外磁场与温度对低温超导光子晶体低频禁带特性的影响

文中用传输矩阵法(TMM)分析了TM波垂直入时,超导光子晶体的低频禁带特性,并讨论了外磁场与温度对禁带的影响.分析结果表明:超导光子晶体存在频率从0开始的低频禁带;当没有外磁场作用时,由于超导中正常态电子的影响,低频禁带的截止频率与温度无关;有外磁场作用时,温度才对截止频率具有可调性.外加恒定磁场时,低频禁带的截止频率随温度升高而减小;而在正常态电子的作用下,温度对处在超导态超导光子晶体禁带截止频率的调节范围相对忽略正常态电子情况下减小.恒温下,通过调节外磁场来控制带隙时,正常态电子的贡献很小可忽略不计;外磁场强度增大禁带截止频率减小.当超导体完全处于正常态时,低频禁带消失.     

Propagation and transformation of light waves in magnetically active periodic structures

The influence of an external magnetic field applied to a magnetoactive periodic structure on the specific features of formation of the photonic band gaps is established. It is shown that abrupt (stepwise) changes in the polarization of the radiation transmitted by the periodic structure and reflected from it exist near the band gap edges. The possibility of a substantial enhancement of the Faraday effect at a low level of optical losses in the magnetoactive periodic structure with a large number of periods and a dielectric contrast and without a defect layer is substantiated.     

外磁场作用下一维光子晶体的光传输特性

采用光学传输矩阵方法,研究了外磁场作用下一维光子晶体的光传输特性.在外磁场作用下,介质介电函数在回旋频率ω.附近受到强烈的调制,使组分材料的色散关系发生明显改变,导致光子晶体的能带发生变化,透射谱出现复杂结构.在光子带隙中出现窄通带,窄带中的光是局域的.这表明,在不改变光子晶体组分材料的条件下,可以通过改变外磁场的大小,调制光子晶体的能带及其光传输性质.     

Electrooptic properties of one-dimensional photonic crystals based on organic ferroelectric and dye

We present the results of our study of the electrooptic properties of a one-dimensional photonic crystal created from alternating thin layers of two organic compounds, a ferroelectric and a dye. We show that the ferroelectric subsystem of molecular layers in such a heterostructure can be polarized by an external electric field, leading to a linear electrooptic effect and bistability of the electrooptic response in the spectral region of the photonic stop band. On the other hand, a quasi-linear electrooptic effect attributable to the quadratic Stark effect and the built-in spatially periodic static electric field is observed in the spectral region of the absorption of dye molecules. The emergence of this built-in field is explained in terms of the continuity of the electric displacement vector in a spatially periodic dielectric heterostructure with a macroscopically polarized subsystem of ferroelectric layers.     

Magneto-optical Faraday effects in dispersive properties for three-dimensional magnetized plasma photonic crystals

The dispersive properties of three-dimensional magnetized plasma photonic crystals composed of homogeneous magnetized plasma spheres immersed in isotropic dielectric host with face-centered-cubic lattices are theoretically studied based on plane wave expansion method, as the magneto-optical Faraday effects of magnetized plasma are considered. The equations for calculating the band structures are theoretically deduced. The photonic band gap and a flatbands region can be obtained. The influences of host dielectric constant, plasma collision frequency, filling factor, external magnetic field and plasma frequency on the dispersive properties are investigated in detail, respectively, and some corresponding physical explanations are also given. The numerical results show that the photonic band gap can be manipulated by the plasma frequency, filling factor, external magnetic field and host dielectric constant, respectively. However, the plasma collision frequency has no effects on photonic band gap. The location of flatbands region cannot be tuned by any parameters except for the plasma frequency and external magnetic field.     

Polariton dynamics of a one-dimensional gyrotropic magnetic photonic crystal in a dc electric field: I. Peculiarities of refraction

It is shown that both TE and TM waves incident on the surface of a semi-infinite one-dimensional thin-layer gyrotropic magnetic photonic crystal of the magnetic-nonmagnetic dielectric type can experience a number of refraction anomalies in an external electric field due to the effect of hybridization of evanescent waves in magnetic and nonmagnetic layers. These anomalies are absent under the same conditions in spatially homogeneous media consisting of the same materials as the photonic crystal.     

Switching mechanism due to the spontaneous emission cancellation in photonic band gap materials doped with nano-particles

We have investigated the switching mechanism due to the spontaneous emission cancellation in a photonic band gap (PBG) material doped with an ensemble of four-level nano-particles. The effect of the dipole–dipole interaction has also been studied. The linear susceptibility has been calculated in the mean field theory. Numerical simulations for the imaginary susceptibility are performed for a PBG material which is made from periodic dielectric spheres. It is predicted that the system can be switched between the absorbing state and the non-absorbing state by changing the resonance energy within the energy bands of the photonic band gap material.     

