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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Keywords: T-C SUPERCONDUCTORS ; HIGH-TEMPERATURE SUPERCONDUCTORS ; NORMAL-STATE ; PENETRATION-DEPTH ; THIN-FILMS ; ELECTRONIC-STRUCTURE ; INPLANE ; RESISTIVITY ; NEUTRON-SCATTERING ; PHASE-SEPARATION ; CHARGE DYNAMICS
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
Record created on 2006-10-03, modified on 2016-08-08