1,013 research outputs found
Giant Electroresistance in Ferroelectric Tunnel Junctions
The interplay between the electron transport in metal/ferroelectric/metal
junctions with ultrathin ferroelectric barriers and the polarization state of a
barrier is investigated. Using a model which takes into account screening of
polarization charges in metallic electrodes and direct quantum tunneling across
a ferroelectric barrier we calculate the change in the tunneling conductance
associated with the polarization switching. We find the conductance change of a
few orders of magnitude for metallic electrodes with significantly different
screening lengths. This giant electroresistance effect is the consequence of a
different potential profile seen by transport electrons for the two opposite
polarization orientations.Comment: 4 page
Ferroelectric Dead Layer Driven by a Polar Interface
Based on first-principles and model calculations we investigate the effect of
polar interfaces on the ferroelectric stability of thin-film ferroelectrics. As
a representative model, we consider a TiO2-terminated BaTiO3 film with LaO
monolayers at the two interfaces that serve as doping layers. We find that the
polar interfaces create an intrinsic electric field that is screened by the
electron charge leaking into the BaTiO3 layer. The amount of the leaking charge
is controlled by the boundary conditions which are different for three
heterostructures considered, namely Vacuum/LaO/BaTiO3/LaO, LaO/BaTiO3, and
SrRuO3/LaO/BaTiO3/LaO. The intrinsic electric field forces ionic displacements
in BaTiO3 to produce the electric polarization directed into the interior of
the BaTiO3 layer. This creates a ferroelectric dead layer near the interfaces
that is non-switchable and thus detrimental to ferroelectricity. Our
first-principles and model calculations demonstrate that the effect is stronger
for a larger effective ionic charge at the interface and longer screening
length due to a stronger intrinsic electric field that penetrates deeper into
the ferroelectric. The predicted mechanism for a ferroelectric dead layer at
the interface controls the critical thickness for ferroelectricity in systems
with polar interfaces.Comment: 33 Pages, 5 figure
Dissipative dynamics of vortex arrays in anisotropic traps
We discuss the dissipative dynamics of vortex arrays in trapped
Bose-condensed gases and analyze the lifetime of the vortices as a function of
trap anisotropy and the temperature. In particular, we distinguish the two
regimes of the dissipative dynamics, depending on the relative strength of the
mutual friction between the vortices and the thermal component, and the
friction of the thermal particles on the trap anisotropy. We study the effects
of heating of the thermal cloud by the escaping vortices on the dynamics of the
system.Comment: RevTeX, 8 pages, 3 eps figure
The linearization method and new classes of exact solutions in cosmology
We develop a method for constructing exact cosmological solutions of the
Einstein equations based on representing them as a second-order linear
differential equation. In particular, the method allows using an arbitrary
known solution to construct a more general solution parameterized by a set of
3\textit{N} constants, where \textit{N} is an arbitrary natural number. The
large number of free parameters may prove useful for constructing a theoretical
model that agrees satisfactorily with the results of astronomical observations.
Cosmological solutions on the Randall-Sundrum brane have similar properties. We
show that three-parameter solutions in the general case already exhibit
inflationary regimes. In contrast to previously studied two-parameter
solutions, these three-parameter solutions can describe an exit from inflation
without a fine tuning of the parameters and also several consecutive
inflationary regimes.Comment: 7 page
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