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Search Results: 1 - 10 of 539257 matches for " A. V. Dukhnenko "
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Intense low-energy ferromagnetic fluctuations in the antiferromagnetic heavy-fermion metal CeB6
H. Jang,G. Friemel,J. Ollivier,A. V. Dukhnenko,N. Yu. Shitsevalova,V. B. Filipov,B. Keimer,D. S. Inosov
Physics , 2013, DOI: 10.1038/nmat3976
Abstract: Heavy-fermion metals exhibit a plethora of low-temperature ordering phenomena, among them the so-called hidden-order phases that in contrast to conventional magnetic order are invisible to standard neutron diffraction. One of the oldest and structurally simplest hidden-order compounds, CeB6, became famous for an elusive phase that was attributed to the antiferroquadrupolar ordering of cerium-4f moments. In its ground state, CeB6 also develops a more usual antiferromagnetic (AFM) order. Hence, its essential low-temperature physics was always considered to be solely governed by AFM interactions between the dipolar and multipolar Ce moments. Here we overturn this established perspective by uncovering an intense ferromagnetic (FM) low-energy collective mode that dominates the magnetic excitation spectrum of CeB6. Our inelastic neutron-scattering data reveal that the intensity of this FM excitation by far exceeds that of conventional spin-wave magnons emanating from the AFM wave vectors, thus placing CeB6 much closer to a FM instability than could be anticipated. This propensity of CeB6 to ferromagnetism may account for much of its unexplained behavior, such as the existence of a pronounced electron spin resonance, and should lead to a substantial revision of existing theories that have so far largely neglected the role of FM interactions.
Magnetic-field and doping dependence of low-energy spin fluctuations in the antiferroquadrupolar compound Ce(1-x)La(x)B(6)
G. Friemel,H. Jang,A. Schneidewind,A. Ivanov,A. V. Dukhnenko,N. Y. Shitsevalova,V. B. Filipov,B. Keimer,D. S. Inosov
Physics , 2015, DOI: 10.1103/PhysRevB.92.014410
Abstract: CeB(6) is a model compound exhibiting antiferroquadrupolar (AFQ) order, its magnetic properties being typically interpreted within localized models. More recently, the observation of strong and sharp magnetic exciton modes forming in its antiferromagnetic (AFM) state at both ferromagnetic and AFQ wave vectors suggested a significant contribution of itinerant electrons to the spin dynamics. Here we investigate the evolution of the AFQ excitation upon the application of an external magnetic field and the substitution of Ce with non-magnetic La, both parameters known to suppress the AFM phase. We find that the exciton energy decreases proportionally to T_N upon doping. In field, its intensity is suppressed, while its energy remains constant. Its disappearance above the critical field of the AFM phase is preceded by the formation of two modes, whose energies grow linearly with magnetic field upon entering the AFQ phase. These findings suggest a crossover from itinerant to localized spin dynamics between the two phases, the coupling to heavy-fermion quasiparticles being crucial for a comprehensive description of the magnon spectrum.
Resonant magnetic exciton mode in the heavy-fermion antiferromagnet CeB6
G. Friemel,Yuan Li,A. V. Dukhnenko,N. Yu. Shitsevalova,N. E. Sluchanko,A. Ivanov,V. B. Filipov,B. Keimer,D. S. Inosov
Physics , 2011, DOI: 10.1038/ncomms1821
Abstract: Resonant magnetic excitations are widely recognized as hallmarks of unconventional superconductivity in copper oxides, iron pnictides, and heavy-fermion compounds. Numerous model calculations have related these modes to the microscopic properties of the pair wave function, but the mechanisms underlying their formation are still debated. Here we report the discovery of a similar resonant mode in the non-superconducting, antiferromagnetically ordered heavy-fermion metal CeB6. Unlike conventional magnons, the mode is non-dispersive, and its intensity is sharply concentrated around a wave vector separate from those characterizing the antiferromagnetic order. The magnetic intensity distribution rather suggests that the mode is associated with a coexisting order parameter of the unusual antiferro-quadrupolar phase of CeB6, which has long remained "hidden" to the neutron-scattering probes. The mode energy increases continuously below the onset temperature for antiferromagnetism, in parallel to the opening of a nearly isotropic spin gap throughout the Brillouin zone. These attributes bear strong similarity to those of the resonant modes observed in unconventional superconductors below their critical temperatures. This unexpected commonality between the two disparate ground states indicates the dominance of itinerant spin dynamics in the ordered low-temperature phases of CeB6 and throws new light on the interplay between antiferromagnetism, superconductivity, and "hidden" order parameters in correlated-electron materials.
Samarium hexaboride: A trivial surface conductor
P. Hlawenka,K. Siemensmeyer,E. Weschke,A. Varykhalov,J. Sánchez-Barriga,N. Y. Shitsevalova,A. V. Dukhnenko,V. B. Filipov,S. Gabáni,K. Flachbart,O. Rader,E. D. L. Rienks
Physics , 2015,
Abstract: Recent theoretical and experimental studies suggest that SmB$_6$ is the first topological Kondo insulator: A material in which the interaction between localized and itinerant electrons renders the bulk insulating at low temperature, while topological surface states leave the surface metallic. While this would elegantly explain the material's puzzling conductivity, we find the experimentally observed candidates for both predicted topological surface states to be of trivial character instead: The surface state at $\bar{\Gamma}$ is very heavy and shallow with a mere $\sim 2$ meV binding energy. It exhibits large Rashba splitting which excludes a topological nature. We further demonstrate that the other metallic surface state, located at $\bar{X}$, is not an independent in-gap state as supposed previously, but part of a massive band with much higher binding energy (1.7 eV). We show that it remains metallic down to 1 K due to reduced hybridization with the energy-shifted surface 4$f$ level.
