外磁场对介质表面次级电子倍增效应的影响

本文采用Particle-in-cell数值方法模拟研究了不同强度外磁场条件下的次级电子倍增效应过程,分析了外磁场对次级电子倍增效应的影响.结果表明,当外磁场达到一定强度时,次级电子倍增效应在微波传输的一半时间内被抑制.通过外磁场抑制,在理想条件下可以使介质窗的微波传输功率容量提高4倍以上.     

Low temperature optical study of Gadolinium molybdate and influence of an external magnetic field

We describe the optical absorption spectrum of a single crystal of Gadolinium Molybdata (GMO) at the temperature of liquid helium. We observe a set of sharp lines in the near ultra violet region; we clasify the lines into three groups A, B, and C. We study the positions of the lines as functions of the orientation of the crystal relative to the polarization of the incident light and we investigate the Zeeman effect on the lines of the groups A and B. We suggest that the observed lines of all three groups are due to transitions between the ground ${}^8\text{S}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ state and the excited ${}^6\text{P}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$, ${}^6\text{P}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ and ${}^6\text{P}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ states of the Gd³⁺ ion in the crystal.     

On the theory of optical properties of anisotropic magnetic crystals in external magnetic field

The calculation of dielectric permeability tensor which are based on the theory of excitons in magnetoordered crystal are made. The dipole exciton energies of crystal are obtained and their dependence on external magnetic field H at arbitrary relation between exchange and single-ion anisotropy constants is established. Refractive index of tetragonal antiferromagnetic is determined and it is shown that it (index) is an odd function of H for a light polarized transverse to the fourth-order symmetry axis of crystal.     

Amplification of optical phonons by a radiation field in semiconductors under strong magnetic fields

The effect of a strong magnetic field on the optical phonon damping in an electron-phonon system is discussed. It is found that as the laser frequency approaches the electron cyclotron frequency the optical phonon population may become unstable.     

Intersubband optical refractive index changes in an asymmetric quantum dot underlying an external static magnetic field

We theoretically investigate the refractive index (RI) changes in an asymmetric quantum dot (QD) underlying an external static magnetic field. We obtain the confined wave functions and energies of an electron in QD by the effective-mass approximation. Using the compact-density-matrix approach and iterative method, we obtain the analytical expressions of linear, nonlinear and total RI changes. The results of numerical calculations for the typical GaAs/AlGaAs QD show that the RI changes are sensitive to the parameters of the asymmetric potential and incident optical intensity. Moreover, the resonance peaks of the RI changes shift with the value of magnetic field B or the radius of the QD changing.     

Tuning the optical transmission through a homogeneous doped semiconductor film by applying an external magnetic field

We theoretically and numerically studied the transmission of light through a homogeneous doped semiconductor film with a Drude tensor in the presence of an external magnetic field. The magneto-induced homogeneous metal films are found to exhibit a magneto-induced light transparency due to cyclotron resonance. In particular, the surface plasmon (SP) resonance mode of the magneto-induced metal film move to higher frequencies with increasing magnetic field, bringing about large changes in the extraordinary light transmission peaks predicted to occur in such a magneto-induced semiconductor film.     

Impurity effects on the magnetization and magnetic susceptibility of an electron confined in a quantum ring under the presence of an external magnetic field

The magnetization and the magnetic susceptibility of a single electron confined in a two-dimensional (2D) parabolic quantum ring under the effect of external uniform magnetic field and in the presence of an acceptor impurity have been studied. The shifted 1/N expansion method was used to solve the Hamiltonian quantum ring within the effective mass approximation. The computed energy spectra, the magnetization and magnetic susceptibility have been displayed as a function of the quantum ring parameters: confinement strength ω₀, magnetic field strength (ω_c), and temperature (T). The obtained energy results show level-crossings, in the absence and presence of acceptor impurity, which are manifested as oscillations in the magnetization and magnetic susceptibility curves.     

