Intralead Interaction Research Articles

Photon-assisted destructive interference through a parallel-coupled double quantum dots

In this paper, we establish a model to realize the photon-assisted destructive interference phenomena, the model consisting of parallel-coupled double quantum dots and Luttinger liquid leads. By applying the canonical transformation and the nonequilibrium Green’s function technique, the general time-dependent current formula is developed. The joint effects of the intralead Coulomb interaction and an external ac field on the quantum interference are investigated. For weak intralead interactions, besides the usual photon-assisted tunneling resonance, there are two types of photon-assisted tunneling destructive interference: one is related to interdot coupling and the other to intralead interactions. For moderately strong intralead interaction, the photon-assisted sidebands are suppressed and the differential conductance scales as a power law in bias voltage. In particular, we show the multiphoton absorption and emission up to four photons in an electron tunneling process. We believe that the photo-assisted destructive interference results obtained in this paper are instructive for future experiments.

Thermoelectric enhancement of a parallel double quantum dot system connecting to Luttinger liquid leads

In this work, we study the thermoelectric properties of the parallel-coupled double quantum dot connected to Luttinger liquid (LL) leads. By applying nonequilibrium Green's function methods, the expressions of the electron current, heat currents, and transport coefficients are derived. We mainly focus on the effect of intralead Coulomb interaction and the spatial asymmetry of the system. Various causes for the enhancement of the thermoelectric efficiency are investigated. We find that Coulomb interactions in the LL not only enhance quantum interference but also considerably enhance thermoelectric effects. For moderately strong intralead interaction, the figure of merit can be considerably high and reach over 60 in the case of weakly coupled to LL leads and detuning of the energy levels, while in the case of strongly coupled to LL leads and the two aligned levels, the figure of merit approaches 8. The quantum interference induced by the Coulomb interaction yields a very high thermoelectric efficiency when the intralead interaction is very strong. These results may provide a design rule for the development of high-efficiency thermoelectric devices and facilitate optimization of device performance.

Destructive interference and Fano antiresonance in T-shaped double quantum dots coupled to Luttinger liquid leads

We investigate the interplay of quantum interference effects and the electronic correlation on the transport through T-shaped spinless double quantum dots coupled to Luttinger liquid leads by using the nonequilibrium Green's function method. We find that the weak intralead Coulomb interaction leads to a zero-bias antiresonance dip in the differential conductance for small interdot tunneling coupling, which is distinct destructive interference characteristic. In particular, an intriguing Fano antiresonance profile for asymmetrically coupling to the Luttinger liquid leads is exhibited, consistent with the experiment findings but different physics screening origin. The strong intralead Coulomb interaction or large interdot coupling tunneling quenches the quantum interference effects, resulting in the disappearance of Fano antiresonance. The scaling behavior of differential conductance on temperature is presented for different intralead interactions. The relationship between destructive interference and two-channel Kondo effect is given. Our results provide a way of adjusting in and out of antiresonance to achieve quantum interference transistors and of switching by tuning the gate voltage controlling the interdot tunneling. • The interplay of interference and intralead Coulomb interaction on transport of T-shaped quantum dots is studied. • Weak intralead interaction leads to zero-bias dip in differential conductance for small interdot tunneling. • New physical mechanism is presented to explain for the antiresonance dip and Fano effect. • Scaling behavior of differential conductance on temperature is presented for different intralead interactions.

Destructive quantum interference phenomenon in series-coupled double quantum dots

In this work, the transport of a model consists of two quantum dots in series and Luttinger liquid leads is researched. The motivation is to reveal the interference characteristics. We comprehensively study the influence of the intralead Coulomb interaction, temperature, detuning levels of the dots, and inter-dot tunneling on transport. By applying the nonequilibrium Green’s function method, a general current formula is derived. The existence of the intralead interaction leads to the appearance of a destructive quantum interference anti-resonant dip at the zero-bias voltage of the differential conductance. The gate-tunable conductance peaks or dips depending on the constructive or destructive interference are demonstrated when the energy levels of the two dots are aligned. While when the energy levels are misaligned, the intriguing Fano anti-resonant interference phenomenon occurs. These results offer a new approach for designing quantum coherent devices.

