Gutzwiller variational theory for the Hubbard model with attractive interaction

We investigate the electronic and superconducting properties of a negative-U Hubbard model. For this purpose we evaluate a recently introduced variational theory based on Gutzwiller-correlated BCS wave functions. We find significant differences between our approach and standard BCS theory, especially for the superconducting gap. For small values of $|U|$, we derive analytical expressions for the order parameter and the superconducting gap which we compare to exact results from perturbation theory.Comment: 10 pages, 2 figure

Asymmetry between the electron- and hole-doped Mott transition in the periodic Anderson model

We study the doping driven Mott metal-insulator transition (MIT) in the periodic Anderson model set in the Mott-Hubbard regime. A striking asymmetry for electron or hole driven transitions is found. The electron doped MIT at larger U is similar to the one found in the single band Hubbard model, with a first order character due to coexistence of solutions. The hole doped MIT, in contrast, is second order and can be described as the delocalization of Zhang-Rice singlets.Comment: 18 pages, 19 figure

Quasiparticle spectral weights of Gutzwiller-projected high T_c superconductors

We analyze the electronic Green's functions in the superconducting ground state of the t-J model using Gutzwiller-projected wave functions, and compare them to the conventional BCS form. Some of the properties of the BCS state are preserved by the projection: the total spectral weight is continuous around the quasiparticle node and approximately constant along the Fermi surface. On the other hand, the overall spectral weight is reduced by the projection with a momentum-dependent renormalization, and the projection produces electron-hole asymmetry in renormalization of the electron and hole spectral weights. The latter asymmetry leads to the bending of the effective Fermi surface which we define as the locus of equal electron and hole spectral weight.Comment: 6 pages, 5 figures; x-labels on Figs. 1 and 2 corrected, footnote on particle number corrected, references adde

Detecting Change in the Urban Road Environment Along a Route Based on Traffic Sign and Crossroad Data

Occurrences of traffic signs that belong to certain sign categories and occurrences of crossroads of various topologies are utilized in detecting change in the urban road environment that moves past an ego-car. Three urban environment types, namely downtown, residential and industrial/commercial areas, are considered in the study and changes between these are to be detected. In the preparatory phase, the ego-car is used for traffic sign and crossroads data collection. In the application phase, the ego-car hosts an advanced driver assistance system (ADAS) that captures and analyzes images of the road environment and computes the required input data to the proposed road environment detection (RoED) subsystem. A statistical inference method relying on the minimum description length (MDL) principle was applied to the change detection problem at hand. The above occurrences along a route are seen as a realization of an inhomogeneous marked Poisson process. Page-Hinkley change detectors tuned to empirical data were set to work to detect change in the urban road environment. The process and the quality of the change detection are demonstrated via examples from three urban settlements in Hungary. Document type: Part of book or chapter of boo

Seasonal dynamics, age structure and reproduction of four Carabus species (Coleoptera: Carabidae) living in forested landscapes in Hungary

Seasonal dynamics and reproductive phenological parameters of four Carabus species (C. convexus, C. coriaceus, C. germarii and C. hortensis) common in Hungary were studied by pitfall trapping and dissection. Beetles were collected in an abandoned apple orchard and in the bordering oak forest near Budapest (Central Hungary), in 1988–1991. The sex ratio was male-dominated, but this was significant only for C. coriaceus. The catch of C. germarii adults showed relatively short activity period with unimodal curve, but activity was longer and bimodal for the other three species. Adults of C. germarii and C. hortensis reached sexual maturity in July, and C. coriaceus adults were matured by early August. We did not find newly hatched individuals of C. coriaceus or C. germarii. The reproductive period was approximately four weeks in C. hortensis, five weeks for C. coriaceus and six weeks for C. germarii. Reproduction lasted much longer, for about four months, in C. convexus. The mean number of ripe eggs per female were 4.2 in C. convexus, 5.4 in C. coriaceus, 6.6 in C. germarii, and 7.4 in C. hortensis. The maximum number found was about three times the average in all studied species. The reproductive allocation (ratio of egg complement mass/body mass) was lowest in C. germarii (0.133) and highest in C. hortensis (0.196), and did not depend on body size. There was minimal overlap of the activity and reproductive periods of the four species

