556 research outputs found
Unconventional Superconductivity in UPd_2Al_3 from Realistic Selfconsistent Calculations
Realistic selfconsistent calculations of unconventional superconductivity in
a heavy-fermion material are reported. Our calculations for UPdAl start
from accurate energy band dispersions that are computed within the local
spin-density functional theory and provide Fermi surfaces in agreement with
experiment. Using physically motivated, realistic pairing potentials it is
shown that the superconducting gap has two lines of nodes around the z-axis,
thus exhibiting d-wave symmetry in the representation of the
point group. Our results suggest that in a superconductor with gap nodes, the
prevailing gap symmetry is dictated by the constraint that nodes must be as far
as possible from high-density areas.Comment: 4 pages and 3 figures (two color figures
Anomalous Ferromagnetism of Monatomic Co Wire at the Pt(111) Surface Step Edge
A first-principles investigation of the anomalous ferromagnetism of a
quasi-one-dimensional Co chain at the Pt(111) step edge is reported. Our
calculations show that the symmetry breaking at the step leads to an easy
magnetization axis at an odd angle of {\em towards} the Pt
step, in agreement with experiment [P. Gambardella {\em et al.}, {\em Nature}
{\bf 416}, 301 (2002)]. Also, the Co spin and orbital moments become
noncollinear, even in the case of a collinear ferromagnetic spin arrangement. A
significant enhancement of the Co orbital magnetic moment is achieved when
modest electron correlations are treated within LSDA+ calculations.Comment: Presented at MRS Meeting in Boston, Dec. 2003; 4 pages including 3
figure
Grain crisis at Prusa : persuading the people in the Imperial Period
This contribution examines an assembly speech that was pronounced by Dio of Prusa in the context of a grain crisis (Or. 46) in order to provide new insights into the politics of the Greek polis under Rome. Whereas inscriptions highlight the eagerness and zeal displayed by elite citizens in helping out their fatherlands, this speech points to the existence of tensions and conflict in the resolution of food crises. The oration’s rhetorical strategies oscillate between the expectations of a popular audience and an elite politician’s desire to shape and control those expectations. A rhetorical analysis of these strategies indicates that Prusan politics was grounded in a civic discourse that provided the people with the ideological means to assert real influence in the local political process. The 46th oration thus attests to the persistence of a democratic tradition of popular political participation in a time when elites had become increasingly powerful
Influence of laser-excited electron distributions on the x-ray magnetic circular dichroism spectra: Implications for femtosecond demagnetization in Ni
In pump-probe experiments an intensive laser pulse creates non-equilibrium
excited electron distributions in the first few hundred femtoseconds after the
pulse. The influence of non-equilibrium electron distributions caused by a pump
laser on the apparent X-ray magnetic circular dichroism (XMCD) signal of Ni is
investigated theoretically here for the first time, considering electron
distributions immediately after the pulse as well as thermalized ones, that are
not in equilibrium with the lattice or spin systems. The XMCD signal is shown
not to be simply proportional to the spin momentum in these situations. The
computed spectra are compared to recent pump-probe XMCD experiments on Ni. We
find that the majority of experimentally observed features considered to be a
proof of ultrafast spin momentum transfer to the lattice can alternatively be
attributed to non-equilibrium electron distributions. Furthermore, we find the
XMCD sum rules for the atomic spin and orbital magnetic moment to remain valid,
even for the laser induced non-equilibrium electron distributions.Comment: 6 pages, 3 figure
Charge-induced spin polarization in non-magnetic organic molecule Alq
Electrical injection in organic semiconductors is a key prerequisite for the
realization of organic spintronics. Using density-functional theory
calculations we report the effect of electron transfer into the organic
molecule Alq. Our first-principles simulations show that electron injection
spontaneously spin-polarizes non-magnetic Alq with a magnetic moment
linearly increasing with induced charge. An asymmetry of the Al--N bond lengths
leads to an asymmetric distribution of injected charge over the molecule. The
spin-polarization arises from a filling of dominantly the nitrogen
orbitals in the molecule's LUMO together with ferromagnetic coupling of the
spins on the quinoline rings.Comment: Accepted 4 pages 4 figure
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