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Evolution and the concomitant disappearance of high-$T_c$ superconductivity with carrier concentration in the $La_{2-x}Sr_xCuO_{4-\delta}$ system $(0.0\leq x \leq 1.2)$: Crossover from a Mott insulator to a band metal

Sreedhar, K and Ganguly, P (1990) Evolution and the concomitant disappearance of high-$T_c$ superconductivity with carrier concentration in the $La_{2-x}Sr_xCuO_{4-\delta}$ system $(0.0\leq x \leq 1.2)$: Crossover from a Mott insulator to a band metal. In: Physical Review B, 41 (1). 371 - 382.

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Abstract

Electrical resistivity, magnetic susceptibility, thermogravimetric analysis, and infrared absorption spectra of the compound $La_{2-x}Sr_xCuO_{4-\delta}$ have been studied for a wide range of $Sr$ concentrations $(0.0\leq x \leq 1.2)$. The samples annealed at an oxygen pressure of 1 bar were stoichiometric $(\delta =0.0)$ in the range 0.0<x<0.33. In this range the compounds are characterized by a decrease in the a parameter, an increase in the c parameter, and a maximum in the c/a ratio (at x =0.33) typical of the formation of low-spin $Cu^{3+}$ ions. In the range 0.15<x<0.33, the compounds show a positive temperature coefficient of resistivity, decrease in the magnitude of the Pauli magnetic susceptibility, infrared oscillator strengths, thermopower S, as well as the Hall coefficient $R_H$. The superconducting transition temperature $T_c$, as well as the percentage Meissner fraction also decrease with x in this range. In particular the stoichiometric x=0.33 composition having a hole concentration of $\sim 0.33$ holes/Cu shows a minimum in the Pauli magnetic susceptibility and disappearance of all infrared absorption bands. The superconductivity also disappears down to 4.2 K at this composition, even though it is more metallic. These results have been attributed to the occurrence of a transition from a highly correlated narrow-band "Mott conductor" to a broadband metal at high carrier concentrations. At still higher $Sr$ concentrations (0.33 <x < 1.0), holes and oxygen vacancies coexist. The decrease in the c/a ratio, increase in resistivity, reappearance of the infrared bands, and the Curietype magnetic susceptibility observed in the range $0.66\leq x\leq 1.2$ indicate the dominating role of oxygen vacancies which induce disorder and localization.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to The American Physical Society.
Department/Centre: Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Depositing User: Ramya Krishna
Date Deposited: 30 Jun 2007
Last Modified: 18 Jan 2012 06:19
URI: http://eprints.iisc.ac.in/id/eprint/11335

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