Electronic band structure and distribution of excited electrons in the conduction band of anatase doped with boron, nitrogen, and carbon

A method for calculating the distribution of excited electrons in the conduction band of semiconductors has been proposed. This method takes into account both the excitation of electrons by means of an external light source and the transitions to the bottom of the conduction band due to the electron-phonon interaction. The interaction of electrons with the light field has been calculated from first principles in the dipole approximation using the linear muffin-tin orbital method. The electron-phonon interaction has been calculated in terms of the density functional perturbation theory. The method has been applied to the calculation of the quasi-steady-state distribution function of excited electrons in anatase doped with boron, nitrogen, and carbon. The correlations of the distribution function with the photocatalytic activity of doped anatase have been discussed.     

Experimental study of influence of external electric field on the photonic band gap of chiral liquid crystals

Influence of an external electric field on the boundaries of photonic band gap of a chiral liquid crystal has been studied experimentally. It is shown that by using a negative chiral liquid crystal and homeotropic boundary conditions one can increase the abruptness of photonic band gap boundaries and control thus the band gap width by application of the external electric field.     

Magnetic field modulation of photonic bandgap on FeCo/NiO half-shell array

FeCo/NiO half-shell arrays were fabricated based on the periodic monolayer polystyrene spheres. The two-dimensional magnetic periodic arrays form well-defined photonic crystals with pronounced stop bands. Quite interestingly, it is found that the stop bands can be tuned by an external magnetic field. The underlying mechanism is attributed to the controllable dielectric constant of the magnetic FeCo film under an applied magnetic field. The results shown here may open up an avenue for magnetically tunable photonic crystal stop bands, which may be useful for the creation of new magneto-optical devices.     

Effect of a magnetic field on energy transfer of band states to the Mn<Superscript>2+</Superscript> 3<Emphasis Type="Italic">d</Emphasis> shell in the CdMgTe matrix with ultrathin CdMnTe layers

The effect of external magnetic fields on two radiative (band-to-band and on-site) recombination channels in II–VI dilute magnetic semiconductors and related nanostructures has been considered. The 3d on-site emission of manganese ions in CdMgTe matrices containing periodic inclusions of CdMnTe narrow-band-gap layers with thicknesses of 0.5, 1.5, and 3.0 monolayers has been investigated in magnetic fields of up to 6 T. It has been shown that, in a magnetic field, luminescence of manganese ions weakens because of the decrease in the rate of spin-dependent excitation transfer from band states to the Mn²⁺ 3d shell. The maximum suppression of 3d luminescence has been observed in the matrix with a CdMnTe layer 3.0 monolayers thick. This indicates that the main factor responsible for the energy transfer is the internal field near the CdMnTe layers, which determines the magnetic splitting and spin polarization of band states.     

Magnetic surface plasmon-induced tunable photonic bandgaps in two-dimensional magnetic photonic crystals

We experimentally studied magnetically controllable photonic band gaps (PBGs) in two-dimensional magnetic photonic crystals consisting of ferrite rods. Besides the conventional PBG that relates to Bragg scattering, two other types of PBG, resulting from magnetic surface plasmon (MSP) resonance and spin-wave resonance, respectively, are observed. The PBG due to MSP resonance is particularly interesting because of its analogy to surface plasmon in metal; furthermore, it is shown to be completely tunable by an external static magnetic field from both an experimental and a theoretical point of view.     

二维色散和各向异性磁化等离子体光子晶体色散特性研究

采用平面波展开法和时域有限差分法研究了二维色散和各向异性磁化等离子体光子晶体的色散特性.当波矢在周期平面时,由于外加磁场的作用使TE模的色散曲线出现两个不同区域的平带,改变磁场的大小不但可以控制平带的位置,而且可以控制光子带隙的位置和大小.增大背景材料的介电常数,可以形成全方向光子带隙,随着背景材料介电常数的增加,带隙的中心位置降低但带隙宽度增加.当波矢偏离周期平面时,色散曲线不再分为TE和TM模,随着非周期平面波矢的增加,带隙位置上移,带隙宽度先增加随后基本保持不变.     

