Search

We investigate two equivalent capacitively and tunnel coupled quantum dots, each coupled to its own pair of leads. Local Holstein type electron-phonon coupling at the dots is assumed. To study many-body effects we use the finite-U mean-field slave boson approach. For vanishing interdot interaction, weak e-ph coupling and finite tunneling, molecular orbital spin Kondo effects occur for single electron or single hole occupations. Phonons influence both correlations and tunneling and additionally they shift the energies of the dots. Depending on the dot energies and the strength of electron-phonon coupling, the system is occupied by a different number of electrons that effectively interact with each other repulsively or attractively leading to a number of different ground states of DQD. Among them are Kondo-like states with spin, orbital or charge correlations resulting from polaron cotunneling processes and states with magnetic intersite correlations., Comment: 8 pages, 5 figures

We calculate the conductance through strongly correlated T-shaped molecular or quantum dot systems under the influence of phonons. The system is modelled by the extended Anderson-Holstein Hamiltonian. The finite-U mean-field slave boson approach is used to study many-body effects. Phonons influence both interference and correlations. Depending on the dot unperturbed energy and the strength of electron-phonon interaction the system is occupied by a different number of electrons which effectively interact with each other repulsively or attractively. This leads together with the interference effects to different spin or charge Fano-Kondo effects, Comment: 16 pages, 11 figures

Spin polarized transport through a quantum dot coupled to ferromagnetic electrodes with noncollinear magnetizations is discussed in terms of nonequilibrium Green functions formalism in the finite-U slave boson mean field approximation. The difference of orientations of the magnetizations of electrodes opens off-diagonal spin-orbital transmission and apart from spin currents of longitudinal polarization also spin-flip currents appear. We also study equilibrium pure spin current at zero bias and discuss its dependence on magnetization orientation, spin-orbit coupling strength and gate voltage. Impact of these factors on tunneling magnetoresistance (TMR) is also undertaken. In general spin-orbit coupling weakens TMR, but it can change its sign., Comment: 5 pages, 4 figures

Strong electron correlations are discussed for the three capacitively coupled quantum dots, each of which is connected to a separate pair of electrodes. The finite-$U$ mean field slave boson approach is used. The analysis is carried out for both repulsive and attractive intra- and inter-dot interactions. Depending on the ratio and the sign of interaction parameters and occupation, either charge ordered states or different spin, spin-charge and charge Kondo resonances arise., Comment: 5 pages, 4 figures

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., Comment: 3 pages, 3 figures

Using the slave boson Kotliar-Ruckenstein approach (SBMFA) for N level Anderson model, we compare fully symmetric SU(N) Kondo resonances occurring for spin and orbital conserving tunneling with many-body resonances for the dot with broken symmetry caused by spin, orbital or full spin-orbital mixing. As a result of interorbital or spin flip processes new interference paths emerge, which manifests in the occurrence of antibonding Dicke like and bonding Kondo like resonances. The analytical expressions for linear conductances and linear temperature thermopower coefficient for arbitrary N are found., Comment: 5 pages, 4 figures

We study magnetoconductance of the small bandgap carbon nanotube quantum dots in the presence of spin-orbit coupling in the strong correlations regime. The finite-U mean field slave boson approach is used to study many-body effects. Different degeneracies are restored in magnetic field and Kondo effects of different symmetries arise including SU(3) effects of different types. Full spin-orbital degeneracy might be recovered for zero field and correspondingly SU(4) Kondo effect sets in. We point out on the possibility of the occurrence of electron-hole Kondo effects in slanting magnetic fields, which we predict will occur in the available magnetic fields for orientation of fields close to perpendicular. When the field approaches transverse orientation a crossover from SU(2) or SU(3) symmetry into SU(4) is observed., Comment: 11 pages, 11 figures

Spin-polarized transport through a quantum dot side attached to a topological superconductor and coupled to a pair of normal leads is discussed in Coulomb and Kondo regimes. For discussion of Coulomb range equation of motion method with extended Hubbard I approximation is used and Kondo regime is analyzed by Kotliar-Ruckenstein slave boson approach. Apart from the occurrence of zero bias anomaly the presence of Majorana states reflects also in splitting of Coulomb lines. In the region of Coulomb borders the spin dependent negative differential conductance is observed. Due to the low energy scale of Kondo effect this probe allows for detection of Majorana states even for extremely weak coupling with topological wire. In this range no signatures of Majorana states appear in Coulomb blockade dominated transport., Comment: 3 pages, 3 figures

