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1.
We analyze inelastic cotunneling through an interacting quantum dot subject to an ambient magnetic field in the weak tunneling regime under a non-adiabatic time-dependent bias-voltage. Our results clearly exhibit photon-assisted satellites and an overall suppression of differential conductance with increasing driving amplitude, which is consistent with experiments. We also predict a zero-anomaly in differential conductance under an appropriate driving frequency. 相似文献
2.
G. Göppert H. Grabert 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(4):687-704
We study the linear conductance of single electron devices showing Coulomb blockade phenomena. Our approach is based on a
formally exact path integral representation describing electron tunneling nonperturbatively. The electromagnetic environment
of the device is treated in terms of the Caldeira-Leggett model. We obtain the linear conductance from the Kubo formula leading
to a formally exact expression which is evaluated in the semiclassical limit. Specifically we consider three models. First,
the influence of an electromagnetic environment of arbitrary impedance on a single tunnel junction is studied focusing on
the limits of large tunneling conductance and high to moderately low temperatures. The predictions are compared with recent
experimental data. Second, the conductance of an array of N tunnel junctions is determined in dependence on the length N of the array and the environmental impedance. Finally, we consider a single electron transistor and compare our results for
large tunneling conductance with experimental findings.
Received 2 February 2000 相似文献
3.
J. Delahaye T. Grenet F. Gay 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,65(1):5-19
We perform electrical field effect measurements at 4 K on insulating granular aluminium thin films. When the samples size
is reduced below ≃100 μm, reproducible and stable conductance fluctuations are seen as a function of the gate voltage. Our results suggest that these
fluctuations reflect the incomplete self-averaging of largely distributed microscopic resistances. We also study the anomalous
field effect (conductance dip) already known to exist in large samples and its slow relaxation in the presence of the conductance
fluctuations. Within our measurements accuracy, the two phenomena appear to be independent of each other, like two additive
contributions to the conductance. We discuss the possible physical meaning of this independence and in particular whether
or not this observation is in favor of an electron glass interpretation of slow conductance anomaly relaxations. 相似文献
4.
In the framework of Green's function theory out of equilibrium, a Landauer-Buttiker (LB) formula for thermal conductance is derived. A simplified model for describing extremely cold dielectric chains is proposed for the first time. Further we apply the present LB formula for studying thermal conductance at low-lying modes, emerging in dielectric atom chains. We find that quantum thermal conductance undergoes an anomalous transition due to new quasiparticle excitations, resulting from nonlinear atom-atom interactions. This theoretical prediction is in excellent agreement with a high-accuracy measurement to thermal conductance quantum. 相似文献
5.
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
6.
Haidong Li 《Physics letters. A》2009,373(5):575-582
The contact conductance between graphene and two quantum wires which serve as the leads to connect graphene and electron reservoirs is theoretically studied. Our investigation indicates that the contact conductance depends sensitively on the graphene-lead coupling configuration. When each quantum wire couples solely to one carbon atom, the contact conductance vanishes at the Dirac point if the two carbon atoms coupling to the two leads belong to the same sublattice of graphene. We find that such a feature arises from the chirality of the Dirac electron in graphene. Such a chirality associated with conductance zero disappears when a quantum wire couples to multiple carbon atoms. The general result irrelevant to the coupling configuration is that the contact conductance decays rapidly with the increase of the distance between the two leads. In addition, in the weak graphene-lead coupling limit, when the distance between the two leads is much larger than the size of the graphene-lead contact areas and the incident electron energy is close to the Dirac point, the contact conductance is proportional to the square of the product of the two graphene-lead contact areas, and inversely proportional to the square of the distance between the two leads. 相似文献
7.
Helical Shell Structures of Ni-A1 Alloy Nanowires and Their Electronic Transport Properties
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Six kinds of Ni-A1 alloy nanowires are optimized by means of simulated annealing. The optimized structures show that the Ni-A1 alloy nanowires are helical shell structures that are wound by three atomic strands, which is very similar to the case with pure metallic nanowires. The densities of states (DOS), transmission function T( E), current-voltage (I - V) curves, and the conductance spectra of these alloy nanowires are also investigated. Our results indicate that the conductance spectra depend on the geometric structure properties and the ingredients of the alloy nanowires. We observe and study the nonlinear contribution to the I-V characteristics that are due to the quantum size effect and the impurity effect. The addition of Ni atoms decreases the conductance of the Ni-A1 alloy nanowire because the doping atom Ni change the electronic band structures and the charge density distribution. The interesting statistical results shed light on the physics of quantum transport at the nano-scale. 相似文献
8.
