90 research outputs found
Probing the field-induced variation of the chemical potential in Bi(2)Sr(2)CaCu(2)O(y) via the magneto-thermopower measurements
Approximating the shape of the measured in
magneto-thermopower (TEP) by asymmetric linear triangle of the
form with positive and defined below and above , we observe that . In order to account for this asymmetry, we
explicitly introduce the field-dependent chemical potential of holes
into the Ginzburg-Landau theory and calculate both an average and fluctuation contributions to the total
magneto-TEP . As a result, we find a rather simple relationship
between the field-induced variation of the chemical potential in this material
and the above-mentioned magneto-TEP data around , viz. .Comment: REVTEX (epsf), 4 pages, 2 PS figures; to be published in JET
EPR study of polycrystalline superconductors with YBa2Cu3O7 structure
Electron paramagnetic resonance (EPR) of Gd3+, Eu2+, and copper ions has been investigated in the high-Tc superconductor with YBa2Cu3O7-α structure. It has been established that the system is heterogeneous at 0.15≤δ≤0.5 and consists of metallic and dielectric regions. The former arises due to oxygen enrichment while the later due to oxygen deficiency. The integral of exchange interaction between Gd3+ localized moments and conduction electrons Jsf=0.016 eV has been determined from the normal state temperature dependence of Gd3+ EPR linewidth for metallic regions. Tc depression by gadolinium-localized moments for GdBa2Cu3O7-α was estimated to be ΔTc{reversed tilde equals}-2K. Anomalies in linewidth temperature dependence upon transition from the normal to the superconducting state have given information about the value and temperature behavior of the superconductor's energy gap. The model, which gives the opportunity to understand some peculiarities of the EPR signal for YBa2Cu3O7-α samples, is proposed in terms of several bottlenecked spinsubsystems: spin-liquid in CuO planes and Cu2+-O- and Cu2+-O2- fragments in CuO chains. © 1989 Plenum Publishing Corporation
Solvegeometry gravitational waves
In this paper we construct negatively curved Einstein spaces describing
gravitational waves having a solvegeometry wave-front (i.e., the wave-fronts
are solvable Lie groups equipped with a left-invariant metric). Using the
Einstein solvmanifolds (i.e., solvable Lie groups considered as manifolds)
constructed in a previous paper as a starting point, we show that there also
exist solvegeometry gravitational waves. Some geometric aspects are discussed
and examples of spacetimes having additional symmetries are given, for example,
spacetimes generalising the Kaigorodov solution. The solvegeometry
gravitational waves are also examples of spacetimes which are indistinguishable
by considering the scalar curvature invariants alone.Comment: 10 pages; v2:more discussion and result
Monotonic growth of interlayer magnetoresistance in strong magnetic field in very anisotropic layered metals
It is shown, that the monotonic part of interlayer electronic conductivity
strongly decreases in high magnetic field perpendicular to the conducting
layers. We consider only the coherent interlayer tunnelling, and the obtained
result strongly contradicts the standard theory. This effect appears in very
anisotropic layered quasi-two-dimensional metals, when the interlayer transfer
integral is less than the Landau level separation.Comment: 4 pages, no figure
Prediction of inorganic superconductors with quasi-one-dimensional crystal structure
Models of superconductors having a quasi-one-dimensional crystal structure
based on the convoluted into a tube Ginzburg sandwich, which comprises a
layered dielectric-metal-dielectric structure, have been suggested. The
critical crystal chemistry parameters of the Ginzburg sandwich determining the
possibility of the emergence of superconductivity and the Tc value in layered
high-Tc cuprates, which could have the same functions in quasi-one-dimensional
fragments (sandwich-type tubes), have been examined. The crystal structures of
known low-temperature superconductors, in which one can mark out similar
quasi-one- dimensional fragments, have been analyzed. Five compounds with
quasi-one-dimensional structures, which can be considered as potential parents
of new superconductor families, possibly with high transition temperatures,
have been suggested. The methods of doping and modification of these compounds
are provided.Comment: 22 pages, 14 figures and 2 table
The structure of streams in the Lena delta and its influence on streamflow transformation processes
The structure of the stream network in the Lena delta has been studied, and its quantitative characteristics have been obtained for the first time. Taking into consideration the discharge of the branches as well as their width, we determined the conventional delta stream orders decreasing in a regular fashion toward the margin of the delta because of channel bifurcation. They have been used as the basis for determining the structural parameters of delta streams and studying the transformation characteristics of the flows of some materials and heat in the Lena delta
EPR study of polycrystalline superconductors with YBa2Cu3O7 structure
Electron paramagnetic resonance (EPR) of Gd3+, Eu2+, and copper ions has been investigated in the high-Tc superconductor with YBa2Cu3O7-α structure. It has been established that the system is heterogeneous at 0.15≤δ≤0.5 and consists of metallic and dielectric regions. The former arises due to oxygen enrichment while the later due to oxygen deficiency. The integral of exchange interaction between Gd3+ localized moments and conduction electrons Jsf=0.016 eV has been determined from the normal state temperature dependence of Gd3+ EPR linewidth for metallic regions. Tc depression by gadolinium-localized moments for GdBa2Cu3O7-α was estimated to be ΔTc{reversed tilde equals}-2K. Anomalies in linewidth temperature dependence upon transition from the normal to the superconducting state have given information about the value and temperature behavior of the superconductor's energy gap. The model, which gives the opportunity to understand some peculiarities of the EPR signal for YBa2Cu3O7-α samples, is proposed in terms of several bottlenecked spinsubsystems: spin-liquid in CuO planes and Cu2+-O- and Cu2+-O2- fragments in CuO chains. © 1989 Plenum Publishing Corporation
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