Search

The influence of Rashba spin-orbit interaction on the transport properties of the two-dimensional quantum ring with finite width has been investigated in the presence of the uniform perpendicular magnetic field. The dependence of magnetoresistance on the magnetic field and Rashba spin-orbit coupling parameter in quantum ring with finite width are investigated. It was shown that in the presence Rashba spin-orbit interaction that the beating pattern is destroyed.

We propose a scheme to investigate the behavior of a ballistic nanowire system with Rashba interaction within a perpendicular magnetic field. The quantum entanglement of a nanowire system is discussed via the negativity. When the strong and weak magnetic fields are applied, we discuss the influence of the spin-orbit interaction and the initial states on the population inversion and the negativity. Our results show that the degree of entanglement for the nanowire system mainly depends on the effect of the spin-orbit interaction and the initial states of the system. This opens up new avenues for designing nanowire systems for future quantum computation and communication applications.

Advances in cylindrical nanowires for 3D information technologies profit from intrinsic curvature that introduces significant differences with regards to planar systems. A model is proposed to control the stochastic and deterministic coding of remanent 3D complex vortex configurations in designed multilayered (magnetic/non-magnetic) cylindrical nanowires. This concept, introduced by micromagnetic simulations, is experimentally confirmed by magnetic imaging in FeCo/Cu multilayered nanowires. The control over the random/deterministic vortex states configurations is achieved by a suitable geometrical interface tilting of almost non-interacting FeCo segments with respect to the nanowire axis, together with the relative orientation of the perpendicular magnetic field. The proper design of the segments' geometry (e.g. tilting) in cylindrical nanowires opens multiple opportunities for advanced nanotechnologies in 3D magnetic networks.

The magnetic moment of the unmodulated bilayer graphene is calculated in the presence of a perpendicular magnetic field B. The oscillatory character of the magnetic moment dependences on the magnetic field is investigated.

The magnetic moment of the molybdenum disulfide monolayer (MoS2) is calculated in the presence of a perpendicular magnetic field B. The field B leads to a significant increase in the spin splitting in the conduction band, which is reflected in the expression of the magnetic moment. The oscillatory character of the magnetic moment dependences on the magnetic field is investigated.

The influence of exchange interaction on the transport properties of a two-dimensional diluted magnetic semiconductor quantum ring with finite width has been investigated in the presence of a uniform perpendicular magnetic field. The dependence of magnetoresistance on the magnetic field, Mn concentration, and quantum ring width are investigated. In the absence of exchange interaction, a typical beating pattern with well-defined node-positions in the oscillating magnetoresistance is observed. It was shown that in the present exchange interactions the beating pattern is destroyed.The influence of exchange interaction on the transport properties of a two-dimensional diluted magnetic semiconductor quantum ring with finite width has been investigated in the presence of a uniform perpendicular magnetic field. The dependence of magnetoresistance on the magnetic field, Mn concentration, and quantum ring width are investigated. In the absence of exchange interaction, a typical beating pattern with well-defined node-positions in the oscillating magnetoresistance is observed. It was shown that in the present exchange interactions the beating pattern is destroyed.

Study on ac loss characteristics of HTS coils with an iron core to simulate an armature winding of ac rotational machine and a method to reduce ac losses in HTS coils combined with the iron core in 3-phase condition are reported in this paper. In this study, the 3-phase test model which combines 6 HTS coils wound by YBCO tapes and the iron core used for an armature of conventional induction motor is fabricated for the ac loss measurement. It is shown that the measured ac losses in the 3-phase condition coincides with the sum of the ac loss of each phase measured in the 1-phase condition. The effectiveness to suppress the perpendicular magnetic field applied to the tape in the coil by use of magnetic materials around the coil winding on the ac loss reduction in the 3-phase condition is investigated. The measured ac loss with placing the magnetic material around the coil winding in the slot of the iron core remarkably decreases. The results of the numerical magnetic field analysis confirmes that the perpendicular magnetic field significantly decreases by arranging the magnetic material and supportes the validity of the measurement results. The results obtained in this study demonstrates that the effectiveness to modify the magnetic field distribution by use of the magnetic material around the coil winding on the ac loss reduction in 3-phase HTS coil combined with the iron core.

