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    Wyświetlanie 1-12 z 12
    Tytuł:
    Electronic Transport through a Quantum Dot Coupled to Non-Collinear Ferromagnetic Electrodes: The Kondo Regime
    Autorzy:
    Świrkowicz, R.
    Wilczyński, M.
    Wawrzyniak, M.
    Barnaś, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1813915.pdf
    Data publikacji:
    2008-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    73.23.Hk
    73.63.Kv
    Opis:
    Linear and non-linear conductance of quantum dots attached to magnetic leads is considered theoretically in the Kondo regime. The considerations are based on the non-equilibrium Green function formalism and the relevant equation of motion method. Splitting of the Kondo anomaly due to coupling of the dot to ferromagnetic electrodes, and its dependence on magnetic configuration of the system and on the lead's spin polarization is studied numerically.
    Źródło:
    Acta Physica Polonica A; 2008, 113, 1; 565-568
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Spin Polarized Transport through Quantum Dots: Coulomb Blockade and Kondo Effect
    Autorzy:
    Barnaś, J.
    Świrkowicz, R.
    Wilczyński, M.
    Weymann, I.
    Martinek, J.
    Dugaev, V.
    Powiązania:
    https://bibliotekanauki.pl/articles/2036886.pdf
    Data publikacji:
    2003-08
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    72.25.-b
    73.23.Hk
    72.15.Qm
    Opis:
    Spin related effects in electronic transport through quantum dots, coupled via tunneling barriers to two metallic leads, are discussed from the point of view of fundamental physics and possible applications in spin electronics. The effects follow either from long spin relaxation time in the dots or from spin dependent tunneling through the barriers when the external leads are ferromagnetic. In the former case large nonequilibrium spin fluctuations in the dot can be induced by flowing current. These fluctuations modify transport characteristics, particularly the shape of the Coulomb steps. In the latter case electric current depends on magnetic configuration of the system, and tunnel magnetoresistance effect due to magnetization rotation can occur. Transport properties in the weak coupling regime are described perturbatively in the first (sequential) and second (cotunneling) orders. In the strong coupling regime, on the other hand, the equation of motion for nonequilibrium Green functions is used to calculate electric current at low temperatures, where the Kondo peak in conductance is formed in the zero bias regime. In symmetrical systems the Kondo peak is split in the parallel magnetic configuration, whereas no splitting occurs for the antiparallel alignment. Theoretical results are discussed in view of available experimental data.
    Źródło:
    Acta Physica Polonica A; 2003, 104, 2; 165-177
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Non-Linear Thermal Current through Multilevel Quantum Dot Coupled to Ferromagnetic Electrodes
    Autorzy:
    Wierzbicki, M.
    Świrkowicz, R.
    Powiązania:
    https://bibliotekanauki.pl/articles/1427586.pdf
    Data publikacji:
    2012-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    73.23.Hk
    73.50.Lw
    85.80.Fi
    Opis:
    We present studies of spin-dependent phenomena in the non-linear energy transport through a multilevel quantum dot/molecule in the Coulomb blockade regime. Calculations are performed within the framework of non-equilibrium Green function formalism based on the equation of motion. Thermal current flowing through the system due to temperature gradient significantly varies with gate voltage. It depends on relative orientation of magnetic moments in the electrodes, so in analogy to tunneling magnetoresistance the magnetothermal conductance is introduced, which describes the effect.
    Źródło:
    Acta Physica Polonica A; 2012, 121, 5-6; 1204-1206
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Electrical and Heat Currents in Nanoscopic System with Ferromagnetic Electrodes of Non-Collinear Magnetic Moments
    Autorzy:
    Wierzbicki, M.
    Świrkowicz, R.
