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Probing Ferroelectricity in PbZr0.2Ti0.8O3 with Polarized Soft X-rays

Description: The reduction in symmetry associated with the onset of ferroelectric order in PbZr{sub 0.2}Ti{sub 0.8}O{sub 3} (PZT) thin films leads to a pronounced difference at the Ti L{sub 3,2} absorption edges between spectra measured with the x-ray linear polarization perpendicular and parallel to the ferroelectric polarization. We introduce a general method to analyze the observed difference spectra using atomic multiplet calculations. Moreover, we find experimental evidence for structural changes in PZT induced by the reversal of the ferroelectric polarization.
Date: June 7, 2010
Creator: Arenholz, E.; van der Laan, G.; Fraile-Rodriguez, A.; Yu, P.; He, Q. & Ramesh, R.
Partner: UNT Libraries Government Documents Department

Gaugino mass without singlets

Description: In models with dynamical supersymmetry breaking in the hidden sector, the gaugino masses in the observable sector have been believed to be extremely suppressed (below 1 keV), unless there is a gauge singlet in the hidden sector with specific couplings to the observable sector gauge multiplets. We point out that there is a pure supergravity contribution to gaugino masses at the quantum level arising from the superconformal anomaly. Our results are valid to all orders in perturbation theory and are related to the ''exact'' beta functions for soft terms. There is also an anomaly contribution to the A terms proportional to the beta function of the corresponding Yukawa coupling. The gaugino masses are proportional to the corresponding gauge beta functions, and so do not satisfy the usual GUT relations.
Date: December 21, 1998
Creator: Giudice, Gian F.; Luty, Markus A.; Murayama, Hitoshi & Rattazzi, Riccardo
Partner: UNT Libraries Government Documents Department

DECAYS OF THE Tz = -2 NUCLEI 20Mg, 24Si AND 36Ca

Description: Beta-delayed protons have been observed from the decays of the mass separated T{sub z} = -2 nuclides {sup 20}Mg, {sup 24}Si, and {sup 36}Ca. From these proton spectra the mass excesses of the lowest T = 2 states in the T{sub z} = -1 nuclei {sup 20}Na, {sup 24}Al, and {sup 36}K are determined to be 13420 {+-} 50 keV ({sup 20}Na), 5903 {+-} 9 keV ({sup 24}Al), and - 13168 {+-} 22 keV ({sup 36}K). The complete A = 20, 24, and 36 isospin quintets have all their members bound against isospin allowed particle-decay modes, providing a stringent test of the isobaric multiplet mass equation. Good agreement is observed for all these quintets using only the quadratic form of this equation. Radioactivity {sup 20}Mg, {sup 24}Si, {sup 36}Ca (mass separated); measured {beta}-delayed protons; deduced T{sub 1/2} and proton branching; derived mass excesses of the lowest 0{sup +}, T = 2 states in {sup 20}Na, {sup 24}Al, and {sup 36}K; deduced coefficients of the isobaric multiplet mass equation.
Date: June 1, 1980
Creator: Aysto, J.; Cable, M.D.; Parry, R.F.; Wouters, J.M.; Moltz, D.M. & Cerny, J.
Partner: UNT Libraries Government Documents Department

Search for signatures of magnetically-induced alignment in the arrival directions measured by the Pierre Auger Observatory

Description: We present the results of an analysis of data recorded at the Pierre Auger Observatory in which we search for groups of directionally-aligned events (or ''multiplets'') which exhibit a correlation between arrival direction and the inverse of the energy. These signatures are expected from sets of events coming from the same source after having been deflected by intervening coherent magnetic fields. The observation of several events from the same source would open the possibility to accurately reconstruct the position of the source and also measure the integral of the component of the magnetic field orthogonal to the trajectory of the cosmic rays. We describe the largest multiplets found and compute the probability that they appeared by chance from an isotropic distribution. We find no statistically significant evidence for the presence of multiplets arising from magnetic deflections in the present data.
Date: November 1, 2011
Creator: Abreu, P.; Aglietta, M.; Ahn, E. J.; Albuquerque, I. F. M.; Allard, D.; Allekotte, I. et al.
Partner: UNT Libraries Government Documents Department

