ab-plane optical properties of Ni-doped Bi2Sr2CaCu2O8+delta
The ab-plane optical reflectance of single crystal of Bi2Sr2Ca(Cu1-xNix)(2)O8+d, for x = 0.0215, has been measured from 80 to 40 000 cm(-l) (10 meV-5 eV) and at temperatures between 20 and 300 K. Through Ni substitution, the optical conductivity shows a broad peak at about 400 cm(-1), which grows in intensity and shifts to lower frequency as the temperature is reduced. We suggest that this peculiar low-frequency feature is associated with the significant disorder induced by Ni impurities. Analysis of the conductivity within the framework of the two-component and the one-component pictures indicates that the main effect of Ni substitution is to increase impurity scattering rate. There is no evidence of a rapid drop in the free carrier scattering rate near T-c. An estimate of the low-frequency spectral weight shows that Ni reduces the carrier density in the CuO2 plane: each Ni removes one carrier. Below T-c, a sum-rule evaluation finds the superconducting condensate contains about a fifth of the total doping-induced, or two thirds of the free-carrier oscillator strength in the normal state. The strength of the condensate is horizontally offset from the Uemura line, with a smaller superfluid density than implied by T-c, This decreased superfluid density in the CuO2 plane could be connected with the effect of impurity-induced disorder. (C) 1999 Elsevier Science B.V. All rights reserved.
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Keywords: infrared spectroscopy ; optical reflectivity ; superconductor ; HIGH-TEMPERATURE SUPERCONDUCTORS ; T-C SUPERCONDUCTORS ; INFRARED ; PROPERTIES ; PENETRATION-DEPTH ; NORMAL-STATE ; PHENOMENOLOGY ; YBA2CU3O6.95 ; REFLECTANCE ; BI2SR2CUO6 ; DISORDER
Univ Florida, Dept Phys, Gainesville, FL 32611 USA. Ecole Polytech Fed Lausanne, Inst Phys Appl, PHB Ecublens, CH-1015 Lausanne, Switzerland. Liu, HL, Univ Illinois, Dept Phys, Urbana, IL 61801 USA. email@example.com
ISI Document Delivery No.: 160VW
Record created on 2006-10-03, modified on 2016-08-08