Aharonov-Bohm Interferometer Research Articles

Shot noise of the hybrid double-quantum-dot Aharonov-Bohm interferometer coupled to normal and superconductive terminals

The shot noise of double-quantum-dot interferometer connected to normal metal and superconductor is investigated by employing the nonequilibrium Green's function approach. The gate voltages control the Aharonov-Bohm oscillation structure of shot noise, and the oscillation peaks can be converted to valleys by changing the gate voltages. The Andreev-reflection-generated shot noise is suppressed resulting from the interference effect and bias voltages. The asymmetric Fano factor with respect to the gate voltages exhibits the peak-valley resonant structure.

An investigation of the gate dependence in an electronic Aharonov–Bohm interferometer

In this study we have obtained the dependence of the electronic distribution on the gate shape and the applied gate voltage in a quantum Hall effect based Aharonov–Bohm interferometer using a method presented in our previous studies. We have discussed the relation between the distribution of incompressible strips and observation of Aharonov–Bohm oscillations. We have obtained the distributions of the incompressible strips for various gate voltages and have shown that a gate potential sweep and a magnetic field sweep would be equivalent. Our calculations also predict that for wider gate separations it is possible observe a silent region while sweeping the magnetic field or the gate voltage.

Time-dependent transport in Aharonov–Bohm interferometers

A numerical approach is employed to explain transport characteristics in realistic, quantum Hall-based Aharonov–Bohm (AB) interferometers. Firstly, the spatial distribution of incompressible strips, and thus the current channels, are obtained by applying a self-consistent Thomas–Fermi method to a realistic heterostructure under quantized Hall conditions. Secondly, the time-dependent Schrödinger equation is solved for electrons injected in the current channels. Distinctive AB oscillations are found as a function of the magnetic flux. The oscillation amplitude strongly depends on the mutual distance between the transport channels and on their width. At an optimal distance the amplitude and thus the interchannel transport is maximized, which determines the maximum visibility condition. On the other hand, the transport is fully suppressed at magnetic fields corresponding to half-integer flux quanta. The results confirm the applicability of realistic AB interferometers as controllable current switches.

Probing crossover from analogous weak antilocalization to localization by an Aharonov-Bohm interferometer on topological insulator surface

We propose a scanning tunneling microscopy Aharonov-Bohm (AB) interferometer on the surface of a topological insulator (TI) to probe the crossover from analogous weak antilocalization to weak localization phenomenon via the AB oscillations in spin-resolved local density of states (LDOS). Based on our analytical and numerical results, we show that with increasing the energy gap of TI surface states, the Φ0/2=hc/2e periodic AB oscillations in spin-resolved LDOS gradually transit into the Φ0 periodic oscillations.

Temperature and voltage probes far from equilibrium

We consider an open system of noninteracting electrons consisting of a small sample connected to several reservoirs and temperature or voltage probes. We study the nonlinear system of equations that determines the probe parameters. We show that it has a unique solution, which can be computed with a fast converging iterative algorithm. We illustrate our method with two well-known models: the three-terminal system and the open Aharonov-Bohm interferometer.

Thermospin effects in parallel coupled double quantum dots in the presence of the Rashba spin-orbit interaction and Zeeman splitting

The thermoelectric and the thermospin transport properties, including electrical conductivity, Seebeck coefficient, thermal conductivity, and thermoelectric figure of merit, of a parallel coupled double-quantum-dot Aharonov—Bohm interferometer are investigated by means of the Green function technique. The periodic Anderson model is used to describe the quantum dot system, the Rashba spin—orbit interaction and the Zeeman splitting under a magnetic field are considered. The theoretical results show the constructive contribution of the Rashba effect and the influence of the magnetic field on the thermospin effects. We also show theoretically that material with a high figure of merit can be obtained by tuning the Zeeman splitting energy only.

Tunable spin manipulation in a quantum dot embedded in an Aharonov-Bohm interferometer

In this paper, we study the electron properties of an Aharonov-Bohm interferometer with an embedded quantum dot (QD) by considering the leads of spin bias. As a result, it is found that a local magnetic flux through the structure can efficiently induce spin accumulation in the QD, unaccompanied by any charge transfer, and it shows that the direction and magnitude of the spin accumulation are tightly dependent on the interplay between the magnetic flux and spin bias. Based on the calculated results, we propose such a structure to be a candidate of the spin-manipulating device.