The dependence of the Hall and bend resistances on a perpendicular magnetic field and on vacancy defects in a four-terminal phosphorene single layer Hall bar is investigated. A tight-binding model in combination with the Landauer-Buttiker formalism is used to calculate the energy spectrum, the lead-to-lead transmissions, and the Hall and bend resistances of the system. It is shown that the terminals with zigzag edge orientation are responsible for the absence of quantized plateaus in the Hall resistance and peaks in the longitudinal resistance. A negative bend resistance in the ballistic regime is found due to the presence of high- and low-energy transport modes in the armchair and zigzag terminals, respectively. The system density of states, with single vacancy defects, shows that the presence of in-gap states is proportional to the number of vacancies. Quantized plateaus in the Hall resistance are only formed in a sufficiently clean system. The effects of different kinds of vacancies where the plateaus are destroyed and a diffusive regime appears in the bend resistance are investigated.

Both the charge- and spin-transport properties of a topological Dirac semimetal (TDSM) nanowire with two lateral gates and a perpendicular magnetic field are investigated by using the Green function method in combination with the Landauer-B\"uttiker formula. A fully spin-polarized surface current can be generated in the considered system and it can be turned on or off by varying the electron energy and magnetic field strength. The underlying physics of this transport phenomenon originates from the quantum anomalous Hall-like insulator state of the TDSM nanowire caused by the magnetic field. Further studies indicate the spin-polarized current with a strong robustness against disorder, displaying the feasibility of designing a topological spin filtering and switch device based on the considered system.

PurposeTo investigate the in-air out-of-field electron streaming effect (ESE) for esophageal cancer radiotherapy in the presence of 1.5 T perpendicular magnetic field.MethodsTen esophageal cancer patients treated with conventional Linac were retrospectively enrolled into a cohort of this study, with the prescription of 4,400 cGy/20 fx. All cases received IMRT replanning using Elekta Unity MR-Linac specified Monaco system, denoted as primary plan. To visualize the in-air dose outside the body in Monaco system, an auxiliary structure was created by extending the external structure. For each case, another comparable plan with no magnetic field was created using the same planning parameters. The plan was also recalculated by placing a bolus upon the neck and chin area to investigate its shielding effect for ESE. Dosimetric evaluations of the out-of-field neck and chin skin area and statistical analysis for these plans were then performed.ResultsOut-of-field ESE was also observed in esophageal cancer treatment planning under 1.5 T magnetic field, while totally absent for plans with no magnetic field. On average, the maximum dose to the neck and chin skin area of the primary plan (657.92 ± 69.07 cGy) was higher than that of plan with no magnetic field (281.78 ± 36.59 cGy, p = 0.005) and plan with bolus (398.43 ± 69.19 cGy, p = 0.007). DVH metrics D1cc (the minimum dose to 1 cc volume) of the neck and chin skin for primary plan was 382.06 ± 44.14 cGy, which can be reduced to 212.42 ± 23.65 cGy by using the 1 cm bolus (with p = 0.005), even lower than the plan without magnetic field (214.45 ± 23.82, p = 0.005). No statistically significant difference of the neck and chin skin dose between the plan with bolus and plan with no magnetic field was observed (all with p > 0.05).ConclusionFor MRI guided esophageal cancer radiotherapy, a relatively high out-of-field neck and chin skin doses will be introduced by ESE in the presence of magnetic field. It is therefore recommended to take this into account during the planning phase. Adding bolus could effectively reduce the ESE dose contributions, achieve the shielding effect almost equivalent to the scenario with no magnetic field. Further explorations of measurement verifications for the ESE dose distributions are required.

