Isotope Effects in the Cuprates

概要

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It is shown that isotope effects observed in the high-T_c cuprates are compatible with unconventional d-wave superconductivity due to a nonphonon mechanism. Because of the high-T_c, a considerable amount of quasi-particle damping exists at T_c, thereby giving rise to pair-breaking effect. The electron-phonon interaction is assumed to contribute only to the pair-breaking effect. The oxygen isotope effects in YBa_2Cu_3O_7 and Bi_2Sr_2CaCu_2O_8 are consistently explained by a moderate amount of the phonon contribution to the pair breaking. Using the parameters determined for these compounds, we obtain the isotope exponents comparable with the experimental results for the oxygen and copper isotope exchange in La_<1.85>Sr_<0.15>CuO_4. The increase of isotope exponent α with decreasing T_c by impurity-substitution to YBa_2Cu_3O_7 is also explained qualitatively. The oxygen isotope effect on the antiferromagnetic transition temperature in La_2CuO_4 is shown to be related with the tilting of CuO_6 octahedra and have nothing to do with the isotope effect on T_c.
社団法人日本物理学会の論文
1995-12-15