416 research outputs found
Temperature-induced reversal of magnetic interlayer exchange coupling
For epitaxial trilayers of the magnetic rare-earth metals Gd and Tb, exchange
coupled through a non-magnetic Y spacer layer, element-specific hysteresis
loops were recorded by the x-ray magneto-optical Kerr effect at the rare-earth
thresholds. This allowed us to quantitatively determine the strength of
interlayer exchange coupling (IEC). In addition to the expected oscillatory
behavior as a function of spacer-layer thickness , a temperature-induced
sign reversal of IEC was observed for constant , arising from
magnetization-dependent electron reflectivities at the magnetic interfaces.Comment: 4 pages, 4 figures; accepted version; minor changes and new Figs. 2
and 4 containing more dat
Rashba Effect at Magnetic Metal Surfaces
We give experimental and theoretical evidence of the Rashba effect at the
magnetic rare-earth metal surface Gd(0001). The Rashba effect is substantially
enhanced and the Rashba parameter changes its sign when a metal-oxide surface
layer is formed. The experimental observations are quantitatively described by
ab initio calculations that give a detailed account of the near-surface charge
density gradients causing the Rashba effect. Since the sign of the Rashba
splitting depends on the magnetization direction, the findings open up new
opportunities for the study of surface and interface magnetism.Comment: 4 Fig
Nodal quasiparticle meltdown in ultra-high resolution pump-probe angle-resolved photoemission
High- cuprate superconductors are characterized by a strong
momentum-dependent anisotropy between the low energy excitations along the
Brillouin zone diagonal (nodal direction) and those along the Brillouin zone
face (antinodal direction). Most obvious is the d-wave superconducting gap,
with the largest magnitude found in the antinodal direction and no gap in the
nodal direction. Additionally, while antinodal quasiparticle excitations appear
only below , superconductivity is thought to be indifferent to nodal
excitations as they are regarded robust and insensitive to . Here we
reveal an unexpected tie between nodal quasiparticles and superconductivity
using high resolution time- and angle-resolved photoemission on optimally doped
BiSrCaCuO. We observe a suppression of the nodal
quasiparticle spectral weight following pump laser excitation and measure its
recovery dynamics. This suppression is dramatically enhanced in the
superconducting state. These results reduce the nodal-antinodal dichotomy and
challenge the conventional view of nodal excitation neutrality in
superconductivity.Comment: 7 pages, 3 figure. To be published in Nature Physic
X-ray magneto-optics of lanthanide materials: principles and applications
Lanthanide metals are a particular class of magnetic materials in which the
magnetic moments are carried mainly by the localized electrons of the 4f shell.
They are frequently found in technically relevant systems, to achieve, e.g.,
high magnetic anisotropy. Magneto-optical methods in the x-ray range are well
suited to study complex magnetic materials in an element-specific way. In this
work, we report on recent progress on the quantitative determination of
magneto-optical constants of several lanthanides in the soft x-ray region and
we show some examples of applications of magneto-optics to hard-magnetic
interfaces and exchange-coupled layered structures containing lanthanide
elements.Comment: 7 pages, 6 figures, invited contribution to the Symposium "X-ray
magneto-optics" of the Spring Meeting of the German Physical Society held in
Regensburg, Germany, 8-12 March 2004. Revised version, minor change
Ce-L3-XAS study of the temperature dependence of the 4f occupancy in the Kondo system Ce2Rh3Al9
We have used temperature dependent x-ray absorption at the Ce-L3 edge to
investigate the recently discovered Kondo compound Ce2Rh3Al9. The systematic
changes of the spectral lineshape with decreasing temperature are analyzed and
found to be related to a change in the occupation number, n_f, as the
system undergoes a transition into a Kondo state. The temperature dependence of
indicates a characteristic temperature of 150K, which is clearly related
with the high temperature anomaly observed in the magnetic susceptibility of
the same system. The further anomaly observed in the resistivity of this system
at low temperature (ca. 20K) has no effect on n_f and is thus not of Kondo
origin.Comment: 7 pages, three figures, submitted to PR
The electronic structure of the doped one-dimensional transition metal oxide Y1-xCaxBaNiO5 studied using x-ray absorption
A strong anisotropic distribution of the holes in Ni 3d and O 2p orbitals is
observed in the polarization dependent O1s and Ni2p3/2 x-ray absorption
spectroscopy of the linear-chain nickelate Y1-xCaxBaNiO5 (x = 0, 0.05, 0.1,
0.2), which demonstrates the one-dimensional nature of the electronic state in
these compounds. Furthermore, the additional holes introduced by Ca-doping
occupy both O 2p and Ni 3d orbitals along the NiO5 chains. By comparing the
experimental Ni 2p3/2 absorption spectra of Y1-xCaxBaNiO5 to those from charge
transfer multiplet calculations we can derive the orbital character of the
additional holes to be of ca. 60% O2p and ca. 40% Ni 3d.Comment: pdf only. Submitted to PR
Prediction of huge X-ray Faraday rotation at the Gd N_4,5 threshold
X-ray absorption spectra in a wide energy range around the 4d-4f excitation
threshold of Gd were recorded by total electron yield from in-plane magnetized
Gd metal films. Matching the experimental spectra to tabulated absorption data
reveals unprecedented short light absorption lengths down to 3 nm. The
associated real parts of the refractive index for circularly polarized light
propagating parallel or antiparallel to the Gd magnetization, determined
through the Kramers-Kronig transformation, correspond to a magneto-optical
Faraday rotation of 0.7 degrees per atomic layer. This finding shall allow the
study of magnetic structure and magnetization dynamics of lanthanide elements
in nanosize systems and dilute alloys.Comment: 4 pages, 2 figures, final version resubmitted to Phys. Rev. B, Brief
Reports. Minor change
Relaxation Dynamics of Photoinduced Changes in the Superfluid Weight of High-Tc Superconductors
In the transient state of d-wave superconductors, we investigate the temporal
variation of photoinduced changes in the superfluid weight. We derive the
formula that relates the nonlinear response function to the nonequilibrium
distribution function. The latter qunatity is obtained by solving the kinetic
equation with the electron-electron and the electron-phonon interaction
included. By numerical calculations, a nonexponential decay is found at low
temperatures in contrast to the usual exponential decay at high temperatures.
The nonexponential decay originates from the nonmonotonous temporal variation
of the nonequilibrium distribution function at low energies. The main physical
process that causes this behavior is not the recombination of quasiparticles as
previous phenomenological studies suggested, but the absorption of phonons.Comment: 18 pages, 12 figures; to be published in J. Phys. Soc. Jpn. Vol. 80,
No.
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