共查询到20条相似文献,搜索用时 15 毫秒
1.
Jürgen Knig Teemu Pohjola Herbert Schoeller Gerd Schn 《Physica E: Low-dimensional Systems and Nanostructures》2000,6(1-4)
We consider electron transport through quantum dots with large level spacing and charging energy. At low temperature and strong coupling to the leads, quantum fluctuations and the Kondo effect become important. They show up, e.g., as zero-bias anomalies in the current–voltage characteristics. We use a recently developed diagrammatic technique as well as a new real-time renormalization-group approach to describe charge and spin fluctuations. The latter gives rise to a Kondo-assisted enhancement of the current through the dot as seen in experiments. 相似文献
2.
V. Antonov O. Astafiev T. Kutsuwa H. Hirai S. Komiyama 《Physica E: Low-dimensional Systems and Nanostructures》2000,6(1-4)
We study single-electron-transistor (SET) operation of the quantum dot (QD) in a strong magnetic field under weak illumination of far-infrared (FIR) radiation, which causes cyclotron resonance (CR) excitation inside the QD. We find that the SET conductance resonance is exceedingly sensitive to the FIR: It switches on (off) upon the excitation of just one electron to a higher Landau level inside the QD, whereby enabling us to detect individual events of FIR-photon (hν 6 meV) absorption. 相似文献
3.
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
4.
This paper investigates Kondo transport properties in a quadruple quantum dot (QD) based on the slave-boson mean field theory and the non-equilibrium Green’s function.In the quadruple QD structure one Kondo-type QD sandwiched between two leads is side coupled to two separate QD structures:a single-QD atom and a double-QD molecule.It shows that the conductance valleys and peaks always appear in pairs and by tuning the energy levels in three side QDs,the one-,two-,or three-valley conductance pattern can be obtained.Furthermore,it finds that whether the valley and the peak can appear is closely dependent on the specific values of the interdot couplings and the energy level difference between the two QDs in the molecule.More interestingly,an extra novel conductance peak can be produced by the coexistence of the two different kinds of side QD structures. 相似文献
5.
We have calculated the transport properties of electron through an
artificial quantum dot by using the numerical renormalization group
technique in this paper. We obtain the conductance for the system of
a quantum dot which is embedded in a one-dimensional chain in zero
and finite temperature cases. The external magnetic field gives rise
to a negative magnetoconductance in the zero temperature case. It
increases as the external magnetic field increases. We obtain the
relation between the coupling coefficient and conductance. If the
interaction is big enough to prevent conduction electrons from
tunnelling through the dot, the dispersion effect is dominant in this
case. In the Kondo temperature regime, we obtain the conductivity of
a quantum dot system with Kondo correlation. 相似文献
6.
Maria A. Davidovich E. V. Anda C. A. Büsser G. Chiappe 《Physica B: Condensed Matter》2002,320(1-4):366-369
The T=0 transport properties of a wire interacting with a lateral two-level quantum dot are studied by using an exact numerical calculation. The wire conductance, the spin–spin correlation and the Kondo temperature are obtained as a function of the dot level energy spacing. When the dot has two electrons and spin SD1, the wire current is totally quenched by the S=1 Kondo effect. The Kondo temperature is maximum at the singlet–triplet transition and its dependence upon the dot energy spacing follows a non-universal scaling law. 相似文献
7.
We study the thermopower, thermal conductance, electric conductance and the thermoelectric figure of merit for a gate-defined T-shaped single quantum dot (QD). The QD is solved in the limit of strong Coulombian repulsion U→∞, inside the dot, and the quantum wire is modeled on a tight-binding linear chain. We employ the X-boson approach for the Anderson impurity model to describe the localized level within the quantum dot. Our results are in qualitative agreement with recent experimental reports and other theoretical researches for the case of a quantum dot embedded into a conduction channel, employing analogies between the two systems. The results for the thermopower sign as a function of the gate voltage (associated with the quantum dot energy) are in agreement with a recent experimental result obtained for a suspended quantum dot. The thermoelectric figure of merit times temperature results indicates that, at low temperatures and in the crossover between the intermediate valence and Kondo regimes, the system might have practical applicability in the development of thermoelectric devices. 相似文献
8.
