Mandal, P and Poddar, A and Choudhury, Pranab and Mandal, J B and Keshri, S and Das, A N and Ghosh, B (1992) Transport, optical-properties and superconductivity in Bi-systems and Tl-systems. Indian Journal of Pure & Applied Physics, 30 (10-11). pp. 531-561. ISSN 0019-5596

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The results of electrical resistivity, excess conductivity, Hall voltage and thermoelectric power of Biand TI-based high-T(c) superconductors are presented and discussed. A metal-insulator transition occurs in Bi-2212 system at x approximately-equal-to 0.55 and for TI-2212 system at x approximately-equal-to 0.48. Analysis of electrical resistivity in the insulating region suggests that the transport is governed by two-dimensional (2D) variable range hopping (VRH) mechanism in the low temperature and phonon assisted hopping of polarons in the high temperature region. With the increase of carrier density, a crossover from 2D-3D VRH is observed near the insulator-metal transition for both the systems. Hall voltage measurements indicate a strong correlation between the transition temperature and the carrier density (n(H)) for both the systems. In Bi-2212, Tl-2212 and Bi-2223 systems T(c) versus n(H) variation is dome-shaped. Excess conductivity analysis shows two-dimensional nature of superconductivity in Bi-2212 and Tl-2212 systems. The inter-layer coupling for these systems is very small compared to 123-system. Superconducting fluctuations in Bi-2212 single crystal shows a 2D-3D crossover close to the transition temperature. Thermoelectric power (S) of Bi2Sr2Ca1-xYCu2O8+y shows that for insulating samples, S is positive, large and weakly temperature dependent in the high temperature region. The value of S decreases with increase in carrier density. For small hole concentration S300K appears to satisfy a relation obtained from one band Hubbard model in the strong correlation limit. The temperature variation of S for samples with different doping level is described by boson-fermion model of Nagaosa and Lee. The study of absorption spectra of Bi2Sr2Ca1-xYx-Cu2O8+y samples in the middle and far infrared region is presented. The metal-insulator transition at x=0.55 shows up in the IR absorption spectra through abrupt screening of some of the vibrational modes. Finally, we discuss briefly the mean field superconducting phase diagram of a Hubbard model with strong correlation in presence of electron-phonon interactions. A t-J model with additional polaron-polaron interaction term is obtained. It is shown that the X-operator technique, which preserves the strict local constraint, could describe at least qualitatively the superconducting phase diagram and some of the normal state properties of high-T(c) oxide superconductors.

Item Type: Article
Subjects: Electronics
Depositing User: Bidhan Chaudhuri
Date Deposited: 28 Nov 2013 07:19
Last Modified: 28 Nov 2013 07:19

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