155 research outputs found
Thermal drag revisited: Boltzmann versus Kubo
The effect of mutual drag between phonons and spin excitations on the thermal
conductivity of a quantum spin system is discussed. We derive general
expression for the drag component of the thermal current using both Boltzmann
equation approach and Kubo linear-response formalism to leading order in the
spin-phonon coupling. We demonstrate that aside from higher-order corrections
which appear in the Kubo formalism both approaches yield identical results for
the drag thermal conductivity. We discuss the range of applicability of our
result and provide a generalization of our consideration to the cases of
fermionic excitations and to anomalous forms of boson-phonon coupling. Several
asymptotic regimes of our findings relevant to realistic situations are
highlighted.Comment: 14 pages, 3 figures, published version, extended discussio
Perspectiveness of correction of accompanying diseases in patients with autism by course of interior use of naturally low mineralized water
The article reviews the pathogenesis and the course of autism. Authors define autism as a psychosomatic disorder. A distinctive feature of mineral waters, as natural therapeutic factors of weak intensity, is their pronounced biological activity, the absence of side effects and the possibility of long-term use in combination with medication therapy. The paper presents data substantiating the possibility of using mineral water with an increased content of organic substances for the correction of the somatic component of autism (problems of the gastrointestinal tract, carbohydrate metabolism disorders, neurosis)
Electronic spectrum in high-temperature cuprate superconductors
A microscopic theory for electronic spectrum of the CuO2 plane within an
effective p-d Hubbard model is proposed. Dyson equation for the single-electron
Green function in terms of the Hubbard operators is derived which is solved
self-consistently for the self-energy evaluated in the noncrossing
approximation. Electron scattering on spin fluctuations induced by kinematic
interaction is described by a dynamical spin susceptibility with a continuous
spectrum. Doping and temperature dependence of electron dispersions, spectral
functions, the Fermi surface and the coupling constant are studied in the hole
doped case. At low doping, an arc-type Fermi surface and a pseudogap in the
spectral function are observed.Comment: 13 pages (revtex), 18 figures, to be published in JET
Irreducible Representations of Diperiodic Groups
The irreducible representations of all of the 80 diperiodic groups, being the
symmetries of the systems translationally periodical in two directions, are
calculated. To this end, each of these groups is factorized as the product of a
generalized translational group and an axial point group. The results are
presented in the form of the tables, containing the matrices of the irreducible
representations of the generators of the groups. General properties and some
physical applications (degeneracy and topology of the energy bands, selection
rules, etc.) are discussed.Comment: 30 pages, 5 figures, 28 tables, 18 refs, LaTex2.0
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
Spatial Structure of Spin Polarons in the t-J Model
The deformation of the quantum Neel state induced by a spin polaron is
analyzed in a slave fermion approach. Our method is based on the selfconsistent
Born approximation for Green's and the wave function for the quasiparticle. The
results of various spin-correlation functions relative to the position of the
moving hole are discussed and shown to agree with those available from small
cluster calculations. Antiferromagnetic correlations in the direct neighborhood
of the hole are reduced, but they remain antiferromagnetic even for J as small
as 0.1 t. These correlation functions exhibit dipolar distortions in the spin
structure, which sensitively depend on the momentum of the quasiparticle. Their
asymptotic decay with the distance from the hole is governed by power laws, yet
the spectral weight of the quasiparticles does not vanish.Comment: 12 pages, 2 postscipt files with figures; uses REVTeX, to be
published in Phys. Rev. B, Feb. 199
Normal Fermi Liquid Behavior of Quasiholes in the Spin-Polaron Model for Copper Oxides
Based on the t-J model and the self-consistent Born approximation, the
damping of quasiparticle hole states near the Fermi surface is calculated in a
low doping regime. Renormalization of spin-wave excitations due to hole doping
is taken into account. The damping is shown to be described by a familiar form
characteristic of the 2-dimensional
Fermi liquid, in contrast with the earlier statement reported by Li and Gong
[Phys. Rev. B {\bf 51}, 6343 (1995)] on the marginal Fermi liquid behavior of
quasiholes
Discontinuity of capacitance at the onset of surface superconductivity
The effect of the magnetic field on a capacitor with a superconducting
electrode is studied within the Ginzburg-Landau approach. It is shown that the
capacitance has a discontinuity at the onset of the surface superconductivity
which is expressed as a discontinuity in the penetration depth of
the electric field into metals. Estimates show that this discontinuity is
observable with recent bridges for both conventional and high-
superconductors of the type-II
High Temperature Macroscopic Entanglement
In this paper I intend to show that macroscopic entanglement is possible at
high temperatures. I analyze multipartite entanglement produced by the
pairing mechanism which features strongly in the fermionic lattice models of
high superconductivity. This problem is shown to be equivalent to
calculating multipartite entanglement in totally symmetric states of qubits. I
demonstrate that we can conclusively calculate the relative entropy of
entanglement within any subset of qubits in an overall symmetric state. Three
main results then follow. First, I show that the condition for
superconductivity, namely the existence of the off diagonal long range order
(ODLRO), is not dependent on two-site entanglement, but on just classical
correlations as the sites become more and more distant. Secondly, the
entanglement that does survive in the thermodynamical limit is the entanglement
of the total lattice and, at half filling, it scales with the log of the number
of sites. It is this entanglement that will exist at temperatures below the
superconducting critical temperature, which can currently be as high as 160
Kelvin. Thirdly, I prove that a complete mixture of symmetric states does not
contain any entanglement in the macroscopic limit. On the other hand, the same
mixture of symmetric states possesses the same two qubit entanglement features
as the pure states involved, in the sense that the mixing does not destroy
entanglement for finite number of qubits, albeit it does decrease it. Maximal
mixing of symmetric states also does not destroy ODLRO and classical
correlations. I discuss various other inequalities between different
entanglements as well as generalizations to the subsystems of any
dimensionality (i.e. higher than spin half).Comment: 14 pages, no figure
Polaron Effects on Superexchange Interaction: Isotope Shifts of , , and in Layered Copper Oxides
A compact expression has been obtained for the superexchange coupling of
magnetic ions via intermediate anions with regard to polaron effects at both
magnetic ions and intermediate anions. This expression is used to analyze the
main features of the behavior of isotope shifts for temperatures of three types
in layered cuprates: the Neel temperatures (), critical temperatures of
transitions to a superconducting state (), and characteristic temperatures
of the pseudogap in the normal state ().Comment: 4 pages, 1 figur
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