9.
Z. H. Liu G. Nachtwei J. Weis K. von Klitzing K. Eberl 《Physica E: Low-dimensional Systems and Nanostructures》1998,1(1-4)
We studied the
–
characteristics of tunneling devices, defined by two trench fingers and an antidot island patterned on Corbino rings in the quantum Hall plateau regime. Well-developed current steps were observed at filling factors near
, which we interpret as a Coulomb staircase phenomenon due to charging of compressible strips around the antidot. The evolution of the current steps with filling factor is explained in the quasi-elastic inter landau level scattering model. 相似文献
10.
R. Franco J. Silva-Valencia M.S. Figueira 《Journal of magnetism and magnetic materials》2008,320(14):e242-e245
We study the thermopower and thermal conductivity of a gate-defined quantum dot, with a very strong Coulomb repulsion inside the dot, employing the X-boson approach for the impurity Anderson model. Our results show a change in the sign of the thermopower as function of the energy level of the quantum dot (gate voltage), which is associated with an oscillatory behavior and a suppression of the thermopower magnitude at low temperatures. We identify two relevant energy scales: a low temperature scale dominated by the Kondo effect and a T∼Δ temperature scale characterized by charge fluctuations. We also discuss the Wiedemann–Franz relation and the thermoelectric figure of merit. Our results are in qualitative agreement with recent experimental reports and other theoretical treatments. 相似文献
11.
We investigate the effect of the mechanical motion of a quantum dot on the transport properties of a quantum dot shuttle.Employing the equation of motion method for the nonequilibrium Green’s function,we show that the oscillation of the dot,i.e.,the time-dependent coupling between the dot’s electron and the reservoirs,can destroy the Kondo effect.With the increase in the oscillation frequency of the dot,the density of states of the quantum dot shuttle changes from the Kondo-like to a Coulomb-blockade pattern.Increasing the coupling between the dot and the electrodes may partly recover the Kondo peak in the spectrum of the density of states.Understanding of the effect of mechanical motion on the transport properties of an electron shuttle is important for the future application of nanoelectromechanical devices. 相似文献
12.
M. Specht M. Sanquer S. Deleonibus G. Guégan 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):503-508
We report observation of the Kondo effect in the Coulomb blockade oscillations of an impurity quantum dot (IQD). This IQD
is formed in the channel of a 100 nm gate length Silicon MOSFET. The quantitative analysis of the anomalous temperature and
voltage dependence for the drain-source current over a series of Coulomb blockade oscillations is performed. It strongly supports
the Kondo explanation for the conductance behavior at very low temperature in this standard microelectronics device.
Received 13 November 2001 and Received in final form 18 February 2002 相似文献
13.
The time-dependent electron transport through a quantum dot with the additional over-dot (bridge) tunneling channel within the evolution operator technique has been studied. The microwave field applied to the leads and quantum dot has been considered and influence of the time-dependent shift of corresponding energy levels on the quantum dot charge and current flowing in the system, its time-averaged values and derivatives of the average current with respect to the gate and source–drain bias voltages have been investigated. The influence of the over-dot tunneling channel on the photon-assisted tunneling has been also studied. 相似文献
14.
David Abusch-Magder F. Simmel D. A. Wharam M. A. Kastner J. P. Kotthaus 《Physica E: Low-dimensional Systems and Nanostructures》2000,6(1-4)
We present an experimental study of the fluctuations of Coulomb blockade peak positions of a quantum dot. The dot is defined by patterning the two-dimensional electron gas of a silicon MOSFET structure using stacked gates. The ratio of charging energy to single-particle energy is considerably larger than in comparable GaAs/AlGaAs quantum dots. The statistical distribution of the conductance peak spacings in the Coulomb blockade regime was found to be unimodal and does not follow the Wigner surmise. The fluctuations of the spacings are much larger than the typical single-particle level spacing and thus clearly contradict the expectation of random matrix theory. Measurements of the natural line width of a set of several adjacent conductance peaks suggest that all of the peaks in the set are dominated by electrons being transported through a single-broad energy level. 相似文献
15.
