21,019 research outputs found
Infrared spectroscopy under multi-extreme conditions: Direct observation of pseudo gap formation and collapse in CeSb
Infrared reflectivity measurements of CeSb under multi-extreme conditions
(low temperatures, high pressures and high magnetic fields) were performed. A
pseudo gap structure, which originates from the magnetic band folding effect,
responsible for the large enhancement in the electrical resistivity in the
single-layered antiferromagnetic structure (AF-1 phase) was found at a pressure
of 4 GPa and at temperatures of 35 - 50 K. The optical spectrum of the pseudo
gap changes to that of a metallic structure with increasing magnetic field
strength and increasing temperature. This change is the result of the magnetic
phase transition from the AF-1 phase to other phases as a function of the
magnetic field strength and temperature. This result is the first optical
observation of the formation and collapse of a pseudo gap under multi-extreme
conditions.Comment: 5 pages, 3 figures, accepted for publication in Phys. Rev.
3alpha clustering in the excited states of 16C
The alpha cluster states of 16C are investigated by using the antisymmetrized
molecular dynamics. It is shown that two different types of alpha cluster
states exist: triangular and linear-chain states. The former has an approximate
isosceles triangular configuration of alpha particles surrounded by four
valence neutrons occupying sd-shell, while the latter has the linearly aligned
alpha particles with two sd-shell neutrons and two pf-shell neutrons. It is
found that the structure of the linear-chain state is qualitatively understood
in terms of the 3/2 pi- and 1/2 sigma- molecular orbit as predicted by
molecular-orbital model, but there exists non-negligible Be+alpha+2n
correlation. The band-head energies of the triangular and linear-chain
rotational bands are 8.0 and 15.5 MeV, and the latter is close to the He+Be
threshold energy. It is also shown that the linear-chain state becomes the
yrast sstate at J=10 with excitation energy 27.8 MeV owing to its very large
moment-of-inertia comparable with hyperdeformation.Comment: 7 pages, 5 figure
Anisotropic Electronic Structure of the Kondo Semiconductor CeFe2Al10 Studied by Optical Conductivity
We report temperature-dependent polarized optical conductivity
[] spectra of CeFeAl, which is a reference material
for CeRuAl and CeOsAl with an anomalous magnetic
transition at 28 K. The spectrum along the b-axis differs
greatly from that in the -plane, indicating that this material has an
anisotropic electronic structure. At low temperatures, in all axes, a shoulder
structure due to the optical transition across the hybridization gap between
the conduction band and the localized states, namely -
hybridization, appears at 55 meV. However, the gap opening temperature and the
temperature of appearance of the quasiparticle Drude weight are strongly
anisotropic indicating the anisotropic Kondo temperature. The strong
anisotropic nature in both electronic structure and Kondo temperature is
considered to be relevant the anomalous magnetic phase transition in
CeRuAl and CeOsAl.Comment: 5 pages, 4 figure
Antisymmetrized molecular dynamics studies for exotic clustering phenomena in neutron-rich nuclei
We present a review of recent works on clustering phenomena in unstable
nuclei studied by antisymmetrized molecular dynamics (AMD). The AMD studies in
these decades have uncovered novel types of clustering phenomena brought about
by the excess neutrons. Among them, this review focuses on the molecule-like
structure of unstable nuclei. One of the earliest discussions on the clustering
in unstable nuclei was made for neutron-rich Be and B isotopes. AMD
calculations predicted that the ground state clustering is enhanced or reduced
depending on the number of excess neutrons. Today, the experiments are
confirming this prediction as the change of the proton radii. Behind this
enhancement and reduction of the clustering, there are underlying shell effects
called molecular- and atomic-orbits. These orbits form covalent and ionic
bonding of the clusters analogous to the atomic molecules. It was found that
this "molecular-orbit picture" reasonably explains the low-lying spectra of Be
isotopes. The molecular-orbit picture is extended to other systems having
parity asymmetric cluster cores and to the three cluster systems. O and Ne
isotopes are the candidates of the former, while the linear chains in
C isotopes are the latter. For both subjects, many intensive studies are now in
progress. We also pay a special attention to the observables which are the
fingerprint of the clustering. In particular, we focus on the monopole and
dipole transitions which are recently regarded as good probe for the
clustering. We discuss how they have and will reveal the exotic clustering.Comment: 96 pages, 44 figure
Phase separation in the vicinity of the surface of -(BEDT-TTF)Cu[N(CN)]Br by fast cooling
Partial suppression of superconductivity by fast cooling has been observed in
the organic superconductor -(BEDT-TTF)Cu[N(CN)]Br by two means:
a marked sample size effect on the magnetic susceptibility and direct imaging
of insulating regions by scanning microregion infrared reflectance
spectroscopy. Macroscopic insulating regions are found in the vicinity of the
crystalline surface after fast cooling, with diameters of 50--100 m and
depths of a few m. The very large in-plane penetration depth reported to
date ( 24--100 m) can be explained by the existence of the
insulating regions.Comment: Several rhetoric alternations to avoid misleadings. 6 pages, 3
figures. to be publihsed in Phys. Rev.
Superdeformation and clustering in Ca studied with Antisymmetrized Molecular Dynamics
Deformed states in Ca are investigated with a method of
antisymmetrized molecular dynamics. Above the spherical ground state,
rotational bands arise from a normal deformation and a superdeformation as well
as an oblate deformation. The calculated energy spectra and transition
strengths in the superdeformed band reasonably agree to the experimental data
of the superdeformed band starting from the state at 5.213 MeV. By the
analysis of single-particle orbits, it is found that the superdeformed state
has particle-hole nature of an - configuration. One of new findings is
parity asymmetric structure with C+Si-like clustering in the
superdeformed band. We predict that C+Si molecular bands may be
built above the superdeformed band due to the excitation of inter-cluster
motion. They are considered to be higher nodal states of the superdeformed
state. We also suggest negative-parity bands caused by the parity asymmetric
deformation.Comment: 13 figures, submitted to Phys. Rev.
Magnetic characterization and switching of Co nano-rings in current-perpendicular-to-plane configuration
We fabricated Co nano-rings incorporated in the vertical pseudo-spin-valve
nanopillar structures with deep submicron lateral sizes. It is shown that the
current-perpendicular-to-plane giant magnetoresistance can be used to
characterize a very small magnetic nano-ring effectively. Both the onion state
and the flux-closure vortex state are observed. The Co nano-rings can be
switched between the onion states as well as between onion and vortex states
not only by the external field but also by the perpendicularly injected dc
current
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