We present a theoretical study of the conductance in an Aharonov-Bohm interferometer containing two coupled quantum dots. The interdot tunneling divides the interferometer into two coupled subrings, where opposite magnetic fluxes are threaded separately while the net flux is kept zero. Using the Green function technique we derive the expression of the linear conductance. It is found that the Aharonov-Bohm effect still exists, and when the level of each dot is aligned, the exchange of the Fano and Breit-Wigner resonances in the conductance can be achieved by tuning the magnetic flux. When the two levels are mismatched the exchange may not happen. Further, for some specific asymmetric systems where the coupling strengths between the two dots and the leads are not equal, the flux can change the Fano resonance into an antiresonance, which is absent in symmetric systems. 相似文献
9.
Alireza Kargar 《中国物理快报》2009,26(6):73-76
A silicon nanowire (Si-NW) sensor for pH detection is presented. The conductance of the device is analytically obtained, demonstrating that the conductance increases with decreasing oxide thickness. To calculate the electrical conductance of the sensor, the diffusion-drift model and nonlinear Poisson-Boltzmann equation are applied. To improve the conductance and sensitivity, a Si-NW sensor with nanoscaie side gate voltage is offered and its characteristics are theoretically achieved. It is revealed that the conductance and sensor sensitivity can be enhanced by adding appropriate side gate voltages. This effect is compared to a similar fabricated structure in the literature, which has a wire with a rectangular cross section. Finally, the effect of NW length on sensor performance is investigated and an inverse relation between sensor sensitivity and NW length is achieved. 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 Andreev reflection (AR) tunneling through a ferromagnet-quantum dot-superconductor (F-QD-S) system in the presence of an external ac field. The intradot spin-flip scattering in the QD is involved. Using the nonequilibrium Green function and BCS quasiparticle spectrum for superconductor, time-averaged AR conductance is formulated. The competition between the intradot spin-flip scattering and photon-assisted tunneling dominates the resonant behaviors of the time-averaged AR conductance. For weak intradot spin-flip scattering strengths, the AR conductance shows a series of equal interval resonant levels. However, the single-peak at main resonant level develops into a well-resolved double-peak resonance at a strong intradot spin-flip scattering strength. Remarkable, multiple-photon-assisted tunneling that generates photonic sideband peaks with a variable interval has been found. In addition, the AR conductance-bias voltage characteristic shows a transition between the single-peak to double-peak resonance as the ratio of the two tunneling strengths varies. 相似文献
12.
We study the thermopower of a multilevel quantum dot which is coupled with the two leads. From our theoretic results, the thermopower of a multilevel quantum dot shows an oscillatory dependence on the gate voltage, which has been found in a lot of experiment data. The Fano effect of the electronic transport through the multilevel quantum dot is also shown as an obvious asymmetric line shape of the thermopower which come from the interference between the resonant and nonresonant multilevel paths of the conductive electrons. In addition, at the higher temperature, to thermopower, not conductance, it is the multilevel that is much easier to do contribution to the Fano effect. 相似文献
13.
By employing the nonequilibrium Green's function, we investigate the spin-dependent linear Andreev reflection (AR) resonant tunneling through a quantum dot connected to a ferromagnetic lead and a superconducting lead, where the magnetization direction in the ferromagnetic lead can be tuned by one. We focus our attention on the effects of the magnetic fields on the AR conductance. One high conductance peak and one low conductance peak are developed in the linear AR conductance when a stronger magnetic field is considered. The interplay between the spin-flip scattering and the magnetic fields on the AR conductance are also studied. 相似文献
14.
J.?Prior A. M.?Somoza M.?Ortu?o 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,70(4):513-521
We have obtained the universal conductance distribution of
two-dimensional disordered systems in the strongly localized limit.
This distribution is directly related to the Tracy-Widom distribution,
which has recently appeared in many different problems.
We first map a forward scattering paths model into a problem
of directed random polymers previously solved.
We show numerically that the same distribution also applies
to other forward scattering paths models and to the Anderson model.
