共查询到19条相似文献,搜索用时 203 毫秒
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利用平均场近似理论,研究了一个嵌入T型弱耦合双量子点的介观环系统的基态性质. 结果表明,体系中复杂的基态性质源于Kondo效应与Fano效应相互竞争. 当介观环的尺寸达到足以产生完全Kondo共振时,随双量子点间耦合强度的增强,尖锐的持续电流峰出现了,且越发显著,这说明体系中存在着显著的Fano 效应. 但介观环的Kondo共振持续电流峰值却几乎不发生变化,这为测定Kondo 屏蔽云提供了一个新的可能模型.
关键词:
耦合量子点
持续电流
Kondo效应
Fano 效应 相似文献
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使用双杂质Anderson模型的哈密顿,从理论上研究了一个嵌入并联耦合双量子点介观环系统 , 当处在Kondo区时的基态性质, 并用slave-boson平均场方法求解了哈密顿.研究的结果表 明, 在这个系统中,当两个量子点处于强耦合时,两个量子点可以相干耦合成一个人造分 子,导致一个增强的Kondo效应和超强持续电流的出现.因此,在未来的纳米装置应用中,这 个系统具有潜在的应用价值.
关键词:
并联耦合双量子点
Kondo效应
超强持续电流 相似文献
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利用非平衡格林函数方法, 理论研究T型双量子点分子Aharonov-Bohm (A-B)干涉仪的电荷及其自旋输运性质. 通过控制T型双量子点分子内量子点间有无耦合, 能够实现在同一电子能级位置处分别出现共振和反共振状态, 根据此性质, 能将体系设计成量子开关器件. 当将两个完全相同的T型双量子点分子分别嵌入A-B干涉仪两臂中时, 磁通取适当数值, 能够出现完全的量子相消干涉. 通过调节量子点能级、左右两电极间的偏压和Rashba自旋轨道相互作用强度, 可对体系自旋流进行调控.
关键词:
非平衡格林函数
T型双量子点分子
Aharonov-Bohm干涉仪
自旋输运 相似文献
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使用双杂质的Ansderson模型的哈密顿 ,从理论上研究了一个嵌入并联耦合量子点(DQD)的介观A -B环系统处在Kondo区时的基态性质 ,并用slave boson平均场方法求解了哈密顿。结果表明 ,在这个系统中 ,由磁通诱导而产生的持续电流依赖于系统的宇称效应和尺寸大小 ,并随隧穿耦合强度的增加而变得越来越复杂。在δ >T0 K 时 ,它的电流的峰值是奇宇称的大于偶宇称的 ,并随隧穿耦合强度的增加而增大 ,但Fano共振却被削弱 ,系统始终存在宇称效应 ,这个系统与单 (串联耦合双 )量子点系统相比 ,有许多不同的物理性质。因此 ,在未来的装置设计中 ,是很有潜力的。 相似文献
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When an asymmetric double dot is hybridized with itinerant electrons, its singlet ground state and lowly excited triplet state cross, leading to a competition between the Zhang-Rice mechanism of singlet-triplet splitting in a confined cluster and the Kondo effect (which accompanies the tunneling through quantum dot under a Coulomb blockade restriction). The rich physics of an underscreened S = 1 Kondo impurity in the presence of low-lying triplet-singlet excitations is exposed and estimates of the magnetic susceptibility and the electric conductance are presented, together with applications for molecule chemisorption on metallic substrates. 相似文献
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D. Quirion J. Weis Klaus v. Klitzing 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(3):413-419
The transport properties of a single quantum dot were
measured at low temperature in a regime of strong asymmetric
tunnel coupling to leads. By tuning this asymmetry, the two
parameters of the Kondo effect in a quantum dot, the Kondo
temperature and the zero-bias zero-temperature conductance, were
independently controlled. A careful analysis of the Coulomb
energies and of the tunnel couplings was performed. It allowed an
estimate of the Kondo temperature independently of its value
obtained via the temperature dependence of the conductance. Both
are in good agreement. We finally compared our experimental data
with an exact solution of the Kondo problem which provides the
dependence of the differential conductance on temperature and
source-drain voltage. Theoretical expectations fit quite well our
experimental data in the equilibrium and out-of-equilibrium
regimes. 相似文献
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We study the Josephson effect through a quantum dot magnet whose spin is isotropic and which is coupled to the dot electron spin via exchange coupling. We calculate the Andreev levels and the supercurrent and examine the intertwined effect of the exchange coupling, Kondo correlation, and superconductivity. The former suppresses Kondo correlations, which triggers phase transitions from the 0 to the pi state, but strong antiferromagnetic coupling restores the 0 state. The asymmetric phase diagram in the exchange coupling suggests that the coupling sign could be determined in experiments. 相似文献
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Shingo Katsumoto Masahiro Sato Hisashi Aikawa Yasuhiro Iye 《Physica E: Low-dimensional Systems and Nanostructures》2006,34(1-2):36
The effect of localized spins on the quantum coherence in solids is discussed. A quantum dot with an odd number of electrons can be a model system for a localized spin. It is experimentally shown that a spin flip scattering by a quantum dot pulls the trigger of quantum decoherence. On the other hand, spin flip scattering is the basic process to construct the Kondo singlet state around a magnetic impurity. Through an interference effect of the Kondo state (the Fano–Kondo effect) in a side-coupled dot system, we show experimentally that the Kondo singlet state is quantum mechanically coherent. The analysis of the Fano–Kondo lineshape indicates the locking of the phase shift to π/2, which is in agreement with theoretical predictions. The Fano–Kondo effect is also observed in an Aharonov–Bohm ring, in which a quantum dot is embedded, and also indicates the phase shift locking to π/2. 相似文献
