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Wyświetlanie 1-15 z 67
Tytuł:
Aharonov-Bohm Effect and Valley Polarization in Nanoscopic Graphene Rings
Autorzy:
Rycerz, A.
Powiązania:
https://bibliotekanauki.pl/articles/1810559.pdf
Data publikacji:
2009-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
73.23.-b
73.63.Rt
85.35.Ds
Opis:
The conductance of an Aharonov-Bohm interferometer is studied in a tight-binding model of graphene. Two point contacts with zigzag edges, which function as valley filters, are connected by a ring with an irregular boundary. We find that the narrowest rings show strong current suppression and nearly sinusoidal magnetoconductance oscillations, whereas for wide rings higher harmonics are equally represented. In the intermediate width range, oscillations with a basic periodicity are suppressed when two valley filters have opposite polarity, while higher harmonics are unaffected. The effect is interpreted in terms of a relatively weak intervalley scattering in the system.
Źródło:
Acta Physica Polonica A; 2009, 115, 1; 322-325
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Andreev Conductance through a Quantum Dot Strongly Coupled to Ferromagnetic and Superconducting Leads
Autorzy:
Wójcik, K.P.
Weymann, I.
Powiązania:
https://bibliotekanauki.pl/articles/1032390.pdf
Data publikacji:
2017-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
73.23.-b
72.15.Qm
74.45.+c
72.25.-b
Opis:
We analyze the Andreev conductance through a quantum dot strongly coupled to one ferromagnetic and one superconducting lead. The transmission due to the Andreev reflection is obtained from the numerical renormalization group method. We show that at low temperatures, depending on the dot level position, the Andreev conductance exhibits a peak at zero bias due to the Kondo effect, which can be split by the exchange field due to spin-dependent coupling to ferromagnetic lead.
Źródło:
Acta Physica Polonica A; 2017, 132, 1; 143-145
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Andreev Transport in Double Quantum Dot Cooper Pair Splitters in the Presence of External Magnetic Field
Autorzy:
Trocha, P.
Weymann, I.
Powiązania:
https://bibliotekanauki.pl/articles/1386830.pdf
Data publikacji:
2015-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
73.23.-b
73.21.La
74.45.+c
Opis:
The effect of external magnetic field on the transport properties of double quantum dots coupled to normal and superconducting leads is studied by means of the real-time diagrammatic technique in the sequential tunneling regime. This device works as a gate-controlled Cooper pair splitter. We focus on the transport regime where the current is blocked due to the spin triplet blockade. It is shown that external magnetic field can modify the Andreev current and differential conductance. In particular, magnetic field can suppress the negative differential conductance associated with the triplet blockade.
Źródło:
Acta Physica Polonica A; 2015, 127, 2; 502-504
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Andreev Transport through a Magnetic Molecule Weakly Coupled to Ferromagnetic Leads
Autorzy:
Pawlicki, F.
Weymann, I.
Powiązania:
https://bibliotekanauki.pl/articles/1030385.pdf
Data publikacji:
2018-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
73.23.-b
74.45.+c
75.50.Xx
Opis:
The Andreev transport through a single molecular magnet coupled to two external ferromagnetic leads and one superconducting electrode is studied theoretically by means of the real-time diagrammatic technique. The calculations are performed by including the sequential tunneling processes between the molecule and ferromagnetic leads, while the coupling to superconductor can be arbitrary. We analyze the dependence of the Andreev current and tunnel magnetoresistance on various intrinsic parameters of the molecule. The superconducting proximity effect results in the formation of molecular Andreev bound states. We show that the transport behavior depends greatly on the type of internal exchange interaction of the molecule, which can lead to corresponding sign changes of the tunnel magnetoresistance of the device.
Źródło:
Acta Physica Polonica A; 2018, 133, 3; 594-596
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Asymmetry Induced Localization
Autorzy:
Kohler, H.
