POSTER SESSION 2PO9: Electrical and Thermal Properties

POSTER SESSION 2PO9: Electrical and Thermal Properties

Tuesday, Feb. 22, 1:30 p.m. – 3:30 p.m., Hall D (GRB)

2PO9-1 Fitting of Experimental Current-Voltage Characteristics of Polycrystalline HTSC + Normal Metal Composites by Theory Based on Andreev Reflection

M.I. Petrov, D.A. Balaev, D.M. Gohfeld, S.V. Ospishchev, K.A. Shaihudtinov, and K.S. Aleksandrov, Kirensky Institute of Physics, 660036 Krasnoyarsk, Russia

Presenting Author: D.M. Gohfeld

In our previous paper [1] measurements of Current-Voltage Characteristics (CVC) of Y_3/4Lu_1/4Ba₂Cu₃O₇+ BaPbO₃ and Y_3/4Lu_1/4Ba₂Cu₃O₇+ BaPb_0.9Sn_0.1O₃ composites modelling network of Superconducting-Normal metal-Superconducting (S-N-S) junctions in effectively "clean" [2] and "dirty" [3] limits respectively have been presented. It has been shown a good qualitative and semi-quantitative agreement of experimental CVCs and simplified model of Kummel-Nicolsky (K-N) theory [4] for S-N-S junction proposed by Pereira and Nicolsky [5]. In the present paper we report on the fitting of our experimental data within the frameworks of K-N theory in complete form [4]. In this case we achieved better quantitative agreement with experiment than for simplified model [1].

So far as Andreev reflection of carriers on S-N and N-S interfaces is considered as the mainland mechanism in theory [4] the coincidence with experiment supports the arguments to Andreev reflection playing the important role for interpretation of resistive properties of S-N-S junctions.

[1] M.I. Petrov, et. al., Physica C 314, 51 (1999).

[2] M.I. Petrov, et. al., Phys. Lett. A 237 85 (1997).

[3] M.I. Petrov, et. al., Physica C 282-287, 2447 (1997).

[4] R. Kümmel, et. al., Phys. Rev. B 42 3932 (1990).

[5] L.A.A. Pereira, R. Nicolsky, Physica C, 282-287 2411 (1997).

2PO9-2 Heavy ions transfer in HTSC and the nature of the current state in d-type superconductors

G.N. Mikhailova 1, A.M. Prokhorov 1, L.Yu. Shchurova 2, and A.V.Troitzkii 1. 1 General Physics Institute, Russian Academy of Sciences,Vavilov Street 38, 117924 Moscow, Russia. 2 P.N.Lebedev Physical Institute, Russian Academy of Sciences, Leninskii Prospect 53, 117924 Moscow, Russia.

Presenting Author: L.Yu. Shchurova

We report observations of heavy ions transfer on a variety of YBCO(123) and Bi(2223) samples at a superconducting state as a result of rather high transport current flowing.

We have proposed a theoretical model to explain the effect of ion transfer as a responce of superconducting d-electrons delocalized on the ion lattice under the external electrical field. The described d-type superconducting state is characterized by combined rotational-translation invariance, where rotational symmetry is constrained with the traffic of electrons in the vortex field of ions.

2PO9-3 Varied Coherent Electron States in Quasi-Two-Dimensional Superconductors

L.Yu. Shchurova, P.N.Lebedev Physical Institute, Russian Academy of Sciences, Leninskii Prospect 53, 117924 Moscow, Russia

Presenting Author: L.Yu. Shchurova

Electron states in quasi-two-dimensional lattice of ions with spins are considered. Employing field-theoretical and topological methods results in obtaining stable global ion field configurations with a finite energy. Scalar fields, which are spins, and vector fields act as the independent components of such stable configurations. The vector fields in the local regions of the topological defects generate vortices. We examine delocalized electron states in the stable configuration of the ion fields. The electrons as a result of interacting with the fields acquire conserved momenta characterized by a symmetry that is consistent with that of the fields of the stable configuration. The electron system is shown to be coherent and possessing conserved total angular momentum (p-states) ore total angular and magnetic momenta (d-states). The coherent electron d-states we found superconducting properties.

2PO9-5 Temperature-Dependent Inelastic Scattering in d-wave High T_c Superconductors

M.F. Smith and M.B. Walker, Physics Dept.,University of Toronto, 60 St. George St. Toronto, Ontario, Canada, M5S 1A7

Presenting Author: M.F. Smith

The quasiparticle lifetime and the related transport relaxation times are the fundamental quantities which must be known in order to obtain a description of the transport properties of the high T_c superconductors. Detailed studies of these quantities have been undertaken for d-wave high-T_c superconductors for the case of temperature-independent elastic impurity scattering. However, much less is known about the temperature-dependent inelastic scattering. Here we describe some temperature-dependent inelastic scattering processes which account for the rapid variation with temperature of the electrical transport relaxation rate measured recently by Hosseini et al. (Phys. Rev. 1999).

2PO9-6 Phonon Dispersion and Specific Heat of Cuprate High-T_c Superconductors

Igor N. Kudryavtsev, Physics Dept., Kharkov State Automobile & HighWay Technical University, Kharkov 310078, Ukraine

Presenting Author: I.N. Kudryavtsev

A phonon spectral density of states is generalized accounting the dispersion of acoustic and optic phonon modes. A theoretical analysis of the specific heat dependence on the characteristic dimensionality of the lattice basis is accomplished. In the frames of approach proposed the numerical calculations of phonon specific heat for Y-Ba-Cu-O HTSC are carried out and agreement with the experimental data is achieved in wide temperature region without using free parameters. It is shown, that cuprate superconductors Y-Ba-Cu-O possess a characteristic two-dimensional basis structure. A single-valued electronic contribution to the specific heat is determined in the superconducting transition region, that allowes us to carry out a detailed analysis of the electronic subsystem's parameters and superconductivity mechanism in cuprate HTSC.

