Electronic Correlations within Fermionic Lattice Models

We investigate two-site electronic correlations within generalized Hubbard model, which incorporates the conventional Hubbard model (parameters: $t$ (hopping between nearest neighbours), $U$ (Coulomb repulsion (attraction)) supplemented by the intersite Coulomb interactions (parameters: $J^{(1)}$(parallel spins), $J^{(2)}$ (antiparellel spins)) and the hopping of the intrasite Cooper pairs (parameter: $V$). As a first step we find the eigenvalues $E_{\alpha}$ and eigenvectors $|E_{\alpha}>$ of the dimer and we represent each partial Hamiltonian $E_{\alpha} |E_{\alpha} > < E_{\alpha} |$ ($\alpha =1,2,..,16$) in the second quantization with the use of the Hubbard and spin operators. Each dimer energy level possesses its own Hamiltonian describing different two-site interactions which can be active only in the case when the level will be occupied by the electrons. A typical feature is the appearence of two generalized $t-J$ interactions ascribed to two different energy levels which do not vanish even for $$ and their coupling constants are equal to $\pm t$ in this case. The competition between ferromagnetism, antiferromagnetism and superconductivity (intrasite and intersite pairings) is also a typical feature of the model because it persists in the case $U=J^{(1)}=J^{(2)}=V=0$ and $t\neq 0$. The same types of the electronic, competitive interactions are scattered between different energy levels and therefore their thermodynamical activities are dependent on the occupation of these levels. It qualitatively explains the origin of the phase diagram of the model. We consider also a real lattice as a set of interacting dimers to show that the competition between magnetism and superconductivity seems to be universal for fermonic lattice models.Comment: 12 page

Hubbard Hamiltonian in the dimer representation. Large U limit

We formulate the Hubbard model for the simple cubic lattice in the representation of interacting dimers applying the exact solution of the dimer problem. By eliminating from the considerations unoccupied dimer energy levels in the large U limit (it is the only assumption) we analytically derive the Hubbard Hamiltonian for the dimer (analogous to the well-known t-J model), as well as, the Hubbard Hamiltonian for the crystal as a whole by means of the projection technique. Using this approach we can better visualize the complexity of the model, so deeply hidden in its original form. The resulting Hamiltonian is a mixture of many multiple ferromagnetic, antiferromagnetic and more exotic interactions competing one with another. The interplay between different competitive interactions has a decisive influence on the resulting thermodynamic properties of the model, depending on temperature, model parameters and assumed average number of electrons per lattice site. A simplified form of the derived Hamiltonian can be obtained using additionally Taylor expansion with respect to $x=\frac{t}{U}$ (t-hopping integral between nearest neighbours, U-Coulomb repulsion). As an example, we present the expansion including all terms proportional to t and to $\frac{t^2}U$ and we reproduce the exact form of the Hubbard Hamiltonian in the limit $U\to \infty$. The nonperturbative approach, presented in this paper, can, in principle, be applied to clusters of any size, as well as, to another types of model Hamiltonians.Comment: 26 pages, 1 figure, LaTeX; added reference

The dynamics of the non-heme iron in bacterial reaction centers from Rhodobacter sphaeroides

AbstractWe investigate the dynamical properties of the non-heme iron (NHFe) in His-tagged photosynthetic bacterial reaction centers (RCs) isolated from Rhodobacter (Rb.) sphaeroides. Mössbauer spectroscopy and nuclear inelastic scattering of synchrotron radiation (NIS) were applied to monitor the arrangement and flexibility of the NHFe binding site. In His-tagged RCs, NHFe was stabilized only in a high spin ferrous state. Its hyperfine parameters (IS=1.06±0.01mm/s and QS=2.12±0.01mm/s), and Debye temperature (θD0~167K) are comparable to those detected for the high spin state of NHFe in non-His-tagged RCs. For the first time, pure vibrational modes characteristic of NHFe in a high spin ferrous state are revealed. The vibrational density of states (DOS) shows some maxima between 22 and 33meV, 33 and 42meV, and 53 and 60meV and a very sharp one at 44.5meV. In addition, we observe a large contribution of vibrational modes at low energies. This iron atom is directly connected to the protein matrix via all its ligands, and it is therefore extremely sensitive to the collective motions of the RC protein core. A comparison of the DOS spectra of His-tagged and non-His-tagged RCs from Rb. sphaeroides shows that in the latter case the spectrum was overlapped by the vibrations of the heme iron of residual cytochrome c2, and a low spin state of NHFe in addition to its high spin one. This enabled us to pin-point vibrations characteristic for the low spin state of NHFe

Infekcyjne zapalenie wsierdzia zastawki aortalnej i płucnej u 20-letniego pacjenta z dwujamową prawą komorą i ubytkiem przegrody międzykomorowej

W niniejszej pracy przedstawiono przypadek 20-letniego pacjenta z dwujamową prawą komorą i z ubytkiem przegrody międzykomorowej (VSD), powikłanym infekcyjnym zapaleniem wsierdzia. U chorego zastosowano terapię przeciwbakteryjną i przeciwgrzybiczą, a następnie zakwalifikowano go do leczenia operacyjnego. Korekcja obejmowała zamknięcie ubytku przegrody międzykomorowej łatą goreteksową, resekcję drogi odpływu prawej komory oraz wszczepienie homogaftu aortalnego i płucnego. W pracy przedstawiono problemy związane z diagnostyką, farmakoterapią oraz leczeniem operacyjnym infekcyjnego zapalenia wsierdzia. (Folia Cardiol. 2004; 11: 681-686

Infekcyjne zapalenie wsierdzia zastawki aortalnej i płucnej u 20-letniego pacjenta z dwujamową prawą komorą i ubytkiem przegrody międzykomorowej

W niniejszej pracy przedstawiono przypadek 20-letniego pacjenta z dwujamową prawą komorą i z ubytkiem przegrody międzykomorowej (VSD), powikłanym infekcyjnym zapaleniem wsierdzia. U chorego zastosowano terapię przeciwbakteryjną i przeciwgrzybiczą, a następnie zakwalifikowano go do leczenia operacyjnego. Korekcja obejmowała zamknięcie ubytku przegrody międzykomorowej łatą goreteksową, resekcję drogi odpływu prawej komory oraz wszczepienie homogaftu aortalnego i płucnego. W pracy przedstawiono problemy związane z diagnostyką, farmakoterapią oraz leczeniem operacyjnym infekcyjnego zapalenia wsierdzia. (Folia Cardiol. 2004; 11: 681-686

Indirect Exchange in Magnetic Semiconductors. III. Effect of Alloying

We apply the extended s-f model to magnetic pseudobinary alloys. We calculate the Curie temperature and magnetic moment in the paramagnetic state as functions of concentration x. The calculated quantities are in good agreement with the quantities experimentally measured for Eu$\text{}_{1-x}$Gd$\text{}_{x}$S, Eu$\text{}_{1-x}$Gd$\text{}_{x}$Se, Re$\text{}_{x}$Gd$\text{}_{1-x}$Al$\text{}_{2}$ (Re = Dy, Ho, Er, La, Lu, Y), Gd(Al$\text{}_{1-x}$Me$\text{}_{x}$)$\text{}_{2}$ (Me = Cu, Ag, Pd, In, Sn),..

Chemical Potential Evidence for Phase Transitions in Magnetic and Superconducting Compounds and Alloys

We announce that all phase transitions (induced by temperature or concentration) including structural ones and transitions between metastable or "exotic" states can be detected by the chemical potential critical behaviour, as well as, from the average occupation numbers of the electronic system (critical electron redistribution)