共查询到20条相似文献,搜索用时 46 毫秒
1.
《中国科学:物理学 力学 天文学(英文版)》2020,(9)
We theoretically studied the thermoelectric transport properties of a strongly correlated quantum dot system in the presence of the Kondo effect based on accurate numerical evaluations using the hierarchical equations of motion approach. The thermocurrent versus gate voltage shows a distinct sawtooth line-shape at high temperatures. In particular, the current changes from positive(hole charge) to negative(particle charge) in the electron number N = 1 region due to the Coulomb blockade effect. However,at low temperatures, where the Kondo effect occurs, the thermocurrent's charge polarity reverses, along with a significantly enhanced magnitude. As anticipated, the current sign can be analyzed by the occupation difference between particle and hole.Moreover, the characteristic turnover temperature can be further defined at which the influences of the Coulomb blockade and Kondo resonance are in an effective balance. Remarkably, the identified characteristic turnover temperature, as a function of the Coulomb interaction and dot-lead coupling, possessed a much higher value than the Kondo temperature. When a magnetic field is applied, a spin-polarized thermocurrent can be obtained, which could be tested in future experiments. 相似文献
2.
《Superlattices and Microstructures》1999,25(5-6):915-923
In the classical Josephson effect the phase difference across the junction is well defined, and the supercurrent is reduced only weakly by phase diffusion. For mesoscopic junctions with small capacitance the phase undergoes large quantum fluctuations, and the current is also decreased by Coulomb blockade effects. We discuss the behavior of the current–voltage characteristics in a large range of parameters comprising the phase diffusion regime with coherent Josephson current as well as the supercurrent peak due to incoherent Cooper pair tunneling in the Coulomb blockade regime. 相似文献
3.
Linear and nonlinear transport through a quantum dot that is weakly coupled to ideal quantum leads is investigated in the parameter regime where charging and geometrical quantization effects coexist. The exact eigenstates and spins of a finite number of correlated electrons confined within the dot are combined with a rate equation. The current is calculated in the regime of sequential tunneling. The analytic solution for an Anderson impurity is given. The phenomenological charging model is compared with the quantum mechanical model for interacting electrons. The current-voltage characteristics show Coulomb blockade. The excited states lead to additional fine-structure in the current voltage characteristics. Asymmetry in the coupling between the quantum dot and the leads causes asymmetry in the conductance peaks which is reversed with the bias voltage. The spin selection rules can cause a ‘spin blockade’ which decreases the current when certain excited states become involved in the transport. In two-dimensional dots, peaks in the linear conductance can be suppressed at low temperatures, when the total spins of the corresponding ground states differ by more than 1/2. In a magnetic field, an electron number parity effect due to the different spins of the many-electron ground states is predicted in addition to the vanishing of the spin blockade effect. All of the predicted features are consistent with recent experiments. 相似文献
4.
Recently observed Aharonov-Bohm quantum interference of the period h/2e in charge density wave rings strongly suggests that correlated density wave electron transport is a cooperative quantum phenomenon. The picture discussed here posits that quantum solitons nucleate and transport current above a Coulomb blockade threshold field. We propose a field-dependent tunneling matrix element and use the Schr?dinger equation, viewed as an emergent classical equation as in Feynman's treatment of Josephson tunneling, to compute the evolving macrostate amplitudes, finding excellent quantitative agreement with voltage oscillations and current-voltage characteristics in NbSe(3). A proposed phase diagram shows the conditions favoring soliton nucleation versus classical depinning. 相似文献
5.
We investigate nonequilibrium transport in the absence of spin-flip energy relaxation in a few-electron quantum dot artificial atom. Novel nonequilibrium tunneling processes involving high-spin states, which cannot be excited from the ground state because of spin blockade, and other processes involving more than two charge states are observed. These processes cannot be explained by orthodox Coulomb blockade theory. The absence of effective spin relaxation induces considerable fluctuation of the spin, charge, and total energy of the quantum dot. Although these features are revealed clearly by pulse excitation measurements, they are also observed in conventional dc current characteristics of quantum dots. 相似文献
6.
G. Vasseur D. Weinmann R. A. Jalabert 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(2):267-275
We study transport through a strongly correlated quantum dot and show
that Coulomb blockade can appear even in the presence of perfect contacts. This
conclusion arises from numerical calculations of the conductance for a
microscopic model of spinless fermions in an
interacting chain connected to each lead via a completely open channel. The
dependence of the conductance on the gate voltage shows well
defined Coulomb blockade peaks which are sharpened as the interaction strength
is increased. Our numerics is based on the embedding method
and the DMRG algorithm. We explain the emergence of Coulomb blockade
with perfect contacts by a reduction of the effective coupling matrix elements
between many-body states corresponding to successive particle numbers in the
interacting region. A perturbative approach, valid in the strong interaction
limit, yields an analytic expression for the interaction-induced suppression of
the conductance in the Coulomb blockade regime. 相似文献
7.