2PO9-7 New Exact Solution Formulas for Specific Heat-Phonon Spectrum Inversion and Its Application in Studies of Supercondcutivity

Wen Tao 1, JiXin Dai 2, and XianXi Dai 1. 1 Department of Physics, Fudan University, Shanghai, 200433, P.R. China. 2 Department of Chemistry, New York University, New York, NY 10003, USA.

Presenting Author: W. Tao

The specific heat-phonon spectrum inversion problem is reviewed. A phonon spectrum of YBCO is obtained from its experimental specific heat data by an exact inversion formula. The results are comparable with that from neutron inelastic scattering experiment. Some key points of specific heat-phonon spectrum inversion (SPI) is discussed. An improved unique existence theorem is presented. A universal function set for the numerical calculation in SPI is derived, which will make the inversion method more applicable and convenient in practice. This is the first time to realize the specific heat-phonon spectrum inversion in a concrete system [1].

For a long period of time, people have been dreaming to get the phonon spectrum by SPI through the linear combination of Debye specific heat functions. Because these functions are real and have correct asymptotic behaviors and clear physical picture. But one can not form a complete set yet. In this paper, we first prove an exaction formula in mathematics, then a new exact solution formula set in real representation will be proposed. The single mode solution not only has all the merits of the Debye specific heat functions, but also can form a complete function set, which can cover all possiblities of the phonon spectrum. The phonon spectrum of real system has been obtained by this new formula and in a good agreement with that of inelastic neutron scattering. The application of the new solutions is discussed.

[1] Dai Xianxi "Some Inversion Problems in the Studies of High T_c Superconductivity". International Conference on New Theories, Discoveries and Applications of Superconductors and Related Materials, June, 1999, USA. (1)

(1) This work is in Project 19834010 and 19575009, supported by National Science Foundation of China.

2PO9-8 Thermopower and Electroconductivity in Oxygen Deficit Y-Ba-Cu-O Thin Films

Arsen A. Hakhoumian 1, Armen S. Kuzanyan 2, Tigran V. Zakaryan 1, and Georgy R. Badalyan 2. 1 Institute of Radiophysics and Electronics, Ashtarak-2, 378410, Armenia. 2 Institute for Physical Researches, Ashtarak-2, 378410, Armenia.

Presenting Author: A.A. Hakhoumian

The thin film structures of oxygen deficit layered oxides have their own interest as thermoelectric, infrared and other sensors. We have investigated three types of Y-Ba-Cu-O films: monocrystalline on (100) LaAlO₂ substrate, texture and polycrystalline on Y-stabilized ZrO₂ (100) plane and non-oriented substrates respectively. The specific resistivity and thermopower against oxygen deficit of present films were measured. First unusual result is the relatively small (15m V/K) thermopower for monocrystall films. This is a consequence of highly orientated large plates boundaries forming the monocrystalline film. The thermopower of texture films is no longer anisotropic and thrice greater (40m V/K).

There is no anisotropy in texture film surface because the plates border on in all possible directions. Increase of thermopower is determined by smaller plate size compared with one of monocrystal film. Increase of the plate boundary density also results in the increase of resistivity, which was observed.

Transition from the low level to the high level thermopower is observed in a rather narrow range of oxygen deficit both for monocrystalline and texture films. The same value of thermopower may be achieved in polycrystalline films, but in a wide range of oxygen deficit.

The experimental results are in a good agreement with the 2D effective media model.

2PO9-9 Thermoelectric Properties of the Complex Cooprate Oxydes

Presenting Author: A.A. Hakhoumian

The thermoelectric power and electrical resistivity of the high-T_c superconducting oxides and their mixtures have been studied from the viewpoint of their possible use in thermoelectric devices. The maximum value of figure of merit (Z) for single-phase R₀Ba₂Cu₃O_7-x (R=Y, Eu, Ho, Dy, Sm, Gd, Nd) is achived at oxygen deficit x=0.5¸ 0.7 corresponding to orthogonal to tetragonal structural transition. At such conditions these oxides represent itself narrow gap semiconductors with E_g=0.04¸ 0.15eV.

It is established that for single-phase R₀Ba₂Cu₃O_7-x mixtures it is impossible to achieve the figure of merit more than 1¸ 2x10^-4 controlling only the oxygen deficit due to the strong interdependence of electroconductivity and thermopower.

In order to enhance the possibility of relatevely independent control of thermopower and resistivity bi-component (R₁-Ba-Cu-O)_1-x(R₂-Ba-Cu-O)(R1,2=Y, Pr, Nd, Gd) have been investigated. The general peculiarities common to all mixtures are:

· There are local minimums on all curves of thermopower at medium values of concentrations of the order of ~60¸ 40%;

· Curves, corresponding to high difference of thermopower in the limiting points x=0 and x=1, have narrow maximums near the point x» 0.1¸ 0.2;

· Complex composition of such ceramics allows to control the value of thermopower by means of more quantity of independent parameters compared with mono-component mixture.