to the channel axis. The trajectories of the particles in the channel, the conditions for trapping particles in the channeling mode are investigated and equations for calculating the orbital angular momentum of radiation are obtained. It is shown that the angular momentum of radiation of a uniform beam of particles in the channel is not equal to zero only if the particles enter the channel at an angle greater than the critical angle. A significant difference between vortex radiation from a bunch of cylindrical channels (for example bunch of carbon nanotubes) from laser or undulator radiation is that the radiation beam of the latter has only one vortex axis. While the radiation from the beam of cylindrical channels has one vortex axis per each channel. Dependence of the angular momentum of radiation on the value of magnetic field and on the incident angle is studied.

Theory for the negative longitudinal magnetoresistance in the quantum limit of Kramers Weyl semimetals

Negative magnetoresistance is rare in non-magnetic materials. Recently, negative magnetoresistance has been observed in the quantum limit of β-Ag2Se, where only one band of Landau levels is occupied in a strong magnetic field parallel to the applied current. β-Ag2Se is a material that hosts a Kramers Weyl cone with band degeneracy near the Fermi energy. Kramers Weyl cones exist at time-reversal invariant momenta in all symmorphic chiral crystals, and at a subset of these momenta, including the Γ point, in non-symmorphic chiral crystals. Here, we present a theory for the negative magnetoresistance in the quantum limit of Kramers Weyl semimetals. We show that, although there is a band touching similar to those in Weyl semimetals, negative magnetoresistance can exist without a chiral anomaly. We find that it requires screened Coulomb scattering potentials between electrons and impurities, which is naturally the case in β-Ag2Se.

Stabilization of the Fulde–Ferrell–Larkin–Ovchinnikov State by Tuning In-plane Magnetic-Field Direction: Application to a Quasi-One-Dimensional Organic Superconductor

The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state in quasi-one-dimensional systems with warped Fermi surfaces is examined in strong parallel magnetic fields. It is shown that the state is extremely stable for field directions around nontrivial optimum directions, at which the upper critical field exhibits cusps, and that the stabilization is due to a Fermi-surface effect analogous to the nesting effect for the spin density wave and charge density wave. Interestingly, the behavior with cusps is analogous to that in a square lattice system in which the hole density is controlled. For the organic superconductor (TMTSF)_2ClO_4, when the hopping parameters obtained by previous authors based on X-ray crystallography results are assumed, the optimum directions are in quadrants consistent with the previous experimental observations. Furthermore, near this set of parameters, we also find sets of hopping parameters that more precisely reproduce the observed optimum in-plane field directions. These results are consistent with the hypothesis that the FFLO state is realized in the organic superconductor.

Dynamic ion shadows behind finite-sized objects in collisionless magnetized plasma flows

The potential and density wake behind a finite-sized object in a magnetized collisionless plasma flow is studied with self-consistent numerical simulations. With increasing magnetization of the plasma, the standard picture of ion focusing in the wake for plasmas with large electron to ion temperature ratios becomes invalid. A strong magnetic field parallel to the flow direction leads to a chain of ion depletions in the wake and enhanced ion density at their envelopes. This is due to a novel mechanism of a dynamic ion shadow, which is not the geometrical shadow of the finite-sized object. It corresponds to a change in topology of the wake potential. Complex ion trajectories resulting from electrostatic collisions with the object can lead to significant variations in electrical charging of other objects in the wake.

Self-organised fractional quantisation in a hole quantum wire

We have investigated hole transport in quantum wires formed by electrostatic confinement in strained germanium two-dimensional layers. The ballistic conductance characteristics show the regular staircase of quantum levels with plateaux at n2e2/h, where n is an integer, e is the fundamental unit of charge and h is Planck’s constant. However as the carrier concentration is reduced, the quantised levels show a behaviour that is indicative of the formation of a zig-zag structure and new quantised plateaux appear at low temperatures. In units of 2e2/h the new quantised levels correspond to values of n = 1/4 reducing to 1/8 in the presence of a strong parallel magnetic field which lifts the spin degeneracy but does not quantise the wavefunction. A further plateau is observed corresponding to n = 1/32 which does not change in the presence of a parallel magnetic field. These values indicate that the system is behaving as if charge was fractionalised with values e/2 and e/4, possible mechanisms are discussed.

Electrostatic two-stream instability in Fermi-Dirac plasmas

In this paper the electrostatic two-stream instability is investigated for a large range of plasma number-density using the quantum hydrodynamic model by incorporating the relativistic degeneracy, electron-exchange, quantum diffraction and strong parallel quantizing magnetic field effects. It is found that the electron diffraction effect significantly alters the instability growth rate in a wide range of plasma number density. Two cases of classical and quantum Landau quantization limits are compared and the parametric instability condition is closely inspected. It is remarked that for a given streaming speed the instability is bounded by an upper plasma number-density limit. It is also shown that for a given stream speed there is a maximal growth rate corresponding to specific plasma number-density and perturbation wavelength. Current study can help in better understanding of electron-beam plasma interactions and energy exchange for a wide area of number densities ranging from solid density, inertial confined plasmas, big planetary cores and compact stars. It may also be useful in understanding of electrostatic beam-plasma interactions and origin of large magnitude sustainable electrical currents in super-intense plasmas with critically high magnetic fields such as, pulsars, white dwarf interiors and neutron star crusts.

