5,429 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
Ferroelectricity in multiferroic magnetite Fe3O4 driven by noncentrosymmetric Fe2+/Fe3+ charge-ordering: First-principles study
By means of first-principles simulations, we unambiguously show that improper
ferroelectricity in magnetite in the low-temperature insulating phase is driven
by charge-ordering. An accurate comparison between monoclinic ferroelectric Cc
and paraelectric P2/c structures shows that the polarization arises because of
"shifts" of electronic charge between octahedral Fe sites, leading to a
non-centrosymmetric Fe2+/Fe3+ charge-ordered pattern. Our predicted values for
polarization, in good agreement with available experimental values, are
discussed in terms of point-charge dipoles located on selected Fe tetrahedra,
pointing to a manifest example of electronic ferroelectricity driven by charge
rearrangement.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev.
Dielectric correction to the Chiral Magnetic Effect
We derive an electric current density in the presence of a magnetic
field and a chiral chemical potential . We show that has
not only the anomaly-induced term (i.e. Chiral Magnetic
Effect) but also a non-anomalous correction which comes from interaction
effects and expressed in terms of the susceptibility. We find the correction
characteristically dependent on the number of quark flavors. The numerically
estimated correction turns out to be a minor effect on heavy-ion collisions but
can be tested by the lattice QCD simulation.Comment: 4 pages, 1 figur
Cr-doping effect on the orbital fluctuation of heavily doped Nd1-xSrxMnO3 (x ~ 0.625)
We have investigated the Cr-doping effect of Nd0.375Sr0.625MnO3 near the
phase boundary between the x2-y2 and 3z2-r2 orbital ordered states, where a
ferromagnetic correlation and concomitant large magnetoresistance are observed
owing to orbital fluctuation. Cr-doping steeply suppresses the ferromagnetic
correlation and magnetoresistance in Nd0.375Sr0.625Mn1-yCryO3 with 0 < y <
0.05, while they reappear in 0.05 < y < 0.10. Such a reentrant behavior implies
that a phase boundary is located at y = 0.05, or a phase crossover occurs
across y = 0.05.Comment: 3 pages, 3 figures, to be published in Journal of Applied Physic
Views of the Chiral Magnetic Effect
My personal views of the Chiral Magnetic Effect are presented, which starts
with a story about how we came up with the electric-current formula and
continues to unsettled subtleties in the formula. There are desirable features
in the formula of the Chiral Magnetic Effect but some considerations would lead
us to even more questions than elucidations. The interpretation of the produced
current is indeed very non-trivial and it involves a lot of confusions that
have not been resolved.Comment: 19 pages, no figure; typos corrected, references significantly
updated, to appear in Lect. Notes Phys. "Strongly interacting matter in
magnetic fields" (Springer), edited by D. Kharzeev, K. Landsteiner, A.
Schmitt, H.-U. Ye
Heavy quark potential in the instanton liquid model
We study the heavy quark potential in the instanton liquid model by carefully
measuring Wilson loops out to a distance of order 3. A random instanton
ensemble with a fixed radius = 1/3 generates a potential
growing very slowly at large . In contrast, a more realistic size
distribution growing as at small and decaying as at
large , leads to a potential which grows linearly with . The string
tension, however, is only about 1/10 of the phenomenological value.Comment: LATTICE98(confine
Negative parity states of B and C and the similarity with $^{12}C
The negative parity states of B and C were studied based on the
calculations of antisymmetrized molecular dynamics(AMD). The calculations well
reproduced the experimental strengths of Gamov-Teller(GT), and monopole
transitions. We, especially, focused on the and states, for
which GT transition strengths were recently measured. The weak and GT
transitions for the in B and C are described by a
well-developed cluster structure of + and +He,
respectively, while the strong transitions for the is characterized
by an intrinsic spin excitation with no cluster structure. It was found that
the state is a dilute cluster state, and its features are similar to
those of the C which is considered to be a gas state of three
clusters.Comment: 10 pages, 4 figures, submitterd to Physical Review
Magnetic-field Induced Screening Effect and Collective Excitations
We explicitly construct the fermion propagator in a magnetic field background
B to take the lowest Landau-level approximation. We analyze the energy and
momentum dependence in the polarization tensor and discuss the collective
excitations. We find there appear two branches of collective modes in one of
two transverse gauge particles; one represents a massive and attenuated gauge
particle and the other behaves similar to the zero sound at finite density.Comment: 5 pages, 3 figures; references on the zero sound added and typos
correcte
Perimeter of sublevel sets in infinite dimensional spaces
We compare the perimeter measure with the Airault-Malliavin surface measure
and we prove that all open convex subsets of abstract Wiener spaces have finite
perimeter. By an explicit counter-example, we show that in general this is not
true for compact convex domains
Dynamics and Control of a Quasi-1D Spin System
We study experimentally a system comprised of linear chains of spin-1/2
nuclei that provides a test-bed for multi-body dynamics and quantum information
processing. This system is a paradigm for a new class of quantum information
devices that can perform particular tasks even without universal control of the
whole quantum system. We investigate the extent of control achievable on the
system with current experimental apparatus and methods to gain information on
the system state, when full tomography is not possible and in any case highly
inefficient
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