Antiresonance and negative differential conductance in parallel-coupled vibrating molecular dots coupled to Luttinger liquid leads

We theoretically study the interplays of electron–phonon interaction, inter-dot coupling tunneling and intralead electron interaction on transport properties of parallel-coupled double quantum dots connected to Luttinger liquid leads. The nonequilibrium Green’s function method is used. Numerical results show several intriguing physic phenomena. In the weak intralead electron interaction, there is a zero-bias antiresonance dip followed by phonon-assisted satellite peaks for strong electron–phonon interaction and inter-dot tunneling. With decreasing inter-dot tunneling, there is an evolution from satellite peaks to dips, which signifies the phase transition from phonon-assisted single-channel to two-channel Kondo physics. When the dot-lead coupling is asymmetric, in the case of moderately strong intralead interaction, strong electron–phonon coupling and weak inter-dot tunneling, there may appear the pronounced negative differential conductance and Fano resonance, while there does not when the coupling is symmetric. These results provide a convenient way to probe destructive quantum interference and extract information of the electron–phonon interaction strength, which is crucial for designing molecular switches and thermoelectric devices. • We study the transport properties of parallel coupled double quantum dots connected to Luttinger liquid leads. • We have theoretically studied a series of problems such as electron phonon interaction . • The method used is nonequilibrium Green’s function. • The phenomena of resonance and peak of satellite are found. • Negative differential conductance and Fano resonance are found.

The interplay of intralead and dot-lead Coulomb electrons on shot noise in the Kondo regime

The interplay of intralead and dot-lead Coulomb interactions on shot noise of a quantum dot coupled to Luttinger-liquid leads is systematically investigated in the Kondo regime. By equation of motion and canonical transformation methods, a general shot noise formula with transmission coefficient is derived, the factors of the above two types of interactions and on-dot Coulomb interaction being taken into account. Then we study in detail the shot noise and Fano factor as a function of bias voltage. Numerical results show for weak and moderately strong intralead Coulomb interactions, the dot-lead interaction not only helps to improve the shot noise, but also narrows the zero-bias Kondo dip. A series of polaron peaks appear in the differential shot noise when the renormalized parameter Y<1, a combination effect of the intralead and dot-lead Coulomb interactions. For Y>1, a novel type of excitonic dips appear only in the case of moderately strong intralead interaction. In the very strong intralead interaction limit, all features of excitonic peaks or dips disappear, and shot noise shows power-law dependence on the voltage with the renormalized exponent Y. The Fano factor is always sub-Poisson noise no matter whether Y is greater or less than 1.

Effect of magnetic fields on the shot noise of a quantum dot with Luttinger leads

We study the shot noise of a strongly correlated quantum dot system in the Kondo regime, concentrating on the joint effect of a magnetic field B and intralead Coulomb interaction. A shot noise formula is derived. The shot noise is suppressed by the magnetic field when the intralead interaction is weak, but improved by the field when the interaction is strong. The differential shot noise has a peak or valley at eV = ±gμBB for weak or moderately strong intralead interaction. As the interactions increase, these singular behaviours gradually disappear. In the strong interaction limit, the shot noise's curve has a power-law dependence on the voltage. The intralead Coulomb interaction also modulates the Fano line shape of shot noise. The Fano factor is enhanced by the magnetic field and dot-lead asymmetric coupling and is always sub-Poissonian noise.

Fano resonance and zero-bias anomaly in parallel double quantum dots coupled to Luttinger liquid leads

We study the nonequilibrium transport through a parallel-coupled double quantum dot coupled to Luttinger liquid leads using the nonequilibrium Green's function method. A current formula is derived, where the inter-dot tunneling, the intralead interaction, and asymmetric dot-lead coupling are taken into account. The interplay of these interactions on the differential conductance is investigated. The differential conductance of the double-dot system exhibits the coexistence of zero-bias dip and Fano resonance for asymmetric coupling. The zero-bias dip of differential conductance scales onto a single universal curve for different temperature with the same scaling exponent as a system of Kondo dot. As temperature increases, the zero-bias minimum is gradually lifted.

