Doping-induced change of optical properties in underdoped cuprate superconductors
We report on the ab-plane optical reflectance measurements of single crystals of Y-doped Bi2Sr2CaCu2O8+delta and Pr-doped YBa2Cu3O7-delta over a wide frequency range from 80 to 40 000 cm(-1) (10 meV-5 eV) and at temperatures between 20 and :300 K. Y and Pr doping both decrease the hole concentration in the CuO2 planes. This has allowed us to investigate the evolution of ab-plane charge dynamics at doping levels ranging from heavily underdoped to nearly optimally doped. Our results of the low-frequency optical conductivity and spectral weight do not show any features associated with the normal-state pseudogap. Instead, one-component analysis for the optical conductivity shows the low-frequency depression in the scattering rate at T > T-c, signalling entry into the pseudogap state. Alternatively, no clear indications of the normal-state pseudogap are detected in the temperature-dependent zero-frequency free-carrier scattering rate by using two-component analysis. In the superconducting state, there is also no convincing evidence of superconducting gap absorption in all spectra. We find that there is a 'universal correlation' between the numbers of carriers and the transition temperature. This correlation holds whether one considers the number of carriers in the superfluid or the total number of carriers.
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Univ Florida, Dept Phys, Gainesville, FL 32611 USA. Florida State Univ, Natl High Magnet Field Lab, Tallahassee, FL 32306 USA. Ecole Polytech Fed Lausanne, Inst Phys Appl, PHB Ecublens, CH-1015 Lausanne, Switzerland. Ecole Polytech Fed Lausanne, Inst Genie Atom, PHB Ecublens, CH-1015 Lausanne, Switzerland. Univ Texas, Dept Phys, Austin, TX 78712 USA. Univ Wisconsin, Dept Phys, Madison, WI 53706 USA. Liu, HL, Univ Illinois, Dept Phys, 1110 W Green St, Urbana, IL 61801 USA.
ISI Document Delivery No.: 164JG
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