Powiązania:
https://bibliotekanauki.pl/articles/1399044.pdf
Data publikacji:
2013-12
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
05.30.-d
03.65.Yz
05.45.Mt
73.23.-b
Opis:
We consider a two-level system, which couples via non-commuting operators to two independent oscillator baths. When the coupling is symmetric, the renormalized hopping matrix element is finite even for infinitely strong coupling strength. The two-level system is in a delocalized phase. For finite coupling strength a localization transition occurs for a critical asymmetry angle, which separates the localized from the delocalized phase. Using the method of flow equations we are able to monitor real time dynamics.
Źródło:
Acta Physica Polonica A; 2013, 124, 6; 1053-1059
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Coherent Transport through Systems of Coupled Quantum Dots
Autorzy:
Trocha, P.
Barnaś, J.
Powiązania:
https://bibliotekanauki.pl/articles/2047730.pdf
Data publikacji:
2007-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
73.23.-b
73.21.La
73.23.Hk
Opis:
Spin-dependent electronic transport through two coupled single-level quantum dots attached to ferromagnetic leads with parallel and antiparallel magnetizations is analyzed theoretically. The intra-dot Coulomb correlation is taken into account, while the inter-dot Coulomb repulsion is omitted. Conductance and tunnel magnetoresistance associated with magnetization rotation are calculated by the nonequilibrium Green function technique. The relevant Green functions are derived by the equation of motion method in the Hartree-Fock approximation. The dot occupation numbers and the Green functions are calculated self-consistently. The interference effects in electronic transport through quantum dots are analyzed in two different configurations. It is shown that the Fano resonance in conductance can be observed even for vanishing inter-dot hopping parameter t. The interplay of the interference effects and the Coulomb interactions in quantum dots is also analyzed.
Źródło:
Acta Physica Polonica A; 2007, 112, 2; 473-480
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Current Shot Noise and Bunching of Electrons in Multilevel Quantum Dots
Autorzy:
Michałek, G.
Bułka, B.
Powiązania:
https://bibliotekanauki.pl/articles/1813512.pdf
Data publikacji:
2008-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
73.23.-b
72.70.+m
Opis:
Currents and their fluctuations in multilevel quantum dots are studied theoretically in the limit of sequential tunneling. The spin degrees of freedom, many-body electronic states (singlet and triplet) as well as relaxation processes between the levels of the quantum dots are considered. In general, due to the rapid relaxation processes the shot noise is sub-Poissonian, however for a large polarization of the outgoing currents from the singlet and triplet states one gets the super-Poissonian type of the shot noise due to the bunching of tunneling events.
Źródło:
Acta Physica Polonica A; 2008, 113, 1; 27-30
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Current Suppression in Transport Through Triple Quantum Dots Coupled to Ferromagnetic Leads
Autorzy:
Wrześniewski, K.
Weymann, I.
Powiązania:
https://bibliotekanauki.pl/articles/1386617.pdf
Data publikacji:
2015-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
73.23.-b
73.21.La
85.75.-d
Opis:
We consider transport through triple quantum dot system in a triangular geometry weakly coupled to external ferromagnetic leads. The real-time diagrammatic technique in the lowest order perturbation theory is used to calculate the current and Fano factor in the parallel and antiparallel magnetic configuration of the system as well as the resulting tunnel magnetoresistance (TMR). We focus on the transport regime where the current is suppressed and show that it can lead to negative differential conductance and large super-Poissonian shot noise, which are present in both magnetic configurations. Furthermore, we show that for voltages where the system is trapped in a one-particle dark state the TMR becomes suppressed, while for two-particle blockade, the TMR is much enhanced.
Źródło:
Acta Physica Polonica A; 2015, 127, 2; 460-462
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Current-Induced Magnetic Dynamics in Asymmetric Ferromagnetic Single-Electron Devices
Autorzy:
Kowalik, M.
Powiązania:
https://bibliotekanauki.pl/articles/1810537.pdf
Data publikacji:
2009-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
72.25.-b
73.23.Hk
85.75.-d
Opis:
The theoretical calculations of possible dynamics for a localized magnetic moment of the central electrode in ferromagnetic single-electron devices are presented. The spin-transfer torque from spin current absorbed by the central electrode is calculated. Thereafter, an in-plane component of spin torque is regarded during the integration of the Landau-Lifshitz-Gilbert equation and the time evolution of the localized magnetic moment of the central electrode is obtained. The necessary conditions for switching of the magnetic moment are discussed.
