Theoretical Condensed Matter Physics

The influence of the Rashba spin-orbit coupling (RSOC) on the two-dimensional (2D) electrons and holes in a strong perpendicular magnetic field leads to different results for the Landau quantization in different spin projections. In the Landau gauge the unidimensional wave vector describing the free motion in one in-plane direction is the same for both spin projections, whereas the numbers of Landau quantization levels are different. For an electron in an s-type conduction band they differ by one, as was established earlier by Rashba (1960 Fiz. Tverd. Tela 2 1224), whereas for heavy holes in a p-type valence band influenced by the 2D symmetry of the layer they differ by three. The shifts and the rearrangements of the 2D hole Landau quantization levels on the energy scale are much larger in comparison with the case of conduction electron Landau levels. This is due to the strong influence of the magnetic field on the RSOC parameter. At sufficiently large values of this parameter the shifts and rearrangements are comparable with the hole cyclotron energy. There are two lowest spin-split Landau levels for electrons as well as four lowest ones for holes in the case of small RSOC parameters. They give rise to eight lowest energy bands of the 2D magnetoexcitons, as well as of the band-to-band quantum transitions. It is shown that three of them are dipole-active, three are quadrupole-active and two are forbidden. The optical orientation under the influence of circularly polarized light leads to optical alignment of the magnetoexcitons with different orbital momentum projections in the direction of the external magnetic field.

The intra-Landau-level excitations of the two-dimensional electron-hole liquid are characterized by two branches of the energy spectrum. The acoustical plasmon branch with in-phase oscillations of electrons and holes has a linear dispersion law in the range of small wavevectors, with a velocity which does not depend on the magnetic field strength, and monotonically increases with saturation at higher values of the wavevectors. The optical plasmon branch with oscillations of electrons and holes in opposite phases has a quadratic dependence in the range of long wavelength, a weak roton-type behaviour at the intermediary values of the wavevectors and monotonically increases with saturation similar to the case of the acoustical branch. The influence of the supplementary in-plane electric field leads to the drift of the charged particles in the crossed electric and magnetic fields and to the energy spectrum as in the reference frame, where the e-h system is moving with the drift velocity. A perturbation theory using the Green function method is developed on the basis of a small parameter v 2 (1 -v 2 ), where v 2 is the filling factor and (1 -v 2 ) displays the phase space filling effect.

z axis. The Dirac nodes were recently observed by ARPES. We have made extensive transport measurements of Cd 3 As 2 . Because of possible Cd vacancy disorder in the very large unit cell (160 atoms), the SdH oscillations reveal a quantum lifetime that is moderately damped. Despite the disorder, the observed resistivity ρ in some crystals displays a RRR of 1000. At 4 K, the residual resistivity is anomalously low (30 nΩ cm). We estimate that the mobility exceeds 10 6 cm 2 V -1 s -1 . A magnetic field H strongly increases ρ by factors of 100 to 1000 at 10 Tesla. This giant magnetoresistance (MR) is highly anisotropic. The MR is largest when H is perpendicular to the axis (110) and minimal when H is ∥(110). We will discuss possible origins of this unusual anisotropic giant MR. We also discuss the possibility of detecting an enhanced longitudinal MR associated with charge pumping between Weyl nodes (the chiral anomaly).

We report on an inelastic (Raman) light scattering study of the local structure of amorphous GeTe films. A detailed analysis of the temperature-reduced Raman spectra has shown that appreciable structural changes occur as a function of temperature. These changes involve modifications of atomic arrangements such as to facilitate the rapid amorphous-to-crystal transformation, which is the major advantage of phase-change materials used in optical data storage media. A particular structural model, supported by polarization analysis, is proposed being compatible with the experimental data as regards both the structure of a-GeTe and the crystallization transition. The remarkable difference between the Raman spectrum of the crystal and the glass can thus naturally be accounted for.

MF Theory proposes a radical departure from conventional physics by postulating that all fundamental interactions emerge from structured energy-space rather than being imposed through gauge symmetries. In this document, we provide a rigorous mathematical treatment, including derivations of field equations, consistency proofs, and experimental predictions.

Oxygen adsorptions on δ-Pu (100) and ( ) surfaces have been studied at both non-spin-polarized and spin-polarized levels using the generalized gradient approximation of density functional theory (GGA-DFT) with Perdew and Wang (PW) functionals. The center position of the (100) surface is found to be the most favorable site with chemisorption energies of 7.386eV and 7.080eV at the two levels of theory. The distances of the oxygen adatom from the Pu surface are found to be 0.92A and 1.02A, respectively. For the (111) surface non-spin-polarized calculations, the center position is also the preferred site with a chemisorption energy of 7.070eV and the distance of the adatom being 1.31A, but for spin-polarized calculations the bridge and the center sites are found to be basically degenerate, the difference in chemisorption energies being only 0.021eV. In general, due to the adsorption of oxygen, plutonium 5f orbitals are pushed further below the Fermi energy, compared to the bare plutonium layers. The work function, in general, increases due to oxygen adsorption on plutonium surfaces. actinides for which experimental work is relatively difficult to perform due to material problems and toxicity. As is known, the actinides are characterized by a gradual filling of the 5f-electron shell with the degree of localization increasing with the atomic number Z along the last series of the periodic table. The open shell of the 5f electrons determines the magnetic and solid state properties of the actinide elements and their compounds and

