1,704 research outputs found
Origin of Large Dielectric Constant with Large Remnant Polarization and Evidence of Magnetoelectric Coupling in Multiferroic La modified BiFeO3-PbTiO3 Solid Solution
The presence of superlattice reflections and detailed analyses of the powder
neutron and x-ray diffraction data reveal that La rich
(BF-LF)-(PT) (BF-LF-PT) has ferroelectric
rhombohedral crystal structure with space group \textit{} at ambient
conditions. The temperature dependence of lattice parameters, tilt angle,
calculated polarization , volume, and integrated intensity of
superlattice and magnetic reflections show an anomaly around 170 K. Impedance
spectroscopy, dielectric and ac conductivity measurements were performed in
temperature range to probe the origin of large remnant
polarization and frequency dependent broad transitions with large dielectric
constant near . Results of impedance spectroscopy measurements
clearly show contributions of both grain and grain boundaries throughout the
frequency range ( Hz Hz). It could be concluded
that the grain boundaries are more resistive and capacitive as compared to the
grains, resulting in inhomogeneities in the sample causing broad frequency
dependent dielectric anomalies. Enhancement in dielectric constant and remnant
polarization values are possibly due to space charge polarization caused by
piling of charges at the interface of grains and grain boundaries. The
imaginary parts of dielectric constant () Vs frequency
data were fitted using Maxwell-Wagner model at K) and model
fits very well with the data up to Hz. Magnetodielectric measurements
prove that the sample starts exhibiting magnetoelectric coupling at
K, which is also validated by neutron diffraction data.Comment: 20 pages, 10 figure
Self-bound many-body states of quasi-one-dimensional dipolar Fermi gases: Exploiting Bose-Fermi mappings for generalized contact interactions
Using a combination of results from exact mappings and from mean-field theory
we explore the phase diagram of quasi-one-dimensional systems of identical
fermions with attractive dipolar interactions. We demonstrate that at low
density these systems provide a realization of a single-component
one-dimensional Fermi gas with a generalized contact interaction. Using an
exact duality between one-dimensional Fermi and Bose gases, we show that when
the dipole moment is strong enough, bound many-body states exist, and we
calculate the critical coupling strength for the emergence of these states. At
higher densities, the Hartree-Fock approximation is accurate, and by combining
the two approaches we determine the structure of the phase diagram. The
many-body bound states should be accessible in future experiments with
ultracold polar molecules
Knowledge based capital and value creation in global supply chains
This paper investigates the role of knowledge-based capital for participation and value appropriation in global value chains (GVC) for a sample of European countries over 1995\u20132011. We distinguish between different forms of participation in GVC entailing a different degree of capability to create value added domestically and examine how different intangible assets contribute to countries' engagement and value appropriation in GVC. We find that knowledge-based capital is positively correlated with participation and value appropriation along the value chain. This finding is robust to introducing separately R&D and non-R&D intangibles. In particular, training and organizational capital have the largest positive effect on value appropriation [JEL Classification: F23, O30]
Induced polarization at a paraelectric/superconducting interface
We examine the modified electronic states at the interface between
superconducting and ferro(para)-electric heterostructures. We find that
electric polarization and superconducting order parameters can be
significantly modified due to coupling through linear terms brought about by
explicit symmetry breaking at the interface. Using an effective action and a
Ginzburg-Landau formalism, we show that an interaction term linear in the
electric polarization will modify the superconducting order parameter at
the interface. This also produces modulation of a ferroelectric polarization.
It is shown that a paraelectric-superconductor interaction will produce an
interface-induced ferroelectric polarization.Comment: 4 pages, 3 figures, Submitted to Phys. Rev.
Zener tunneling in two-dimensional photonic lattices
We discuss the interband light tunneling in a two-dimensional periodic
photonic structure, as was studied recently in experiments for
optically-induced photonic lattices [H. Trompeter et al., Phys. Rev. Lett.
\textbf{96}, 053903 (2006)]. We identify the Zener tunneling regime at the
crossing of two Bloch bands, which occurs in a generic case of the Bragg
reflection when the Bloch index crosses the edge of the irreducible Brillouin
zone. Similarly, the higher-order Zener tunneling involves four Bloch bands
when the Bloch index passes through a high-symmetry point on the edge of the
Brillouin zone. We derive simple analytical models that describe the tunneling
effect, and calculate the corresponding tunneling probabilities.Comment: 6 pages, 6 figures, submitted to Phys Rev E; changes: band structure
added (fig1) and the error estimates for the Landau-Zener model (fig 6
Chaotic properties of quantum many-body systems in the thermodynamic limit
By using numerical simulations, we investigate the dynamics of a quantum
system of interacting bosons. We find an increase of properly defined mixing
properties when the number of particles increases at constant density or the
interaction strength drives the system away from integrability. A
correspondence with the dynamical chaoticity of an associated -number system
is then used to infer properties of the quantum system in the thermodynamic
limit.Comment: 4 pages RevTeX, 4 postscript figures included with psfig; Completely
restructured version with new results on mixing properties added
Ideal barriers to polarization reversal and domain-wall motion in strained ferroelectric thin films
The ideal intrinsic barriers to domain switching in c-phase PbTiO_3 (PTO),
PbZrO_3 (PZO), and PbZr_{1-x}Ti_xO_3 (PZT) are investigated via
first-principles computational methods. The effects of epitaxial strain on the
atomic structure, ferroelectric response, barrier to coherent domain reversal,
domain-wall energy, and barrier to domain-wall translation are studied. It is
found that PTO has a larger polarization, but smaller energy barrier to domain
reversal, than PZO. Consequentially the idealized coercive field is over two
times smaller in PTO than PZO. The Ti--O bond length is more sensitive to
strain than the other bonds in the crystals. This results in the polarization
and domain-wall energy in PTO having greater sensitivity to strain than in PZO.
Two ordered phases of PZT are considered, the rock-salt structure and a (100)
PTO/PZO superlattice. In these simple structures we find that the ferroelectric
properties do not obey Vergard's law, but instead can be approximated as an
average over individual 5-atom unit cells.Comment: 9 pages, 13 figure
Universal behavior at discontinuous quantum phase transitions
Discontinuous quantum phase transitions besides their general interest are
clearly relevant to the study of heavy fermions and magnetic transition metal
compounds. Recent results show that in many systems belonging to these classes
of materials, the magnetic transition changes from second order to first order
as they approach the quantum critical point (QCP). We investigate here some
mechanisms that may be responsible for this change. Specifically the coupling
of the order parameter to soft modes and the competition between different
types of order near the QCP. For weak first order quantum phase transitions
general results are obtained. In particular we describe the thermodynamic
behavior at this transition when it is approached from finite temperatures.
This is the discontinuous equivalent of the non-Fermi liquid trajectory close
to a conventional QCP in a heavy fermion material.Comment: 7 pages, 3 figure
- …