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Results for “SKYRME POTENTIAL”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records

Description of induced nuclear fission with Skyrme energy functionals: Static potential energy surfaces and fission fragment properties

Eighty years after its experimental discovery, a description of induced nuclear fission based solely on the interactions between neutrons and protons and quantum many-body methods still poses formidable challenges. The goal of this paper is to contribute to the development of a predictive microscopic framework for the accurate calculation of static properties of fission fragments for hot fission and thermal or slow neutrons. To this end, we focus on the 239 Pu($n ,f$ ) reaction and employ nuclear density functional theory with Skyrme energy densities. Potential energy surfaces are computed at the Hartree-Fock-Bogoliubov approximation with up to five collective variables. We find that the triaxial degree of freedom plays an important role, both near the fission barrier and at scission. The impact of the parametrization of the Skyrme energy density and the role of pairing correlations on deformation properties from the ground state up to scission are also quantified. We introduce a general template for the quantitative description of fission fragment properties. It is based on the careful analysis of scission configurations, using both advanced topological methods and recently proposed quantum many-body techniques. We conclude that an accurate prediction of fission fragment properties at low incident neutron energies, although technologically demanding, should be within the reach of current nuclear density functional theory.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

Cascaded spin motive force driven by the dynamics of the skyrmion lattice

We numerically investigate the spin motive force (SMF) driven by the dynamics of a Skyrmion lattice. The rotating mode of the Skyrmion core excited by the AC magnetic field induces the large spin-dependent electric field near the core. Due to the collective dynamics of Skyrmion lattice, the measurable voltage is enhanced by the cascade effect of the SMF. The amplitude of the AC voltage is estimated to 30 μV in a macroscopic sample, where 100 Skyrmions exist between two probes. We also investigate the SMF due to the dynamics of the helical magnetic state, where the enhancement of the SMF does not occur.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Neutrino-nucleus scattering of {sup 95,97}Mo and {sup 116}Cd

Accurate knowledge about the nuclear responses to supernova neutrinos for relevant nuclear targets is important both for neutrino detection and for astrophysical applications. In this paper we discuss the cross sections for the charged-current neutrino-nucleus scatterings off {sup 95,97}Mo and {sup 116}Cd. The microscopic quasiparticle-phonon model is adopted for the odd-even nuclei {sup 95,97}Mo. In the case of {sup 116}Cd we present cross sections both for the Bonn one-boson-exchange potential and self-consistent calculations based on modern Skyrme interactions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

Skyrmion based microwave detectors and harvesting

Magnetic skyrmions are topologically protected states that are very promising for the design of the next generation of ultra-low-power electronic devices. In this letter, we propose a magnetic tunnel junction based spin-transfer torque diode with a magnetic skyrmion as ground state and a perpendicular polarizer patterned as nano-contact for a local injection of the current. The key result is the possibility to achieve sensitivities (i.e., detection voltage over input microwave power) larger than 2000 V/W for optimized contact diameters. We also pointed out that large enough voltage controlled magnetocrystalline anisotropy could significantly improve the sensitivity. Our results can be very useful for the identification of a class of spin-torque diodes with a non-uniform ground state and to understand the fundamental physics of the skyrmion dynamical properties.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Generation of spin currents in the skyrmion phase of a helimagnetic insulator Cu{sub 2}OSeO{sub 3}

We report spin-current generation related to skyrmion dynamics resonantly excited by a microwave in a helimagnetic insulator Cu{sub 2}OSeO{sub 3}. A Pt layer was fabricated on Cu{sub 2}OSeO{sub 3} and voltage in the Pt layer was measured upon magnetic upon magnetic resonance of Cu{sub 2}OSeO{sub 3} to electrically detect injected spin currents via the inverse spin Hall effect (ISHE) in Pt. We found that ISHE-induced electromotive forces appear in the skyrmion phase of Cu{sub 2}OSeO{sub 3} as well as in the ferrimagnetic phase, which shows that magnetic skyrmions can contribute to the spin pumping effect.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Basics and prospective of magnetic Heusler compounds