We employ the Green's function technique to investigate the vacancy-induced quasi-localized magnetic moment formation in monolayer graphene starting with the Dirac Hamiltonian, which focuses on the πorbitals only, involving the nearest neighbor(NN)(t) and moderate second neighbor(SN)(t′ < t/3) hopping integrals. The vacancy defect is modeled by the addition of the on-site perturbation potential to the Hamiltonian. We find that, when (t′/t) << 1, the vacancy induced π-state at the zero of energy(zero-mode state(ZMS)) does not inhabit the minority sub-lattice due to the strong scalar potential induced by the vacancy(the ZMSs get lodged in the majority sub-lattice) whereas, when (t′/t) is increased, the ZMS is somewhat suppressed. This shows that, not only the shift of the Fermi energy away from the linearly-dispersive Dirac points, the issue of this topological localization is also hinged on the ratio (t′/t). Furthermore, when a vacancy is present, the three sp 2hybridized σ states of each of the three nearest-neighbor carbon atoms, forming a carbon triangle surrounding the vacancy, are close to the Fermi energy (E F ). The Hund's coupling between these σ electrons and the remaining electron which occupies the π state spin polarizes the π state leading to local moment formation close to E F . Since the system at the Fermi level has low electronic density, there is poor screening of such magnetic moments. This may lead to a high Curie temperature for such vacancy-induced moments.

A study of magnetism in the novel 2D spin system Ni 5 (TeO 3 ) 4 Br 2 , featuring a frustrated triangular geometry, is presented. We combine magnetization, heat capacity and high-field electron spin resonance measurements to investigate a long-range magnetic ordering below T N = 29 K. Additional peculiar behaviour, most likely related to the spin system, is observed below T = 14 K.

We studied the band structures of Gallium compounds (GaX, X=P,As,Sb) under III-V semiconductor compounds in this paper. Our calculations were performed using a generalized gradient approximation (GGA) and the modified Becke-Johnson potential (mBJ) within the Wien2k code. We have compared our results calculated by GGA and mBJ and we found that the mBJ approximation gives better results in semiconductor compounds compared to GGA. We also obtained the results on the band structures with the inclusion of spin-orbit interaction (SOI) on both approximations and also compared the results. We have found that the inclusion of SOI affects the band structures and the splitting of degenerate valence band occurs on high symmetry Γ-point. We have also measured the value of the splitting energy and our results are similar to the experimental value.

In zero magnetic field the superconductor Sr2RuO4 is believed to have a chiral spin triplet pairing state in which the gap function d-vector is aligned along the crystal c-axis. Using a phenomenological but orbital specific description of the spin dependent electron-electron attraction and a realistic quantitative account of the electronic structure in the normal state we analyze the orientation of the spin triplet Cooper pair d-vector in response to an external c-axis magnetic field. We show that for suitable values of the model parameters a c-axis field of only 20 mT is able to cause a reorientation phase transition of the d-vector from along c to the a -b plane, in agreement with recent experiments.

Single molecule scanning tunneling spectroscopy (STS), with dephasing due to elastic and inelastic scattering, is of some current interest. Motivated by this, we report an extended Hückel theory (EHT) based mean-field Non-equilibrium Green's function (NEGF) transport model with electron-phonon scattering treated within the self-consistent Born approximation (SCBA). Furthermore, a procedure based on EHT basis set modification is described. We use this model to study the effect of the temperature dependent dephasing, due to low lying modes in far-infrared range for which hω ≪ k B T , on the resonant conduction through highest occupied molecular orbital (HOMO) level of a phenyl dithiol molecule sandwiched between two fcc-Au(111) contacts. Furthermore, we propose to include dephasing in room temperature molecular resonant conduction calculations.

Florida -We apply molecular dynamics and molecular static methods to calculate the effect of tensile misfit dislocation on Ni adatom diffusion for Ni/Cu(111) system and compare the results with those calculated previously for Cu adatom on the Cu/Ni(111) system [1] which has compressive dislocation. Our Ni/Cu(111) substrate model system consists of 5 layers of Ni on top of a 7-layer Cu(111) slab which after energy minimization displays an isolated misfit dislocation buried at the Cu-Ni interface, causing the Ni film to be under tensile stress. In contrast to the isotropic trajectory that emerges on a defect-free surface, in this tensile stressed system we find that presence of the defect under the surface strongly affects the adatom trajectory, introducing anisotropy in atomic diffusion similar to compressive system, but with the difference: tensile misfit dislocation enhances diffusion in the direction perpendicular to the misfit dislocation line and decreases it in the direction parallel to it, whereas compressive dislocation induces the opposite behavior. We present the calculated energy barriers for the adatom and compare them with adatom diffusion on defect -free and on the surface containing compressive dislocation. [1] M. Aminpour, O. Trushin, and T. S. Rahman, Physical Review B, 84, 035455 (2011).