I–V characteristics and the spectrum width during electron tunneling through nanosandwiches W-WO2-(Au 147 − )-Al2O3-Al and Nd-Nd2O3-(Au 55 − )-Nd2O3-Nd. Part I: Quantum-chemical calculation of energies of orbitals for anions of nanoclusters Au55 and Au147

This work is devoted to the investigation of electron tunneling through “magical” nanoclusters Au55 and Au147. Using the quantum-chemical calculation, it is shown that the energy of the highest occupied molecular orbital (HOMO) level is \({E_{HOMOAu5{5^ - }}} = - 3.2eV\) and EHOMOAu147 = −4.4 eV, respectively. It is established that the difference between energy ELUMO− of the lowest unoccupied level LUMO and energy ELUMO− for the anions of clusters (Au55− and Au147−) is 0.86 and 0.24 eV, respectively. Based on the results of the calculations, it is assumed that nanosandwiches W-WO2-(Au147−)-Al2O3-Al can be promising structures for implementation of metal nanodiodes based on them, while nanosandwiches Nd-Nd2O3-(Au55−)-Nd2O3-Nd can be promising for implementation of energy filters not producing hot electrons and allowing the fabrication of the ring Aharonov-Bohm interferometers based on normal metals at liquid-helium temperatures.

Thermoelectric effect in an Aharonov-Bohm ring with an embedded quantum dot

Thermoelectric effect is studied in an Aharonov-Bohm interferometer with an embedded quantum dot (QD) in the Coulomb blockade regime. The electrical conductance, electron thermal conductance, thermopower, and thermoelectric figure-of-merit are calculated by using the Keldysh Green's function method. It is found that the figure-of-merit ZT of the QD ring may be quite high due to the Fano effect originated from the quantum interference effect. Moreover, the thermoelectric efficiency is sensitive to the magnitude of the dot-lead and inter-lead coupling strengthes. The effect of intradot Coulomb repulsion on ZT is significant in the weak-coupling regime, and then large ZT values can be obtained at rather high temperature.

Current-conserving Aharonov-Bohm interferometry with arbitrary spin interactions

We propose a general scattering matrix formalism that guarantees the charge conservation at junctions between conducting arms with arbitrary spin interactions. By using our formalism, we find that the spin-flip scattering can happen even at nonmagnetic junctions if the spin eigenstates in arms are not orthogonal. We apply our formalism to the Aharonov-Bohm interferometer consisting of $n$-type semiconductor ring with both the Rashba spin-orbit coupling and the Zeeman splitting. We discuss the characteristics of the interferometer as conditional/unconditional spin switch in the weak/strong-coupling limit, respectively.

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.

Edge state distribution in an Aharonov-Bohm electron interferometer in the integer quantum Hall regime

In this study we analyze the density distributions of the two dimensional electron system for an experimental geometry which is topologically equivalent of an Aharonov-Bohm interferometer in three dimensions in the quantum Hall regime and obtain the spatial distribution of the edge states. We employ the Thomas-Fermi approximation in our analysis and solve the Poisson equation in three dimensional using a multi grid technique. Also we obtain the distribution of incompressible strips for a wide range of magnetic fields strengths and comment on their relation with experimental results in literature.

Asymmetric transmission-induced probe-configuration-dependent dephasing in an Aharonov-Bohm ring

We investigate the dephasing rates in quasiballistic Aharonov-Bohm (AB) rings with local- and nonlocal-probe configurations by tuning the transmission through one arm of the ring. The dephasing rates are independent of the probe configuration while the transmissions through the ring paths are equal. In contrast, as AB interferometers are tuned to be strongly asymmetric, the dephasing rate of the local configuration becomes larger than that of the nonlocal configuration. We find that our observations can be qualitatively explained by voltage fluctuations from the measurement circuit, as proposed by G. Seelig, S. Pilgram, A. N. Jordan, and M. B\"uttiker [Phys. Rev. B 68, 161310(R) (2003)].

Fano-Rashba effect in thermoelectricity of a double quantum dot molecular junction

We examine the relation between the phase-coherent processes and spin-dependent thermoelectric effects in an Aharonov-Bohm (AB) interferometer with a Rashba quantum dot (QD) in each of its arm by using the Green's function formalism and equation of motion (EOM) technique. Due to the interplay between quantum destructive interference and Rashba spin-orbit interaction (RSOI) in each QD, an asymmetrical transmission node splits into two spin-dependent asymmetrical transmission nodes in the transmission spectrum and, as a consequence, results in the enhancement of the spin-dependent thermoelectric effects near the spin-dependent asymmetrical transmission nodes. We also examine the evolution of spin-dependent thermoelectric effects from a symmetrical parallel geometry to a configuration in series. It is found that the spin-dependent thermoelectric effects can be enhanced by controlling the dot-electrode coupling strength. The simple analytical expressions are also derived to support our numerical results.PACS numbers: 73.63.Kv; 71.70.Ej; 72.20.Pa

