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1.
We demonstrate the formation of a dynamic optical superlattice through the modulation of a semiconductor microcavity by stimulated acoustic phonons. The high coherent phonon population produces a folded optical dispersion relation with well-defined energy gaps and renormalized energy levels, which are accessed using reflection and diffraction experiments.  相似文献   

2.
Energy spectra of the graphene-based Fibonacci superlattice (SL) in the presence of the band gap in graphene have been investigated. The lattice consists of rectangular barriers, which are arranged along axis Ox. The quasi-periodic modulation is performed due to the difference in the values of the mass term of the Hamiltonian in various SL elements. It is shown that effective splitting of allowed bands (and thereby the formation of a series of gaps) under the effect of the quasi-periodic factor is implemented with both oblique and normal incidence of the electron wave on the SL surface. The energy spectra have a clearly pronounced periodic character over the entire energy scale. The bands split in separate fragments of the spectrum (conventionally periods) according to the Fibonacci inflation rule in each new generation. The band gap associated with a new Dirac point is formed in all Fibonacci generations similarly to the periodic graphene-based SLs. The location of the Dirac point is independent of the SL period; it is very sensitive to the potential barrier height and to the width ratio between the quantum well and the barrier and depends weakly on the mass term in the Hamiltonian. The dependence of the spectra on the incidence angle of the electron wave is insignificant.  相似文献   

3.
Layered Pb/Ag thin films were produced by vacuum evaporation on cooled glass substrates. Measured x-ray diffraction spectra showed peaks characteristic of a superlattice. The superconducting energy gap and the transition temperature of the Pb/Ag superlattice were measured by tunneling experiments. BCS-reduced tunneling conductance revealed the dependence the phonon structure on the superlattice period value. It was also observed that the order of the crystal structure has an influence on the superconducting parameters.  相似文献   

4.
A new class of superlattice, crystalline amorphous superlattice (CASL), by alternatively depositing two semiconductor materials, is proposed. CASL displays three states depending on the component materials' phase: both polycrystalline phases, both amorphous phases, and one polycrystalline phase while another amorphous phase. Using materials capable of reversible phase transition, CASL can demonstrate reversibility among three states. GeTe/Sb(2)Te(3) CASL has been synthesized and proved by x-ray reflectometry and TEM results. The reversible transition among three states induced by electrical and laser pulse was observed. The changes in the optical absorption edge, electrical resistivity, thermal conductivity, and crystallization temperature as a function of layer thickness are interpreted as quantum or nanoeffects. The unique properties of CASL enable the design of materials with specific properties.  相似文献   

5.
Surface superlattice gap solitons   总被引:1,自引:0,他引:1  
He YJ  Chen WH  Wang HZ  Malomed BA 《Optics letters》2007,32(11):1390-1392
We demonstrate that specific surface superlattice gap solitons can be supported at an interface between a one-dimensional photonic superlattice and a uniform medium with saturable nonlinearity. The solitons are stable in the semi-infinite gap but do not exist in the first gap. With the decrease of the power, the solitons jump from the surface site to the next one, and they may continue the motion into the lattices, which offers potential applications for the routing of optical signals.  相似文献   

6.
The electronic transport properties of graphene-based superlattice structures are investigated. A graphene-based modulation-doped superlattice structure geometry is proposed consisting of periodically arranged alternate layers: InAs/graphene/GaAs/graphene/GaSb. The undoped graphene/GaAs/graphene structure displays a relatively high conductance and enhanced mobilities at increased temperatures unlike the modulation-doped superlattice structure, which is more steady and less sensitive to temperature and the robust electrical tunable control on the screening length scale. The thermionic current density exhibits enhanced behavior due to the presence of metallic (graphene) monolayers in the superlattice structure. The proposed superlattice structure might be of great use for new types of wide-band energy gap quantum devices.  相似文献   

7.
Coupled double quantum dots and quantum dot superlattices are formed by utilizing the strain of an InP island on top of a near-surface multi-quantum-well structure. The number and composition of the quantum wells together with the thickness of the barrier separating the quantum wells are varied to investigate the coupling of the wave functions of the carriers confined in separate vertically stacked dots. Photoluminescence studies show that the reduction of the barrier thickness and the increase of the number of wells enhance the coupling, which is observed as red shift and narrowing of the quantum dot peak. The calculated shifts of the peak positions agree closely with the experimental values.  相似文献   