Non-linear charge and heat transport through a single-level quantum dot in the Coulomb blockade regime is investigated within the framework of non-equilibrium Green function formalism and power output and efficiency of the device are studied. It is found that maximum power as well as efficiency depends on the relative orientation of magnetic moments in electrodes and can vary with polarization factor p. In general, power output is suppressed in magnetic systems and decreases with polarization. The highest efficiency can be attained in antiparallel configuration, and moreover, it does not depend on p. Spin power as well as spin efficiency of the system is introduced and discussed. It is also shown that in the Coulomb blockade regime the (spin) efficiency of the device operating under maximum power conditions varies with temperature bias in a non-monotonic way and shows a flat maximum for low ΔT. 相似文献
16.
We study the persistent current circulating along a mesoscopic ring with a dot side-coupled to it when threaded by a magnetic field. A cluster including the dot and its vicinity is diagonalized and embedded into the rest of the system. The result is numerically exact. We show that in the Kondo regime, the current can be a smooth or a strongly dependent function of the gate potential according to the structure of occupation of the highest energetic electrons of the system. 相似文献
17.
Transport through symmetric parallel coupled quantum dot system has been studied, using non-equilibrium Green function formalism.
The inter-dot tunnelling with on-dot and inter-dot Coulomb repulsion is included. The transmission coefficient and Landaur-Buttiker
like current formula are shown in terms of internal states of quantum dots. The effect of inter-dot tunnelling on transport
properties has been explored. Results, in intermediate inter-dot coupling regime show signatures of merger of two dots to
form a single composite dot and in strong coupling regime the behaviour of the system resembles the two decoupled dots.
相似文献
18.
The Coulomb blockade (CB) in quantum dots (QDs) is by now well documented. It has been used to guide the fabrication of single
electron transistors. Even the most sophisticated techniques for synthesizing QDs (e.g. MOCVD/MBE) result in an assembly in
which a certain amount of disorder is inevitable. On the other hand, theoretical approaches to CB limit themselves to an analysis
of a single QD. In the present work we consider two types of disorders: (i) size disorder; e.g. QDs have a distribution of
sizes which could be unimodal or bimodal in nature. (ii) Potential disorder with the confining potential assuming a variety
of shapes depending on growth condition and external fields. We assume a Gaussian distribution in disorder in both size and
potential and employ a simplified mean field theory. To do this we rely on the scaling laws for the CB (also termed as Hubbard
U) obtained for an isolated QD [1]. We analyze the distribution in the Hubbard U as a consequence of disorder and observe that Coulomb blockade is partially suppressed by the disorder. Further, the distribution
in U is a skewed Gaussian with enhanced broadening.
相似文献
19.
Quantum dots are useful model systems for studying quantum thermoelectric behavior because of their highly energy-dependent electron transport properties, which are tunable by electrostatic gating. As a result of this strong energy dependence, the thermoelectric response of quantum dots is expected to be nonlinear with respect to an applied thermal bias. However, until now this effect has been challenging to observe because, first, it is experimentally difficult to apply a sufficiently large thermal bias at the nanoscale and, second, it is difficult to distinguish thermal bias effects from purely temperature-dependent effects due to overall heating of a device. Here we take advantage of a novel thermal biasing technique and demonstrate a nonlinear thermoelectric response in a quantum dot which is defined in a heterostructured semiconductor nanowire. We also show that a theoretical model based on the Master equations fully explains the observed nonlinear thermoelectric response given the energy-dependent transport properties of the quantum dot. 相似文献
20.
G.-Y. Sun C.-X. Wu Y. Chen Z.-L. Yang 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,49(4):459-464
Using the Keldysh nonequilibrium Green function method, we
theoretically investigate the electron transport properties of a
quantum dot coupled to two ferromagnetic electrodes, with
inelastic electron-phonon interaction and spin flip scattering
present in the quantum dot. It is found that the electron-phonon
interaction reduces the current, induces new satellite polaronic
peaks in the differential conductance spectrum, and at the same
time leads to oscillatory tunneling magnetoresistance effect. Spin
flip scattering suppresses the zero-bias conductance peak and
splits it into two, with different behaviors for parallel and
anti-parallel magnetic configuration of the two electrodes.
Consequently, a negative tunneling magnetoresistance effect may
occur in the resonant tunneling region, with increasing spin flip
scattering rate. 相似文献