18 research outputs found
Kondo - exchange interaction in the CuO plane as the long sought mechanism of high temperature superconductivity in cuprates
The well-known Pavarini et al. [Phys. Rev. Lett. 87, 047003 (2001)]
correlation between the critical temperature , max and the shape of the
Fermi contour of the optimally hole-doped cuprates are explained within the
framework of the BCS theory with Kondo exchange interaction incorporated as a
pairing mechanism. The strong influence of the relative position of the Cu4
level with respect to the Cu3 level on the critical temperature
reveals why the - hybridization of the conduction band is so
important. This hybridization is proportional to the - exchange
scattering amplitude between the conduction electrons -- the mechanism of
d-wave pairing in the CuO plane. In other words the Kondo interaction
considered as a pairing mechanism in the CuO plane gives a natural
explanation of the correlation between the critical temperature and the shape
of the Fermi contour. The lack of an alternative explanation for the
description of the critical temperature of optimally doped cuprates for several
decades gives a hint that the long sought pairing mechanism has already been
found.Comment: 9 pages, 3 figures, 2 tables, 43 ref
Possible zero sound in layered perovskites with ferromagnetic - exchange interaction
We analyze the conditions for observation of zero sound in layered
perovskites with transition metal ion on chalcogenide oxidizer. We conclude
that propagation of zero sound is possible only for anti-ferromagnetic sign of
the - interaction. If the - exchange integral has
antiferromagnetic sign, as it is perhaps in the case for layered cuprates, zero
sound is a thermally activated dissipation mode,which generates only "hot
spots" in the Angle Resolved Photoemission Spectroscopy (ARPES) data along the
Fermi contour. We predict that zero sound will be observable for transition
metal perovskites with 4 and 3 levels close to the -level of the
chalcogenide. The simultaneous lack of superconductivity, the appearance of hot
spots in ARPES data, and the proximity of the three named levels, represents
the significant hint for the choice of material to be investigated.Comment: 7 pages, 4 figures, 30 reference
Hot spots along the Fermi contour of high- cuprates analyzed by - exchange interaction
We perform a thorough theoretical study of the electron properties of a
generic CuO plane in the framework of Shubin-Kondo-Zener - exchange
interaction that simultaneously describes the correlation between and the
Cu4 energy. To this end, we apply the Pokrovsky theory [J. Exp. Theor. Phys.
13, 447-450 (1961)] for anisotropic gap BCS superconductors. It takes into
account the thermodynamic fluctuations of the electric field in the dielectric
direction perpendicular to the conducting layers. We microscopically derive a
multiplicatively separable kernel able to describe the scattering rate in the
momentum space, as well as the superconducting gap anisotropy within the BCS
theory. These findings may be traced back to the fact that both the Fermi
liquid and the BCS reductions lead to one and the same reduced Hamiltonian
involving a separable interaction, such that a strong electron scattering
corresponds to a strong superconducting gap and vice versa. Moreover, the
superconducting gap and the scattering rate vanish simultaneously along the
diagonals of the Brillouin zone. We would like to stress that our theoretical
study reproduces the phenomenological analysis of other authors aiming at
describing Angle Resolved Photoemission Spectroscopy measurements. Within
standard approximations one and the same - exchange Hamiltonian describes
gap anisotropy of the superconducting phase and the anisotropy of scattering
rate of charge carriers in the normal phase.Comment: 10 pages, 3 figures, 56 reference
Electric Oscillations Generated by Fluctuation Cooper Pairs
A short review of the history and the contemporary numerical calculations of
the operation of an electronic device for generation of electric oscillations
by negative differential conductivity of a supercooled below the critical
temperature superconductor. The superconductor is cooled below the critical
temperature at applied small constant electric field, which keeps the
superconductor in normal state. To simulate the device operation, beforehand
analytical expressions for the conductivity of nano-structured superconductors
supercooled below the critical temperature in electric field are used. The
numerical analysis meant to alleviate the development of a device shows that
the region of negative differential conductivity of the current voltage
characteristics leads to generation of electric oscillations. The study of
layered high temperature superconductors and radiated electromagnetic waves in
space will be an important problem of the future space technology.Comment: Master degree thesis of Aleksander Petkov with scientific advisor
Albert Varonov and consultant Todor Mishonov, 20 pages, 16 figures, 1 table;
version 2 has the master thesis added to the source files (filename
"MasterThesis.pdf", Bulgarian translation