一类弯曲量子线的量子束缚态

对电子在弯曲量子线中的弹道输运性质进行了理论研究.弯曲量子线由T型量子线和单曲量子线组成.该有限长的量子结构分别与两半无限长的量子通道相连,当施加一偏压时,量子通道分别可作为电子的发射极和收集极.计算结果表明,当入射电子的能量小于量子结构横向上的第一个本征模时,电导存在两个峰.进一步指出,这些峰来自于电子共振隧穿量子结构中的量子束缚态.并详尽地讨论了这些量子束缚态的性质. 关键词： 量子束缚态 共振隧穿 电导 量子线     

Spatially inhomogeneous states of charge carriers in graphene

The interaction of two-dimensional quasiparticles characterized by a linear dispersion E = ±u|p| (graphene) with impurity potentials is studied. It is shown that discrete levels corresponding to localized states are present in a one-dimensional potential well (quantum wire), whereas such states are absent in a two-dimensional well (quantum dot). The cross section for the scattering of electrons (holes) of graphene by an axially symmetric potential well is determined. It is shown that the cross section tends to a constant value in the limit of infinite particle energy. The effective Hamiltonian is derived for a curved quantum wire of graphene.     

High-frequency conductance of a thin rectangular metal wire

The high-frequency conductance of a straight metal wire of rectangular cross section is calculated. The case when the transverse dimensions of the wire are several times smaller than its length is considered. The condition of diffuse reflection of electrons from the internal surfaces of the wire are taken as the boundary conditions for the problem. The limiting cases are considered, and the results are discussed.     

The effect of impurity on transition frequency of bound polaron in quantum rods

The Hamiltonian of a quantum rod with an ellipsoidal boundary is given after a coordinate transformation that changes the ellipsoidal boundary into a spherical one. The properties of the quantum rods constituting the bridge between two-dimensional quantum wells, zero-dimensional quantum dots and one-dimensional quantum wires are explored theoretically using linear combination operator method. The first internal excited state energy, the excitation energy and the transition frequency between the first internal excited and the ground states of the strong-coupled impurity-bound polaron in the rod with Coulomb-bound potential, the transverse effective confinement length, the ellipsoid aspect ratio and the electron–phonon coupling strength are studied. It is found that the first internal excited state energy, the excitation energy and the transition frequency are increasing functions of the Coulomb-bound potential and the electron–phonon coupling strength, whereas they are decreasing functions of the ellipsoid aspect ratio and the transverse effective confinement length. These results can be attributed to the interesting quantum size confining effects.     

Highly asymmetric atom-lead coupling in nanowires for resonance regime

Concerning quantum transport at resonant states in a one-atom nanowire (nanoconstriction), for the first time, a theoretical study is presented upon strongly asymmetric coupling between the atom at the nanoconstriction and the involved leads. Under these conditions, an approximate relationship for the conductance at resonance in a single-atom wire is considered and an expression for the number of resonant states is derived and discussed. In addition, the density of resonant electronic states is determined under a quantum-box approach by which the conduction electrons are assumed to behave as quantum harmonic oscillators confined in a potential well transverse to the wire.     

Optical and electronic properties of single modulation doped GaAs/AlGaAs V-grooved quantum wire modified by ion implantation

1 Introduction Recently, there is considerable interest in the fabrication and study of quasi-one di-mensional quantum wires (QWRs) due to their potential application for novel optoelec-tronic devices such as QWR laser array [1,2] etc. Among the various techniques devel-oped for producing quasi-one dimensional (quasi-1D) QWRs, the self-organized growth on patterned substrates has been proven to be one of the most promising methods, due to the simplicity of fabrication[3―5]. The QWR is fa…     

Shallow Donor Impurities in Quantum Well WiresIEffects of Image potential

We calculate the shallow donor impurity binding.energies including image potential in quasione- dimensional GaAs/AIAs quantum well wires with rectangular cross section using the variational approach. The results we have obtained show that when impurity ion image potential is considered the variations of binding energy are remarkable, and when the image potentials of impurity ion and electron are considered simultaneously the corresponding variations of binding energy are small. The results also show that the image potential is important, especially when the cross section dimensions of quantum wires become small.     

Release of the Joule heat upon passage of the electric current in nanostructures (a review)

The generation of the Joule heat upon collisionless passage of the direct and alternating electric currents in semiconductor quantum wires connecting two classical reservoirs has been discussed. The transverse dimension of the quantum wire is of the order of the de Broglie wavelength of conduction electrons. The spatial distribution of the Joule heat has been considered. The heat is released in the reservoirs at a distance of the electron mean free path. The total production of the Joule heat has been found to be identical in both reservoirs.     