Negative Parity 70-plet Baryon Masses in the 1/N{sub c} Expansion

Description: The masses of the negative parity SU(6) 70-plet baryons are analyzed in the 1/N{sub c} expansion to order 1/N{sub c} and to first order in SU(3) breaking. At this level of precision there are twenty predictions. Among them there are the well known Gell-Mann Okubo and equal spacing relations, and four new relations involving SU(3) breaking splittings in different SU(3) multiplets. Although the breaking of SU(6) symmetry occurs at zeroth order in 1/N{sub c}, it turns out to be small. The dominant source of the breaking is the hyperfine interaction which is of order 1/N{sub c}. The spin-orbit interaction, of zeroth order in 1/N{sub c}, is entirely fixed by the splitting between the singlet states A(1405) and A(1520), and the spin-orbit puzzle is resolved by the presence of other zeroth order operators involving flavor exchange.
Date: August 1, 2002
Creator: Goity, Jose; Schat, Carlos L. & Scoccola, Norberto N.
Partner: UNT Libraries Government Documents Department

Core-Level Satellites and Outer Core-Level Multiplet Splitting in Mn Model Compounds

Description: We report a systematic study of the Mn 2p, 3s and 3p core-level photoemission and satellite structures for Mn model compounds. Charge-transfer from the ligand state to the 3d metal state is observed and is distinguished by prominent shake-up satellites. We also observe that the Mn 3s multiplet splitting becomes smaller as the Mn oxidation state increases, and that 3s-3d electron correlation reduces the branching ratio of the 7S:5S states in the Mn 3s spectra. In addition, as the ligand electronegativity decreases, the spin state purity is lost in the 3s spectra as evidenced by peak broadening. Our results are best understood in terms of the configuration-interaction (CI) model including intrashell electron correlation, charge-transfer and final-state screening.
Date: October 18, 1999
Creator: Nelson, A.J.; Reynolds, J.G. & Roos, J.W.
Partner: UNT Libraries Government Documents Department

INFINITE MULTIPLETS.

Description: The main ingredients of the method of infinite multiplets consists of: (1) the use of wave functions with an infinite number of components for describing an infinite tower of discrete states of an isolated system (such as an atom, a nucleus, or a hadron), (2) the use of group theory, instead of dynamical considerations, in determining the properties of the wave functions.
Date: January 1, 1967
Creator: Nambu, Y.
Partner: UNT Libraries Government Documents Department

An alternative NMSSM phenomenology with manifest perturbative unification

Description: Can supersymmetric models with a moderate stop mass be made consistent with the negative Higgs boson searches at LEP, while keeping perturbative unification manifest? The NMSSM achieves this rather easily, but only if extra matter multiplets filling complete SU(5) representations are present at intermediate energies. As a concrete example which makes use of this feature, we give an analytic description of the phenomenology of a constrained NMSSM close to a Peccei-Quinn symmetry point. The related pseudo-Goldstone boson appears in decays of the Higgs bosons and possibly of the lightest neutralino, and itself decays into (b anti-b) and (tau anti-tau).
Date: December 18, 2007
Creator: Hall, Lawrence; Barbieri, Riccardo; Pappadopulo, Duccio; Rychkov, Vyacheslav S.; Hall, Lawrence J. & Papaioannou, Anastasios Y.
Partner: UNT Libraries Government Documents Department

Relativistic Effects, QCD Mixing Angles and N->N<sub>gamma</sub> and Delta->N<sub>gamma</sub> Transition Form Factors

