Hefei National Laboratory for Physical Science at Microscale, University of Science and Technology of China, Anhui, People's Republic of China.
Phys Rev Lett. 2011 Aug 5;107(6):067001. doi: 10.1103/PhysRevLett.107.067001. Epub 2011 Aug 2.
We systematically investigated the in-plane resistivity anisotropy of electron-underdoped EuFe(2-x)Co(x)As(2) and BaFe(2-x)Co(x)As(2) and hole-underdoped Ba(1-x)K(x)Fe(2)As(2). Large in-plane resistivity anisotropy was found in the former samples, while tiny in-plane resistivity anisotropy was detected in the latter ones. When it is detected, the anisotropy starts above the structural transition temperature and increases smoothly through it. As the temperature is lowered further, the anisotropy takes a dramatic enhancement through the magnetic transition temperature. We found that the anisotropy is universally tied to the presence of T-linear behavior of resistivity. Our results demonstrate that the nematic state is caused by electronic degrees of freedom, and the microscopic orbital involvement in the magnetically ordered state must be fundamentally different between the hole- and electron-doped materials.
我们系统地研究了电子欠掺杂 EuFe(2-x)Co(x)As(2) 和 BaFe(2-x)Co(x)As(2)以及空穴欠掺杂 Ba(1-x)K(x)Fe(2)As(2) 的面内电阻率各向异性。在前一种样品中发现了大的面内电阻率各向异性，而在后一种样品中则检测到了微小的面内电阻率各向异性。当检测到各向异性时，它从结构相变温度以上开始平滑地增加。随着温度进一步降低，各向异性通过磁转变温度急剧增强。我们发现各向异性与电阻率的 T-线性行为普遍相关。我们的结果表明，向列态是由电子自由度引起的，并且在空穴和电子掺杂材料中，磁有序态下的微观轨道参与必须从根本上不同。
