Cyclotron resonance studies on bulk and two-dimensional conduction electrons in InSe

Cyclotron resonance is reported for both bulk electrons and electrons bound to charged defect planes in the layer compound InSe. At temperatures below 20 K all carriers present are bound to defect planes and behave as two-dimensional accumulation layers. At higher temperatures the electrons are excited into bulk regions between the defects, and show three-dimensional, bulk behaviour. The conduction band is shown to exhibit an “anomalous anisotropy” with m_∥ = 0.08m₀ and m_⊥ = 0.14m₀. The bound, two-dimensional carriers exhibit a strong non-parabolicity, and show a band edge mass m_⊥ = 0.13 which is considerably lower than the bulk value possibly due to a reduction in the polaron constant in the degenerate electron gas.     

Optical constants and interband transitions in the layer compound InSe

The relevant optical constants of InSe are obtained by applying the Kramers-Kronig relations to accurate near normal incidence reflectance data in the 1.5–5.5 eV energy range. In absence of band calculations, the observed structures are tentatively interpreted by analogy with GaSe ones.     

声子色散对极性晶体中磁极化子基态能量的影响

利用线性组合算符和幺正变换相结合的方法,研究了声子色散对极性晶体中磁极化子基态能量的影响。计及纵光学（LO）声子色散,在抛物近似下导出了极性晶体中磁极化子基态能量随电子-纵光学声子耦合常数、回旋共振频率和声子色散系数的变化关系。数值计算结果表明磁极化子基态能量随声子色散系数和电子-纵光学声子耦合常数的增大而减小,随回旋共振频率增大而增大。     

声子色散对极性晶体中磁极化子基态能量的影响

利用线性组合算符和幺正变换相结合的方法,研究了声子色散对极性晶体中磁极化子基态能量的影响.计及纵光学(LO)声子色散,在抛物近似下导出了极性晶体中磁极化子基态能量随电子-纵光学声子耦合常数、回旋共振频率和声子色散系数的变化关系.数值计算结果表明磁极化子基态能量随声子色散系数和电子-纵光学声子耦合常数的增大而减小,随回旋共振频率增大而增大.     

Directional dispersion of extraordinary phonons in layer compound InSe

The resonant Raman scattering of polar optical phonons has been measured in trigonal γ-InSe at the E'₁ exciton edge. The two-phonon scattering spectrum widely spreads over the frequency range of 50 cm^-1 with an extremely asymmetric lineshape. This spectrum has been interpreted in terms of the directional dispersion of extraordinary LO and TO phonons.     

极性晶体膜中束缚磁极化子的声子平均数与回旋共振频率的关系

采用改进的线性组合算符法和幺正变换方法,研究极性晶体膜中束缚磁极化子的声子平均数与回旋共振频率ωc的变化关系.得出束缚磁极化子的声子平均数由两部分组成:第一部分是由于电子一体LO声子相互作用所引起的;第二部分则是电子-SO声子相互作用引起的.而且当λ＜20× 1012s-1时,声子平均数随着回旋共振频率ωc的增加而迅速增加,这主要是由于磁场的加入使电子声子的相互作用增强而引起的.     

Hot electrons in nonparabolic bands with acoustic and polar optical phonon scattering

Most compound semiconductors have nonparabolic energy bands, and in pure material the dominant scattering mechanisms are usually by acoustic and polar optical phonons. In this paper, general expressions for the high-field transport properties of such materials are derived, using the balance-of-energy method and assuming a drifted Maxwellian distribution function. Under certain conditions the resultant drift velocity-field curves show a single-band negative differential resistance, arising not only from the increase in effective mass with carrier energy, but also from the change in relative scattering efficiencies of the two mechanisms as the applied field is increased. This effect is more marked at low temperatures. The model gives good agreement with previously reported experimental results on n-type PbTe at 77°K.     

Effect of laser-cyclotron resonance on the optical phonon damping in semiconductors

The optical phonon damping in an electron-phonon system in a semiconductor in the presence of laser and magnetic fields is calculated. It is found that the application of a magnetic field parallel to the laser field direction stimulates a stronger amplification of optical phonons as the electron cyclotron frequency approaches the laser frequency.     

