3,167 research outputs found
Definitive Identification of the Transition between Small- to Large-Scale Clustering for Lyman Break Galaxies
We report angular correlation function (ACF) of Lyman Break Galaxies (LBGs)
with unprecedented statistical quality on the basis of 16,920 LBGs at z=4
detected in the 1 deg^2 sky of the Subaru/XMM-Newton Deep Field. The ACF
significantly departs from a power law, and shows an excess on small scale.
Particularly, the ACF of LBGs with i'<27.5 have a clear break between the small
and large-scale regimes at the angular separation of ~7'' whose projected
length corresponds to the virial radius of dark halos with a mass of 10^11-12
Mo, indicating multiple LBGs residing in a single dark halo. Both on small
(2''<theta<3'') and large (40''<theta<400'') scales, clustering amplitudes
monotonically increase with luminosity for the magnitude range of i'=24.5-27.5,
and the small-scale clustering shows a stronger luminosity dependence than the
large-scale clustering. The small-scale bias reaches b~10-50, and the outskirts
of small-scale excess extend to a larger angular separation for brighter LBGs.
The ACF and number density of LBGs can be explained by the cold dark matter
model.Comment: Accepted for publication in ApJL. 5 pages, 4 figures. The text and
Figures 2-4 have been revised. There is no major change which affects to the
main discussion shown in the original preprint. This paper with high
resolution figures is available at
http://www-int.stsci.edu/~ouchi/work/astroph/sxds_z4LBG/ouchi_highres.pdf
(PDF
Origin of the Verwey transition in magnetite: Group theory, electronic structure, and lattice dynamics study
The Verwey phase transition in magnetite has been analyzed using the group
theory methods. It is found that two order parameters with the symmetries
and induce the structural transformation from the high-temperature
cubic to the low-temperature monoclinic phase. The coupling between the order
parameters is described by the Landau free energy functional. The electronic
and crystal structure for the cubic and monoclinic phases were optimized using
the {\it ab initio} density functional method. The electronic structure
calculations were performed within the generalized gradient approximation
including the on-site interactions between 3d electrons at iron ions -- the
Coulomb element and Hund's exchange . Only when these local interactions
are taken into account, the phonon dispersion curves, obtained by the direct
method for the cubic phase, reproduce the experimental data. It is shown that
the interplay of local electron interations and the coupling to the lattice
drives the phonon order parameters and is responsible for the opening of the
gap at the Fermi energy. Thus, it is found that the metal-insulator transition
in magnetite is promoted by local electron interactions, which significantly
amplify the electron-phonon interaction and stabilize weak charge order
coexisting with orbital order of the occupied states at Fe ions. This
provides a scenario to understand the fundamental problem of the origin of the
Verwey transition in magnetite.Comment: 17 pages, 5 figures, 8 tables. Accepted version to be published in
Phys. Rev.
Angle-resolved photoemission study of insulating and metallic Cu-O chains in PrBaCuO and PrBaCuO
We compare the angle-resolved photoemission spectra of the hole-doped Cu-O
chains in PrBaCuO (Pr123) and in PrBaCuO (Pr124).
While, in Pr123, a dispersive feature from the chain takes a band maximum at
(momentum along the chain) and loses its spectral weight
around the Fermi level, it reaches the Fermi level at in
Pr124. Although the chains in Pr123 and Pr124 are approximately 1/4-filled,
they show contrasting behaviors: While the chains in Pr123 have an instability
to charge ordering, those in Pr124 avoid it and show an interesting spectral
feature of a metallic coupled-chain system.Comment: 4 pages, 5 figures, to be published in PR
Enhanced Kondo Effect in an Electron System Dynamically Coupled with Local Optical Phonon
We discuss Kondo behavior of a conduction electron system coupled with local
optical phonon by analyzing the Anderson-Holstein model with the use of a
numerical renormalization group (NRG) method. There appear three typical
regions due to the balance between Coulomb interaction and
phonon-mediated attraction . For , we
observe the standard Kondo effect concerning spin degree of freedom. Since the
Coulomb interaction is effectively reduced as , the
Kondo temperature is increased when is increased. On
the other hand, for , there occurs the Kondo effect
concerning charge degree of freedom, since vacant and double occupied states
play roles of pseudo-spins. Note that in this case, is decreased
with the increase of . Namely, should be maximized for
. Then, we analyze in detail the Kondo behavior
at , which is found to be explained by the polaron
Anderson model with reduced hybridization of polaron and residual repulsive
interaction among polarons. By comparing the NRG results of the polaron
Anderson model with those of the original Anderson-Holstein model, we clarify
the Kondo behavior in the competing region of .Comment: 8 pages, 8 figure
High-energy spin and charge excitations in electron-doped copper oxide superconductors
The evolution of electronic (spin and charge) excitations upon carrier doping
is an extremely important issue in superconducting layered cuprates and the
knowledge of its asymmetry between electron- and hole-dopings is still
fragmentary. Here we combine x-ray and neutron inelastic scattering
measurements to track the doping dependence of both spin and charge excitations
in electron-doped materials. Copper L3 resonant inelastic x-ray scattering
spectra show that magnetic excitations shift to higher energy upon doping.