PURPOSE: The purpose of this study was to evaluate the potential skin dose toxicity contribution of spiralling contaminant electrons (SCE) generated in the air in an MR-linac with a 0.35 or 1.5 T magnetic field using the EGSnrc Monte Carlo (MC) code. Comparisons to experimental results at 1.5 T are also performed. METHODS: An Elekta generated phase space file for the Unity MR-linac is used in conjunction with the EGSnrc enhanced electric and magnetic field transport macros to simulate surface dose profiles and depth-dose curves in panels located 5 cm away from the beam edge and positioned either parallel or perpendicular to the magnetic field. Electrons generated in the air will spiral along the magnetic field lines, and though surface doses within the field will be reduced, the electrons can contribute to out-of-field surface doses. RESULTS: Surface dose profiles showed good agreement with experimental findings and the maximum simulated doses at surfaces perpendicular to the magnetic field were 3.77 ± 0.01% and 3.55 ± 0.01% for 1.5 and 0.35 T. These results are expressed as a percentage of the maximum dose to water delivered by the photon beam. The surface dose variations in the out-of-field region converge to the 0 T doses within the first 0.5 cm of material. An asymmetry in the dose distribution in surfaces positioned on either side of the photon beam and aligned parallel to the magnetic field is determined to be due to the magnetic field directing electrons deeper into, or localizing them to the surface of, the measurement panel. CONCLUSIONS: These results confirm the SCE dose contribution in surfaces perpendicular to the magnetic field and show these doses to be of the order of a few percentage of the maximum dose to water of the beam. Good agreement in the dose profiles is seen in comparisons between the MC simulations and experimental work. The effect is apparent in 0.35 and 1.5 T magnetic fields and dissipates within the first few millimeters of material. It should be noted that only SCEs from beam anteriorly incident on the patient will influence the patient surface dose, and the use of beams incident over different angles will reduce the dose to any particular patient surface.

In order to investigate the effective mass of a single-crystalline WTe2 layer, we measured the temperature dependence of the Shubnikov-de Haas oscillation. In this method, the magnetoresistance with a perpendicular magnetic field is monitored by changing the temperature from 1.9 K to 6 K. The extracted effective mass of WTe2 for magnetic fields ranging from 6.8 T to 8.7 T is m* = 0.327m0 which is almost constant in this range. The theoretical expectation values of m*/m0 for the valence and the conduction bands are 0.58 and 0.26, respectively; the experimental value of the effective mass is between these two values. Thus, our results clearly show that single-crystalline WTe2 has both electron- and hole-like pockets that simultaneously contribute to electrical transport in the channel.

The tensile strain is a promising tool for creation and manipulation of magnetic solitonic textures in the chiral helimagnets via tunable control of magnetic anisotropy and Dzyaloshinskii-Moriya interaction. Here, by using the in-situ resonant small-angle x-ray scattering we demonstrate that the skyrmion and chiral soliton lattices can be achieved as metastable states in FeGe lamella as distinct states or even simultaneously by combining the tensile strain and magnetic fields in various orientations with respect to the deformation. The small-angle scattering data are discussed in the frame of the analytical model which is sufficient to describe the experimental results for soliton lattice. By using the experimental results and analytical theory, unwinding of the metastable skyrmions in the perpendicular magnetic field as seen by small-angle scattering experiment was analyzed by the micromagnetic simulation.

The formation of magnetic bubbles and the domain-evolution processes, induced by a perpendicular magnetic field in Fe/Gd multilayer films and nanodots, have been investigated. At room temperature, the stripe domains in a continuous film transform into magnetic bubbles in an external field, while bubbles form spontaneously in nanodots due to the existence of shape anisotropy. When the temperature decreases to 20 K, the enhancement of the perpendicular magnetic anisotropy of the samples results in an increase of the domain size in the continuous film and the magnetization-reversal behavior of each nanodot becomes independent, and most reversed dots do not depend on each other, indicating the magnetic characteristics of a single domain. The present research provides further understanding of the evolution of magnetic bubbles in the Fe/Gd system and suggests their promising applications in patterned recording materials.

