114 research outputs found
Compact Spacelike Surfaces in the 3-Dimensional de Sitter Space
We establish several sufficient conditions for a compact spacelike surface in the 3-dimensional de Sitter space to be totally geodesic or spherical
Measuring the gap in ARPES experiments
Angle-resolved photoemission spectroscopy (ARPES) is considered as the only
experimental tool from which the momentum distribution of both the
superconducting and pseudo-gap can be quantitatively derived. The binding
energy of the leading edge of the photoemission spectrum, usually called the
leading edge gap (LEG), is the model-independent quantity which can be measured
in the modern ARPES experiments with the very high accuracy--better than 1 meV.
This, however, may be useless as long as the relation between the LEG and the
real gap is unknown. We present a systematic study of the LEG as a function of
a number of physical and experimental parameters. The absolute gap values which
have been derived from the numerical simulation prove, for example that the
nodal direction in the underdoped Bi-2212 in superconducting state is really
the node--the gap is zero. The other consequences of the simulations are
discussed.Comment: revtex4, 9 pages, 6 figure
An ARPES view on the high-Tc problem: phonons vs spin-fluctuations
We review the search for a mediator of high-Tc superconductivity focusing on
ARPES experiment. In case of HTSC cuprates, we summarize and discuss a
consistent view of electronic interactions that provides natural explanation of
both the origin of the pseudogap state and the mechanism for high temperature
superconductivity. Within this scenario, the spin-fluctuations play a decisive
role in formation of the fermionic excitation spectrum in the normal state and
are sufficient to explain the high transition temperatures to the
superconducting state while the pseudogap phenomenon is a consequence of a
Peierls-type intrinsic instability of electronic system to formation of an
incommensurate density wave. On the other hand, a similar analysis being
applied to the iron pnictides reveals especially strong electron-phonon
coupling that suggests important role of phonons for high-Tc superconductivity
in pnictides.Comment: A summary of the ARPES part of the Research Unit FOR538,
http://for538.wmi.badw.d
Asymptotic Properties of Hilbert Geometry
It is shown that the spheres in Hilbert geometry have the same volume growth entropy as those in the Lobachevsky space. Asymptotic estimates for the ratio of the volume of metric ball to the area of the metric sphere in Hilbert geometry are given. Derived estimates agree with the well-known fact in the Lobachevsky space
Evaluation of information systems
У статті розглядається узагальнений критерій оцінки ефективності інформаційних систем як засіб порівняння між собою різних систем, що вирішують одне і те саме завдання. Це дозволяє вибрати серед них найбільш ефективне. Такий критерій повинен поєднувати в собі окремі критерії таким чином, щоб урівноважити вплив кожного з них на об'єднувальний узагальнений критерій. Вдало вибраний узагальнений критерій дає можливість знаходити ефективні нестандартні рішення під час побудови і роботи складних систем.
При цитуванні документа, використовуйте посилання http://essuir.sumdu.edu.ua/handle/123456789/24412В статье рассматривается обобщенный критерий оценки эффективности информационных систем как способ сравнения между собой различных систем, решающих одну и ту же задачу. Это позволяет выбрать среди них наиболее эффективную. Такой критерий должен объединять в себе частные критерии таким образом, чтобы уравновесить влияние каждого из них на объединяющий обобщенный критерий. Удачно выбранный обобщенный критерий дает возможность находить эффективные нестандартные решения при построении и работе сложных систем.
При цитировании документа, используйте ссылку http://essuir.sumdu.edu.ua/handle/123456789/24412The article deals with the generalized criterion evaluating the efficiency of information systems as a way to compare different systems that solve the same problem with each other. This allows to choose the most effective among them. Such a criterion must combine the partial criteria in order to counterbalance the influence of each of them on the combined generalized criterion. Well chosen generalized criterion allows to find effective innovative solutions in the construction and operation of complex systems.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2441
ARPES on high-temperature superconductors: simplicity vs. complexity
A notable role in understanding of microscopic electronic properties of high temperature superconductors
(HTSC) belongs to angle resolved photoemission spectroscopy (ARPES). This technique
supplies a direct window into the reciprocal space of solids: the momentum–energy space
where quasiparticles (electrons dressed in clouds of interactions) dwell. Any interaction in the
electronic system, e.g., superconducting pairing, leads to modification of the quasiparticle spectrum—to
redistribution of the spectral weight over the momentum–energy space probed by
ARPES. Continued development of the technique had the effect that the picture seen through the
ARPES window became clearer and sharper until the complexity of the electronic band structure
of the cuprates had been resolved. Now, in the doping range optimal for superconductivity, the
cuprates much resemble a normal metal with well-predicted electronic structure, though with
rather strong electron–electron interaction. This principal disentanglement of the complex physics
from complex structure reduced the mystery of HTSC to the tangible problem of the interaction responsible
for quasiparticle formation. Here we present a short overview of resent ARPES results,
which, we believe, suggest a way to resolve the HTSC puzzle
Amorphization kinetics under electron irradiation
A model is brought forward of the kinetics of amorphization occurring under electron irradiation. The model is based on consideration of the phase transformations controlled by the structural relaxation of small-scale unstable atomic configurations excited by electrons.Наведено модель кінетики аморфізації під електронним випромінюванням. Модель грунтується на розгляді фазових перетворень, які контролюються структурной релаксацієй дрібномасштабних нестабільних атомних конфігурацій, які збуджуються електронами.Приведена модель кинетики аморфизации под электронным облучением. Модель основывается на рассмотрении фазовых превращений, которые контролируются структурной релаксацией мелкомасштабных нестабильных атомных конфигураций, которые возбуждаются электронами
About the relation between the quasiparticle Green's function in cuprates obtained from ARPES data and the magnetic susceptibility
Angle resolved photoemission spectroscopy (ARPES) provides a detailed view of
the renormalized band structure in cuprates and, consequently, is a key to the
self-energy and the quasiparticle Green's function. Such information gives a
clue to the comparison of ARPES with scanning tunneling microscopy, inelastic
neutron scattering (INS), and Raman scattering data. Here we touch on a
potential possibility of such a comparison with the dynamical magnetic
susceptibility measured in INS experiments. Calculations based on the
experimentally measured quasiparticle self-energies in cuprates lead to the
estimated magnetic susceptibility response with many-body effects taken into
account.Comment: Will be presented at the M2S-HTSC-VIII conference in Dresde
From tunneling to photoemission: correlating two spaces
Correlating the data measured by tunneling and photoemission spectroscopies
is a long-standing problem in condensed matter physics. The quasiparticle
interference, recently discovered in high-Tc cuprates, reveals a possibility to
solve this problem. Application of modern phase retrieval algorithms to Fourier
transformed tunneling data allows to recover the distribution of the
quasiparticle spectral weight in the reciprocal space of solids measured
directly by photoemission. This opens a direct way to unify these two powerful
techniques and may help to solve a number of problems related with space/time
inhomogeneities predicted in strongly correlated electron systems.Comment: more info at http://www.imp.kiev.ua/~kord/AC-ARPES/index.htm
Origin of the shadow Fermi surface in Bi-based cuprates
We used angle-resolved photoemission spectroscopy to study the shadow Fermi
surface in one layer Bi2Sr1.6La0.4CuO6+delta and two layer
(Bi,Pb)2Sr2CaCu2O8+delta. We find the shadow band to have the same peakwidth
and dispersion as the main band. In addition, the shadow band/main band
intensity ratio is found to be binding energy independent. Consequently, it is
concluded that the shadow bands in Bi-based HTSC do not originate from
antiferromagnetic interactions but have a structural origin.Comment: 10 pages, 2 figure
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