8.
A dielectric medium consisting of roughly polarized molecules has been treated as a 3D disordered spin system (spin glass). Having in view the study of the statistical properties of this system on a micrometer scale and nanosecond time scale of a standing electromagnetic wave, a microscopic approach has been developed. Using the Birkhoff ergodic hypothesis, the initial 3D spin problem is reduced to two conditionally separate 1D problems along the external electromagnetic field propagation. The first problem describes a disordered N-particle quantum system with relaxation in the framework of a Langevin-Schrödinger (L-Sch)-type equation, while the second one describes a steric disordered spin-chain system. The statistical properties of both systems were investigated in detail. Based on these constructions, the coefficient of polarizability related to the collective orientational effects was calculated. The Clausius-Mossotti relation for the dielectric constant was generalized. Taking into account the generalized Clausius-Mossotti relation, a generalized equation for the dielectric permittivity function has been found. A simple formula was derived for the dielectric permittivity function in the X-ray frequency range, which can be larger than unity on the micrometer scale and nanosecond time scale.  相似文献   

9.
The fundamental physics of the resonant tunnelling lifetime (RTL) in superlattices have been theoretically studied. The modelling of this RTL is based on a relationship between the resonant tunnelling and the half-width at half-maximum of the transmission peak. The lifetime of resonant states and the current density accompany the resonant tunnelling change as a function of mole fraction of the barrier layer, well width and barrier width. The energies and the lifetime of the electrons at the resonant states are correlated with the band structure of the superlattices. It is seen that the variation in RTL with resonance energy has a special minima, and that these minima occur around the centre of the allowed bands.  相似文献   

10.
The structural and magnetic properties of the multilayer holmium-yttrium system are investigated by superconducting quantum interference device (SQUID) magnetometry and X-ray and neutron scattering. The sample synthesized by molecular beam epitaxy is the Al2O3/Nb50 Å/Y200 Å/(Ho60 Å/Y30 Å) × 30/Nb50 Å layer sequence. The occurrence of a helical magnetic structure with a period of 24 Å and a spiral coherence length of about 500 Å is observed at a temperature of T N = 123 K upon the identical population of domains with left and right magnetic spirals after zero-field cooling of the sample to a temperature of 10 K. The transition to the ferromagnetic structure at a temperature of 20 K in the investigated sample is suppressed.  相似文献   

11.
《Physics letters. A》1999,260(5):406-410
We study the energy spectrum of the strong-coupled superlattice. The barriers affect the energy spectral statistics in a small scale. The nearest-neighbor energy-level distribution P(s) and the spectral rigidity Δ3(L) demonstrated the GOE (Gaussian Orthogonal Ensemble) distribution. In the whole scale, with the electric field increasing, the spectral rigidity Δ3(L) changes from the Poisson-type like distribution to the Wigner-type like distribution due to the change of the energy-level long-correlation, while the P(s) indicates that the system demonstrates to be integrable. The near-degeneracy of levels makes the level statistics complex.  相似文献   

12.
We report a superlattice parametric oscillator (SPO), with a GaAs/AlAs superlattice as the active element. The SPO was pumped by a microwave field (power 4 mW) and produced third harmonic radiation at subterahertz frequencies (near 300 GHz; 0.1 mW). We attribute the parametric gain to the nonlinearity of the miniband transport.  相似文献   

13.
Strained-layer superlattices (SLS's) are a new kind of semiconductor material, grown from lattice-mismatched constituents, whose electronic properties may be tailored over a wide range. We report the growth by metal-organic chemical vapor deposition of a GaAs0.4P0.6/GaP SLS, and the characterization of its room temperature electronic properties by photocurrent spectroscopy. The results are consistent with predictions of an effective-mass (Kronig-Penney) model.  相似文献   

