508 research outputs found
Magnetic-Field-Induced Antiferromagnetism in Two-Dimensional Hubbard Model: Analysis of CeRhIn
We propose the mechanism for the magnetic-field-induced antiferromagnetic
(AFM) state in a two-dimensional Hubbard model in the vicinity of the AFM
quantum critical point (QCP), using the fluctuation-exchange (FLEX)
approximation by taking the Zeeman energy due to the magnetic field into
account. In the vicinity of the QCP, we find that the AFM correlation
perpendicular to is enhanced, whereas that parallel to is reduced. This
fact means that the finite magnetic field increases , with the AFM order
perpendicular to . The increment in can be understood in terms of the
reduction of both quantum and thermal fluctuations due to the magnetic field,
which is caused by the self-energy effect within the FLEX approximation. The
present study naturally explains the increment in in CeRhIn_5 under the
magnetic field found recently.Comment: 5 page
Different mechanism of two-proton emission from proton-rich nuclei Al and Mg
Two-proton relative momentum () and opening angle ()
distributions from the three-body decay of two excited proton-rich nuclei,
namely Al p + p + Na and Mg p
+ p + Ne, have been measured with the projectile fragment separator
(RIPS) at the RIKEN RI Beam Factory. An evident peak at MeV/c as
well as a peak in around 30 are seen in the two-proton
break-up channel from a highly-excited Mg. In contrast, such peaks are
absent for the Al case. It is concluded that the two-proton emission
mechanism of excited Mg is quite different from the Al case, with
the former having a favorable diproton emission component at a highly excited
state and the latter dominated by the sequential decay process
F-Theory and the Mordell-Weil Group of Elliptically-Fibered Calabi-Yau Threefolds
The Mordell-Weil group of an elliptically fibered Calabi-Yau threefold X
contains information about the abelian sector of the six-dimensional theory
obtained by compactifying F-theory on X. After examining features of the
abelian anomaly coefficient matrix and U(1) charge quantization conditions of
general F-theory vacua, we study Calabi-Yau threefolds with Mordell-Weil
rank-one as a first step towards understanding the features of the Mordell-Weil
group of threefolds in more detail. In particular, we generate an interesting
class of F-theory models with U(1) gauge symmetry that have matter with both
charges 1 and 2. The anomaly equations --- which relate the Neron-Tate height
of a section to intersection numbers between the section and fibral rational
curves of the manifold --- serve as an important tool in our analysis.Comment: 29 pages + appendices, 5 figures; v2: minor correction
Monte Carlo simulations of an impurity band model for III-V diluted magnetic semiconductors
We report the results of a Monte Carlo study of a model of (III,Mn)V diluted
magnetic semiconductors which uses an impurity band description of carriers
coupled to localized Mn spins and is applicable for carrier densities below and
around the metal-insulator transition. In agreement with mean field studies, we
find a transition to a ferromagnetic phase at low temperatures. We compare our
results for the magnetic properties with the mean field approximation, as well
as with experiments, and find favorable qualitative agreement with the latter.
The local Mn magnetization below the Curie temperature is found to be spatially
inhomogeneous, and strongly correlated with the local carrier charge density at
the Mn sites. The model contains fermions and classical spins and hence we
introduce a perturbative Monte Carlo scheme to increase the speed of our
simulations.Comment: 17 pages, 24 figures, 2 table
PReS-FINAL-2125: A Japanese girl with childhood-onset anti-Ku antibody positive generalized morphea-myositis overlap syndrome
POSTER PRESENTATIONProceedings of 20th Pediatric Rheumatology European Society (PReS) Congress / 25-29 September 2013 / Ljubljana, Sloveni
Hindered proton collectivity in 28S: Possible magic number at Z=16
The reduced transition probability B(E2;0 ->2+) for 28S was obtained
experimentally using Coulomb excitation at 53 MeV/nucleon. The resultant B(E2)
value 181(31) e2fm4 is smaller than the expectation based on empirical B(E2)
systematics. The double ratio |M_n/M_p|/(N/Z) of the 0+ ->2+ transition in 28S
was determined to be 1.9(2) by evaluating the M_n value from the known B(E2)
value of the mirror nucleus 28Mg, showing the hindrance of proton collectivity
relative to that of neutrons. These results indicate the emergence of the magic
number Z=16 in the |T_z|=2 nucleus 28S.Comment: 10 pages, 3 figures. Published in Phys. Rev. Lett
(http://link.aps.org/doi/10.1103/PhysRevLett.108.222501
Quantum states and linear response in dc and electromagnetic fields for charge current and spin polarization of electrons at Bi/Si interface with giant spin-orbit coupling
An expansion of the nearly free-electron model constructed by Frantzeskakis,
Pons and Grioni [Phys. Rev. B {\bf 82}, 085440 (2010)] describing quantum
states at Bi/Si(111) interface with giant spin-orbit coupling is developed and
applied for the band structure and spin polarization calculation, as well as
for the linear response analysis for charge current and induced spin caused by
dc field and by electromagnetic radiation. It is found that the large
spin-orbit coupling in this system may allow resolving the spin-dependent
properties even at room temperature and at realistic collision rate. The
geometry of the atomic lattice combined with spin-orbit coupling leads to an
anisotropic response both for current and spin components related to the
orientation of the external field. The in-plane dc electric field produces only
the in-plane components of spin in the sample while both the in-plane and
out-of-plane spin components can be excited by normally propagating
electromagnetic wave with different polarizations.Comment: 10 pages, 9 figure
F-theory on Genus-One Fibrations
We argue that M-theory compactified on an arbitrary genus-one fibration, that
is, an elliptic fibration which need not have a section, always has an F-theory
limit when the area of the genus-one fiber approaches zero. Such genus-one
fibrations can be easily constructed as toric hypersurfaces, and various
and models are presented as examples. To each
genus-one fibration one can associate a -function on the base as well as
an representation which together define the IIB axio-dilaton
and 7-brane content of the theory. The set of genus-one fibrations with the
same -function and representation, known as the
Tate-Shafarevich group, supplies an important degree of freedom in the
corresponding F-theory model which has not been studied carefully until now.
Six-dimensional anomaly cancellation as well as Witten's zero-mode count on
wrapped branes both imply corrections to the usual F-theory dictionary for some
of these models. In particular, neutral hypermultiplets which are localized at
codimension-two fibers can arise. (All previous known examples of localized
hypermultiplets were charged under the gauge group of the theory.) Finally, in
the absence of a section some novel monodromies of Kodaira fibers are allowed
which lead to new breaking patterns of non-Abelian gauge groups.Comment: 53 pages, 9 figures, 6 tables. v2: references adde
Hindered proton collectivity in the proton-rich nucleus ^<28>S : Possible magic number Z = 16
NUCLEAR STRUCTURE AND DYNAMICS 20129–13 July 201
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