Weak Transverse Magnetic Field Research Articles

Investigating the effects of electron bounce-cyclotron resonance on plasma dynamics in capacitive discharges operated in the presence of a weak transverse magnetic field

Recently, Patil et al. [Phys. Rev. Res. 4, 013059 (2022)] have reported the existence of an enhanced operating regime when a low-pressure (5 mTorr) capacitively coupled discharge (CCP) is driven by a very high radio frequency (60 MHz) source in the presence of a weak external magnetic field applied parallel to its electrodes. Their particle-in-cell simulations show that a significantly higher bulk plasma density and ion flux can be achieved at the electrode when the electron cyclotron frequency equals half of the applied radio frequency for a given fixed voltage. In the present work, we take a detailed look at this phenomenon and further delineate the effect of this “electron bounce-cyclotron resonance (EBCR)” on the electron and ion dynamics of the system. We find that the ionization collision rate and stochastic heating are maximum under resonance condition. The electron energy distribution function also indicates that the population of tail-end electrons is highest for the case where EBCR is maximum. Formation of electric field transients in the bulk plasma region is also seen at lower values of applied magnetic field. Finally, we demonstrate that the EBCR-induced effect is a low-pressure phenomenon and weakens as the neutral gas pressure increases. The potential utility of this effect to advance the operational performance of CCP devices for industrial purposes is discussed.

The influence of weak transverse magnetic field on plasma dissipation process in the post-arc phase in a vacuum interrupter

Transverse magnetic field (TMF) contacts and applying external TMF are often adopted for reducing the ablation of the contact surface, but TMF will also affect the breaking performance of the vacuum interrupters. In this work, we investigated the influence of weak TMF on the expansion of the plasma in the post-arc phase with one-dimensional implicit particle-in-cell/Monte Carlo collision model, and we added an external circuit to the model to ensure the correctness of the calculation results. We simulated multiple magnetic field strengths (<30 mT), compared the plasma expansion process with the TMF strengths of 0 mT and 10 mT, and discussed the influence of metal vapor density on the insulation performance recovery of the vacuum interrupter. From the results, applying TMF with strength below 5 mT has little effect on the expansion of the plasma, and the TMF can increase the plasma density which improve the flow capacity of vacuum circuit breakers when the magnetic field above 10 mT, which is because the particles become more difficult to leave the discharge area under the force of the magnetic field. In general, we find that weak external TMF may adversely affect the breaking performance of the vacuum circuit breakers.

Tailoring Microstructure and Microsegregation in a Directionally Solidified Ni-Based SX Superalloy by a Weak Transverse Static Magnetic Field

Tailoring Microstructure and Microsegregation in a Directionally Solidified Ni-Based SX Superalloy by a Weak Transverse Static Magnetic Field

Vanishing Hall Response of Charged Fermions in a Transverse Magnetic Field.

We study the Hall response of two-dimensional lattice systems of charged fermions in a transverse magnetic field, in the ballistic coherent limit. We identify a setup in which this response vanishes over wide regions of parameter space: the "Landauer-Büttiker" setup commonly studied for coherent quantum transport, consisting of a strip contacted to biased ideal reservoirs of charges. We show that this effect does not rely on particle-hole symmetry, and is robust to a variety of perturbations including variations of the transverse magnetic field, chemical potential, and temperature. We trace this robustness back to a topological property of the Fermi surface: the number of Fermi points with positive velocity of the system. We argue that the mechanism leading to a vanishing Hall response applies to noninteracting and interacting systems alike, which we verify in concrete examples using density-matrix renormalization group simulations.

Magnetic field induced band formation and crystal orientation in directionally solidified Cu-20 wt.% Sn peritectic alloys

The influence of a weak transverse magnetic field on the microstructure in directionally solidified Cu-20 wt.% Sn peritectic alloys at low speeds was investigated. Experimental results indicated that the magnetic field caused the evolution of the two-phase microstructure from coupled growth to band. Moreover, it was also found that the magnetic field induced the crystal orientation of the primary phase. The above results may be attributed to the effect of the magnetic field on the mass and heat transfer during directional solidification.