A. H. Phillips N. A. I. Aly K. Kirah H. E. El-Sayes 《中国物理快报》2008,25(1):250-253
The transport property of a quantum dot under the influence of external time-dependent field is investigated. The mesoscopic device is modelled as semiconductor quantum dot coupled weakly to superconducting leads via asymmetric double tunnel barriers of different heights. An expression for the current is deduced by using the Landauer-Buttiker formula, taking into consideration of both the Coulomb blockade effect and the magnetic field. It is found that the periodic oscillation of the current with the magnetic field is controlled by the ratio of the frequency of the applied ac-field to the electron cyclotron frequency. Our results show that the present device operates as a radio-frequency single electron transistor. 相似文献
8.
G. Michałek B. R. Bułka 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(3):411-419
Conductance and other physical quantities are calculated in double quantum dots (DQD) connected in series in the limit of
coherent tunnelling using a Green's function technique. The inter-dot Coulomb repulsion and the exchange interaction are studied
by means of the Kotliar and Ruckenstein slave-boson mean-field approach. The crossover from the atomic to the molecular limit
is analyzed in order to show how the conductance in the model depends on the competition between the level broadening (dot-lead
coupling) and the dot-dot transmission. The double Kondo effect
was found in the gate voltage characteristics of the conductance in the atomic limit. In the case, when each dot accommodates
one electron, the Kondo resonant states are formed between dots and their adjacent leads and transport is dominated by hopping
between these two resonances. In the molecular limit the conductance vanishes for sufficiently low gate voltages, which means
the Kondo effect disappeared. For small dot-lead coupling the transport characteristics are very sensitive on the influence
of the inter-dot Coulomb repulsion and the position of the local energy level. The
resonance region is widened with increase of the inter-dot Coulomb interactions while the exchange interaction has opposite
influence. 相似文献
9.
Inelastic transport through double quantum dot systems with coupling between electronic and vibrational degrees of freedom is examined by means of a master equation approach. The current and the conductance are analyzed for both weak and strong interdot couplings. The results show that an asymmetry in the current-voltage characteristic and appearance of negative differential conductance due to electron-phonon interaction. The influence of temperature on the current is studied and found that increasing temperature gives rise to eliminating the current blockade and, thus, removing the Coulomb diamonds in the conductance spectra. 相似文献
10.
We report measurements of spin transitions for GaAs quantum dots in the Coulomb blockade regime and compare ground and excited state transport spectroscopy to direct measurements of the spin polarization of emitted current. Transport spectroscopy reveals both spin-increasing and spin-decreasing transitions, as well as higher-spin ground states, and allows g factors to be measured down to a single electron. The spin of emitted current in the Coulomb blockade regime, measured using spin-sensitive electron focusing, is found to be polarized along the direction of the applied magnetic field regardless of the ground state spin transition. 相似文献
11.
12.
《Superlattices and Microstructures》2000,28(3):177-187
We have successfully fabricated a single-electron transistor based on undoped Si nanocrystals having radii of approximately 3 nm. Gate voltage oscillation was observed from low temperature to room temperature and Coulomb diamonds found to decrease in size with increasing gate voltage. The 3D calculation of the energy band structure of the Si nanocrystals and the interactions among the nanocrystals shows the increase of the quantum confinement effect when the dimensionality of the system decreases. At the same time the reduction in the dimensionality causes a decrease in the interaction among nanocrystals in an exponential manner. The carrier transport properties observed experimentally have been well understood in terms of carrier tunneling and Coulomb blockade effects. It is concluded that for the present single-electron transistor, the energy separation of the first excited sublevel and the ground state is rather large so that the Coulomb diamonds observed in the carrier transport characteristics are determined mainly by the Coulomb charging effect. 相似文献
13.
在20 mK的极低温下测量了石墨烯纳米带量子点的电子输运性质,观测到清晰的库仑阻塞菱形块和对应量子点激发态的电导峰.对库仑阻塞近邻电导峰间距和峰值进行了统计分析,发现其统计分布分别满足无规矩阵理论描述的Wigner-Dyson分布和Porter-Thomas分布,说明石墨烯纳米带量子点在低温下出现了量子混沌现象.还讨论了这种长方形量子点中量子混沌的可能成因.
关键词:
石墨烯纳米带
量子点
库仑阻塞
量子混沌 相似文献
14.
Y. Wang J.F. Jiang Q.Y. Cai 《Physica E: Low-dimensional Systems and Nanostructures》2006,31(2):196-199
In the nanometer structure, the island with discrete energy spectrum should be considered. The transport characteristics of an electromechanical quantum dots device at zero temperature are investigated by using Monte Carlo method. An indirect and effective method is applied to estimate the trend of the current curves, by analyzing the average electrostatic forces. The current–voltage curves show the Coulomb blockade phenomena, which is the result of the interaction between discrete levels and the island vibration. 相似文献
15.