Confinement of spin-orbit induced Dirac states in quantum point contacts

The quantum transmission problem for a particle moving in a quantum point contact in the presence of a Rashba spin-orbit interaction and applied magnetic field is solved semiclassically. A strong Rashba interaction and parallel magnetic field form emergent Dirac states at the center of the constriction, leading to the appearance of resonances which carry spin current and become bound at high magnetic fields. These states can be controlled in situ by modulation of external electric and magnetic fields, and can be used to turn the channel into a spin pump which operates at zero bias. It is shown that this effect is currently experimentally accessible in $p$-type quantum point contacts.

Permeability Measurement System up to 10 GHz Using All Shielded Shorted Microstrip Line

The wideband measurement system of permeability for magnetic thin slab was proposed for up to 10 GHz, using the all shielded shorted microstrip lines. In order to analyze this configuration, the reference plane was set on the other end of specimen where the LC parallel resonant circuit was assumed. The permeability was derived from the measurement of S11 by VNA (Vector Network Analyzer) comparing between with strong static magnetic field parallel to rf magnetic field and without it. The shorted microstrip line was calibrated by the standard sample of rectangular shape NSS (Noise Suppression Sheet) comparing with the results of toroidal core measured by the shorted coaxial line.

Two-Dimensional Superconducting State of Monolayer Pb Films Grown on GaAs(110) in a Strong Parallel Magnetic Field

Two-dimensional (2D) superconductivity was studied by magnetotransport measurements on single-atomic-layer Pb films on a cleaved GaAs(110) surface. The superconducting transition temperature shows only a weak dependence on the parallel magnetic field up to 14T, which is higher than the Pauli paramagnetic limit. Furthermore, the perpendicular-magnetic-field dependence of the sheet resistance is almost independent of the presence of the parallel field component. These results are explained in terms of an inhomogeneous superconducting state predicted for 2D metals with a large Rashba spin splitting.

Effects of parallel magnetic field on electrocodeposition behavior of Fe/nano-Si particles composite electroplating

The influence of an external parallel strong parallel magnetic field (respect to current) on the electrocodeposition of nano-silicon particles into an iron matrix has been studied in this paper. Test results show that magnetic field has a great influence on the distribution of silicon, as well as the surface morphology and the thickness of the composite coatings. When no magnetic field was applied, a high current density was needed to get high concentration of silicon particles, while that could be easily obtained at a low current density with a 2T parallel magnetic field. However, Owing to the unevenness of the current density J-distribution on the surface of the electrode in 8T, the thicker and rougher composite deposits appear in the edge region (L or R region), and the thinner and smoother ones appear in the middle region (M). Meanwhile, the distribution curve of silicon content looks like a “pan” along the center line of coatings. A possible mechanism combining to the numerical simulation results was suggested out to illustrate the obtained experiment results.

Ion-Wake-Mediated Particle Interaction in a Magnetized-Plasma Flow

The interaction forces between dust grains in a flowing plasma are strongly modified by the formation of ion wakes. Here, we study the interparticle forces mediated by ion wakes in the presence of a strong magnetic field parallel to the ion flow. For increasing magnetic flux densities a continuous decay of the interaction force is observed. This transition occurs at parameters, where the ion cyclotron frequency starts to exceed the ion plasma frequency, which is in agreement with theoretical predictions. The modification of the interparticle forces is important for the understanding of the structure and dynamics of magnetized dusty plasmas.

Current Induced Spin Injection in Si-MOSFET

Longitudinal resistivity in strong parallel magnetic fields up to B = 14 Tesla was measured in Si-MOSFET with a narrow slot (90nm) in the upper metallic gate that allows to apply different gate voltage across the slot and, therefore, to control the electron density n1 and n2 in two parts of the sample independently. The experimental scheme allows us to pass through the source-drain channel relatively large DC current (IDC), while the dynamic resistance was measured using a standard lock-in technique with small AC current. It was shown that the sample resistance is asymmetric with respect to the direction of DC current. The asymmetry increases with increase of magnetic field, DC current, and difference between n1 and n2. Results are interpreted in terms of a current-induced spin accumulation or depletion near the slot, as described by a spin drift-diffusion equation. The effect on the sample resistance is due to the positive magnetoresistance of Si-MOSFETs in parallel magnetic fields.

Magnetoplasma resonance in a GaAs/AlGaAs quantum well in a strong parallel magnetic field

The dispersion of magnetoplasma excitations in two-dimensional electron systems in a strong parallel magnetic field has been studied. A considerable increase in the electron cyclotron mass with an increase in the parallel component of magnetic field has been detected. It has been found that the cyclotron mass increment is a quadratic function of the magnetic field parallel to the interface. It has been shown that the mass anisotropy of 2D electrons induced by the parallel magnetic field reaches nearly 2.5 in B ‖ = 7 T. The energy of space quantization of the electron in the quantum well has been estimated from the magnetic field dependence of the anisotropy.