We show that most of the electric current follows a preferential percolation-type
path. The particular form of the distribution depends on the type of leads
used to measure the conductance.
The application of a moderate magnetic field changes the average conductance
and the size of fluctuations, but not the distribution when properly scaled.
Although the presence of magnetic field changes the universality
class, we show that the conductance distribution in the strongly localized limit
is the same for both classes. 相似文献
15.
We investigate theoretically the electron transport of a two-level quantum dot irradiated under a weak laser field at low temperatures in the rotating wave approximation. Using the method of the Keldysh equation of motion for nonequilibrium Green function, we examine the conductance for the system with photon polarization perpendicular to the tunnelling current direction. It is demonstrated that by analytic analysing and numerical examples, a feature of conductance peak splitting appears, and the dependence of conductance on the incident laser frequency and self-energy are discussed. 相似文献
16.
Fang Cheng 《Solid State Communications》2011,151(7):569-572
We investigate the theoretically combined effect of spin-orbit interactions and Coulomb interaction on the ground state and transport property of a quantum wire oriented along different crystallographic directions in the (110) plane. We find that the electron’s ground state exhibits phase transition among spin density wave, charge density wave, singlet superconductivity and metamagnetism, which can be controlled by changing the crystallographic orientation, the strengths of the spin-orbit interactions and the Coulomb interaction. The ac conductance exhibits a significant anisotropic behavior and a out-of-plane spin polarization which can be tuned by an in-plane electric field. 相似文献
17.
《Superlattices and Microstructures》1997,21(1):137-142
Transport measurements were performed on surface superlattices, formed by a grating gate on a two-dimensional electron gas. We find a suppression of the differential conductance with increasing electric fields, on a scale of a few V cm−1. Even more remarkable is a strong suppression of conductance with increasing temperatureT, where theT-dependence is quadratic. We attribute these observations to electron–electron (e–e) scattering which, in the presence of an external modulated potential, can have a significant influence on the conductance. We also discuss the role of disorder in these systems. 相似文献
18.
We investigate the transport properties of T-shaped junctions composed of armchair graphene nanoribbons of different widths. Three types of junction geometries are considered. The junction conductance strongly depends on the atomic features of the junction geometry. When the shoulders of the junction have zigzag type edges, sharp conductance resonances usually appear in the low energy region around the Dirac point, and a conductance gap emerges. When the shoulders of the junction have armchair type edges, the conductance resonance behavior is weakened significantly, and the metal-metal-metal junction structures show semimetallic behaviors. The contact resistance also changes notably due to the various interface geometries of the junction. 相似文献
19.
L. Qin Y. Guo 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(4):395-403
We present a theoretical study of the spin-dependent conductance
spectra in a FM/semiconductor quantum-dot (QD)/FM system. Both the
Rashba spin-orbit (SO) coupling in the QD and spin-flip scattering
caused by magnetic barrier impurities are taken into account. It
is found that in the single-level QD system with parallel magnetic
moments in the two FM leads, due to the interference between
different tunneling paths through the spin-degenerate level, a dip
or a narrow resonant peak can appear in the conductance spectra,
which depends on the property of the spin-flip scattering. When
the magnetizations of the two FM leads are noncollinear, the
resonant peak can be transformed into a dip. The Rashba SO
coupling manifests itself by a Rashba phase factor, which changes
the phase information of every tunneling path and can greatly
modulate the conductance. When the QD has multiple levels, the
Rashba interlevel spin-flip effect appears, which changes the
topological property of the structure. Its interplay with the
Rashba phase can directly tune the coupling strengths between dot
and leads, and can result in switching from resonance into
antiresonance in the conductance spectra. 相似文献
20.
A simple Kronig-Penney model for 1D mesoscopic systems with δ peak potentials is used to study numerically the influence of spatial disorder on conductance fluctuations and distribution at different regimes. The Lévy laws are used to investigate the statistical properties of the eigenstates. It is found that an Anderson transition occurs even in 1D meaning that the disorder can also provide constructive quantum interferences. The critical disorder Wc for this transition is estimated. In these 1D systems, the metallic phase is well characterized by a Gaussian conductance distribution. Indeed, the results relative to conductance distribution are in good agreement with the previous works in 2D and 3D systems for other models. At this transition, the conductance probability distribution has a system size independent shape with large fluctuations in good agreement with previous works. 相似文献