共查询到20条相似文献,搜索用时 15 毫秒
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The density and character of the quantum states in the impurity band arising from broadening of the local impurity level are studied. When the impurity concentration is small, the energy levels and states in the impurity band admit an apparent geometric systematics in the main approximation. In this systematics, the wave functions are localized at one or two centers, though the energy levels depend on the positions of orther centers. The density of states and the space correlators calculated in the main approximation are of universal nature, i.e., are represented in a certain scale as universal functions independent of the concentration. In the immediate vicinity of the local level, where in terms of the geometric systematics the density of states has a gap, different states become significant, which collectivize a larger number of centers. They fill the gap, the filling degree essentially depending on the impurity concentration. The general structure of the impurity band spectrum is discussed. 相似文献
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By adopting the concept of fidelity, we investigated efficiency of quantum state transfer with the XX chain as the quantum channel. Different from the previous works, we concentrated on effects of spin and magnetic impurity on fidelity of quantum state transfer. Our results revealed that the spin impurity cannot prevent one from implementing perfect transfer of an arbitrary one-qubit pure state across the spin channel, however, the presence of magnetic impurity or both spin and magnetic impurities may destroy the otherwise perfect spin channels. 相似文献
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In this paper, we studied the effects of an electric field on a hydrogenic impurity confined in a spherical parabolic quantum dot using nondegenerate and degenerate perturbation methods. The binding energies of the ground and three low-excited states are calculated as a function of the confinement strength and as a function of the intensity of an applied electric field. Moreover, we computed the oscillator strength and the second-order nonlinear optical rectification coefficient based on the computed energies and wave functions. The results show that the electric and optical properties of hydrogenic impurity states are strongly affected by the confinement strength and the applied electric field. 相似文献
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Christopher Williams Sergey Lee John Ferraris A. Anvar Zakhidov 《Journal of luminescence》2004,110(4):396-406
The electronic dopants, like tetrafluorocyanoquinodimethane (F4–TCNQ) molecules, used for p-doping of hole transport layers in organic light-emitting diodes (OLEDs) are found to quench the electroluminescence (EL) if they diffuse into the emissive layer. We observed EL quenching in OLED with F4-TCNQ doped N,N′-diphenyl-N′N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine hole transport layer at large dopant concentrations, >5%. To separate the effects of exciton–dopant quenching, from exciton–polaron quenching we have intentionally doped the emissive layer of (8-tris-hydroxyquinoline) with three acceptors (A) of different electron affinities: F4-TCNQ, TCNQ, and C60, and found that C60 is the strongest EL-quencher, while F4-TCNQ is the weakest, contrary to intuitive expectations. The new effects of charge transfer and usually considered energy transfer from exciton to neutral (A) and charged acceptors (A−) are compared as channels for non-radiative Ex–A decay. At high current loads the EL quenching is observed, which is due to decay of Ex on free charge carriers, hole polarons P+. We consider contributions to Ex–P+ interaction by short-range charge transfer and describe the structure of microscopic charge transfer (CT)-processes responsible for it. The formation of metastable states of ‘charged excitons’ (predicted and studied by Agranovich et al. Chem. Phys. 272 (2001) 159) by electron transfer from a P to an Ex is pointed out, and ways to suppress non-radiative Ex–P decay are suggested. 相似文献
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Within the framework of effective-mass approximation, using a variational method, the effect of high-frequency laser field on intersubband transitions and the binding energy of shallow-donor impurities in a semiconductor quantum well are investigated. We have found that the increase of the laser-dressing parameter leads to important effects on the electronic and optical properties of a quantum well. This gives a new degree of freedom in various device applications based on the intersubband transition of electrons. 相似文献
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M. Vos G.A. Sawatzky M. Davies P. Weightman P.T. Andrews 《Solid State Communications》1984,52(2):159-162
We show that the local impurity density of states and the impurity electron—electron interactions can be obtained from impurity Auger spectra. For a Ag0.95Pd0.05 alloy we find 11% Pd(d) character in the Ag d band and Pd(4d-4d) Coulomb interactions which are much larger than the virtual bound state widths. 相似文献
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Using the perturbation method and the effective mass approximation, we studied the combined effects of impurity and external electric field on Raman scattering in a spherical quantum dot with a parabolic potential. Based on the computed energies and wave functions, the differential cross-section involved in this process is investigated, and the selection rules are also calculated. Our results suggest that the scattering intensity is strongly affected by the impurity and external electric field considered in this work. 相似文献