Suppression of Superconductivity in Lu$_x$Zr$_{1-x}$B$_{12}$ : Evidence of Static Magnetic Moments Induced by Non-Magnetic Impurities
N. E. Sluchanko,A. N. Azarevich,M. A. Anisimov,A. V. Bogach,S. Yu. Gavrilkin,V. V. Glushkov,S. V. Demishev,A. L. Khoroshilov,A. V. Dukhnenko,K. V. Mitsen,N. Yu. Shitsevalova,V. B. Filippov,V. V. Voronov,K. Flachbart
Physics , 2015,
Abstract: Based on low temperature resistivity, heat capacity and magnetization investigations we show that the unusually strong suppression of superconductivity in Lu$_x$Zr$_{1-x}$B$_{12}$ BSC-type superconductors in the range $x$$<$0.08 is caused by the emergence of static spin polarization in the vicinity of non-magnetic lutetium impurities. The analysis of received results points to a formation of static magnetic moments with $\mu_{eff}$$\approx$$3\mu_B$ per Lu-ion. The size of these spin polarized nanodomains was estimated to be about 5 ${\AA}$.
Pressure induced softening of YB_6: pressure effect on the Ginzburg-Landau parameter κ=λ/ξ
R. Khasanov,P. S. H?fliger,N. Shitsevalova,A. Dukhnenko,H. Keller
Physics , 2006, DOI: 10.1103/PhysRevLett.97.157002
Abstract: Measurements of the transition temperature T_c, the second critical filed H_{c2} and the magnetic penetration depth \lambda under hydrostatic pressure (up to 9.2 kbar) in the YB_6 superconductor were carried out. A pronounced and {\it negative} pressure effects (PE) on T_c and H_{c2} with dT_c/dp=-0.0547(4) K/kbar and \mu_0dH_{c2}(0)/dp =-4.84(20) mT/kbar, and zero PE on \lambda(0) were observed. The PE on the coherence length d\xi(0)/dp=0.28(2) nm/kbar was calculated from the measured pressure dependence of H_{c2}(0). Together with the zero PE on the magnetic penetration depth \lambda(0), our results imply that the Ginzburg-Landau parameter \kappa(0)=\xi(0)/\lambda(0) depends on pressure and that pressure "softens" YB_6, e.g. moves it to the type-I direction.
Black Hole in Binary System is the Source of Cosmic Gamma-Ray Bursts and Their Counterparts  [PDF]
A. V. Kuznetsov
Journal of Modern Physics (JMP) , 2011, DOI: 10.4236/jmp.2011.27082
Abstract: Discovery of GRB clusters allows us to determine coordinates and characteristics of their sources. The objects radiating GRBs are reliably identified with black hole binaries, including the Galactic binaries. One of the unusual GRB properties, which are determined by black hole, is revealed in that the measured arrival direction of GRB does not coincide with the real location of its source. Just this fact allows us to find the objects radiating GRBs. On the basis of the general relativity theory's effects, observed in the GRB clusters, the technique of the black hole masses measurement is developed. The calculated black hole masses for the majority of known Galactic BH binaries are presented. It is briefly shown how the incorrect interpretations of observational facts result in an erroneous idea of the GRB cosmological origin. In fact, two problems are solved in the paper: the GRB origin and the reality of BH existence.
Book Review of Non-Traditional Dynamics in Electronics: Theory and Practice  [PDF]
V. A. Banakh
Journal of Modern Physics (JMP) , 2012, DOI: 10.4236/jmp.2012.34049
Abstract: Book Review of Non-Traditional Dynamics in Electronics: Theory and Practice
Feynman Formulas Representation of Semigroups Generated by Parabolic Difference-Differential Equations  [PDF]
V. Sakbaev, A. Yaakbarieh
American Journal of Computational Mathematics (AJCM) , 2012, DOI: 10.4236/ajcm.2012.24040
Abstract: We establish that the Laplas operator with perturbation by symmetrised linear hall of displacement argument operators is the generator of unitary group in the Hilbert space of square integrable functions. The representation of semigroup of Cauchy problem solutions for considered functional differential equation is given by the Feynman formulas.
Quantum Entanglement on Cosmological Scale  [PDF]
A. Nicolaidis, V. Kiosses
Journal of Modern Physics (JMP) , 2013, DOI: 10.4236/jmp.2013.48A014
Abstract:

It has been indicated that relational logic may serve as the common foundation of quantum mechanics and string theory. A relation may be represented by a spinor and the Cartan-Penrose connection of spinor to geometry, allows to abstract geometry as the outcome of entangled relations-spinors. Our approach goes in parallel with Wheelers pregeometry, where pregeometry, the stage preceding geometry, is based on a calculus of relations-propositions. With a single spinor related to the null cone of Minkowski space-time, we search for the geometry when we couple a left-handed spinor and a right-handed spinor. We find that a Majorana-type coupling gives rise to the ordinary entanglement, while a Diractype coupling generates an extra dimension with two branes coexisting in the extra dimension. One brane hosts lefthanded particles (our brane), while the other brane hosts right-handed particles. A distinct phenomenology accompanies our proposal. The left-right symmetry is achieved with having two mirror branes and the neutrino appears as the ideal mediator between the branes. We may revisit also the dark matter, dark energy issues, with everything on the other brane and in the bulk appearing dark to us. During the brane collision all points are causally connected, making less pressing the inflationary scenario. Our scheme brings closer logic—quantum theory—cosmology, while space-time, rather than an abstract and an a priori construction, appears as the outcome of a quantum logical act.

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