Źródło:
Acta Physica Polonica A; 2009, 115, 1; 290-292
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Dark States and Transport through Quantum Dots
Autorzy:
Tooski, S.
Bułka, B.
Powiązania:
https://bibliotekanauki.pl/articles/1428598.pdf
Data publikacji:
2012-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.10.-w
33.57.+c
73.23.-b
73.63.Kv
Opis:
We consider current through triple and quadruple quantum dot systems in an in-plane electric field and in the sequential tunneling regime. The electric field breaks symmetry of the system and can trap electron in a dark state in which current flow can completely be blocked. Consequently rotating the electric field, one can observe current oscillations and blockades due to dark state.
Źródło:
Acta Physica Polonica A; 2012, 121, 5-6; 1231-1233
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Different Quantization Mechanisms in Single-Electron Pumps Driven by Surface Acoustic Waves
Autorzy:
Utko, P.
Gloos, K.
Bindslev Hansen, J.
Sørensen, C.
Lindelof, P.
Powiązania:
https://bibliotekanauki.pl/articles/2047039.pdf
Data publikacji:
2006-09
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
73.23.-b
72.50.+b
73.21.La
Opis:
We have studied the acoustoelectric current in single-electron pumps driven by surface acoustic waves. We have found that in certain parameter ranges two different sets of quantized steps dominate the acoustoelectric current versus gate-voltage characteristics. In some cases, both types of quantized steps appear simultaneously though at different current values, as if they were superposed on each other. This could indicate two independent quantization mechanisms for the acoustoelectric current.
Źródło:
Acta Physica Polonica A; 2006, 110, 3; 403-408
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Electric Conductivity of Carbon Nanoparticles Stimulated by Electric Field
Autorzy:
Markowski, D.
Kempiński, W.
Kempiński, M.
Trybuła, Z.
Kaszyńska, K.
Śliwińska-Bartkowiak, M.
Powiązania:
https://bibliotekanauki.pl/articles/1535906.pdf
Data publikacji:
2010-09
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
73.22.Pr
73.21.La
73.23.Hk
73.25.+i
73.63.-b
73.23.-b
Opis:
Host-guest interactions can be the unique method of spin manipulation in nanoscale. Strong changes in spin localization are generated when potential barriers between nanographitic units of activated carbon fibers are modified by interaction with adsorbed molecules. Stronger modifications occur when dipolar guest molecules are stimulated with external electric field. We report experimental results which show the influence of electric field on the spin localization in activated carbon fibers.
Źródło:
Acta Physica Polonica A; 2010, 118, 3; 457-458
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Electron Transport in Magnetic Quantum Point Contacts
Autorzy:
Pietsch, T.
Egle, S.
Espy, C.
Strigl, F.
Scheer, E.
Powiązania:
https://bibliotekanauki.pl/articles/1490057.pdf
Data publikacji:
2012-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
73.23.-b
72.25.-b
73.63.-b
Opis:
In recent years, the fabrication of novel building blocks for quantum computation- and spintronics devices gained significant attention. The ultimate goal in terms of miniaturization is the creation of single-atom functional elements. Practically, quantum point contacts are frequently used as model systems to study the fundamental electronic transport properties of such mesoscopic systems. A quantum point contact is characterised by a narrow constriction coupling two larger electron reservoirs. In the absence of a magnetic field, the conductance of these quantum point contacts is quantised in multiples of $2 e^2//h$, the so-called conductance quantum $(G_0)$. However, in the presence of magnetic fields the increased spin-degeneracy often gives rise to a deviation from the idealized behaviour and therefore leads to a change in the characteristic conductance of the quantum point contact. Herein, we illustrate the complex magnetotransport characteristics in quantum point contacts and magnetic heterojunctions. The theoretical framework and experimental concepts are discussed briefly together with the experimental results as well as potential applications.
Źródło:
Acta Physica Polonica A; 2012, 121, 2; 401-409
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:
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
Wyświetlanie 1-15 z 67

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