    Powiązania:
    https://bibliotekanauki.pl/articles/1426962.pdf
    Data publikacji:
    2012-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    73.23.Hk
    73.50.Lw
    85.80.Fi
    Opis:
    Thermoelectric properties of nanoscopic system composed of a single-level quantum dot attached to ferromagnetic electrodes are studied with the use of the non-equilibrium Green function formalism. Electrical and heat currents flowing through the system under temperature gradient and bias voltage are calculated in the non-linear regime. Both charge and heat currents strongly depend on configuration of magnetic moments in the leads. TMR ratio is mostly positive, but in a region of small bias voltages, where the electron flow is determined by the temperature gradient, electrical current in parallel and antiparallel configurations flows in opposite directions leading to considerable negative TMR.
    Źródło:
    Acta Physica Polonica A; 2012, 121, 5-6; 1073-1075
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Electron Transport through Double Quantum Dots with Interdot Coulomb Repulsion
    Autorzy:
    Sztenkiel, D.
    Świrkowicz, R.
    Powiązania:
    https://bibliotekanauki.pl/articles/2047016.pdf
    Data publikacji:
    2006-09
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    73.23.-b
    73.21.La
    73.23.Hk
    Opis:
    Electron transport through a system of two quantum dots connected in series is studied theoretically with the use of non-equilibrium Green function formalism based on the equation of motion method. Each dot is described by the one-level Anderson Hamiltonian and interdot Coulomb interactions in the form of the Hubbard-like term are taken into account. The electric current and occupation numbers are calculated with the use of two different approaches. The results of the methods are compared and discussed in detail. Strong asymmetry of I-V characteristics with respect to bias voltage reversal are obtained when energy levels of the dots are not aligned.
    Źródło:
    Acta Physica Polonica A; 2006, 110, 3; 389-394
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Electron Transport through Double Quantum Dot System with Inter-Dot Coulomb Interaction
    Autorzy:
    Sztenkiel, D.
    Świrkowicz, R.
    Powiązania:
    https://bibliotekanauki.pl/articles/2047295.pdf
    Data publikacji:
    2007-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    73.23.-b
    73.21.La
    73.23.Hk
    Opis:
    A theoretical approach to a problem of electron transport through double quantum dot systems based on non-equilibrium Green function formalism using equation of motion method is presented. I-V characteristics and differential conductance are calculated and discussed in detail in the intermediate regime with tunneling rate between the quantum dots comparable to coupling constants with external electrodes. Effects of inter-dot Coulomb correlations are studied for various values of interaction parameter U. It is shown that the interaction influences transport properties in a pronounced way and apart from the simple Coulomb blockade additional effects can be obtained. When energy levels of two quantum dots are not aligned, the asymmetry in conductance characteristics is closely related to a voltage dependence of population numbers in both quantum dots. For a one bias polarization electrons are well localized in quantum dots in a low voltage region, whereas for the opposite one they are partly delocalized.
    Źródło:
    Acta Physica Polonica A; 2007, 111, 3; 361-372
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Spin Polarized Transport through the Double-Dot System
    Autorzy:
    Sztenkiel, D.
    Świrkowicz, R.
    Powiązania:
    https://bibliotekanauki.pl/articles/2044544.pdf
    Data publikacji:
    2005-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.20.Hr
    72.15.Qm
    72.25.-b
    73.23.Hk
    Opis:
    Spin-dependent electron transport through two quantum dots in series attached to ferromagnetic electrodes is analyzed within the framework of the non-equilibrium Green function formalism. Regime of a weak coupling between the dots is investigated. I-V characteristics and tunnel magnetoresistance are calculated and discussed in detail.
    Źródło:
    Acta Physica Polonica A; 2005, 108, 5; 885-890
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Phonon-Assisted Kondo Resonance in Spin-Dependent Transport through a Quantum Dot
    Autorzy:
    Świrkowicz, R.
    Wilczyński, M.
    Barnaś, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1810522.pdf
    Data publikacji:
    2009-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    73.23.Hk
    73.63.Kv
    73.43.Qt
    72.25.-b
    Opis:
    Effects of local vibrational modes on electron transport through a quantum dot attached to ferromagnetic electrodes are studied in the Kondo regime by the non-equilibrium Green function formalism based on the equation of motion method. Differential conductance is calculated for parallel and antiparallel configurations of the leads' magnetic moments, and well defined Kondo resonance peaks and their phonon satellites are found. The influence of a compensating magnetic field on the peak positions is also discussed.
