63 research outputs found
Central peak position in magnetization loops of high- superconductors
Exact analytical results are obtained for the magnetization of a
superconducting thin strip with a general behavior J_c(B) of the critical
current density. We show that within the critical-state model the magnetization
as function of applied field, B_a, has an extremum located exactly at B_a=0.
This result is in excellent agreement with presented experimental data for a
YBCO thin film. After introducing granularity by patterning the film, the
central peak becomes shifted to positive fields on the descending field branch
of the loop. Our results show that a positive peak position is a definite
signature of granularity in superconductors.Comment: $ pages, 6 figure
Pseudogap from ARPES experiment: three gaps in cuprates and topological superconductivity
A term first coined by Mott back in 1968 a `pseudogap' is the depletion of
the electronic density of states at the Fermi level, and pseudogaps have been
observed in many systems. However, since the discovery of the high temperature
superconductors (HTSC) in 1986, the central role attributed to the pseudogap in
these systems has meant that by many researchers now associate the term
pseudogap exclusively with the HTSC phenomenon. Recently, the problem has got a
lot of new attention with the rediscovery of two distinct energy scales
(`two-gap scenario') and charge density waves patterns in the cuprates. Despite
many excellent reviews on the pseudogap phenomenon in HTSC, published from its
very discovery up to now, the mechanism of the pseudogap and its relation to
superconductivity are still open questions. The present review represents a
contribution dealing with the pseudogap, focusing on results from angle
resolved photoemission spectroscopy (ARPES) and ends up with the conclusion
that the pseudogap in cuprates is a complex phenomenon which includes at least
three different `intertwined' orders: spin and charge density waves and
preformed pairs, which appears in different parts of the phase diagram. The
density waves in cuprates are competing to superconductivity for the electronic
states but, on the other hand, should drive the electronic structure to
vicinity of Lifshitz transition, that could be a key similarity between the
superconducting cuprates and iron based superconductors. One may also note that
since the pseudogap in cuprates has multiple origins there is no need to recoin
the term suggested by Mott.Comment: invited review, more info at http://www.imp.kiev.ua/~kor
Paraconductivity of K-doped SrFe2As2 superconductor
Paraconductivity of the optimally K-doped SrFe2As2 superconductor is
investigated within existing fluctuation mechanisms. The in-plane excess
conductivity has been measured in high quality single crystals, with a sharp
superconducting transition at Tc=35.5K and a transition width less than 0.3K.
The data have been also acquired in external magnetic field up to 14T. We show
that the fluctuation conductivity data in zero field and for temperatures close
to Tc, can be explained within a three-dimensional Lawrence-Doniach theory,
with a negligible Maki-Thompson contribution. In the presence of the magnetic
field, it is shown that paraconductivity obeys the three-dimensional
Ullah-Dorsey scaling law, above 2T and for H||c. The estimated upper critical
field and the coherence length nicely agree with the available experimental
data.Comment: 12 pages, 5 figure
Semiconductor Spintronics
Spintronics refers commonly to phenomena in which the spin of electrons in a
solid state environment plays the determining role. In a more narrow sense
spintronics is an emerging research field of electronics: spintronics devices
are based on a spin control of electronics, or on an electrical and optical
control of spin or magnetism. This review presents selected themes of
semiconductor spintronics, introducing important concepts in spin transport,
spin injection, Silsbee-Johnson spin-charge coupling, and spindependent
tunneling, as well as spin relaxation and spin dynamics. The most fundamental
spin-dependent nteraction in nonmagnetic semiconductors is spin-orbit coupling.
Depending on the crystal symmetries of the material, as well as on the
structural properties of semiconductor based heterostructures, the spin-orbit
coupling takes on different functional forms, giving a nice playground of
effective spin-orbit Hamiltonians. The effective Hamiltonians for the most
relevant classes of materials and heterostructures are derived here from
realistic electronic band structure descriptions. Most semiconductor device
systems are still theoretical concepts, waiting for experimental
demonstrations. A review of selected proposed, and a few demonstrated devices
is presented, with detailed description of two important classes: magnetic
resonant tunnel structures and bipolar magnetic diodes and transistors. In most
cases the presentation is of tutorial style, introducing the essential
theoretical formalism at an accessible level, with case-study-like
illustrations of actual experimental results, as well as with brief reviews of
relevant recent achievements in the field.Comment: tutorial review; 342 pages, 132 figure
The features of the non-equilibrium equation of state in heavy-ion collisions at intermediate energies
The features of the non-equilibrium equation of state in heavy-ion collisions at intermediate energies
Diverse Modes of Reactivity of 6‐(Chloromethyl)‐6‐methylfulvene
The title compound exhibits a number of modes of reactivity toward nucleophiles/bases owing to the presence of several electrophilic and potentially nucleophilic sites in the molecule. We explored the reactions of 6-(chloromethyl)-6-methylfulvene with oxygen and nitrogen nucleophiles and bases as well as a carbon-based nucleophile (an enamine) and realized all possible reactivity modes predicted on the basis of electrophilic and nucleophilic positions in this compound.United States Department of Health & Human Services National Institutes of Health (NIH) - USA - SC1 GM082340National Science Foundation (NSF) - CHE-1565852 - CHE-1228656United States Department of Health & Human Services National Institutes of Health (NIH) - USA - R25-GM059298 Appeared in source as:NIH MBRS-RISE scholarshipNIH-MS-PhD Bridge scholarship - R-25-GM048972National Science Foundation (NSF) NSF - Directorate for Mathematical & Physical Sciences (MPS) - 156585
Complexes of cobalt(III) with derivatives of oximes as catalysts of electron transfer from the components of the respiratory chain
Hydrolytic polycondensation and exchange reaction of methyltrichlorosilane with sodium metasilicate
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