Description: It is shown that relativistic effects, considered in the framework of a relativistic quark model constructed in infinite momentum frame, improve the argument between theory and experiment for delta->N<sub>gamma</sub> transition. They enlarge the magnitudes of the amplitudes A<sup>P</sup><sub>(1/2)</sub> and A<sup>P</sup><sub>(3/2)</sub> and suppress with increasing Q<sup>2</sup> the magnetic form factor of delta->N<sub>gamma</sub> transition in comparison with proton magnetic form factor. The additional inclusion of not large QCD-inspired mixings of multiplet (56',0<sup>+</sup>) into the N and the delta improves further the agreement with experiment for this form factor and permits to describe its Q<sup>2</sup>-dependence at Q<sup>2</sup> < 3 GeV<sup>2</sup>. Predominantly due to the relativistic effects non-zero values for electric and Coulombic form factors of delta->N<sub>gamma</sub> transition are obtained. It is predicted that the electric form factor is positive at Q<sup>2</
Date: January 1, 1992
Creator: Aznauryan, Inna
Partner: UNT Libraries Government Documents Department

Room-temperature photomagnetism in the spinel ferrite (Mn,Zn,Fe)3O4 as seen via soft x-ray magnetic circular dichroism

Description: We have used X-ray magnetic circular dichroism (XMCD) in conjunction with multiplet simulations to directly probe the origin of photomagnetism in nanocrystalline (Mn,Zn,Fe){sub 3}O{sub 4}. A photomagnetic effect at room temperature has been observed in these films with HeNe illumination. We have verified an intervalence charge transfer among octahedral Fe cations to account for the increase in magnetization observed at and above room temperature in small magnetic fields. Using XMCD, we demonstrate that the dichroism of Fe in octahedral sites increases by 18% at room temperature while the dichroism of Fe in tetrahedral sites does not change.
Date: August 1, 2009
Creator: Bettinger, J.S.; Piamonteze, C.; Chopdekar, R.V.; Liberati, M.; Arenholz, E. & Suzuki, Y.
Partner: UNT Libraries Government Documents Department

Site Determination and Magnetism of Mn Doping in Protein Encapsulated Iron Oxide Nanoparticles

Description: Soft-X-ray absorption spectroscopy, soft-X-ray magnetic circular dichroism, and alternating current magnetic susceptibility were performed on 6.7 nm iron oxide nanoparticles doped with (5-33%) Mn grown inside the horse-spleen ferritin protein cages and compared to similarly protein encapsulated pure Fe-oxide and Mn-oxide nanoparticles to determine the site of the Mn dopant and to quantify the magnetic behavior with varying Mn concentration. The Mn dopant is shown to substitute preferentially as Mn{sup +2} and prefers the octahedral site in the defected spinel structure. The Mn multiplet structure for the nanoparticles is simpler than for the bulk standards, suggesting that the nanoparticle lattices are relaxed from the distortions present in the bulk. Addition of Mn is found to alter the host Fe-oxide lattice from a defected ferrimagnetic spinel structure similar to {gamma}-Fe{sub 2}O{sub 3} to an non-ferromagnetic spinel structure with a local Fe environment similar to Fe{sub 3}O{sub 4}.
Date: January 11, 2010
Creator: Pool, V.; Klem, M.; Jolley, J.; Arenholz, E.A.; Douglas, T.; Young, M. et al.
Partner: UNT Libraries Government Documents Department

Strain induced electronic structure changes in magnetic transition metal oxides thin films

Description: We show that the angular dependence of x-ray magnetic circular dichroism (XMCD) is strongly sensitive to strain-induced electronic structure changes in magnetic transition metal oxides. We observe a pronounced dependence of the XMCD spectral shape on the experimental geometry as well as nonvanishing XMCD with distinct spectral features in transverse geometry in compressively strained MnCr{sub 2}O{sub 4} films. The angular dependent XMCD can be described as a sum over an isotropic and anisotropic contribution, the latter linearly proportional to the axial distortion due to strain. The XMCD spectra are well reproduced by atomic multiplet calculations.
Date: July 8, 2010
Creator: van der Laan, G.; Chopdekar, R.V.; Suzuki, Y. & Arenholz, E.
Partner: UNT Libraries Government Documents Department