Heusler compounds are a remarkable class of materials with more than 1000 members and a wide range of extraordinary multi-functionalities including halfmetallic high-temperature ferri- and ferromagnets, multi-ferroics, shape memory alloys, and tunable topological insulators with a high potential for spintronics, energy technologies, and magneto-caloric applications. The tunability of this class of materials is exceptional and nearly every functionality can be designed. Co{sub 2}-Heusler compounds show high spin polarization in tunnel junction devices and spin-resolved photoemission. Manganese-rich Heusler compounds attract much interest in the context of spin transfer torque, spin Hall effect, and rare earth free hard magnets. Most Mn{sub 2}-Heusler compounds crystallize in the inverse structure and are characterized by antiparallel coupling of magnetic moments on Mn atoms; the ferrimagnetic order and the lack of inversion symmetry lead to the emergence of new properties that are absent in ferromagnetic centrosymmetric Heusler structures, such as non-collinear magnetism, topological Hall effect, and skyrmions. Tetragonal Heusler compounds with large magneto crystalline anisotropy can be easily designed by positioning the Fermi energy at the van Hove singularity in one of the spin channels. Here, we give a comprehensive overview and a prospective on the magnetic properties of Heusler materials.

36 MATERIALS SCIENCE↗

Topological Structures in a Model Cuprate

We address a minimal model to describe the charge degree of freedom in the CuO{sub 2} planes with the on-site Hilbert space reduced to only a charge triplet of the three effective valence centers, nominally Cu{sup 1+;2+;3+}, and made use of the S = 1 pseudospin formalism. The 2D S = 1 pseudospin system is prone to a creation of different topological structures which form topologically protected inhomogeneous distributions of the eight local S = 1 pseudospin order parameters including charge density and superfluid order parameters. We focus on the so-called quadrupole skyrmion which is believed to be a candidate for a topological charge excitation in parent or underdoped cuprates. Puzzlingly, such an unconventional structure is characterized by a uniform distribution of the mean on-site charge that makes the quadrupole skyrmion texture to be invisible for X-rays. We suppose that the parent insulating antiferromagnetic cuprates may be unstable with regard to nucleation of topological defects in the unconventional form of the one- or multi-center skyrmion-like object with ring-shaped superfluid regions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

No Signature of Room Temperature Ferromagnetism in Fe-Doped ITO Thin Films

Iron (Fe)-doped indium tin oxide thin films (In{sub 0.95 − x}Fe{sub x}Sn{sub 0.05}){sub 2}O{sub 3} at x = 0.00, 0.05, 0.10, and 0.15 were deposited onto glass substrates using an electron beam evaporation technique. The coated thin films were characterized by X-ray diffractometer (XRD), UV-VIS-NIR spectrophotometer, photoluminescence spectrophotometer, scanning electron microscope, and vibrating sample magnetometer to study their structural, optical, morphological, and magnetic properties, respectively. The crystallite size of the films increased from 18 to 30 nm with Fe concentration (x). The morphology showed the formation of nanorods. The bandgap of the films decreased from 3.94 to 3.81 eV. The X-ray photoelectron spectroscopy (XPS) studies confirm the presence of Fe ions in two different oxidation states (Fe{sup 2+}, Fe{sup 3+}). The magnetic studies revealed the paramagnetic behavior of the films at room temperature and at low temperature (5 K). The effective magnetic moment (μ{sub eff}) of Fe-doped indium tin oxide thin films was calculated using Langevin theory of paramagnetism extending to Curie’s law. The effective magnetic moment (μ{sub eff}) was increased on increasing the dopant concentration.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Topological Structures in Unconventional Scenario for 2D Cuprates