Effective mass and spin susceptibility of dilute two-dimensional holes in GaAs

We report effective hole mass (${m}^{*}$) measurements through analyzing the temperature dependence of Shubnikov--de Haas oscillations in dilute (density $p\ensuremath{\sim}7\ifmmode\times\else\texttimes\fi{}{10}^{10}$ cm${}^{\ensuremath{-}2}$, ${r}_{s}\ensuremath{\sim}6$) two-dimensional (2D) hole systems confined to a 20-nm-wide, (311)A GaAs quantum well. The holes in this system occupy two nearly degenerate spin subbands whose ${m}^{*}$ we measure to be $\ensuremath{\sim}$0.2 (in units of the free electron mass). Despite the relatively large ${r}_{s}$ in our 2D system, the measured ${m}^{*}$ is in reasonably good agreement with the results of our energy band calculations, which do not take interactions into account. We then apply a sufficiently strong parallel magnetic field to fully depopulate one of the spin subbands, and measure ${m}^{*}$ for the populated subband. We find that this latter ${m}^{*}$ is close to the ${m}^{*}$ we measure in the absence of the parallel field. We also deduce the spin susceptibility of the 2D hole system from the depopulation field, and we conclude that the susceptibility is enhanced by about 50$%$ relative to the value expected from the band calculations.

Initial stage of nematic twist-straining in strong magnetic field

The initial stage of straining of a planar-oriented nematic liquid crystal (NLC) cell in a strong magnetic field parallel to substrates is theoretically analyzed. It is pointed out that, in this case, the influence of boundaries on the development of instability is insignificant. Equations that describe the dynamics of NLC straining with allowance for flows are obtained in the framework of the Ericksen-Leslie-Parodi theory. It is established that simple wave solutions of these equations can be obtained in the given system geometry.

Calculation of Charge Carrier Concentration Profile in a Wide Potential Well with Electric and Magnetic Fields

We investigated an equilibrium state of Fermi electrons in modulation doped structures with a wide quantum well in a strong parallel magnetic field. We studied the charge carrier system with a sufficiently high density, such that the de Broglie wavelength of electrons is smaller than the potential well width. We have formulated hydrodynamic equations for this carrier system both in the absence of magnetic field and in a parallel magnetic field. We have obtained analytical solutions for the charge carrier concentration as a function of coordinates in the potential well. In a quantum area near the interface, we carried out quantum mechanical calculations taking into account the effect of electric and magnetic fields. The concentration profile is presented for modulation doped Si/SiGe/Si heterostructures. We discuss large positive magnetoresistance in a strong parallel magnetic field in these structures.

Energy spectrum of graphene multilayers in a parallel magnetic field

We study the orbital effect of a strong magnetic field parallel to the layers on the energy spectrum of the Bernal-stacked graphene bilayer and multilayers, including graphite. We consider the minimal model with the electron tunneling between the nearest sites in the plane and out of the plane. Using the semiclassical analytical approximation and exact numerical diagonalization, we find that the energy spectrum consists of two domains. In the low- and high-energy domains, the semiclassical electron orbits are closed and open, so the spectra are discrete and continuous, correspondingly. The discrete energy levels are the analogs of the Landau levels for the parallel magnetic field. They can be detected experimentally using electron tunneling and optical spectroscopy. In both domains, the electron wave functions are localized on a finite number of graphene layers, so the results can be applied to graphene multilayers of a finite thickness.

Conductance asymmetry of a slot gate Si‐MOSFET in a strong parallel magnetic field

AbstractWe report measurements on a Si‐MOSFET sample with a slot in the upper gate, allowing for different electron densities n1,2 across the slot. The dynamic longitudinal resistance was measured by the standard lock‐in technique, while maintaining a large DC current through the source‐drain channel. We find that the conductance of the sample in a strong parallel magnetic field is asymmetric with respect to the DC current direction. This asymmetry increases with magnetic field. The results are interpreted in terms of electron spin accumulation or depletion near the slot.

Conductance asymmetry of a slot gate Si-MOSFET in a strong parallel magnetic field

We report measurements on a Si-MOSFET sample with a slot in the upper gate, allowing for different electron densities n1,2 across the slot. The dynamic longitudinal resistance was measured by the standard lock-in technique, while maintaining a large DC current through the source-drain channel. We find that the conductance of the sample in a strong parallel magnetic field is asymmetric with respect to the DC current direction. This asymmetry increases with magnetic field. The results are interpreted in terms of electron spin accumulation or depletion near the slot.

Anomalous corrections to the Hall resistivity of spin-polarized holes in a two-dimensionalGaAs/AlxGa1−xAsheterostructure

Hall effect of two-dimensional holes that are spin-polarized by a strong parallel magnetic field was explored with a small tilt angle. The Hall resistivity increases nonlinearly with the magnetic field and exhibits negative corrections. The anomalous negative corrections increase with the perpendicular magnetization of the two-dimensional hole system. We attribute this to the anomalous Hall effect of spin-polarized carriers in a nonmagnetic system. The anomalous corrections to the conductivity exhibit nonmonotonic dependence on the magnetic field.