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Dynamical mean-field theory for spin-dependent electron transport in spin-valve devices
Get PDFWe present a combination of density functional theory and dynamical mean-field theory (DMFT) for comput-ing the electron transmission through two-terminal nanoscale devices. The method is then applied to metallic junctions presenting alternating Cu and Co layers, which exhibit spin-dependent charge transport and the giant magnetoresistance (GMR) effect. The calculations show that the coherent transmission through the 3d states is greatly suppressed by electron correlations. This is mainly due to the finite lifetime induced by the electron-electron interaction and is directly related to the imaginary part of the computed many-body DMFT self-energy. At the Fermi energy, where in accordance with the Fermi-liquid behavior the imaginary part of the self-energy vanishes, the suppression of the transmission is entirely due to the shifts of the energy spectrum induced by electron correlations. Based on our results, we finally suggest that the GMR measured in Cu/Co heterostructures for electrons with energies about 1 eV above the Fermi energy is a manifestation of dynamical correlation effects
Emerging Fermi liquids from regulated quantum electron stars
Get PDFWe construct a fully quantum zero-temperature electron star in a soft-wall regulated anti-de-Sitter Einstein-Maxwell-Dirac theory that is thermodynamically stable compared to the Reissner-Nordström black hole. The soft wall only acts on the effective mass of the fermionic degrees of freedom, and allows for a controlled fully backreacted solution. The star is holographically dual to an RG flow where a gapped Fermi liquid starts to emerge from a UV CFT, but decouples again once the effective energy scale becomes lower than the gap of the fermionic degrees of freedom. The RG flow then returns to a non-trivial strongly coupled relativistic fixed point with a holographic dual. Our regulated quantum electron star is thus the fermionic analogue of the Horowitz-Roberts-Gubser-Rocha AdS-to-AdS domain wall solution for the holographic superconductor
Nature of Dynamic Friction in a Humid Hydrophobic Nanocontact
Get PDFThe physics of dynamic friction on water molecule contaminated surfaces is still poorly understood. In line with the growing interest in hydrophobic contact for industrial applications, this paper focuses on friction mechanisms in such interfaces. As a commonly used material, contact with graphite is considered in a twin-fold approach based on experimental investigations using the circular mode atomic force microscopy technique combined with molecular dynamic simulations. We demonstrate that an intuitive paradigm, which asserts that water molecules are squeezed out of a hydrophobic contact, should be refined. As a consequence, we introduce a mechanism considering a droplet produced within the sliding nanocontact by the accumulation of water adsorbed on the substrate. Then we show that a full slip regime of the droplet sliding on the hydrophobic substrate explains the experimental tribological behavior
Replicas, averaging and factorization in the IIB matrix model
Get PDFWe study the partition functions of multiple replicas (copies) of D-brane configurations in the type IIB (IKKT) matrix model. We consider the quenched regime, where small fluctuations of the matrices are superimposed onto the slow (quenched) dynamics of the background, so the partition function is an ensemble average over the background. Interacting D-branes always factorize in a simple way. On the other hand, the non-interacting BPS configurations may or may not factorize depending on the number of replicas, and their factorization mechanism is more involved as the corresponding saddle-point solutions (half-wormholes) break the replica symmetry. We argue that the simple factorization mechanism of interacting branes is actually more interesting as it carries the specific signatures of quantum gravity, which are absent from disordered field theories like the SYK model
Patched patterns and emergence of chaotic interfaces in arrays of nonlocally coupled excitable systems
No full textWe disclose a new class of patterns, called patched patterns, in arrays of non-locally coupled excitable units with attractive and repulsive interactions. The self-organization process involves the formation of two types of patches, majority and minority ones, characterized by uniform average spiking frequencies. Patched patterns may be temporally periodic, quasiperiodic, or chaotic, whereby chaotic patterns may further develop interfaces comprised of units with average frequencies in between those of majority and minority patches. Using chaos and bifurcation theory, we demonstrate that chaos typically emerges via a torus breakup and identify the secondary bifurcation that gives rise to chaotic interfaces. It is shown that the maximal Lyapunov exponent of chaotic patched patterns does not decay, but rather converges to a finite value with system size. Patched patterns with a smaller wavenumber may exhibit diffusive motion of chaotic interfaces, similar to that of the incoherent part of chimeras
Collective Activity Bursting in a Population of Excitable Units Adaptively Coupled to a Pool of Resources
