118,760 research outputs found
Nucleon Resonances with Hidden Charm in Coupled-Channel Models
The model dependence of the predictions of nucleon resonances with hidden
charm is investigated. We consider several coupled-channel models which are
derived from relativistic quantum field theory by using (1) a unitary
transformation method, and (2) the three-dimensional reductions of
Bethe-Salpeter Equation. With the same vector meson exchange mechanism, we find
that all models give very narrow molecular-like nucleon resonances with hidden
charm in the mass range of 4.3 GeV 4.5 GeV, in consistent with the
previous predictions.Comment: 17 pages, 3 figure
Spin-Coupled Local Distortions in Multiferroic Hexagonal HoMnO3
Local structural measurements have been performed on hexagonal HoMnO3 in
order to ascertain the specific changes in bond distances which accompany
magnetic ordering transitions. The transition from paramagnetic to the
antiferromagetic (noncollinear) phase near ~70 K is dominated by changes in the
a-b plane Mn-Mn bond distances. The spin rotation transition near ~40 K
involves both Mn-Mn and nearest neighbor Ho-Mn interactions while the low
temperature transition below 10 K involves all interactions, Mn-Mn, Ho-Mn
(nearest and next nearest) and Ho-Ho correlations. These changes in bond
distances reveal strong spin-lattice coupling. The similarity in magnitude of
the change in J(Mn-Mn) and J(Ho-Mn) enhances the system frustration. The
structural changes are interpreted in terms of a model of competing spin order
and local structural distortions. Density functional calculations are used to
estimate the energies associated with ionic displacements. The calculations
also reveal asymmetric polarization of the charge density of Ho, O3 and O4
sites along the z-axis in the ferroelectric phase. This polarization
facilitates coupling between Ho atoms on neighboring planes normal to the
z-axis.Comment: 8 figure
Theoretical studies of 63Cu Knight shifts of the normal state of YBa2Cu3O7
The 63Cu Knight shifts and g factors for the normal state of YBa2Cu3O7 in
tetragonal phase are theoretically studied in a uniform way from the high
(fourth-) order perturbation formulas of these parameters for a 3d9 ion under
tetragonally elongated octahedra. The calculations are quantitatively
correlated with the local structure of the Cu2+(2) site in YBa2Cu3O7. The
theoretical results show good agreement with the observed values, and the
improvements are achieved by adopting fewer adjustable parameters as compared
to the previous works. It is found that the significant anisotropy of the
Knight shifts is mainly attributed to the anisotropy of the g factors due to
the orbital interactions.Comment: 5 page
Investigations of the g factors and local structure for orthorhombic Cu^{2+}(1) site in fresh PrBa_{2}Cu_{3}O_{6+x} powders
The electron paramagnetic resonance (EPR) g factors g_x, g_y and g_z of the
orthorhombic Cu^{2+}(1) site in fresh PrBa_{2}Cu_{3}O_{6+x} powders are
theoretically investigated using the perturbation formulas of the g factors for
a 3d^9 ion under orthorhombically elongated octahedra. The local orthorhombic
distortion around the Cu^{2+}(1) site due to the Jahn-Teller effect is
described by the orthorhombic field parameters from the superposition model.
The [CuO6]^{10-} complex is found to experience an axial elongation of about
0.04 {\AA} along c axis and the relative bond length variation of about 0.09
{\AA} along a and b axes of the Jahn-Teller nature. The theoretical results of
the g factors based on the above local structure are in reasonable agreement
with the experimental data.Comment: 6 pages, 1 figur
TeV Scale Lee-Wick Fields out of Large Extra Dimensional Gravity
We study the gravitational corrections to the Maxwell, Dirac and Klein-Gorden
theories in the large extra dimension model in which the gravitons propagate in
the (4+n)-dimensional bulk, while the gauge and matter fields are confined to
the four-dimensional world. The corrections to the two-point Green's functions
of the gauge and matter fields from the exchanges of virtual Kaluza-Klein
gravitons are calculated in the gauge independent background field method. In
the framework of effective field theory, we show that the modified one-loop
renormalizable Lagrangian due to quantum gravitational effects contains a TeV
scale Lee-Wick partner of every gauge and matter field as extra degrees of
freedom in the theory. Thus the large extra dimension model of gravity provides
a natural mechanism to the emergence of these exotic particles which were
recently used to construct an extension of the Standard Model.Comment: 17 pages, 3 figures, references added, to appear in Phys. Rev.
Magnetic influence on the frequency of the soft-phonon mode in the incipient ferroelectric EuTiO3
The dielectric constant of the incipient ferroelectric EuTiO exhibits a
sharp decrease at about 5.5K, at which temperature antiferromagnetic ordering
of the Eu spins simultaneously appears, indicating coupling between the
magnetism and dielectric properties. This may be attributed to the modification
of the soft-phonon mode, , which is the main contribution to the
large dielectric constant, by the Eu spins(7 per Eu). By adding the
coupling term between the magnetic and electrical subsystems as we show that the variation of the frequency of
soft-phonon mode depends on the spin correlation between the nearest neighbors
Eu spins and is substantially changed under a magnetic field.Comment: 13 pages, 4 figure
Laser-driven collimated tens-GeV monoenergetic protons from mass-limited target plus preformed channel
Proton acceleration by ultra-intense laser pulse irradiating a target with cross-section smaller than the laser spot size and connected to a parabolic density channel is investigated. The target splits the laser into two parallel propagating parts, which snowplow the back-side plasma electrons along their paths, creating two adjacent parallel wakes and an intense return current in the gap between them. The radiation-pressure pre-accelerated target protons trapped in the wake fields now undergo acceleration as well as collimation by the quasistatic wake electrostatic and magnetic fields. Particle-in-cell simulations show that stable long-distance acceleration can be realized, and a 30 fs monoenergetic ion beam of >10 GeV peak energy and <2 degrees divergence can be produced by a circularly polarized laser pulse at an intensity of about 10(22) W/cm(2). (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4775728]Physics, Fluids & PlasmasSCI(E)EI3ARTICLE1null2
Interface characterization of all-perovskite oxide field effect heterostructures
All-oxide devices consisting of Niobium-doped Strontium Titanate (Nb:STO)/Strontium Titanate (STO)/Lanthanum Strontium Cuprous Oxide (LSCO) heterostructures were fabricated and characterized electrically for their interface properties through capacitance-voltage (C-V) and current-voltage (I-V) techniques, in the context of electric field effect studies. The C-V studies establish the occurrence of charge modulation in the LSCO channel. Absence of hysteresis in the C-V characteristic when the voltage is retraced suggests the absence of mobile ions in the gate oxide and slow interface traps. This is further corroborated by the absence of drift in the C-V characteristic and shift in the flat band voltage (V FB) when the device is subjected to temperature-bias aging. The interface state density obtained from V FB is ~1012/cm2. The uncompensated hole concentration in the LSCO channel calculated from the measured room temperature C-V data is ~1020/cm3 and is in good agreement with the expected hole concentration in LSCO. Current-time and current-voltage plots are invariant with respect to the polarity of the applied voltage up to ~5 V. This, in a structure with asymmetric interfaces, indicates that the electrical contacts to STO are non-blocking and the conduction through STO is bulk-limited in this voltage regime. Thickness dependent current and capacitance studies also corroborate the bulk-limited nature of conduction through the device in this voltage regime. However, I-V characteristic shows a rectifying nature beyond ~8 V indicating that the mechanism in this voltage regime could be interface limited
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