354 research outputs found
Out-of-plane nesting driven spin spiral in ultrathin Fe/Cu(001) films
Epitaxial ultrathin Fe films on fcc Cu(001) exhibit a spin spiral (SS), in
contrast to the ferromagnetism of bulk bcc Fe. We study the in-plane and
out-of-plane Fermi surfaces (FSs) of the SS in 8 monolayer Fe/Cu(001) films
using energy dependent soft x-ray momentum-resolved photoemission spectroscopy.
We show that the SS originates in nested regions confined to out-of-plane FSs,
which are drastically modified compared to in-plane FSs. From precise
reciprocal space maps in successive zones, we obtain the associated real space
compressive strain of 1.5+-0.5% along c-axis. An autocorrelation analysis
quantifies the incommensurate ordering vector q=(2pi/a)(0,0,~0.86), favoring a
SS and consistent with magneto-optic Kerr effect experiments. The results
reveal the importance of in-plane and out-of-plane FS mapping for ultrathin
films.Comment: 4 pages, 3 figure
Three-dimensional bulk band dispersion in polar BiTeI with giant Rashba-type spin splitting
In layered polar semiconductor BiTeI, giant Rashba-type spin-split band
dispersions show up due to the crystal structure asymmetry and the strong
spin-orbit interaction. Here we investigate the 3-dimensional (3D) bulk band
structures of BiTeI using the bulk-sensitive -dependent soft x-ray angle
resolved photoemission spectroscopy (SX-ARPES). The obtained band structure is
shown to be well reproducible by the first-principles calculations, with huge
spin splittings of meV at the conduction-band-minimum and
valence-band-maximum located in the plane. It provides the first
direct experimental evidence of the 3D Rashba-type spin splitting in a bulk
compound.Comment: 9 pages, 4 figure
Temperature-Dependence of Magnetically-Active Charge Excitations in Magnetite across the Verwey Transition
We have studied the electronic structure of bulk single crystals and
epitaxial films of magnetite FeO. Fe core-level spectra show clear
differences between hard x-ray (HAX-) and soft x-ray (SX-) photoemission
spectroscopy (PES), indicative of surface effects. The bulk-sensitive spectra
exhibit temperature ()-dependent charge excitations across the Verwey
transition at =122 K, which is missing in the surface-sensitive spectra.
An extended impurity Anderson model full-multiplet analysis reveals roles of
the three distinct Fe-species (A-Fe, B-Fe, B-Fe) below
for the Fe spectra, and its dependent evolution. The Fe
HAXPES spectra show a clear magnetic circular dichroism (MCD) in the metallic
phase of magnetized 100-nm-thick films. The model calculations also reproduce
the MCD and identify the magnetically distinct sites associated with the charge
excitations. Valence band HAXPES shows finite density of states at for
the polaronic metal with remnant order above , and a clear gap formation
below . The results indicate that the Verwey transition is driven by
changes in the strongly correlated and magnetically active B-Fe and
B-Fe electronic states, consistent with resistivity and bulk-sensitive
optical spectra.Comment: 5 pages, 4 figures Accepted in Physical Review Letter
Evidence for a correlated insulator to antiferromagnetic metal transition in CrN
We investigate the electronic structure of Chromium Nitride (CrN) across the
first-order magneto-structural transition at T_N ~ 286 K. Resonant
photoemission spectroscopy shows a gap in the 3d partial density of states at
the Fermi level and an On-site Coulomb energy U ~ 4.5 eV, indicating strong
electron-electron correlations. Bulk-sensitive high resolution (6 meV) laser
photoemission reveals a clear Fermi edge indicating an antiferromagnetic metal
below T_N. Hard x-ray Cr 2p core-level spectra show T-dependent changes across
T_N which originate from screening due to coherent states as substantiated by
cluster model calculations using the experimentally observed U. The electrical
resistivity confirms an insulator above T_N (E_g ~ 70 meV) which becomes a
disordered metal below T_N. The results indicate CrN transforms from a
correlated insulator to an antiferromagnetic metal, coupled to the
magneto-structural transition.Comment: Submitted to Physical Review Letters (February 2010) 11 pages, 3
figures in the main text, 1 Supplementary Informatio
Whole-genome sequencing of Theileria parva strains provides insight into parasite migration and diversification in the african continent
The disease caused by the apicomplexan protozoan parasite Theileria parva, known as East Coast fever or Corridor disease, is one of the most serious cattle diseases in Eastern, Central, and Southern Africa. We performed whole-genome sequencing of nine T. parva strains, including one of the vaccine strains (Kiambu 5), field isolates from Zambia, Uganda, Tanzania, or Rwanda, and two buffalo-derived strains. Comparison with the reference Muguga genome sequence revealed 34 814–121 545 single nucleotide polymorphisms (SNPs) that were more abundant in buffalo-derived strains. High-resolution phylogenetic trees were constructed with selected informative SNPs that allowed the investigation of possible complex recombination events among ancestors of the extant strains. We further analysed the dN/dS ratio (non-synonymous substitutions per non-synonymous site divided by synonymous substitutions per synonymous site) for 4011 coding genes to estimate potential selective pressure. Genes under possible positive selection were identified that may, in turn, assist in the identification of immunogenic proteins or vaccine candidates. This study elucidated the phylogeny of T. parva strains based on genome-wide SNPs analysis with prediction of possible past recombination events, providing insight into the migration, diversification, and evolution of this parasite species in the African continent
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