Local Hole Distribution in the CuO_2 Plane of High-T_c Cu-Oxides Studied by Cu and Oxygen NQR/NMR

概要

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The hole numbers at Cu and oxygen sites in the CuO_2 plane in a wide variety of high-T_c materials have been extracted from the measured nuclear quadrupole frequency, ν_Q. The hole number in the Cu-3d_<x^2-y^2> orbit, n_<x^2-y^2>, is found to be more than 0.85 in La_<2-x>Sr_xCuO_4 (x=0.075〜0.24), while decreases to 0.74 in Tl_2Ba_2Ca_2Cu_3O_<10>. Thus estimated n_<x^2-y^2> is supported by the result that the orbital Knight shift along the c-axis, K^c_<orb>, increases in proportion to n_<x^2-y^2>. In contrast to the decrease of n_<x^2-y^2>, the hole number in the O-2p_σ orbit, n_<pσ>, increases in going from the La- to the Tl-systems. It has been found that T_c is determined by two parameters about holes, i.e., n_<x^2-y^2>+2n_<pσ> and n_<x^2-y^2>/2n_<pσ>. The former tells the microscopic "doping level" of the CuO_2 plane, while a smaller n_<x^2-y^2>/2n_<pσ> results in a weaker antiferromagnetic spin fluctuations of low energy. It has been found that not only a proper n_<x^2-y^2>+2n_<pσ> but also a sufficiently small n_<x^2-y^2>/2n_<pσ>(≃1) are needed to obtain a high value of T_c.
社団法人日本物理学会の論文
1995-07-15