14.
《Physics letters. A》2020,384(4):126092
The purpose of this paper is to theoretically investigate the spin-orbit interactions of common semiconductor superlattices. Spin splitting and spin-orbit interaction coefficients are calculated based on interactions between the interface-related-Rashba effect and Dresselhaus effect. Semiconductor superlattice shows a series of specific characteristics in spin splitting as follows. The spin splitting of the superlattice structure is greater than that of a single quantum well, contributing to significant spin polarization, spin filtering, and convenient manipulation of spintronic devices. The spin splitting of some superlattice structures does not change with variation of the size of some constituent quantum wells, reducing the requirements for accuracy in the size of quantum wells. The total spin splitting of lower sub-levels of some superlattice can be designed to be zero, realizing a persistent spin helix effect and long spin relaxation time, however, the total spin splitting of higher sub-levels is still appreciable, contributing to desirable spin polarization. These results demonstrate that one superlattice structure can realize two functions, acting as a spin field effect transistor and a spin filter.  相似文献   

15.
We considered the propagation of laser monochromatic radiation in a superlattice that contains regions with an elevated concentration of carriers. The model of the energy spectrum of electrons is chosen in the strong coupling approximation. The electromagnetic field is described quasiclassically with Maxwell equations, which, as applied to the problem under study, are reduced to a non-one-dimensional sine-Gordon wave equation for the vector-potential. We analyzed the wave equation in the approximation of slowly varying amplitudes and phases and obtained and numerically solved an effective equation that describes the electromagnetic field in the superlattice. We studied different regimes of propagation of laser radiation, analyzed diffraction by regions with an elevated electron concentration.  相似文献   

16.
Presented in this paper is a theoretical calculation of the vortex solution in a chosen superlattice (Nb/NbZr) using the Gibbs free energy of an inhomogeneous superconductor. The eigenvalue obtained in this geometry from de Gennes-Werthamer proximity coupling theory is first examined according to a set of experimental data, while the correspondent eigenfunctions are then used to construct vortex solutions with either square lattice or triangle lattice symmetry. The Gibbs free energy is calculated in terms of the vortex solutions of both symmetries. The effective Ginzburg-Landau parameter,K NS , for this superlattice is determined asK NS =0.218 by requiring a consistency between the microscopic and macroscopic theoretical calculations. Of particular importance is a new mechanism revealed by this calculation that a highly localized state of superconducting condensate in its hosting layer, despite the spatially rapid varying characteristic of its correspondent nucleating order parameter, provides a lower eigenvalue state, which results in a dimensional crossover. A further examination of this mechanism is carried out in the mixed state calculation. Finally, a generalization of the present theoretical results to a large class of superlatices is discussed.  相似文献   

17.
X-ray scattering by a superlattice consisting of two types of alternating layers is considered, including both the statistical spread in the layer thicknesses and the phase slippage at inter-layer boundaries. The Bragg peak is not only smeared out, but it is also displaced by an amount proportional to the phase slippage.  相似文献   

18.
The differential dc and hf conductivities of semiconductor superlattices with various electron miniband dispersion relations are studied. It is shown that, due to the anharmonicity of Bloch oscillations, the hf conductivity can be negative at frequencies equal to integral multiples of the Bloch frequency. This effect can arise even in the regions where the differential dc conductivity is positive. The results of the study suggest that superlattices with a miniband dispersion law in which the effective electron mass is positive in a sizable part of the miniband and decreases as the electron energy increases can be used to generate and amplify terahertz-range (microwave) fields.  相似文献   

19.
《Physics letters. A》1987,124(3):181-184
By modifying the mixed-Bethe-lattice model, the properties of spin wave spectra of a ferromagnetic supperlattice are studied. The local density of magnon states (LDOMS) are obtained.  相似文献   

20.
In the IR spectra of mono-, di-, and polysaccharides, the profile shapes of eight absorption bands have been investigated. They turned out to be symmetric and very close to the dispersion one for all the bands considered. It has been found that in mono- and disaccharides the minimum halfwidth of the bands is 10 cm–1 and in polysaccharides it is higher by a factor of two or more. The halfwidth ratios of different bands in one and the same spectrum can differ severalfold. As is shown, double differentiation of the IR spectra makes it possible to investigate the profile shape of absorption bands when there is marked background absorption or these bands significantly overlap with other bands.  相似文献   

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