What types of spatial soliton can be formed based on two-photon-isomerisation?

In this paper we answer the question: “what types of spatial soliton can be formed based on two-photon-isomerisation (TPI)”. The conclusion that anti-dark solitons are not supported by monotonic nonlinearity should cast light on the notion of fundamental spatial solitons. The idea to obtain a bright TPI soliton with the joining of a background light or with the coupling of a dark soliton offers new schemes of light-controlling-light.     

The perturbed Korteweg-de Vries equation: Evolution of solitons

Summary In this paper we examine the dynamic of solitons in the presence of external forces expressed by an-degree polynomial perturbative term or by a combination of polynomial and differential terms in the dependent variable. Under the action of these forces the soliton profile will no longer be a simple translation: asymptotic behaviour of the wave amplitude to threshold values (stationary equilibrium states) are now possible and “explosions” may occur at some finite “critical time” at which the soliton amplitude becomes infinite.     

μ+SR studies on superconducting YBa2(Cu1−xFex)3Oy system

Spin-glass like magnetic ordering of iron moments was observed in both orthorhombic and tetragonal YBa₂(Cu_1−xFe_x)₃O_y (x=0.08) by μ⁺SR measurements. In a “Tetra” sample, all the muons sense the superconducting transition at 60 K and magnetic ordering at around 15 K, while in an “Ortho” sample they reveal that two magnetically different parts exist in the sample: about 40% of the sample is superconducting withT _c ≈90K and the remaining part is magnetic withT _M≈33K. These phenomena can be explained in terms of clustering of the Fe atoms in the “Ortho” sample.     

Pentaquarks in chiral soliton models

The spectra of pentaquarks, some of them observed recently, are discussed within the topological soliton model and compared with the simplified quark picture. The results obtained within the chiral soliton model depend to some extent on the quantization scheme: rigid rotator, soft rotator, or bound state model. The similarity of the spectra of baryon resonances obtained within the quark model and the chiral soliton model is pointed out, although certain differences take place as well, which require careful interpretation. In particular, considerable variation of the strange antiquark mass in different SU(3) multiplets of pentaquarks is required to fit their spectra obtained from chiral solitons. Certain difference in the masses of “good” and “bad” diquarks is required as well, in qualitative agreement with previously made estimates. The partners of exotic states with different values of spin which belong to higher SU(3) multiplets have energy considerably higher than the states with the lowest spin, and this could be a point where the difference from simple quark models is striking. The antiflavor excitation energies for multibaryons are estimated as well, and the binding energies of gJ-hypernuclei and anticharm (antibeauty) hypernuclei are presented for several baryon numbers. Some deficiencies are pointed out in the arguments in the literature against the validity of the chiral soliton approach and/or the SU(3) quantization models. Based partly on the talks presented at the International Seminar on High Energy Physics Quarks-2004, Pushkinogorie, Russia, May 24–30, 2004; International Workshop on Quantum Field Theory and High Energy Physics QFTHEP-04, Saint-Petersburg, Russia, June 17–23, 2004, and Symposium of London Mathematical Society “Topological Solitons and their Applications,” Durham, UK, August 2–12, 2004. A slightly reduced version of this paper is available as E-print HEP-PH/0507028. The text was submitted by the author in English.     

Breathing solitons in optical fiber links

We introduce the concept of “breathing” solitons to describe the dynamics of optical pulses in transmission lines with passive compensation of fiber chromatic dispersion. The “breathing” pulse can be used as the information carrier. The theory presented is complimentary to the concept of the guiding-center soliton. It is shown that an average bright soliton can propagate in a system with large variations of the dispersion, including segments with high normal dispersion. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 10, 814–819 (25 May 1996) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Studies of magnetism by nuclear orientation and NMRON

Low temperature nuclear orientation (NO) and nuclear magnetic resonance on oriented nuclei (NMRON) are used to investigate the magnetic properties of solids, and are especially useful when high sensitivity is required, for example in the study of small or dilute systems. Measurement of the static hyperfine interaction and the nuclear spin-lattice and spin-spin relaxation times T ₁ and T ₂ yield information about the electronic magnetization and spin dynamics, respectively. A number of NMRON techniques are available and their application to the study of magnetism will be briefly discussed. In particular, the pulsed technique has been shown to be effective for studying insulators. Recent NO and NMRON measurements, primarily on insulating magnets and magnetic multilayers, will be reviewed. Spins of stable isotopes can also be investigated using NMR thermally detected by NO (NMR-TDNO), and this method, in combination with NMRON, has been recently applied in both metals and insulators to obtain information about nuclear spin-spin couplings, “frequency pulling” and nuclear magnons. This revised version was published online in August 2006 with corrections to the Cover Date.     

