Low density approach to the Kondo-lattice model

We propose a new approach to the (ferromagnetic) Kondo-lattice model in the low density region, where the model is thought to give a reasonable frame work for manganites with perovskite structure exhibiting the "colossal magnetoresistance" -effect. Results for the temperature- dependent quasiparticle density of states are presented. Typical features can be interpreted in terms of elementary spin-exchange processes between itinerant conduction electrons and localized moments. The approach is exact in the zero bandwidth limit for all temperatures and at T=0 for arbitrary bandwidths, fulfills exact high-energy expansions and reproduces correctly second order perturbation theory in the exchange coupling.Comment: 11 pages, 7 figures, accepted by PR

Ferromagnetism within the periodic Anderson model: A new approximation scheme

We introduce a new approach to the periodic Anderson model (PAM) that allows a detailed investigation of the magnetic properties in the Kondo as well as the intermediate valence regime. Our method is based on an exact mapping of the PAM onto an effective medium strong-coupling Hubbard model. For the latter, the so-called spectral density approach (SDA) is rather well motivated since it is based on exact results in the strong coupling limit. Besides the T=0 phase diagram, magnetization curves and Curie temperatures are presented and discussed with help of temperature-dependent quasiparticle densities of state. In the intermediate valence regime, the hybridization gap plays a major role in determining the magnetic behaviour. Furthermore, our results indicate that ferromagnetism in this parameter regime is not induced by an effective spin-spin interaction between the localized levels mediated by conduction electrons as it is the case in the Kondo regime. The magnetic ordering is rather a single band effect within an effective f-band.Comment: 13 pages, 16 figures, Phys. Stat. Sol. in pres

Time Delay Induced Death in Coupled Limit Cycle Oscillators

We investigate the dynamical behaviour of two limit cycle oscillators that interact with each other via time delayed coupling and find that time delay can lead to amplitude death of the oscillators even if they have the same frequency. We demonstrate that this novel regime of amplitude "death" also exists for large collections of coupled identical oscillators and provide quantitative measures of this death region in the parameter space of coupling strength and time delay. Its implication for certain biological and physical applications is also pointed out.Comment: 4 aps formatted revtex pages; 3 figures; to be published in Phys. Rev. Let

The Stability of Strange Star Crusts and Strangelets

We construct strangelets, taking into account electrostatic effects, including Debye screening, and arbitrary surface tension sigma of the interface between vacuum and quark matter. We find that there is a critical surface tension sigma_crit below which large strangelets are unstable to fragmentation and below which quark star surfaces will fragment into a crystalline crust made of charged strangelets immersed in an electron gas. We derive a model-independent relationship between sigma_crit and two parameters that characterize any quark matter equation of state. For reasonable model equations of state, we find sigma_crit typically of order a few MeV/fm^2. If sigma <= sigma_crit, the size-distribution of strangelets in cosmic rays could feature a peak corresponding to the stable strangelets that we construct.Comment: 11 pages, LaTe

Spin Response and Neutrino Emissivity of Dense Neutron Matter

We study the spin response of cold dense neutron matter in the limit of zero momentum transfer, and show that the frequency dependence of the long-wavelength spin response is well constrained by sum-rules and the asymptotic behavior of the two-particle response at high frequency. The sum-rules are calculated using Auxiliary Field Diffusion Monte Carlo technique and the high frequency two-particle response is calculated for several nucleon-nucleon potentials. At nuclear saturation density, the sum-rules suggest that the strength of the spin response peaks at $\omega \simeq$ 40--60 MeV, decays rapidly for $\omega \geq$100 MeV, and has a sizable strength below 40 MeV. This strength at relatively low energy may lead to enhanced neutrino production rates in dense neutron-rich matter at temperatures of relevance to core-collapse supernova.Comment: 11 pages, 4 figures. Minor change. Published versio

Synthesis and photoluminescence studies on catalytically grown Zn1 – xMnxS nanowires

Zn1 – xMnxS alloy nanowires with composition (x = 0.0, 0.1 and 0.3) have been successfully synthesized by a simple thermal evaporation on the silicon substrate coated with a gold film of 2 nm thickness. X-ray powder diffraction measurements reveal that as synthesized products were hexagonal wurtzite structure. The as grown nanowires have been investigated by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Energy Dispersive Analysis of X-rays (EDAX) and photoluminescence studies. The results reveal that the as grown nanowires consist of Zn, Mn, and S material and diameter ranging from 70 - 150 nm with lengths up to several tens of micrometers. Photoluminescence studies on Zn1 – xMnxS exhibited peaks at 600 and 613 nm for x = 0.1 and 0.3 respectively. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/1053