回到Na_xCoO_2：光谱和热电性质
Getting back to Na_xCoO_2: spectral and thermoelectric properties
摘要：
钴酸钠Na_xCoO_2作为一种具有三角形亚晶格的强关联层状材料，在凝聚态研究中仍然是一个具有挑战性的问题。晶格，电荷，自旋和轨道自由度之间的有趣的相互作用，导致一个复杂的相图由名义莫特（x=0）制度和带绝缘（x=1）相。利用电荷自洽密度泛函理论（DFT）和动力学平均场论（DMFT）方法，在赝势框架下，结合连续时间量子Monte-Carlo方法，研究了单粒子谱函数A（k，ω）和热电势S（T）.计算结果可以解释在较低掺杂下A（k，ω）中e_g'口袋的抑制，与光电发射实验一致。增强的热电势内验证本精心设计的多轨道方法来处理相关的材料。此外，基于简化的紧束缚方法研究了两粒子动态自旋极化率χ s（ω，q），但在DMFT线性响应中考虑了顶点贡献.除了在高掺杂时发现顺磁子分支外，在χ_s（ω，q）中还发现了一个接近x=0.67的高能反铁磁模，这可能与CoO_2亚晶格上扩展的跳跃项有关。
英文摘要：
Sodium cobaltate Na_xCoO_2 as dopable strongly correlated layered material with a triangular sublattice still poses a challenging problem in condensed matter. The intriguing interplay between lattice, charge, spin and orbital degrees of freedom leads to a complex phase diagram bounded by a nominal Mott (x=0) regime and a band-insulating (x=1) phase. By means of the charge self-consistent density functional theory (DFT) plus dynamical mean-field theory (DMFT) scheme, built on a pseudopotential framework combined with a continuous-time quantum Monte-Carlo solver, we here study the one-particle spectral function A(k,ω) as well as the thermopower S(T). The computations may account for the suppression of the e_g' pockets in A(k,ω) at lower doping in line with photoemission experiments. Enhancement of the thermopower is verified within the present elaborate multi-orbital method to treat correlated materials. In addition, the two-particle dynamic spin susceptibility χ_s(ω,q) is investigated based on a simplified tight-binding approach, yet by including vertex contributions in the DMFT linear response. Besides the identification of paramagnon branches at higher doping, a prominent high-energy antiferromagnetic mode close to x=0.67 is therewith identified in χ_s(ω,q), which can be linked to extended hopping terms on the CoO_2 sublattice.
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