    Źródło:
    Acta Physica Polonica A; 2009, 115, 1; 272-274
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Poor Mans Scaling and Green Function Analysis of the Kondo Anomaly in Single-Level Quantum Dots
    Autorzy:
    Wawrzyniak, M.
    Świrkowicz, R.
    Wilczyński, M.
    Barnaś, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1813883.pdf
    Data publikacji:
    2008-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.20.Hr
    72.15.Qm
    72.25.-b
    73.23.Hk
    Opis:
    Kondo effect in a single-level quantum dot attached to magnetic leads is studied theoretically by the "poor man's scaling" and non-equilibrium Green function methods. From the scaling equations we derive the Kondo temperature as a function of the model parameters - in particular as a function of the angle between magnetic moments. Transport characteristics, i.e. differential conductance and tunnel magnetoresistance associated with magnetization rotation, were calculated within the non-equilibrium Green function formalism based on the equation of motion method.
    Źródło:
    Acta Physica Polonica A; 2008, 113, 1; 553-556
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Electronic Transport through the Double-Dot System
    Autorzy:
    Świrkowicz, R.
    Sztenkiel, D.
    Powiązania:
    https://bibliotekanauki.pl/articles/2038086.pdf
    Data publikacji:
    2004-06
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.20.Hr
    72.15.Qm
    72.25.-b
    73.23.Hk
    Opis:
    Electron tunnelling through two quantum dots in series is theoretically studied. A limit of intermediate coupling between the dots is considered. The non-equilibrium Green function formalism is used to calculate electric current and mean number of electrons accumulated on the dots. Lesser and retarded Green functions are calculated in the Hartree-Fock approximation with the use of the equation of motion method. Current flowing through the system calculated in dependency on gate voltages shows two resonant peaks, each peak with two additional shoulders. I-V characteristics and differential conductance in a resonance and out of resonance cases are calculated and discussed.
    Źródło:
    Acta Physica Polonica A; 2004, 105, 6; 523-528
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Nonequilibrium Kondo Effect in a Single-Channel Quantum Dot Asymmetrically Coupled to Two Ferromagnetic Reservoirs
    Autorzy:
    Świrkowicz, R.
    Wilczyński, M.
    Barnaś, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/2037118.pdf
    Data publikacji:
    2004
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.20.Hr
    72.15.Qm
    72.25.-b
    73.23.Hk
    Opis:
    Nonequilibrium Kondo effect in a quantum dot asymmetrically coupled to two ferromagnetic metallic leads is analyzed theoretically. The nonequilibrium Green function technique is used to calculate density of states and electric current. The lesser and retarded (advanced) Green functions are calculated by the equation of motion method within a consistent approximation scheme. The case where one electrode is half-metallic is analyzed numerically in details.
    Źródło:
    Acta Physica Polonica A; 2004, 105, 1-2; 149-154
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Electron Transport through Double Quantum Dot: from SU(4) Kondo to SU(2) Symmetry
    Autorzy:
    Sztenkiel, D.
    Świrkowicz, R.
    Powiązania:
    https://bibliotekanauki.pl/articles/2047706.pdf
    Data publikacji:
    2007-08
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    73.63.Kv
    72.15.Qm
    73.40.Gk
    73.23.Hk
    Opis:
    Electron transport across two capacitively coupled quantum dots in a parallel geometry is theoretically studied in the non-linear response regime with spin and orbital degrees of freedom taken into account and the Kondo effect induced by on-site and inter-dot Coulomb correlations is analyzed. For a system with each dot symmetrically coupled to a separate set of electrodes a well-defined spin and orbital contributions to zero-bias Kondo resonance are obtained. The Kondo peak splits if spin and/or orbital degeneracies are removed. A suppression of the orbital Kondo anomaly due to orbital asymmetry and channel mixing effects is discussed.
    Źródło:
    Acta Physica Polonica A; 2007, 112, 2; 387-393
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-12 z 12

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