Strong electron correlations and interference effects are discussed in capacitively coupled side attached and embedded quantum dots. The finite - U mean field slave boson approach is used to study many-body effects. In the linear range the many-body resonances exhibit SU(4) Kondo or Kondo-Fano like character and their properties in the corresponding arms are close to the properties of embedded or T- shape double dot systems respectively. Breaking of the spin symmetry in one of the arms or in both allows for the formation of many-body resonances of SU(3) or SU(2) symmetries in the linear range., Comment: 8 pages, 5 figures

The linear response transport properties of carbon nanotube quantum dot in the strongly correlated regime are discussed. The finite-U mean field slave boson approach is used to study many-body effects. Magnetic field can rebuilt Kondo correlations, which are destroyed by the effect of spin-orbit interaction or valley mixing. Apart from the field induced revivals of SU(2) Kondo effects of different types: spin, valley or spin-valley, also more exotic phenomena appear, such as SU(3) Kondo effect. Threefold degeneracy occurs due to the effective intervalley exchange induced by short-range part of Coulomb interaction or due to the intershell mixing. In narrow gap nanotubes the full spin-orbital degeneracy might be recovered in the absence of magnetic field opening the condition for a formation of SU(4) Kondo resonance., Comment: 17 pages, 13 figures

Strong electron correlations and interference effects are discussed in parallel-coupled single-level and orbitally doubly degenerate quantum dots. The finite-U mean-field slave boson approach is used to study many-body effects. The analysis is carried out in a wide range of parameter space including both atomic-like and molecular-like Kondo regimes and taking into account various perturbations, like interdot tunneling, interdot interaction, mixing of the electrode channels and exchange interaction. We also discuss the influence of singularities of electronic structure and the impact of polarization of electrodes. Special attention is paid to potential spintronic applications of these systems showing how current polarization can be controlled by adjusting interference conditions and correlations by gate voltage. Simple proposals of double dot spin valve and bipolar electrically tunable spin filter are presented., Comment: 14 pages, 16 figures

The impact of symmetry breaking perturbations on the spin dependent transport through carbon nanotube quantum dots in the Kondo regime is discussed., Comment: 10 pages, 6 figures

Magnetic impurity adsorbed on one of the carbon planes of a bilayer graphene is studied. The formation of the many-body SU(2) and SU(4) resonances close to the bandgap is analyzed within the mean field Kotliar-Ruckenstein slave boson approach. Impact of enhanced hybridization and magnetic instability of bilayer doped near the Van Hove singularity on the screening of magnetic moment is discussed., Comment: 10 pages, 8 figures

The out-of-equilibrium electron transport of carbon nanotube semiconducting quantum dot placed in a magnetic field is studied in the Kondo regime by means of the non-equilibrium Green functions. The equation of motion method is used. For parallel magnetic field the Kondo peak splits in four peaks, following the simultaneous splitting of the orbital and spin states. For perpendicular field orientation the triple peak structure of density of states is observed with the central peak corresponding to orbital Kondo effect and the satellites reflecting the spin and spin-orbital fluctuations., Comment: 3 pages, 3 figures

The coherent spin dependent transport through a set of two capacitively coupled quantum dots placed in a magnetic field is considered within the equation of motion method. The magnetic field breaks the spin degeneracy. For special choices of gate voltages the dot levels are tuned to resonance and the orbital Kondo effect results. For different Zeemann splittings at the dots the Kondo resonance can be formed for only one spin channel. In this case the system operates as an efficient spin filter., Comment: 4 pages, 3 figures

The coherent transport through a set of N quantum dots coupled in parallel is considered in the limit of infinite intradot and finite or infinite interdot interactions. The mean field slave boson approach and the equation of motion method are used. For the full spin-orbit degenerate case the low energy behavior is characterized by an SU(2N) symmetry with entangled spin and charge correlations. The magnetic field breaks the spin degeneracy, but for the special choices of gate voltages the degeneracy might be recovered in one spin channel allowing the spin filtering., Comment: 9 pages, 4 figures