Weak Pseudogap Behavior in the Underdoped Cuprate Superconductors

We report on an exact solution of the nearly antiferromagnetic Fermi liquid spin fermion model in the limit \pi T << \omega_{sf}, which demonstrates that the broad high energy features found in ARPES measurements of the spectral density of the underdoped cuprate superconductors are determined by strong antiferromagnetic (AF) correlations and precursor effects of an SDW state. We show that the onset temperature, T^{cr}, of weak pseudo-gap (pseudoscaling) behavior is determined by the strength, \xi, of the AF correlations, and obtain the generic changes in low frequency magnetic behavior seen in NMR experiments with \xi(T^{cr}) \approx 2, confirming the Barzykin and Pines crossover criterion.Comment: REVTEX, 4 pages, 3 EPS figure

Theory of the Optical Conductivity in the Cuprate Superconductors

We present a study of the normal state optical conductivity in the cuprate superconductors using the nearly antiferromagnetic Fermi liquid (NAFL) description of the magnetic interaction between their planar quasiparticles. We find that the highly anisotropic scattering rate in different regions of the Brillouin zone, both as a function of frequency and temperature, a benchmark of NAFL theory, leads to an average relaxation rate of the Marginal Fermi Liquid form for overdoped and optimally doped systems, as well as for underdoped systems at high temperatures. We carry out numerical calculations of the optical conductivity for several compounds for which the input spin fluctuation parameters are known. Our results, which are in agreement with experiment on both overdoped and optimally doped systems, show that NAFL theory explains the anomalous optical behavior found in these cuprate superconductors.Comment: REVTEX file, 8 PostScript figure

Optical Conductivity and Hall Coefficient in High-Tc Superconductors: Significant Role of Current Vertex Corrections

We study AC conductivities in high-Tc cuprates, which offer us significant information to reveal the true electronic ground states. Based on the fluctuation-exchange (FLEX) approximation, current vertex corrections (CVC's) are correctly taken into account to satisfy the conservation laws. We find the significant role of the CVC's on the optical Hall conductivity in the presence of strong antiferromagnetic (AF) fluctuations. This fact leads to the failure of the relaxation time approximation (RTA). As a result, experimental highly unusual behaviors, (i) prominent frequency and temperature dependences of the optical Hall coefficient, and (ii) simple Drude form of the optical Hall andge for wide range of frequencies, are satisfactorily reproduced. In conclusion, both DC and AC transport phenomena in (slightly under-doped) high-Tc cuprates can be explained comprehensively in terms of nearly AF Fermi liquid, if one take the CVC's into account.Comment: 5 page

Zeolit kao faktor poboljšanja nekih proizvodnih osobina kod krava muzara

Milk yield and milk chemical composition are largely affected by diet quality. Natural zeolite has been successfully used in livestock production as a feed supplement for some types and categories of domestic animals. This experiment was conducted over a period of 15 months involving Domestic Spotted dairy cattle. The test animals were assigned to three groups, each receiving different levels of supplemental zeolite. The control group comprised cows that received no zeolite supplement. Experimental groups I and II were fed compound feeds supplemented with 4% and 2% zeolite, respectively. The production traits studied included the following milk performance traits: whole lactation length, milk and fat yields over whole lactations, milk and fat yields over standard lactations. The results obtained suggest that zeolite supplementation affects some production traits, depending on the zeolite level present in livestock feed.Kontrolna grupa krava imala je prosečno trajanje laktacije od 312 dana, sa varijacijama od 300 do 360 dana. Ova grupa se po dobijenim rezultatima nalazi između ostale dve grupe krava. Statističke razlike u trajanju celih laktacija među grupama su značajne (P (lt) 0,05). Najniža proizvodnja mleka u celim laktacijama zabeležena je kod krava Kgrupe (6395,20 kg), viša kod krava I-O grupe (6714,13 kg) i najviša kod krava II-O grupe (6934,13 kg) koja je dobijala 2% zeolita preko krmnih smeša. Statističke razlike u proizvodnji mleka u celim laktacijama među grupama su vrlo značajne (P (lt) 0,01). Najmanja prosečna produkcija mleka zabeležena je kod krava K-grupe (6342,33 kg). Znatno veća proizvodnja je bila kod krava koje su dobijale zeolit. Krave I-O grupe dobijale su 4% zeolita i postigle su prosečnu mlečnost od 6690.86 kg. Krave II-O grupe dobijale su 2% zeolita i postigle su najveću prosečnu mlečnost od 6711.80 kg. Krave II-O grupe imale su najveću prosečnu proizvodnju mleka u standardnim laktacijama i najniži koeficijent varijacije među grupama. Statističke razlike u proizvodnji mleka u standardnim laktacijama među grupama su vrlo značajne (P (lt) 0,01). Krave K-grupe imale su najmanju prosečnu priozvodnju mlečne masti u mleku, a krave II-O grupe najveću. Statističke razlike u količini mlečne masti u celim laktacijama među grupama su vrlo značajne (P (lt) 0,01). Takođe su vrlo značajne (P (lt) 0,01) i statističke razlike među grupama u količini mlečne masti u standardnim laktacijama

