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General condition for realizing a collinear spin-orbit effective magnetic field in two-dimensional electron systems and its application to zinc-blende and wurtzite quantum wells
摘要： In this paper, we have studied two-dimensional (2D) electron systems described by the effective Hamiltonians containing spin-orbit coupling (SOC) terms up to an arbitrary odd order in wave vector k. The general condition for realizing a SOC-induced effective magnetic field (SOF) in such systems, formulated only in terms of the SOC parameters, is derived. When this condition is satisfied, the projection of the electron spin on the direction of the collinear SOF is a conserved quantity. The complete set of the k-linear and k-cubic Dresselhaus SOC contributions to the effective 2D Hamiltonian of an arbitrarily oriented zinc-blende quantum well is computed by a proper averaging of the corresponding tight-binding bulk SOC Hamiltonian. We investigate possibilities for realization of the collinear SOF in zinc-blende quantum wells of different orientation and obtain some interesting findings, which supplement the results of earlier works. Application of the developed formalism to wurtzite semiconductor 2D systems shows that the collinear SOF can be also realized in a wide class of such quantum wells.
关键词： effective magnetic field,spin-orbit coupling,quantum wells,wurtzite,zinc-blende
更新于2025-09-23 15:23:52
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Monolayer transition metal dichalcogenides in strong magnetic fields: Validating the Wannier model using a microscopic calculation
摘要： Using an equation of motion (EOM) approach, we calculate excitonic properties of monolayer transition metal dichalcogenides perturbed by an external magnetic field. We compare our findings to the widely used Wannier model for excitons in two-dimensional materials and to recent experimental results. We find good agreement between the calculated excitonic transition energies and the experimental results. In addition, we find that the exciton energies calculated using the EOM approach are slightly lower than the ones calculated using the Wannier model. Finally, we also show that the effect of the dielectric environment on the magnetoexciton transition energy is minimal due to counteracting changes in the exciton energy and the exchange self-energy correction.
关键词： monolayer transition metal dichalcogenides,magnetic field,Wannier model,excitons,magnetoexcitons,equation of motion
更新于2025-09-23 15:23:52
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[IEEE 2018 19th International Conference of Young Specialists on Micro/Nanotechnologies and Electron Devices (EDM) - Erlagol (Altai Republic), Russia (2018.6.29-2018.7.3)] 2018 19th International Conference of Young Specialists on Micro/Nanotechnologies and Electron Devices (EDM) - Evaluation of Hall Effective Masses in Callium Arsenide Monocrystal in Quantizing Magnetic Field
摘要： Results of calculation of the holes effective masses values in a 3D GaAs monocrystal in a quantizing magnetic field are presented, the masses were evaluated using perturbation theory in the proximity of the point for the magnetic field oriented along [001] crystallographic direction. The masses were calculated for the Landau levels n = 0,1. The condition for application of the considered holes effective mass spectrum for thin monocrystalline films is formulated.
关键词： magnetic field,holes spectrum,holes masses
更新于2025-09-23 15:23:52
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Solar total and spectral irradiance reconstruction over the last 9000 years
摘要： Context. Changes in solar irradiance and in its spectral distribution are among the main natural drivers of the climate on Earth. However, irradiance measurements are only available for less than four decades, while assessment of solar influence on Earth requires much longer records. Aims. The aim of this work is to provide the most up-to-date physics-based reconstruction of the solar total and spectral irradiance (TSI/SSI) over the last nine millennia. Methods. The concentrations of the cosmogenic isotopes 14C and 10Be in natural archives have been converted to decadally averaged sunspot numbers through a chain of physics-based models. TSI and SSI are reconstructed with an updated SATIRE model. Reconstructions are carried out for each isotope record separately, as well as for their composite. Results. We present the first ever SSI reconstruction over the last 9000 years from the individual 14C and 10Be records as well as from their newest composite. The reconstruction employs physics-based models to describe the involved processes at each step of the procedure. Conclusions. Irradiance reconstructions based on two different cosmogenic isotope records, those of 14C and 10Be, agree well with each other in their long-term trends despite their different geochemical paths in the atmosphere of Earth. Over the last 9000 years, the reconstructed secular variability in TSI is of the order of 0.11%, or 1.5 W m?2. After the Maunder minimum, the reconstruction from the cosmogenic isotopes is consistent with that from the direct sunspot number observation. Furthermore, over the nineteenth century, the agreement of irradiance reconstructions using isotope records with the reconstruction from the sunspot number by Chatzistergos et al. (2017, A&A, 602, A69) is better than that with the reconstruction from the WDC-SILSO series (Clette et al. 2014, Space Sci. Rev., 186, 35), with a lower χ2-value.