The computational paradigm represented by Cellular Neural/nonlinear Networks (CNN) and the CNN Universal Machine (CNN-UM) as a Cellular Wave Computer, gives new perspectives for computational physics. Many numerical problems and simulations can be elegantly addressed on this fully parallelized and analogic architecture. Here we study the possibility of performing stochastic simulations on this chip. First a realistic random number generator is implemented on the CNN-UM, and then as an example the two-dimensional Ising model is studied by Monte Carlo type simulations. The results obtained on an experimental version of the CNN-UM with 128 × 128 cells are in good agreement with the results obtained on digital computers. Computational time measurements suggests that the developing trend of the CNN-UM chips -increasing the lattice size and the number of local logic memories -will assure an important advantage for the CNN-UM in the near future.

Matrix product state methods are known to be efficient for computing ground states of local, gapped Hamiltonians, particularly in one dimension. We introduce the multi-targeted density matrix renormalization group method that acts on a bundled matrix product state, holding many excitations. The use of a block or banded Lanczos algorithm allows for the simultaneous, variational optimization of the bundle of excitations. The method is demonstrated on a Heisenberg model and other cases of interest. A large of number of excitations can be obtained at a small bond dimension with highly reliable local observables throughout the chain.

Plateaus can be observed in the zero-temperature magnetization curve of quantum spin systems at rational values of the magnetization. In one dimension, the appearance of a plateau is controlled by a quantization condition for the magnetization which involves the length of the local spin and the volume of a translational unit cell of the ground state. We discuss examples of geometrically frustrated quantum spin systems with large (in general unbounded) periodicities of spontaneous breaking of translational symmetry in the ground state. In two dimensions, we discuss the square, triangular and Kagomé lattices using exact diagonalization (ED) for up to N = 40 sites. For the spin-1/2 XXZ model on the triangular lattice we study the nature and stability region of a plateau at one third of the saturation magnetization. The Kagomé lattice gives rise to particularly rich behaviour with several plateaus in the magnetization curve and a jump due to local magnon excitations just below saturation.

Macroscale model & Devices (B) (chair: C. Visone) Materials for Energy (E) (chair: S. Fabbrici) Spintronics, multiferroics and voltage control of magnetism (A) (chair C. Rinaldi) Fontcuberta (I) Sepehri-Amin (I) Non destructive tests (chiar: A. Tamburrino) Reboud (I) Recording & Sensors (B) (chair: F. Casoli) Garello (I)

It is widely believed that topological superconductivity, a hitherto elusive phase of quantum matter, can be achieved by inducing superconductivity in topological materials. In search of such topological superconductors, certain topological insulators (like, Bi 2 Se 3 ) were successfully turned into superconductors by metal-ion (Cu, Pd, Sr, Nb etc. ) intercalation. Superconductivity could be induced in topological materials through applying pressure as well. for example, a pressureinduced superconducting phase was found in the topological insulator Bi 2 Se 3 . However, in all such cases, no conclusive signature of topological superconductivity was found. In this review, we will discuss about another novel way of inducing superconductivity in a non-superconducting topological material -by creating a mesoscopic interface on the material with a non-superconducting, normal metallic tip where the mesoscopic interface becomes superconducting. Such a phase is now *

Single-crystal magnetic tunnel junctions employing bcc (100) Fe electrodes and MgO(100) insulating barrier are elaborated by molecular beam epitaxy. The magneto-transport properties are investigated in two extreme regimes. First, for extremely small MgO thickness, we show that the equilibrium tunnel transport in Fe/MgO/Fe systems leads to antiferromagnetic interactions, mediated by the tunnelling of the minority spin interfacial resonance state. Second, for large MgO barrier thickness, the tunnel transport validates specific spin filtering effects in terms of symmetry of the electronic Bloch function and symmetry-dependent wavefunction attenuation in the single-crystal barrier. Within this framework, we present giant tunnel magnetoresistive effects at room temperature (125-160%). Moreover, we illustrate that the interfacial chemical and electronic structure plays a crucial role in the spin filtering. We point out imperfect filtering effects and a strong implication of the minority surface state of Fe on the low voltage variation of tunnel magnetoresistance. The insertion of carbon impurities at the Fe/MgO interface changes radically the voltage response of the tunnel magnetoresistance and activates a resonant tunnelling mechanism via the interfacial resonance state.

