221 research outputs found
Maximally-localized Wannier Functions in Antiferromagnetic MnO within the FLAPW Formalism
We have calculated the maximally-localized Wannier functions of MnO in its
antiferromagnetic (AFM) rhombohedral unit cell, which contains two formula
units. Electron Bloch functions are obtained with the linearized augmented
plane-wave method within both the LSD and the LSD+U schemes. The thirteen
uppermost occupied spin-up bands correspond in a pure ionic scheme to the five
Mn 3d orbitals at the Mn_1 (spin-up) site, and the four O 2s/2p orbitals at
each of the O_1 and O_2 sites. Maximal localization identifies uniquely four
Wannier functions for each O, which are trigonally-distorted sp^3-like
orbitals. They display a weak covalent bonding between O 2s/2p states and
minority-spin d states of Mn_2, which is absent in a fully ionic picture. This
bonding is the fingerprint of the interaction responsible for the AFM ordering,
and its strength depends on the one-electron scheme being used. The five Mn
Wannier functions are centered on the Mn_1 site, and are atomic orbitals
modified by the crystal field. They are not uniquely defined by the criterion
of maximal localization and we choose them as the linear combinations which
diagonalize the r^2 operator, so that they display the D_3d symmetry of the
Mn_1 site.Comment: 11 pages, 6 PostScript figures. Uses Revtex4. Hi-res figures
available from the author
Facile route to effective antimicrobial aluminum oxide layer realized by co-deposition with silver nitrate
The emergence and spreading of the SARS-CoV-2 pandemic has forced the focus of attention on a significant issue: the realization of antimicrobial surfaces for public spaces, which do not require extensive use of disinfectants. Silver represents one of the most used elements in this context, thanks to its excellent biocidal performance. This work describes a simple method for the realization of anodized aluminum layers, whose antimicrobial features are ensured by the co-deposition with silver nitrate. The durability and the chemical resistance of the samples were evaluated by means of several accelerated degradation tests, such as the exposure in a salt spray chamber, the contact with synthetic sweat and the scrub test, highlighting the residual influence of silver in altering the protective behavior of the alumina layers. Furthermore, the ISO 22196:2011 standard was used as the reference protocol to set up an assay to measure the effective antibacterial activity of the alumina-Ag layers against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria, even at low concentrations of silver. Finally, the Ag-containing aluminum oxide layers exhibited excellent antimicrobial performances also following the chemical–physical degradation processes, ensuring good durability over time of the antimicrobial surfaces. Overall, this work introduces a simple route for the realization of anodized aluminum surfaces with excellent antibacterial properties
Influence of the MCT1 rs1049434 on Indirect Muscle Disorders/Injuries in Elite Football Players
The aim of this study was to investigate the association between MCT1 rs1049434 polymorphism and indirect muscle injuries in elite football players. One hundred and seventy-three male elite Italian football players (age = 19.2 ± 5.3 years) were recruited from a first-league football club participating at the Official National Italian Football Championship (Serie A, Primavera, Allievi, Giovanissimi). The cohort was genotyped for the MCT1 rs1049434 polymorphism, and muscle injuries data were collected during the period of 2009-2014 (five football seasons).Genomic DNA was extracted using a buccal swab, and genotyping was performed using PCR method. Structural-mechanical injuries and functional muscle disorder were included in the acute indirect muscle injury group.Participants with the MCT1 AA (AA = 1.57 ± 3.07, n = 69) genotype exhibit significantly higher injury incidents compared to participants with the TT genotype (TT = 0.09 ± 0.25, n = 22, P = 0.04).The MCT1 rs1049434 polymorphism is associated with the incidence of muscle injuries in elite football players. We anticipate that the knowledge of athletes' genetic predisposition to sports-related injuries might aid in individualizing training programs
The effect of magnetic impurities in a two-band superconductor: A point-contact study of Mn-substituted MgB2 single crystals
We present the first results of directional point-contact measurements in
Mg_{1-x}Mn_{x}B_2 single crystals, with x up to 0.015 and bulk T_c down to 13.3
K. The order parameters Delta_{sigma} and Delta_{pi} were obtained by fitting
the conductance curves with the two-band Blonder-Tinkham-Klapwijk (BTK) model.
Both Delta_{pi} and Delta_{sigma} decrease with the critical temperature of the
junctions T_c^A, but remain clearly distinct up to the highest Mn content. Once
analyzed within the Eliashberg theory, the results indicate that spin-flip
scattering is dominant in the sigma band, as also confirmed by first-principle
band structure calculations.Comment: 4 pages, 5 eps figures. New theoretical results added, text and some
figures changed. References adde
Point defects, ferromagnetism and transport in calcium hexaboride
The formation energy and local magnetic moment of a series of point defects
in CaB are computed using a supercell approach within the generalized
gradient approximation to density functional theory. Based on these results,
speculations are made as to the influence of these defects on electrical
transport. It is found that the substitution of Ca by La does not lead to the
formation of a local moment, while a neutral B vacancy carries a moment of
2.4 Bohr magnetons, mostly distributed over the six nearest-neighbour B atoms.
A plausible mechanism for the ferromagnetic ordering of these moments is
suggested. Since the same broken B-B bonds appear on the preferred (100)
cleavage planes of the CaB structure, it is argued that internal surfaces
in polycrystals as well as external surfaces in general will make a large
contribution to the observed magnetization.Comment: Calculated defect formation energies had to be corrected, due to the
use of a wrong reference energy for the perfect crystal in the original pape
Electronic Fine Structure in the Electron-Hole Plasma in SrB6
Electron-hole mixing-induced fine structure in alkaline earth hexaborides
leads to lower energy (temperature) scales, and thus stronger tendency toward
an excitonic instability, than in their doped counterparts (viz.
