Extraordinary THz transmission through subwavelength semiconductor slits under antiparallel external magnetic fields

We theoretically study the resonant transmission of electromagnetic waves at the THz frequencies through subwavelength semiconductor slits under external static magnetic fields. The dispersion relations of the surface plasmon polaritons (SPPs) inside a subwavelength slit are analytically derived. It is found that the SPPs propagating along one direction and its reverse are symmetric when parallel external magnetic fields are applied, but are asymmetric when antiparallel external magnetic fields are applied. The transmission properties of periodic subwavelength semiconductor slit arrays with the antiparallel magnetic fields in each unit cell are investigated by the mode expansion technique. The two significant transmission characteristics are observed: (i) The resonant peaks are redshifted with increasing external magnetic fields; (ii) The transmissions in the two opposite directions through the slit arrays are asymmetric. The origin of the transmission asymmetry is reasonably explained by the magnetic-field induced asymmetric SPP propagation losses.     

Possible negative refraction in two dimensional ferromagnetic wire lattice

In this paper, we present theoretical and experimental results for the indication of negative refraction in ferromagnetic metallic wire lattice. We have studied microwave transmission through a two dimensional wire lattice made of ferromagnetic metallic wires under the applied static magnetic field. We have found that, the microwave transmission were significantly changed at ferromagnetic resonance frequency region. Thus the magnetic permeability can be tuned by external dc magnetic field. Since the dielectric permittivity of metallic wire lattice is negative and can take a value close to unity then the crystal exhibits negative index of refraction at microwave region under the external magnetic field.     

横电波激励下亚波长一维金属光栅的异常透射性

针对一维亚波长金属光栅异常透射现象实现的问题,利用时域有限差分法,对横电波（TE波）激励带电介质的亚波长一维金属光栅的光场分布进行了模拟分析,得到了TE波的透射率与电介质折射率的变化关系,从而发现TE波在所研究的模型下具有异常透射现象.基于导模共振理论建立了类导模共振理论,并应用该理论较好地解释了TE波在所研究模型下的异常透射现象,确定类导模共振是TE波产生异常透射性的主要原因.应用所建立的理论解决了传统透射理论无法解决的问题.类导模共振理论揭示了异常透射现象的物理本质,为进一步研究异常透射性的物理本质提 关键词： 金属光栅 横电波 异常透射 类导模共振     

Optical cavity resonance with magnetized plasma

Indefinite media with mixed signs of dielectric tensor elements possess unbounded equifrequency surfaces that have been utilized for diverse applications such as superimaging, enhanced spontaneous emission, and thermal radiation. One particularly interesting application of indefinite media is an optical cavity supporting anomalous scaling laws. In this Letter, we show that by replacing an indefinite medium with magnetized plasma one can construct a tunable indefinite cavity. The magnetized plasma model is based on realistic semiconductor material properties at terahertz frequencies that show hyperbolic dispersion in a certain frequency regime. The hyperbolic dispersion features are utilized for the design of optical cavities. Dramatically different sizes of cavities can support the same resonance mode at the same frequency. For a cavity of fixed size, the anomalous scaling law between the resonance frequency and mode number is confirmed. The resonance frequency can be strongly modulated by changing the strength of the applied magnetic field. The proposed model provides active controllability of terahertz resonances on the deep subwavelength scale with realistic semiconductor materials.     

Spin-dependent shot noise in diluted-magnetic-semiconductor/ semiconductor heterostructures

We investigated the shot noise properties in the diluted-magnetic-semiconductor/semiconductor heterostructures, where the sp-d exchange interaction gives rise to a giant spin splitting when an external magnetic field is applied along the growth direction of the heterostructures. It is found that the noise becomes strongly spin-dependent and can be greatly modulated not only by the external magnetic and electric fields, but also by the structural configuration and geometric parameters. Both the spin-up and spin-down components of the noise spectral density can be greatly suppressed by the magnetic field. The Fano factor is notably sensitive to the transmission probabilities, which varies greatly with the spin-polarization, the external magnetic field, and the structural configuration.     

Tunable enhanced transmission of terahertz radiation through an array of subwavelength holes perforated on a semiconductor film by applying external static magnetic fields

We numerically investigated the tunability of resonance terahertz frequencies of enhanced transmission through a two-dimensional array of holes perforated on a semiconductor film by external static magnetic fields using FDTD methods. We found that the in-plane surface-plasmon polaritons-induced transmission peaks shifted appreciably to longer wavelengths when a moderate magnetic field is applied parallel to the patterned semiconductor film and perpendicular to the electric fields of the incident electromagnetic waves. In particular, there is another transmission peak on which the tuning effect is neglectable, indicating that different mechanism accounts for it.     