关键词： solar-terrestrial relations,Sun: faculae, plages,Sun: activity,Sun: magnetic fields
更新于2025-09-23 15:22:29
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[IEEE 2018 International Conference on Simulation of Semiconductor Processes and Devices (SISPAD) - Austin, TX (2018.9.24-2018.9.26)] 2018 International Conference on Simulation of Semiconductor Processes and Devices (SISPAD) - FANTASI: A Novel Devices-to-Circuits Simulation Framework for Fast Estimation of Write Error Rates in Spintronics
摘要： Though physical mechanisms such as spin-transfer torque (STT), spin-orbit torque (SOT), and voltage-controlled magnetic anisotropy (VCMA) has potential to enable energy-efficient and ultra-fast switching of spintronic devices, the switching dynamics are stochastic due to thermal fluctuations. Thus, there is a need in spintronics to understand the interactions between circuit design and the error rate in the switching mechanism, called as write error rate. In this paper, we propose a novel devices-to-circuits simulation framework (FANTASI) for fast estimation of the write error rates (WER) in different spintronic devices and circuits. Here, we show that, FANTASI enables efficient spintronic device-circuit co-design, with results in good agreement with the experimental measurements.
关键词： Fokker-Planck equation,spin-orbit torque,Spin-transfer torque,voltage-controlled magnetic anisotropy,spintronics
更新于2025-09-23 15:22:29
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A Gain-Enhanced Tri-Band Microstrip Square Antenna with Consistent Radiation Patterns by Manipulating its Higher-Order Modes
摘要： A gain-enhanced tri-band microstrip antenna using higher-order modes was analyzed and designed in this communication. It firstly proved in theory that by manipulating the equivalent magnetic currents' (EMCS) relative magnitudes, the higher-order modes' radiation patterns could be converted from conical to broadside. Their zenithal directivities would therefore greatly increase. The relationships between the EMCS' relative magnitudes and the directivities were studied. Then, those analyses were applied to design a gain-enhanced tri-band microstrip antenna using three higher-order modes. A simpler one-port differential feeding and several shorting pins and slots were used to control the antenna's EMCS to improve its radiation patterns. They could further increase the antenna's gains, suppress its side-lobe levels (SLLs) and cross-polarizations. The proposed antenna worked at 3.9 GHz, 4.95 GHz, and 5.9 GHz with consistent broadside radiation patterns and the same polarization. Their measured gains were about 10.0 dBi, 10.4 dBi, and 10.2 dBi, respectively.
关键词： gain-enhanced,microstrip antenna,slot,equivalent magnetic currents,shorting pins,higher-order modes
更新于2025-09-23 15:22:29
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One-dimensional coordination polymers based on a new 3-position substituted imidazo[1,2-a]pyridine ligand: Crystal structures, photoluminescent and magnetic properties
摘要： A new 3-position substituted imidazo[1,2-a]pyridine ligand, namely, 5-(2-chloroimidazo[1,2-a]pyridine-3-carboxamido) isophthalic acid (H2L) was synthesized and characterized by 1H NMR spectroscopy. Based on this ligand, three isostructural one-dimensional coordination polymers, [ML(H2O)2]n (M = Zn (1), Ni (2) and Co (3)) were synthesized under the solvothermal conditions, and structurally characterized by single crystal X-ray diffraction, infrared spectroscopy, powder X-ray diffraction and elemental analyses. The coordination polymer 1 reveals similar photoluminescent spectrum to H2L ligand, but possesses the enhanced phosphorescent emission and higher phosphorescent quantum yield, compared to H2L ligand. Furthermore, the magnetic properties of coordination polymers 2 and 3 have been investigated, the results show there are antiferromagnetic interactions between the NiII ions or CoII ions in 2 or 3.
