81,796 research outputs found
Ab-inito study on different phases of ferromagnetic CeMnNi4
Using first-principles density functional calculations, we study the possible
phases of CeMnNi and show that the ground state is ferromagnetic. We
observed the hexagonal phase to be lowest in energy whereas experimentally
observed cubic phase lies slightly higher in energy. We optimized the structure
in both phases and in all different magnetic states to explore the possibility
of the structural and magnetic phase transitions at ground state. We do not
find any phase transitions between the magnetic and non-magnetic phases. The
calculated structural, magnetic properties of cubic phase are in excellent
agreement with experiments. Further, we do not observe half metallic behavior
in any of the phases. However, the cubic phase does have fewer density of
states for down-spin component giving a possibility of forming half metallic
phase artificially, introducing vacancies, and disorder in lattice
A challenge for critical point of spin glass in ground state
We show several calculations to identify the critical point in the ground
state in random spin systems including spin glasses on the basis of the duality
analysis. The duality analysis is a profound method to obtain the precise
location of the critical point in finite temperature even for spin glasses. We
propose a single equality for identifying the critical point in the ground
state from several speculations. The equality can indeed give the exact
location of the critical points for the bond-dilution Ising model on several
lattices and provides insight on further analysis on the ground state in spin
glasses.Comment: 7 pages, 2 figures, to appear in Proceedings of 4th YSM-SPIP (Sendai,
14-16 December 2012
Statistical Mechanical Formulation and Simulation of Prime Factorization of Integers
We propose a new formulation of the problem of prime factorization of
integers. With replica exchange Monte Carlo simulation, the behavior which is
seemed to indicate exponential computational hardness is observed. But this
formulation is expected to give a new insight into the computational complexity
of this problem from a statistical mechanical point of view.Comment: 5 pages, 5figures, Proceedings of 4th YSM-SPIP (Sendai, 14-16
December 2012
Degenerate ground state in the classical pyrochlore antiferromagnet NaMn(CO)Cl
In an ideal classical pyrochlore antiferromagnet without perturbations, an
infinite degeneracy at a ground state leads to absence of a magnetic order and
spin-glass transition. Here we present NaMn(CO)Cl as a new
candidate compound where classical spins are coupled antiferromagnetically on
the pyrochlore lattice, and report its structural and magnetic properties.The
temperature dependences of the magnetic susceptibility and heat capacity, and
the magnetization curve are consistent with those of an = 5/2 pyrochlore
lattice antiferromagnet with nearest-neighbor interactions of 2 K. Neither an
apparent signature of a spin-glass transition nor a magnetic order is detected
in magnetization and heat capacity measurements, or powder neutron diffraction
experiments. On the other hand, an antiferromagnetic short-range order from the
nearest neighbors is evidenced by the -dependence of the diffuse scattering
which develops around 0.85 \AA. A high degeneracy near the ground state
in NaMn(CO)Cl is supported by the magnetic entropy estimated as
almost 4 J K mol at 0.5 K.Comment: 9 pages, 7 figures, accepted to PR
Classical Nonrelativistic Effective Field Theory and the Role of Gravitational Interactions
Coherent oscillation of axions or axion-like particles may give rise to
long-lived clumps, called axion stars, because of the attractive gravitational
force or its self-interaction. Such a kind of configuration has been
extensively studied in the context of oscillons without the effect of gravity,
and its stability can be understood by an approximate conservation of particle
number in a non-relativistic effective field theory (EFT). We extend this
analysis to the case with gravity to discuss the longevity of axion stars and
clarify the EFT expansion scheme in terms of gradient energy and Newton's
constant. Our EFT is useful to calculate the axion star configuration and its
classical lifetime without any ad hoc assumption. In addition, we derive a
simple stability condition against small perturbations. Finally, we discuss the
consistency of other non-relativistic effective field theories proposed in the
literature.Comment: 37 pages, 3 figure
A Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). II. Physical Properties derived from the SED Fitting with Optical, Infrared, and Radio Data
We present physical properties of radio galaxies (RGs) with 1 mJy discovered by Subaru Hyper Supreme-Cam (HSC) and VLA Faint Images of
the Radio Sky at Twenty-Centimeters (FIRST) survey. For 1056 FIRST RGs at with HSC counterparts in about 100 deg, we compiled
multi-wavelength data of optical, near-infrared (IR), mid-IR, far-IR, and radio
(150 MHz). We derived their color excess (), stellar mass, star
formation rate (SFR), IR luminosity, the ratio of IR and radio luminosity
(), and radio spectral index () that are
derived from the SED fitting with CIGALE. We also estimated Eddington ratio
based on stellar mass and integration of the best-fit SEDs of AGN component. We
found that , SFR, and IR luminosity clearly depend on redshift
while stellar mass, , and do not significantly
depend on redshift. Since optically-faint () RGs that are
newly discovered by our RG survey tend to be high redshift, they tend to not
only have a large dust extinction and low stellar mass but also have high SFR
and AGN luminosity, high IR luminosity, and high Eddington ratio compared to
optically-bright ones. The physical properties of a fraction of RGs in our
sample seem to differ from a classical view of RGs with massive stellar mass,
low SFR, and low Eddington ratio, demonstrating that our RG survey with HSC and
FIRST provides us curious RGs among entire RG population.Comment: 30 pages, 20 figures, and 4 tables, accepted for publication in ApJS.
