周期排列的电介质小球所诱发的金属-电介质表面上的表面等离子激元的光学性质

研究了金属板的上下表面附近各放置一层按周期排列的电介质小球的体系的光学性质.用多重散射法计算的结果显示金属上侧的周期性排列的电介质小球可诱发金属-电介质表面上的表面等离子激元.这些表面等离子激元的存在可通过非常尖锐的吸收峰反映出来.对于无限厚的金属板，这些吸收峰的峰值位置主要与电介质小球的周期有关，且与解析理论符合得相当好.在有限厚度的金属板中，金属板的两侧表面会产生对称和反对称的两种表面等离子激元，从而使原来在无限厚的金属表面上所出现的单一频率的表面等离子激元劈裂为双频率.由于对称和反对称的表面等离子激元模式在金属板的两侧表面均有相当强的电磁场，因而它们可导致强的电磁波穿透.通过在金属板的下侧加入玻璃球层可将表面等离子激元的电磁场引导出金属，并产生透射波.用多重散射法计算的结果证实，在此体系中由表面等离子激元所引起的透射可达到相当的强度. 对该体系中的物理机理进行了详细分析，从而能够通过调节该体系中的一些参数来控制表面等离子激元出现的频率，使强吸收峰或强透射峰出现在所希望的频率上. 关键词： 表面等离子激元 吸收谱 透射     

Effect of nonpolar optical phonon scattering on free-carrier absorption in heavily doped n-type germanium

The effect of nonpolar optical phonon scattering on the free-carrier absorption in n-type semiconductors such as germanium has been investigated quantum mechanically in quantizing magnetic fields. It is assumed that the energy band of electrons in semiconductors is nonparabolic and the dominant scattering mechanism for electrons in solids is that of nonpolar optical phonon scattering. When the radiation field is polarized parallel to the magnetic field, the absorption coefficient will be of complex value due to the interaction of the radiation field and the optical phonon field with electrons in semiconductors. Results show that real and imaginary parts of the absorption coefficient oscillate quite considerably with the magnetic field in the high fields for the heavily doped n-type Ge. Both real and imaginary parts of the absorption coefficient appear as positive and negative values when changing the magnetic field. In low magnetic fields, the imaginary part of the absorption coefficient disappears. However, if the density of electrons increases, the imaginary part of the absorption coefficient will increase with the magnetic field in low fields. Moreover, it is also shown that the amplitudes of oscillations for the real and imaginary parts of the absorption coefficient do not vary in a regular trend with the density of electrons.     

基模磁激元诱导的多带完美吸收

本文提出一种方向不敏感多带吸收的新结构,即结合光学声子色散材料及无色散介电材料,将其作为单一尺寸金属/介质/金属微光栅的介质分离层.在红外大气窗口波段激发了基模磁激元谐振因此导致多频带吸收.基于有限元方法求解了混合结构的吸收率及电磁场分布,并研究了入射角及结构参数的变化对多峰值吸收的影响.考虑到磁激元的本质是由金属光栅...     

Temperature effect on the threshold frequency of absorption in a quantum pseudodot

The threshold frequency of absorption in a quantum pseudodot under the influence of temperature and applied magnetic field is calculated. The threshold frequency of absorption is computed as a function of temperature and applied magnetic field. The linear and nonlinear dependence of the absorption threshold frequency on magnetic field and temperature has been showed. According to the results obtained from the present work, we find that the linear and nonlinear dependence of the absorption threshold frequency depends on used range of the temperatures and magnetic fields.     

Optical intersubband transitions in double Si -doped GaAs under an applied magnetic field

For different applied magnetic fields, the intersubband transitions of double Si δ-doped GaAs structures is theoretically investigated for a uniform donor distribution. The electronic structure has been calculated by solving the Schrödinger and Poisson equations self-consistently. It is found that the intersubband optical absorption and mobility are sensitive to the applied magnetic field: for all allowed intersubband transitions the intersubband absorption spectra show blueshifts. The results open the possibility to design devices for use as optical filters controlled by an applied magnetic field, depending on the δ-doped structure. It is hoped that these results will provide important improvement in device applications, for a suitable choice of magnetic field.     