Their dispersion becomes steeper near the magnetic zone center and deeply mix
with charge excitations, indicating that electrons acquire a highly itinerant
character in the doped metallic state. Moreover, above the magnetic
excitations, an additional dispersing feature is observed near the
{\Gamma}-point, and we ascribe it to particle-hole charge excitations. These
properties are in stark contrast with the more localized spin-excitations
(paramagnons) recently observed in hole-doped compounds even at high
doping-levels.Comment: 20 page
Doping dependence of the shadow band in La-based cuprates studied by angle-resolved photoemission spectroscopy
The shadow band (SB) in La-based cuprate family (La214) was
studied by angle-resolved photoemission spectroscopy (ARPES) over a wide doping
range from to . Unlike the well-studied case of the Bi-based
cuprate family, an overall strong, monotonic doping dependence of the SB
intensity at the Fermi level () was observed. In contrast to a previous
report for the presence of the SB only close to , we found it exists in
a wide doping range, associated with a doping-independent wave
vector but strongly doping-dependent intensity: It is the strongest at and systematically diminishes as the doping increases until it becomes
negligible in the overdoped regime. This SB with the observed doping dependence
of intensity can in principle be caused by the antiferromagnetic fluctuations
or a particular form of low-temperature orthorhombic lattice distortion known
to persist up to in the system, with both being weakened with
increasing doping. However, a detailed binding energy dependent analysis of the
SB at does not appear to support the former interpretation, leaving
the latter as a more plausible candidate, despite a challenge in quantitatively
linking the doping dependences of the SB intensity and the magnitude of the
lattice distortion. Our finding highlights the necessity of a careful and
global consideration of the inherent structural complications for correctly
understanding the cuprate Fermiology and its microscopic implication.Comment: Note the revised conclusion and author list; To appear in New J. Phy
Investigation of the Two-Particle-Self-Consistent Theory for the Single-Impurity Anderson Model and an Extension to the Case of Strong Correlation
The two-particle-self-consistent theory is applied to the single-impurity
Anderson model. It is found that it cannot reproduce the small energy scale in
the strong correlation limit. A modified scheme to overcome this difficulty is
proposed by introducing an appropriate vertex correction explicitly. Using the
same vertex correction, the self-energy is investigated, and it is found that
under certain assumptions it reproduces the result of the modified perturbation
theory which interpolates the weak and the strong correlation limits.Comment: 5 pages, 7 figures, submitted to J. Phys. Soc. Jp
Janus faced fluorocyclohexanes for supramolecular assembly : synthesis and solid state structures of equatorial mono-, di- and tri alkylated cyclohexanes and with tri-axial C–F bonds to impart polarity
We thank the EPSRC for a studentship (TJP) through the CRITICAT Doctoral Training Centre. FAPESP is also gratefully acknowledged for a studentship (BAP, #2021/09716-5) and a Young Researcher Award (RAC, #2018/03910-1).Concise and general synthesis protocols are reported to generate all-syn mono-, di- and tri-alkylated cyclohexanes where a single fluorine is located on the remaining carbons of the ring. The alkyl groups are positioned to lie equatorially and to have triaxial C–F bonds imparting polarity to these ring systems. Intermolecular electrostatic interactions in the solid-state structure of the trialkylated systems are explored and the resultant supramolecular order opens up prospects for design in soft materials.Publisher PDFPeer reviewe
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