Bauer Thomas, Falter Claus
Institut für Festkörpertheorie, Westfälische Wilhelms-Universität, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany.
J Phys Condens Matter. 2009 Sep 30;21(39):395701. doi: 10.1088/0953-8984/21/39/395701. Epub 2009 Sep 8.
The phonon dynamics of the low-temperature superconductor Sr(2)RuO(4) is calculated quantitatively in linear response theory and compared with that of the structurally isomorphic high-temperature superconductor La(2)CuO(4). Our calculation corrects for a typical deficiency of local density approximation-based calculations, which always predict too large an electronic k(z)-dispersion insufficient for describing the c-axis response of real materials. With a more realistic computation of the electronic band structure, the frequency and wavevector dependent irreducible polarization part of the density response function is determined and used for adiabatic and nonadiabatic phonon calculations. Our analysis for Sr(2)RuO(4) reveals important differences from the lattice dynamics of p- and n-doped cuprates. Consistently with experimental evidence from inelastic neutron scattering, the anomalous doping related softening of the strongly coupling high-frequency oxygen bond-stretching modes which is generic for the cuprate superconductors is largely suppressed or completely absent, respectively, depending on the actual value of the on-site Coulomb repulsion of the Ru 4d orbitals. Also the presence of a characteristic Λ(1) mode in La(2)CuO(4) with a very steep dispersion coupled strongly to the electrons is not found for Sr(2)RuO(4). Moreover, we evaluate the possibility of a phonon-plasmon scenario for Sr(2)RuO(4), which has been shown recently to be realistic for La(2)CuO(4). In contrast to the case for La(2)CuO(4), in Sr(2)RuO(4) the plasmons that are very low lying are overdamped along the c-axis.
在低温超导体Sr₂RuO₄的线性响应理论中对声子动力学进行了定量计算，并与结构同构的高温超导体La₂CuO₄的声子动力学进行了比较。我们的计算纠正了基于局域密度近似计算的一个典型缺陷，这种计算总是预测电子k(z)色散过大，不足以描述真实材料的c轴响应。通过对电子能带结构进行更实际的计算，确定了密度响应函数的频率和波矢相关的不可约极化部分，并将其用于绝热和非绝热声子计算。我们对Sr₂RuO₄的分析揭示了它与p型和n型掺杂铜酸盐晶格动力学的重要差异。与非弹性中子散射的实验证据一致，取决于Ru 4d轨道的在位库仑排斥的实际值，铜酸盐超导体中普遍存在的与掺杂相关的强耦合高频氧键拉伸模式的反常软化分别在很大程度上受到抑制或完全不存在。对于Sr₂RuO₄，也没有发现La₂CuO₄中存在的具有非常陡峭色散且与电子强烈耦合的特征Λ(1)模式。此外，我们评估了Sr₂RuO₄的声子 - 等离子体情景的可能性，最近已证明这种情景对La₂CuO₄是现实的。与La₂CuO₄的情况相反，在Sr₂RuO₄中，非常低能的等离子体沿c轴是过阻尼的。
