Double-dot Aharonov-Bohm Interferometer Research Articles

Phonon-Assisted Transport through Double-Dot Aharonov-Bohm Interferometer in Kondo Regime

The effect of electron-phonon coupling on transport through a pair of strongly correlated quantum dots embedded in the Aharonov-Bohm ring is considered in the mean field slave boson Kotliar-Ruckenstein approach. It is shown that coupling with phonons opens transport gap in the region of double occupancy. Low-bias conductance and thermopower provide information on electron-phonon coupling strength.

Nonreciprocity and thermoelectric performance in a double-dot Aharonov–Bohm interferometer

We investigate nonreciprocity and thermoelectric performance beyond the linear response regime in a double-dot Aharonov–Bohm interferometer that is connected to three reservoirs. In the presence of a magnetic flux (broken time-reversal symmetry), we find that the difference between the forward and reverse particle currents can reach the order of 10% under certain conditions. We also show that when the temperature gradient is reversed, the thermoelectric efficiency and output power both change; however, the discrepancies are minimal. Indeed, although breaking time-reversal symmetry can enhance the maximum efficiency, it reduces the maximum power in the present model. These results could be useful for the design of nanoscale thermoelectric devices.

Manipulating quantum coherence of charge states in interacting double-dot Aharonov–Bohm interferometers

We investigate the dynamics of charge-state coherence in a degenerate double-dot Aharonov–Bohm interferometer with finite inter-dot Coulomb interactions. The quantum coherence of the charge states is found to be sensitive to the transport setup configurations, involving both the single-electron impurity channels and the Coulomb-assisted ones. We numerically demonstrate the emergence of a complete coherence between the two charge states, with the relative phase being continuously controllable through the magnetic flux. Interestingly, a fully coherent charge qubit arises at the double-dots electron pair tunneling resonance condition, where the chemical potential of one electrode is tuned at the center between a single-electron impurity channel and the related Coulomb-assisted channel. This pure quantum state of charge qubit could be experimentally realized at the current–voltage characteristic turnover position, where differential conductance sign changes. We further elaborate the underlying mechanism for both the real-time and the stationary charge-states coherence in the double-dot systems of study.

Magnetotransport in Aharonov-Bohm interferometers: Exact numerical simulations

The linear conductance of a two-terminal Aharonov-Bohm interferometer is an even function of the applied magnetic flux, as dictated by the Onsager-Casimir symmetry. Away from linear response this symmetry may be broken when many-body interactions are in effect. Using a numerically exact simulation tool, we study the dynamics and the steady-state behavior of the out-of-equilibrium double-dot Aharonov-Bohm interferometer, while considering different types of interactions: Model I includes a closed interferometer with an interdot electron-electron repulsion energy. In model II the interferometer is interacting with a dissipative environment, possibly driven away from equilibrium. In both cases we show that depending on the (horizontal, vertical) mirror symmetries of the setup, nonlinear transport coefficients obey certain magnetosymmetries. We compare numerically exact simulations to phenomenological approaches and special limits: The behavior of model I is compared to self-consistent mean-field calculations and master equation results in the Coulomb blockade regime. Model II, allowing heat dissipation to a thermal bath, is mimicked by an Aharonov-Bohm junction with a voltage probe. In both cases we find that phenomenological treatments capture the relevant transport symmetries, yet significant deviations in magnitude may show up.

The probe technique far from equilibrium: Magnetic field symmetries of nonlinear transport

The probe technique is a simple mean to incorporate elastic and inelastic processes into quantum dynamics. Using numerical simulations, we demonstrate that this tool can be employed beyond the analytically tractable linear response regime, providing a stable solution for the probe parameters: temperature and chemical potential. Adopting four probes: dephasing, voltage, temperature, and voltage-temperature, mimicking different elastic and inelastic effects, we focus on magnetic field and gate voltage symmetries of charge current and heat current in Aharonov-Bohm interferometers, potentially far-from-equilibrium. Considering electron current, we prove analytically that in the linear response regime inelastic scattering processes do not break the Onsager symmetry. Beyond linear response, even (odd) conductance terms obey an odd (even) symmetry with the threading magnetic flux, as long as the system acquires a spatial inversion symmetry. When spatial asymmetry is introduced particle-hole symmetry assures that nonlinear conductance terms maintain certain symmetries with respect to magnetic field and gate voltage. These analytic results are supported by numerical simulations. Analogous results are obtained for the electron heat current. We also demonstrate that a double-dot Aharonov-Bohm interferometer acts as a rectifier when two conditions are met: (i) many-body effects are included, here in the form of inelastic scattering, and (ii) time reversal symmetry is broken.