In an ultrahigh mobility 2D electron gas, even a weak nonparabolicity of the electron dispersion, by violating Kohn's theorem, can have a drastic effect on dc magnetotransport under ac drive. In this paper, we study theoretically the manifestation of this effect in the dc response to the combined action of two driving ac-fields (bichromatic irradiation). Compared to the case of monochromatic irradiation, which is currently intensively studied both experimentally and theoretically, the presence of a second microwave source provides additional insight into the properties of an ac-driven 2D electron gas in weak magnetic field. In particular, we find that nonparabolicity, being the simplest cause for a violation of Kohn's theorem, gives rise to new qualitative effects specific to bichromatic irradiation. Namely, when the frequencies ω1 and ω2 are well away from the cyclotron frequency, ωc, our simple classical considerations demonstrate that the system becomes unstable with respect to fluctuations with frequency 1 2 (ω1 + ω2). The most favorable condition for this parametric instability is 1 2 (ω1 + ω2) ≃ ωc. The saturation level of this instability is also determined by the nonparabolicity. We also demonstrate that, as an additional effect of nonparabolicity, this parametric instability can manifest itself in the dc properties of the system. This happens when ω1, ω2 and ωc are related as 3 : 1 : 2, respectively. Even for weak detuning between ω1 and ω2, the effect of the bichromatic irradiation on the dc response in the presence of nonparabolicity can differ dramatically from the monochromatic case. In particular, we demonstrate that, beyond a critical intensity of the two fields, the equations of motion acquire multistable solutions. As a result, the diagonal dc-conductivity can assume several stable negative values at the same magnetic field.

In this work we describe the observations of structural transitions in ferronematics based on the thermotropic nematics 6CHBT (4-trans-4 -n-hexyl-cyclohexyl-isothiocyanato-benzene). The ferronematic droplets were observed in solutions of nematogenic 6CHBT dissolved in phenyl isocyanate and doped with fine magnetic particles. The phase diagram of the transitions from the isotropic phase to the nematic phase via a droplet state was found. Magneto-dielectric measurements of various structural transitions in this new system enabled us to estimate the type of anchoring of the nematic molecules on the magnetic particle surfaces in the droplets.

Coherent conversion between microwave and optical photons are among the key challenges for long-distance coherent quantum information transfer. Recent advances in magnon hybrid systems provide new opportunities for coherent manipulation of microwave-optical transduction, where a facile and phase-coherent detection of the magnon dynamics in the context of magnon-photon and magnon-magnon couplings is required. Here, we demonstrate the magnetically-induced transparency (MIT) effect in Y3Fe5O12(YIG)/Permalloy(Py) coupled bilayers. The measurement is achieved via stroboscopic detection of the coupled magnetization dynamics using a single wavelength that simultaneously probes the magneto-optical Kerr and Faraday effects of Py and YIG, respectively. Clear features of the MIT effect are evident from the deeply modulated ferromagnetic resonance of Py due to the perpendicular-standing-spin-wave of YIG. We develop a phenomenological model that nicely reproduces the observed MIT effect includin...

In this paper the re-enhancement results demonstrate the restoration process on MRI image and compare with various others techniques showing that the proposed calculation is more successful than a portion of the previous calculations. The proposed work uses restoration using adaptive approach and a hybridization of the previous approaches. The system works with two phase, the first system works to detect the noise intervals or degradation factor in image and the second phase is the removal of the degradation constants from the main effected regions and then try to restore the regions back to original form, the placement of noise in not known that is why the prediction of the noise is made adaptive so as to locally track the variation of the system and then restore the values using local values, as a result the edge values and the overall detail of the system remains preserved and the restored image does not deviate much from the original form when compared to the previous method out...

The possibility of quantum computation using non-Abelian anyons has been considered for over a decade. However the question of how to obtain and process information about what errors have occurred in order to negate their effects has not yet been considered. This is in stark contrast with quantum computation proposals for Abelian anyons, for which decoding algorithms have been tailor-made for many topological error-correcting codes and error models. Here we address this issue by considering the properties of non-Abelian error correction in general. We also choose a specific anyon model and error model to probe the problem in more detail. The anyon model is the charge submodel of D(S3). This shares many properties with important models such as the Fibonacci anyons, making our method applicable in general. The error model is a straightforward generalization of those used in the case of Abelian anyons for initial benchmarking of error correction methods. It is found that error correction is possible under a threshold value of 7% for the total probability of an error on each physical spin. This is remarkably comparable with the thresholds for Abelian models.