Resonant photoluminescence and dynamics of a hybrid Mn hole spin in a positively charged magnetic quantum dot

We analyze, through resonant photoluminescence, the spin dynamics of an individual magnetic atom (Mn) coupled to a hole in a semiconductor quantum dot. The hybrid Mn-hole spin and the positively charged exciton in a CdTe/ZnTe quantum dot forms an ensemble of $\Lambda$ systems which can be addressed optically. Auto-correlation of the resonant photoluminescence and resonant optical pumping experiments are used to study the spin relaxation channels in this multilevel spin system. We identified for the hybrid Mn-hole spin an efficient relaxation channel driven by the interplay of the Mn-hole exchange interaction and the coupling to acoustic phonons. We also show that the optical $\Lambda$ systems are connected through inefficient spin-flips than can be enhanced under weak transverse magnetic field. The dynamics of the resonant photoluminescence in a p-doped magnetic quantum dot is well described by a complete rate equation model. Our results suggest that long lived hybrid Mn-hole spin could be obtained in quantum dot systems with large heavy-hole/light-hole splitting.

Effect of a Weak Transverse Magnetic Field on the Microstructures in Directionally Solidified Zn-2.2 at.% Cu Peritectic Alloy

Effect of a Weak Transverse Magnetic Field on the Microstructures in Directionally Solidified Zn-2.2 at.% Cu Peritectic Alloy

Publisher's Note: Diamond-nitrogen-vacancy electronic and nuclear spin-state anticrossings under weak transverse magnetic fields [Phys. Rev. A 94 , 021401(R) (2016)

Publisher's Note: Diamond-nitrogen-vacancy electronic and nuclear spin-state anticrossings under weak transverse magnetic fields [Phys. Rev. A <b>94</b> , 021401(R) (2016)

Effect of a weak transverse magnetic field on the microstructure in directionally solidified peritectic alloys.

Effect of a weak transverse magnetic field on the microstructures in directionally solidified Fe-Ni and Pb-Bi peritectic alloys has been investigated experimentally. The results indicate that the magnetic field can induce the formation of banded and island-like structures and refine the primary phase in peritectic alloys. The above results are enhanced with increasing magnetic field. Furthermore, electron probe micro analyzer (EPMA) analysis reveals that the magnetic field increases the Ni solute content on one side and enhances the solid solubility in the primary phase in the Fe-Ni alloy. The thermoelectric (TE) power difference at the liquid/solid interface of the Pb-Bi peritectic alloy is measured in situ, and the results show that a TE power difference exists at the liquid/solid interface. 3 D numerical simulations for the TE magnetic convection in the liquid are performed, and the results show that a unidirectional TE magnetic convection forms in the liquid near the liquid/solid interface during directional solidification under a transverse magnetic field and that the amplitude of the TE magnetic convection at different scales is different. The TE magnetic convections on the macroscopic interface and the cell/dendrite scales are responsible for the modification of microstructures during directional solidification under a magnetic field.

Diamond-nitrogen-vacancy electronic and nuclear spin-state anticrossings under weak transverse magnetic fields

We report on detailed studies of electronic and nuclear spin states in the diamond-nitrogen-vacancy (NV) center under weak transverse magnetic fields. We numerically predict and experimentally verify a previously unobserved NV hyperfine level anticrossing (LAC) occurring at bias fields of tens of gauss---two orders of magnitude lower than previously reported LACs at $\ensuremath{\sim}500$ and $\ensuremath{\sim}1000$ G axial magnetic fields. We then discuss how the NV ground-state Hamiltonian can be manipulated in this regime to tailor the NV's sensitivity to environmental factors and to map into the nuclear spin state.