The photon-assisted shot noise of a strongly correlated quantum dot coupled to the Luttinger liquid leads

Abstract The joint effects of an ac field and intralead interaction on shot noise of a Kondo quantum dot coupled to Luttinger liquid leads is investigated. A general photon-assisted zero-frequency shot noise formula is derived by use of the extended equation of motion of the nonequilibrium Green function. The photon-assisted shot noise demonstrates antiresonant-like behavior. The differential shot noise versus bias voltage exhibits steps the widths of which are just the ac frequency. With the increase of the intralead interaction, the antiresonances and step-structure are gradually smoothed and eventually disappear in the limit of the strong intralead interaction. In the limit, the shot noise scales as a power law in bias voltage, a signature of strong intralead interactions. The measurements of the photon-assisted zero-frequency shot noise can provide valuable information of the intralead interaction.

Magnetic Field Effects on Transport Through a Strongly Correlated Dot Coupled to Luttinger Leads

The effects of the magnetic field and intralead electron interaction on the transport have been investigated in the Kondo regime by means of the nonequilibrium Green functions with the equation of motion method. The numerical results show that for weak intralead interaction, in addition to the Kondo dip zero bias, the differential conductance shows two peaks separated from the origin by the Zeeman energy. When the intralead interaction becomes moderately strong, the Zeeman splitting peaks turn into Zeeman splitting dips. With the further increase in the intralead interaction, all the dips disappear and the differential conductance is characterized by a power law scaling in bias voltage in the limit of the strong intralead interaction. Our results are valuable for analyzing transport in carbon nanotubes.

Effects of Luttinger leads on the AC conductance of a quantum dot

We investigate the joint effects of the intralead electron interaction and an external alternating gate voltage on the transport of a quantum dot coupled to two Luttinger liquid leads in the Kondo regime. We find the transferring between two Kondo physics mechanics by investigation of differential conductance. For very weak intralead interaction, the satellite and main Kondo resonant peaks appear in the differential conductance. For moderately strong intralead interaction, all the peaks disappear and evolve into dips, which signifies that a photon-assisted single-channel Kondo (1CK) physics turns into two-channel Kondo (2CK) physics. The 1CK and 2CK mechanisms can coexist within a region of the intralead interaction parameter. The 1CK physics transits to the 2CK one gradually, not suddenly. In the limit of strong interaction, all dips disappear. When the bias voltage is small, there is no photon exchange between the quantum dot and alternative field, and the differential conductance scales as a power law both in bias voltage and in temperature. As the field becomes stronger, the quantum dot will emit and absorb photons.

Magnetic field effects on the DOS of a Kondo quantum dot coupled to LL leads

Abstract We investigate the joint effects of a magnetic field and electron-electron interaction on the tunneling density of states (DOS) of a quantum dot coupled to the Luttinger liquid leads in the Kondo regime. We find that for intralead electron interaction, the DOS develops two peaks deviated from the origin by the Zeeman energy. With the increase of the intralead interaction, a phase transition occurs. For moderately strong interaction, the Zeeman splitting peaks develop into two dips. The splitting of the Kondo peak and dip is not symmetric with respect to up and down spins. In the limit of strong interaction the Zeeman splitting behavior disappears and there appears a power-law scaling behavior.

AC-field-induced quantum phase transitions in density of states

We investigate the joint effects of the intralead electron interaction and an external alternating gate voltage on the time-averaged local density of states (DOSs) of a quantum dot coupled to two Luttinger-liquid leads in the Kondo regime. A rich dependence of the DOSs on the driving amplitude and intralead interaction is demonstrated. We show that the feature is quite different for different interaction strengths in the presence of the ac field. It is shown that the photon-assisted transport processes cause an additional splitting of the Kondo peak or dip, which exhibits photon-assisted single-channel (1CK) or two-channel Kondo (2CK) physics behavior. The phase transition between photon-assisted 1CK and 2CK physics occurs when the interaction strength is moderately strong. The inelastic channels associated with photon-assisted electron tunneling can dominate electron transport for weak interaction when the ac amplitude is greater than the frequency by one order of magnitude. In the limit of strong interaction the DOSs scale as a power-law behavior which is strongly affected by the ac field.

