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

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

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

Diode Based on Amorphous SiC

Diode structure on the basis of amorphous silicon carbide and p-type polycrystalline silicon (Eurosolar) were obtained with magnetron RF-nonreactive sputtering method from solid-phase target in argon atmosphere. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3365

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

Study of the radiochemical and thermal conversions mechanism in products of processing of grapes

The extraction of biologically active substance was carried out with help of combination of the physical factors: various conditions of temperature (40, 50, 60°С) and pressure of vacuum drying (8, 14, 16 mm Hg), and also various radiation doses by electrons with energy 12 МeV (10, 20, 40 kGy). The investigations of dynamics of definition of extract acidity and formation level of intermediate active products are carried out. It was established that the modification of properties of grape raw material depends on type of grapes, requirements of vacuum drying and radiation dose by electrons.Екстракцію біологічно активних речовин було проведено за допомогою комбінації фізичних факторів: різні режими температури (40, 50, 60°С) і тиску вакуумного сушіння (8, 14, 16 мм Hg), а також різні дози опромінення електронами з енергією 12 МеВ (10, 20, 40 кГр). Проведено дослідження динаміки кислотності екстрактів і рівня утворення проміжних активних продуктів. Показано, що зміна властивостей виноградної сировини залежить від сорту винограду, умов вакуумного сушіння і дози опромінення електронами.Экстракция биологически активных веществ была проведена с помощью комбинации физических факторов: различные режимы температуры (40, 50, 60°С) и давления вакуумной сушки (8, 14, 16 мм Hg), а также различные дозы облучения электронами с энергией 12 МэВ (10, 20, 40 кГр). Проведены исследования динамики определения кислотности экстрактов и уровня образования промежуточно-активных продуктов. Показано, что изменение свойств виноградного сырья зависит от сорта винограда, условий вакуумной сушки и дозы облучения электронами

Mass-renormalized electronic excitations at (π\pi, 0) in the superconducting state of Bi2Sr2CaCu2O8+δBi_{2}Sr_{2}CaCu_{2}O_{8+\delta}

Using high-resolution angle-resolved photoemission spectroscopy on $Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta}$, we have made the first observation of a mass renormalization or "kink" in the E vs. $\vec k$ dispersion relation localized near $(\pi, 0)$. Compared to the kink observed along the nodal direction, this new effect is clearly stronger, appears at a lower energy near 40 meV, and is only present in the superconducting state. The kink energy scale defines a cutoff below which well-defined quasiparticle excitations occur. This effect is likely due to coupling to a bosonic excitation, with the most plausible candidate being the magnetic resonance mode observed in inelastic neutron scattering