NMR in 55Mn2+ nuclei in the quasi-one-dimensional antiferromagnetic CsMnBr3

The NMR spectrum of the quasi-one-dimensional easy-plane antiferromagnetic CsMnBr₃, which has trigonal spin lattice, is investigated in detail. The measurements were performed on a wide-band NMR decimeter microwave-band spectrometer over a wide range of magnetic fields at temperatures 1.3–4.2 K. All three branches of the NMR spectrum previously found by us [JETP Lett. 64, 225 (1996)] are severely distorted because of the dynamic interaction with the Goldstone mode in the antiferromagnetic resonance spectrum. The experimental results in fields up to 40 kOe are described satisfactorily by an equation obtained by Zaliznyak et al. [JETP Lett. 64, 473 (1996)]. Formulas are obtained in our work that agree very well with experiment at all fields up to the “collapse” field H _c of all sublattices. The unbiased NMR frequency in CsMnBr₃ is determined to be v _n0=416 MHz (T=1.3 K) in zero external magnetic field, and in this way the reduction in the spontaneous moment due to the quasi-one-dimensional nature of the system of Mn²⁺ spins, which according to our data amounts to 28%, is determined more accurately. The field dependences of the directions of the magnetic sublattices with respect to the magnetic field are obtained from the NMR spectra, confirming the equations of Chubukov [J. Phys. Condens. Matter 21, 441 (1988)]. The results on the field dependence of the width and intensities of the NMR lines are discussed, along with three observed anomalies: 1) a strong increase in the NMR frequency for nuclei in sublattices that are perpendicular to the magnetic field; 2) the nonmonotonic temperature dependence of the resonance field for the lower branch of the spectrum; 3) the presence of two branches of the NMR spectrum in large H _c fields, in which the CsMnBr₃ must be a quasi-one-dimensional antiferromagnetic. Zh. éksp. Teor. Fiz. 113, 352–368 (January 1998) Deceased.     

Ferromagnetic resonance and bistability field in a uniaxial magnetic film

Peculiarities of ferromagnetic resonance (FMR) corresponding to bias along the “hard” magnetic axis of a film with 2D uniaxial anisotropy are studied based on numerical solution of magnetic moment dynamics equations. It is shown that an additional resonance peak is formed in the FMR spectrum in the vicinity of “bistability field” H _b . The dependence of this field on the amplitude of the microwave field and damping parameters is analyzed.     

Fast-field-cycling NMR: Applications and instrumentation

Magnetic field cycling in nuclear magnetic resonance (NMR) experiments has been used since the early days of NMR. Originally such time-dependent magnetic field experiments were motivated to study cross relaxation, spin system thermodynamics and indirect detection of quadrupolar resonance. The first apparatus used mechanical or pneumatic systems to shoot the sample between two magnets, the typical “flying time” being a few hundreds of milliseconds. As a natural evolution of the experimental technique and the need to extend its application to samples with higher relaxation rates, faster magnetic field switching devices were developed during the last years. Special electric networks combined with sophisticated air core magnets allowed one to switch magnetic fields between zero and fields of the order of 0.5 T in a few milliseconds. Today we refer to this new generation of instruments as “fast-field-cycling” devices. The technique has been successfully used during the last years to obtain information on the molecular dynamics and order in different materials, ranging from organic solids, metals, polymers, liquid crystals, porous media to biological systems. At present it is also turning to be an important tool for the design of contrast agents for magnetic resonance imaging. Fast field cycling was mainly oriented toT ₁ relaxometry as a unique technique offering a dynamic window of several decades, ranging from few kilohertz to several megahertz. However, there exist less conventional applications of the technique that can also provide relevant information concerning molecular dynamics, structure and molecular order. In this article we will briefly deal with basic aspects of the technique, its evolution, present-day relevant applications and the last improvements concerning specialized instrumentation.     

Prospects for the rapid detection of mealiness in apples by nondestructive NMR relaxometry

The potential of nuclear magnetic resonance (NMR) relaxometry for quantitative evaluation of apple mealiness has been investigated. The degree of “mealiness” was defined by several mechanical techniques, including penetration, compression and shear rupture as well as by the BRIX (soluble solids) and juiciness levels. These data were correlated with both magnetic resonance imaging (MRI) and NMR water proton transverse relaxation time measurements on a fruit-by-fruit basis. It was found that increasing mealiness caused a systematic increase in the transverse relaxation rate. The potential for rapid, on-line NMR/MRI detection of apple mealiness is discussed.     