Enhancement of superconductivity by an external magnetic field in magnetic alloys

An infinite-volume limit solution of the thermodynamics of a BCS superconductor containing spin 1/2 and 7/2 magnetic impurities, obtained recently in [D. Borycki, J. Ma?kowiak, Supercond. Sci. Technol. 24, 035007 (2011)] is exploited to derive the expressions for critical magnetic field $\mathcal{H}_c$ (T). The credibility of the resulting thermodynamically limited theoretical equations, which depend on the magnetic coupling constant g and impurity concentration c, is verified on the experimental data for the following superconducting alloys: LaCe, ThGd and SmRh₄B₄. Good quantitative agreement with experimental data is found for sufficiently small values of c. The discrepancies between theoretical and experimental values of $\mathcal{H}_c$ (T) for larger values of c in case of LaCe and ThGd are reduced by introducing the concept of the effective temperature $\tilde T$ , which accounts for the Coulomb interactions between the electron gas and impurity ions. At low temperatures, the critical magnetic field is found to increase with decreasing temperature T. This enhancement of the critical magnetic field provides evidence of the Jaccarino-Peter effect, which was experimentally observed in the Kondo systems like LaCe, (La_{1 ? x} Ce _x )Al₂ and also in the pseudoternary compounds, including Sn_{1 ? x} Eu _x Mo₆S₈, Pb_{1 ? x} Eu _x Mo₆S₈ and La_{1.2 ? x} Eu _x Mo₆S₈. The effect of an external magnetic field $\mathcal{H}$ on a BCS superconductor perturbed by magnetic impurities was also studied. On these grounds, by analyzing the dependence of superconducting transition temperature T _c on $\mathcal{H}$ of (La_{1 ? x} Ce _x )Al₂, we have shown, that for certain parameter values, external magnetic field compensates the destructive effect of magnetic impurities.     

Interaction of optical phonons with magnons in orthorhombic crystals and the effect of magnetic field on structural phase transitions

The interaction of polar optical phonons with magnons in RMn₂O₅ manganates (R is a rare earth ion) has been studied in the approximation of collinear antiferromagnetic ordering of manganese sublattices. The effect of magnetic field on the structural phase transitions in these oxides has been analyzed.     

Effects on planetary motion of an external electromagnetic field

By considering an uncharged mass embedded in an external electromagnetic field we show that the Einstein corrections to the Newtonian results may further be modified.     

Effects of a magnetic field on the optical properties of dielectric mirrors

We have measured the changes in the polarization state of a monochromatic (λ=514.5 nm) light beam on reflection at normal incidence by a multilayer dielectric mirror placed in a time-modulated magnetic field. The dominant effect is a Faraday rotationΦ?3.7×10^?10 rad/G. The sensitivity (around 40Hz) obtained is \( \simeq 6 \times 10^{ - 9} {\text{ rad/}}\sqrt {{\text{Hz}}} \) which is dominated by the shot-noise limit (100 mW of light power).     

Quantum confinement effects on the optical phonons of CdTe quantum dots

We present Raman-scattering results for CdTe nanocrystals in doped glasses which clearly show the confinement effects on the phonon spectra as a function of the quantum-dot size. We observed optical phonon modes, surface phonons and some of their overtone combinations. We show that the surface-phonon scattering intensity increases as the quantum-dot size decreases. Our results also show a decrease in the electron–phonon coupling as the nanocrystal size is decreased. These confinement effects are observed by changing the laser excitation energy, and thus by tuning to resonance with the optical transitions for quantum dots of different sizes within their broad size distribution in semiconductor-doped glasses.     

Structurization of ferrofluids in the absence of an external magnetic field

Structural transformations in a model ferrofluid in the absence of an external magnetic field have been theoretically studied. The results agree with well-known laboratory experiments and computer simulations in showing that, if the concentration of particles and their magnetic interaction energy are below certain critical values, most particles form separate linear chains. If these parameters exceed the critical values, most particles concentrate so as to form branched network structures. The passage from chains to network has a continuous character rather than represents a discontinuous first-order phase transition.     

Effect of annealing in an external magnetic field on the magnetic texture of Mo-containing nanocrystalline alloys

The magnetic texture of (Fe_1?x Co_x)₇₆Mo₈Cu₁B₁₅ (x = 0, 0.5) nanocrystalline alloys is studied for different amounts of nanocrystalline grains. The originally amorphous alloys were annealed in external longitudinal and transverse magnetic fields of 0.025 T and 0.8T, respectively. Mössbauer measurements were carried out at room and liquid nitrogen temperatures in order to gain information on the hyperfine interactions and the orientation of the magnetization. The obtained results are compared with those received from zero-field annealed samples. Magneto-optical Kerr effect (MOKE) was applied for the investigation of possible changes at the surface of the x = 0 ribbon as a function of annealing temperature and applied magnetic field. A combination of uniaxial anisotropy, which originates from the shape anisotropy, and four-fold anisotropy, which is a contribution from crystallites of nanometre size embedded in the residual amorphous matrix, is unveiled.     

The dynamics of the Heisenberg-Mattis model with an external magnetic field

We have obtained the energy of spin waves for disordered magnetic systems in an external magnetic field which are described by the Heisenberg-Mattis model.