1,193 research outputs found
Cleaving-temperature dependence of layered-oxide surfaces
The surfaces generated by cleaving non-polar, two-dimensional oxides are
often considered to be perfect or ideal. However, single particle
spectroscopies on Sr2RuO4, an archetypal non-polar two dimensional oxide, show
significant cleavage temperature dependence. We demonstrate that this is not a
consequence of the intrinsic characteristics of the surface: lattice parameters
and symmetries, step heights, atom positions, or density of states. Instead, we
find a marked increase in the density of defects at the mesoscopic scale with
increased cleave temperature. The potential generality of these defects to
oxide surfaces may have broad consequences to interfacial control and the
interpretation of surface sensitive measurements
Epitaxial influence on the ferromagnetic semiconducotor EuO
From first principles calculations we investigate the electronic structure
and the magnetic properties of EuO under hydrostatic and epitaxial forces.
There is a complex interdependence of the O 2p and Eu 4f and 5d bands on the
magnetism in EuO, and decreasing lattice parameters is an ideal method to
increase the Curie temperature, T_c. Compared to hydrostatic pressure, the
out-of-plane compensation that is available to epitaxial films influences this
increase in T_c, although it is minimized by the small value of poisson's ratio
for EuO. We find the semiconducting gap closes at a 6% in-plane lattice
compression for epitaxy, at which point a significant conceptual change must
occur in the active exchange mechanisms
Coupling Of The B1g Phonon To The Anti-Nodal Electronic States of Bi2Sr2Ca0.92Y0.08Cu2O(8+delta)
Angle-resolved photoemission spectroscopy (ARPES) on optimally doped
Bi2Sr2Ca0.92Y0.08Cu2O(8+delta) uncovers a coupling of the electronic bands to a
40 meV mode in an extended k-space region away from the nodal direction,
leading to a new interpretation of the strong renormalization of the electronic
structure seen in Bi2212. Phenomenological agreements with neutron and Raman
experiments suggest that this mode is the B1g oxygen bond-buckling phonon. A
theoretical calculation based on this assignment reproduces the electronic
renormalization seen in the data.Comment: 4 Pages, 4 Figures Updated Figures and Tex
Doping dependence of the coupling of electrons to bosonic modes in the single-layer high-temperature Bi2Sr2CuO6 superconductor
A recent highlight in the study of high-Tc superconductors is the observation
of band renormalization / self-energy effects on the quasiparticles. This is
seen in the form of kinks in the quasiparticle dispersions as measured by
photoemission and interpreted as signatures of collective bosonic modes
coupling to the electrons. Here we compare for the first time the self-energies
in an optimally doped and strongly overdoped, non-superconducting single-layer
Bi-cuprate (Bi2Sr2CuO6). Besides the appearance of a strong overall weakening,
we also find that weight of the self-energy in the overdoped system shifts to
higher energies. We present evidence that this is related to a change in the
coupling to c-axis phonons due to the rapid change of the c-axis screening in
this doping range.Comment: 4 pages, 3 figure
Extreme population inversion in the fragments formed by UV photoinduced S-H bond fission in 2-thiophenethiol
H atom loss following near ultraviolet photoexcitation of gas phase 2-thiophenethiol molecules has been studied experimentally, by photofragment translational spectroscopy (PTS) methods, and computationally, by ab initio electronic structure calculations. The long wavelength (277.5 ℠λphot â„ 240 nm) PTS data are consistent with SâH bond fission after population of the first 1ÏÏ* state. The partner thiophenethiyl (R) radicals are formed predominantly in their first excited Ă2AâČ state, but assignment of a weak signal attributable to H + R([X with combining tilde]2AâČâČ) products allows determination of the SâH bond strength, D0 = 27 800 ± 100 cmâ1 and the Ăâ[X with combining tilde] state splitting in the thiophenethiyl radical (ÎE = 3580 ± 100 cmâ1). The deduced population inversion between the Ă and [X with combining tilde] states of the radical reflects the non-planar ground state geometry (wherein the SâH bond is directed near orthogonal to the ring plane) which, post-photoexcitation, is unable to planarise sufficiently prior to bond fission. This dictates that the dissociating molecules follow the adiabatic fragmentation pathway to electronically excited radical products. Ï* â Ï absorption dominates at shorter excitation wavelengths. Coupling to the same 1ÏÏ* potential energy surface (PES) remains the dominant dissociation route, but a minor yield of H atoms attributable to a rival fragmentation pathway is identified. These products are deduced to arise via unimolecular decay following internal conversion to the ground (S0) state PES via a conical intersection accessed by intra-ring CâS bond extension. The measured translational energy disposal shows a more striking change once λphot †220 nm. Once again, however, the dominant decay pathway is deduced to be SâH bond fission following coupling to the 1ÏÏ* PES but, in this case, many of the evolving molecules are deduced to have sufficiently near-planar geometries to allow passage through the conical intersection at extended SâH bond lengths and dissociation to ground ([X with combining tilde]) state radical products. The present data provide no definitive evidence that complete ring opening can compete with fast SâH bond fission following near UV photoexcitation of 2-thiophenethiol
Quantitative analysis of Sr2RuO4 ARPES spectra: Many-body interactions in a model Fermi liquid
ARPES spectra hold a wealth of information about the many-body interactions
in a correlated material. However, the quantitative analysis of ARPES spectra
to extract the various coupling parameters in a consistent manner is extremely
challenging, even for a model Fermi liquid system. We propose a fitting
procedure which allows quantitative access to the intrinsic lineshape,
deconvolved of energy and momentum resolution effects, of the correlated
2-dimensional material Sr2RuO4. For the first time in correlated 2-dimensional
materials, we find an ARPES linewidth that is narrower than its binding energy,
a key property of quasiparticles within Fermi liquid theory. We also find that
when the electron-electron scattering component is separated from the
electron-phonon and impurity scattering terms it decreases with a functional
form compatible with Fermi liquid theory as the Fermi energy is approached. In
combination with the previously determined Fermi surface, these results give
the first complete picture of a Fermi liquid system via ARPES. Furthermore, we
show that the magnitude of the extracted imaginary part of the self-energy is
in remarkable agreement with DC transport measurements.Comment: 10 pages, 5 figure
Estrogen as therapy for breast cancer
High-dose estrogen was generally considered the endocrine therapy of choice for postmenopausal women with breast cancer prior to the introduction of tamoxifen. Subsequently, the use of estrogen was largely abandoned. Recent clinical trial data have shown clinically meaningful efficacy for high-dose estrogen even in patients with extensive prior endocrine therapy. Preclinical research has demonstrated that the estrogen dose-response curve for breast cancer cells can be shifted by modification of the estrogen environment. Clinical and laboratory data together provide the basis for developing testable hypotheses of management strategies, with the potential of increasing the value of endocrine therapy in women with breast cancer
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