Numerous experimental data point to cuprates as d-d charge transfer unstable systems whose description implies the inclusion of the three many-electron valence states CuO{sub 4}{sup 7−,6−,5−} (nominally Cu{sup 1+,2+,3+}) on an equal footing as a well-defined charge triplet. We introduce a minimal model to describe the charge degree of freedom in cuprates with the on-site Hilbert space reduced to only the three states and make use of the S = 1 pseudospin formalism. The formalism constitutes a powerful method to study complex phenomena in interacting quantum systems characterized by the coexistence and competition of various ordered states. Overall, such a framework provides a simple and systematic methodology to predict and discover new kinds of orders. In particular, the pseudospin formalism provides the most effective way to describe different topological structures, in particular, due to a possibility of a geometrical two-vector description of the on-site states. We introduce and analyze effective pseudospin Hamiltonian with on-site and inter-site charge correlations, two types of a correlated one-particle transfer and two-particle, or the composite boson transfer. The latter is of a principal importance for the HTSC perspectives. The 2D S = 1 pseudospin system is prone to a creation of different topological structures, which form topologically protected inhomogeneous distributions of the eight local S = 1 pseudospin order parameters. We present a short overview of localized topological structures, typical for S = 1 (pseudo)spin systems, focusing on unexpected antiphase domain walls in parent cuprates and so-called quadrupole skyrmion, which are believed to be candidates for a topological charge excitation in parent or underdoped cuprates. Puzzlingly, these unconventional structures can be characterized by an uniform distribution of the mean on-site charge, that makes these invisible for X-rays. Quasi-classical approximation and computer simulation are applied to analyze localized topological defects and evolution of the domain structures in “negative-U” model under charge order-superfluid phase transition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Skyrmion Emergence Mediated by Antiferromagnetic Interlayer Exchange Coupling

Skyrmions are considered as topologically protected magnetic textures; they are covering a large area of applications. In this work, we studied using micromagnetic simulations the emergence of skyrmions in a nanodisk stacked in a FM/NM/FM multilayer system. We show how the skyrmion is formed through the antiferromagnetic interlayer exchange coupling (IEC). We also show the impact of the IEC on skyrmion size in both layers. We try as a conclusion to identify the range of IEC where skyrmions could exist in such systems.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

Brownian motion of massive skyrmions in magnetic thin films

We report on the thermal effects on the motion of current-driven massive magnetic skyrmions. The reduced equation for the motion of skyrmion has the form of a stochastic generalized Thiele’s equation. We propose an ansatz for the magnetization texture of a non-rigid single skyrmion that depends linearly with the velocity. By using this ansatz it is found that the skyrmion mass tensor is closely related to intrinsic skyrmion parameters, such as Gilbert damping, skyrmion-charge and dissipative force. We have found an exact expression for the average drift velocity as well as the mean-square velocity of the skyrmion. The longitudinal and transverse mobility of skyrmions for small spin-velocity of electrons is also determined and found to be independent of the skyrmion mass.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Entropic information for travelling solitons in Lorentz and CPT breaking systems

In this work we group four research topics apparently disconnected, namely solitons, Lorentz symmetry breaking, supersymmetry, and entropy. Following a recent work (Gleiser and Stamatopoulos, 2012), we show that it is possible to construct in the context of travelling wave solutions a configurational entropy measure in functional space, from the field configurations. Thus, we investigate the existence and properties of travelling solitons in Lorentz and CPT breaking scenarios for a class of models with two interacting scalar fields. Here, we obtain a complete set of exact solutions for the model studied which display both double and single-kink configurations. In fact, such models are very important in applications that include Bloch branes, Skyrmions, Yang–Mills, Q-balls, oscillons and various superstring-motivated theories. We find that the so-called Configurational Entropy (CE) for travelling solitons shows that the best value of parameter responsible to break the Lorentz symmetry is one where the energy density is distributed equally around the origin. In this way, the information-theoretical measure of travelling solitons in Lorentz symmetry violation scenarios opens a new window to probe situations where the parameters responsible for breaking the symmetries are arbitrary. In this case, the CE selects the best value of the parameter in the model.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Weyl type spin–orbit coupled ferromagnetic Bose–Einstein condensates under rotation

Highlights: Spinor Bose–Einstein condensates with Weyl type spin–orbit coupling and rotation are considered. Different topological patterns are obtained in the full parameter space. Effects of spin-independent and spin-dependent interactions on the ground state are also discussed. -- Abstract: We investigate the ground state of ferromagnetic Bose–Einstein condensates with Weyl type spin–orbit coupling and rotation. When the spin–orbit coupling is strong, the ground state of the system exhibits square lattice phase for the non-rotation case, while two half-skyrmion chains can occur, which is perpendicular to each other, for the rotation case. For the weak spin–orbit coupling case, half-skyrmion displays the symmetrical arrangement around Mermin–Ho vortex at the center of condensates as the rotation frequency is increased. Moreover, the effects of spin-independent and spin-dependent interactions on the ground state are also studied.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Zero point fluctuations for magnetic spirals and Skyrmions, and the fate of the Casimir energy in the continuum limit

