222 research outputs found
Knot invariants from Virasoro related representation and pretzel knots
We remind the method to calculate colored Jones polynomials for the plat
representations of knot diagrams from the knowledge of modular transformation
(monodromies) of Virasoro conformal blocks with insertions of degenerate
fields. As an illustration we use a rich family of pretzel knots, lying on a
surface of arbitrary genus g, which was recently analyzed by the evolution
method. Further generalizations can be to generic Virasoro modular
transformations, provided by integral kernels, which can lead to the Hikami
invariants.Comment: 29 page
S-Duality and Modular Transformation as a non-perturbative deformation of the ordinary pq-duality
A recent claim that the S-duality between 4d SUSY gauge theories, which is
AGT related to the modular transformations of 2d conformal blocks, is no more
than an ordinary Fourier transform at the perturbative level, is further traced
down to the commutation relation [P,Q]=-i\hbar between the check-operator
monodromies of the exponential resolvent operator in the underlying
Dotsenko-Fateev matrix models and beta-ensembles. To this end, we treat the
conformal blocks as eigenfunctions of the monodromy check operators, what is
especially simple in the case of one-point toric block. The kernel of the
modular transformation is then defined as the intertwiner of the two
monodromies, and can be obtained straightforwardly, even when the eigenfunction
interpretation of the blocks themselves is technically tedious. In this way, we
provide an elementary derivation of the old expression for the modular kernel
for the one-point toric conformal block.Comment: 15 page
Colored knot polynomials for Pretzel knots and links of arbitrary genus
A very simple expression is conjectured for arbitrary colored Jones and
HOMFLY polynomials of a rich -parametric family of Pretzel knots and
links. The answer for the Jones and HOMFLY polynomials is fully and explicitly
expressed through the Racah matrix of U_q(SU_N), and looks related to a modular
transformation of toric conformal block.Comment: 5 page
Electronic Structure of Transition-Metal Dicyanamides Me[N(CN)] (Me = Mn, Fe, Co, Ni, Cu)
The electronic structure of Me[N(CN)] (Me=Mn, Fe, Co, Ni, Cu)
molecular magnets has been investigated using x-ray emission spectroscopy (XES)
and x-ray photoelectron spectroscopy (XPS) as well as theoretical
density-functional-based methods. Both theory and experiments show that the top
of the valence band is dominated by Me 3d bands, while a strong hybridization
between C 2p and N 2p states determines the valence band electronic structure
away from the top. The 2p contributions from non-equivalent nitrogen sites have
been identified using resonant inelastic x-ray scattering spectroscopy with the
excitation energy tuned near the N 1s threshold. The binding energy of the Me
3d bands and the hybridization between N 2p and Me 3d states both increase in
going across the row from Me = Mn to Me = Cu. Localization of the Cu 3d states
also leads to weak screening of Cu 2p and 3s states, which accounts for shifts
in the core 2p and 3s spectra of the transition metal atoms. Calculations
indicate that the ground-state magnetic ordering, which varies across the
series is largely dependent on the occupation of the metal 3d shell and that
structural differences in the superexchange pathways for different compounds
play a secondary role.Comment: 20 pages, 11 figures, 2 table
Spin States of Cobalt Ions in the Bulk and on the Surface of LaCoO3 Probed by X-ray Absorption, Emission, and Photoelectron Spectra
We present X-ray photoelectron, Co L2,3 and O K X-ray absorption, as well as Co Kβ1,3 X-ray emission spectroscopy results of studies of the spin states of trivalent cobalt ions in single-crystal cobaltite LaCoO3. We show that at room temperature, in the bulk of a LaCoO3 single crystal, Co3+ ions are in the low-spin state, while high-spin Co2+, high-spin Co3+, low-spin Co3+ , and probably also intermediate-spin Co3+ ions are localated on the surface
Dimerization and low-dimensional magnetism in nanocrystalline TiO2 semiconductors doped by Fe and Co
The report is devoted to an analysis of the structural and magnetic state of the nanocrystalline diluted magnetic semiconductors based on TiO2 doped with Fe and Co atoms. Structural and magnetic characterization of samples was carried out using X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS), electron paramagnetic resonance (EPR) spectroscopy, SQUID magnetometry, and the density functional theory (DFT) calculations. Analysis of the experimental data suggests the presence of non-interacting paramagnetic Fe3+ and Co2+ ions in the high-spin state and negative exchange interactions between them. The important conclusions is that the distribution of dopants in the TiO2 matrix, even at low concentrations of 3d-metal dopant (less than one percent), is not random, but the 3d ions localization and dimerization is observed both on the surface and in the nanoparticles core. Thus, in the paper the quantum mechanical model for describing the magnetic properties of TiO2:(Fe, Co) was suggested. The model operates only with two parameters: paramagnetic contribution of non-interacting 3d-ions and dimers having different exchange interactions between 3d magnetic carriers. © Published under licence by IOP Publishing Ltd
High Magnetic Field Behaviour of the Triangular Lattice Antiferromagnet, CuFeO_2
The high magnetic field behaviour of the triangular lattice antiferromagnet
CuFeO_2 is studied using single crystal neutron diffraction measurements in a
field of up to 14.5 T and also by magnetisation measurements in a field of up
to 12 T. At low temperature, two well-defined first order magnetic phase
transitions are found in this range of applied magnetic field (H // c): at
H_c1=7.6(3)/7.1(3) T and H_c2=13.2(1)/12.7(1) T when ramping the field up/down.
In a field above H_c2 the magnetic Bragg peaks show unusual history dependence.
In zero field T_N1=14.2(1) K separates a high temperature paramagnetic and an
intermediate incommensurate structure, while T_N2=11.1(3) K divides an
incommensurate phase from the low-temperature 4-sublattice ground state. The
ordering temperature T_N1 is found to be almost field independent, while T_N2
decreases noticeably in applied field. The magnetic phase diagram is discussed
in terms of the interactions between an applied magnetic field and the highly
frustrated magnetic structure of CuFeO_2Comment: 7 pages, 8 figures in ReVTeX. To appear in PR
Unconventional magnetism of non-uniform distribution of Co in TiO2 nanoparticles
High-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) analysis, electron paramagnetic resonance (EPR), X-ray absorption spectroscopy (XAS), magnetic methods, and density-functional theory (DFT) calculations were applied for the investigations of Co-doped anatase TiO2 nanoparticles (∼20 nm). It was found that high-spin Co2+ ions prefer to occupy the interstitial positions in the TiO2 lattice which are the most energetically favourable in compare to the substitutional those. A quantum mechanical model which operates mainly on two types of Co2+ – Co2+ dimers with different negative exchange interactions and the non-interacting paramagnetic Co2+ ions provides a satisfactorily description of magnetic properties for the TiO2:Co system. © 2020 Elsevier B.V.Russian Foundation for Basic Research. Ministry of Science and Higher Education of the Russian Federatio
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