On the Magnetic Excitation Spectra of High-T_c Cu Oxides at Energies Up to the Region Far above the Resonance Energy(Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties)

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The magnetic excitation spectra χ″(q, ω) of YBa_2Cu_3O_y and La214 systems have been studied. For a sample of the latter system, La_<1.88>Sr_<0.12>CuO_4, χ″(q, ω) has been measured up to ∿30meV. Existing data of these two kinds of system have been analyzed at energies up to the values far above ω_r, around which χ″(q, ω) exhibits the commensurate peak. In the analyses, we have used the phenomenological expression of the generalized magnetic susceptibility χ(q, ω)=χ_0(q, ω)/{1+J(q)χ_0(q, ω)}, where χ_0(q, ω) is the susceptibility of the electrons without the exchange coupling J(q) among them. In the energy region up to ∿ω_r, it has been reported by the authors' group that the expression can explain the characteristics of the q-and ω-dependences of the spectra of YBa_2Cu_3O_y (YBCO or YBCO_y). Here, it is also pointed out that the expression can reproduce the rotation of the four incommensurate peaks of χ″(q, ω) within the a^*-b^* plane about (π/a, π/a) [or so-called (π, π)] point by 45, which occurs as ω goes to the region far above ω_r from an energy below ω_r. This indicates that for the rotation, "stripe" correlation is not required. For La214, the observed and calculated results of χ″(q, ω) are comparatively discussed up to the ω region far above ω_r. These results indicate that for YBCO, the characteristics of χ″(q, ω) can be explained qualitatively by the above expression throughout the ω region studied, while for the La214 system, effects of "stripes" on χ″(q, ω), which cannot be explained by the expression, are more significant in the low-energy region of ω(<ω_r) than at high energies.
社団法人日本物理学会の論文
2005-01-15

On the Magnetic Excitation Spectra of High-T_c Cu Oxides at Energies Up to the Region Far above the Resonance Energy(Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties)

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