arXiv subjects

T. M. Mishonov

Publications and source records attributed to T. M. Mishonov.

30 records · Page 2Linked to original sources

arXiv2007

Evidence for nonmonotonic magnetic field penetration in a type-I superconductor

Polarized neutron reflectometry (PNR) provides evidence that nonlocal electrodynamics governs the magnetic field penetration in an extreme low-k superconductor. The sample is an indium film with a large elastic mean free path (11 mkm) deposited on a silicon oxide wafer. It is shown that PNR can resolve the difference between the reflected neutron spin asymmetries predicted by the local and nonlocal theories of superconductivity. The experimental data support the nonlocal theory, which predicts a nonmonotonic decay of the magnetic field.

cond-mat.supr-con↗

arXiv2007

On the origin of solar wind. Alfven waves induced jump of coronal temperature

Absorbtion of Alfven waves is considered to be the main mechanism of heating in the solar corona. It is concluded that the sharp increase of the plasma temperature by two orders of magnitude is related to a self-induced opacity with respect to Alfven waves. The maximal frequency for propagation of Alfven waves is determined by the strongly temperature dependent kinematic viscosity. In such a way the temperature jump is due to absorption of high frequency Alfven waves in a narrow layer above the solar surface. It is calculated that the power per unit area dissipated in this layer due to damping of Alfven waves blows up the plasma and gives birth to the solar wind. A model short wave-length (WKB) evaluation takes into account the 1/f^2 frequency dependance of the transversal magnetic field and velocity spectral densities. Such spectral densities agree with old magnetometric data taken by Voyager 1 and recent theoretical calculations in the framework of Langevin-Burgers MHD. The present theory predicts existence of intensive high frequency MHD Alfven waves in the cold layer beneath the corona. It is briefly discussed how this statement can be checked experimentally. It is demonstrated that the magnitude of the Alfven waves generating random noise and the solar wind velocity can be expressed only in terms of satellite experimental data. It is advocated that investigation of properties of the solar surface as a random driver by optical methods is an important task for future solar physics. Jets of accretion disks are speculated as a special case of the wind from magnetized turbulent plasma.

astro-ph↗

arXiv2007

Theory of heating of hot magnetized plasma by Alfven waves. Application for solar corona

The heating of magnetized plasma by propagation of Alfven waves is calculated as a function of the magnetic field spectral density. The results can be applied to evaluate the heating power of the solar corona at known data from satellites' magnetometers. This heating rate can be incorporated in global models for heating of the solar corona and creation of the solar wind. The final formula for the heating power is illustrated with a model spectral density of the magnetic field obtained by analysis of the Voyager 1 mission results. The influence of high frequency dissipative modes is also taken into account and it is concluded that for evaluation of the total coronal heating it is necessary to know the spectral density of the fluctuating component of the magnetic field up to the frequency of electron-proton collisions.

astro-ph↗

arXiv2007

Burgulence and Alfven waves heating mechanism of solar corona

Heating of magnetized turbulent plasma is calculated in the framework of Burgers turbulence [A.M. Polyakov, Phys. Rev. E. 52, 6183 (1995)]. Explicit formula for the energy flux of Alfven waves along the magnetic field is presented. The Alfven waves are considered as intermediary between the turbulent energy and the heat. The derived results are related to a wave channel of heating of the solar corona. If we incorporate amplification of Alfven waves by shear flow the suggested model of heating can be applied to analysis of the missing viscosity of accretion discs and to reveal why the quasars are the most powerful sources of light in the universe. We suppose that the Langevin-Burgers approach to turbulence we have applied in the current work can be also helpful for other systems where we have intensive interaction between a stochastic turbulent system and waves and can be used in many multidisciplinary researches in hydrodynamics and MHD.

astro-ph↗

arXiv2006

Superconductivity of overdoped cuprates: the modern face of the ancestral two-electron exchange

The single-site two-electron exchange amplitude J_sd between the Cu 4s and Cu 3d_{x^2-y^2} states is found to be the pairing mechanism of high-T_c overdoped cuprates. The noninteracting part of the Hamiltonian spans the copper Cu 4s, Cu 3d_{x^2-y^2} and oxygen O 2p_x and O 2p_y states. Within the standard BCS treatment an explicit expression for the momentum dependence of the gap Delta_p is derived and shown to fit the angle-resolved photoemission spectroscopy (ARPES) data. The basic thermodynamic and electrodynamic properties of the model (specific heat C(T), London penetration depth lambda(T)) are analytically derived. These are directly applicable to cuprates without complicating structural accessories (chains, double CuO_2 planes, etc.). We advocate that the pairing mechanism of overdoped and underdoped cuprates is the same, as T_c displays smooth doping dependence. Thus, a long-standing puzzle in physics is possibly solved.

cond-mat.supr-con↗

arXiv2005

Quantization of conductivity of nanotechnological point contact. Simple derivation of the Landauer formula

A simple methodical derivation for Landauer quantization of the conductivity is derived as a simple consequence of the Bohr quantization laws. The level of explanation corresponds to high-school level of Physics education and can be used as popular lecture for students. The purpose of the work is to introduce students in an achievement of nano-technology which is relevant to the future electronics. Using only the fundamental laws of quantization students can understand a contemporary experimental research and to follow future development in the field.

physics.ed-ph↗

arXiv2004

Comment on "Band-Structure Trend in Hole-Doped Cuprates and Correlation with T_c_max"