Geometrical resonance of the Rayleigh sound wave absorption as a method for direct measurements of the electron specular reflection coefficient from the metal surface

A theory of resonant absorption of the Rayleigh sound waves in metals has been developed for the case of weak magnetic fields (i.e. the Pippard type geometrical oscillations). The amplitude and shape of resonance lines have been studied in relation to the nature of electron reflection from the surface. It has been shown that observations of the geometrical resonance oscillations may serve for investigating directly surface reflectivity of the metal with respect to conduction electrons.     

Linear dynamics of a magnetic subsystem in a quasi-Ising magnet

Microwave absorption at frequencies from 37 to 85 GHz was studied for a Dy_0.3Y_2.7Fe₅O₁₂ single crystal in pulsed magnetic fields of up to 30 T at T=4.2 K. The magnetic field was aligned with the [100] direction. For the fields above 4 T, several soft magnetic-resonance modes were observed, most of them being caused by the static phase transitions induced by a strong external magnetic field. The field-independent absorption lines away from the points of phase transition may be due to the dynamic Jahn-Teller magnetic effect.     

Spin structure of antiprotonic helium in a magnetic field

The spin structure of the (37,35) energy level of antiprotonic helium-4 in permanent homogenous external magnetic field has been calculated in first order of perturbation theory. For weak magnetic fields the effect is observed as an additional broadening of the spectral lines. For magnetic fields of the order of kG and higher, the magnetic and hyperfine interactions become comparable to each other, and the hyperfine spectrum is rearranged.     

利用空气芯电磁铁产生周期会切磁场

给出了一种利用薄金属带构造的、能够产生周期会切磁场的空气芯电磁铁的设计方案,研究了该类型电磁铁产生周期会切磁场的规律。结果表明,通过增加电磁铁的周期长度,减小电子束通道的高度,或在金属带自身的电阻性发热所能承受的范围内增大金属带上传输电流的线密度,都可以提高电磁铁的励磁强度。增加电磁铁的周期长度,还可以提高周期磁场轴向分布的均匀性。     

利用空气芯电磁铁产生周期会切磁场

给出了一种利用薄金属带构造的、能够产生周期会切磁场的空气芯电磁铁的设计方案,研究了该类型电磁铁产生周期会切磁场的规律。结果表明,通过增加电磁铁的周期长度,减小电子束通道的高度,或在金属带自身的电阻性发热所能承受的范围内增大金属带上传输电流的线密度,都可以提高电磁铁的励磁强度。增加电磁铁的周期长度,还可以提高周期磁场轴向分布的均匀性。     

Pressure dependence of electronic transitions of Fe,Co and Ni ions in layered dihalides

Abstract

The near infra-red absorption peaks due to transition metal ions in four halides of Fe, Co and Ni have been studied as a function of pressure. The behaviors of these ions' absorption peaks under pressure are found to be quite different. While the energy of the absorption peak in Col₂ increases with pressure similar to the behavior of transition metal ions in cubic crystal fields, the absorption peaks in the Fe halides are found to be almost independent of pressure. In Nil₂ two absorption peaks exhibit level-crossing at about 2GPa. The results have been interpreted in terms of a theory proposed by da Silva and Falicov [Phys. Rev. B 45,11511 (1992)] in which pressure changes the trigonal component of the crystal field at the transition metal ions.     

Optical absorption of EuTe in high magnetic fields

For the first time, the optical absorption edge of the magnetic semiconductor europium telluride has been studied at low temperature (1.7 K) as a function of magnetic field in the high field range 0 ≤ H ≤ 9.5 Tesla, and related to the magnetic phase diagram of this material. The exponential absorption edge has been parameterized using a magnetic field dependent extension of Urbach's rule, and the observations are found to be consistent with a simple dependence of the gap parameter on polarization and magnetic field.     

Impact of silicon dopant on the absorption and Raman spectroscopy of metal clusters with seven atoms

The structural, optical, and magnetic properties of silicon-doped copper, silver, and gold clusters with D_5h symmetry and seven atoms have been investigated using density functional theory calculations. The global optimized structures of silicon-doped metal clusters are predicted to have a higher HOMO–LUMO gap and higher binding energy than nondoped metal clusters, and nondoped metal clusters have a higher magnetic moment than silicon-doped metal clusters. The silicon doping in metal clusters changes absorption strength and range of absorption wavelength. The silicon dopant also provides a significant impact on the absorption and Raman spectroscopy of nondoped metal clusters. The Raman activities of silicon-doped and nondoped metal clusters are helpful in determining the size and structure of the experimental clusters.     