Transmission through a quantum dot molecule embedded in an Aharonov–Bohm interferometer

We study theoretically the transmission through a quantum dot molecule embedded in the arms of an Aharonov–Bohm four quantum dot ring threaded by a magnetic flux. The tunable molecular coupling provides a transmission pathway between the interferometer arms in addition to those along the arms. From a decomposition of the transmission in terms of contributions from paths, we show that antiresonances in the transmission arise from the interference of the self-energy along different paths and that application of a magnetic flux can produce the suppression of such antiresonances. The occurrence of a period of twice the quantum of flux arises at the opening of the transmission pathway through the dot molecule. Two different connections of the device to the leads are considered and their spectra of conductance are compared as a function of the tunable parameters of the model.

石墨烯圆环中的Aharonov-Bohm 效应

We have fabricated a graphene Aharonov-Bohm (AB) interferometer of diameter 1 μm and measured its electron conductance down to 0.3 K and in magnetic fields in a ³He cryostat. Conductance AB oscillations was observed, with magnetic field periods in agreement with the geometry of the AB ring. Our result demonstrated that the phase coherent length in graphene reached to ~2.5 μm at 0.3 K.

Spin-polarized Andreev reflection and spin accumulation in a quantum-dot Aharonov-Bohm interferometer with spin-orbit interaction effects

We theoretically investigate the spin-orbit interaction effects on the Andreev reflection and the spin accumulation in a quantum dot embedded in an Aharonov-Bohm interferometer. Due to the spin-dependent phase caused by the spin-orbit (SO) interaction, the electron occupation number becomes spin dependent and the spin accumulation can appear in the quantum dot (QD). Furthermore, in the presence of a magnetic flux, the spin accumulation of the dot can even be reversed by tuning the gate voltage. The magnitude and direction of the spin accumulation in the QD can be easily controlled by the gate voltage, magnetic flux, and the SO interaction. The Andreev reflection current also exhibits a spin polarization under the influence of both the spin-orbit interaction and the magnetic field through the ring. The spin polarization of the current can be tuned by varying the spin-orbit interaction strength and the magnetic flux. This provides an efficient mechanism to control the spin accumulation and the Andreev reflection in the quantum dot.

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.

Phase and amplitude of Aharonov-Bohm oscillations in nonlinear three-terminal transport through a double quantum dot

We study three-terminal linear and nonlinear transport through an Aharonov-Bohm interferometer containing a double quantum dot using the nonequilibrium Green function method. Under the condition that one of the three terminals is a voltage probe, we show that the linear conductance is symmetric with respect to the magnetic field (phase symmetry). However, in the nonlinear-transport regime, the phase symmetry is broken. Unlike two-terminal transport, the phase symmetry is broken even in noninteracting electron systems. Based on the lowest-order nonlinear conductance coefficient with respect to the source-drain bias voltage, we discuss the direction in which the phase shifts with the magnetic field. When the higher harmonic components of the Aharonov-Bohm oscillations are negligible, the phaseshift is a monotonically increasing function with respect to the source-drain bias voltage. To observe the Aharonov-Bohm oscillations with higher visibility, we need strong coupling between the quantum dots and the voltage probe. However, this leads to dephasing since the voltage probe acts as a B\"uttiker dephasing probe. The interplay between such antithetic concepts provides a peak in the visibility of the Aharonov-Bohm oscillations when the coupling between the quantum dots and the voltage probe changes.

The role of Coulomb interaction in thermoelectric effects of an Aharonov–Bohminterferometer

We investigate the thermoelectric effects of an Aharonov–Bohm (AB) interferometer with aquantum dot (QD) embedded in each of its arms, where the intra-dot Coulomb interactionbetween electrons in each QD is taken into account. Using Green’s function methods andthe equation of motion (EOM) technique, we find that the Seebeck coefficient and Lorenznumber can be strongly enhanced when the chemical potential sweeps the molecularstates associated with the Fano line-shapes in the transmission spectra, due toquantum interference effects between the bonding and antibonding molecular states.It is found that enhancement of the thermoelectric effects occurs between thetwo groups of conductance peaks in the presence of strong intra-dot Coulombinteraction—the reason being that a transmission node is developed in the Coulombblockade regime. In this case, the maximum value of the Lorenz number approaches10π2kB2/(3e2). Itsthermoelectric conversion efficiency in the absence of phonon thermal conductance, described by the figureof merit ZT, approaches 2 at room temperature. Therefore, it may be used as a high-efficiencysolid-state thermoelectric conversion device under certain circumstances.