15,579 research outputs found
Geometric and combinatorial realizations of crystal graphs
For irreducible integrable highest weight modules of the finite and affine
Lie algebras of type A and D, we define an isomorphism between the geometric
realization of the crystal graphs in terms of irreducible components of
Nakajima quiver varieties and the combinatorial realizations in terms of Young
tableaux and Young walls. For affine type A, we extend the Young wall
construction to arbitrary level, describing a combinatorial realization of the
crystals in terms of new objects which we call Young pyramids.Comment: 34 pages, 17 figures; v2: minor typos corrected; v3: corrections to
section 8; v4: minor typos correcte
Coexistence of ferromagnetism and superconductivity near quantum phase transition: The Heisenberg- to Ising-type crossover
A microscopic mean-field theory of the phase coexistence between
ferromagnetism and superconductivity in the weakly ferromagnetic itinerant
electron system is constructed, while incorporating a realistic mechanism for
superconducting pairing due to the exchange of critical spin fluctuations. The
self-consistent solution of the resulting equations determines the
superconducting transition temperature which is shown to depend strongly on the
exchange splitting. The effect of phase crossover from isotropic
(Heisenberg-like) to uniaxial (Ising-like) spin fluctuations near the quantum
phase transition is analysed and the generic phase diagram is obtained. This
scenario is then applied to the case of itinerant ferromagnet ZrZn2, which
sheds light on the proposed phase diagram of this compound. Possible
explanation of superconductivity in UGe2 is also discussed.Comment: 5 pages, 3 figure
A-site Randomness Effect on Structural and Physical Properties of Ba-based Perovskite Manganites
The discovery of novel structural and physical properties in the -site
ordered manganite BaMnO ( = Y and rare earth elements) has
demanded new comprehension about perovskite manganese oxides. In the present
study, the -site disordered form, BaMnO, has been
investigated and compared with both BaMnO and
MnO (: Sr, Ca) in the structures and electromagnetic
properties. BaMnO has a primitive cubic perovskite cell
in the structure and magnetic glassy states are dominant as its ground state,
in contrast to the ordinary disordered MnO (: Sr, Ca).
In Pr-compounds with various degrees of Pr/Ba randomness at the -sites, the
-site disorder gradually suppresses both ferromagnetic and A-type
antiferromagnetic transitions and finally leads to a magnetic glassy state in
PrBaMnO. A peculiar behavior, multi-step magnetization
and resistivity change, has been observed in PrBaMnO.
These properties could be closely related to any spatial heterogeneity caused
by the random distribution of Ba and with much different
ionic radius.Comment: 9 pages, to be published in J. Phys. Soc. Jpn. 73 Aug. (2004
High-Energy Spin Dynamics in LaSrNiO
We have mapped out the spin dynamics in a stripe-ordered nickelate,
LaSrNiO with , using inelastic neutron
scattering. We observe spin-wave excitations up to 80 meV emerging from the
incommensurate magnetic peaks with an almost isotropic spin-velocity: eV \AA, very similar to the velocity in the undoped, insulating
parent compound, LaNiO. We also discuss the similarities and
differences of the inferred spin-excitation spectrum with those reported in
superconducting high- cuprates.Comment: 4 figure
The Mean Ultraviolet Spectrum of a Representative Sample of Faint z~3 Lyman Alpha Emitters
We discuss the rest-frame ultraviolet emission line spectra of a large (~100)
sample of low luminosity redshift z~3.1 Lyman alpha emitters (LAEs) drawn from
a Subaru imaging survey in the SSA22 survey field. Our earlier work based on
smaller samples indicated that such sources have high [OIII]/[OII] line ratios
possibly arising from a hard ionising spectrum that may be typical of similar
sources in the reionisation era. With optical spectra secured from VLT/VIMOS,
we re-examine the nature of the ionising radiation in a larger sample using the
strength of the high ionisation diagnostic emission lines of CIII]1909,
CIV1549, HeII1640, and OIII]1661,1666 in various stacked subsets. Our analysis
confirms earlier suggestions of a correlation between the strength of Ly-alpha
and CIII] emission and we find similar trends with broad band UV luminosity and
rest-frame UV colour. Using various diagnostic line ratios and our stellar
photoionisation models, we determine both the gas phase metallicity and
hardness of the ionisation spectrum characterised by xi_ion - the number of
Lyman continuum photons per UV luminosity. We confirm our earlier suggestion
that xi_ion is significantly larger for LAEs than for continuum-selected Lyman
break galaxies, particularly for those LAEs with the faintest UV luminosities.
We briefly discuss the implications for cosmic reionisation if the metal-poor
intensely star-forming systems studied here are representative examples of
those at much higher redshift.Comment: 15 pages, 9 figures. Accepted for publication in MNRA
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