Bogdan R. Bułka

Fano and Kondo Resonance in Electronic Current through Nanodevices

Electronic transport through a quantum dot strongly coupled to electrodes is studied within a model with two conduction channels. It is shown that multiple scattering and interference of transmitted waves through both channels lead to Fano resonance associated with Kondo resonance. Interference effects are also pronouncedly seen in transport through the Aharonov-Bohm ring with the Kondo dot, where the current characteristics continuously evolve with the magnetic flux.

Current and power spectrum in a magnetic tunnel device with an atomic-size spacer

Current and its noise in a ferromagnetic double tunnel barrier device with a small spacer particle were studied in the framework of the sequential tunneling approach. Analytical formulas were derived for electron tunneling through the spacer particle containing only a single energy level. It was shown that Coulomb interactions of electrons with a different spin orientation lead to an increase of the tunnel magnetoresistance. Interactions can also be responsible for the negative differential resistance. A current noise study showed which relaxation processes can enhance or reduce fluctuations leading either to a super-Poissonian or a sub-Poissonian shot noise.

Spin effects in ferromagnetic single-electron transistors

Electron tunneling in ferromagnetic single-electron transistors is considered theoretically in the sequential tunneling regime. A formalism is developed, which operates in a two-dimensional space of states, instead of one-dimensional space used in the spinless case. It is shown that spin fluctuations can be significantly larger than the charge fluctuations. The influence of discrete energy spectrum of a small central electrode on tunneling current, charge and spin accumulation, charge and spin fluctuations, and on tunnel magnetoresistance is analyzed in detail. Two different scales are found in the bias dependence of the basic transport characteristics; the shorter one originates from the discrete energy spectrum and the longer one from discrete charging of the central electrode. The features due to discrete spectrum and discrete charging disappear at high temperatures.

SUPERCONDUCTIVITY IN THE HUBBARD MODEL WITH PAIR HOPPING

The phase diagrams and superconducting properties of the extended Hubbard model with pair hopping interaction, i.e. the Penson-Kolb-Hubbard model are studied. The analysis of the model is performed for d-dimensional hypercubic lattices, including d=1 and d=

Thermal entanglement in a triple quantum dot system

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SHOT NOISE IN FERROMAGNETIC SINGLE-ELECTRON TUNNELING DEVICES

, by means of the (broken symmetry) Hartree-Fock approximations and, for d=

Fano versus Kondo resonances in a multilevel "semiopen" quantum dot.

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Current rectification in molecular junctions produced by local potential fields

, by the slave-boson mean-field method. For d=1, at half-filling the phase diagram is shown to consist of nine different phases including two superconducting states with center-of-mass momentum q=0 and q=Q (

Linear and nonlinear Stark effect in a triangular molecule

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Electrical transport properties of polyacetylene tetrachloroferrate - [CH(FeCl4)y]x]

-pairing), site and bond-located antiferromagnetic and charge-density wave states as well as three mixed phases with coexisting site and bond orderings. The stability range of the bond-type orderings is shrank with increasing lattice dimensionality d and for d=