Department of Applied Physics and Chemistry, The University of Electro-Communications, Chofu, Tokyo 182-8585, Japan.
Phys Rev Lett. 2010 Jul 30;105(5):057003. doi: 10.1103/PhysRevLett.105.057003.
In order to explore the reason why the single-layered cuprates, La(2-x)(Sr/Ba)(x)CuO4 (T(c)≃40 K) and HgBa2CuO(4+δ) (T(c)≃90 K) have such a significant difference in T(c), we study a two-orbital model that incorporates the d(z2) orbital on top of the d(x2-y2) orbital. It is found, with the fluctuation exchange approximation, that the d(z2) orbital contribution to the Fermi surface, which is stronger in the La system, works against d-wave superconductivity, thereby dominating over the effect of the Fermi surface shape. The result resolves the long-standing contradiction between the theoretical results on Hubbard-type models and the experimental material dependence of T(c) in the cuprates.
为了探究单层 cuprates（La(2-x)(Sr/Ba)(x)CuO4，T(c)≃40 K 和 HgBa2CuO(4+δ)，T(c)≃90 K）在 T(c)方面存在显著差异的原因，我们研究了一个包含 d(z2)轨道的双轨道模型在 d(x2-y2)轨道之上。通过 Fluctuation Exchange Approximation（FLEX），我们发现，在 La 体系中更强的费米面的 d(z2)轨道贡献，对 d 波超导性不利，从而主导了费米面形状的影响。这一结果解决了 Hubbard 型模型的理论结果与 cuprates 中 T(c)的实验材料依赖性之间长期存在的矛盾。
