We study current fluctuations in an interacting three-terminal quantum dot with ferromagnetic leads. For appropriately polarized contacts, the transport through the dot is governed by a novel dynamical spin blockade, i.e., a spin-dependent bunching of tunneling events not present in the paramagnetic case. This leads for instance to positive zero-frequency cross-correlations of the currents in the output leads even in the absence of spin accumulation on the dot. We include the influence of spin-flip scattering and identify favorable conditions for the experimental observation of this effect with respect to polarization of the contacts and tunneling rates.
We use the Aharonov-Bohm effect in a four-terminal ring based on a Ga[Al]As heterostructure for the measurement of the relative transmission phase. In each of the two interfering paths we induce a quantum dot. The number of electrons in the two dots can be controlled independently. The transmission phase is measured as electrons are added to or taken away from the individual quantum dots.
Within the scheme of quantum rate equations, we investigate the spin-resolved transport through a double quantum dot system with four ferromagnetic terminals. It is found that the injection efficiency of spin-polarized electrons can be significantly improved compared with single dot case. When the magnetization in one of four ferromagnetic terminals is antiparallel with the other three, the polarization rate of the current through one dot can be greatly enhanced, accompanied by the drastic decrease of the current polarization rate through the other one. The mechanism is the exchange interactio…
Electronic transport through a triple-quantum-dot ring with three terminals is theoretically studied. By introducing local Rashba spin-orbit interaction on an individual quantum dot, we find that the spin bias in one terminal drives apparent charge currents in the other terminals, accompanied by the similar amplitude and opposite directions of them. Meanwhile, it shows that the characteristics of the spin currents induced by the spin bias are notable. When a magnetic flux is applied through this ring, we see its nontrivial role in the manipulation of the charge and spin currents. With the obta…
In quantum dot circuits, screening electron clouds in strongly-coupled leads will hybridize with the states of the artificial atom. Using a three-terminal geometry, we directly probe the atomic structure of a quantum dot with Kondo coupling. Our measurements reveal that this hybrid system behaves as a non-linear entity with orbital degeneracy. Geometric distortion reduces the symmetry, lowers the energy, and lifts the degeneracy--the Jahn-Teller effect.
Three terminal tunnelling experiments on quantum dots in the Coulomb blockade regime allow a quantitative determination of the coupling strength of individual quantum states to the leads. Exploiting this insight we have observed independent fluctuations of the coupling strengths as a function of electron number and magnetic field due to changes in the shape of the wave function in the dot. Such a detailed understanding and control of the dot-lead coupling can be extended to more complex systems such as coupled dots, and is essential for building functional quantum electronic systems.
We consider two modifications of a recently proposed three-terminal quantum dot heat engine. First, we investigate the necessity of the thermalization assumption, namely that electrons are always thermalized by inelastic processes when traveling across the cavity where the heat is supplied. Second, we analyze various arrangements of tunneling-coupled quantum dots in order to implement a transmission function that is superior to the Lorentzian transmission function of a single quantum dot. We show that the maximum power of the heat engine can be improved by about a factor of two, even for a sma…
We study an interacting single-level quantum dot weakly coupled to three electrodes. When two electrodes are biased by voltages with opposite polarities, while keeping the third lead (the stem) grounded, the current through the stem is a measure of electron-hole asymmetry of the dot. In this setup we calculate the stem current for both metallic and ferromagnetic (collinearly polarized) leads and discuss how the three-terminal device gives additional information compared to the usual two-terminal setup. We calculate both the sequential and cotunneling contribution for the currents. For the latt…
We consider the time-dependent electron transport through a quantum dot connected to multiple leads in the presence of the additional over-dot (bridge) tunnelling channels by using the evolution operator technique. Each terminal and quantum dot are disturbed by an external oscillating field resulting in a time-dependence of the corresponding energy levels. The final analytical expressions for the currents flowing in the system are given assuming the wide-band limit approximation. We investigate also the transient-current characteristics in the case of the rectangular-pulse modulations imposed …
We report measurements of multi-path transport through a triple quantum dot (TQD) in the few-electron regime using a GaAs three-terminal device with a separate lead attached to each dot. When two paths reside inside the transport window and are simultaneously spin-blockaded, the leak currents through both paths are significantly enhanced. We suggest that the transport processes in the two paths cooperate to lift the spin blockade. Fine structures in transport spectra indicate that different kinds of cooperative mechanisms are involved, depending on the details of the three-electron spin states…