The shot noise of a strongly correlated quantum dot coupled to the Luttinger liquid leads

We study the shot noise of a strongly correlated quantum dot weakly coupled to Luttinger liquid leads in the Kondo regime by means of the extended equation of motion method. A general zero-frequency shot noise formula with good convergence is derived. The shot noise exhibits a non-monotonic dependence on voltage for weak intralead interaction. There is a peak around the Kondo temperature at low voltage when the interaction is very weak, and its height decreases rapidly with the intralead interaction increasing. When the interaction is moderately strong the peak disappears and the shot noise scales as a power law in bias voltage, indicating that the intralead electron interaction suppresses the shot noise. It is possible that the measurements of the shot noise spectrum can extract the information of the intralead interaction.

Phonon-assisted zero bias anomaly in a single-molecule quantum dot coupled to the Luttinger liquid leads

Abstract The joint effects of the electron–phonon interaction and electron–electron interaction in the Luttinger liquid leads on nonequilibrium transport through a single-molecule transistor in the Kondo regime are investigated by using the improved canonical transformation scheme and equation of motion approach. For weak intralead electron interaction, a pronounced dip around zero bias, accompanied by a series of discrete single-electron tunneling peaks is observed in the differential conductance. With the increase of the intralead interaction, the phonon-assisted peaks turn into dips, which demonstrates a phonon-assisted two-channel Kondo physics. For a certain region of interaction strength the inelastic electron tunneling can dominate electron transport. Our results well explain the experiments of zero bias anomaly.

The zero-bias anomaly conductance of a strongly correlated dot coupled to Luttinger liquid leads

We study the low-temperature differential conductance and density of states of a quantum dot coupled to Luttinger liquid (LL) leads in the Kondo regime using the nonequilibrium Green's function approach. Around zero bias, the Kondo peak decays and finally vanishes with the increasing of the intralead interaction, and then a dip develops for moderate interaction. The appearance of the dip manifests the zero-bias anomaly (ZBA). It illustrates that the combination of the Coulomb interaction on the dot and LL electrodes leads to a transition from one-channel Kondo physics to two-channel Kondo physics. The ZBA is strongly temperature-dependent. Our model explains experiments of the ZBA well.

Density of states of a strongly correlated quantum dot coupled to Luttinger liquid leads

Abstract We theoretically investigate the density of states (DOS) of a quantum dot weakly coupled to Luttinger liquid (LL) leads in the Kondo regime by use of the equation-of-motion technique of the nonequilibrium Green functions. At zero temperature, the Kondo peak in DOS is suppressed by the intralead interaction. When the LL interaction parameter K is about 0.77, a moderately strong interaction, the Kondo peak disappears and then a dip develops, a signature of the intermediate two-channel Kondo (2CK) physics. This shows that the condition for the 2CK to occur ever addressed is not necessary. Applying a finite voltage bias splits the dip in the DOS. Each split dip is located at the chemical potential of a LL lead. This again appears the stabilized 2CK physics for moderately strong interaction K 1 .

Transport Through a Quantum Dot with Coulombic Dot-Lead Coupling

We investigate joint effects of the Coulombic dot-lead interaction and intralead electron interaction on current through a quantum dot weakly coupled to Luttinger liquid leads. A general formula of current is derived by applying the canonical transformation and the nonequilibrium Green function technique. At low temperature and weak intralead interaction, the current exhibits staircase behavior with the Coulombic dot-lead interaction. When temperature or the intralead interaction increases, the steps are rounded. For a weak or moderately strong interaction the differential conductance as a function of bias voltage demonstrates resonant behavior. The dot-lead exchange scattering processes can dominate electron transport for a certain region of interaction strength. This result implies the possibility of controlling the differential conductance of the transistor by tuning the Coulombic dot-lead coupling.

Enhanced Fano factor in a molecular transistor coupled to phonons and Luttinger-liquid leads

We study the effects of electron-phonon interactions on the transport properties of a molecular quantum dot coupled to two Luttinger-liquid leads. In particular, we investigate the effects on the steady state current and DC noise characteristics. We consider both equilibrated and unequilibrated on-dot phonons. The density matrix formalism is applied in the high temperature approximation and the resulting semi-classical rate equation is numerically solved for various strengths of electron-electron interactions in the leads and electron-phonon coupling. The current and the noise are in general smeared out and suppressed due to intralead electron interaction. On the other hand, the Fano factor, which measures the noise normalized by the current, is more enhanced as the intralead interaction becomes stronger. As the electron-phonon coupling becomes greater than order one, the Fano factor exhibits super-Poissonian behaviour.