We investigate the evolution of multicritical points under pressure and magnetic field in a model described by two 5f bands (called α and β) that hybridize with a single itinerant conduction band. The interaction is given by the direct Coulomb and the Hund’s rule exchange terms. Three types of orderings are considered: two conventional spin density waves (SDWs) and an exotic SDW, i.e., with no magnetic moment formation. The conventional SDWs phases, are characterized by m f β &gt; m f α and m f α &gt; m f β , respectively, where m f α and m f β are the intraband staggered magnetizations. The exotic SDW, which has time reversal symmetry, is described by a purely imaginary order parameter. This phase is related to a band mixing given by the spin-flip part of the Hund’s rule exchange interaction. As result, without magnetic field, the phase diagrams of temperature (T) versus pressure (given by the variation of the bandwidth (W)) shows a sequence of phase transitions involving the three...

The Roth's two-pole approximation has been used by the present authors to investigate the role of d − p hybridization in the superconducting properties of an extended d−p Hubbard model. Superconductivity with singlet d x 2 −y 2-wave pairing is treated by following Beenen and Edwards formalism. In this work, the Coulomb interaction, the temperature and the superconductivity have been considered in the calculation of some relevant correlation functions present in the Roth's band shift. The behavior of the order parameter associated with temperature, hybridization, Coulomb interaction and the Roth's band shift effects on superconductivity are studied.

The competition among spin glass (SG), antiferromagnetism (AF) and local pairing superconductivity (PAIR) is studied in a two-sublattice fermionic Ising spin glass model with a local BCS pairing interaction in the presence of an applied magnetic transverse field Γ. In the present approach, spins in different sublattices interact with a Gaussian random coupling with an antiferromagnetic mean J0 and standard deviation J. The problem is formulated in the path integral formalism in which spin operators are represented by bilinear combinations of Grassmann variables. The saddle-point Grand Canonical potential is obtained within the static approximation and the replica symmetric ansatz. The results are analysed in phase diagrams in which the AF and the SG phases can occur for small g (g is the strength of the local superconductor coupling written in units of J), while the PAIR phase appears as unique solution for large g. However, there is a complex line transition separating the PAIR phase from the others. It is second order at high temperature that ends in a tricritical point. The quantum fluctuations affect deeply the transition lines and the tricritical point due to the presence of Γ.

We show that swallowtail catastrophe consisting of various-order non-Hermitian and Hermitian degeneracies naturally exists in the dynamics of two-mode driven-dissipative quadrature squeezing systems that break pseudo-Hermiciticy by judiciously engineered losses. We reveal that the swallowtail degeneracy structure enables nontrivial braiding of complex eigenvalues by looping around an exceptional line in the parameter space. Our findings provide a comprehensive understanding of the degeneracy geometry in two-mode driven-dissipative bosonic quadratic systems, opening pathways toward topologically nontrivial control of Gaussian states.

Systems not conserving the total momentum have both extrinsic, momentum-dissipating and intrinsic, momentum-conserving interactions. Inspired by a recently conjectured universal bound for thermoelectric diffusion constants in critical incoherent strongly coupled systems and relying on holographic analytical computations, we obtain bounds for the intrinsic contributions to the diffusion constants in different holographic systems featuring momentum dissipation. The model-independence of the intrinsic contributions suggests a possible universal relevance of the results within, and possibly beyond, the gauge/gravity context. We also study an incoherent limit where the complete diffusion constants confirm the shape of the expected bounds, although presenting non-universal coefficients.

Quantum physics, despite its observables being intrinsically of a probabilistic nature, does not have a quantum entropy assigned to them. We propose a quantum entropy that quantify the randomness of a pure quantum state via a conjugate pair of observables forming the quantum phase space. The entropy is dimensionless, it is a relativistic scalar, it is invariant under coordinate transformation of position and momentum that maintain conjugate properties, and under CPT transformations; and its minimum is positive due to the uncertainty principle. We expand the entropy to also include mixed states and show that the proposed entropy is always larger than von Neumann's entropy. We conjecture an entropy law whereby that entropy of a closed system never decreases, implying a time arrow for particles physics.

Institute for Theoretical Physics-The magnon Bose-Einstein condensation in Yttirum Iron Garnet films at room temperature was discovered by the Mnster experimental group (S.O. Demokritov) in 2006. Since the magnon condensate is coherent the natural question is whether the condensate is superfluid. Though the normal magnon density exceeds the condensate density in about 100 times, the velocity of the superfluid part is by 5-7 decimal orders larger than that of the normal part at the same field gradients. Thus, the spin current is dominated by the condensate, i.e. superfluid. A deeper obstacle is that the phase trapping is inconsistent with the free motion whose phase linearly depends on coordinate. The superfluidity can start only after submission of a finite (threshold) energy to the condensate by an external source. At energy close to threshold, the phase on long intervals of length remains close to the trapped values and changes by 2π on a comparatively short intervals (phase solitons). The superfluid velocity remains almost zero between solitons and acquires finite value inside solitons. At large energy the superfluidity of magnons becomes close to a uniform flow.

