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1.
Quantum Phase Transition and Ferromagnetic Spin Correlation in Parallel Double Quantum Dots 下载免费PDF全文
We investigate electronic transport through a parallel double quantum dot (DQD) system with strong on-site Coulomb interaction, as well as the interdot tunnelling. By applying numerical renormalization group method, the ground state of the system and the transmission probability at zero temperature are obtained. For a system of quantum dots with degenerate energy levels and small interdot tunnel coupling, the spin correlations between the DQDs is ferromagnetic, and the ground state of the system is a spin-1 triplet state. The linear conductance will reach the unitary limit (2e^2/h) due to the Kondo effect at low temperature. As the interdot tunnel coupling increases, there is a quantum phase transition from ferromagnetic to anti-ferromagnetic spin correlation in DQDs and the linear conductance is strongly suppressed. 相似文献
2.
Kondo and Coulomb Interaction Effects in Spin-Polarized Transport through Double Quantum Dots 总被引:1,自引:0,他引:1 下载免费PDF全文
By means of the slave-boson mean-field approximation, we theoretically investigate the Kondo and Coulomb interaction effects in spin-polarized transport through two coupled quantum dots coupled to two ferromagnetic leads by the Anderson Hamiltonian. The density of states is calculated in the Kondo regime for the effect of the interdot Coulomb repulsion with both parallel and antiparallel lead-polarization alignments. Our results reveal that the interdot Coulomb interaction between quantum dots greatly influence the density of states of the dots. 相似文献
3.
AC field-controlled Andreev tunneling through two serially-coupled quantum dots are investigated theoretically by using the nonequilibrium Green's function method. The photon-assisted Andreev tunneling is studied in detail. It is found that the average current depends distinctly on the interdot coupling. In the weak interdot coupling case, the average current versus the gate voltage exhibit negative peaks on the left-hand side and positive peaks on the right-hand side of the Fermi level. However, in the strong interdot coupling case, the current exhibit both negative and positive peaks on each side of the Fermi level. Furthermore, the system can function as an electron pump capable of transporting electrons through the resonant photon-assisted Andreev tunneling. 相似文献
4.
Shuji Tsubaki Naoki Fujita Fujio Wakaya Yoshihiko Yuba Kenji Gamo 《Superlattices and Microstructures》2000,27(5-6)
Series of double quantum dots each with a size around 400 × 400nm2 have been realized by delineating a 2DEG in modulation-doped AlGaAs/GaAs with 100 nm wide Schottky split gates fabricated by an electron-beam lithography and a lift-off technique. The split gate in the middle of the double dot allows us to control interdot coupling widely. The charging diagram obtained from linear transports in the Coulomb blockade regime shows that the isolated dots merge into a single composite dot with increase of interdot coupling. A clear Coulomb staircase has been observed in the double-dot system at a limited high-bias condition. 相似文献
5.
《Superlattices and Microstructures》1996,20(3):411-417
We report low-temperature conductance measurements in the Coulomb blockade regime on two nominally identical tunnel-coupled quantum dots in parallel defined electrostatically in the two-dimensional electron gas of a GaAs/AlGaAs heterostructure. At low interdot tunnel coupling we find that the conductance measured through one dot is sensitive to the charge state of the neighboring dot. At larger interdot coupling the conductance data reflect the role of quantum charge fluctuations between the dots. As the interdot conductance approaches 2e2/h, the coupled dots behave as a single large dot. 相似文献
6.
H. Pan S.-Q. Duan L.-N. Zhao W.-D. Chu W. Zhang 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(1):71-76
We theoretically study the spin pump effects of the rotating
magnetic field on the spin current through two coupled quantum dots.
Owing to the interdot coupling, two molecular states with different
bands can be formed, resulting asymmetric spin current peaks. The
possibility of manipulating the spin current is explored by tuning
the strength, the frequency, and the direction of the rotating
magnetic field. The number and location of the spin current peaks
can be controlled by making use of various tunings. Furthermore, the
normal 2π period of the spin current with respect to the
magnetic flux can be destroyed by the interdot coupling. 相似文献
7.
We study the capacitance spectra of artificial molecules consisting of two and three coupled quantum dots from an extended Hubbard Hamiltonian model that takes into account quantum confinement, intra- and inter-dot Coulomb interaction and tunneling coupling between all single particle states in nearest neighbor dots. We find that, for weak coupling, the interdot Coulomb interaction dominates the formation of a collective molecular state. We also calculate the effects of correlations on the tunneling probability through the evaluation of the spectral weights, and corroborate the importance of selection rules for understanding experimental conductance spectra. 相似文献
8.
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
9.
A system consisting of two independently contacted quantum dots with a strong electrostatic interaction shows an interdot Coulomb blockade when the dots are weakly tunnel coupled to their leads. How the blockade can be overcome by correlated tunneling when tunnel coupling to the leads increases is studied experimentally. The experimental results are compared with numerical renormalization group calculations using predefined (measured) parameters. Combining our experimental and theoretical results we identify transport through Kondo correlations due to the electrostatic interaction between the two dots. 相似文献
10.
11.
We study the thermoelectric transport through a double-quantum-dot system with spin-dependent interdot coupling and ferromagnetic electrodes by means of the non-equilibrium Green’s function in the linear response regime.It is found that the thermoelectric coefficients are strongly dependent on the splitting of the interdot coupling,the relative magnetic configurations,and the spin polarization of leads.In particular,the thermoelectric efficiency can reach a considerable value in the parallel configuration when the effective interdot coupling and the tunnel coupling between the quantum dots and the leads for the spin-down electrons are small.Moreover,the thermoelectric efficiency increases with the intradot Coulomb interaction increasing and can reach very high values at appropriate temperatures.In the presence of the magnetic field,the spin accumulation in the leads strongly suppresses the thermoelectric efficiency,and a pure spin thermopower can be obtained. 相似文献
12.