The purpose of the present Comment is to emphasize that the missing link has already been found, and the correlation reported by Pavarini et al., Phys. Rev. Lett. 87, 047003 (2001) [http://dx.doi.org/10.1103/PhysRevLett.87.047003] can be used as a crucial test for theoretical models of HTSC. Perhaps the simplest possible interpretation, though one could search for alternatives, is given within the framework of the Cu 4s-Cu 3d two-electron exchange theory of HTSC, J. Phys.: Condens. Matter 15, 4429 (2003) [http://dx.doi.org/10.1088/0953-8984/15/25/312].

cond-mat.supr-con↗

arXiv2004

Temperature dependence of the specific heat and the penetration depth of anisotropic-gap BCS superconductors for a factorizable pairing potential

An explicit expression for the temperature dependence of the specific heat of clean anisotropic-gap superconductors is derived within the weak-coupling BCS approximation. The specific heat is presented as a functional of the superconducting gap on the Fermi surface. The obtained formula interpolates between the correct low coupling jump at T_c and the low temperature behavior for T<<T_c. For isotropic superconductors the formula gives a relation between the specific heat and the superconducting gap. For anisotropic superconductors, the interpolation formula incorporates averaging of powers of the gap anisotropy function over the Fermi surface and provides a suitable set for fitting model Hamiltonians to experimental data. The work of the interpolation formula is illustrated by (i) the Pokrovsky formula for the specific heat jump, (ii) Gor'kov and Melik-Barkhudarov formulas for the Ginzburg-Landau coefficients, (iii) the Moskalenko two-band formula for the specific heat jump, (iv) the temperature dependence of the specific heat for the two-band model, applicable to MgB_2, (v) the two-dimensional d-wave model, applicable for YBa_2Cu_3O_{7-delta}, and (vi) the Zhitomirsky and Rice triplet p-wave model with horizontal line nodes for Sr_2RuO_4. The temperature dependence of the penetration depth is illustrated by fitting the general theoretical formula to the experimental data for MgB_2, YBa_2Cu_3O_{7-delta}, and the triplet superconductor Sr_2RuO_4.

cond-mat.supr-con↗

arXiv2002

The 3d-to-4s-by-2p highway to superconductivity in cuprates

High-temperature superconductors are nowadays found in great variety and hold technological promise. It is still an unsolved mystery that the critical temperature T_c of the basic cuprates is so high. The answer might well be hidden in a conventional corner of theoretical physics, overlooked in the recent hunt for exotic explanations of new effects in these materials. A forgotten intra-atomic s-d two-electron exchange in the Cu atom is found to provide a strong (~eV) electron pairing interaction. A Bardeen-Cooper-Schrieffer approach can explain the main experimental observations and predict the correct d_{x^2-y^2} symmetry of the gap.

cond-mat.supr-con↗

arXiv2002

Reduced pairing hamiltonian for interatomic two-electron exchange in layered cuprates

A detailed Linear Combination of Atomic Orbitals (LCAO) tight-binding model is developed for the layered High-Temperature Superconductor cuprates. The band structure of these materials is described using a sigma-band Hamiltonian employing Cu4s, Cu3d_x^2-y^2, O2p_x and O2p_y atomic orbitals. The Fermi level and the shape of the resulting Fermi surface are fitted to recent Angle Resolved Photon Emission Spectroscopy (ARPES) data to realistically determine the dispersion in the conduction band. Electron-electron interactions and, ultimately, Cooper pairing is obtained by introducing a Heitler-London, two-electron exchange between adjacent orbitals within the CuO_2 plane. Finally, using the LCAO wavefunctions determined by the band structure fit, the Bardeen-Cooper-Schrieffer type kernel is derived for interatomic exchange.

cond-mat.supr-con↗

arXiv2002

Comment on ``Anisotropic s-wave superconductivity: comparison with experiments on MgB_2 [A. I. Posazhennikova, T. Dahm and K. Maki, cond-mat/0204272; submitted to Europhys. Lett.]

An analytical result for the renormalization of the jump of the heat capacity Delta C/C_N by the anisotropy of the order parameter is derived within the framework of the very recent model proposed by Posazhennikova, Dahm and Maki [cond-mat/0204272, submitted to Europhys. Lett.], for both oblate and prolate anisotropy. The graph of Delta C/C_N versus the ratio of the gaps on the equator and the pole of the Fermi surface, Delta_e/Δ_p, allows a direct determination of the gap anisotropy parameter Delta_e/Δ_p by fitting data from specific heat measurements Delta C/C_N. Using the experimental value Delta C/C_N=0.82 +/- 10% by Wang, Plackowski, and Junod [Physica C 355 (2001) 179] we find Delta_e/Δ_p = 4.0.

cond-mat.supr-con↗

arXiv2000

Superconducting gap anisotropy within the framework of a simple exchange model for layered cuprates. The theory of HTSC

The oxygen O2p_sigma and copper Cu4s and Cu3d_x^2-y^2 orbitals are involved in a simple LCAO model for determination of the conduction band and the oxygen-oxygen hopping is considered as a small parameter with respect to the transition amplitude between nearest neighbours. The traditional Cooper pairing is obtained by taking into account the double-electron exchange between the nearest neighbours within the two-dimensional CuO_2 plane. The equation for the superconducting gap is obtained as a result of the standard BCS treatment. It is shown that the order parameter could have either s-type or d-type symmetry depending on the ratio between the transition amplitudes. This model allows understanding the experiments reporting a pi-shift of the Josephson phase indicative for a d-type gap symmetry as well as the observed s-type in the case of strongly irradiated samples.

cond-mat.supr-con↗