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10 June 1996 Magnetic Raman scattering in cuprate antiferromagnetic insulators and doped superconductors
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We present results of low-temperature two-magnon resonance Raman excitation profile measurements for single layer Sr2CuO2Cl2 and bilayer YBa2Cu3O6.1 antiferromagnets over the excitation region from 1.65 to 3.05 eV. These data reveal composite structure of the two-magnon line shape with peaks at approximately 2.8 and approximately 4 J and strong nonmonotic dependence of the scattering intensity on excitation energy. We analyze these data using the triple resonance theory of Chubukov and Frenkel [Phys. Rev. Lett., 74, 3057 (1995)] and deduce information about magnetic interaction and electronic band parameters in these antiferromagnetic insulators. We study the evolution of the magnetic excitation with hole doping in CuO2 planes of YBa2Cu3O6+(delta ) and YBa2Cu408 single crystals. We find that the spin excitations at energy approximately equal to 3 J, similar to the two-magnon excitations in the insulators, persist with doping and are evidence that antiferromagnetic fluctuations with spatial extent of at least three lattice constants are not overdamped in the underdoped superconductors. The two-magnon resonance study shows the existence of the charge-transfer gap in the underdoped cuprates and provides information about evolution of electronic band parameters with doping. We report a magnetic Raman scattering study of YBa2Cu408 superconductor with substitution of Zn on the Cu(2) site. Two and five-tenths percent of substitution softens the two-magnon excitation frequency from 2900 to 2300 cm-1. This softening is attributed to the absence of a defined spin projection on at least one of eight Cu(2)/Zn sites involved in the superexchange, and it signifies that the Zn- introduced magnetic distortion extends to at lest four Cu sites neighboring a Zn site. The electronic Raman continuum intensity weakens with increasing Zn doping, manifesting a relationship between the Raman continuum and the spin fluctuations.
© (1996) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Girsh Blumberg, Peter M. Abbamonte, and Miles V. Klein "Magnetic Raman scattering in cuprate antiferromagnetic insulators and doped superconductors", Proc. SPIE 2696, Spectroscopic Studies of Superconductors, (10 June 1996);

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