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3 Materials Science Poland

3 2004

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Formation of the Kondo resonance in two-atom molecular systems for various interaction limits

100%

Babiaczyk W. I. , Bułka B. R.

tom Vol. 22, No. 4

529--536

We consider a two-atom molecule connected to ferromagnetic leads, in the Kondo transport regime. To investigate the Kondo effect in the system, we use the slave-boson mean field approximation (SBMFA) techniques. Results are obtained for both the strong interaction limit, in which an infinite Coulomb repulsion U1-2 between atoms is assumed, and a finite U1-2 case. The transport is considered in the T = 0 and V = 0 equilibrium limit.

Effects of Coulomb interactions in electron transport through short molecular chains

100%

Kostyrko T. , Bułka B. R.

tom Vol. 22, No. 4

497--506

Charge transport properties of short molecular chains connected to electrodes are studied using the non-equilibrium Green function method. The chains are described using a single-orbital Hubbard model. In the weak interaction range and low-temperature limit, the current flowing through the system was analysed within the Hartree-Fock approximation (HFA). It was found that for a weak coupling between the molecule and the leads I-V characteristics can be represented as a sequence of plateaus, alternating with regions of a finite slope. This finite slope in the I-V characteristics is related to the self-consistent molecular level being pinned down to the Fermi levels of the electrodes over a finite voltage regions. It is also related to a continuous change in the charge state of the molecule. In the strong repulsion limit, the HFA method is no longer credible and we resort to decoupling the equations of motion (EOM) for the Green functions of the chains, in order to treat all intrachain correlations and hopping exactly but to neglect some correlations between the molecule and the leads. A comparison of the results obtained with these two approaches for the same parameters allows us to make general observations concerning the role of correlations in transport through molecular junctions.

Spin-dependent transport through a double dot system

80%

Lipiński S. , Bułka B. R. , Krychowski D.

tom Vol. 22, No. 4

513--522

The coherent transport through a set of two capacitively coupled quantum dots placed in a magnetic field and coupled to ferromagnetic electrodes is considered in the limit of infinite intra- and interdot interactions. The densities of states are calculated in an approximation that favours separate fluctuations of spin, orbital isospin, and simultaneous fluctuations of both of them. Apart from the Kondo peak, satellite many-body peaks are also found in the densities of states. Their positions and weights depend on the magnetic field and polarization of electrodes. This is reflected in the spin dependence of conductance remarkably varying for the voltage bias corresponding to the peak positions.