Mn L2,3_{2,3} edge resonant x-ray scattering in manganites: Influence of the magnetic state

We present an analysis of the dependence of the resonant orbital order and magnetic scattering spectra on the spin configuration. We consider an arbitrary spin direction with respect to the local crystal field axis, thus lowering significantly the local symmetry. To evaluate the atomic scattering in this case, we generalized the Hannon-Trammel formula and implemented it inside the framework of atomic multiplet calculations in a crystal field. For an illustration, we calculate the magnetic and orbital scattering in the CE phase of \lsmo in the cases when the spins are aligned with the crystal lattice vector ${\vec a}$ (or equivalently ${\vec b}$) and when they are rotated in the $ab$-plane by 45$^{\circ}$ with respect to this axis. Magnetic spectra differ for the two cases. For the orbital scattering, we show that for the former configuration there is a non negligible $\sigma \to \sigma'$ ($\pi \to \pi'$) scattering component, which vanishes in the 45$^\circ$ case, while the $\sigma \to \pi'$ ($\pi \to \sigma'$) components are similar in the two cases. From the consideration of two 90$^\circ$ spin canted structures, we conclude there is a significant dependence of the orbital scattering spectra on the spin arrangement. Recent experiments detected a sudden decrease of the orbital scattering intensity upon increasing the temperature above the N\' eel temperature in \lsmo. We discuss this behavior considering the effect of different types of misorientations of the spins on the orbital scattering spectrum.Comment: 8 figures. In the revised version, we added a note, a reference, and a few minor changes in Figure 1 and the text. Accepted in Physical Review

Decuplet baryon magnetic moments in a QCD-based quark model beyond quenched approximation

We study the decuplet baryon magnetic moments in a QCD-based quark model beyond quenched approximation. Our approach for unquenching the theory is based on the heavy baryon perturbation theory in which the axial couplings for baryon - meson and the meson-meson-photon couplings from the chiral perturbation theory are used together with the QM moment couplings. It also involves the introduction of a form factor characterizing the structure of baryons considered as composite particles. Using the parameters obtained from fitting the octet baryon magnetic moments, we predict the decuplet baryon magnetic moments. The $\Omega^-$ magnetic moment is found to be in good agreement with experiment: $\mu_{\Omega^-}$ is predicted to be $-1.97 \mu_N$ compared to the experimental result of ($-$2.02 $\pm$ 0.05) $\mu_N$.Comment: 19 pages, 2 figure

The "quasi-stable" lipid shelled microbubble in response to consecutive ultrasound pulses

Controlled microbubble stability upon exposure to consecutive ultrasound exposures is important for increased sensitivity in contrast enhanced ultrasound diagnostics and manipulation for localised drug release. An ultra high-speed camera operating at 13 × 10 6 frames per second is used to show that a physical instability in the encapsulating lipid shell can be promoted by ultrasound, causing loss of shell material that depends on the characteristics of the microbubble motion. This leads to well characterized disruption, and microbubbles follow an irreversible trajectory through the resonance peak, causing the evolution of specific microbubble spectral signatures. © 2012 American Institute of Physics

Analytical description of ballistic spin currents and torques in magnetic tunnel junctions

In this work we demonstrate explicit analytical expressions for both charge and spin currents which constitute the 2x2 spinor in magnetic tunnel junctions with noncollinear magnetizations under applied voltage. The calculations have been performed within the free electron model in the framework of the Keldysh formalism and WKB approximation. We demonstrate that spin/charge currents and spin transfer torques are all explicitly expressed through only three irreducible quantities, without further approximations. The conditions and mechanisms of deviation from the conventional sine angular dependence of both spin currents and torques are shown and discussed. It is shown in the thick barrier approximation that all tunneling transport quantities can be expressed in an extremely simplified form via Slonczewski spin polarizations and our effective spin averaged interfacial transmission probabilities and effective out-of-plane polarizations at both interfaces. It is proven that the latter plays a key role in the emergence of perpendicular spin torque as well as in the angular dependence character of all spin and charge transport considered. It is demonstrated directly also that for any applied voltage, the parallel component of spin current at the FM/I interface is expressed via collinear longitudinal spin current components. Finally, spin transfer torque behavior is analyzed in a view of transverse characteristic length scales for spin transport.Comment: 10 pages, 6 figure