Spin-orbit inversion of excited heavy quark mesons

Description: The mesonic heavy quark spin multiplets with s{sub l}{sup {pi}{sub l}}=(1/2){sup +} and (3/2){sup +} are expected to be the lowest-lying excitations about the pseudoscalar and vector ground states with s{sub l}{sup {pi}{sub l}}=(1/2){sup {minus}}. The author shows that for charm and bottom these multiplets are probably inverted, with the 2{sup +} and 1{sup +} states with s{sub l}{sup {pi}{sup l}}=(3/2){sup +} about 150 MeV below the 1{sup +} and 0{sup +} states with s{sub l}{sup {pi}{sub l}}=(1/2){sup +}. If verified, such an inversion would both support the expectation that confinement has no dynamical spin-dependence and indicate that heavy and light quark systems may be characterized by the same effective low-energy degrees of freedom. As an important byproduct, this work establishes the dynamics of the strange quark as a critical link between heavy- and light-quark hadrons, justifying efforts toward a much more complete experimental and theoretical understanding of strange mesons and baryons and of strangeonia.
Date: June 1, 1997
Creator: Isgur, Nathan
Partner: UNT Libraries Government Documents Department

Masses of the 70- Baryons in Large Nc QCD

Description: The masses of the negative parity 70-plet baryons are analyzed in large N{sub c} QCD to order 1/N{sub c} and to first order in SU(3) symmetry breaking. The existing experimental data are well reproduced and twenty new observables are predicted. The leading order SU(6) spin-flavor symmetry breaking is small and, as it occurs in the quark model, the subleading in 1/N{sub c} hyperfine interaction is the dominant source of the breaking. It is found that the Lambda(1405) and Lambda(1520) are well described as three-quark states and spin-orbit partners. New relations between splittings in different SU(3) multiplets are found.
Date: November 1, 2001
Creator: Schat, C. L.; Goity, J. L. & Scoccola, N. N.
Partner: UNT Libraries Government Documents Department

Radiative Transitions in Heavy Mesons in a Relativistic Quark Model

Description: The radiative decays of D*, B*, and other excited heavy mesons are analyzed in a relativistic quark model for the light degrees of freedom and in the limit of heavy quark spin-flavor symmetry. The analysis of strong decays carried out in the corresponding chiral quark model is used to calculate the strong decays and determine the branching ratios of the radiative D* decays. Consistency with the observed branching ratios requires the inclusion of the heavy quark component of the electromagnetic current and the introduction of an anomalous magnetic moment for the light quark. It is observed that not only D, but also B meson transitions within a heavy quark spin multiplet are affected by the presence of the heavy quark current.
Date: December 1, 2000
Creator: Goity, J.L. & Roberts, W.
Partner: UNT Libraries Government Documents Department

Relativistic statistical mechanics and particle spectroscopy

Description: The author reviews the formulation of manifestly covariant relativistic statistical mechanics as the description of an ensemble of events in spacetime parameterized by an invariant proper time {tau}. He discusses the linear and cubic mass spectra which result from this formulation (the latter with the inclusion of anti-events) as the actual spectra of an individual hadronic multiplet and hot hadronic matter, respectively. These spectra allow one to predict the masses of particles nucleated to quasi-levels in such an ensemble. As an example, the masses of the ground state mesons and baryons are considered, the results are in excellent agreement with the measured hadron masses. Additivity of inverse Regge slopes is established and shown to be consistent with available experimental data on the D{sup *} meson and {Gamma}{sub c} baryon production.
Date: December 1998
Creator: Burakovsky, L.
Partner: UNT Libraries Government Documents Department

