含stubs量子波导系统的电子自旋极化输运性质

理论上研究了含stubs的Rashba自旋轨道耦合（spin-orbit coupling, SOC）量子波导系统的自旋极化输运性质. 利用晶格格林函数方法,发现由于stubs和SOC产生的势阱使系统中出现束缚态,这些束缚态与传播态之间相互干涉导致电导中出现Fano共振结构,同时在对应的自旋极化率中也出现Fano共振或反共振结构. 此外,由于系统结构的突变使电子被反向散射和量子干涉效应,电导中出现一系列的共振峰. 但是,当系统加上外磁场后,所有这些效应都被抑制, 系统重新出现量子化电导, 同时自旋电导也出 关键词： 量子波导 自旋极化输运 自旋轨道耦合     

Magnetoresistance calculations for a quantum wire with periodically modulated width

We present numerical calculations of the magnetoresistance in a ballistic quantum wire with periodically modulated width. Surprisingly, the negative magnetoresistance peak is found to persist to a field strength which is two orders of magnitude larger than in single quantum dots. In the weakB-field regime, our results are in good agreement with recent experiments. We argue that the wide peak is due to multiple backscattering among the segments of the wire, leading to a novel weak localization effect.     

Voltage fluctuations on a superconductor grain attached to a quantum wire

When a finite superconductor is in contact with a 1D normal conductor, superconducting phase fluctuations lead to power-law response of the normal subsystem. As a result, the charge fluctuations on the superconductor at zero temperature have logarithmic correlator and a 1 / ω power spectrum ( 1 / f -noise). At higher temperatures 1 / ω is pushed to the high frequency region, and 1 / ω²behavior prevails.     

异侧非重叠三封闭端量子波导中的声子输运与热导

研究了异侧非重叠三封闭端量子波导中的声学声子传输和热导率性质.结果表明:由于激发模的产生,总传输系数在整数约化频率的时发生跳跃;各个激发模所产生的温度条件不一样,温度越高,被激发的模越多,并且高阶模对热导的影响较小;声子传输和热导性质与不连续结构的形状和位置有直接的关系,声子传输和热导性质对量子线的温度环境相当敏感.     

异侧非重叠三封闭端量子波导中的声子输运与热导

研究了异侧非重叠三封闭端量子波导中的声学声子传输和热导率性质。结果表明：由于激发模的产生,总传输系数在整数约化频率的时发生跳跃;各个激发模所产生的温度条件不一样,温度越高,被激发的模越多,并且高阶模对热导的影响较小;声子传输和热导性质与不连续结构的形状和位置有直接的关系,声子传输和热导性质对量子线的温度环境相当敏感。     

Effects of photon field on heat transport through a quantum wire attached to leads

We theoretically investigate photo-thermoelectric transport through a quantum wire in a photon cavity coupled to electron reservoirs with different temperatures. Our approach, based on a quantum master equation, allows us to investigate the influence of a quantized photon field on the heat current and thermoelectric transport in the system. We find that the heat current through the quantum wire is influenced by the photon field resulting in a negative heat current in certain cases. The characteristics of the transport are studied by tuning the ratio, $?{\omega }_{\gamma }/k_{\mathrm{B}}\mathrm{\Delta }T$, between the photon energy, $?{\omega }_{\gamma }$, and the thermal energy, $k_{\mathrm{B}}\mathrm{\Delta }T$. The thermoelectric transport is enhanced by the cavity photons when $k_{\mathrm{B}}\mathrm{\Delta }T>?{\omega }_{\gamma }$. By contrast, if $k_{\mathrm{B}}\mathrm{\Delta }T<?{\omega }_{\gamma }$, the photon field is dominant and a suppression in the thermoelectric transport can be found in the case when the cavity-photon field is close to a resonance with the two lowest one-electron states in the system. Our approach points to a new technique to amplify thermoelectric current in nano-devices.     

Competing effects of interactions and spin-orbit coupling in a quantum wire

We study the interplay of electron-electron interactions and Rashba spin-orbit coupling in one-dimensional ballistic wires. Using the renormalization group approach we construct the phase diagram in terms of Rashba coupling, Tomonaga-Luttinger stiffness and backward scattering strength. We identify the parameter regimes with a dynamically generated spin gap and show where the Luttinger liquid prevails. We also discuss the consequences for the operation of the Datta-Das transistor.     