Effect of the electric field on “incommensurate-commensurate” magnetic phase transitions in BiFeO3-type multiferroics

The specific features of the “incommensurate-commensurate” phase transitions induced by a magnetic field in multiferroics (materials with coexisting magnetic and electric ordering) are considered. These materials are ferroelectromagnets, for example, bismuth ferrite BiFeO₃ and BiFeO₃-based compounds, which have spatially modulated spin structures. It is shown that the interaction between the electric and magnetic subsystems of the multiferroic material can lead to an electric-field-induced shift of the critical magnetic field corresponding to the transition from a spatially modulated state to a homogeneous antiferromagnetic state. According to the theoretical estimates obtained for material parameters characteristic of the bismuth ferrite, this shift is of the order of 0.5 T in an electric field of 50 kV/cm. The phase diagrams are constructed in the “electric field-magnetic field” coordinates. The results of calculations performed in the harmonic incommensurate structure approximation are compared with the exact soliton solution.     

Emission of supersonic soliton wave beams—generators of restructuring of nanocrystals under atom bombardment,and the self-organization of a dynamic superlattice of complexes of soliton atomic vibrations

It has been shown that the dynamic superlattice of pulsed complexes of soliton vibrations or, actually, a “soliton crystal” is self-organized in crystalline materials at high levels of thermal and dynamic excitations of atomic vibrations. The results obtained have been adapted to the alpha uranium crystal system. It has been demonstrated that the atom bombardment of crystalline materials leads to the generation of beams of nonlinear subsonic and supersonic soliton and breather waves. The breathers and solitons initiate threshold kinetic processes of defect formation, such as surface vibrations and evaporation of surface atoms, multiple reflection of bombarding atoms, and restructuring of nanocrystals. The results obtained can be used in experimental investigations of microdynamics of materials under high dynamic and temperature loads by the neutron and ion scattering methods.     

Stabilization of two-dimensional solitons and vortices against supercritical collapse by lattice potentials

It is known that optical-lattice (OL) potentials can stabilize solitons and solitary vortices against the critical collapse, generated by cubic attractive nonlinearity in the 2D geometry. We demonstrate that OLs can also stabilize various species of fundamental and vortical solitons against the supercritical collapse, driven by the double-attractive cubic-quintic nonlinearity (however, solitons remain unstable in the case of the pure quintic nonlinearity). Two types of OLs are considered, producing similar results: the 2D Kronig-Penney “checkerboard”, and the sinusoidal potential. Soliton families are obtained by means of a variational approximation, and as numerical solutions. The stability of all families, which include fundamental and multi-humped solitons, vortices of oblique and straight types, vortices built of quadrupoles, and supervortices, strictly obeys the Vakhitov-Kolokolov criterion. The model applies to optical media and BEC in “pancake” traps.     

Magnons and solitons in CsNiF3 investigated by nuclear spin-lattice relaxation

By nuclear spin-lattice relaxation of¹³³Cs we studied linear and nonlinear magnetic excitations in the one-dimensional easy-plane ferromagnet CsNiF₃. The measurements were performed in the temperature range from 3 to 20 K and with external magnetic fields from 3 to 55 kOe applied perpendicular to the chain direction. Universal dependence on was obtained forT/T ₁. A quantitative interpretation of theT ₁ data in terms of two-magnon and soliton contributions could be achieved by considering renormalization effects resulting from magnon-magnon and soliton-magnon interaction as well as from quantum corrections. The instability of solitons due to out-of-plane fluctuations expected in high magnetic fields is discussed.     

Domain walls in a generalized Chern–Simons model

In this paper we study the structure of one dimensional topological solitons in a generalized Abelian-Higgs Chern–Simons model where the kinetic term is non-canonical. We present an example of an analytical self-dual electrically charged soliton solution which has a finite momentum per unit length along its direction. We compared the physical properties of our soliton with those for wall of Jackiw–Lee–Weinberg wall presented in Jackiw et al. (Phys. Rev. D 42:3488, 1990) to conclude that the non-canonical kinetic term can make the wall “thicker” redistributing uniformly the momentum flow along it.     