Gauge unification in higher dimensions

Description: A complete 5-dimensional SU(5) unified theory is constructed which, on compactification on the orbifold with two different Z{sub 2}'s (Z{sub 2} and Z{sub 2}{prime}), yields the minimal supersymmetric standard model. The orbifold accomplishes SU(5) gauge symmetry breaking, doublet-triplet splitting, and a vanishing of proton decay from operators of dimension 5. Until 4d supersymmetry is broken, all proton decay from dimension 4 and dimension 5 operators is forced to vanish by an exact U(1){sub R} symmetry. Quarks and leptons and their Yukawa interactions are located at the Z{sub 2} orbifold fixed points, where SU(5) is unbroken. A new mechanism for introducing SU(5) breaking into the quark and lepton masses is introduced, which originates from the SU(5) violation in the zero-mode structure of bulk multiplets. Even though SU(5) is absent at the Z{sub 2}{prime} orbifold fixed point, the brane threshold corrections to gauge coupling unification are argued to be negligibly small, while the logarithmic corrections are small and in a direction which improves the agreement with the experimental measurements of the gauge couplings. Furthermore, the X gauge boson mass is lowered, so that p {yields} e{sup +}{pi}{sup 0} is expected with a rate within about one order of magnitude of the current limit. Supersymmetry breaking occurs on the Z{sub 2}{prime} orbifold fixed point, and is felt directly by the gauge and Higgs sectors, while squarks and sleptons acquire mass via gaugino mediation, solving the supersymmetric flavor problem.
Date: January 14, 2001
Creator: Hall, Lawrence & Nomura, Yasunori
Partner: UNT Libraries Government Documents Department

Symmetry Breaking and Quark-Hadron Duality in Structure Functions

Description: We identify conditions under which a summation over nucleon resonances can yield, via quark-hadron duality, parton model results for electromagnetic and neutrino structure functions at large x. While a summation over the lowest even and odd parity multiplets is sufficient to achieve duality in the symmetric quark model, a suppression of transitions to specific final states is required for more realistic cases incorporating SU(6) breaking. We outline several scenarios consistent with duality, discuss their implications for the high Q{sup 2} behavior of transition form factors, and illustrate how they can expose the patterns in the flavor-spin dependence of short-distance forces in the strong-QCD limit.
Date: January 1, 2003
Creator: Close, Frank & Melnitchouk, Wally
Partner: UNT Libraries Government Documents Department

Resonant Enhancement of Charge Density Wave Diffraction in the Rare-Earth Tri-Tellurides

Description: We performed resonant soft X-ray diffraction on known charge density wave (CDW) compounds, rare earth tri-tellurides. Near the M{sub 5} (3d - 4f) absorption edge of rare earth ions, an intense diffraction peak is detected at a wavevector identical to that of CDW state hosted on Te{sub 2} planes, indicating a CDW-induced modulation on the rare earth ions. Surprisingly, the temperature dependence of the diffraction peak intensity demonstrates an exponential increase at low temperatures, vastly different than that of the CDW order parameter. Assuming 4f multiplet splitting due to the CDW states, we present a model to calculate X-ray absorption spectrum and resonant profile of the diffraction peak, agreeing well with experimental observations. Our results demonstrate a situation where the temperature dependence of resonant X-ray diffraction peak intensity is not directly related to the intrinsic behavior of the order parameter associated with the electronic order, but is dominated by the thermal occupancy of the valence states.
Date: May 15, 2012
Creator: Lee, W.S.; Sorini, A.P.; Yi, M.; Chuang, Y.D.; Moritz, B.; Yang, W.L. et al.
Partner: UNT Libraries Government Documents Department

Direct contact vs. solvent-shared ion pairs in nicl2 electrolytesmonitored by multiplet effects at the ni(ii) l-edge x-ray absorptionDOC_XNOTE=Published by BESSY, Germany in collaboration with LawrenceBerkeley National Laboratory staff.

Description: We investigate the local electronic structure in aqueous NiCl{sub 2} electrolytes by Ni L edge x-ray absorption spectroscopy. The experimental findings are interpreted in conjunction with multiplet calculations of the electronic structure and the resulting spectral shape. In contrast to the situation in the solid, the electronic structure in the electrolyte reflects the absence of direct contact Ni-Cl ion pairs. We observe a systematic change of the intensity ratio of singlet and triplet-related spectral features as a function of electrolyte concentration. These changes can be described theoretically by a changed weight of transition matrix contributions with different symmetry. We interpret these findings as being due to progressive distortions of the local symmetry induced by solvent-shared ion pairs.
Date: March 29, 2007
Creator: Aziz, E.F.; Eisebitt, S.; Eberhardt, W.; de Groot, F.; Chiou,J.W.; Dong, C.L. et al.
Partner: UNT Libraries Government Documents Department