Magnetoacoustic effect in non-degenerate semiconductors

The effect of ultrasonic waves propagating at an angle ? relative to the direction of a magnetic field in nondegenerate semiconductors such as n-type InSb has been studied by using a quantum treatment which is valid at high frequencies and in strong magnetic fields. Numerical results show that both the absorption coefficient and the change in the sound velocity depend on the direction of the propagation of ultrasonic waves relative to the magnetic field.     

Stabilization effect of Weibel modes due to inverse bremsstrahlung absorption in laser fusion plasma using Krook collisions model

In this work, the Weibel instability due to inverse bremsstrahlung absorption in laser fusion plasma has been investigated. The stabilization effect due to the coupling of the self-generated magnetic field by Weibel instability with the laser wave field is explicitly showed. The main result obtained in this work is that the inclusion of self-generated magnetic field due to Weibel instability to the inverse bremsstrahlung absorption causes a stabilizing effect of excited Weibel modes. We found a decrease in the spectral range of Weibel unstable modes. This decrease is accompanied by a reduction of two orders in the growth rate of instability or even stabilization of these modes. It has been shown that the previous analyses of the Weibel instability due to inverse bremsstrahlung have overestimated the values of the generated magnetic fields. Therefore, the generation of magnetic fields by the Weibel instability due to inverse bremsstrahlung should not affect the experiences of an inertial confinement fusion.     

Optical and electronic properties of anisotropic parabolic quantum disks in the presence of tilted magnetic fields

In the present work, the electronic and optical properties of anisotropic parabolic quantum disks are studied in the presence of an applied magnetic field. For this goal, we first obtain the electron energy levels of an anisotropic parabolic quantum disk under axial, tilted, and in-plane magnetic fields. According to the results obtained for the energy levels reveal that there is no degeneracy at zero magnetic field due to symmetry breaking. With increasing the anisotropy, the energy level spacing increases. At a constant anisotropy, the energy levels splitting decreases with increasing tilt angle of magnetic field. The total refractive index changes decrease when the tilt angle of magnetic field and the anisotropy increase. Also, the total absorption coefficients increase as the tilt angle of magnetic field and anisotropy increase.     

Hydrogen atom in strong magnetic field: a high accurate calculation in spheroidal coordinates

A B-spline-type basis set method for the calculation of hydrogen atom in strong magnetic fields in the frame of spheroidal coordinates has been introduced. High accurate energy levels of hydrogen in the magnetic field, with strength ranging from 0 to 1000 a.u., have been obtained. For the ground state, 1s₀, energies with at least 11 significant digits have been obtained. For the low-lying excited state, 2p₋₁, energies with at least 9 significant digits are obtained. The method has also been applied to the calculation of hydrogen Rydberg states in laboratory magnetic fields. Energy spectra with at least 10 significant digits are presented. A comparison with other results in the literatures has been performed. Our results are comparable to the most accurate one up to date. A possible extension to the cases of parallel and crossed electric and magnetic fields have been discussed.     

Non-Langevin behaviour of the uncompensated magnetization in nanoparticles of artificial ferritin

The magnetic behaviour of nanoparticles of antiferromagnetic artificial ferritin has been investigated by ⁵⁷Fe M?ssbauer absorption spectroscopy and magnetization measurements, in the temperature range 2.5-250 K and with magnetic fields up to 7 T. Samples containing nanoparticles with an average number of ⁵⁷Fe atoms ranging from 400 to 2 500 were studied. By analysing the magnetic susceptibility and zero field M?ssbauer data, the anisotropy energy per unit volume is found, in agreement with some of the earlier studies, to have a value typical for ferric oxides, i.e. a few 10⁵ ergs/cm³. By comparing the results of the two experimental methods at higher fields, we show that, contrary to what is currently assumed, the uncompensated magnetization of the ferritin cores in the superparamagnetic regime does not follow a Langevin law. For magnetic fields below the spin-flop field, we propose an approximate law for the field and temperature variation of the uncompensated magnetization, which was early evoked by Néel but has so far never been applied to real antiferromagnetic systems. More generally, this approach should apply to randomly oriented antiferromagnetic nanoparticles systems with weak uncompensated moments. Received 20 January 2000