Magnetic-flux penetration and critical currents in superconducting strips with slits

We theoretically investigate transport-current-induced magnetic-flux penetration into superconducting strip lines with slits. Even when the individual strips have no bulk pinning, geometrical barriers prevent penetration of magnetic flux into the innermost strips while flux quasistatically penetrates into the outermost slits. The critical current of strip lines with 2N slits at zero applied magnetic field is found to be enhanced by a factor of (N+1)(1/2) above that of a single strip line without slits. Under suitable conditions, a domelike flux distribution due to the geometrical barrier can appear in the individual strips even in the absence of an applied magnetic field.     

Transport Characteristics of Mesoscopic Radio-Frequency Single Electron Transistor

The transport property of a quantum dot under the influence of external time-dependent field is investigated. The mesoscopic device is modelled as semiconductor quantum dot coupled weakly to superconducting leads via asymmetric double tunnel barriers of different heights. An expression for the current is deduced by using the Landauer-Buttiker formula, taking into consideration of both the Coulomb blockade effect and the magnetic field. It is found that the periodic oscillation of the current with the magnetic field is controlled by the ratio of the frequency of the applied ac-field to the electron cyclotron frequency. Our results show that the present device operates as a radio-frequency single electron transistor.     

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.     

Ⅱ-Ⅵ族稀磁半导体多层结构中的自旋极化隧穿

采用转移矩阵法和Airy函数,研究了ZnSe/ZnMnSe/ZnSe/ZnBeSe/ZnSe/ZnBeSe/ZnSe异质结构的自旋极化输运。在外加偏压和磁场对电子透射系数和自旋极化率的影响方面,所得到的结论显现出复杂而有趣的特性。磁场对自旋向上和向下电子隧穿的影响是不同的:对于自旋向上情况,出现双共振向单共振转换现象。     

Transmission through array of subwavelength metallic slits curved with a single step or mutli-step

The transmission of normally incident plane wave through an array of subwavelength metallic slits curved with a sin- gle step or mutli-step has been explored theoretically. The transmission spectrum is simulated by using the finite-difference time-domain method. The influences of surface plasmon polaritons make the end of finite long sub-wavelength metallic slit behaves as magnetic-reflecting barrier. The electromagnetic fields in the subwavelength metallic slits are the superpo- sition of standing wave and traveling wave. The standing electromagnetic oscillation behaves like LC oscillating circuit to decide the resonance wavelength. Therefore, the parameters of adding step may change the LC circuit and influence the transmission wavelength. A new explanation model is proposed in which the resonant wavelength is decided by four factors： the changed length for electric field, the changed length for magnetic field, the effective coefficient of capacitance, and the effective coefficient of inductance. The effect of adding step is presented to analyze the interaction of two steps in slit with mutli-step. This explanation model has been proved by the transmission through arrayed subwavelength metallic slits curved with two steps and fractal steps. All calculated results are well explained by our proposed model.     

Propagation of terahertz waves in nonuniform plasma slab under "electromagnetic window"

The application of magnetic fields, electric fields, and the increase of the electromagnetic wave frequency are up-and-coming solutions for the blackout problem. Therefore, this study considers the influence of the external magnetic field on the electron flow and the effect of the external electric field on the electron density distribution, and uses the scattering matrix method (SMM) to perform theoretical calculations and analyze the transmission behavior of terahertz waves under different electron densities, magnetic field distributions, and collision frequencies. The results show that the external magnetic field can improve the transmission of terahertz waves at the low-frequency end. Magnetizing the plasma from the direction perpendicular to the incident path can optimize the right-hand polarized wave transmission. The external electric field can increase the transmittance to some extent, and the increase of the collision frequency can suppress the right-hand polarized wave cyclotron resonance caused by the external magnetic field. By adjusting these parameters, it is expected to alleviate the blackout phenomenon to a certain extent.     

Surface magnetic anisotropy in glass-coated amorphous microwires as determined from ferromagnetic resonance measurements

The ferromagnetic resonance frequency of different Co base glass-coated amorphous magnetic microwires about 3.5 μm in diameter with negative, vanishing and positive magnetostriction has been investigated from power absorption measurements in the microwave frequency range. The experimental technique employed here involves the replacement of the dielectric of a coaxial transmission line by the sample to be measured. From the evolution of the resonance frequency with DC applied magnetic field, the surface magnetic anisotropy field of the microwires has been quantitatively obtained and, as expected, found to depend on the sign and strength of the magnetostriction. Similar values for the surface anisotropy are obtained in comparison with bulk anisotropy as determined from quasi-static hysteresis loops measurements.     

Zeeman effect in α-quartz

The helical crystal structure in α-quartz acts as the natural micro-solenoids for an electromagnetic wave passing through them, producing a longitudinal magnetic field in the direction of the optical axis. The longitudinal magnetic field further induces the Larmor frequency for the rotation of the bound electrons. The calculated Larmor frequency was experimentally confirmed by monitoring a line splitting of the infrared OH-band in the transmission spectra of α-quartz. A shift in the resonance frequency of the OH-band is equal to the Larmor frequency induced by the natural Zeeman effect.     