二维点缺陷正方光子晶体的微腔结构

通过平面波展开法对由Al₂O₃介质棒在空气背景介质中构成含有点缺陷的二维正方光子晶体微腔结构进行研究,计算得出缺陷态能带以及缺陷态模场分布。缺陷模对应的电磁波波长为470~476nm。对该微腔结构的品质因数的求解,得出缺陷态光谱曲线。在光谱曲线中,随着传输波长的增大,将产生几个峰值,并且在475nm处的波动最为明显,反映出在475nm附近的电磁波段在缺陷处的光强较大。进一步利用全矢量等效折射率法研究该结构缺陷模频率的稳定性,得出等效折射率的变化曲线。从等效折射率变化曲线可以看出,当传输波长达到475nm时,该结构已经达到稳定传输的区域。含缺陷模的二维光子晶体微腔结构在光子晶体发光二极管以及高阈值半导体激光器等方面有着重要的应用价值。     

基于自发辐射相干效应的可调光子带隙反射率的提高方法

光子带隙是指某一频率范围的波不能在周期变化的空间介质中传播,即这种结构本身存在“禁带”,并已成功地应用于滤波器、放大器和混频器等器件的设计中.此前,许多专家都致力于提高带隙的反射率,但其只能逐渐接近1.本文在囚禁于一维光晶格中的冷原子介质中实现两个可调光子带隙,并通过选择两基态为精细结构的三能级∧型原子系统,考虑自发辐射相干效应来探究这两个带隙的反射率.适当调节参数,探测场出现增益,从而获得较高反射率的带隙结构,甚至可以超过1.此外,两个带隙反射率还可以通过调节偶极矩之间的夹角以及非相干驱动场强度等参数来操控.     

Anisotropic photonic crystals: Generalized plane wave method and dispersion symmetry properties

This article presents a generalized vector plane wave expansion method, applicable to isotropic and anisotropic periodic dielectric media of arbitrary geometry and dimension. The influence of anisotropic material orientation on the symmetry properties of photonic crystal dispersion surface is discussed. It is shown that the overall Brillouin zone symmetry is formed by the intersection of the photonic crystal lattice symmetry and the symmetry determined by the anisotropic material orientation. This work explains how to define the irreducible Brillouin zone of a two-dimensional anisotropic photonic crystal and demonstrates that doing it correctly allows one to avoid erroneous results, when calculating band gap diagrams of anisotropic photonic crystals. With the help of the methods presented, the possibility of controlling the band gaps of anisotropic photonic crystals by means of external electric field is shown.     

Anomalous influence of an external magnetic field on spin fluctuations in magnetic semiconductors with strong p-d hybridization and the colossal magnetoresistance effect

The colossal magnetoresistance effect in magnetic semiconductors based on lanthanum manganites has been investigated in terms of the model allowing for the effects of p-d hybridization and electronelectron Coulomb correlations. The influence of an external magnetic field on spin fluctuations has been considered under the conditions where the chemical potential is in a narrow heavy-fermion band formed in the hybridization gap. It has been shown that, in the vicinity of the Curie point T _C, the strong spin anharmonicity leads to an anomalously strong suppression of spin fluctuations by the external magnetic field, a phenomenon contributing significantly to the formation of colossal negative magnetoresistance.     

多功能磁光子晶体太赫兹可调偏振控制器件

通过对磁场控制下的二维磁光子晶体太赫兹波偏振传输特性的研究,利用铁氧体磁光材料的磁导率随外磁场改变而变化的特点,设计了具有可控起偏、偏振分束和可调谐波片功能的光子晶体太赫兹偏振控制器件.利用平面波展开法和严格耦合波分析分别计算了光子晶体带隙位置和透过率随外磁场强度变化的关系,用时域有限差分法计算了场分布和相位.结果表明,该结构可以实现高偏振消光比的偏振起偏器和分束器,以及在1 THz附近-π-π相位范围的连续可调谐波片. 关键词： 太赫兹 光子晶体 铁氧体 偏振控制     

Magnetic quantization of the energy states in heavily doped semiconductors with nonparabolic energy bands

A formula for carrier concentration, and a relationship between mobility and diffusivity, have been presented for degenerate semiconductors with a nonparabolic energy band structure under the influence of a magnetic field. The relationships are general; they involve no approximation related to the comparative values of energy bandgap and spin orbit coupling. They should therefore, be applicable to both non-degenerate and degenerate semiconductors. They are quite suitable for the investigation of electrical transport in heavily doped semiconductors under the influence of a magnetic field. PACS 72.20.-I; 73.50.-h     

Nonlinear localization of excitations and the dynamics of solitons in self-modulated systems

The nonlinear dynamics of systems with a spatially periodic ground state was studied. The dynamics of kinks against the background of a periodic soliton structure was considered for the example of the sine-Klein-Gordon model that described a fluxon lattice in a long Josephson contact in an external magnetic field and an incommensurate structure of a surface atomic layer or adatom chains on the surface of a crystal. The velocity of moving kinks was shown to be bounded from above and from below if the ground state was spatially periodic.