Wilson chains are not thermal reservoirs

The effects of transverse electric field on the electronic structures, exciton states and excitonic absorption spectra in a cylindrical quantum wire are theoretically investigated in detail. The quantum wire is assumed to GaAs material surrounded by the infinite potential barrier. The results show that the external electric field removes the degeneracy of the electron or hole states. The energy levels of electron and hole, exciton binding energy, excitonic absorption coefficient and absorption energy decrease with increasing the strength of the electric field or the wire radius. The effects of the electric field become more significant for wide wires. The phenomena can be explained by the reduced spatial overlap of ground electron and hole states.     

抛物量子线中强耦合极化子的有效质量

采用改进的线性组合算符法、Lagrange乘子和变分法,在考虑电子与LO声子相互作用情况下,研究了抛物量子线中强耦合极化子的有效质量和光学声子平均数。通过数值计算,讨论了约束强度ω₀和拉格朗日乘子u对极化子的有效质量m^*和光学声子平均数N及极化子振动频率λ的影响。计算结果表明:有效质量m^*和光学声子平均数N及极化子振动频率λ都随着约束强度ω₀和拉格朗日乘子u的增加而增大。     

Magnetooptical properties of a molecular D<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack>-ion in a quantum wire

In the framework of a model of zero-range potential, the problem of bound states of an electron in the field of two D0 centers (a two-center problem) in a semiconductor quantum wire is considered in the presence of a longitudinal magnetic field. It is shown that the magnetic field produces a significant shift of g and u terms and stabilizes the D ₂ ^? states in quantum wires. It is found that, in the case of transverse polarization of light, the spectral dependence of the photoionization cross section of a D ₂ ^? center exhibits the quantum-confined Zeeman effect with strongly pronounced oscillations of interference nature.     

图形衬底量子线生长制备与荧光特性研究

报道了在V型槽图形衬底上利用分子束外延技术外延生长的GaAs/AlGaAs量子线.外延截面在扫描电子显微镜下可以看到在V型槽底部形成了弯月型量子线结构,量子线尺寸约为底边60 nm高14 nm的近三角形.低温87 K下光致发光谱测试在793.7和799.5 nm处出现峰值,验证了量子线的存在.理论近似计算结果显示,相比等宽度量子阱有8 meV的蓝移正是由于横向量子限制引起的. 关键词： V型槽图形衬底 量子线 GaAs     

抛物量子线中弱耦合极化子的有效质量和光学声子平均数

讨论电子与体纵光学(LO)声子弱耦合时对抛物量子线中极化子性质的影响.采用Tokuda改进的线性组合算符法、Lagrange乘子和变分法,导出了抛物量子线中弱耦合极化子的有效质量和光学声子平均数随拉格朗日乘子变化的规律及极化子振动频率随量子线约束强度的变化规律.并以ZnS量子线为例进行了数值计算,结果表明:抛物量子线中弱耦合极化子的有效质量m^*和光学声子平均数N随着拉格朗日乘子u的增加而增大;该结论与体材料中结论基本一致,但量子线中的效应比体材料更明显,表明量子线对电子约束的增强,使极化子效应更明显.同时,极化子振动频率λ随约束强度ω₀的增强而增大.     

Application of coordinate transformation and finite differences method for electron and hole states calculations

In this work we are particularly interested for GaAs/Ga_1−xAl_xAs V-groove quantum wires. The paper presents an efficient and simple method for energy spectra and wave function calculations of electrons and holes in V-groove quantum wires. The method is based on the coordinate transformation of the V-groove quantum wire structure and the computational domain using a function proposed by Inoshita. Then, the Hamiltonian followed by implementation of the FDM (Finite Difference Method) in the new computational space leads to an eigenvalues problem resolved using specialized LAPACK’s routines. The influence of the parameters introduced in the mathematical function, is studied on the energy levels of electrons and holes as well as the oscillator strengths.     

