307 research outputs found
From soft harmonic phonons to fast relaxational dynamics in CHNHPbBr
The lead-halide perovskites, including CHNHPbBr, are
components in cost effective, highly efficient photovoltaics, where the
interactions of the molecular cations with the inorganic framework are
suggested to influence the electronic and ferroelectric properties.
CHNHPbBr undergoes a series of structural transitions
associated with orientational order of the CHNH (MA) molecular
cation and tilting of the PbBr host framework. We apply high-resolution
neutron scattering to study the soft harmonic phonons associated with these
transitions, and find a strong coupling between the PbBr framework and
the quasistatic CHNH dynamics at low energy transfers. At higher
energy transfers, we observe a PbBr octahedra soft mode driving a
transition at 150 K from bound molecular excitations at low temperatures to
relatively fast relaxational excitations that extend up to 50-100 meV.
We suggest that these temporally overdamped dynamics enables possible indirect
band gap processes in these materials that are related to the enhanced
photovoltaic properties.Comment: (main text - 5 pages, 4 figures; supplementary information - 3 pages,
3 figures
Relativistic and retardation effects in the two--photon ionization of hydrogen--like ions
The non-resonant two-photon ionization of hydrogen-like ions is studied in
second-order perturbation theory, based on the Dirac equation. To carry out the
summation over the complete Coulomb spectrum, a Green function approach has
been applied to the computation of the ionization cross sections. Exact
second-order relativistic cross sections are compared with data as obtained
from a relativistic long-wavelength approximation as well as from the scaling
of non-relativistic results. For high-Z ions, the relativistic wavefunction
contraction may lower the two-photon ionization cross sections by a factor of
two or more, while retardation effects appear less pronounced but still give
rise to non-negligible contributions.Comment: 6 pages, 2 figure
Magnetic properties of the overdoped superconductor LaSrCuO with and without Zn impurities
The magnetic properties of the Zn-substituted overdoped high-
superconductor LaSrCuZnO have been studied by
magnetization measurements and neutron scattering. Magnetization measurements
reveal that for Zn-free samples with a Curie term is induced in
the temperature dependence of the magnetic susceptibility implying the
existence of local paramagnetic moments. The induced Curie constant corresponds
to a moment of 0.5 per additional Sr ion that exceeds .
Zn-substitution in the overdoped \lsco also induces a Curie term that
corresponds to 1.2 per Zn ion, simultaneously suppressing .
The relationship between and the magnitude of the Curie term for Zn-free
\lsco with and for Zn-substituted \lsco with are
closely similar. This signifies a general competitive relationship between the
superconductivity and the induced paramagnetic moment. Neutron scattering
measurements show that Zn-substitution in overdoped \lsco anomalously enhances
the inelastic magnetic scattering spectra around the position,
peaking at meV. These facts are discussed on the basis of a
"swiss-cheese" model of Zn-substituted systems as well as a microscopic phase
separation scenario in the overdoped region indicated by muon-spin-relaxation
measurements.Comment: 10 pages, 8 figure
Novel Coexistence of Superconductivity with Two Distinct Magnetic Orders
The heavy fermion Ce(Rh,Ir)In5 system exhibits properties that range from an
incommensurate antiferromagnet on the Rh-rich end to an exotic superconductor
on the Ir-rich end of the phase diagram. At intermediate composition where
antiferromagnetism coexists with superconductivity, two types of magnetic order
are observed: the incommensurate one of CeRhIn5 and a new, commensurate
antiferromagnetism that orders separately. The coexistence of f-electron
superconductivity with two distinct f-electron magnetic orders is unique among
unconventional superconductors, adding a new variety to the usual coexistence
found in magnetic superconductors.Comment: 3 figures, 4 page
Chancen und Grenzen nichtfachlicher Beratung in stationären Pflegeeinrichtungen am Beispiel eines eigenen Coaching-Prozesses
nicht vorhande
Magnetic structure of antiferromagnetic NdRhIn5
The magnetic structure of antiferromagnetic NdRhIn5 has been determined using
neutron diffraction. It has a commensurate antiferromagnetic structure with a
magnetic wave vector (1/2,0,1/2) below T_N = 11K. The staggered Nd moment at
1.6K is 2.6mu_B aligned along the c-axis. We find the magnetic structure to be
closely related to that of its cubic parent compound NdIn3 below 4.6K. The
enhanced T_N and the absence of additional transitions below T_N for NdRhIn5
are interpreted in terms of an improved matching of the
crystalline-electric-field (CEF), magnetocrystalline, and exchange interaction
anisotropies. In comparison, the role of these competing anisotropies on the
magnetic properties of the structurally related compound CeRhIn5 is discussed.Comment: 4 pages, 4 figure
Relativistic Kramers-Pasternack Recurrence Relations
Recently we have evaluated the matrix elements ,O={1,\beta, i\mathbf{\alpha n}\beta} _{3}F_{2}(1) $ for all suitable powers and established two sets of
Pasternack-type matrix identities for these integrals. The corresponding
Kramers--Pasternack three-term vector recurrence relations are derived here.Comment: 12 pages, no figures Will appear as it is in Journal of Physics B:
Atomic, Molecular and Optical Physics, Special Issue on Hight Presicion
Atomic Physic
Electronic properties of UCuSn
Crystallographic analysis shows that UCuSn does not form in the hexagonal CaIn{sub 2} structure as reported previously, but is an ordered ternary compound and forms in an orthorhombic structure. Bulk and neutron-diffraction measurements reveal that UCuSn orders antiferromagnetically below 60 K. At 4.2 K, high-field magnetization reveal a complex magnetization process with two metamagnetic transitions. Furthermore, bulk investigations show an additional anomaly at 25 K, but a regular temperature dependence of various magnetic peaks down to the lowest temperature gives no evidence for a second magnetic transition. Possible scenarios responsible for the drastic changes in the electronic properties around 25 K are discussed
Lamb Shift of 3P and 4P states and the determination of
The fine structure interval of P states in hydrogenlike systems can be
determined theoretically with high precision, because the energy levels of P
states are only slightly influenced by the structure of the nucleus. Therefore
a measurement of the fine structure may serve as an excellent test of QED in
bound systems or alternatively as a means of determining the fine structure
constant with very high precision. In this paper an improved analytic
calculation of higher-order binding corrections to the one-loop self energy of
3P and 4P states in hydrogen-like systems with low nuclear charge number is
presented. A comparison of the analytic results to the extrapolated numerical
data for high ions serves as an independent test of the analytic
evaluation. New theoretical values for the Lamb shift of the P states and for
the fine structure splittings are given.Comment: 33 pages, LaTeX, 4 tables, 4 figure
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