LiFe1-xCoxAs体系中由费米面嵌套引起的自旋涨落及非费米液体行为
（Spin-Fluctuation-Induced Non-Fermi-Liquid Behavior with Suppressed Superconductivity in LiFe1-xCoxAs）
Y. M. Dai, H. Miao, L. Y. Xing, X. C. Wang, P. S. Wang, H. Xiao, T. Qian, P. Richard, X. G. Qiu, W. Yu, C. Q. Jin, Z. Wang, P. D. Johnson, C. C. Homes and H. Ding
Physi. Rev. X, 5, 031035 (2015)
我们通过输运、红外光谱、角分辨光电子能谱以及核磁共振实验手段对一系列Co掺杂的LiFe1?xCoxAs铁基超导体进行了研究。随着Co掺杂含量的增加，超导转变温度呈现出线性下降的关系，同时观察到了费米液体-非费米液体-费米液体（FL-NFL-FL）的过渡行为。与这种过渡行为相对应的是，低能自旋涨落和费米面的嵌套都是先增强后减弱，表明这种非费米液体行为是由于低能自旋涨落诱导的，而这种自旋涨落则很可能是由费米面的嵌套进行调制的。我们LiFe1?xCoxAs的研究结果揭示了一个独特的相图，尽管非费米液体行为出现在了超导相的边界处但是非费米液体行为和超导特性是通过不同的机制来进行调控的。
We study a series of LiFe1-xCoxAs compounds with different Co concentrations by transport, optical spectroscopy, angle-resolved photoemission spectroscopy, and nuclear magnetic resonance. We observe a Fermi-liquid to non-Fermi-liquid to Fermi-liquid (FL-NFL-FL) crossover alongside a monotonic suppression of the superconductivity with increasing Co content. In parallel to the FL-NFL-FL crossover, we find that both the low-energy spin fluctuations and Fermi surface nesting are enhanced and then diminished, strongly suggesting that the NFL behavior in LiFe1-xCoxAs is induced by low-energy spin fluctuations that are very likely tuned by Fermi surface nesting. Our study reveals a unique phase diagram of LiFe1-xCoxAs where the region of NFL is moved to the boundary of the superconducting phase, implying that they are probably governed by different mechanisms.