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Three different internal conversion spectra were measured on the 14.4 keV transition of57Fe in Au metals. Adaptability of our method for analysing the line intensity, i.e. the deconvolution-reconvolution method with the constant tail fraction rule was tested experimentally. The obtained 4s electron densities, 4s(o), of Fe impurity atoms in Au agreed on four samples within the error. The weighted mean value of 4s(o) of Fe in Au is 4.98±0.68a
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. It is concluded that the method of analysis is reasonable in this type of experiment. 相似文献
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在HL-lM装置上利用激光吹气技术,在等离子体边缘瞬态注入少量Al杂质粒子,通过对真空紫外光谱和软X射线区的杂质辐射测量,分别研究了欧姆等离子体和低杂波电流驱动等离子体两种情况下,Al杂质粒子输运与约束特性。结果表明:在欧姆等离子体和低杂波电流驱动等离子体两种情况下,等离子体中心区,在没有MHD锯齿震荡和有MHD锯齿震荡非锯齿破裂期间,杂质粒子输运基本上受新经典规律支配;在有MHD锯齿震荡锯齿破裂期间,杂质粒子输运受MHD不稳定性支配,但其时间很短(通常小于300μs),所以在这种情况下,杂质粒子输运的平均效应比新经典值稍大。而约束区杂质粒子输运则比新经典的值大很多,是反常的。在一定条件下低混杂波电流驱动可以改善等离子体粒子约束。 相似文献
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本文采用蒙特卡罗杂质输运程序DIVIMP,针对先进实验超导托卡马克(EAST)的上单零位形放电,模拟研究了不同漂移情况下(无漂移、离子BíB漂移向下/上)的钨杂质产生和输运特性。结果表明,经典漂移显著影响了钨杂质自偏滤器靶板的溅射通量及其在上游区域的含量。 相似文献
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The influence of external uniaxial stress on the different indium-donor complexes in silicon has been studied using the perturbed γ –γ angular correlation (PAC) method. Such effect of an applied stress is detected by means of the probe atoms situated at different complexes in the sample. The current results showed that the responses of the probes in an extrinsic silicon samples are found to be dissimilar for the same value of stress. Such change in the local environments of the probe atoms could be associated with the various strain field created by the implantations of varied size of impurities. The phosphorous implantation in silicon has even lead to the complete absence of observable effect of the applied stress suggesting significant lose of the elasticity of the sample. 相似文献
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Low temperature electrical measurements of conductivity, the Hall effect and magnetoconductance were performed on a degenerate AlGaN sample. The sample exhibited negative magnetoconductance at low magnetic fields and low temperatures, with the magnitude being systematically dependent on temperature. The measured magnetoconductance was compared with models proposed previously by Sondheimer and Wilson [Proc. R. Soc. Lond. Ser. A 190 (1947) p. 435] and Lee and Ramakrishan [Rev. Mod. Phys. 57 (1985) p. 287]. Data were analyzed as the sum of the contribution of a two-band and electron–electron interactions to the magnetoconductance, applying these models to describe the observed behavior. Least-squares fits to the data are presented. In the sample, magnetoconductance can be explained reasonably well by assuming these contributions to the measured magnetoconductance. It was found that theoretical and experimental data were in excellent agreement. 相似文献
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Ailin Xia Chuangui JinDexin Du Yaxin SunLiuniu Tong 《Journal of magnetism and magnetic materials》2011,323(15):2080-2082
Ni-Zn-Cu ferrite powders with nominal composition Ni0.4−xZn0.6CuxFe2O4 (x=0.00-0.20) were prepared via chemical coprecipitation method. X-ray diffractometer, vibrating sample magnetometer, scanning electron microscopy, inductively coupled plasma-atomic emission spectrometry and energy dispersive spectrum were used to study the effects of impurity Na+ ions on the structural and magnetic properties. As a result, it was found that the impurity Na+ ions affect the crystalline structures and magnetic properties greatly. Moreover, the heterogeneous distribution of impurity Na+ ions and the formation of Na compounds retard the phase formation and the grain growth of specimens. Our study also reveals that for the chemical coprecipitation method, a second washing process introduced after drying can eliminate the impurity Na+ ions effectually and thus helps in the formation of single-phase structure and the growth of grains, which is very important for the improvement of magnetic properties and the preparation of ferrites via chemical coprecipitation method. 相似文献
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The magnetic penetration depth of a quasi-two dimensional d-wave superconductor in the presence of nonlineary, nonlocality, and impurity effects is investigated by using Green’s function method. It is shown that a d-wave superconductor would inevitably avoid the violation of the Nernst theorem by creating a T2 term in its penetration depth through a competition of nonlinear, nonlocal, and impurity effects and this system may be stable at low temperatures. I also show that in the impure sample at low temperatures, T < T* ∝ γ the impurity effect determines the temperature dependence of the penetration depth, i.e., nonlocal and nonlinear effects are completely masked by impurities. 相似文献
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Using the perturbation approach, we have calculated the donor impurity related photoionization cross-section in a quantum dot under different temperature and hydrostatic pressure conditions. Our calculation have revealed the dependence of the photoionization cross-section on the confinement strength, temperature and hydrostatic pressure. 相似文献