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1.
本从与真空接触的存在二支声子的半无限极性晶体表面附近极化子的哈密顿算符入手,应用二支模型理论,分别对GaAs和ZnO两种材料计算了外表面电子的量子像势及其极化子的基态能量,计算结果表明,利用二支模型理论求出的外表面极化子的基态能量与利用一支模型理论求出的外表在面极化子的基态能量相差较大,对GaAs,误差约为31.1%, 对ZnO,误差约为14.8%。 相似文献
2.
T. V. Ramakrishnan H. R. Krishnamurthy S. R. Hassan G. Venketeswara Pai 《Journal of Chemical Sciences》2003,115(5-6):767-774
Manganites of the LA1−x
Ca
x
MnO3 family show a variety of new and poorly understood electronic, magnetic and structural effects. Here we outline a new approach
recently proposed by us, where we argue that due to strong Jahn-Teller (JT) coupling with phonons the twofold degeneratee
g
states at the Mn sites dynamically reorganize themselves into localised, JT polaronsl with exponentially small inter-site hopping, and band-like, nonpolaronic statesb, leading to anew 2-band model for manganites which includes strong Coulomb and Hund’s couplings. We also discuss some results from a dynamical mean-field theory treatment
of the model which explains quantitatively a wide variety of experimental results, including insulator-metal transitions and
CMR, in terms of the influence of physical conditions on the relative energies and occupation of thel andb states. We argue that this microscopic coexistence of the two types of electronic states, and their relative occupation and
spatial correlation is the key to manganite physics.
Dedicated to Professor C N R Rao on his 70th birthday 相似文献
3.
4.
在有效质量近似下,利用量子力学密度矩阵理论,从理论上研究了考虑极化子效应后核壳量子点中线性、三阶非线性以及总的光吸收系数在不同条件下随入射光能量变化的关系。通过数值计算,分析了电子-LO声子和电子-IO声子相互作用对ZnS/CdSe柱型核壳结构量子点光吸收系数的影响。结果表明,极化子效应对光吸收系数有很大影响,不同声子模式对光吸收系数影响大小不同。考虑电子-LO声子后,光吸收系数被大大提高。另外,入射光强和弛豫时间对系统的吸收系数也有很大影响。 相似文献
5.
利用固相反应烧结法制备了La067Pb033MnO3单相多晶样品.研究了其结构、磁性及输运特性.结果表明,样品呈菱面相晶体结构,空间群为R3C,居里温度TC(=353K)非常接近TMI(=360K).在居里温度附近,发生铁磁-顺磁转变,导电特性由金属特征向半导体特征过渡.磁电阻在居里点达到极大值.当H=16T时,磁电阻的极大值为145%;当H=08T时,磁电阻的极大值为9%.输运性质表明,TTMI时
关键词:
磁电阻
输运特性
磁极化子
钙钛石 相似文献
6.
根据有机半导体中的电流自旋极化注入和输运实验现象,理论上研究了铁磁/有机半导体/铁磁系统的电流自旋极化性质.考虑到有机半导体的具体特性,从自旋扩散理论和欧姆定律出发,得到了系统的电流自旋极化率.假设自旋极化子和不带自旋的双极化子为有机半导体中的载流子.通过计算发现,极化子为实现有机半导体中电流极化注入和输运的有效自旋载流子,即使它只占总载流子很少一部分.还进一步研究了自旋相关界面电阻和电导率匹配以及有机半导体长度等因素对系统电流自旋极化的影响.
关键词:
自旋电子学
自旋注入
有机半导体
极化子 相似文献
7.
Javed Ahmad Muhammad Ehsan MazharMuhammad Qadeer Awan Muhammad Naeem Ashiq 《Physica B: Condensed Matter》2011,406(18):3484-3488
Potassium substituted nanosized magnesium aluminates having a nominal composition Mg1−xKxAl2O4 where x=0.0, 0.25, 0.5, 0.75, 1.0 have been synthesized by the chemical co-precipitation method. The samples have been characterized by means of X-ray diffraction (XRD), scanning electron microscope (SEM), and dc electrical resistivity measurements. The XRD results reveal that the samples are spinel single phase cubic close packed crystalline materials. The calculated crystallite size ranges between 6 and 8 nm. The behaviour of the lattice constant seems to deviate from the Vegard's law. While X-ray density clearly increases, the bulk density and consequently, the percentage porosity do not exhibit a significant change on increasing the K+ content. The SEM micrographs suggest homogeneous distribution of the nanocrystallites in the samples. The dc electrical resistivity exhibits a typical semiconducting behaviour. Substitution of a Mg2+ ion by a K+ ion provides an extra hole to the system, which forms small polaron. Thermally activated hopping of these small polarons is believed to be the conduction mechanism in the Mg1−xKxAl2O4. The activation energy of hopping of small polarons has been calculated and found K+ ions content dependent. 相似文献
8.
C. Grimaldi L. Pietronero M. Scattoni 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(2):247-255
In the theory of nonadiabatic superconductivity several features are governed by the electron-phonon vertex correction which
has a complex structure both in momentum and frequency. We derive a physical interpretation of such nonadiabatic effects that
permits to link them to specific material properties. We show how the nonadiabatic vertex correction can be decomposed into
two terms with different physical origins. In particular, the first term describes the lattice polarization induced by the
electrons and it is essentially a single-electron process whereas the second term is governed by the particle-hole excitations
due to the exchange part of the phonon-mediated electron-electron interaction. We show that by weakening the influence of
the exchange interaction the vertex takes mostly positive values giving rise to an enhanced effective coupling in the scattering
with phonons. This weakening of the exchange interaction can be obtained by lowering the density of the electrons, or by considering
only long-ranged (small q) electron-phonon couplings.
Received 23 November 1998 and Received in final form 22 January 1999 相似文献
9.
Magnetic dipole and electric quadrupole responses of elliptic quantum dots in magnetic fields 总被引:1,自引:0,他引:1
E. Lipparini Ll. Serra A. Puente 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):409-415
The magnetic dipole (M1) and electric quadupole (E2) responses of two-dimensional quantum dots with an elliptic shape are
theoretically investigated as a function of the dot deformation and applied static magnetic field. Neglecting the electron-electron
interaction we obtain analytical results which indicate the existence of four characteristic modes, with different B-dispersion of their energies and associated strengths. Interaction effects are numerically studied within the time-dependent
local-spin-density and Hartree approximations, assessing the validity of the non-interacting picture.
Received 29 November 2001 Published online 6 June 2002 相似文献
10.
W. Hanke O. Schmitt H. Endres R. Kleiner P. Müller 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):465-471
A quantitative analysis of a microscopic model for the intrinsic Josephson effect in high-temperature superconductors based
on interlayer tunneling is presented both within a mean-field BCS evaluation and a numerically essentially exact Quantum Monte-Carlo
study. The pairing correlations in the CuO2-planes are modelled by a 2D Hubbard model with attractive interaction, a model which accounts well for some of the observed
features such as the short planar coherence length. The stack of Hubbard planes is arranged on a torus, which is threaded
by a magnetic flux. The current perpendicular to the planes is calculated as a function of applied flux (i.e. the phase), and - after careful elimination of finite-size effects due to single-particle tunneling - found to display a
sinusoidal field dependence in accordance with interlayer Josephson tunneling. Studies of the temperature dependence of the
supercurrent reveal at best a mild elevation of the Josephson transition temperature compared to the planar Kosterlitz-Thouless
temperature. These and other results on the dependence of the model parameters are compared with a standard BCS evaluation.
Received: 24 February 1998 / Revised: 28 April 1998 / Accepted: 23 June 1998 相似文献