Measurement of the transmission phase through a quantum dot (QD) embedded in an arm of a two-terminal Aharonov-Bohm (AB) interferometer is inhibited by phase symmetry, i.e. the property that the linear response conductance of a two-terminal device is an even function of magnetic field. It is demonstrated that in a setup consisting of an interferometer with a QD in each of its arms, with one of the QDs capacitively coupled to a nearby quantum point contact (QPC), phase symmetry is broken when a finite voltage bias is applied to the QPC. The transmission phase via the uncoupled QD can then be de…
The recently suggested mechanism [Y. Song and H. Dery, Phys. Rev. Lett. 113, 047205 (2014)] of the three-terminal spin transport is based on the resonant tunneling of electrons between ferromagnetic and normal electrodes via an impurity. The sensitivity of current to a weak external magnetic field stems from a spin blockade, which, in turn, is enabled by strong on-site repulsion. We demonstrate that this sensitivity exists even in the absence of repulsion when a single-particle description applies. Within this description, we calculate exactly the resonant-tunneling current between the electro…
We investigate transport in a three-terminal graphene quantum dot. All nine elements of the conductance matrix have been independently measured. In the Coulomb blockade regime accurate measurements of individual conductance resonances reveal slightly different resonance energies depending on which pair of leads is used for probing. Rapid changes in the tunneling coupling between the leads and the dot due to localized states in the constrictions has been excluded by tuning the difference in resonance energies using in-plane gates which couple preferentially to individual constrictions. The inte…
Finite bias spectroscopy measurements of a three-terminal graphene quantum dot are presented. Numerous lines of enhanced differential conductance are observed outside the Coulomb diamonds. In the single-level transport regime such lines are often associated with transport through excited states. Here the system is in the multi-level transport regime. We argue that the lines are most likely a result of strong coupling to only a few of the excited states available in the bias window. We also discuss the option that fluctuations of the density of states in the leads are fully or partly responsibl…
We investigate the Josephson effect in one triple-terminal junction with embedded parallel-coupled double quantum dots. It is found that the inter-superconductor supercurrent has opportunities to oscillate in $4π$ period, with the adjustment of the phase differences among the superconductors. What is notable is that such a result is robust and independent of fermion parities, intradot Coulomb strength, and the dot-superconductor coupling manner. By introducing the concept of spinful many-particle Majorana modes, we present the analytical definition of the Majorana operator via superposing elec…
In this work, we show that in a four-quantum-dot ring, via introducing a local Rashba spin-orbit interaction the spin bias in the transverse terminals can be detected by observing the charge currents in the longitudinal probes. It is found that due to the Rashba interaction, the quantum interference in this system becomes spin-dependent and the opposite-spin currents induced by the spin bias can present different magnitudes, so charge currents emerge. Besides, the charge currents rely on both the magnitude and spin polarization direction of the spin bias. It is believed that this method provid…
We have studied the electron transport through a quantum dot coupled to three leads in the presence of external microwave fields supplied to different parts of the considered mesoscopic system. Additionally, we introduced a possible nonresonant tunneling channels between leads. The quantum dot charge and currents were determined in terms of the appropriate evolution operator matrix elements and under the wide band limit the analytical formulas for time-averaged currents and differential conductance were obtained. We have also examined the response of the considered system on the rectangular-pu…
We propose a scheme of multilayer thermoelectric engine where {\em one} electric current is coupled to {\em two} temperature gradients in three-terminal geometry. This is realized by resonant tunneling through quantum dots embedded in two thermal and electrical resisting polymer matrix layers between highly conducting semiconductor layers. There are two thermoelectric effects, one of which is pertaining to inelastic transport processes (if energies of quantum dots in the two layers are different) while the other exists also for elastic transport processes. {These two correspond to the transver…
Rectification of thermal fluctuations in mesoscopic conductors is the key idea of today's attempts to build nanoscale thermoelectric energy harvesters in order to convert heat into a useful electric power. So far, most concepts make use of the Seebeck effect in a two-terminal geometry where heat and charge are both carried by the same particles. Here, we experimentally demonstrate the working principle of a new kind of energy harvester, proposed recently using two capacitively coupled quantum dots. We show that due to its novel three-terminal design which spatially separates the heat reservoir…