Angle-dependent Ni2+ x-ray magnetic linear dichroism: Interfacialcoupling revisited

Description: Using x ray magnetic linear dichroism (XMLD) for magnetometry requires detailed knowledge of its dependence on the relative orientation of polarization, magnetic moments, and crystallographic axes. We show that Ni{sup 2+} L{sub 2,3} XMLD in cubic lattices has to be described as linear combination of two fundamental spectra - not one as previously assumed. The spectra are calculated using atomic multiplet theory and the angular dependence is derived from crystal field symmetry. Applying our results to Co/NiO(001) interfaces, we find perpendicular coupling between Ni and Co moments.
Date: August 25, 2007
Creator: Arenholz, Elke; van der Laan, Gerrit; Chopdekar, Rajesh V. & Suzuki, Yuri
Partner: UNT Libraries Government Documents Department

Anisotropic x-ray magnetic linear dichroism at the Fe L2,3 edgesin Fe3O4

Description: X-ray magnetic linear dichroism at the Fe L{sub 2,3} edges of the ferrimagnet Fe{sub 3}O{sub 4} was found to exhibit a strong dependence on the relative orientation of external magnetic field, x-ray polarization, and crystalline axes. Spectral shape and magnitude of the effect were determined for Fe{sub 3}O{sub 4}(011) and Fe{sub 3}O{sub 4}(001) thin films varying the in-plane orientation of field and polarization. All dichroism spectra can be described as a linear combination of three fundamental spectra which in turn give a good agreement with calculated spectra using atomic multiplet theory. The angular dependence of the magnetic dichroism reflects the crystal field symmetry. It can be used to estimate the crystal field splitting and allows determining the spin quantization axis.
Date: April 30, 2006
Creator: Arenholz, Elke; van der Laan, Gerrit; Chopdekar, Rajesh V. & Suzuki, Yuri
Partner: UNT Libraries Government Documents Department

Magnetic order and interfacial coupling in oxide thin films and heterostructures probed with soft x-ray dichroism

Description: The combination of novel magnetic properties induced by reduced dimensionality and strong magnetic interactions across interfaces leads to intriguing new properties in magnetic hetero- and nanostructures not observed in the constituent materials in bulk form. It is the careful optimization of the characteristics of the individual layers as well as the magnetic coupling across the interface that allows us to control the magnetic properties and tailor them for devices, e.g., in information storage and processing technology. Soft x-ray magnetic spectroscopies can make unique contributions to improving our understanding of complex magnetic nanostructures since these techniques provide elemental, valence- and site-symmetry specific information with high sensitivity and tunable probing depth. X-ray magnetic circular dichroism (XMCD) is sensitive to (unidirectional) ferromagnetic order, while x-ray magnetic linear dichroism (XMLD) can also detect (uniaxial) antiferromagnetic order. A crystalline electric field with cubic symmetry induces only a weak angular dependence in XMCD spectra [1] but can cause a very pronounced anisotropy in XMLD spectra [2]. Furthermore, non-magnetic sites with a distorted local cubic symmetry can give rise to an x-ray linear dichroism (XLD). In this presentation, we discuss how to distinguish between the individual contributions to soft x-ray dichroism spectra in order to extract the wealth of information about magnetic thin films, interfaces and hetero- and nanostructures contained in the data [3, 4, 5] We determined the magnetic structure of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} (LSMO)/La{sub 0.7}Sr{sub 0.3}FeO{sub 3} (LSFO) superlattices with 6 unit cell thick sublayers using soft x-ray magnetic dichroism [5]. Circular dichroism was employed to study the characteristics of the ferromagnetic LSMO layer indicating a reduced magnetic ordering temperature of 200 K compared to the bulk value of 360 K. Linear dichroism is used to analyze the antiferromagnetic order in the LSFO layers which persists up to the bulk Neel temperature near 400 ...
Date: February 1, 2009
Creator: Arenholz, Elke & van der Laan, G.
Partner: UNT Libraries Government Documents Department