关键词： Photoluminescence,Coordination polymers,Imidazo[1,2-a]pyridine,X-ray structures,Magnetic properties
更新于2025-09-23 15:22:29
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High cadence, linear, and circular polarization monitoring of OJ 287
摘要： Aims. We present a multifrequency, dense radio monitoring program of the blazar OJ 287 using the 100-m Effelsberg radio telescope. The program aims to test different binary supermassive black hole (SMBH) scenarios and studying the physical conditions in the central region of this bright blazar. Here, we analyze the evolution in total flux density, linear and circular polarization as a means to study the OJ 287 jet structure and its magnetic field geometry. Methods. We used a recently developed, high-precision data analysis methodology to recover all four Stokes parameters. We measured the total flux density of OJ 287 at nine bands from 2.64 GHz to 43 GHz, the linear polarization parameters at four bands between 2.64 GHz and 10.45 GHz, and the circular polarization at two bands, 4.85 GHz and 8.35 GHz. The mean cadence of our measurements is ten days. Results. Between December 2015 and January 2017 (MJD 57370–57785), OJ 287 showed flaring activity and complex linear and circular polarization behavior. The radio electric vector position angle (EVPA) showed a large clockwise (CW) rotation by ～340? with a mean rate of ?1.04?/day. Based on concurrent very long baseline interferometric (VLBI) polarization data at 15 GHz and 43 GHz, the rotation seems to originate within the jet core at 43 GHz (projected angular size ≤0.15 mas or 0.67 pc at the redshift of the source). Moreover, optical polarization data show a similar monotonic CW rotation with a rate of about ?1.1?/day which is superposed with shorter and faster rotations that exhibit rates of about 7.8?/day, mainly in the CW sense. Conclusions. The flux density and polarization variability of the single dish, VLBI and optical data is consistent with a polarized emission component propagating on a helical trajectory within a bent jet. We constrained the helix arc length to 0.26 pc and radius to ≤0.04 pc as well as the jet bending arc length projected on the plane of the sky to ≤1.9–7.6 pc. A similar bending has been observed also in high angular resolution VLBI images of the OJ 287 jet at its innermost regions. The helical trajectory covers only a part of the jet width, possibly its spine. In addition, our results indicate the presence of a stable polarized emission component. Its EVPA (?10?) is oriented perpendicular to the large scale jet, suggesting dominance of the poloidal magnetic field component. Finally, the EVPA rotation begins simultaneously with an optical flare and hence the two might be physically connected. That optical flare has been suggested to be linked to the interaction of a secondary SMBH with the inner accretion disk or originating in the jet of the primary.
关键词： BL Lacertae objects: individual: OJ 287,galaxies: active,quasars: supermassive black holes,magnetic fields,galaxies: jets,polarization
更新于2025-09-23 15:22:29
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Real-time tracking of fluorescent magnetic spore–based microrobots for remote detection of <i>C. diff</i> toxins
摘要： A rapid, direct, and low-cost method for detecting bacterial toxins associated with common gastrointestinal diseases remains a great challenge despite numerous studies and clinical assays. Motion-based detection through tracking the emerging micro- and nanorobots has shown great potential in chemo- and biosensing due to accelerated 'chemistry on the move'. Here, we described the use of fluorescent magnetic spore–based microrobots (FMSMs) as a highly efficient mobile sensing platform for the detection of toxins secreted by Clostridium difficile (C. diff) that were present in patients' stool. These microrobots were synthesized rapidly and inexpensively by the direct deposition of magnetic nanoparticles and the subsequent encapsulation of sensing probes on the porous natural spores. Because of the cooperation effect of natural spore, magnetic Fe3O4 nanoparticles, and functionalized carbon nanodots, selective fluorescence detection of the prepared FMSMs is demonstrated in C. diff bacterial supernatant and even in actual clinical stool samples from infectious patients within tens of minutes, suggesting rapid response and good selectivity and sensitivity of FMSMs toward C. diff toxins.
关键词： biosensing,real-time tracking,C. diff toxins,fluorescent magnetic spore-based microrobots,remote detection
更新于2025-09-23 15:22:29
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Magneto-Optical Effects in Colloidal Solutions of Barium Hexaferrite
摘要： Hydrothermal synthesis was used to obtain lamellar magnetic particles of barium hexaferrite, and colloidal solutions were prepared on their basis. Magneto-optical effects in colloid solutions of barium hexaferrite were examined. It was found that the aqueous colloidal solution of coarse planar particles of barium hexaferrite is a magneto-optical medium that is nearly two orders of magnitude more effective than the colloid formed from isometric cobalt ferrite particles. It was shown that measuring the frequency dependence of the magneto-optical effects and approximating the experimental data with the Debye function makes it possible to find the frequency f0 characteristic of the given colloid and to calculate the characteristic size of particles (or aggregates) creating the optical anisotropy in the colloid under the action of a magnetic field. A dichroism is observed in the aqueous colloid formed by coarse planar barium hexaferrite particles. This phenomenon is due to the change in the light scattering on coarse particles upon their orientation by a magnetic field.
关键词： lamellar magnetic particles,barium hexaferrite,colloidal solution,hydrothermal synthesis,magneto-optical effects
更新于2025-09-23 15:22:29