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10 June 1996 Doping and charge-carrier density effects in the cuprate superconductors
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The undoped phases of the copper-oxide materials are antiferromagnetic insulators, with a gap of 1.5 - 2 eV. Infrared spectroscopy of these compounds reveals weak absorption, possibly of magnetic origin, in this gap. When the materials are doped, oscillator strength is removed from the charge transfer band. This oscillator strength moves to low frequency, to become midinfrared and free carrier absorption. A systematic study of the electron-doped Nd2- xCexCuO4-y system reveals that the growth of low-frequency oscillator strength with doping concentration x is twice as rapid as in the case of hole-doped materials, such as La2-xSrxCuO4. This behavior is in accord with electronic structure models based on the 3-band Hubbard model and inconsistent with one-band behavior. However, an anomaly occurs for samples which are doped to the critical concentration for superconductivity; these have a greater than expected free-carrier concentration and weaker charge-transfer bands.
© (1996) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
David B. Tanner, Young-Duck Yoon, Axel Zibold, H. L. Liu, Manuel A. Quijada, S. W. Moore, John B. Graybeal, Beomhoan O, John T. Markert, Ronald J. Kelley, Marshall Onellion, and J-H. Cho "Doping and charge-carrier density effects in the cuprate superconductors", Proc. SPIE 2696, Spectroscopic Studies of Superconductors, (10 June 1996);

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