Li Yang, Xue Jijun, Hu Shixin, Pang Hua
Institute of Applied Magnetics, Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000, People's Republic of China.
J Phys Condens Matter. 2021 Apr 29;33(20). doi: 10.1088/1361-648X/abeca7.
The origin of the nematic order remains unclear due to the strong coupling between orbital, spin and lattice degrees of freedom in iron-based superconductors. Although the driving force of hole-doped BeFeAsis still controversial, the nematic fluctuation of electron-doped compounds is generally believed to be spin fluctuation driven. Here, we present a comprehensive study of the nematic phase transition in Ba(FeCu)Assingle crystal by using Mössbauer spectroscopy. The electric field gradient and its in-plane asymmetry on Fe nucleus, which are directly determined by the occupation of individualorbital, are sensitive to the local nematicity of Fe ions. The nematic phase transition happens at≈ 73.8 K in the compound while the band splitting between/orbitals begins far aboveand reaches 18.8 meV at 30 K. The temperature evolution of the hyperfine parameters proves the existence of electron-phonon interaction and non-Fermi-liquid behaviour near. However, the spin-lattice relaxation signal is only evident below. These observations show that the role of orbital degrees of freedom is more active in driving nematicity than in Co- or Ni-doped BaFeAscompounds, and can be attributed to enhanced electronic localization caused by Cu doping.
由于铁基超导体中轨道、自旋和晶格自由度之间的强耦合，向列序的起源仍不清楚。尽管空穴掺杂的BeFeAs的驱动力仍存在争议，但电子掺杂化合物的向列涨落通常被认为是由自旋涨落驱动的。在这里，我们通过穆斯堡尔谱对Ba(FeCu)As单晶中的向列相变进行了全面研究。直接由单个轨道占据情况决定的铁原子核上的电场梯度及其面内不对称性，对铁离子的局部向列性很敏感。该化合物中的向列相变发生在约73.8 K，而轨道之间的能带分裂在远高于此温度时就已开始，并在30 K时达到18.8 meV。超精细参数的温度演化证明了电子 - 声子相互作用的存在以及在附近存在非费米液体行为。然而，自旋 - 晶格弛豫信号仅在低于此温度时才明显。这些观察结果表明，在驱动向列性方面，轨道自由度的作用比在Co或Ni掺杂的BaFeAs化合物中更活跃，这可归因于Cu掺杂导致的电子局域化增强。
