Pair Breaking and Isotope Effect in d-Wave Superconductivity

抄録

The question as to whether d-wave superconductivity is compatible with the small but nonvanishing isotope effects observed in high-T_c copper oxides is addressed. On the assumption that a nonphonon mechanism, most likely via antiferromagnetic spin fluctuations, is dominant in both normal and superconducting states, only a few percent contribution to the quasi-particle damping rate from the electron-phonon interaction gives rise to a correct order of the observed isotope effects. The heavier the isotope mass, the lower T_c becomes, since the damping increases via lowering in frequency of the phonon spectrum. The pairing and pair-breaking effects for YBa₂Cu₃O₇ and La_1.85Sr_0.15CuO₄ are examined, and the impurity-concentration dependence of T_c is briefly discussed.