5,353 research outputs found
Modified critical correlations close to modulated and rough surfaces
Correlation functions are sensitive to the presence of a boundary. Surface
modulations give rise to modified near surface correlations, which can be
measured by scattering probes. To determine these correlations, we develop a
perturbative calculation in deformations in height from a flat surface. The
results, combined with a renormalization group around four dimensions, are also
used to predict critical behavior near a self-affinely rough surface. We find
that a large enough roughness exponent can modify surface critical behavior.Comment: 4 pages, 1 figure. Revised version as published in Phys. Rev. Lett.
86, 4596 (2001
Synthesis of atomically thin hexagonal boron nitride films on nickel foils by molecular beam epitaxy
Hexagonal boron nitride (h-BN) is a layered two-dimensional material with
properties that make it promising as a dielectric in various applications. We
report the growth of h-BN films on Ni foils from elemental B and N using
molecular beam epitaxy. The presence of crystalline h-BN over the entire
substrate is confirmed by Raman spectroscopy. Atomic force microscopy is used
to examine the morphology and continuity of the synthesized films. A scanning
electron microscopy study of films obtained using shorter depositions offers
insight into the nucleation and growth behavior of h-BN on the Ni substrate.
The morphology of h-BN was found to evolve from dendritic, star-shaped islands
to larger, smooth triangular ones with increasing growth temperature
Phase diagram and single-particle spectrum of CuO layers within a variational cluster approach to the 3-band Hubbard model
We carry out a detailed numerical study of the three-band Hubbard model in
the underdoped region both in the hole- as well as in the electron-doped case
by means of the variational cluster approach. Both the phase diagram and the
low-energy single-particle spectrum are very similar to recent results for the
single-band Hubbard model with next-nearest-neighbor hoppings. In particular,
we obtain a mixed antiferromagnetic+superconducting phase at low doping with a
first-order transition to a pure superconducting phase accompanied by phase
separation. In the single-particle spectrum a clear Zhang-Rice singlet band
with an incoherent and a coherent part can be seen, in which holes enter upon
doping around . The latter is very similar to the coherent
quasi-particle band crossing the Fermi surface in the single-band model. Doped
electrons go instead into the upper Hubbard band, first filling the regions of
the Brillouin zone around . This fact can be related to the enhanced
robustness of the antiferromagnetic phase as a function of electron doping
compared to hole doping.Comment: 14 pages, 15 eps figure
Intellectual property as complex innovation projects component
The materials presented the possibilities development of intellectual property complex innovation projects modern highly effective science-based problems of improving the use of wastes of different industries on a complex enterprise that can provide all its energy needs alone. Some features of the possibilities of solving evidence-based problems of development of mechanisms for identifying syner-gistic processes, their scientific justification improving the use of wastes of different industries on a complex enterprise. The problem of wastes utilization and recycling is present as complex synergetic processes research and analysis of energy- and resource saving process-es for treatment of polymer wastes of various origin. The research focused on the study of issues such as the development of models of waste-modifying polymer. The investigation are focused in researching such problems as selection of scientific based methods of wastes to be utilized or recycled; the development of appropriated process flow sheets and choice of modifications additives and equipment for polymers waste recycling. The choice of appropriate plants with selected energy resources is very important for projects realization
Distinct magnetotransport and orbital fingerprints of chiral bobbers
While chiral magnetic skyrmions have been attracting significant attention in
the past years, recently, a new type of a chiral particle emerging in thin
films a chiral bobber has been theoretically predicted and
experimentally observed. Here, based on theoretical arguments, we provide a
clear pathway to utilizing chiral bobbers for the purposes of future
spintronics by uncovering that these novel chiral states possess inherent
transport fingerprints that allow for their unambiguous electrical detection in
systems comprising several types of chiral states. We reveal that unique
transport and orbital characteristics of bobbers root in the non-trivial
magnetization distribution in the vicinity of the Bloch points, and demonstrate
that tuning the details of the Bloch point topology can be used to drastically
alter the emergent response properties of chiral bobbers to external fields,
which bears great potential for engineering chiral dynamics and cognitive
computing.Comment: Supplementary available upon reques
Anomalous bond stretching phonons as a probe of charge fluctuations in perovskites
Important information on momentum resolved low energy charge response can be
extracted from anomalous properties of bond stretching in plane phonons
observed in inelastic neutron and X-ray scattering in cuprates and some other
perovskites. We discuss a semiphenomenological model based on coupling of
phonons to a single charge mode. The phonon dispersion and linewidth allow to
locate the energy of the charge excitation in the mid infrared part of the
spectrum and to determine some of its characteristics. New experiments on
oxygen isotope substitution could allow to achieve a more detailed description.
Corresponding relations following from the model can be used for the
interpretation of experiments and as test of the model.Comment: presented at the M2S-HTSC-VIII conference in Dresde
Correlation functions near Modulated and Rough Surfaces
In a system with long-ranged correlations, the behavior of correlation
functions is sensitive to the presence of a boundary. We show that surface
deformations strongly modify this behavior as compared to a flat surface. The
modified near surface correlations can be measured by scattering probes. To
determine these correlations, we develop a perturbative calculation in the
deformations in height from a flat surface. Detailed results are given for a
regularly patterned surface, as well as for a self-affinely rough surface with
roughness exponent . By combining this perturbative calculation in
height deformations with the field-theoretic renormalization group approach, we
also estimate the values of critical exponents governing the behavior of the
decay of correlation functions near a self-affinely rough surface. We find that
for the interacting theory, a large enough can lead to novel surface
critical behavior. We also provide scaling relations between roughness induced
critical exponents for thermodynamic surface quantities.Comment: 31 pages, 2 figure
Change of quasiparticle dispersion in crossing T_c in the underdoped cuprates
One of the most remarkable properties of the high-temperature superconductors
is a pseudogap regime appearing in the underdoped cuprates above the
superconducting transition temperature T_c. The pseudogap continously develops
out of the superconducting gap. In this paper, we demonstrate by means of a
detailed comparison between theory and experiment that the characteristic
change of quasiparticle dispersion in crossing T_c in the underdoped cuprates
can be understood as being due to phase fluctuations of the superconducting
order parameter. In particular, we show that within a phase fluctuation model
the characteristic back-turning BCS bands disappear above T_c whereas the gap
remains open. Furthermore, the pseudogap rather has a U-shape instead of the
characteristic V-shape of a d_{x^2-y^2}-wave pairing symmetry and starts
closing from the nodal k=(pi/2,pi/2) directions, whereas it rather fills in at
the anti-nodal k=(pi,0) regions, yielding further support to the phase
fluctuation scenario.Comment: 6 pages, 4 eps-figure
Comment on "Why is the DNA denaturation transition first order?"
In this comment we argue that while the conclusions in the original paper (Y.
Kafri, D. Mukamel and L. Peliti, Phys. Rev. Lett. 85, 4988 (2000)) are correct
for asymptotically long DNA chains, they do not apply to the chains used in
typical experiments. In the added last paragraph, we point out that for real
DNA the average distance between denatured loops is not of the order of the
persistence length of a single-stranded chain but much larger. This
corroborates our reasoning that the double helix between loops is quite rigid,
and thereby our conclusion.Comment: 1 page, REVTeX. Last paragraph adde
- …