2,529 research outputs found
A parity-breaking electronic nematic phase transition in the spin-orbit coupled metal CdReO
Strong electron interactions can drive metallic systems toward a variety of
well-known symmetry-broken phases, but the instabilities of correlated metals
with strong spin-orbit coupling have only recently begun to be explored. We
uncovered a multipolar nematic phase of matter in the metallic pyrochlore
CdReO using spatially resolved second-harmonic optical anisotropy
measurements. Like previously discovered electronic nematic phases, this
multipolar phase spontaneously breaks rotational symmetry while preserving
translational invariance. However, it has the distinguishing property of being
odd under spatial inversion, which is allowed only in the presence of
spin-orbit coupling. By examining the critical behavior of the multipolar
nematic order parameter, we show that it drives the thermal phase transition
near 200 kelvin in CdReO and induces a parity-breaking lattice
distortion as a secondary order.Comment: 9 pages main text, 4 figures, 10 pages supplementary informatio
Investigations of excitation energy transfer and intramolecular interactions in a nitrogen corded distrylbenzene dendrimer system.
The photophysics of an amino-styrylbenzene dendrimer (A-DSB) system is probed by time-resolved and steady state luminescence spectroscopy. For two different generations of this dendrimer, steady state absorption, emission, and photoluminescence excitation spectra are reported and show that the efficiency of energy transfer from the dendrons to the core is very close to 100%. Ultrafast time-resolved fluorescence measurements at a range of excitation and detection wavelengths suggest rapid (and hence efficient) energy transfer from the dendron to the core. Ultrafast fluorescence anisotropy decay for different dendrimer generations is described in order to probe the energy migration processes. A femtosecond time-scale fluorescence depolarization was observed with the zero and second generation dendrimers. Energy transfer process from the dendrons to the core can be described by a Förster mechanism (hopping dynamics) while the interbranch interaction in A-DSB core was found to be very strong indicating the crossover to exciton dynamics
Doping evolution and polar surface reconstruction of the infinite-layer cuprate SrLaCuO
We use angle-resolved photoemission spectroscopy to study the doping
evolution of infinite-layer SrLaCuO thin films grown by
molecular-beam epitaxy. At low doping, the material exhibits a dispersive lower
Hubbard band typical of the superconducting cuprate parent compounds. As
carriers are added to the system, a continuous evolution from charge-transfer
insulator to superconductor is observed, with the initial lower Hubbard band
pinned well below the Fermi level and the development of a coherent low-energy
band with electron doping. This two-component spectral function emphasizes the
important role that strong local correlations play even at relatively high
doping levels. Electron diffraction probes reveal a surface
reconstruction of the material at low doping levels. Using a number of simple
assumptions, we develop a model of this reconstruction based on the polar
nature of the infinite-layer structure. Finally, we provide evidence for a
thickness-controlled transition in ultrathin films of SrCuO grown on
nonpolar SrTiO, highlighting the diverse structural changes that can occur
in polar complex oxide thin films
Nodeless superconductivity arising from strong (pi,pi) antiferromagnetism in the infinite-layer electron-doped cuprate Sr1-xLaxCuO2
The asymmetry between electron and hole doping remains one of the central
issues in high-temperature cuprate superconductivity, but our understanding of
the electron-doped cuprates has been hampered by apparent discrepancies between
the only two known families: Re2-xCexCuO4 and A1-xLaxCuO2. Here we report in
situ angle-resolved photoemission spectroscopy measurements of
epitaxially-stabilized films of Sr1-xLaxCuO2 synthesized by oxide
molecular-beam epitaxy. Our results reveal a strong coupling between electrons
and (pi,pi) antiferromagnetism that induces a Fermi surface reconstruction
which pushes the nodal states below the Fermi level. This removes the hole
pocket near (pi/2,pi/2), realizing nodeless superconductivity without requiring
a change in the symmetry of the order parameter and providing a universal
understanding of all electron-doped cuprates
Tetrahedral Symmetry in Ground- and Low-Lying States of Exotic A ~ 110 Nuclei
Recent theoretical calculations predict a possible existence of nuclei with
tetrahedral symmetry: more precisely, the mean-field hamiltonians of such
nuclei are symmetric with respect to double point-group Td. In this paper, we
focus on the neutron-rich Zirconium isotopes as an example and present
realistic mean-field calculations which predict tetrahedral ground-state
configurations in 108,110Zr and low-lying excited states of tetrahedral
symmetry in a number of N > 66 isotopes. The motivations for focusing on these
nuclei, as well as a discussion of the possible experimental signatures of
tetrahedral symmetry are also presented.Comment: Accepted in Phys. Rev. C - Rapid Communication
Nuclear Tetrahedral Symmetry: Possibly Present Throughout the Periodic Table
More than half a century after the fundamental, spherical shell structure in
nuclei has been established, theoretical predictions indicate that the
shell-gaps comparable or even stronger than those at spherical shapes may
exist. Group-theoretical analysis supported by realistic mean-field
calculations indicate that the corresponding nuclei are characterized by the
('double-tetrahedral') group of symmetry, exact or approximate. The
corresponding strong shell-gap structure is markedly enhanced by the existence
of the 4-dimensional irreducible representations of the group in question and
consequently it can be seen as a geometrical effect that does not depend on a
particular realization of the mean-field. Possibilities of discovering the
corresponding symmetry in experiment are discussed.Comment: 4 pages in LaTeX and 4 figures in eps forma
Probabilistic models of information retrieval based on measuring the divergence from randomness
We introduce and create a framework for deriving probabilistic models of Information Retrieval. The models are nonparametric models of IR obtained in the language model approach. We derive term-weighting models by measuring the divergence of the actual term distribution from that obtained under a random process. Among the random processes we study the binomial distribution and Bose--Einstein statistics. We define two types of term frequency normalization for tuning term weights in the document--query matching process. The first normalization assumes that documents have the same length and measures the information gain with the observed term once it has been accepted as a good descriptor of the observed document. The second normalization is related to the document length and to other statistics. These two normalization methods are applied to the basic models in succession to obtain weighting formulae. Results show that our framework produces different nonparametric models forming baseline alternatives to the standard tf-idf model
Who I Am: The Meaning of Early Adolescents’ Most Valued Activities and Relationships, and Implications for Self-Concept Research
Self-concept research in early adolescence typically measures young people’s self-perceptions of competence in specific, adult-defined domains. However, studies have rarely explored young people’s own views of valued self-concept factors and their meanings. For two major self domains, the active and the social self, this mixed-methods study identified factors valued most by 526 young people from socioeconomically diverse backgrounds in Ireland (10-12 years), and explored the meanings associated with these in a stratified subsample (n = 99). Findings indicate that self-concept scales for early adolescence omit active and social self factors and meanings valued by young people, raising questions about content validity of scales in these domains. Findings also suggest scales may under-represent girls’ active and social selves; focus too much on some school-based competencies; and, in omitting intrinsically salient self domains and meanings, may focus more on contingent (extrinsic) rather than true (intrinsic) self-esteem
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