We exploit the pumped spin-current and current noise spectra under equilibrium conditions in a single quantum dot connected to two normal leads as an electrical scheme for detection of the electron spin resonance (ESR) and decoherence. We propose spin-resolved quantum rate equations with correlation functions in Laplace space for the analytical derivation of the zero-frequency auto- and cross-shot noise spectra of charge and spin current. Our results show that in the strong Coulomb blockade regime, ESR-induced spin flip generates a finite spin current and quantum partition noises in the absence of net charge transport. Moreover, spin shot noise is closely related to the magnetic Rabi frequency and decoherence and would be a sensitive tool to measure them. 相似文献
16.
D. N. Son N. ArboledaJr W. A. Dino H. Kasai 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(1):27-35
We consider a two-terminal Aharonov-Bohm (AB) interferometer with a quantum dot inserted in one path of the AB ring.
We investigate the transport properties of this system in and out of the Kondo regime. We utilize perturbation theory to
calculate the electron self-energy of the quantum dot with respect to the intradot Coulomb interaction. We show the expression
of the Kondo temperature as a function of the AB phase together with its dependence on other characteristics such as the
linewidth of the ring and the finite Coulomb interaction and the energy levels of the quantum dot. The current oscillates
periodically as a function
of the AB phase. The amplitude of the current oscillation decreases with increasing Coulomb interaction. For a given temperature,
the electron transport through the AB interferometer
can be selected to be in or out of the Kondo regime by changing the magnetic flux threading perpendicular to the AB ring of
the system. 相似文献
17.
Stefan Krompiewski 《Central European Journal of Physics》2011,9(2):369-371
This contribution reports on charge and spin transport through graphene nanoribbons (GrNs) and carbon nanotubes (CNTs). The
paper focuses on the giant magnetoresistance effect in these materials, and their potential usefulness for spintronic applications.
As examples, the following devices are shortly discussed: GrNs in the ballistic transport regime, a CNT-based Schottky-barrier
field effect transistor (CNT SB-FET), as well as CNT quantum dots in the Coulomb blockade limit. 相似文献
18.
A. A. Zhukov Ch. Volk A. Winden H. Hardtdegen Th. Schäpers 《Journal of Experimental and Theoretical Physics》2013,116(1):138-144
We performed measurements at helium temperatures of the electronic transport in the linear regime in an InAs quantum wire in the presence of a charged tip of an atomic force microscope (AFM) at low electron concentration. We show that at certain concentration of electrons, only two closely placed quantum dots, both in the Coulomb blockade regime, govern conductance of the whole wire. Under this condition, two types of peculiarities—wobbling and splitting—arise in the behavior of the lines of the conductance peaks of Coulomb blockade. These peculiarities are measured in quantum-wire-based structures for the first time. We explain both peculiarities as an interplay of the conductance of two quantum dots present in the wire. Detailed modeling of wobbling behavior made in the framework of the orthodox theory of Coulomb blockade demonstrates good agreement with the obtained experimental data. 相似文献
19.
We investigate the transport properties of a (small) quantum dot connected
to Fermi liquid leads with a power-law density of states (DOS).
Such a system, if experimentally realizable, will have interesting physical properties including: (i) non-saturating Coulomb
blockade peak widths; (ii) a non-unitary Kondo peak symmetrically placed between Coulomb blockade peaks; (iii) an absence
of conductance away from particle-hole symmetry at sufficiently low temperatures; and (iv) evidence of a quantum critical
point as a function of dot-lead hopping. These properties are compared and contrasted with one dimensional Luttinger
systems exhibiting a power-law “tunneling-DOS”. 相似文献
20.
A. G. Pogosov M. V. Budantsev A. A. Shevyrin A. E. Plotnikov A. K. Bakarov A. I. Toropov 《JETP Letters》2008,87(3):150-153
The tunneling of electrons that is limited by the Coulomb blockade effect in a single-electron transistor with a quantum dot based on a narrow GaAs/AlGaAs quantum wire suspended over a substrate is investigated. By means of a direct comparison experiment, the tunneling features associated with the separation of the quantum dot from the substrate are revealed. In addition to an increase in the charge energy (Coulomb gap), which reaches 170 K in temperature units, the dependence of this energy on the number of electrons in the quantum dot, which varies from zero to four, is observed. This dependence is explained by a change in the effective size of the dot due to the effect of the depleting gate voltage. Moreover, the additional blockade of tunneling that is different from the Coulomb blockade and is specific for suspended structures is observed. It is shown that this blockade is not associated with the dynamical effect of exciting local phonon modes and can be attributed to the change in the static elastic strains in the quantum wire that accompany the tunneling of an electron to/from the quantum dot. 相似文献