The Unruh effect posits that an accelerating observer perceives blackbody radiation where an inertial observer would detect none. Exploiting this phenomenon within plasma physics could unlock unprecedented control over plasma dynamics. This thesis presents a theoretical and experimental framework for using attosecond lasers to generate accelerated magnetic monopole-like excitations within a plasma, creating an intensely charged orb of light capable of defying gravitational forces. By meticulously manipulating the acceleration of these excitations, we aim to control the intensity of Unruh radiation, establishing feedback loops that influence both the plasma dynamics and the behavior of the monopole. Furthermore, we integrate the concept of force-free time-harmonic plasmoids, as explored in advanced plasma physics, into our framework. By utilizing these plasmoids, which are stable, self-contained plasma structures with force-free magnetic fields, we propose a novel method to sustain and manipulate magnetic monopole-like excitations. This integration allows for groundbreaking findings in plasma stability, energy transfer mechanisms, and could potentially lead to conditions conducive to fusion reactions at lower temperatures. This self-sustaining mechanism could revolutionize our understanding of plasma states and offers a potential pathway to achieving conditions akin to cold fusion. The work builds upon and extends the theories of Winterberg, Puthoff, Davis, White, and Pais, providing a comprehensive approach to harnessing quantum vacuum effects in practical applications.

York, NY 10031-Static packings of soft frictionless spheres are a simple model to understand the jamming transition in granular media, and have provided great insight. However, friction in granular media plays an important role in determining the structural and mechanical properties of jammed packings. In particular, the number and location of contacts near the Coulomb sliding threshold is strongly correlated with plastic rearrangements. To better understand friction, we numerically generate jammed packings of bumpy spherical particles as a function of the rms roughness of the particles without incorporating ad hoc single contact frictional forces between particles, i.e. frictional contacts in the Hertz-Mindlin (HM) model. The frictional interactions in the bumpy particle model emerge in a natural way via the interdigitation of bumps between contacting particles. We calculate the number of contacts, packing fraction, interparticle forces, eigenmodes of the dynamical matrix, and mechanical properties of jammed packings of bumpy particles and compare our results with those obtained using the HM model.

We consider the Anomalous Hall (AH) state induced by interactions in a three-orbital per unitcell model. To be specific we consider a model appropriate for the Copper-Oxide lattice to highlight the necessary conditions for time-reversal breaking states which are AH states and which are not. We compare the singularities of the wave-functions of the three-orbital model, which are related to the nonzero Berry curvature, and their variation with a change of gauge to those in the two-orbital model introduced in a seminal paper by Haldane. Explicit derivation using wave-functions rather than the more powerful abstract methods may provide additional physical understanding of the phenomena.

We present a method of calculation of the effective magnetic permeability of magnonic metamaterials containing periodically arranged magnetic inclusions of arbitrary shapes. The spectrum of spin wave modes confined in the inclusions is fully taken into account. Within the scope of the proposed method, we compare two approaches. The first approach is based on a simple semi-analytical theory that uses the numerically calculated susceptibility tensor of an isolated inclusion as input data. Within the second approach, micromagnetic packages with periodic boundary conditions (PBC) are used to calculate the susceptibility of a single 2D periodic array of such inclusions, with the whole 3D metamaterial consisting of a stack of such arrays. To calculate the susceptibility tensor of an isolated inclusion, we have implemented and compared two different methods: (a) a micromagnetic method, in which we have employed three different micromagnetic packages: the finite element package NMAG and the two finite differences packages OOMMF and MicroMagus; and (b) the modified dynamical matrix method. To illustrate the methodology, we have calculated the effective permeability of a metamaterial consisting of a stack of hexagonal arrays of magnetic nanodisks in a non-magnetic matrix. The range of geometrical parameters for which such a metamaterial is characterized by the negative permeability has been identified. The critical comparison of the different micromagnetic packages and the dynamical matrix method (based on the calculation of the susceptibility tensor of an isolated inclusion) has demonstrated that their results agree to within 3 %.

We study the thermodynamic efficiency of the Malkus-Lorenz waterwheel. For this purpose, we derive an exact analytical formula that describes the efficiency of this dissipative structure as a function of the phase space variables and the constant parameters of the dynamical system. We show that, generally, as the machine is progressively driven far from thermodynamic equilibrium by increasing its uptake of matter from the environment, it also tends to increase its efficiency. However, sudden drops in the efficiency are found at critical bifurcation points leading to chaotic dynamics. We relate these discontinuous crises in the efficiency to a reduction of the attractor's average value projected along the phase space dimensions that contribute to the rate of entropy generation in the system. In this manner, we provide a thermodynamic criterion that, presumably, governs the evolution of far-from-equilibrium dissipative systems towards their self-assembly and synchronization into increasingly complex networks and structures.