We study three-terminal linear and nonlinear transport through an Aharonov-Bohm interferometer containing a double quantum dot using the nonequilibrium Green's 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 t…
We examine transport and microwave properties of two coupled quantum dots taken in parallel connection to the common left lead and connected to separate leads at their right side. In addition, the area between the left lead and the double-dot structure is threaded by Aharonov-Bohm magnetic flux. We determine the energies and populations of double-dot levels on the microscopic basis taking into account the interdot Coulomb interaction and show that at large lead-to-lead bias the population inversion can be achieved. For the case of strong Coulomb repulsion, this inversion leads to level crossin…
By applying a local Rashba spin-orbit interaction on an individual quantum dot of a four-terminal four-quantum-dot ring and introducing a finite bias between the longitudinal terminals, we theoretically investigate the charge and spin currents in the transverse terminals. It is found that when the quantum dot levels are separate from the chemical potentials of the transverse terminals, notable pure spin currents appear in the transverse terminals with the same amplitude and opposite polarization directions. Besides, the polarization directions of such pure spin currents can be inverted by alte…
Nanodevices consisting of a quantum dot tunnel coupled to one superconducting and two normal electrodes may serve as a source of entangled electrons. As a result of crossed Andreev reflection the Cooper pair of s-wave character may be split into two electrons and each of them goes into a distinct normal electrode, preserving entanglement. Efficiency of the process depends on the specific system and is tunable by electric means. Our calculations show that in the studied device this efficiency may attain values as large as $80 \%$.
We prepare a triple quantum dot with a separate contact lead to each dot to study Pauli spin blockade in the tunnel-coupled three dots in a row. We measure the tunneling current flowing between the center dot and either the left or right dot with the left and right leads as a common source and the center lead as a drain. In the biased stability diagram, we establish Pauli spin blockade in the respective neighboring dots, with features similarly obtained in double quantum dot systems. We further realize Pauli spin blockade with two different conditions by tuning the inter-dot coupling gates: st…
A theory of spin-transport in hybrid normal metal - ferromagnetic electronic circuits is developed, taking into account non-collinear spin-accumulation. Spin-transport through resistive elements is described by 4 conductance parameters. Microscopic expression for these conductances are derived in terms of scattering matrices and explicitly calculated for simple models. The circuit theory is applied to 2-terminal and 3-terminal devices attached to ferromagnetic reservoirs.
We study transport through a double quantum dot with interdot hopping $t$, intradot repulsion $U$ and interdot repulsion $U^{\prime}$, using the numerical renormalization group (NRG) method. At half-filling, the conductances in two-terminal series and four-terminal parallel configuration are calculated via two phase shifts for quasi-particles of double quantum dot connected to two noninteracting leads with hybridization strength $Γ$. For small values of $t/Γ$ and $U^{\prime}/U$, conductance in the two-terminal series configuration is suppressed to almost zero. In this region, plateau of conduc…
We study thermoelectric effects in Kondo correlated quantum dot coupled to ferromagnetic electrodes by calculating thermopower S in the Kondo regime as function of on-dot energy level and temperature. The system is represented by the Anderson model and the results agree well with those recently measured for a quantum dot coupled to nonmagnetic leads. For magnetic electrodes one observes marked dependence of S on the degree of their polarization.
We investigate current fluctuations in a three-terminal quantum dot in the sequential tunneling regime. In the voltage-bias configuration chosen here, the circuit is operated like a beam splitter, i.e. one lead is used as an input and the other two as outputs. In the limit where a double occupancy of the dot is not possible, a super-Poissonian Fano factor of the current in the input lead and positive cross-correlations between the current fluctuations in the two output leads can be obtained, due to dynamical channel-blockade. When a single orbital of the dot transports current, this effect can…
We suggest a series of transport experiments on spin precession in quantum dots coupled to one or two ferromagnetic leads. Dot spin states are created by spin injection and analyzed via the linear conductance through the dot, while an applied magnetic field gives rise to the Hanle effect. Such a Hanle experiment can be used to determine the spin lifetime in the quantum dot, to measure the spin injection efficiency into the dot, as well as proving the existence of intrinsic spin precession which is driven by the Coulomb interaction.