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
13.
Phonon-Assisted Resonant Tunnelling through a Triple-Quantum-Dot: a Phonon-Signal Detector 下载免费PDF全文
We study the effect of electron-phonon interaction on current and zero-frequency shot noise in resonant tunnelling through a series triple-quantum-dot coupling to a local phonon mode by means of a nonperturbative mapping technique along with the Green function formulation. By fixing the energy difference between the first two quantum dots to be equal to phonon frequency and sweeping the level of the third quantum dot, we find a largely enhanced current spectrum due to phonon effect, and in particular we predict current peaks corresponding to phonon-absorption and phonon-emission assisted resonant tunnelling processes, which show that this system can be acted as a sensitive phonon-signal detector or as a cascade phonon generator. 相似文献
14.
Topological quantum-phase coherence in full counting statistics of transport electrons with two-body interaction 下载免费PDF全文
The full counting statistics of electron transport through two parallel quantum dots with antiparallel magnetic fluxes is investigated as a probe to detect the topological quantum-phase coherence (TQPC), which results in the characteristic oscillation of the zero-frequency cumulants including the shot noise and skewness. We show explicitly the phase transition of cumulant spectrum-patterns induced by the topology change of electron path-loops while the pattern period, which depends only on the topology (or Chern number), is robust against the variation of Coulomb interaction and interdot coupling strengths. Most importantly we report for the first time on a new type of TQPC, which is generated by the two- particle interaction and does not exist in the single-particle wave function interference. Moreover, the accurately quantized peaks of Fano-factor spectrum, which characterize the super- and sub-Poissonian shot noises, are of fundamental importance in technical applications similar to the superconducting quantum interference device. 相似文献
15.
McClure DT Dicarlo L Zhang Y Engel HA Marcus CM Hanson MP Gossard AC 《Physical review letters》2007,98(5):056801
We report measurements of the cross correlation between temporal current fluctuations in two capacitively coupled quantum dots in the Coulomb blockade regime. The sign of the cross-spectral density is found to be tunable by gate voltage and source-drain bias. We find good agreement with the data by including an interdot Coulomb interaction in a sequential-tunneling model. 相似文献
16.
Numerical results for transport properties of two coupled double-level quantum dots (QDs) strongly suggest that under appropriate conditions the dots develop a novel ferromagnetic (FM) correlation at quarter filling (one electron per dot). In the strong coupling regime (Coulomb repulsion larger than electron hopping) and with interdot tunneling larger than tunneling to the leads, an S=1 Kondo resonance develops in the density of states, leading to a peak in the conductance. A qualitative "phase diagram," incorporating the new FM phase, is presented. In addition, the necessary conditions for the FM regime are less restrictive than naively believed, leading to its possible experimental observation in real QDs. 相似文献
17.
C. Livermore C.H. Crouch R.M. Westervelt K.L. Campman A.C. Gossard 《Superlattices and Microstructures》1996,20(4):633-639
We report a measurement of linear conductance through a series double dot as a function of the total double dot charge and the charge difference for interdot tunnel conductances between zero and one mode. The dots are defined by ten independently tunable electrostatic gates on the surface of a GaAs/AlGaAs heterostructure to allow separate adjustment of dot charge and interdot conductance. For weak interdot tunneling the measured double dot conductance agrees with a transport model in which each dot is individually governed by Coulomb blockade theory. As interdot tunnel conductance increases toward one mode, the measured conductance peak positions and shapes indicate both a relaxation of the charge quantization condition for individual dots and quantum mechanical charge sharing between dots. The results are in quantitative agreement with many body charge fluctuation theory. 相似文献
18.
V. Moldoveanu I. V. Dinu B. Tanatar 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(2):231-238
We study the coherent transport in a one-dimensional lead with two side-coupled quantum dots using the Keldysh’s Green function
formalism.The effect of the interdot Coulomb interaction is taken into account by computing the firstand second order contributions
to the self-energy.We show that the Fano interference due to the resonance of one dotis strongly affected by the fixed parameters
that characterize the second dot. If the second dot is tuned close to resonance an additionalpeak develops between the peak
and dip of the Fano line shape of the current. In contrast, when the second dotis off-resonance and its occupation number
is close to unity the interdot Coulomb interaction merely shifts the Fano line and no other maxima appear.The system we consider
is more general than the single-dot interferometer studied experimentally by Kobayashi et al. [Phys. Rev. B 70, 035319 (2004)] and may be used for controlling quantum interference and studying decoherence effects in mesoscopic transport. 相似文献
19.
We report a new transport feature in a GaAs lateral double quantum dot that emerges for magnetic-field sweeps and shows hysteresis due to dynamic nuclear spin polarization (DNP). This DNP signal appears in the Coulomb blockade regime by virtue of the finite interdot tunnel coupling and originates from the crossing between ground levels of the spin triplet and singlet extensively used for nuclear spin manipulations in pulsed-gate experiments. The magnetic-field dependence of the current level is suggestive of unbalanced DNP between the two dots, which opens up the possibility of controlling electron and nuclear spin states via dc transport. 相似文献
20.
We report for the first time on rich and tunable transport phenomena in closed-packed arrays of PbSe colloidal nanocrystals (NCs) in the form of thin films. As the interdot coupling is increased, the system evolves from an insulating regime dominated by Coulomb blockade to a semiconducting regime, where hopping conduction is the dominant transport mechanism. The observed phenomena can be interpreted using the framework established mainly in the context of transport measurements in metallic quantum dots and disordered semiconductors. 相似文献