33,955 research outputs found
Comparative study of ordered and disordered Y1-xSrxCoO3-d
We have succeeded in preparing A-site ordered- and disordered-Y1/4Sr3/4CoO3-d
with various oxygen deficiencies delta, and have made comparative study of
their structural and physical properties. In the A-site ordered structure,
oxygen vacancies order, and d = 0.34 sample shows a weak ferromagnetic
transition beyond 300 K. On the other hand, in the A-site disordered structure,
no oxygen vacancy ordering is observed, and d = 0.16 sample shows a
ferromagnetic metallic transition around 150 K. A-site disordering destroys the
orderings of oxygen-vacancies and orbitals, leading to the strong modification
of the electronic phases.Comment: 3 pages, 3 figures, proceeding of 52nd Mangetism and Magnetic
Materials Conference (MMM 2007), published in Journal of Applied Physic
Formation of cosmological mass condensation within a FRW universe: exact general relativistic solutions
Within the framework of an exact general relativistic formulation of gluing
manifolds, we consider the problem of matching an inhomogeneous overdense
region to a Friedmann-Robertson-Walker background universe in the general
spherical symmetric case of pressure-free models. It is shown that, in general,
the matching is only possible through a thin shell, a fact ignored in the
literature. In addition to this, in subhorizon cases where the matching is
possible, an intermediate underdense region will necessarily arise.Comment: 6 page
Drastic change in transport of entropy with quadrupolar ordering in PrFeP
The antiferroquadrupolar ordering of PrFeP is explored by
probing thermal and thermoelectric transport. The lattice thermal conductivity
drastically increases with the ordering, as a consequence of a large drop in
carrier concentration and a strong electron-phonon coupling. The low level of
carrier density in the ordered state is confirmed by the anomalously large
values of the Seebeck and Nernst coefficients. The results are reminiscent of
URuSi and suggest that both belong to the same class of aborted
metal-insulator transitions. The magnitude of the Nernst coefficient, larger
than in any other metal, indicates a new route for Ettingshaussen cooling at
Kelvin temperatures.Comment: final published versio
On the Existence of Local Observables in Theories With a Factorizing S-Matrix
A recently proposed criterion for the existence of local quantum fields with
a prescribed factorizing scattering matrix is verified in a non-trivial model,
thereby establishing a new constructive approach to quantum field theory in a
particular example. The existence proof is accomplished by analyzing nuclearity
properties of certain specific subsets of Fermionic Fock spaces.Comment: 13 pages, no figures, comment in sect. 3 adde
Four-spin-exchange- and magnetic-field-induced chiral order in two-leg spin ladders
We propose a mechanism of a vector chiral long-range order in two-leg
spin-1/2 and spin-1 antiferromagnetic ladders with four-spin exchanges and a
Zeeman term. It is known that for one-dimensional quantum systems, spontaneous
breakdown of continuous symmetries is generally forbidden. Any vector chiral
order hence does not appear in spin-rotationally [SU(2)]-symmetric spin
ladders. However, if a magnetic field is added along the S^z axis of ladders
and the SU(2) symmetry is reduced to the U(1) one, the z component of a vector
chiral order can emerge with the remaining U(1) symmetry unbroken. Making use
of Abelian bosonization techniques, we actually show that a certain type of
four-spin exchange can yield a vector chiral long-range order in spin-1/2 and
spin-1 ladders under a magnetic field. In the chiral-ordered phase, the Z_2
interchain-parity (i.e., chain-exchange) symmetry is spontaneously broken. We
also consider effects of perturbations breaking the parity symmetry.Comment: 8 pages, 1 figure, RevTex, published versio
Laughlin states on the Poincare half-plane and its quantum group symmetry
We find the Laughlin states of the electrons on the Poincare half-plane in
different representations. In each case we show that there exist a quantum
group symmetry such that the Laughlin states are a representation of
it. We calculate the corresponding filling factor by using the plasma analogy
of the FQHE.Comment: 9 pages,Late
Similarity of Fermi Surface in the Hidden Order State and in the Antiferromagnetic State of URu2Si2
Shubnikov-de Haas measurements of high quality URu2Si2 single crystals reveal
two previously unobserved Fermi surface branches in the so-called hidden order
phase. Therefore about 55% of the enhanced mass is now detected. Under pressure
in the antiferromagnetic state, the Shubnikov-de Haas frequencies for magnetic
fields applied along the crystalline c axis show little change compared with
the zero pressure data. This implies a similar Fermi surface in both the hidden
order and antiferromagnetic states, which strongly suggests that the lattice
doubling in the antiferromagnetic phase due to the ordering vector QAF = (0 0
1) already occurs in the hidden order. These measurements provide a good test
for existing or future theories of the hidden order parameter.Comment: 4 pages, 4 figure
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