57 research outputs found
Depolarizing field and "real" hysteresis loops in nanometer-scale ferroelectric films
We give detailed analysis of the effect of depolarizing field in
nanometer-size ferroelectric capacitors studied by Kim et al. [Phys. Rev. Lett.
95, 237602 (2005)]. We calculate a critical thickness of the homogeneous state
and its stability with respect to domain formation for strained thin films of
BaTiO3 on SrRuO3/SrTiO3 substrate within the Landau theory. While the former
(2.5nm) is the same as given by ab-initio calculations, the actual critical
thickness is set by the domains at 1.6nm. There is a large Merz's activation
field for polarization relaxation. Remarkably, the results show a_negative_
slope of the "actual" hysteresis loops, a hallmark of the domain structures in
ideal thin films with imperfect screening.Comment: 4 pages, 2 figure
Domain enhanced interlayer coupling in ferroelectric/paraelectric superlattices
We investigate the ferroelectric phase transition and domain formation in a
periodic superlattice consisting of alternate ferroelectric (FE) and
paraelectric (PE) layers of nanometric thickness. We find that the polarization
domains formed in the different FE layers can interact with each other via the
PE layers. By coupling the electrostatic equations with those obtained by
minimizing the Ginzburg-Landau functional we calculate the critical temperature
of transition Tc as a function of the FE/PE superlattice wavelength and
quantitatively explain the recent experimental observation of a thickness
dependence of the ferroelectric transition temperature in KTaO3/KNbO3
strained-layer superlattices.Comment: Latest version as was published in PR
Fast Molecular-Dynamics Simulation for Ferroelectric Thin-Film Capacitors Using a First-Principles Effective Hamiltonian
A newly developed fast molecular-dynamics method is applied to BaTiO3
ferroelectric thin-film capacitors with short-circuited electrodes or under
applied voltage. The molecular-dynamics simulations based on a first-principles
effective Hamiltonian clarify that dead layers (or passive layers) between
ferroelectrics and electrodes markedly affect the properties of capacitors, and
predict that the system is unable to hop between a uniformly polarized
ferroelectric structure and a striped ferroelectric domain structure at low
temperatures. Simulations of hysteresis loops of thin-film capacitors are also
performed, and their dependence on film thickness, epitaxial constraints, and
electrodes are discussed.Comment: 12 figures, 1 table. Submitted to PRB v2->v3: Major changes are
underlined in the manuscript. Added new reference
Smearing of phase transition due to a surface effect or a bulk inhomogeneity in ferroelectric nanostructures
The boundary conditions, customarily used in the Landau-type approach to
ferroelectric thin films and nanostructures, have to be modified to take into
account that a surface of a ferroelectric (FE) is a defect of the ``field''
type. The surface (interface) field is coupled to a normal component of
polarization and, as a result, the second order phase transitions are generally
suppressed and anomalies in response are washed out. In FE films with a
compositional (grading) or some other type of inhomogeneity, the transition
into a monodomain state is suppressed, but a transition with formation of a
domain structure may occur.Comment: 5 pages, 1 figure; the effective bias field is very large, the
estimate is adde
Universal Properties of Ferroelectric Domains
Basing on Ginzburg-Landau approach we generalize the Kittel theory and derive
the interpolation formula for the temperature evolution of a multi-domain
polarization profile P(x,z). We resolve the long-standing problem of the
near-surface polarization behavior in ferroelectric domains and demonstrate the
polarization vanishing instead of usually assumed fractal domain branching. We
propose an effective scaling approach to compare the properties of different
domain-containing ferroelectric plates and films.Comment: Phys. Rev. Lett. to be publishe
Abrupt appearance of the domain pattern and fatigue of thin ferroelectric films
We study the domain structure in ferroelectric thin films with a `passive'
layer (material with damaged ferroelectric properties) at the interface between
the film and electrodes within a continuous medium approximation. An abrupt
transition from a monodomain to a polydomain state has been found with the
increase of the `passive' layer thickness . The domain width changes very
quickly at the transition (exponentially with ). We have estimated the
dielectric response (the slope of the hysteresis loop) in the
`fatigued' multidomain state and found that it is in agreement with experiment,
assuming realistic parameters of the layer. We derive a simple universal
relation for the dielectric response, which scales as , involving only the
properties of the passive layer. This relation qualitatively reproduces the
evolution of the hysteresis loop in fatigued samples and it could be tested
with controlled experiments. It is expected that the coercive field should
increase with decreasing lateral size of the film. We believe that specific
properties of the domain structure under bias voltage in ferroelectrics with a
passive layer can resolve the long-standing `paradox of the coercive field'.Comment: 5 pages, REVTeX 3.1 with two eps-figures. Minor amendments. To appear
in Phys. Rev. Letter
BAIKAL experiment: status report
We review the present status of the Baikal Neutrino Project and present the
results obtained with the deep underwater neutrino telescope NT-200.Comment: 4 pages, 3 figures. Presented at TAUP 2001 (7th international
workshop on Topics in Astroparticle and Underground Physics), Sep. 2001,
Laboratori Nazionali del Gran Sasso, Assergi, Ital
The Lake Baikal neutrino experiment: selected results
We review the present status of the lake Baikal Neutrino Experiment and
present selected physical results gained with the consequetive stages of the
stepwise increasing detector: from NT-36 to NT-96. Results cover atmospheric
muons, neutrino events, very high energy neutrinos, search for neutrino events
from WIMP annihilation, search for magnetic monopoles and environmental
studies. We also describe an air Cherenkov array developed for the study of
angular resolution of NT-200.Comment: 25 pages, 12 figures. To appear in the Procrrdings of International
Conference on Non-Accelerator New Physics, June 28 - July 3, 1999, Dubna,
Russi
Simultaneous measurements of water optical properties by AC9 transmissometer and ASP-15 Inherent Optical Properties meter in Lake Baikal
Measurements of optical properties in media enclosing Cherenkov neutrino
telescopes are important not only at the moment of the selection of an adequate
site, but also for the continuous characterization of the medium as a function
of time. Over the two last decades, the Baikal collaboration has been measuring
the optical properties of the deep water in Lake Baikal (Siberia) where, since
April 1998, the neutrino telescope NT-200 is in operation. Measurements have
been made with custom devices. The NEMO Collaboration, aiming at the
construction of a km3 Cherenkov neutrino detector in the Mediterranean Sea, has
developed an experimental setup for the measurement of oceanographic and
optical properties of deep sea water. This setup is based on a commercial
transmissometer. During a joint campaign of the two collaborations in March and
April 2001, light absorption, scattering and attenuation in water have been
measured. The results are compatible with previous ones reported by the Baikal
Collaboration and show convincing agreement between the two experimental
techniques.Comment: 16 pages, submitted to NIM-
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