We consider a system of Fermions interacting with a coherent electromagnetic field and calculate the entropy dynamics. We obtain a negative term describing an entropy decrease depending on the electromagnetic field, which can cancel the positive term obtained according to the second law of thermodynamics. For the application of this theory to a semiconductor structure converting the environmental heat into coherent electromagnetic energy, we obtain a physical interpretation of the two processes, as field radiation by quantum transitions, and heat absorption by the Peltier effect.

, following , stated that derivations of the Black-Scholes PDE which follow the original approach of are flawed, in that the time differential of the value of the hedge portfolio omits a term, but that a second error cancels out the first so that the option pricing formula is correct. In this paper we suggest that the error is one of terminology rather than methodology. Changes of value arising from additional investment or consumption should be excluded from rates of return, for example when considering arbitrage, and the original Black-Scholes analysis did employ the correct process. However, the distinction between rate of change of value and rate of return is not always made clear in expositions which follow the PDE approach.

Magnetization and Mössbauer studies have been performed on the polymer coated magnetite nanoparticles with particle size from 5.1 to 14.7 nm. The maximum in the temperature dependence of magnetization (T M ) is found to be inconsistent with the particle size (D TEM ). The effective magnetic anisotropy (K an ) is found to increase with the decrease of D TEM , which is attributed to the increase of surface anisotropy. The absence of coercivity and remanence of magnetization noticed well above T M indicates the superparamagnetic behaviour, which has also been observed in the temperature dependent Mössbauer results. The temperature dependence of hyperfine field is found to follow similar dependence of saturation magnetization for bulk magnetite.

We have studied the effect of rapid thermal annealing (RTA) in the context of phase evolution and stabilization in hydrogenated amorphous silicon nitride (a-SiN x :H) thin films having different stoichiometries, deposited by an Hg-sensitized photo-CVD (chemical vapor deposition) technique. RTA-treated films showed substantial densification and increase in refractive index. Our studies indicate that a mere increase in flow of silicon (Si)-containing gas would not result in silicon-rich a-SiN x :H films. We found that out-diffusion of hydrogen, upon RTA treatment, plays a vital role in the overall structural evolution of the host matrix. It is speculated that less incorporation of hydrogen in as-deposited films with moderate Si content helps in the stabilization of the silicon nitride (Si 3 N 4) phase and may also enable unreacted Si atoms to cluster after RTA. These studies are of great interest in silicon photonics where the post-treatment of silicon-rich devices is essential.

We investigated the thermal transition of coated nano-particles of the title compound, on a set of samples of average diameter d ∼ 30, 50, 70, 110 nm, with rather broad size distributions. As expected, the width of the major hysteresis loop was an increasing function of d. We recorded first-order reversal curves (FORC), the initial parts of which displayed a finite slope, revealing the presence of reversible contributions expected from particles smaller than the critical size dC associated with the collapse of the hysteresis loop. Kinetic effects were also evidenced thanks to isothermal stages. Reversibility of the FORC curves at the vicinity of the reversal temperature was controlled. Thanks to the reversibility property we could determine the reversible contributions to the total response of all samples and derive the corresponding dC values. Consistent results were obtained by accounting for an anhysteretic contribution from the large particles, leading to an accurate determination dC ∼ 45−50 nm, much better than the width of the size distributions.

In fusion reactions, the Coulomb barrier selects particles from the high-momentum part of the distribution. Therefore, small variations of the high-momentum tail of the velocity distribution can produce strong effects on fusion rates. In plasmas several potential mechanisms exist that can produce deviations from the standard Maxwell-Boltzmann distribution. Quantum broadening of the energy-momentum dispersion relation of the plasma quasi-particles modifies the high-momentum tail and could explain the fusion-rate enhancement observed in low-energy nuclear reaction experiments.

The influence of the Rashba spin-orbit coupling (RSOC) on the two-dimensional (2D) electrons and holes in a strong perpendicular magnetic field leads to different results for the Landau quantization in different spin projections. In the Landau gauge the unidimensional wave vector describing the free motion in one in-plane direction is the same for both spin projections, whereas the numbers of Landau quantization levels are different. For an electron in an s-type conduction band they differ by one, as was established earlier by Rashba (1960 Fiz. Tverd. Tela 2 1224), whereas for heavy holes in a p-type valence band influenced by the 2D symmetry of the layer they differ by three. The shifts and the rearrangements of the 2D hole Landau quantization levels on the energy scale are much larger in comparison with the case of conduction electron Landau levels. This is due to the strong influence of the magnetic field on the RSOC parameter. At sufficiently large values of this parameter the shifts and rearrangements are comparable with the hole cyclotron energy. There are two lowest spin-split Landau levels for electrons as well as four lowest ones for holes in the case of small RSOC parameters. They give rise to eight lowest energy bands of the 2D magnetoexcitons, as well as of the band-to-band quantum transitions. It is shown that three of them are dipole-active, three are quadrupole-active and two are forbidden. The optical orientation under the influence of circularly polarized light leads to optical alignment of the magnetoexcitons with different orbital momentum projections in the direction of the external magnetic field.

