37 research outputs found
High-energy magnetic excitations in overdoped LaSrCuO studied by neutron and resonant inelastic X-ray scattering
We have performed neutron inelastic scattering and resonant inelastic X-ray
scattering (RIXS) at the Cu- edge to study high-energy magnetic
excitations at energy transfers of more than 100 meV for overdoped
LaSrCuO with ( K) and
(non-superconducting) using identical single crystal samples for the two
techniques. From constant-energy slices of neutron scattering cross-sections,
we have identified magnetic excitations up to ~250 meV for . Although
the width in the momentum direction is large, the peak positions along the (pi,
pi) direction agree with the dispersion relation of the spin-wave in the
non-doped LaCuO (LCO), which is consistent with the previous RIXS
results of cuprate superconductors. Using RIXS at the Cu- edge, we have
measured the dispersion relations of the so-called paramagnon mode along both
(pi, pi) and (pi, 0) directions. Although in both directions the neutron and
RIXS data connect with each other and the paramagnon along (pi, 0) agrees well
with the LCO spin-wave dispersion, the paramagnon in the (pi, pi) direction
probed by RIXS appears to be less dispersive and the excitation energy is lower
than the spin-wave of LCO near (pi/2, pi/2). Thus, our results indicate
consistency between neutron inelastic scattering and RIXS, and elucidate the
entire magnetic excitation in the (pi, pi) direction by the complementary use
of two probes. The polarization dependence of the RIXS profiles indicates that
appreciable charge excitations exist in the same energy range of magnetic
excitations, reflecting the itinerant character of the overdoped sample. A
possible anisotropy in the charge excitation intensity might explain the
apparent differences in the paramagnon dispersion in the (pi, pi) direction as
detected by the X-ray scattering.Comment: 7 pages, 7 figure
Direct observation of bulk charge modulations in optimally-doped BiPbSrCaCuO
Bulk charge density modulations, recently observed in high
critical-temperature () cuprate superconductors, coexist with the
so-called pseudogap and compete with superconductivity. However, its direct
observation has been limited to a narrow doping region in the underdoped
regime. Using energy-resolved resonant x-ray scattering we have found evidence
for such bulk charge modulations, or soft collective charge modes (soft CCMs),
in optimally doped BiPbSrCaCuO
(Pb-Bi2212) around the summit of the superconducting dome with momentum
transfer reciprocal lattice units (r.l.u.) along the
Cu-O bond direction. The signal is stronger at than at
lower temperatures, thereby confirming a competition between soft CCMs and
superconductivity. These results demonstrate that soft CCMs are not constrained
to the underdoped regime, suggesting that soft CCMs appear across a large part
of the phase diagram of cuprates and are intimately entangled with
high- superconductivity.Comment: 6 pages, 3 figures, 1 tabl
Magnetic excitations in stripe-ordered LaBaCuO studied using resonant inelastic x-ray scattering
The charge and spin correlations in LaBaCuO (LBCO
1/8) are studied using Cu edge resonant inelastic x-ray scattering
(RIXS). The static charge order (CO) is observed at a wavevector of
and its charge nature confirmed by measuring the dependence of this peak on the
incident x-ray polarization. The paramagnon excitation in LBCO 1/8 is then
measured as it disperses through the CO wavevector. Within the experimental
uncertainty no changes are observed in the paramagnon due to the static CO, and
the paramagnon seems to be similar to that measured in other cuprates, which
have no static CO. Given that the stripe correlation modulates both the charge
and spin degrees of freedom, it is likely that subtle changes do occur in the
paramagnon due to CO. Consequently, we propose that future RIXS measurements,
realized with higher energy resolution and sensitivity, should be performed to
test for these effects.Comment: 5 pages, 4 figure
Magnetic excitations and phonons simultaneously studied by resonant inelastic x-ray scattering in optimally doped BiPbSrLaCuO
Magnetic excitations in the optimally doped high-
superconductor BiPbSrLaCuO
(OP-Bi2201, K) are investigated by Cu edge
resonant inelastic x-ray scattering (RIXS), below and above the pseudogap
opening temperature. At both temperatures the broad spectral distribution
disperses along the (1,0) direction up to 350~meV at zone boundary,
similarly to other hole-doped cuprates. However, above 0.22 reciprocal
lattice units, we observe a concurrent intensity decrease for magnetic
excitations and quasi-elastic signals with weak temperature dependence. This
anomaly seems to indicate a coupling between magnetic, lattice and charge modes
in this compound. We also compare the magnetic excitation spectra near the
anti-nodal zone boundary in the single layer OP-Bi2201 and in the bi-layer
optimally doped BiPbSrCaCuO
(OP-Bi2212, K). The strong similarities in the
paramagnon dispersion and in their energy at zone boundary indicate that the
strength of the super-exchange interaction and the short-range magnetic
correlation cannot be directly related to , not even within the
same family of cuprates
Preocupações de carreira e adaptabilidade : estudo exploratório com uma amostra de candidatos a sargentos e oficiais do Exército Português
Tese de mestrado, Psicologia (Psicologia dos Recursos Humanos, do Trabalho e das Organizações), Universidade de Lisboa, Faculdade de Psicologia, 2010O presente trabalho consiste num estudo exploratório sobre as preocupações de
carreira e as dimensões da adaptabilidade, baseando-se na Perspectiva de
Desenvolvimento da Carreira de Donald Super e na Perspectiva Construtivista de
Mark Savickas. Pretende-se, ainda, contribuir para a investigação acerca do Inventário
sobre Adaptabilidade, que se encontra ainda em estudo no âmbito de um Projecto
Internacional.