声子色散对量子点中弱耦合磁极化子声子平均数的影响

利用线性组合算符和幺正变换相结合的方法,研究了声子色散对抛物量子点中弱耦合磁极化子电子周围光学声子平均数的影响．计及纵光学(LO)声子色散,在抛物近似下导出了基态能量与量子点有效受限长度、声子色散系数、回旋共振频率以及电子-声子耦合常数之间的关系,电子周围光学声子平均数与声子色散系数以及电子-声子耦合常数的关系．数值计算结果表明在弱耦合情况下抛物量子点中磁极化子的基态能量随声子色散系数的增大而减小;电子周围光学声子平均数随声子色散系数增大而增大,随电子-声子耦合常数的增大而增大．     

声子色散对量子点中弱耦合磁极化子声子平均数的影响

利用线性组合算符和幺正变换相结合的方法,研究了声子色散对抛物量子点中弱耦合磁极化子电子周围光学声子平均数的影响。计及纵光学（ LO）声子色散,在抛物近似下导出了基态能量与量子点有效受限长度、声子色散系数、回旋共振频率以及电子－声子耦合常数之间的关系,电子周围光学声子平均数与声子色散系数以及电子－声子耦合常数的关系。数值计算结果表明在弱耦合情况下抛物量子点中磁极化子的基态能量随声子色散系数的增大而减小;电子周围光学声子平均数随声子色散系数增大而增大,随电子－声子耦合常数的增大而增大。     

A first-principles molecular dynamics approach for predicting optical phonon lifetimes and far-infrared reflectance of polar materials

The Lorentz oscillator model is well-known for its effectiveness to describe the far-infrared optical properties of polar materials. The oscillator strength and damping factor in this model are usually obtained by fitting to experimental data. In this work, a method based on first-principles simulations is developed to parameterize the Lorentz oscillator model without any fitting parameters. The high frequency dielectric constant is obtained from density functional perturbation theory, while the optical phonon frequencies and damping factors are calculated using an analysis of ab initio molecular dynamics trajectories. This method is then used to predict the far-infrared properties of GaAs, and the results are in good agreement with experimental data.     

Characterization of porous polar semiconductors by their optical spectra in the region of phonon and plasmon-phonon excitations

Optical properties of porous A ³ B ⁵ semiconductors (GaAs, InP, and GaP) in the far-infrared region, in particular, the specular reflection and attenuated total reflection, including the excitation regime of surface polaritons, are considered. Considering a porous material as a composite, we performed calculations in the context of the effective medium model using two modifications of it, Maxwell-Garnett and Bruggeman, which correspond to two different topologies of the composite material—matrix and statistical. The effect of porosity of the material and of such parameters as doping, anisotropy, and penetration depth of an electromagnetic wave to a porous material on optical spectra is analyzed. In addition, some experimental data are presented and the adequacy of the performed numerical simulation is demonstrated.     

Cyclotron dynamics of neutral atoms in optical lattices with additional magnetic field and harmonic trap potential

We analytically and numerically discuss the stability and dynamics of neutral atoms in a two-dimensional optical lattice subjected to an additional harmonic trap potential and artificial magnetic field. The harmonic trap potential plays a key role in modifying the equilibrium state properties of the system and stabilizing the cyclotron orbits of the condensate.Meanwhile, the presence of the harmonic trap potential and lattice potential results in rich cyclotron dynamics of the condensate. The coupling effects of lattice potential, artificial magnetic field, and harmonic trap potential lead to single periodic, multi-periodic or quasi-periodic cyclotron orbits of the condensate. So we can control the cyclotron dynamics of neutral atoms in optical lattice by manipulating the strength of harmonic confinement, artificial magnetic field, and initial conditions. Our results provide a direct theoretical evidence for the cyclotron dynamics of neutral atoms in optical lattices exposed to the artificial gauge magnetic field and harmonic trap potential.     

声子色散对量子点中弱耦合磁极化子性质的影响(英文)

利用线性组合算符和幺正变换的方法,研究声子色散对磁场中抛物量子点弱耦合磁极化子性质的影响.计及LO声子色散,在抛物近似下导出了基态能量与量子点有效受限长度、声子色散系数、磁场强度以及耦合强度之间的关系.我们可以得到在弱耦合情况下抛物量子点中磁极化子的基态能量E0随量子点有效受限长度l0、电子声子耦合常数α和声子色散系数γ的增大而减小,随磁场回旋频率ωc增大而增大.自陷能Eotr随声子色散系数γ增大而增大.     

Investigation of Fano resonance in compound resonant waveguide gratings for optical sensing

An optical sensor is designed to support the Fano effect based on a compound resonant waveguide grating(CRWG).The transmission spectra of the CRWG are investigated by utilizing a theoretical method that combines the temporal coupled mode theory with the eigenmode information of the grating structure.The theoretical results,which are observed to agree closely with those acquired by rigorous coupled-wave analysis,show that the linewidth of the transmission spectrum decreases upon increasing the distance between the grating strips,and the central resonance frequency decreases as the refractive index of the analyte increases.Here,the proposed CRWG structures will find potential uses in optical sensing.     