Controlling droplet distribution using thermoelectric magnetic forces during bulk solidification processing of a Zn–6 wt.%Bi immiscible alloy

Bulk solidification of a Zn–6wt.%Bi immiscible alloy was investigated under a weak transverse magnetic field. The results show that the thermoelectric magnetic flow induced by the thermoelectric magnetic force is present during the solidification process. An equation was established to describe the movement of Bi-rich droplets in the melt. Thermoelectric magnetic force affected the mass transfer and changed the segregation behavior of the Bi-rich phase. Thermoelectric magnetic flow affected the Stokes sedimentation of the Bi-rich droplets and modified the spatial and size distribution of the Bi-rich particles. This technique can be used to control the distribution of the immiscible phases in other similar alloys.

Effect of a weak transverse magnetic field on the morphology and orientation of directionally solidified Al–Ni alloys

The influence of a weak transverse magnetic field on the morphology and orientation of Al3Ni dendrites in directionally solidified Al-12wt% Ni alloys was investigated. The experimental results indicated that the magnetic field caused segregation. It was also found that the application of a magnetic field decreased the primary dendrite spacing. By means of electronic backscatter diffraction (EBSD) analysis, the orientation of the Al3Ni dendrite was studied. In the case of no magnetic field, the 〈010〉 crystal direction of the Al3Ni crystal was oriented along the solidification direction. When a transverse magnetic field was applied, the 〈001〉 crystal direction rotated to the magnetic field direction, whereas the 〈010〉 crystal direction remained oriented along the solidification direction. The above experimental results are discussed in the context of thermoelectric magnetic convection (TEMC) and crystal anisotropy.

Effect of a transverse magnetic field on solidification morphology and microstructures of pure Sn and Sn–15 wt% Pb alloys grown by a Czochralski method

The pure Sn and Sn–15wt% Pb alloys were grown by a Czochralski method under various magnetic flux densities in this paper. The influence of thermoelectric magnetic (TEM) flows and buoyancy flows on solidification morphology, macrosegregation and microstructures had been investigated experimentally, and the velocity magnitude of TEM flows and buoyancy flows had been studied by 3D numerical simulations. The experimental results indicate that the modification of solidification morphology and microstructures is attributed to the unidirectional Pb solutes transport caused by TEM flows. The 3D numerical simulations results show that the buoyancy flows dominate the flows in the melt under a weak transverse magnetic field (B≤0.43T), and the unidirectional TEM flows at the vicinity of solid–liquid interface become the dominant flows in the melt with the increase of magnetic field. The interaction of TEM flows and buoyancy flows affecting solidification morphology and microstructures during directional solidification of alloys by the Czochralski method under various magnetic flux densities has been discussed and a corresponding simple evolution mechanism of dendritic growth has been proposed.

Theory of optical spin control in quantum dot microcavities

We present a microscopic theory of optical initialization, control and detection for a single electron spin in a quantum dot embedded into a zero-dimensional microcavity. The strong coupling regime of the trion and the cavity mode is addressed. We demonstrate that efficient spin orientation by a single circularly polarized pulse is possible in relatively weak transverse magnetic fields. The possibilities for spin control by additional circularly polarized pulse are analyzed. Under optimal conditions the Kerr and Faraday rotation angles induced by the spin polarized electron may reach tens of degrees.

Directional Solidification Microstructure of a Ni-Based Superalloy: Influence of a Weak Transverse Magnetic Field

A Ni-based superalloy CMSX-6 was directionally solidified at various drawing speeds (5–20 μm·s−1) and diameters (4 mm, 12 mm) under a 0.5 T weak transverse magnetic field. The results show that the application of a weak transverse magnetic field significantly modified the solidification microstructure. It was found that if the drawing speed was lower than 10 μm·s−1, the magnetic field caused extensive macro-segregation in the mushy zone, and a change in the mushy zone length. The magnetic field significantly decreases the size of γ’ and the content of γ-γ’ eutectic. The formation of macro-segregation under a weak magnetic field was attributed to the interdendritic solute transport driven by the thermoelectric magnetic convection (TEMC). The γ’ phase refinement could be attributed to a decrease in nucleation activation energy owing to the magnetic field during solid phase transformation. The change of element segregation is responsible for the content decrease of γ-γ’ eutectic.

Spatially dependent electromagnetically induced transparency.