We study the role of zero-point quantum fluctuations in a range of magnetic states which on the classical level are close to spin-aligned ferromagnets. These include Skyrmion textures characterized by non-zero topological charge, and topologically-trivial spirals arising from the competition of the Heisenberg and Dzyaloshin-skii–Moriya interactions. For the former, we extend our previous results on quantum exactness of classical Bogomolny–Prasad–Sommerfield (BPS) ground-state degeneracies to the general case of Kähler manifolds, with a specific example of Grassmann manifolds Gr(M,N). These are relevant to quantum Hall ferromagnets with N internal states and integer filling factor M. A promising candidate for their experimental implementation is monolayer graphene with N = 4 corresponding to spin and valley degrees of freedom at the charge neutrality point with M = 2 filled Landau levels. We find that the vanishing of the zero-point fluctuations in taking the continuum limit occurs differently in the case of BPS states compared to the case of more general smooth textures, with the latter exhibiting more pronounced lattice effects. This motivates us to consider the vanishing of zero-point fluctuations in such near-ferromagnets more generally. We present a family of lattice spin models for which the vanishing of zero-point fluctuations is evident, and show that some spirals can be thought of as having nonzero but weak zero-point fluctuations on account of their closeness to this family. Between them, these instances provide concrete illustrations of how the Casimir energy, dependent on the full UV-structure of the theory, evolves as the continuum limit is taken.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Stability of atomic-sized skyrmions in antiferromagnetic bilayers

We perform a stability analysis of an isolated atomic-sized antiferromagnetic skyrmion (AFM-Sk), formed on the superior layer of a magnetic bilayer. The coupling between both square lattices acts as an effective staggered magnetic field that stabilizes the AFM-Sk and reduces its radius. A suitable anisotropy constant of the bottom layer material keeps it close to the homogeneous AFM state. We compare the energy of the AFM-Sk with the energy of the AFM ground state. In addition, an estimation of the energy barrier that protects the skyrmion from being destabilized is provided and its value determined to be in the order of ∼300 K. The remarkable reduction in the skyrmion radius towards atomic size and avoiding an external magnetic field are key points in order to increase our ability to manipulate AFM-Sk on skyrmionic devices. Our calculations provide an insight into novel ways to create and manipulate AFM-Sk at the atomic scale.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Skyrmions and composite vortex states in three-component Bose–Einstein condensates with spin–orbit coupling

Stable and metastable vortex states in two-dimensional three-component Bose–Einstein condensates are studied in the presence of spin–orbit coupling. The ground states exhibit two skyrmion structures which respectively correspond to the d-skyrmion in antiferromagnetic or the F-skyrmion in ferromagnetic condensates. The half skyrmion and full skyrmion can be controlled by changing the strength of the spin–orbit coupling. We also find a stable composite vortex state which is associated to mixing of the ferromagnetic and antiferromagnetic manifolds.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Dynamical system analysis of Einstein–Skyrme model in a Kantowski–Sachs spacetime

The present work deals with anisotropic (but zero heat flux) Skyrme fluid with a constant radial profile in locally rotational Kantowski–Sachs spacetime in the background of Einstein gravity. By suitably change of variables the field equations are transformed to an autonomous system. To examine the stability of the system critical points are determined. For hyperbolic critical points the analysis of the system is done using Hartman–Grobman theorem, while center manifold theory is used to analyze non-hyperbolic critical points. Also stability at infinity is analyzed to visualize the global evolution of the Universe. As a result the 3D-phase space is identified with the Poincaré 3-sphere embedded in R{sup 4}. It is found that the parameters in the autonomous system play a crucial role for phase transition of the Universe. Finally possible bifurcation scenarios are discussed to identify the point of phase transition.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Skyrmions

The Skyrme model provides a soliton description of atomic nuclei. In the past, it has been used to describe the properties of nucleons as well as the rotational spectra of some small nuclei. More recently, {alpha}-particle clustering has been observed in the Skyrme model, and it predicts interesting structures for nuclei of baryon number B divisible by four. A promising approach to find some Skyrmions with intermediate baryon numbers is to remove single nucleons from Skyrmions made from {alpha}-particles. More insight into the interactions of two {alpha}-particles has been gained recently, and it seems now possible to find vibrational spectra.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