Optical coherent transient effects in a magnetized semiconductor quantum wire

Effects of an external magnetic field on free induction decay (FID) and the Stark effect in GaAs/GaAlAs quantum wires have been investigated analytically. Our results show that both FID and the Stark effect become enhanced due to the presence of a magnetic field. We have also seen that the magnetic field plays an important role in wider wires while in thinner wires, the geometric confinement dominates over the magnetic effects. The results are found to be in good qualitative agreement with that available in the literature.     

GaAs抛物量子线中弱耦合极化子的磁场效应

应用变分法和改进的线性组合算符法,研究了磁场对抛物量子线中弱耦合极化子振动频率和相互作用能的影响.给出了GaAs抛物量子线中弱耦合极化子的振动频率和相互作用能与磁场和约束强度的依赖关系.对GaAs晶体作了数值计算,结果显示:极化子振动频率和相互作用能都随约束强度和外磁场的增加而增大.     

通过带有侧向耦合量子点的量子线中的光辅助隧穿

应用非平衡格林函数方法,研究了带有微波调制的侧向耦合量子点的量子线中的光辅助隧穿.在考虑了量子干涉和微波场的情况下,得出并讨论了电子传榆幅度和相位方面的信息.电子传输幅度显示出一系列的反共振峰(对应图中的谷结构).峰值的高度与振荡的微波场的幅度和频率有关,而峰的位置只与微波场的频率有关.在有限温的情况下,反共振峰值的高度随着温度的增加而减小,当温度足够高时,反共振峰会消失,特别地,在一定的温度下,低温下谷的地方会演变成峰.     

Mass-asymmetry effects in coupled electron-hole quantum wire system

The effect of mass-asymmetry on the ground-state of coupledelectron-hole quantum wire system is investigated within thequantum version of the self-consistent mean-field approximationof Singwi, Tosi, Land, and Sjölander. The pair-correlationfunctions, static density susceptibility, and correlation energy arecalculated over a range of wire parameters.We find that themass-asymmetry affects appreciably both the intra- and inter-wire correlations,which in turn bring in a marked change in the e-h ground-state.Below a critical density, the e-h correlations now favor theliquid-Wigner crystal phase transition at a sufficiently large wirespacing. This result is in striking difference with the correspondingstudy on the mass-symmetric e-h wire model since here transition to theWigner crystal phase occurs in the adequately closeproximity of two wires at a much lower density, and there also occurs acrossover from Wigner to a charge-density-wave phase at relatively higherdensities. We find that for a GaAsbased e-h wire the critical density for Wignercrystallization is enhanced by a factor of about 2.6.As an important result, our theory captures nicely the recentexperimental observation of Wigner crystallization in anun-equal density GaAs based e-h wire by Steinberg et al.[Phys. Rev. B 73, 113307 (2006)].     

Characteristics of transmission of electrons in a quantum wire tangentially attached to a superconductor ring threaded by magnetic flux

We present numerical investigations of the transmission properties of electrons in a normal quantum wire tangentially attached to a superconductor ring threaded by magnetic flux. A point scatterer with a δ -function potential is placed at node to model scattering effect. We find that the transmission characteristics of electrons in this structure strongly depend on the normal or superconducting state of the ring. The transmission probability as a function of the energy of incident electrons, in the case of a superconductor ring threaded by one quantum magnetic flux, emerges one deep dip, imposed upon the first broad bump in spectrum. This intrinsic conductance dip originates from the superconductor state of the ring. When increasing the magnetic flux from one quantum magnetic flux to two, the spectrum shifts toward higher energy region in the whole. This conductance dip accordingly shifts and appears in the second bump. In the presence of a point-scatterer at the node, the spectrum is substantially modified. Based on the condition of the formation of the standing wave functions in the ring and the broken of the time-reserve symmetry of Schr?dinger equation after switching magnetic flux, the characteristics of transmission of electrons in this structure can be well understood. Received 6 November 2001     

Electrons in a curvilinear quantum wire

The adiabatic motion of electrons in curvilinear quantum wires was studied. It was assumed that the cross section of a wire was constant along its length. The potential that limited electron motion across a wire and the shape of the cross section of the wire were considered arbitrary, while the curvature and the torsion (defined as the derivative of the cross section rotation angle with respect to the length) were assumed to be small. An effective nonrelativistic Hamiltonian for the motion of electrons along a wire with the conservation of transverse quantum numbers was obtained. The spin-orbit coupling Hamiltonian related to the curvature and torsion of a wire was found. Particular cases of a rectilinear twisted quantum wire with a noncircular cross section and a curvilinear quantum wire on a plane were studied. Various transverse potential models limiting the motion of electrons were considered. In particular, the coefficients of the effective Hamiltonian for quantum wires with rectangular and circular cross sections and hard walls and for wires with a parabolic potential were found.     