We propose an efficient mechanism for the operation of writing spin in a quantum dot, which is an ideal candidate for qubit. The idea is based on the Andreev reflection induced spin polarization (ARISP) in a ferromagnetic / quantum-dot / superconductor system. We find that on the resonance of Andreev reflection, the spin polarization of quantum dot strongly denpends on the magnetization of ferromagnetic electrode, and the sign of the spin polarization is controllable by bias voltage. In the presence of intradot Coulomb interaction, we show that ARISP effect can still survive as long as the cha…
The quantum Hall and longitudinal resistances in multi-terminal ferromagnetic graphene p-n junctions under a perpendicular magnetic field are investigated. In the Hall measurements, the transverse contacts are assumed to be located at p-n interface to avoid the mixing of edge states at the interface and the resulting quantized resistances are then topologically protected. According to the charge carrier type, the resistances in four-terminal p-n junction can be naturally divided into nine different regimes. The symmetric Hall and longitudinal resistances are observed, with lots of new robust q…
We study thermoelectric effects in Kondo correlated quantum dot coupled to ferromagnetic electrodes by calculating conductance, thermopower and thermal conductance in the Kondo regime. We also study the effect of the asymmetry in the coupling to the leads, which has important consequences for anti-parallel magnetization configuration. We discuss the thermoelectric figure of merit, tunnel magnetoresistance and violation of the Wiedemann-Franz law in this system. The results agree with recently measured thermopower of the quantum dot defined in a two dimensional electron gas.
We study electronic transport through quantum dots weakly coupled to ferromagnetic leads with collinear magnetization directions. Tunneling contributions of first and second order in the tunnel-coupling strength are taken into account. We analyze the tunnel magnetoresistance (TMR) for all combinations of linear and nonlinear response, at or off resonance, with an even or odd dot-electron number. Different mechanisms for transport and spin accumulation the various regimes give rise to different TMR behavior.
Spin-polarized transport through a quantum dot strongly coupled to ferromagnetic electrodes with non-collinear magnetic moments is analyzed theoretically in terms of the non-equilibrium Green function formalism. Electrons in the dot are assumed to be coupled to a phonon bath. The influence of electron-phonon coupling on tunnelling current, linear and nonlinear conductance, and on tunnel magnetoresistance is studied in detail. Variation of the main Kondo peaks and phonon satellites with the angle between magnetic moments of the leads is analyzed.
We study heat rectification through quantum dots in the Coulomb blockade regime using a master equation approach. We consider both cases of two-terminal and four-terminal devices. In the two-terminal configuration, we analyze the case of a single quantum dot with either a doubly-degenerate level or two non-degenerate levels. In the sequential tunneling regime we analyze the behaviour of heat currents and rectification as functions of the position of the energy levels and of the temperature bias. In particular, we derive an upper bound for rectification in the closed-circuit setup with the doub…
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 pre…
We discuss the possibility to generate, manipulate, and probe single spins in single-level quantum dots coupled to ferromagnetic leads. The spin-polarized currents flowing between dot and leads lead to a non-equilibrium spin accumulation, i.e., a finite polarization of the dot spin. Both the magnitude and the direction of the dot's spin polarization depends on the magnetic properties of leads and their coupling to the dot. They can be, furthermore, manipulated by either an externally applied magnetic field or an intrinsically present exchange field that arises due to the tunnel coupling of the…
A three terminal nanoscale refrigeration concept based on a vibron-coupled quantum dot hybrid system coupled to two electronic reservoirs and a phonon bath is proposed and analyzed in detail. While investigating the non-trivial role of electron-phonon interactions, we show that, although they are well known to be detrimental from a general refrigeration perspective, can be engineered to favorably improve the trade-off between the cooling power (CP) and the coefficient-of-performance (COP). Furthermore, an additional improvement in the trade-off can be facilitated by applying a high electronic …
We investigate real-time dynamics of spin-polarized current in a quantum dot coupled to ferromagnetic leads in both parallel and antiparallel alignments. While an external bias voltage is taken constant in time, a gate terminal, capacitively coupled to the quantum dot, introduces a periodic modulation of the dot level. Using non equilibrium Green's function technique we find that spin polarized electrons can tunnel through the system via additional photon-assisted transmission channels. Owing to a Zeeman splitting of the dot level, it is possible to select a particular spin component to be pho…
