Superconducting nickelates are a new family of strongly correlated electron materials with a phase diagram closely resembling that of superconducting cuprates. While analogy with the cuprates is natural, very little is known about the metallic state of the nickelates, making these comparisons difficult. We probe the electronic dispersion of thin-film superconducting five-layer (𝑛=5) and metallic three-layer (𝑛=3) nickelates by measuring the Seebeck coefficient 𝑆. We find a temperature-independent and negative 𝑆/𝑇 for both 𝑛=5 and 𝑛=3 nickelates. These results are in stark contrast to the strongly temperature-dependent 𝑆/𝑇 measured at similar electron filling in the cuprate La1.36⁢Nd0.4⁢Sr0.24⁢CuO4. The electronic structure calculated from density-functional theory can reproduce the temperature dependence, sign, and amplitude of 𝑆/𝑇 in the nickelates using Boltzmann transport theory. This demonstrates that the electronic structure obtained from first-principles calculations provides a reliable description of the fermiology of superconducting nickelates and suggests that, despite indications of strong electronic correlations, there are well-defined quasiparticles in the metallic state. Finally, we explain the differences in the Seebeck coefficient between nickelates and cuprates as originating in strong dissimilarities in impurity concentrations. Our study demonstrates that the high elastic scattering limit of the Seebeck coefficient reflects only the underlying band structure of a metal, analogous to the high magnetic field limit of the Hall coefficient. This opens a new avenue for Seebeck measurements to probe the electronic band structures of relatively disordered quantum materials.

中文翻译：

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由无序极限中的 Seebeck 系数探测的超导镍酸盐的电子能带结构


超导镍酸盐是一类新的强相关电子材料，其相图与超导铜酸盐的相图非常相似。虽然与铜酸盐的类比是很自然的，但对镍酸盐的金属状态知之甚少，这使得这些比较变得困难。我们通过测量塞贝克系数 S 来探测薄膜超导五层 （n=5） 和金属三层 （n=3） 镍酸盐的电子色散。我们发现 n=5 和 n=3 镍酸盐的 S/T 与温度无关且为负。这些结果与在铜酸盐 La1.36Nd0.4Sr0.24CuO4 中的相似电子填充下测得的强烈温度依赖性 S/T 形成鲜明对比。根据密度泛函理论计算的电子结构可以使用玻尔兹曼输运理论再现镍酸盐中 S/T 的温度依赖性、符号和振幅。这表明，从第一性原理计算中获得的电子结构为超导镍酸盐的费米学提供了可靠的描述，并表明，尽管有迹象表明存在很强的电子相关性，但在金属状态下存在定义明确的准粒子。最后，我们解释了镍酸盐和铜酸盐之间塞贝克系数的差异，这些差异源于杂质浓度的强烈差异。我们的研究表明，塞贝克系数的高弹性散射极限仅反映了金属的底层能带结构，类似于霍尔系数的高磁场极限。 这为 Seebeck 测量开辟了一条新的途径，以探测相对无序量子材料的电子能带结构。