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The conductance through a mesoscopic system of interacting electrons coupled to two adjacent leads is conventionally derived via the Keldysh nonequilibrium Green’s function technique, in the limit of noninteracting leads [Y. Meir, N.S. Wingreen, Phys. Rev. Lett. 68 (1992) 2512]. We extend the standard formalism to cater for a quantum dot system with Coulombic interactions between the quantum dot and the leads. The general current expression is obtained by considering the equation of motion of the time-ordered Green’s function of the system. The nonequilibrium effects of the interacting leads are then incorporated by determining the contour-ordered Green’s function over the Keldysh loop and applying Langreth’s theorem. The dot–lead interactions significantly increase the height of the Kondo peaks in density of states of the quantum dot. This translates into two Kondo peaks in the spin differential conductance when the magnitude of the spin bias equals that of the Zeeman splitting. There also exists a plateau in the charge differential conductance due to the combined effect of spin bias and the Zeeman splitting. The low-bias conductance plateau with sharp edges is also a characteristic of the Kondo effect. The conductance plateau disappears for the case of asymmetric dot–lead interaction. 相似文献
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This paper investigates the electronic transport properties in an
Aharonov--Bohm interferometer with a quantum dot coupling to left and
right electrodes. By employing cluster expansions, it transforms the equations of
motion of Green's functions into the corresponding
equation of motion of connected Green's functions, which provides a
natural and uniform truncation scheme. With this method under the
Lacroix's truncation approximation, it shows that the asymmetric line
shape of zero bias conductance manifests itself as the Fano effect,
and the Kondo effect has been observed in the narrow peak of
differential conductance curve of the system. Our numerical results
also show that the building of Fano state suppresses the amplitude
of Kondo resonance. 相似文献
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The Kondo effect and the Andreev reflection tunneling through a normal (ferromagnet)-double quantum dots-superconductor hybrid system is examined in the low temperature by using the nonequilibrium Green's function technique in combination with the slave-boson mean-field theory. The interplay of the Kondo physics and the Andreev bound state physics can be controlled by varying the interdot hopping strength. The Andreev differential conductance is mainly determined by the competition between Kondo states and Andreev states. The spin-polarization of the ferromagnetic electrode increases the zero-bias Kondo peak. The spin-flip scattering influences the Kondo effect and the Andreev reflection in a nontrivial way. For the ferromagnetic electrode with sufficiently large spin polarization, the negative Andreev differential conductance is found when the spin flip strength in the double quantum dots is sufficiently strong. 相似文献
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Junction of three off-critical quantum Ising chains and two-channel Kondo effect in a superconductor
Domenico Giuliano Gabriele Campagnano Arturo Tagliacozzo 《The European Physical Journal B - Condensed Matter and Complex Systems》2016,89(11):251
We show that a junction of three off-critical quantum Ising chains can be regarded as a quantum spin chain realization of the two-channel spin-1/2 overscreened Kondo effect with two superconducting leads. We prove that, as long as the Kondo temperature is larger than the superconducting gap, the equivalent Kondo model flows towards the two channel Kondo fixed point. We argue that our system provides the first controlled realization of two channel Kondo effect with superconducting leads. Besides its theoretical interest, this result is of importance for potential applications to a number of contexts, including the analysis of the quantum entanglement properties of a Kondo system. 相似文献
19.
The nonequilibrium Kondo effect is studied in a molecule
quantum dot coupled asymmetrically to two ferromagnetic electrodes
by employing the nonequilibrium Green function technique. The
current-induced deformation of the molecule is taken into account,
modeled as interactions with a phonon system, and
phonon-assisted Kondo satellites arise on both sides of the usual main
Kondo peak. In the antiparallel electrode configuration, the
Kondo satellites can be split only for the asymmetric dot-lead
couplings, distinguished from the parallel configuration where
splitting also exists, even though it is for symmetric case. We also
analyze how to compensate the splitting and restore the suppressed
zero-bias Kondo resonance. It is shown that one can change the TMR
ratio significantly from a negative dip to a positive peak only by
slightly modulating a local external magnetic field, whose value is
greatly dependent on the electron--phonon coupling strength. 相似文献