Polar optical phonon states and their electron-phonon coupling properties in a wurtzite nitride quantum dot

Within the framework of the macroscopic dielectric continuum model, the interface-optical-propagating (IO-PR) mixing phonon modes of a quasi-zero-dimensional (Q0D) wurtzite cylindrical quantum dot (QD) structure are derived and studied. The approximative analytical-phonon-states of IO-PR mixing modes are given. It is found that there are two types of IO-PR mixing phonon modes, i.e. ρ-IO/z-PR mixing modes and the z-IO/ρ-PR mixing modesexisting in Q0D wurtzite QDs. And each IO-PR mixing modes also have symmetrical and antisymmetrical forms. Via a standard procedure of field quantization, the Fröhlich Hamiltonians of electron-(IO-PR) mixing phonons interaction are obtained. And the orthogonal relations of polarization eigenvectors for these IO-PR mixing modes are also deduced. Numerical calculations of dispersive relation and electron-phonon coupling properties on a wurtzite GaN cylindrical QD are carried out. The behaviors that the IO-PR mixing phonon modes in wurtzite QDs reduce to the IO modes and PR modes in wurtzite QW and QWR systems are analyzed deeply from both of the viewpoints of physics and mathematics. The result shows that the present theories of polar mixing phonon modes in wurtzite cylindrical QDs are consistent with the phonon modes theories in wurtzite QWs and QWR systems. The coupling properties of electron-(IO-PR) mixing modes interactions are studied and analyzed in detail. An abnormal increase of electron-phonon coupling strength are observed as the azimuthal quantum numbers and order of phonon modes increase, which is ascribed to the modulation effect of different dielectric functions of wurtzite crystals in radius- and axial-directions. The analytical electron-phonon interaction Hamiltonians obtained here are useful for further investigating phonon influence on optoelectronics properties of wurtzite Q0D QD structures.     

Confinement of polar optical phonons in quasi-one-dimensional Wurtzite GaN-based quantum well wires: propagating and half-space phonon modes

With the aid of the macroscopic dielectric continuum and Loudon’s uniaxial crystal models, the propagating (PR) and half-space (HS) optical phonon modes and corresponding Fröhlich-like electron-phonon interaction Hamiltonians in a quasi-one-dimensionality (Q1D) wurtzite quantum well wire (QWW) structure are derived and studied. Numerical calculations on a wurtzite GaN/A_l0.15Ga_0.85N QWW are performed, and discussion is focused mainly on the dependence of the frequency dispersions of PR and HS modes on the free wave-number k _z in the z-direction and on the azimuthal quantum number m. The calculated results show that, for given k _z and m, there usually exist infinite branches of PR and HS modes in the high-frequency range, and only finite branches of HS modes in the low-frequency range in wurtzite QWW systems. The reducing behaviors of the PR modes to HS modes, and of the HS mode to interface phonon mode have been observed clearly in Q1D wurtzite heterostructures. Moreover, the dispersive properties of the PR and HS modes in Q1D QWWs have been compared with those in Q2D quantum well structures. The underlying physical reasons for these features have also been analyzed in depth.     

Cyclotron resonance of electrons and holes in TlBr

Cyclotron resonance measurements on TlBr with circularly polarized waves at 34 GHz show the presence of an electron resonance at (0.52 ± 0.03)m_o and a hole resonance at (0.70 ± 0.03)m_o. Mobilities of both electrons and holes are determined in the temperature range 6.5°K to 14°K.     

Extraordinary optical transmission: coupling of the Wood-Rayleigh anomaly and the Fabry-Perot resonance

In this Letter, we demonstrate for the first time that by combining the effects of the Wood-Rayleigh anomaly (WRA) and the Fabry-Perot (FP) resonance, transmission efficiencies of one-dimensional metallo-dielectric gratings on substrates can be significantly improved compared to when these two phenomena work separately. Results of combining the WRA and the FP resonance can be utilized to eliminate the necessity of using the index matching technique and the core-shell structure for enhancing the performance of extraordinary optical transmission devices. Further, the outcomes of combining the WRA and the FP resonance can elucidate some of the unexplained results in the literature.     

Electron-phonon coupling and the soft phonon mode in TiSe2

We report high-resolution inelastic x-ray measurements of the soft phonon mode in the charge-density-wave compound TiSe(2). We observe a complete softening of a transverse optic phonon at the L point, i.e., q=(0.5, 0, 0.5), at T≈T(CDW). Detailed ab initio calculations for the electronic and lattice dynamical properties of TiSe(2) are in quantitative agreement with experimental frequencies for the soft phonon mode. The observed broad range of renormalized phonon frequencies, (0.3, 0, 0.5)≤q≤(0.5, 0, 0.5), is directly related to a broad peak in the electronic susceptibility stabilizing the charge-density-wave ordered state. Our analysis demonstrates that a conventional electron-phonon coupling mechanism can explain a structural instability and the charge-density-wave order in TiSe(2) although other mechanisms might further boost the transition temperature.