Ca(1-x)La(x)B(6), x=0.005), which are high Curie temperature, small moment
ferromagnets. Comparison of Fermi surfaces and spectral distributions with de
Haas - van Alphen (dHvA), optical, transport, and tunneling data indicates that
SrB6 remains a fermionic semimetal down to (at least) 5 K, rather than forming
an excitonic condensate. For the doped system the Curie temperature is higher
than the degeneracy temperature.Comment: Four two-column pages, three postscript figures. Phys. Rev. Lett.
(April 2000, in press
Excitonic order at strong-coupling: pseudo-spins, doping, and ferromagnetism
A tight binding model is introduced to describe the strong interaction limit
of excitonic ordering. At stoichiometry, the model reduces in the strong
coupling limit to a pseudo-spin model with approximate U(4) symmetry. Excitonic
order appears in the pseudo-spin model as in-plane pseudo-magnetism. The U(4)
symmetry unifies all possible singlet and triplet order parameters describing
such states. Super-exchange, Hunds-rule coupling, and other perturbations act
as anisotropies splitting the U(4) manifold, ultimately stabilizing a
paramagnetic triplet state. The tendency to ferromagnetism with doping
(observed experimentally in the hexaborides) is explained as a spin-flop
transition to a different orientation of the U(4) order parameter. The physical
mechanism favoring such a reorientation is the enhanced coherence (and hence
lower kinetic energy) of the doped electrons in a ferromagnetic background
relative to the paramagnet. A discussion of the physical meaning of various
excitonic states and their experimental consequences is also provided.Comment: 16 pages, 5 figure
Electronic structure of the MO oxides (M=Mg, Ca, Ti, V) in the GW approximation
The quasiparticle band structures of nonmagnetic monoxides, MO (M=Mg, Ca, Ti,
and V), are calculated by the GW approximation. The band gap and the width of
occupied oxygen 2p states in insulating MgO and CaO agree with experimental
observation. In metallic TiO and VO, conduction bands originated from metal 3d
states become narrower. Then the partial densities of transition metal e_g and
t_2g states show an enhanced dip between the two. The effects of static
screening and dynamical correlation are discussed in detail in comparison with
the results of the Hartree-Fock approximation and the static Coulomb hole plus
screened exchange approximation. The d-d Coulomb interaction is shown to be
very much reduced by on-site and off-site d-electron screening in TiO and VO.
The dielectric function and the energy loss spectrum are also presented and
discussed in detail.Comment: 10 pages, 5 figure
Ferromagnetism below the Stoner limit in La-doped SrB_6
Spin-polarized band calculations for LaSr_7B_{48} show a weak ferro-magnetic
state. This is despite a low density-of-states (DOS) and a low Stoner factor.
The reason for the magnetic state is found to be associated with a gain in
potential energy in addition to the exchange energy, as a spin-splitting is
imposed. An impurity like La DOS is essential for this effect. It makes a
correction to the Stoner factor, and provides an explanation of the recently
observed weak ferro-magnetism in doped hexaborides.Comment: 6 pages, 2 tables, 1 figur
Tight-binding modelling of the electronic band structure of layered superconducting perovskites
A detailed tight-binding analysis of the electron band structure of the CuO_2
plane of layered cuprates is performed within a sigma-band Hamiltonian
including four orbitals - Cu3d_x^2-y^2, Cu4s, O2p_x, and O2p_y. Both the
experimental and theoretical hints in favor of Fermi level located in a Cu or O
band, respectively, are considered. For these two alternatives analytical
expressions are obtained for the LCAO electron wave functions suitable for the
treatment of electron superexchange. Simple formulae for the Fermi surface and
electron dispersions are derived by applying the Loewdin down-fold procedure to
set up the effective copper and oxygen Hamiltonians. They are used to fit the
experimental ARUPS Fermi surface of Pb_0.42Bi_1.73Sr_1.94Ca_1.3Cu_1.92O_8+x and
both the ARPES and LDA Fermi surface of Nd_2-xCe_xCuO_4-delta. The value of
presenting the hopping amplitudes as surface integrals of ab initio atomic wave
functions is demonstrated as well. The same approach is applied to the RuO_2
plane of the ruthenate Sr_2RuO_4. The LCAO Hamiltonians including the three
in-plane pi-orbitals Ru4d_xy, O_a 2p_y, O_b 2p_x and the four transversal
pi-orbitals Ru4d_zx, Ru4d_yz, O_a 2p_z, O_b 2p_z, are separately considered. It
is shown that the equation for the constant energy curves and the Fermi
contours has the same canonical form as the one for the layered cuprates.Comment: 21 pages, 10 figures, published in J. Phys.: Condens. Matter
(complete and corrected References section
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