Wigner-Mott scaling of transport near the two-dimensional metal-insulator transition

Electron-electron scattering usually dominates the transport in strongly correlated materials. It typically leads to pronounced resistivity maxima in the incoherent regime around the coherence temperature $T^{*}$, reflecting the tendency of carriers to undergo Mott localization following the demise of the Fermi liquid. This behavior is best pronounced in the vicinity of interaction-driven (Mott-like) metal-insulator transitions, where the $T^{*}$ decreases, while the resistivity maximum $\rho_{max}$ increases. Here we show that, in this regime, the entire family of resistivity curves displays a characteristic scaling behavior $\rho(T)/\rho_{max}\approx F(T/T_{max}),$ while the $\rho_{max}$ and $T_{max}\sim T^{*}$ assume a powerlaw dependence on the quasi-particle effective mass $m^{*}$. Remarkably, precisely such trends are found from an appropriate scaling analysis of experimental data obtained from diluted two-dimensional electron gases in zero magnetic fields. Our analysis provides strong evidence that inelastic electron-electron scattering -- and not disorder effects -- dominates finite temperature transport in these systems, validating the Wigner-Mott picture of the two-dimensional metal-insulator transition.Comment: 7 page

Electromagnetically induced coherent effects in laser excited Raman resonances in rubidium vapor

Ova teza predstavlja teorijsku analizu različitih koherentnih efekata u laserski pobuđivanim Ramanovim rezonancama u sistemima sa više nivoa u atomima rubidijuma. Proučavani koherentni efekti uključuju elektromagnet- ski indukovanu transparenciju (EIT), elektromagnetski indukovanu apsor- pciju (EIA) i Štarkovski brzi adijabatski prelaz (engl. SCRAP). EIT i EIA rezonance su ispitivane u Hanle konfiguraciji u vakuumskim ćelijama para rubidijuma detaljnim teorijskim modeliranjem odgovarajućih realističnih sistema. Razvijeni numerički model je pokazao odlično slaganje sa odgovarajućim eksperimentalnim rezultatima i omogućio njihovo uspešno objašnjenje. Dodatno, postojeća teorija SCRAP-a u sistemima sa dva i tri nivoa je proširena na slučajeve dva i tri nivoa sa proizvoljnim brojem degenerisanih podnivoa. Vakuumske ćelije para alkalnih metala su često korišćene u kvantnoj optici prilikom istraživanja koherentnih pojava u interakciji lasera sa atomima. Jedna od osnovnih osobina laserskog zračenja koja utiče na koherentnu evoluciju atoma je njegov lokalni intenzitet. Uopšteno gledano, koherentni efekti zavise nelinearno od intenziteta lasera. Neposredna posledica toga je da profil intenziteta laserskog snopa mora uticati na koherentnu atomsku evoluciju. Štaviše, različiti delovi jednog istog laserskog snopa trebalo bi da različito doprinose koherentnim efektima...This thesis presents the theoretical analysis of various coherent effects in laser excited Raman resonances in multilevel systems in rubidium atoms. Studied coherent effects include electromagnetically induced transparency (EIT), electromagnetically induced absorption (EIA) and Stark-chirped rapid adiabatic passage (SCRAP). EIT and EIA resonances are examined in Hanle configuration in rubidium vapor vacuum cells using detailed theoretical modeling of related realistic systems. Developed numerical model provided excellent agreement with actual experimental results and their successful explanation. Furthermore, existent theory of SCRAP in two- and three-level systems is extended to the case of two and three degenerate-level manifolds with arbitrary number of substates. Vacuum alkali-metal vapor cells are commonly used in quantum optics for research of coherent phenomena in laser-atom interaction. One of basic properties of laser radiation that in uences the coherent atomic evolution is its local intensity. Generally, the coherent effects depend non-linearly on the laser intensity. Immediate consequence is that the laser beam intensity profile must affect the atomic coherent evolution. Moreover, different parts of the same laser beam should have different contribution to the coherent effects..

Quality of silage of mixed sunchoke and lucerne forage

The paper presents the chemical composition, nutritional and usable value of sunchoke (Helianthus tuberosus L.) and the possibility of using it for animal nutrition in fresh and canned form. Tests show that sunchoke cut in mid-June contains about 9.43% of crude protein, 2.49% of crude fat, 19.93% of crude cellulose, 50.50% of NFE (nitrogen-free extractives) and 17.65% of ash in the dry matter. Although lucerne biomass had a more favorable chemical composition (18.13% crude protein, 6.72% crude fat, 25.24% crude cellulose, 39.35% BEM and 10.56% ash), the benefits of sunchoke are in the more successful growing in less favorable natural, primarily soil conditions, the more suitable it is for ensiling and the longer it stays on one planted plot. Since it is predominantly an energy (carbohydrate) nutrient, the possibility of ensiling the green biomass of sunchoke in a mixture with 25, 50 and 75% fresh lucerne (25% dry matter) was investigated. The obtained results show that with the increase of lucerne participation, the nutritional value of silage increases, but the quality decreases. In addition to its role in conventional feed production, sunchoke can be an important plant in the system of organic production, production for industrial processing and for extensive cultivation in hunting grounds

Transmission through correlated Cun_nCoCun_n heterostructures

The effects of local electronic interactions and finite temperatures upon the transmission across the Cu$_4$CoCu$_4$ metallic heterostructure are studied in a combined density functional and dynamical mean field theory. It is shown that, as the electronic correlations are taken into account via a local but dynamic self-energy, the total transmission at the Fermi level gets reduced (predominantly in the minority spin channel), whereby the spin polarization of the transmission increases. The latter is due to a more significant $d$-electrons contribution, as compared to the non-correlated case in which the transport is dominated by $s$ and $p$ electrons.Comment: 29 pages, 7 figures, submited to PR

Emergence of classical behavior from the quantum spin

Classical Hamiltonian system of a point moving on a sphere of fixed radius is shown to emerge from the constrained evolution of quantum spin. The constrained quantum evolution corresponds to an appropriate coarse-graining of the quantum states into equivalence classes, and forces the equivalence classes to evolve as single units representing the classical states. The coarse-grained quantum spin with the constrained evolution in the limit of the large spin becomes indistinguishable from the classical system

On the superconducting nature of the Bi-II phase of elemental Bismuth

The superconductivity in the Bi-II phase of elemental Bismuth (transition temperature $T_{\rm c}\simeq3.92$ K at pressure $p\simeq 2.80$ GPa) was studied experimentally by means of the muon-spin rotation as well as theoretically by using the Eliashberg theory in combination with Density Functional Theory calculations. Experiments reveal that Bi-II is a type-I superconductor with a zero temperature value of the thermodynamic critical field $B_{\rm c}(0)\simeq31.97$~mT. The Eliashberg theory approach provides a good agreement with the experimental $T_{\rm c}$ and the temperature evolution of $B_{\rm c}$. The estimated value for the retardation (coupling) parameter $k_{\rm B}T_{\rm c}/\omega_{\rm ln} \approx 0.07$ ($\omega_{\rm ln}$ is the logarithmically averaged phonon frequency) suggests that Bi-II is an intermediately-coupled superconductor.Comment: 6 pages, 2 figure