NMR and other magnetic resonance techniques in unstable magnets

This paper reviews and compares the use of nuclear magnetic resonance (NMR) and related hyperfine techniques [muon spin rotation (μSR) and, to a lesser extent, other methods] in the study of 4f and 5f magnetism in “unstable magnets”, i.e., intermediate-valent and heavy-fermion materials. In both NMR and μSR the features of interest are the spectral shape, the frequency shiftK (Knight shift in metals) and the spin-lattice relaxation rate 1/T ₁. For temperatures below the characteristic or “Kondo” temperatureT ₀ these experiments given evidence for (1) modification of the transferred hyperfine field [nonlinearK(χ)]. (2) spin fluctuations with a characteristic fluctuation rate ∼k _B T ₀/h, (3) strong energy-gap anisotropy (zeros of the gap along lines on the Fermi surface) in heavy-fermion superconductors, (4) spin-singlet Cooper pairing from the change in muon Knight shift in superconducting UBe₁₃, and (5) very weak static magnetism (10⁻¹–10⁻³ μ_B/f atom) in CeAl₃, CeCu₂Si₂, U_1−x Th _x Be₁₃ (x=0.033), and UPt₃. There is some controversy concerning the interpretation of 1/T ₁ well aboveT ₀ in UBe₁₃; the situation is reviewed.     

Regular and stochastic motion of dissipative optical solitons

Investigations of the motion of dissipative optical solitons and their complexes in wide-aperture nonlinearly optical (with coherent pump radiation) and laser (with incoherent pump radiation) systems have been reviewed. An important characteristic of dissipative solitons is the topology of the energy fluxes, which determines the internal structure of individual solitons and makes it possible to certainly separate the cases of the weak and strong interactions between the solitons. It has been shown that the character of the regular motion of dissipative soliton structures in a homogeneous system is determined by the symmetry of the transverse distributions of the intensity and energy flux; the motion of asymmetric structures is curvilinear. This is also valid for complexes of three-dimensional dissipative optical solitons, “laser bullets.” The extreme possibilities of localization of solitons are determined by quantum noises. The corresponding Brownian motion of the center of the dissipative optical soliton is characterized by a much lower level of the statistic dispersion of the coordinates of its center and velocity than that in the case of conservative solitons.     

Specific heat of magnetic clusters with S=2 YBa2Cu3O7−δ

An analysis is made of published data from measurements of the temperature-and-field dependence of the specific heat in YBaCuO high-temperature superconductors at temperatures below 10 K. It is shown that the “excess” contribution to the specific heat can be explained by spin splittings in copper-oxygen clusters with S=2. The magnitudes of the necessary splittings agree with the available magnetic resonance data. Fiz. Tverd. Tela (St. Petersburg) 39, 1320–1322 (August 1997)     

Proton NMR study of molecular motion in bulk and in highly drawn fiber polyamide-6

The proton motion in bulk and highly drawn fiber polyamide-6 has been studied by field cycling relaxometry and proton line shape measurements. The dips in theT ₁ dispersion allowed for the determination of the¹⁴N quadrupole coupling tensor. The fact that only one set of¹⁴N nuclear quadrupole resonance lines, has been found shows that all N-H groups in nylon-6 are H-bonded. A striking difference in the main line width transition and the low-frequency molecular dynamics has been observed between a slowly cooled “bulk” polyamide-6 sample and a rapidly cooled and highly drawn “fiber” sample by wide line proton nuclear magnetic resonance line shape and spin-lattice relaxation time measurements. This result is consistent with the picture that shearing melt processing procedures, such as spinning, plant stable and long-lived crystallization nuclei into the amorphous phase which impose additional motional constraints on the surroundings and inhibit the self-diffusion process.     

Quantum fluctuations in a scale-free network-connected Ising system

We study the effect of quantum fluctuations in an Ising spin system on a scale-free network of degree exponent γ>5 using a quantum Monte Carlo simulation technique. In our model, one can adjust the magnitude of the magnetic field perpendicular to the Ising spin direction and can therefore control the strength of quantum fluctuations for each spin. Our numerical analysis shows that quantum fluctuations reduce the transition temperature T_c of the ferromagnetic-paramagnetic phase transition. However, the phase transition belongs to the same mean-field type universality class both with and without the quantum fluctuations. We also study the role of hubs by turning on the quantum fluctuations exclusively at the nodes with the most links. When only a small number of hub spins fluctuate quantum mechanically, T_c decreases with increasing magnetic field until it saturates at high fields. This effect becomes stronger as the number of hub spins increases. In contrast, quantum fluctuations at the same number of “non-hub” spins do not affect T_c. This implies that the hubs play an important role in maintaining order in the whole network.