Tunable quantum dot resonator embedded in a quantum wire

Combined quantum wire and quantum dot system is theoretically predicted to show unique conductance properties associated with Coulomb interactions. We use a split gate technique to fabricate a quantum wire containing a quantum dot with two tunable potential barriers in a two-dimensional electron gas. We observe the effects of the quantum dot cavity on the electron transport through the quantum wire, such as Coulomb oscillations near the pinch-off voltage and periodic conductance oscillations on the first conductance plateau.     

Observation of the Fano-Kondo antiresonance in a quantum wire with a side-coupled quantum dot

We have observed the Fano-Kondo antiresonance in a quantum wire with a side-coupled quantum dot. In a weak coupling regime, dips due to the Fano effect appeared. As the coupling strength increased, conductance in the regions between the dips decreased alternately. From the temperature dependence and the response to the magnetic field, we conclude that the conductance reduction is due to the Fano-Kondo antiresonance. At a Kondo valley with the Fano parameter q approximately 0, the phase shift is locked to pi/2 against the gate voltage when the system is close to the unitary limit in agreement with theoretical predictions by Gerland et al. [Phys. Rev. Lett. 84, 3710 (2000)].     

Spin texturing in a parabolically confined quantum wire with Rashba and Dresselhaus spin-orbit interactionsSpin texturing in a parabolically confined quantum wire with Rashba and Dresselhaus spin-orbit interactionsSpin texturing in a parabolically confined quantum wire with Rashba and Dresselhaus spin-orbit interactions

In this study, we investigate theoretically the effect of spin-orbit coupling on the energy level spectrum and spin texturing of a quantum wire with a parabolic confining potential subjected to the perpendicular magnetic field. Highly accurate numerical calculations have been carried out using a finite element method. Our results reveal that the interplay between the spin-orbit interaction and the effective magnetic field significantly modifies the band structure, producing additional subband extrema and energy gaps. Competing effects between external field and spin-orbit interactions introduce comp｜ex features in spin texturing owing to the couplings in energy subbands. We obtain that spatia~ modulation of the spin density along the wire width can be considerably modified by the spin-orbit coupling strength, magnetic field and charge carrier concentration.     

The phonon effects on the impurity states in cylindrical quantum wire with a finite confining potential

The variational method and the effective mass approximation are applied to calculate the binding energies of the hydrogenic impurity states in a cylindrical quantum wire with finite deep potential well. The phonon effects on the impurity states are considered by taking both the couplings of the electron-phonon and the impurity ion-phonon into account. The numerical results for the GaAs cylindrical quantum wire are given and discussed. It is found that the ion-phonon interaction reduces the impurity binding energy and supplies key contribution to the energy shift, but the electron-phonon coupling enhances the binding energy less. Longitudinal optical (LO) phonons play more important role than interface optical (IO) phonons in the impurity potential screening. The polaron effect caused by LO phonons is more important when the wire is thinner, otherwise the LO phonons are dominant for the thicker wires.     

Spectral properties of a periodically kicked quantum Hamiltonian

We study the spectral properties of the Floquet operator for the periodically kicked HamiltonianH(t) =H ₀+ ₊ ^– (t–nT),H ₀ being self-adjoint and pure point. We show that the Floquet operator is pure point for almost every , if is cyclic forH ₀ and has absolutely convergent expansion in the basis of eigenstates ofH ₀. When this last condition is not satisfied, the Floquet operator can have a continuous spectrum, as we show by an example.     

Spin-orbit-induced spin-density wave in a quantum wire

We present analysis of the interacting quantum wire problem in the presence of magnetic field and spin-orbit interaction. We show that an interesting interplay of Zeeman and spin-orbit terms, facilitated by the electron-electron interaction, results in the spin-density wave state when the magnetic field and spin-orbit axes are orthogonal. This strongly affects charge transport through the wire: With the spin-density wave stabilized, single-particle backscattering off a nonmagnetic impurity becomes irrelevant. The sensitivity of the effect to the direction of the magnetic field can be used for experimental verification of this proposal.