Flux-dependent occupations and occupation difference in geometrically symmetric and energy degenerate double-dot Aharonov-Bohm interferometers

We study the steady-state characteristics and the transient behavior of the nonequilibrium double-dot Aharonov-Bohm interferometer using analytical tools and numerical simulations. Our simple setup includes noninteracting degenerate quantum dots that are coupled to two biased metallic leads at the same strength. A magnetic flux $\ensuremath{\Phi}$ pierces the interferometer perpendicularly. As we tune the degenerate dot energies away from the symmetric point, we observe four nontrivial magnetic flux-control effects: (i) flux dependency of the occupation of the dots, (ii) magnetic-flux-induced occupation difference between the dots, at degeneracy, (iii) the effect of ``phase localization'' of the dots' coherence holds only at the symmetric point, while in general both real and imaginary parts of the coherence are nonzero, and (iv) coherent evolution survives even when the dephasing strength, introduced via B\"uttiker probes, is large and comparable to the dot energies and the bias voltage. In fact, finite dephasing can actually introduce new types of coherent oscillations into the system dynamics. These four phenomena take place when the dot energies are gated, to be positioned away from the symmetric point, demonstrating that the combination of bias voltage, magnetic flux, and gating field can provide delicate control over the occupation of each of the quantum dots and their coherence.

Large-deviation analysis for counting statistics in double-dot Aharonov-Bohm interferometer

The Coulomb correlation and quantum coherence in a double-dot Aharonov-Bohm interferometer can result in two distinct transport channels: a fast channel and a slow one, while their coupling is tunable by changing the magnetic flux passing through an interference loop. However, these effects cannot be manifested by the conventional transport current. In this work, employing the large-deviation method which was originally developed in the nonequilibrium statistical mechanics, we perform a large-deviation analysis for the transport through this double-dot interferometer system and reveal a clear dynamical phase transition behavior.

Thermoelectric effects in a double-dot Aharonov-Bohm interferometer with Rashba spin-orbit interaction

We investigate the thermoelectric effects in a double-dot Aharonov-Bohm interferometer coupled to ferromagnetic leads held at different temperatures. The interplay of Rashba spin-orbit interaction (RSOI) and magnetic flux ϕ induces various interesting spin-dependent interference phenomena. The thermoelectric transport oscillates with ϕ. The peak of the thermopower S and figure of merit ZT splits into two new peaks and its splitting increases with the Rashba induced phase factor φR. With increasing φRS and ZT at ϕ = ± 2nπ (n = 0,1,2,...) exhibit a conversion from a peak to a valley. In the presence of the interplay of RSOI and ϕ by increasing spin polarization the splitting peaks of S (ZT) become asymmetric and ZT is greatly enhanced. The influence of the quantum dot levels on thermoelectric effects is also analyzed.

Interference and interaction effects in adiabatic pumping through quantum dots

In order to investigate the effects of interference and interaction in adiabatic pumping, we consider an Aharonov-Bohm (AB) interferometer with a quantum dot embedded either in one or in both arms. We employ a real-time formalism and we perform an expansion both in the tunnel-coupling strengths between dot and leads and in the pumping frequency, taking into account the Coulomb interaction non perturbatively. We find that pumping in a single-dot AB interferometer has a peristaltic but phase-coherent character. In a double-dot AB interferometer, we find a pumping mechanism that relies purely on quantum mechanical interference and has no classical counterpart.

Controlling spin-dependent transport via inhomogeneous magnetic flux in double-dot Aharonov–Bohm interferometer

We study the spin-dependent electron transport through parallel coupled quantum dots (QDs) embedded in an Aharonov–Bohm (AB) interferometer connected asymmetrically to leads. Both the Rashba spin–orbit interaction (RSOI) inside one of the QDs, which acquires a spin-dependent phase factor in the tunnel-coupling strengths when the electrons flow through this arm of the AB ring, and an inhomogeneous magnetic flux penetrating the structure are taken into account. Due to the existence of the RSOI induced phase factor, magnetic flux and the interdot coupling, a spin-dependent Fano effect will arise. We pay special attention on the properties of the local density of states and the conductance when the electron phase factor is close to integer multiplies of a quantum of flux. It is shown that the roles and lifetimes of the bonding and antibonding states of the two spin components are very sensitive to the phase factor and can be well controlled accordingly. This manipulation of the spin degree of freedom relies on the existence of RSOI but can be fulfilled even when its strength is very weak. The proposed structure can be easily realized with present technology and might be of practical applications in spintronics devices and quantum computing.

Electron Transport Through Double-Dot Aharonov-Bohm Interferometer in the Kondo Regime**The project supported by National Natural Science Foundation of China under Grant No. 19975031

By applying the slave boson technique, we have studied the electron transport through double-dot Aharonov–Bohm interferometer in the Kondo regime. For the system with symmetric quantum dots, the linear conductance is shown to be enhanced by Kondo effect, but it is suppressed in the deep dot level regime in the presence of nonzero magnetic flux. The Aharonov–Bohm oscillations of the conductance are also investigated.