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

From Termination Dependent Chemical Sensitivity of Spin Orientation in All-bcc Fe/Co Magnetic Superlattices toward the Concept of an Artificial Surface of a Ferromagnet

AbstractAdsorption of gases on the surface of all-bcc (Fe/Co)N superlattices drives the in-plane, 90° magnetization rotation of the bulk-like Fe(110) supporting ferromagnet. Both experimental and theoretical results prove that terminating the surface of (Fe/Co)N superlattices either by Co or by Fe switches “ON” or “OFF” the spin orientation sensitivity to adsorption. Results indicate that purely surface limited adsorption processes strongly modify the magnetic anisotropy of the entire (Fe/Co)N superlattice, which acts as a kind of “artificial” surface of the bulky Fe(110) ferromagnet. Such an artificial magnetic surface anisotropy concept not only enhances the surface contribution in classical surface–bulk competition but also provides its additional chemical sensitivity.Abstract Adsorption of gases on the surface of all-bcc (Fe/Co)N superlattices drives the in-plane, 90° magnetization rotation of the bulk-like Fe(110) supporting ferromagnet. Both experimental and theoretical results prove that terminating the surface of (Fe/Co)N superlattices either by Co or by Fe switches “ON” or “OFF” the spin orientation sensitivity to adsorption. Results indicate that purely surface limited adsorption processes strongly modify the magnetic anisotropy of the entire (Fe/Co)N superlattice, which acts as a kind of “artificial” surface of the bulky Fe(110) ferromagnet. Such an artificial magnetic surface anisotropy concept not only enhances the surface contribution in classical surface–bulk competition but also provides its additional chemical sensitivity

Understanding the Growth of Electrodeposited PtNi Nanoparticle Films Using Correlated In Situ Liquid Cell Transmission Electron Microscopy and Synchrotron Radiation

Electrodeposition is a versatile method for synthesizing nanostructured films, but controlling the morphology of films containing two or more elements requires a detailed understanding of the deposition process. We used liquid cell transmission electron microscopy to follow the electrodeposition of PtNi nanoparticle films on a carbon electrode during cyclic voltammetry. These in situ observations show that the film thickness increases with each cycle, and by the fourth cycle, branched and porous structures could be deposited. Synchrotron studies using in situ transmission X-ray microscopy further revealed that Ni was deposited in the oxide phase. Ex situ studies of bulk electrodeposited PtNi nanoparticle films indicated the number of cycles and the scanning rate were the most influential parameters, resulting in a different thickness, a different homogeneity, a different nanoparticle size, and a different surface structure, while the precursor concentration did not have a significant influence. By varying the potential range, we were able to obtain films with different elemental compositions

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

Aluminous phyllosilicates promote exceptional nanoscale preservation of biogeochemical heterogeneities in Archaean siliciclastic microbial mats

Exceptional preservation of biogeochemical complexity in the Precambrian is largely limited to cherts, phosphates and shales; however, ancient fossils, including microbial mats and microbially induced sedimentary structures, also occur, more rarely, in poorly sorted, coarse-grained siliciclastics. The precise micromechanics by which exceptional retention of organic microbial traces occur within such rocks over billion-year geological timescales remain poorly understood. Herein, we explore the micro–nano-scale characteristics of microbial mats preserved in ~2.9 billion-year-old sandstones from the Mosquito Creek Formation (Pilbara, Australia) using a suite of advanced spatially correlated microscopy and geochemistry techniques. We demonstrate that sedimentary horizons rich in K–Al-phyllosilicates exhibit exceptional and unexpected preservation of biogeochemical complexity despite the age and metamorphic grade of the sequence. We propose that authigenic phyllosilicates intercalated with microbial kerogen at the nanoscale promote the preservation of nanoscopic domains of poorly ordered amorphous and turbostratic carbonaceous materials through pressure compensation associated with the kaolinite–illite transition during burial diagenesis and metamorphism, impeding the maturation of organic materials. Elucidating organic preservation in coarse-grained siliciclastics opens new avenues for biosignature searches both in ancient Earth sequences and on Mars, where similar phyllosilicate-bearing sandstones have been collected by the Mars 2020 Perseverance rover for near-future sample return