arXiv subjects

Nedeltcho I. Zahariev

Publications and source records attributed to Nedeltcho I. Zahariev.

3 recordsLinked to original sources

arXiv2025

Kondo $s$-$d$ exchange in the CuO$_2$ plane as the long sought interaction determining $T_c$ in cuprates

The well-known Pavarini et al. [Phys. Rev. Lett. 87, 047003 (2001)] correlation between the critical temperature $T_{c,\,\mathrm{max}}$ and the shape of the Fermi contour of the optimally hole-doped cuprates is 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$s$ level with respect to the Cu3$d_{x^2-y^2}$ level on the critical temperature $T_c$ reveals the importance of the $s$-$d$ hybridization of the conduction band. This hybridization is proportional to the $s$-$d$ exchange scattering amplitude between the conduction electrons -- the mechanism of $d$-wave pairing in the CuO$_2$ plane. In other words the Kondo interaction considered as a pairing mechanism in the CuO$_2$ plane gives a natural explanation of the correlation between the critical temperature and the shape of the Fermi contour. This result suggests that the long-sought pairing mechanism in high-$T_c$ superconducting cuprates has possibly been found and that the Kondo exchange interaction as a property of strongly correlated quantum matter deserves further attention in the physics of layered cuprates. To test the developed theoretical scheme, we explored in detail the recent results of the scanned Josephson modulation microscopy experiment of the modulation of the order parameter due to apex distance super-modulation. Our analysis shows a satisfactory agreement between our theory and the named experiment.

cond-mat.supr-con↗

arXiv2022

The Influence of $s$-$d$ Exchange Interaction on the Gap Anisotropy and Anisotropy of the Lifetime of Normal State Charge Carriers of Layered Cuprates

The anisotropy of the electron scattering rate and lifetime $Γ_\mathbf{p}=1/τ_\mathbf{p}$ observed by Angle Resolved Photoemission Spectroscopy (ARPES) is evaluated using $s$-$d$ Kondo-Zener exchange Hamiltonian used previously to describe superconducting properties of high-$T_c$ cuprates; for correlation between critical temperature $T_c$ and BCS coupling constant, for example. The performed qualitative analysis reveals that "cold spots" correspond to nodal regions of the superconducting phase where the superconducting gap is zero, because the exchange interaction is annulled. Vice versa, "hot spots" and intensive scattering in the normal state correspond to the regions with maximal gap in the superconducting phase. We have obtained that separable kernel postulated in the Fermi liquid approach to the normal phase is the same kernel which is exactly calculated in the framework of the $s$-$d$ approach in the Linear Combination of Atomic Orbital (LCAO) approximation for CuO$_2$ plane. In this sense, at least on the qualitative level, the superconducting cuprates are described by one and the same Hamiltonian applied to their superconducting and normal properties. For the overdopedcuprates having conventional Fermi liquid behavior we derived the corresponding Stoss-integral for the $s$-$d$ interaction in the framework of LCAO approximation which is the central result of the present study. Repeating the thermodynamics we observed that for optimally doped cuprates $2Δ_\mathrm{max}/T_c$ is in good agreement with Pokrovsky theory for anisotropic gap superconductors.

cond-mat.supr-con↗

arXiv2016

Heating of the solar corona by Alfven waves - self-induced opacity

Static distributions of temperature and wind velocity at the transition region are calculated within the framework of magnetohydrodynamics (MHD) of completely ionized hydrogen plasma. The numerical solution of the derived equations gives the width of the transition layer between the chromosphere and the corona as a self-induced opacity of high-frequency Alfven waves (AW). The domain wall is direct consequence of the self-consistent MHD treatment of AW propagation. The low-frequency MHD waves coming from the Sun are strongly reflected by the narrow transition layer, while the high-frequency waves are absorbed - that is why we predict considerable spectral density of the AW in the photosphere. The numerical method allows consideration of incoming AW with arbitrary spectral density. The idea that Alfven waves might heat the solar corona belongs to Alfven, we simply solved the corresponding MHD equations. The comparison of the solution to the experiment is crucial for revealing the heating mechanism.

astro-ph.SR↗