Get PDFWe study the collective dynamics in a population of excitable units (neurons) adaptively interacting with a pool of resources. The resource pool is influenced by the average activity of the population, whereas the feedback from the resources to the population is comprised of components acting homogeneously or inhomogeneously on individual units of the population. Moreover, the resource pool dynamics is assumed to be slow and has an oscillatory degree of freedom. We show that the feedback loop between the population and the resources can give rise to collective activity bursting in the population. To explain the mechanisms behind this emergent phenomenon, we combine the Ott-Antonsen reduction for the collective dynamics of the population and singular perturbation theory to obtain a reduced system describing the interaction between the population mean field and the resources
Simulation study of random sequential deposition of binary mixtures of lattice animals on a three-dimensional cubic lattice
Get PDFRandom sequential adsorption of mixtures of objects of various shapes on a three-dimensional (3D) cubic lattice is studied numerically by means of Monte Carlo simulations. Depositing objects are 'lattice animals', made of a certain number of nearest neighbor sites on a lattice. We analyzed binary mixtures composed of shapes of equal size, n = 3, 4, 5. We concentrate here on the influence of geometrical properties of the shapes on the jamming coverage theta (J) and on the temporal evolution of the density theta(t). The approach of the coverage theta(t) to the jamming limit theta (J) is found to be exponential, theta (J) - theta(t) similar to exp(-t/sigma), both for the mixtures and their components. The values of the relaxation time sigma are determined by the number of different orientations m that lattice animals can take when placed on a cubic lattice. The value of the relaxation time sigma for a mixture is approximately twice the relaxation time for the pure component shape with a larger number m of possible orientations. Depending on the local geometry of the objects making the mixture, the jamming coverage of a mixture theta (J) can be either greater than both single-component jamming coverages or it can be in between these values. The first case is the most common, while in the second case, the jamming density of the mixture is very close to the higher jamming density for the pure component shapes. For a majority of the investigated mixtures, a component with a larger number of orientations m has a larger value of the fractional jamming density
Dva elementa pojma alternativnog investicionog fonda u srpskom pravu
Get PDFLegal regulations related to investment funds in the Republic of Serbia were reformed in 2019. In order to harmonize Serbian law with the European Union directives two new laws that regulate investment funds were enacted – one regulating open investment funds and the other alternative investment funds. This paper analyzes the current legal notion of the alternative investment fund, but the emphasis is placed on the two key elements of the said notion in a wider sense – the notion of the investment fund and the notion of the investor. The concepts are examined in the light of the above mentioned legislation, and the specific legal implications arising from them are described. In conclusion, the author proposes a lege ferenda solution with the ultimate objective of developing the market for alternative investment funds in the Republic of Serbia
Mott domain walls: A (strongly) non-Fermi liquid state of matter
No full textMost Mott systems display a low-temperature phase coexistence region around the metal-insulator transition. The domain walls separating the respective phases have very recently been observed displaying unusual properties both in simulations and in experiments. First, they often cover a significant volume fraction, thus cannot be neglected. Second, they resemble neither a typical metal nor a standard insulator, displaying unfamiliar temperature dependence of (local) transport properties. Here we take a closer look at such domain wall matter by examining an appropriate unstable solution of the Hubbard model. We show that transport in this regime is dominated by the emergence of “resilient quasiparticles” displaying strong non-Fermi liquid features, reflecting the quantum-critical fluctuations in the vicinity of the Mott point
Percolation and jamming properties in particle shape-controlled seeded growth model
Get PDFWe consider the percolation model with nucleation and simultaneous growth of multiple finite clusters, taking the initial seed concentration rho as a tunable parameter. Growing objects expand with constant speed, filling the nodes of the triangular lattice according to rules that control their shape. As growing objects of predefined shape, we consider needle-like objects and "wrapping" objects whose size is gradually increased by wrapping the walks in several different ways, making triangles, rhombuses, and hexagons. Growing random walk chains are also analyzed as an example of objects whose shape is formed randomly during the growth. We compare the percolation properties and jamming densities of the systems of various growing shapes for a wide range of initial seed densities rho < 0.5. To gain a basic insight into the structure of the jammed states, we consider the size distribution of deposited growing objects. The presence of the most numerous and the largest growing objects is recorded for the system in the jamming state. Our results suggest that at sufficiently low seed densities rho, the way of the object growth has a substantial influence on the percolation threshold. This influence weakens with increasing rho and ceases near the value of the site percolation threshold for monomers on the triangular lattice, rho(p)* = 0.5