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1.
The cotunneling current through a two-level quantum dot weakly coupled to ferromagnetic leads is studied in the Coulomb blockade regime. The cotunneling current is calculated analytically under simple but realistic assumptions as follows: (i)?the quantum dot is described by the universal Hamiltonian, (ii)?it is doubly occupied, and (iii)?it displays a fast spin relaxation. We find that the dependence of the differential conductance on the bias voltage is significantly affected by the exchange interaction on the quantum dot. In particular, for antiparallel magnetic configurations in the leads, the exchange interaction results in the appearance of interference-type contributions from the inelastic processes to the cotunneling current. Such dependence of the cotunneling current on the tunneling amplitude phases should also occur in multi-level quantum dots weakly coupled to ferromagnetic leads near the mesoscopic Stoner instabilities. 相似文献
2.
We investigate the signature of a complete Coulomb interaction in transport properties of double-orbital nanoscale devices. We analyze the specific effects of Hund exchange and pair hopping terms, calculating in particular stability diagrams. It turns out that a crude model, with partial Coulomb interaction, may lead to a misinterpretation of experiments. In addition, it is shown that spectral weight transfers induced by gate and bias voltages strongly influence charge current. The low temperature regime is also investigated, displaying inelastic cotunneling associated with the exchange term, as well as Kondo conductance enhancement. 相似文献
3.
We derive general expressions for the current and the shot noise, taking into account non-Markovian memory effects. In generalization of previous approaches, our theory is valid for an arbitrary Coulomb interaction and coupling strength and is applicable to quantum dots and more complex systems such as molecules. A fully consistent diagrammatic expansion up to second order in the coupling strength, taking into account cotunneling processes, allows for a study of transport in an intermediate coupling strength regime relevant to many current experiments. We discuss a single-level quantum dot as a first example, focusing on the Coulomb-blockade regime where the cotunneling processes dominate. We find super-Poissonian shot noise due to inelastic spin-flip cotunneling processes at an energy scale different from the one expected from first-order calculations. 相似文献
4.
We report the characterization of electronic shell filling in metallic single-walled carbon nanotubes by low-temperature transport measurements. Nanotube quantum dots with average conductance approximately (1-2)e(2)/h exhibit a distinct four-electron periodicity for electron addition as well as signatures of Kondo and inelastic cotunneling. The Hartree-Fock parameters that govern the electronic structure of metallic nanotubes are determined from the analysis of transport data using a shell-filling model that incorporates the nanotube band structure and Coulomb and exchange interactions. 相似文献
5.
Spin-dependent electronic transport through a quantum
dot has been analyzed theoretically in the cotunneling regime by
means of the second-order perturbation theory. The system is
described by the impurity Anderson Hamiltonian with arbitrary
Coulomb correlation parameter U. It is assumed that the dot
level is intrinsically spin-split due to an effective molecular
field exerted by a magnetic substrate. The dot is coupled to two
ferromagnetic leads whose magnetic moments are noncollinear. The
angular dependence of electric current, tunnel magnetoresistance,
and differential conductance are presented and discussed. The
evolution of a cotunneling gap with the angle between magnetic
moments and with the splitting of the dot level is also
demonstrated. 相似文献
6.
We show that electron transport through a long multichannel wire, connected to leads by tunnel junctions, at low temperatures
T and voltages V is dominated by inelastic cotunneling. This mechanism results in experimentally observed power-law dependence of conductance
on T and V, in the diffusive regime where usual Coulomb anomaly theory leads to exponentially low conductance. The power-law exponent
α* is proportional to the distance between contacts L.
The article is published in the original. 相似文献
7.
《Superlattices and Microstructures》1998,23(1):161-172
Recent measurements of mesoscopic tunneling and cotunneling fluctuations in Coulomb blockaded ballistic quantum dots are presented. The statistics and parametric fluctuations (as a function of magnetic field) of Coulomb blockade peak heights are found to be consistent with random-matrix-theory predictions. Mesoscopic fluctuations of elastic cotunneling, measured in the valleys between blockade peaks, are also presented along with a semiclassical explanation of the observed enhancement of the magnetic field scale of cotunneling fluctuations compared to resonant tunneling fluctuations. 相似文献
8.
G. Z. Cohen V. Fleurov K. Kikoin 《The European Physical Journal B - Condensed Matter and Complex Systems》2012,85(2):70
The problem of electron transport by means of a dumbbell shaped shuttle in strong Coulomb
blockade regime is solved. The electrons may be shuttled only in the cotunneling regime
during the time spans when both shoulders of the shuttle approach the metallic banks. The
conventional Anderson-like tunneling model is generalized for this case and the tunneling
conductance is calculated in the adiabatic regime of slow motion of the shuttle.
Non-adiabatic corrections are briefly discussed 相似文献
9.
Tran TB Beloborodov IS Lin XM Bigioni TP Vinokur VM Jaeger HM 《Physical review letters》2005,95(7):076806
We investigate the effects of inelastic cotunneling on the electronic transport properties of gold nanoparticle multilayers and thick films at low applied bias, inside the Coulomb-blockade regime. We find that the zero-bias conductance, g(0)(T), in all systems exhibits Efros-Shklovskii-type variable range hopping transport. The resulting typical hopping distance, corresponding to the number of tunnel junctions participating in cotunneling events, is shown to be directly related to the power-law exponent in the measured current-voltage characteristics. We discuss the implications of these findings in light of models on cotunneling and hopping transport in mesoscopic, granular conductors. 相似文献
10.
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
11.