Electromagnetic Moments of the Baryon Decuplet

We compute the leading contributions to the magnetic dipole and electric quadrupole moments of the baryon decuplet in chiral perturbation theory. The measured value for the magnetic moment of the $\Omega^-$ is used to determine the local counterterm for the magnetic moments. We compare the chiral perturbation theory predictions for the magnetic moments of the decuplet with those of the baryon octet and find reasonable agreement with the predictions of the large--$N_c$ limit of QCD. The leading contribution to the quadrupole moment of the $\Delta$ and other members of the decuplet comes from one--loop graphs. The pionic contribution is shown to be proportional to $I_z$ (and so will not contribute to the quadrupole moment of $I=0$ nuclei), while the contribution from kaons has both isovector and isoscalar components. The chiral logarithmic enhancement of both pion and kaon loops has a coefficient that vanishes in the $SU(6)$ limit. The third allowed moment, the magnetic octupole, is shown to be dominated by a local counterterm with corrections arising at two loops. We briefly mention the strange counterparts of these moments.Comment: Uses harvmac.tex, 15 pages with 3 PostScript figures packed using uufiles. UCSD/PTH 93-22, QUSTH-93-05, Duke-TH-93-5

Jahn-Teller Spectral Fingerprint in Molecular Photoemission: C60

The h_u hole spectral intensity for C60 -> C60+ molecular photoemission is calculated at finite temperature by a parameter-free Lanczos diagonalization of the electron-vibration Hamiltonian, including the full 8 H_g, 6 G_g, and 2 A_g mode couplings. The computed spectrum at 800 K is in striking agreement with gas-phase data. The energy separation of the first main shoulder from the main photoemission peak, 230 meV in C60, is shown to measure directly and rather generally the strength of the final-state Jahn-Teller coupling.Comment: 5 pages, 3 figure

Splitting The Gluon?

In the strongly correlated environment of high-temperature cuprate superconductors, the spin and charge degrees of freedom of an electron seem to separate from each other. A similar phenomenon may be present in the strong coupling phase of Yang-Mills theories, where a separation between the color charge and the spin of a gluon could play a role in a mass gap formation. Here we study the phase structure of a decomposed SU(2) Yang-Mills theory in a mean field approximation, by inspecting quantum fluctuations in the condensate which is formed by the color charge component of the gluon field. Our results suggest that the decomposed theory has an involved phase structure. In particular, there appears to be a phase which is quite reminiscent of the superconducting phase in cuprates. We also find evidence that this phase is separated from the asymptotically free theory by an intermediate pseudogap phase.Comment: Improved discussion of magnetic nature of phases; removed unsubstantiated speculation about color confinemen

Voltage Dependence of Spin Transfer Torque in Magnetic Tunnel Junctions

Theoretical investigations of spin transfer torque in magnetic tunnel junctions using the tight-binding model in the framework of non-equilibrium Green functions formalism are presented. We show that the behavior of the spin transfer torque as a function of applied voltage can vary over a wide range depending on the band parameters of the ferromagnetic electrodes and the insulator that comprise the magnetic tunnel junction. The behavior of both the parallel and perpendicular components of the spin torque is addressed. This behavior is explained in terms of the spin and charge current dependence and on the interplay between evanescent states in the insulator and the Fermi surfaces of ferromagnetic electrodes comprising the junction. The origin of the perpendicular (field-like) component of spin transfer torque at zero bias, i.e. exchange coupling through the barrier between ferromagnetic electrodes is discussed.Comment: 5 pages,4 figure

Testing common classical LTE and NLTE model atmosphere and line-formation codes for quantitative spectroscopy of early-type stars

It is generally accepted that the atmospheres of cool/lukewarm stars of spectral types A and later are described well by LTE model atmospheres, while the O-type stars require a detailed treatment of NLTE effects. Here model atmosphere structures, spectral energy distributions and synthetic spectra computed with ATLAS9/SYNTHE and TLUSTY/SYNSPEC, and results from a hybrid method combining LTE atmospheres and NLTE line-formation with DETAIL/SURFACE are compared. Their ability to reproduce observations for effective temperatures between 15000 and 35000 K are verified. Strengths and weaknesses of the different approaches are identified. Recommendations are made as to how to improve the models in order to derive unbiased stellar parameters and chemical abundances in future applications, with special emphasis on Gaia science.Comment: 12 pages, 8 figures; accepted for publication in Journal of Physics: Conference Series, GREAT-ESF Workshop: Stellar Atmospheres in the Gaia Er