Recent years have seen vast progress in the generation and detection of structured light, with potential applications in high capacity optical data storage and continuous variable quantum technologies. Here we measure the transmission of structured light through cold rubidium atoms and observe regions of electromagnetically induced transparency (EIT), using the phase profile as control parameter for the atomic opacity. With q plates we generate a probe beam with azimuthally varying phase and polarization structure, and its right and left circular polarization components provide the probe and control of an EIT transition. We observe an azimuthal modulation of the absorption profile that is dictated by the phase and polarization structure of the probe laser. Conventional EIT systems do not exhibit phase sensitivity. We show, however, that a weak transverse magnetic field closes the EIT transitions, thereby generating phase-dependent dark states which in turn lead to phase-dependent transparency, in agreement with our measurements.

Chemical diffusion characteristics of Al–Si alloy melts under a transverse magnetic field

Effect of a transverse magnetic field on the chemical diffusion (interdiffusion) characteristics between Al–10 at.% Si metallic melts and pure Al melts has been investigated experimentally. Results show that the application of a weak transverse magnetic field has evidently decreased the diffusivity of solute atoms and retarded the interdiffusion process. This effect can be attributed to the combined suppression action of interior Hall Effect and Lorentz force on the atoms mobility.

Effect of negative magnetoresistance in a transverse magnetic field in quantum Bi wires

We observed for the first time the effect of the negative magnetoresistance (NMR) in transverse magnetic fields (B ⊥ I) in quantum Bi wires at 4.2 K; this effect is described in this work. The single crystal bismuth wires in a glass cover were produced using the liquid phase casting methods. The Bi wires are strictly cylindrical with the (1011) orientation along the wire axis and diameters ranging from 50 to 400 nm. In wires with a diameter of d < 80 nm, there was observed a semimetal-semiconductor transition, which is associated with the quantum size effect and is attended with a “semiconductor” temperature dependence of the resistance R(T). In weak transverse magnetic fields, there was observed an NMR effect both at B ‖ C2 and at B ‖ C3. The increase in the wire diameter d, temperature T, and magnetic field B results in the weakening and total disappearance of the found peculiarities of NMR in weak magnetic fields, thus reflecting the suppression of the size quantization effect. An analytical simulation of the quantum wire that makes it possible to explain the nonmonotonic character of the transverse magnetoresistance in Bi wires is considered. To interpret this NMR effect, we have used a theoretical model in which the electrical conductivity is calculated using the Cubo formula with account for the elastic scattering of the carriers on phonons and the size quantization of the energy spectrum. The comparison of the experimental results with the analytic model allows us to conclude that the observed NMR effect in the transverse magnetic field in Bi nanowires has a quantum nature.

Magnetohydrodynamic channel flows with weak transverse magnetic fields.

Magnetohydrodynamic flow of an incompressible fluid through a plane channel with slowly varying walls and a magnetic field applied transverse to the channel is investigated in the high Reynolds number limit. It is found that the magnetic field can first influence the hydrodynamic flow when the Hartmann number reaches a sufficiently large value. The magnetic field is found to suppress the steady and unsteady viscous flow near the channel walls unless the wall shapes become large.

Transformation of Ramsey electromagnetically induced absorption into magnetic-field induced transparency in a paraffin-coated Rb vapor cell

We report on magnetic-field induced transparency (MIT) based on Ramsey electromagnetically induced absorption (EIA) in a paraffin-coated Rb vapor cell. Changing the laser polarization from linear to circular in the presence of a weak residual transverse magnetic field to the laser propagation, the narrow absorption due to the Ramsey EIA transformed into the transparency due to MIT of the 5S1/2 (F = 2)-5P3/2 (F' = 3) transition of 87Rb in the paraffin-coated Rb vapor cell. The spectral widths of the EIA and MIT in the Hanle configuration were measured to be 0.6 mG (425 Hz) and 1.2 mG, respectively. MIT depended on the long preservation time of the ground-state coherent spin states and the transverse magnetic field. From the numerical results, the crossover between the Ramsey EIA and the MIT could be illustrated as the superposition of both signals.