We study the full counting statistics of electronic transport through a single-level quantum dot weakly coupled to two leads, with either one or both of them being ferromagnetic. The interplay of Coulomb interaction and finite spin polarization implies spin-correlation induced charge correlations that give rise to super-Poissonian transport behavior and positive cross correlations of the currents of the two spin species. In the case of two ferromagnetic leads, we analyze the nontrivial dependence of the cumulants on the angle between the polarization directions of the leads. We find diverging …
We study adiabatic pumping of electrons through quantum dots attached to ferromagnetic leads. Hereby we make use of a real-time diagrammatic technique in the adiabatic limit that takes into account strong Coulomb interaction in the dot. We analyze the degree of spin polarization of electrons pumped from a ferromagnet through the dot to a nonmagnetic lead (N-dot-F) as well as the dependence of the pumped charge on the relative leads' magnetization orientations for a spin-valve (F-dot-F) structure. For the former case, we find that, depending on the relative coupling strength to the leads, spin …
We study the nonequilibrium spectral function of the single-impurity Anderson model connecting with multi-terminal leads. The full dependence on frequency and bias voltage of the nonequilibrium self-energy and spectral function is obtained analytically up to the second-order perturbation regarding the interaction strength $U$. High and low bias voltage properties are analyzed for a generic multi-terminal dot, showing a crossover from the Kondo resonance to the Coulomb peaks with increasing bias voltage. For a dot where the particle-hole symmetry is not present, we construct a current-preservin…
We present measurements of tunneling magneto-resistance (TMR) in single-wall carbon nanotubes attached to ferromagnetic contacts in the Coulomb blockade regime. Strong variations of the TMR with gate voltage over a range of four conductance resonances, including a peculiar double-dip signature, are observed. The data is compared to calculations in the "dressed second order" (DSO) framework. In this non-perturbative theory, conductance peak positions and linewidths are affected by charge fluctuations incorporating the properties of the carbon nanotube quantum dot and the ferromagnetic leads. Th…
The spin-polarized transport through two-level quantum dots weakly coupled to ferromagnetic leads is considered theoretically in the Coulomb blockade regime. It is assumed that the dot is doubly occupied, so that the current flows due to cotunneling through singlet and triplet states of the dot. It is shown that transport characteristics strongly depend on the ground state of quantum dot. If the ground state is a singlet, differential conductance ($G$) displays a broad minimum at low bias voltage, while tunnel magnetoresistance (TMR) is given by the Julliere value. If triplet is the ground sta…
Multi-terminal multi-dot devices have been put forward as versatile and performant setups for thermoelectric energy harvesting at the nanoscale. With a technique that encompasses and overtakes several of the usual theoretical tools used in this context, we explore a three-terminal Coulomb-coupled-dot device for refrigeration purposes. The refrigerator is monitored by either a voltage or a thermal bias. This comparative study shows that heat driven refrigerator is much underperforming than the power driven one, due to scarce on-dot charge fluctuations.
Many-particle electron states in semiconductor quantum dots with carrier-mediated ferromagnetism are studied theoretically within the self-consistent Boltzmann equation formalism. Depending on the conditions, a quantum dot may contain there phases: partially spin-polarized ferromagnetic, fully spin-polarized ferromagnetic, and paramagnetic phases. The physical properties of many-body ferromagnetic confined systems come from the competing carrier-mediated ferromagnetic and Coulomb interactions. The magnetic phases in gated quantum dots with holes can be controlled by the voltage or via optical …
Equilibrium transport properties of a single-level quantum dot tunnel-coupled to ferromagnetic leads and exchange-coupled to a side nonmagnetic reservoir are analyzed theoretically in the Kondo regime. The equilibrium spectral functions and conductance through the dot are calculated using the numerical renormalization group (NRG) method. It is shown that in the antiparallel magnetic configuration, the system undergoes a quantum phase transition with increasing exchange coupling $J$, where the conductance drops from its maximum value to zero. In the parallel configuration, on the other hand, th…
Weakly coupled quantum dots in the Pauli spin blockade regime are considered with respect to spin-dependent transport. By attaching one half-metallic and one non-magnetic lead, the Pauli spin blockade if formed by a pure triplet state with spin moment $S_z=1$ or -1. Furthermore, additional spin blockade regimes emerge because of full occupation in states with opposite spin to that of the half-metallic lead.