We have developed empirical interatomic potentials for studying radiation defects and dislocations in tungsten. The potentials use the embedded atom method formalism and are fitted to a mixed database, containing various experimentally measured properties of tungsten and ab initio formation energies of defects, as well as ab initio interatomic forces computed for random liquid configurations. The availability of data on atomic force fields proves critical for the development of the new potentials. Several point and extended defect configurations were used to test the transferability of the potentials. The trends predicted for the Peierls barrier of the 1 2 111 screw dislocation are in qualitative agreement with ab initio calculations, enabling quantitative comparison of the predicted kink-pair formation energies with experimental data.

Polaritonic lattice configurations in dimensions D=2 are used as simulators of topological phases, based on symmetry class A Hamiltonians. Numerical and topological studies are performed in order to characterise the bulk topology of insulating phases, which is predicted to be connected to non-trivial edge mode states on the boundary. By using spectral-flattened Hamiltonians on specific lattice geometries with time-reversal symmetry breaking, e.g. Kagome lattice, I obtain maps from the Brillouin zone into Grassmannian spaces, which are further investigated by the topological method of space fibrations. Numerical evidence reveals a connection between the sum of valence band Chern numbers and the index of the projection operator onto the valence band states. Along these lines, I discover an index formula which resembles other index theorems and the classical result of Atiyah-Singer, but without any Dirac operator and from a different perspective. Through a combination of different tools, in particular homotopy and homology-cohomology duality, we provide a comprehensive mathematical framework, which fully addresses the source and structure of topological phases in coupled polaritonic array systems. Based on these results, it becomes possible to infer further designs and models of two-dimensional single sheet Chern insulators, implemented as polaritonic simulators.

Applying the generalization of the model for chain formation in break-junctions (Di Napoli et al 2012 J. Phys.: Condens. Matter 24 135501), we study the effect of light impurities on the energetics and elongation properties of Pt and Ir chains. Our model enables us to develop a tool ideal for detailed analysis of impurity-assisted chain formation, in which zigzag bonds play an important role. In particular we focus on H (s-like) and O (p-like) impurities and assume, for simplicity, that the presence of impurity atoms in experiments results in a ..M-X-M-X-... (M: metal, X: impurity) chain structure in between the metallic leads. Feeding our model with material-specific parameters from systematic full-potential first-principles calculations, we find that the presence of such impurities strongly affects the binding properties of the chains. We find that, while both types of impurities enhance the probability of chains being elongated, the s-like impurities lower the chain&#39;s stabili...

Let K be the closure of one of the complementary domains of a 2-sphere S topologically embedded in the 3-sphere, S 3. We give first (Theorem 1) a characterization of those points p e S with the following property: there exists a homeomorphism h: K-> S 3 such that h(S) can be pierced with a tame arc at h(p). The topological property of K which distinguishes such a "piercing point" p is this: K-p is 1-ULC. Using this result, we find (Theorems 2 and 3) that p is a piercing point of K if and only if S is arcwise accessible at p by a tame arc from S 3-K (note: perhaps S cannot be pierced with a tame arc at p, even if p is a piercing point of K). Thus, the "tamely arcwise accessible" property is independent of the embedding of K in S 3. The corollary to Theorem 2 gives an alternate proof of an as yet unpublished fact, first proven by R. H. Bing: a topological 2-sphere in S 3 is arcwise accessible at each point by a tame arc from at least one of its complementary domains. In the last section of the paper, we give two applications of the above theorems. First, we show in Theorem 4 that S can be pierced with a tame arc at p if and only if p is a piercing point of both K and the closure of *S 3-K. Finally, we remark in Theorem 5 that S can be pierced with a tame arc at each of its points if it is "free" in the sense that for each ε > 0, S can be mapped into each of its complementary domains by a mapping which moves each point less than ε. It is not known whether each 2-sphere S with this last property is tame.

QMCPACK is an open source quantum Monte Carlo package for ab initio electronic structure calculations. It supports calculations of metallic and insulating solids, molecules, atoms, and some model Hamiltonians. Implemented real space quantum Monte Carlo algorithms include variational, diffusion, and reptation Monte Carlo. QMCPACK uses Slater-Jastrow type trial wave functions in conjunction with a sophisticated optimizer capable of optimizing tens of thousands of parameters. The orbital space auxiliary field quantum Monte Carlo method is also implemented, enabling cross validation between different highly accurate methods. The code is specifically optimized for calculations with large numbers of electrons on the latest high performance computing architectures, including multicore central processing unit (CPU) and graphical processing unit (GPU) systems. We detail the program&#39;s capabilities, outline its structure, and give examples of its use in current research calculations. The p...