The catalog and SED template of radio galaxies will be accessible through an
online servic
Final-State Interactions in e^+e^- -> t\bar{t} -> b l^+ \nu \bar{b} W^- Near Top Quark Threshold
We calculate final-state interaction corrections to the energy-angular
distribution of l^+ in semi-leptonic top quark decay, where the parent top
quark is produced via e^+e^- -> t\bar{t} near threshold. These are the
corrections due to gluon exchange between t and \bar{b} (\bar{t} and b) and
between b and \bar{b}. Combining with previously known other corrections, we
explicitly write down the l^+ energy-angular distribution including the full
O(alpha_s)=O(beta) corrections near t\bar{t} threshold. Numerical analyses of
the final-state interaction corrections are given. We find that they deform the
l^+ distribution typically at the 10% level. We also find that all qualitative
features of the numerical results can be understood from intuitive pictures.
The mechanisms of various effects of the final-state interactions are
elucidated. Finally we define an observable which is proper to the decay
process of the top quark (dependent only on d\Gamma_{t -> b l^+ \nu}/ dE_l
d\Omega_l of a free polarized top quark) near t\bar{t} threshold. Such a
quantity will be useful in extracting the decay property of the top quark using
the highly polarized top quark samples.Comment: Section 6 is enlarged substantially and a paragraph is added to
Section 8 correspondingly. Reference list is also improved. (27 pages
including figures, LaTeX
Chiral phase transition at high temperature in the QCD-like gauge theory
The chiral phase transition at high temperature is investigated using the
effect ive potential in the framework of the QCD-like gauge theory with a
variational a pproach. We have a second order phase transition at MeV.
We also investigate numerically the temperature dependence of condensate,
a nd (coefficient of the quadratic term in the effective
potential) and es timate the critical exponents of these quantities.Comment: 12 pages,7 figure
Optical probe of carrier doping by X-ray irradiation in organic dimer Mott insulator -(BEDT-TTF)Cu[N(CN)Cl
We investigated the infrared optical spectra of an organic dimer Mott
insulator -(BEDT-TTF)Cu[N(CN)]Cl, which was irradiated with
X-rays. We observed that the irradiation caused a large spectral weight
transfer from the mid-infrared region, where interband transitions in the dimer
and Mott-Hubbard bands take place, to a Drude part in a low-energy region; this
caused the Mott gap to collapse. The increase of the Drude part indicates a
carrier doping into the Mott insulator due to irradiation defects. The strong
redistribution of the spectral weight demonstrates that the organic Mott
insulator is very close to the phase border of the bandwidth-controlled Mott
transition.Comment: 4 pages, 4 figure
Orbital Liquid in Perovskite Transition-Metal Oxides
We study the effects of the degeneracy of the orbitals as well as the
double exchange interaction with spins in perovskite transition-metal
oxides. In addition to the spin field , the isospin field is introduced to describe the orbital degrees of freedom. The isospin is
the quantum dynamical variable, and is represented by the boson with a
constraint. The dispersion of this boson is flat along
(: lattice constant) and the other two equivalent directions. This enables
the orbital disordered phase down to low temperatures. We interpret some of the
anomalous experiments, i.e., optical absorption and d.c. resistivity, in the
low temperature ferromagnetic phase of LaSrMnO with
in terms of this orbital liquid picture.Comment: 4 pages, RevTex and 1 Postscript figur
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