1,879 research outputs found
Magnetic transitions induced by tunnelling electrons in individual adsorbed M-Phthalocyanine molecules (M Fe, Co)
We report on a theoretical study of magnetic transitions induced by
tunnelling electrons in individual adsorbed M-Phthalocyanine (M-Pc) molecules
where M is a metal atom: Fe-Pc on a Cu(110)(21)-O surface and Co-Pc
layers on Pb(111) islands. The magnetic transitions correspond to the change of
orientation of the spin angular momentum of the metal ion with respect to the
surroundings and possibly an applied magnetic field. The adsorbed Fe-Pc system
is studied with a Density Functional Theory (DFT) transport approach showing
that i) the magnetic structure of the Fe atom in the adsorbed Fe-Pc is quite
different from that of the free Fe atom or of other adsorbed Fe systems and ii)
that injection of electrons (holes) into the Fe atom in the adsorbed Fe-Pc
molecule dominantly involves the Fe orbital. These results fully
specify the magnetic structure of the system and the process responsible for
magnetic transitions. The dynamics of the magnetic transitions induced by
tunnelling electrons is treated in a strong-coupling approach. The Fe-Pc
treatment is extended to the Co-Pc case. The present calculations accurately
reproduce the strength of the magnetic transitions as observed by magnetic IETS
(Inelastic Electron Tunnelling Spectroscopy) experiments; in particular, the
dominance of the inelastic current in the conduction of the adsorbed M-Pc
molecule is accounted for
Quenching of magnetic excitations in single adsorbates at surfaces: Mn on CuN/Cu(100)
The lifetimes of spin excitations of Mn adsorbates on CuN/Cu(100) are
computed from first-principles. The theory is based on a strong-coupling
T-matrix approach that evaluates the decay of a spin excitation due to
electron-hole pair creation. Using a previously developed theory [Phys. Rev.
Lett. {\bf 103}, 176601 (2009) and Phys. Rev. B {\bf 81}, 165423 (2010)], we
compute the excitation rates by a tunneling current for all the Mn spin states.
A rate equation approach permits us to simulate the experimental results by
Loth and co-workers [Nat. Phys. {\bf 6}, 340 (2010)] for large tunnelling
currents, taking into account the finite population of excited states. Our
simulations give us insight into the spin dynamics, in particular in the way
polarized electrons can reveal the existence of an excited state population. In
addition, it reveals that the excitation process occurs in a way very different
from the deexcitation one. Indeed, while excitation by tunnelling electrons
proceeds via the s and p electrons of the adsorbate, deexcitation mainly
involves the d electrons
Non perturbative renormalization group and momentum dependence of n-point functions (II)
In a companion paper (hep-th/0512317), we have presented an approximation
scheme to solve the Non Perturbative Renormalization Group equations that
allows the calculation of the -point functions for arbitrary values of the
external momenta. The method was applied in its leading order to the
calculation of the self-energy of the O() model in the critical regime. The
purpose of the present paper is to extend this study to the next-to-leading
order of the approximation scheme. This involves the calculation of the 4-point
function at leading order, where new features arise, related to the occurrence
of exceptional configurations of momenta in the flow equations. These require a
special treatment, inviting us to improve the straightforward iteration scheme
that we originally proposed. The final result for the self-energy at
next-to-leading order exhibits a remarkable improvement as compared to the
leading order calculation. This is demonstrated by the calculation of the shift
, caused by weak interactions, in the temperature of Bose-Einstein
condensation. This quantity depends on the self-energy at all momentum scales
and can be used as a benchmark of the approximation. The improved
next-to-leading order calculation of the self-energy presented in this paper
leads to excellent agreement with lattice data and is within 4% of the exact
large result.Comment: 35 pages, 11 figure
Open cluster candidates in the VVVX area: VVVX CL 076 and CL 077
We are reporting some basic parameters of two newly discovered clusters, VVVX CL 076 and CL 077, recently discovered in the galactic disk area covered by the VISTA Variables in the Via Lactea eXtended (VVVX) ESO Public Survey. The preliminary analysis shows that both clusters are young and relatively close to the Sun.Peer reviewedFinal Published versio
Towards an abstract characterization of the subargument relation
Dung’s classic framework is formed by abstract arguments and a binary relation denoting attacks between arguments. Several semantic elaboration and extensions based on this framework are present in the literature. The notion of subargument, however, was not widely studied as an abstract concept although it is an important part of fully implemented argument systems. In this paper we introduce the characterization of properties of a sensible subargument relation in abstract argumentation frameworksWorkshop de Agentes y Sistemas Inteligentes (WASI)Red de Universidades con Carreras en Informática (RedUNCI
Algebraic Cycles as Residues of Meromorphic Forms
According to a classical result of Weil [15], a divisor α of a smooth n-dimensional projective variety X is homologous to zero if and only if it is the residue of a closed meromorphic 1-form on X. Griffiths proved recently [9, pp. 3-8] that a 0-cycle α of X is homologous to zero if and only if it is the Grothendieck residue of a meromorphic n-form ώ on X having poles in the union of a family of complex hypersurfaces Y1 . . . . . Yn, of X, such that ∩ Yi is 0-dimensional and contains the support of α. We show in this paper (Theorem 3.7) that, in fact, any q-dimensional algebraic cycle α of X, 0≦ q ≦ n, is the analytic residue of a semimeromorphic (n-q)-form ώ on X, having poles in the union of a family F = {Y1 . . . . . Yn-q} of hypersurfaces in X such that ∩ F contains the support of α.Facultad de Ciencias Exacta
- …