We investigate correlated electronic transport in single-walled carbon nanotubes with two intramolecular tunneling barriers. We suggest that below a characteristic temperature the long-range nature of the Coulomb interaction becomes crucial to determine the temperature dependence of the maximum G(max) of the conductance peak. Correlated sequential tunneling dominates transport yielding the power law G(max) proportional, variant T(alpha(end-end)-1), typical for tunneling between the ends of two Luttinger liquids. Our predictions are in agreement with recent measurements. 相似文献
12.
We explore inelastic cotunneling through a strongly Coulomb-blockaded
quantum dot attached to two ferromagnetic leads in the weak coupling limit using a generic quantum Langevin equation approach. We first develop a Bloch-type equation microscopically to describe the
cotunneling-induced spin relaxation dynamics, and then develop explicit
analytical expressions for the local magnetization, current, and its
fluctuations. On this basis, we predict a novel zero-bias anomaly of
the differential conductance in the absence of a magnetic field for the
anti-parallel configuration, and asymmetric peak splitting in a magnetic field. Also, for the same system with large polarization, we find a negative
zero-frequency differential shot noise in the low positive bias-voltage
region. All these effects are ascribed to rapid spin-reversal due to
underlying spin-flip cotunneling. 相似文献
13.
We study the nonlinear cotunneling current through a spinful quantum dot contacted by two superconducting leads. Applying a general nonequilibrium Green function formalism to an effective Kondo model, we study the rich variation in the IV characteristics with varying asymmetry in the tunnel coupling to source and drain electrodes. The current is found to be carried, respectively, by multiple Andreev reflections in the symmetric limit, and by spin-induced Yu-Shiba-Rusinov bound states in the strongly asymmetric limit. The interplay between these two mechanisms leads to qualitatively different IV characteristics in the crossover regime of intermediate symmetry, consistent with recent experimental observations of negative differential conductance and repositioned conductance peaks in subgap cotunneling spectroscopy. 相似文献
14.
We report observation of Coulomb blockade lifting in GaAs vertical double quantum dot caused by cotunneling processes. One
characteristic feature of investigated sample is relatively low potential barriers between dots and reservoirs, which makes
cotunneling processes favorable. The measurement of current through the sample under variable bias and gate voltages was carried
out at temperature of dilution refrigerator 10 mK. Several distinct features, specific to double dot, were observed and appropriate
explanation for them was given. 相似文献
15.
Schleser R Ihn T Ruh E Ensslin K Tews M Pfannkuche D Driscoll DC Gossard AC 《Physical review letters》2005,94(20):206805
We present finite-bias transport measurements on a few-electron quantum dot. In the Coulomb-blockade regime, strong signatures of inelastic cotunneling occur which can directly be assigned to excited states observed in the nonblockaded regime. In addition, we observe structures related to sequential tunneling through the dot, occurring after it has been excited by an inelastic cotunneling process. We explain our findings using transport calculations within the real-time Green's function approach, including diagrams up to fourth order in the tunneling matrix elements. 相似文献
16.
We theoretically study thermoelectric properties of a coupled double quantum dot (DQD) system coupled to normal leads using two impurity Anderson model with intra- as well as interdot Coulomb interactions. A generic formulation, which was earlier developed to study electronic properties (zero bias maximum of differential conductance and interesting partial swapping in Fano phenomena) of DQD system within Coulomb blockade regime for a non-magnetic case, is extended to investigate thermoelectric properties i.e. electrical conductance, thermoelectric power and thermal conductance of the same system, as a function of temperature by varying interdot Coulomb interaction and interdot tunneling. Interdot Coulomb interaction is found to trigger some novel features like crossover in thermoelectric power with temperature in all the configurations (series, parallel and T-shape) and a small peak in thermal conductance toward low temperatures, T≈Γ/10, in series and T-shape configurations, which is found to be missing in case of symmetric parallel configuration. The origin of these novel features is attributed to the interplay of renormalization of energy levels caused by the interdot Coulomb interaction which is interpreted in terms of local density of states and the asymmetry effects related to dot-lead couplings/interference effects. 相似文献
17.
We compute the zero bias conductance of electrons through a single ballistic channel weakly coupled to a side quantum dot with Coulomb interaction. In contrast to the standard setup which is designed to measure the transport through the dot, the channel conductance reveals Coulomb blockade dips rather then peaks due to the Fano-like backscattering. At zero temperature the Kondo effect leads to the formation of broad valleys of small conductance corresponding to an odd number of electrons on the dot. By applying a magnetic field in the dot region we find two dips corresponding to a total suppression in the conductance of spins up and down separated by an energy of the order of the Coulomb interaction. This provides a possibility of a perfect spin filter.Received: 6 November 2003, Published online: 2 April 2004PACS:
72.15.Qm Scattering mechanisms and Kondo effect - 73.23.Ad Ballistic transport - 72.25.-b Spin polarized transport 相似文献
18.
We introduce a thermal conductance by using the fluctuation-dissipation theorem to analyze the heat transfer between two nanoparticles separated by a submicron distance. Using either a molecular dynamics technique or a model based on the Coulomb interaction between fluctuating dipoles, we derive the thermal conductance. Both models agree for distances larger than a few diameters. For separation distances smaller than the particle diameter, we find a transition regime characterized by a thermal conductance larger than the contact conductance. 相似文献
19.
Onac E Balestro F Trauzettel B Lodewijk CF Kouwenhoven LP 《Physical review letters》2006,96(2):026803
An on-chip detection scheme for high frequency signals is used to detect noise generated by a quantum dot formed in a single wall carbon nanotube. The noise detection is based on photon assisted tunneling in a superconductor-insulator-superconductor junction. Measurements of shot noise over a full Coulomb diamond are reported with excited states and inelastic cotunneling clearly resolved. Super-Poissonian noise is detected in the case of inelastic cotunneling. 相似文献