Balance-equation approach to terahertz-field-driven magnetotransport in semiconductors

We investigate the magnetotransport in semiconductors under the influence of a dc or slowly-varying electric field, an intense polarized radiation field of terahertz frequency, and a uniform magnetic field, being in arbitrary directions and having arbitrary strengths. Effective force- and energy-balance equations are derived by using a gauge that the magnetic field and the high-frequency radiation field are described by a vector potential and the dc or slowly-varying field by a scalar potential, and by distinguishing the slowly-varying velocity from the rapidly-oscillating velocity related to the high-frequency field. These equations, which include the elastic photon process and all orders of multiphoton absorption and emission processes, are applied to the examination of the effect of a terahertz radiation on the magnetophonon resonance of the longitudinal resistivity in the transverse configuration in nonpolar and polar semiconductors. We find that the previous zero-photon resonance peaks are suppressed by the irradiation of the terahertz field, while many new peaks, which may be related to multiphoton absorption and emission processes, emerge and can become quite distinct, at moderately strong radiation field. Received 17 May 1999     

Optical strong coupling in hybrid metal-graphene metamaterial for terahertz sensing

We propose a terahertz hybrid metamaterial composed of subwavelength metallic slits and graphene plasmonic ribbons for sensing application. This special design can cause the interaction between the plasmon resonances of the metallic slits and graphene ribbons, giving rise to a strong coupling effect and Rabi splitting. Intricate balancing in the strong coupling region can be perturbed by the carrier concentration of graphene, which is subject to the analyte on its surface. Thereby, the detection of analyte can be reflected as a frequency shift of resonance in terahertz transmission spectra. The result shows that this sensor can achieve a theoretical detection limit of 325 electrons or holes per square micrometer. Meanwhile, it also works well as a refractive index sensor with the frequency sensitivity of 485 GHz/RIU. Our results may contribute to design of ultra-micro terahertz sensors.     

Positively and negatively large Goos–Hänchen lateral displacements from a symmetric gyrotropic slab

A detailed study on the lateral displacements of a transverse magnetic (TM) wave transmitted and reflected from a symmetric gyrotropic slab is presented. We give the analytic formulas for the transmission coefficient and the reflection coefficient, as well as the corresponding lateral displacements. It is found that due to the external magnetic field the displacement of a transmitted beam is different from that of reflected one, even for a lossless symmetric configuration. Furthermore, within the chosen frequency band, when the incident angle is near the Brewster angle, the shift of a reflected wave can be large with nonzero reflectance, and can be positive or negative depending on the direction of the applied magnetic field and the incident wave.     

Theory of electronic light scattering in lateral superlattices with Rashba spin–orbit coupling under quantizing electric and magnetic fields

The influence of an in-plane electric and out-of-plane magnetic field on the electronic light scattering is calculated for a lateral semiconductor superlattice within Rashba spin–orbit interaction. Sharp resonances are predicted to appear when the Raman shift matches one frequency of the Wannier–Stark ladder. The spin–orbit interaction gives rise to a dispersion of the exact one-particle eigenstates and an associated finite width of the Raman line, which can be tuned by the electric and magnetic field. When the Bloch frequency is located in this Raman line, a Fano resonance is observed.     

Spin dynamics at low microwave frequencies in crystalline Fe ultrathin film double layers using co-planar transmission lines

Magnetic damping has been studied in magnetic double layers using a network analyzer (NA) with a coplanar transmission line. The magnetic films consisted of ultrathin crystalline films of Fe separated by an Au spacer. The films were deposited on GaAs(0 0 1) substrates using the molecular beam epitaxy (MBE) technique. NA-ferromagnetic resonance (NA-FMR) measurements were carried out along the magnetic hard axis, allowing one to follow the frequency FMR linewidth down to the 1 GHz range of frequencies. It will be shown that the FMR linewidth in the NA-FMR measurements is not entirely described by Gilbert damping. The additional contribution in the frequency linewidth increases with decreasing frequency, and is most likely caused by dipolar fields associated with an inhomogeneous RF field around the coplanar transmission line.     

Studies on magnetic photonic band-gap material at microwave frequency

The microwave transmission characteristics of magnetic photonic band-gap (MPBG) materials, in which the periodic structures are composed of alternating layers of polycarbonate with and without ferromagnetic nanowires, are studied. We present a theoretical method to investigate the transmission spectra of the MPBG material. The band-gap effect varies with the periodic parameters of the MPBG structure. Our calculation can describe well the experimental measurement value. The influence of the applied static magnetic field on the MPBG and the ferromagnetic resonance phenomenon has been studied.