We investigated the behavior of a mixed-gas plasma flow driven by a compact plasma focus device into a perpendicular magnetic field, by using a one-dimensional hybrid particle-in-cell simulation. When the plasma flowed into the perpendicular magnetic field, some accelerated ions were generated in front of the plasma flow owing to the compression of the magnetic field. The behavior of the compressed magnetic field changed by mixing heavy ions with the collisionless plasma. The maximum velocity of the accelerated light ions was proportional to the square root of the average ion mass of the plasma. These results indicate that the effect of the multi-ion species strongly affects the injection of light ions.

The upper critical field ( B c 2 ) of superconducting thin films of Nb (film thickness d = 40 nm) and NbN ( d = 10, 50 and 100 nm) have been measured and analyzed as a function of temperature ( T = 1.8–15 K) in both parallel and perpendicular magnetic field ( B = 0–7 T) directions with respect to the film plane. Dimensional crossover from 2D to 3D is observed for all the thin films except for the 10 nm thick NbN film which exhibits only 2D behavior in the measured T and B range. Further, the upper critical fields were found to be anisotropic in case of both Nb and NbN films. However, the anisotropy shows different behavior in all the four samples. In case of Nb, below the 2D–3D crossover temperature, the B c 2 ∥ ( T ) is higher than B c 2 ⊥ ( T ) and both curves branch away further from each other. On the other hand, in case of NbN (50 and 100 nm), there is a reversal of anisotropy, i.e., in the 2D region B c 2 ∥ ( T ) > B c 2 ⊥ ( T ) and in the 3D region at some temperature B c 2 ⊥ ( T ) > B c 2 ∥ ( T ) . In the NbN films with increasing thickness, the 2D region shrinks and 3D region expands, and the 2D–3D crossover and anisotropy reversal characteristic temperatures shift toward T c . These observations are quantitatively explained using the Ginzburg–Landau theoretical approach after Schneider and Locquet (Physica C, 179 (1991) 125).

The photon count rate (PCR) of superconducting single-photon detectors made of ${\mathrm{Mo}}_{x}{\mathrm{Si}}_{1\text{\ensuremath{-}}x}$ films shaped as a 2-$\ensuremath{\mu}\mathrm{m}$-wide strip and a 115-nm-wide meander strip line is studied experimentally as a function of the dc biasing current at different values of the perpendicular magnetic field. For the wide strip, a crossover current ${I}_{\mathrm{cross}}$ is observed, below which the PCR increases with an increasing magnetic field and above which it decreases. This behavior contrasts with the narrow ${\mathrm{Mo}}_{x}{\mathrm{Si}}_{1\text{\ensuremath{-}}x}$ meander, for which no crossover current is observed, thus suggesting different photon-detection mechanisms in the wide and narrow strips. Namely, we argue that in the wide strip the absorbed photon destroys superconductivity locally via the vortex-antivortex mechanism for the emergence of resistance, while in the narrow meander superconductivity is destroyed across the whole strip line, forming a hot belt. Accordingly, the different photon-detection mechanisms associated with vortices and the hot belt determine the qualitative difference in the dependence of the PCR on the magnetic field.

A gate-defined quantum dot in bilayer graphene is utilized as a sensitive electrometer for probing the charge density of its environment. Under the influence of a perpendicular magnetic field, the charge carrier density of the channel region next to the quantum dot oscillates due to the formation of Landau levels. This is experimentally observed as oscillations in the gate-voltage positions of the Coulomb resonances of the nearby quantum dot. From the frequency of the oscillations, we extract the charge carrier density in the channel and from the amplitude the shift of the quantum dot potential. We compare these experimental results with an electrostatic simulation of the device and find good agreement., Comment: 5 Pages, 4 Figures

The spin Hall torque induced by DC current was studied experimentally. A Pt/Co/Pt structure with perpendicular magnetic anisotropy was grown, and magnetization reversal due to the spin Hall effect was observed. An extra magnetic field perpendicular to the sample was applied in addition to a constant bias field. It was found that the switching current shifted in proportion to the additional perpendicular field. The spin Hall angle was estimated from this relation, and the small perpendicular magnetic field can be measured accurately based on this effect.