Energy spectra and quantum crystallization in two-electron quantum dots in a magnetic field

Quantum crystallization of electrons in a quantum dot (QD) subjected to an external magnetic field is considered. Two-electron QDs with two-dimensional (2D) parabolic confining potential in an external transverse magnetic field are calculated. The Hamiltonian is numerically diagonalized in the basis of one-particle functions to find the energy spectra and wave functions for the relative motion of electrons with inclusion of electron-electron interaction for a broad range of the confining-potential steepness (α) and external magnetic fields (B). The region of the external parameters (α, B) within which a gradual transition to quantum crystalline order occurs is numerically determined. In contrast to a 2D unbounded system, a magnetic field acts nonmonotonically on “crystallization” in a quantum dot with several electrons because of a competition between two effects taking place with increasing B, namely, decreasing spread of the electron wave functions and increasing effective steepness of the confining potential, which reduces the average separation between electrons. Fiz. Tverd. Tela (St. Petersburg) 40, 1753–1759 (September 1998)     

Polaron Shift of the Levels of a Quantum Wire in a Hybrid Structure with a Bose—Einstein Condensate

JETP Letters - The wavefunction of the transverse motion of electrons in a quantum wire located near a two-dimensional layer of dipole excitons is perturbed by fluctuations of the exciton density...     

电子在圆柱形半导体量子线中的行为研究

用计算一维势阱波函数的方法简化了圆柱形量子线波函数的计算, 得出了量子线中电子的能态、 能级图和波函数。 在确定温度条件下, 讨论了量子线的线宽与它的光谱蓝移、 能级分离或兼并以及电子能态的关系。The wave function of column quantum wires has been calculated with the means of calculation for the quantum wave function in one dimensional potential well. The energy state, energy level diagram and wave function of column quantum wire have gained. Under assured temperature, the relations of column quantum wire diameter to its spectrum blue shift, separation or annexation of energy level, and electrons energy state have been discussed.     

Polaronic States Incorporating Effects of Phonon Confinement in a Rectangular Quantum Well Wire

The electron self-energy due to the interaction of the electron with the LO-phonon incorporating effects of phonon confinement in a rectangular quan tum well wire has been calculated as a function of the size of the wire by the perturbative method within the framework of the effective mass approximation. The results show that in a very smaU wire the self-energy has a peak at the beginning and then increases gradually to the two-dimensional limit value as the wire expands in one direction while keeping fixed in the other direction. The peak values are about at the square cross sections. For larger wires, the self-energy increases monotonically without appearing peaks and approaches slowly to the two-dimensional limit values. The results also present that the self-energy is related to the size of the cross section rather than to the cross sectional area of the wire, and the absolute values of the self-energies are lese than those in comparable two-dimensional quantum wells.     

Electron Raman scattering in cylindrical quantum wires

Electron Raman scattering (ERS) is investigated in a free-standing semiconductor quantum wire of cylindrical geometry for two classes of materials CdS and GaAs. The differential cross section (DCS) involved in this process is calculated as a function of a scattering frequency and the radius of the cylinder. Electron states are considered to be confined within a free-standing quantum wire (FSW). Single parabolic conduction and valence bands are assumed. The selection rules are studied. Singularities in the spectra are found and interpreted for various radii of the cylinder.     

Electronic conductance via atomic wires: a phase field matching theory approach

A model is presented for the quantum transport of electrons, across finite atomic wire nanojunctions between electric leads, at zero bias limit. In order to derive the appropriate transmission and reflection spectra, familiar in the Landauer-Büttiker formalism, we develop the algebraic phase field matching theory (PFMT). In particular, we apply our model calculations to determine the electronic conductance for freely suspended monatomic linear sodium wires (MLNaW) between leads of the same element, and for the diatomic copper-cobalt wires (DLCuCoW) between copper leads on a Cu(111) substrate. Calculations for the MLNaW system confirm the correctness and functionality of our PFMT approach. We present novel transmission spectra for this system, and show that its transport properties exhibit the conductance oscillations for the odd- and even-number wires in agreement with previously reported first-principle results. The numerical calculations for the DLCuCoW wire nanojunctions are motivated by the stability of these systems at low temperatures. Our results for the transmission spectra yield for this system, at its Fermi energy, a monotonic exponential decay of the conductance with increasing wire length of the Cu-Co pairs. This is a cumulative effect which is discussed in detail in the present work, and may prove useful for applications in nanocircuits. Furthermore, our PFMT formalism can be considered as a compact and efficient tool for the study of the electronic quantum transport for a wide range of nanomaterial wire systems. It provides a trade-off in computational efficiency and predictive capability as compared to slower first-principle based methods, and has the potential to treat the conductance properties of more complex molecular nanojunctions.