We investigate the effects induced by spin polarization in the contacts attached to a serial double quantum dot. The polarization generates effective magnetic fields and suppresses the Kondo effect in each dot. The super-exchange interaction ($J_{\mathrm{AFM}}$), tuned by the inter-dot tunnelling rate $t$, can be used to compensate the effective fields and restore the Kondo resonance when the contact polarizations are aligned. As a consequence, the direction of the spin conductance can be controlled and even reversed using electrostatic gates alone. Furthermore, we study the associated two-imp…
The energy efficiency and power of a three-terminal thermoelectric nanodevice are studied by considering elastic tunneling through a single quantum dot. Facilitated by the three-terminal geometry, the nanodevice is able to generate simultaneously two electrical powers by utilizing only one temperature bias. These two electrical powers can add up constructively or destructively, depending on their signs. It is demonstrated that the constructive addition leads to the enhancement of both energy efficiency and output power for various system parameters. In fact, such enhancement, dubbed as thermoe…
Spintronics devices rely on spin-dependent transport behavior evoked by the presence of spin-polarized electrons. Transport through nanostructures, on the other hand, is dominated by strong Coulomb interaction. We study a model system in the intersection of both fields, a quantum dot attached to ferromagnetic leads. The combination of spin-polarization in the leads and strong Coulomb interaction in the quantum dot gives rise to an exchange field acting on electron spins in the dot. Depending on the parameter regime, this exchange field is visible in the transport either via a precession of an …
We examine cross-correlations (CCs) in the tunneling currents through two parallel interacting quantum dots coupled to four independent ferromagnetic electrodes. We find that when either one of the two circuits is in the parallel configuration with sufficiently strong polarization strength, a new mechanism of dynamical spin blockade, i.e., a spin-dependent bunching of tunneling events, governs transport through the system together with the inter-dot Coulomb interaction, leading to a sign-reversal of the zero-frequency current CC in the dynamical channel blockade regime, and to enhancement of p…
The Andreev transport through a quantum dot coupled to two external ferromagnetic leads and one superconducting lead is studied theoretically by means of the real-time diagrammatic technique in the sequential and cotunneling regimes. We show that the tunnel magnetoresistance (TMR) of the Andreev current displays a nontrivial dependence on the bias voltage and the level detuning, and can be described by analytical formulas in the zero temperature limit. The cotunneling processes lead to a strong modification of the TMR, which is most visible in the Coulomb blockade regime. We find a zero-bias a…
Nonequilibrium electronic transport through a quantum dot coupled to ferromagnetic leads (electrodes) is studied theoretically by the nonequilibrium Green function technique. The system is described by the Anderson model with arbitrary correlation parameter $U$. Exchange interaction between the dot and ferromagnetic electrodes is taken into account {\it via} an effective molecular field. The following situations are analyzed numerically: (i) the dot is symmetrically coupled to two ferromagnetic leads, (ii) one of the two ferromagnetic leads is half-metallic with almost total spin polarization …
We study a system composed of a quantum dot in contact with ferromagnetic leads, held at different temperatures. Spin analogues to the thermopower and thermoelectric figures of merit are defined and studied as a function of junction parameters. It is shown that in contrast to bulk ferromagnets, the spin thermopower coefficient in a junction can be as large as the Seebeck coefficient, resulting in a large spin figure of merit. In addition, it is demonstrated that the junction can be tuned to supply only spin current but no charge current. We also discuss experimental systems where our predictio…
Spin-dependent transport through an interacting single-level quantum dot coupled to ferromagnetic leads with non-collinear magnetizations is analyzed theoretically. The transport properties and average spin of the dot are investigated within the nonequilibrium Green function technique based on the equation of motion in the Hartree-Fock approximation. Numerical results show that Coulomb correlations on the dot and strong spin polarization of the leads significantly enhance precession of the average dot spin around the effective molecular field created by the external electrodes. Moreover, they …
Motivated by recent experiments, we consider a single-electron transistor in the Kondo regime which is coupled to three leads in the presence of large bias voltages. Such a steady-state non-equilibrium system is to a large extent governed by a decoherence rate induced by the current through the dot. As the two-terminal conductance turns out to be rather insensitive to the decoherence rate, we study the conductance in a three-terminal device using perturbative renormalization group and calculate the characteristic splitting of the Kondo resonance. The interplay between potential biases and anis…
Thermoelectric effects through a serial double quantum dot system weakly coupled to ferromagnetic leads are analyzed. Formal expressions of electrical conductance, thermal conductance, and thermal coefficient are obtained by means of Hubbard operators. The results show that although the thermopower is independent of the polarization of the leads, the figure of merit is reduced by an increase of polarization. The influences of temperature and interdot tunneling on the figure of merit are also investigated, and it is observed that increase of the interdot tunneling strength results in reduction …