Magnetoresistance in Heavily Underdoped YBa_2Cu_3O_{6+x}: Antiferromagnetic Correlations and Normal-State Transport

We report on a contrasting behavior of the in-plane and out-of-plane magnetoresistance (MR) in heavily underdoped antiferromagnetic (AF) YBa_2Cu_3O_{6+x} (x<0.37). The out-of-plane MR (I//c) is positive over most of the temperature range and shows a sharp increase, by about two orders of magnitude, upon cooling through the Neel temperature T_N. A contribution associated with the AF correlations is found to dominate the out-of-plane MR behavior for H//c from far above T_N, pointing to the key role of spin fluctuations in the out-of-plane transport. In contrast, the transverse in-plane MR (I//a(b);H//c) appears to be small and smooth through T_N, implying that the development of the AF order has little effect on the in-plane resistivity.Comment: 4 pages, 5 figures, accepted for publication in Phys.Rev.Let

Impurity-induced spin polarization and NMR line broadening in underdoped cuprates

We present a theory of magnetic (S=1) Ni and nonmagnetic Zn impurities in underdoped cuprates. Both types of impurities are shown to induce S=1/2 moments on Cu sites in the proximity of the impurity, a process which is intimately related to the spin gap phenomenon in cuprates. Below a characteristic Kondo temperature, the Ni spin is partially screened by the Cu moments, resulting in an effective impurity spin S=1/2. We further analyze the Ruderman-Kittel-Kasiya-Yosida-type response of planar Cu spins to a polarization of the effective impurity moments and derive expressions for the corresponding ^{17}O NMR line broadening. The peculiar aspects of recent experimental NMR data can be traced back to different spatial characteristics of Ni and Zn moments as well as to an inherent temperature dependence of local antiferromagnetic correlations.Comment: PRB B1 01June9

Uticaj kukuruzne silaže u obroku krava muzara na sadržaj kalcijuma, fosfora i magnezijuma u krvnom serumu

The amount of calcium, phosphorus and magnesium in milking cows, blood was tested and it is one of indicators that cows were fed with these substances. The average amount of calcium, phosphorus and magnesium in blood of milking cows was tested and it is one of indicators that cows were fed with these substances. The average amount of calcium in tested cows, blood is 2.82 mmol/l, the average amount of phosphorus is 1.66 and the average amount of magnesium is 1.29 mmol/l. Cows, were fed by corn silage, alfalfa hay, along with concentrate of standard mineral composition.Ispitivan je sadržaj kalcijuma, fosfora i magnezijuma u krvnom serumu krava, kao jednog od indikatora obezbeđenosti životinja ovim elementima. Prosečan sadržaj kalcijuma u krvnom serumu ispitivanih krava iznosio je 2.82 mmol/l, fosfora 1.66 mmol/l i magnezijuma 1.29 mmol/l seruma. Krave su hranjene kukuuznom silažom, senom lucerke i krmnom smešom za krave muzare