SU(N) quantum spin models: A variational wavefunction study

The study of SU(N) quantum spin models is relevant to a variety of physical systems including ultracold atoms in optical lattices, and also leads to insights into novel quantum phases and phase transitions of SU(2) spin models. We use Gutzwiller projected fermionic variational wavefunctions to explore the phase diagram and correlation functions of SU(N) spin models in the self-conjugate representation, with Heisenberg bilinear and biquadratic interactions. In 1D, the variational phase diagram of the SU(4) spin chain is constructed by examining instabilities of the Gutzwiller projected free fermion ground state to various broken symmetries, and it agrees well with exact results.The spin and dimer correlations of the Gutzwiller projected free fermion state with N flavors of fermions are also in good agreement with exact and 1/N calculations for the critical points of SU(N) spin chains. In 2D, the variational phase diagram on the square lattice is obtained by studying instabilities of the Gutzwiller projected pi-flux state. The variational ground state of the pure Heisenberg model is found to exhibit long range Neel order for N=2,4 and spin Peierls order for N > 4. For N=4 and 6, biquadratic interactions lead to a complex phase diagram which includes an extended valence bond crystal in both cases, as well as a stable pi-flux phase for N=6. The spin correlations of the projected pi-flux state at N=4 are in good agreement with 1/N calculations. We find that this state also shows strongly enhanced dimer correlations, in qualitative accord with the large-N results. We compare our results with a recent QMC study of the SU(4) Heisenberg model.Comment: 22 pages, 7 figs, added references to arxiv versio

Electrical field induced shift of the Mott Metal-Insulator transition in thin films

The ground state properties of a paramagnetic Mott insulator are investigated in the presence of an external electrical field using the inhomogeneous Gutzwiller approximation for a single band Hubbard model in a slab geometry. The metal insulator transition is shifted towards higher Hubbard repulsions by applying an electric field perpendicular to the slab. The spatial distribution of site dependent quasiparticle weight shows that the quasiparticle weight is maximum in few layers beneath the surface. Moreover only at higher Hubbard repulsion, larger than the bulk critical U, the electric field will be totally screened only for centeral cites. Our results show that by presence of an electric field perpendicular to a thin film made of a strongly correlated material, states near the surface will remain metallic while the bulk becomes insulating after some critical U. In contrast, in the absence of the electric field the surface becomes insulating before the bulk

Phase diagram of the one-dimensional extended Hubbard model with attractive and/or repulsive interactions at quarter filling

We study the phase diagram of the one dimensional (1D) $U-V$ model at quarter filling in the most general case where the on-site and first-neighbour interactions $U$ and $V$ can be both attractive and repulsive. The results have been obtained using exact diagonalization of small clusters and variational techniques, as well as exact results in various limits. We have analyzed four properties of the groundstate: i)~whether it is insulating or metallic; \hbox{ii)~whether} it is homogenous or phase separated; iii)~whether it has a spin gap; iv)~whether it has dominant superconducting fluctuations. With eight phases, the resulting phase diagram is unexpectedly rich. The four phases not found in the weak coupling limit are: i) an insulating phase when $U$ and $V$ are large enough; ii) a region of phase separation when $V$ is attractive; iii) another region of phase separation when $V$ is large enough and $U$ small; iv) a region with dominant superconducting fluctuations when $V$ is intermediate and $U$ small. The actual nature of this last phase, which has pairs but no spin gap, is not fully clear yet.Comment: 24 pages, RevTeX (4 postscript figures attached to the end

Random walks near Rokhsar-Kivelson points

There is a class of quantum Hamiltonians known as Rokhsar-Kivelson(RK)-Hamiltonians for which static ground state properties can be obtained by evaluating thermal expectation values for classical models. The ground state of an RK-Hamiltonian is known explicitly, and its dynamical properties can be obtained by performing a classical Monte Carlo simulation. We discuss the details of a Diffusion Monte Carlo method that is a good tool for studying statics and dynamics of perturbed RK-Hamiltonians without time discretization errors. As a general result we point out that the relation between the quantum dynamics and classical Monte Carlo simulations for RK-Hamiltonians follows from the known fact that the imaginary-time evolution operator that describes optimal importance sampling, in which the exact ground state is used as guiding function, is Markovian. Thus quantum dynamics can be studied by a classical Monte Carlo simulation for any Hamiltonian that is free of the sign problem provided its ground state is known explicitly.Comment: 12 pages, 9 figures, RevTe

In vitro sensitivity of Monilinia laxa to fungicides approved in integrated and organic production systems

The aim of this study was to test the in vitro sensitivity of two isolates of Monilinia laxa to fungicides approved in integrated andorganic production systems. In vitro efficacy of 7 fungicides (Champion 50 WP, Kocide 2000, Nordox 75 WG, Olajos rézkén, Kumulus S,Rézkén, Rézoxiklorid) and another 6 fungicides (Score 25 EC, Efuzin 500 SC, Systane, Folicur Solo, Zato Plusz, Rovral) approved in organicand integrated production systems, respectively, were tested against brown rot of sour cherry. The three isolates showed differences insensitivity to fungicides. Fungicides (with active ingredients of copper and sulphur) applied in organic production showed relatively highpercent growth capacity of M. laxa. Rézkén and Kocide 2000 showed the highest and Kumilus S the lowest efficacy against brown rot.Fungicides applied in integrated production showed relatively low percent growth capacity of M. laxa. Score 25 EC showed the lowest andRovral and Folicur solso the highest efficacy against M. laxa