Foram aplicados o Inventário das Preocupações de Carreira e o Inventário sobre
Adaptabilidade a uma amostra de 75 adultos candidatos a Sargentos e Oficiais do
Exército Português. Os resultados obtidos tendem a confirmar as hipóteses de
investigação formuladas, apontando para a relação entre a variável idade e as tarefas
de desenvolvimento das fases da carreira Exploração e Estabelecimento, para a
predominância das dimensões Confiança e Cooperação, e para a relação entre
preocupações de carreira e dimensões da adaptabilidade. Apresentam-se as
conclusões do presente estudo, algumas limitações deste e futuras linhas de
investigação. Tecem-se também algumas considerações sobre as implicações do
estudo para as práticas de gestão de carreira.This work is an exploratory study about the career concerns and the dimensions of
adaptability, based on the Perspective of the Career Development of Donald Super
and the Constructivist Perspective of Mark Savickas. It is also intended to contribute
to the research on the Career Adapt-Abilities Inventory, which is still under
investigation as part of an International Project.
The Career Concerns Inventory and the Career Adapt-Abilities Inventory were
applied to a sample of 75 adult candidates to Sergeants and Officers of the Portuguese
Army. The results seem to confirm the research hypotheses, pointing to the relation
between the variable age and the developmental tasks of the Exploration and
Establishment career phases, to the predominance of the dimensions Cooperation, and
Confidence and also to the relation between career concerns and adaptability
dimensions. The findings of this study, some of its limitations and future research
paths are presented. Some reflections are also discussed in what concerns the study's
implications for the career management practices
Giant phonon anomalies and central peak due to charge density wave formation in YBaCuO
The electron-phonon interaction is a major factor influencing the competition
between collective instabilities in correlated-electron materials, but its role
in driving high-temperature superconductivity in the cuprates remains poorly
understood. We have used high-resolution inelastic x-ray scattering to monitor
low-energy phonons in YBaCuO (superconducting
K), which is close to a charge density wave (CDW) instability. Phonons in a
narrow range of momentum space around the CDW ordering vector exhibit extremely
large superconductivity-induced lineshape renormalizations. These results imply
that the electron-phonon interaction has sufficient strength to generate
various anomalies in electronic spectra, but does not contribute significantly
to Cooper pairing. In addition, a quasi-elastic "central peak" due to CDW
nanodomains is observed in a wide temperature range above and below ,
suggesting that the gradual onset of a spatially inhomogeneous CDW domain state
with decreasing temperature is a generic feature of the underdoped cuprates
Influence of apical oxygen on the extent of in-plane exchange interaction in cuprate superconductors
In high Tc superconductors the magnetic and electronic properties are
determined by the probability that valence electrons virtually jump from site
to site in the CuO2 planes, a mechanism opposed by on-site Coulomb repulsion
and favored by hopping integrals. The spatial extent of the latter is related
to transport properties, including superconductivity, and to the dispersion
relation of spin excitations (magnons). Here, for three antiferromagnetic
parent compounds (single-layer Bi2Sr0.99La1.1CuO6+delta, double-layer
Nd1.2Ba1.8Cu3O6 and infinite-layer CaCuO2) differing by the number of apical
atoms, we compare the magnetic spectra measured by resonant inelastic x-ray
scattering over a significant portion of the reciprocal space and with
unprecedented accuracy. We observe that the absence of apical oxygens increases
the in-plane hopping range and, in CaCuO2, it leads to a genuine 3D
exchange-bond network. These results establish a corresponding relation between
the exchange interactions and the crystal structure, and provide fresh insight
into the materials dependence of the superconducting transition temperature.Comment: 9 pages, 4 figures, 1 Table, 42 reference
4f excitations in Ce Kondo lattices studied by resonant inelastic x-ray scattering
The potential of resonant inelastic soft x-ray scattering to measure 4f crystal electric-field excitation spectra in Ce Kondo lattices has been examined. Spectra have been obtained for several Ce systems and show a well-defined structure determined by crystal-field, spin-orbit, and charge-transfer excitations only. The spectral shapes of the excitation spectra can be well understood in the framework of atomic multiplet calculations. For CeCu2Si2 we found notable disagreement between the inelastic x-ray-scattering spectra and theoretical calculations when using the crystal-field scheme proposed from inelastic neutron scattering. Modified sets of crystal-field parameters yield better agreement. Our results also show that, with the very recent improvements of soft x-ray spectrometers in resolution to below 30 meV at the Ce M4,5 edges, resonant inelastic x-ray scattering could be an ideal tool to determine the crystal-field scheme in Ce Kondo lattices and other rare-earth compounds