Efikasnost primene preparata na bazi zeolita u obrocima jagnjadi u tovu

The paper presents the results of a research on the impact of products based on natural zeolite on the production results of fattening lambs. The experiment involved two groups of lambs (the control - C and experimental - E groups), each consisting of 15 heads, for a period of 90 days. The meal was made from sheep milk, feed mixtures for fattening lambs and meadow hay. The test group lambs, unlike the ones from the control group, were given mixtures based on natural zeolite. Min-a-Zel S mixture (in the form of 25% composite) was fed to lambs from birth till their 14th day of life, directly into the mouth, once a day (before the morning feed), in the amount of 10 ml. Min-a-Zel Plus was given to them from their 15th day of life, together with the feed mixture (0.5%). Feeding was at will. The average weight of lambs at the end of the experiment, in accordance with the sequence of treatments (C:E) was 24.40:26.94 kg (P (lt) 0.01). Daily weight gain of lambs, during the experiment, was 229:256 g and in the experimental group it was by 27g or 11.79% higher (P (lt) 0.01). The test group lambs had a better utilization of dry matter, protein and energy, which justifies the use of products based on natural zeolite in fattening lambs.U radu su prikazani rezultati istraživanja o uticaju preparata na bazi prirodnog zeolita na proizvodne rezultate jagnjadi u tovu. Ogled je izveden na dve grupe jagnjadi (kontrolna - K i ogledna - O), po 20 jagnjadi u trajanju od 90 dana. Obrok se sastojao od ovčjeg mleka, krmne smeše za tov jagnjadi i livadskog sena. Iskorišćavanje preparata na bazi zeolita (Min-a-Zel S i Min-a-Zel Plus) pozitivno je uticalo na prirast, iskorišćavanje i efikasnost iskorišćavanja suve materije, proteina i energije. Prosečan dnevni prirast bio je veći kod jagnjadi ogledne grupe za 27 g ili 11,79 posto. Utrošak suve materije za kilogram prirasta u istoj gupi, bio je manji za 12,21 posto a proteina i energije za 10,58 posto. Manja učestalost javljanja proliva bila je kod jagnjadi ogledne gupe

Microscopic theory of weak pseudogap behavior in the underdoped cuprate superconductors I: General theory and quasiparticle properties

We derive in detail a novel solution of the spin fermion model which is valid in the quasi-static limit pi T<<omega_sf, found in the intermediate (pseudoscaling) regime of the magnetic phase diagram of cuprate superconductors, and use it to obtain results for the temperature and doping dependence of the single particle spectral density, the electron-spin fluctuation vertex function, and the low frequency dynamical spin susceptibility. The resulting strong anisotropy of the spectral density and the vertex function lead to the qualitatively different behavior of_hot_ (around k=(pi,0)) and_cold_ (around k=(pi/2,pi/2)) quasiparticles seen in ARPES experiments. We find that the broad high energy features found in ARPES measurements of the spectral density of the underdoped cuprate superconductors are determined by strong antiferromagnetic (AF) correlations and incoherent precursor effects of an SDW state, with reduced renormalized effective coupling constant. The electron spin-fluctuation vertex function, i.e. the effective interaction of low energy quasiparticles and spin degrees of freedom, is found to be strongly anisotropic and enhanced for hot quasiparticles; the corresponding charge-fluctuation vertex is considerably diminished. We thus demonstrate that, once established, strong AF correlations act to reduce substantially the effective electron-phonon coupling constant in cuprate superconductors.Comment: REVTEX with EPS figures, uses multicol.sty, epsfig,sty, psfig.st

A regularisation approach to causality theory for C^{1,1}Lorentzian metrics

We show that many standard results of Lorentzian causality theory remain valid if the regularity of the metric is reduced to C^{1,1}. Our approach is based on regularisations of the metric adapted to the causal structure