title: Measurements of the anisotropic in-plane resistivity of underdoped FeAs-based pnictide superconductors.
abstract: 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.
authors: Hefei National Laboratory for Physical Science at Microscale, University of Science and Technology of China, Anhui, People's Republic of China.
authors: J J
authors: JJ
authors: Ying
authors: X F
authors: XF
authors: Wang
authors: T
authors: T
authors: Wu
authors: Z J
authors: ZJ
authors: Xiang
authors: R H
authors: RH
authors: Liu
authors: Y J
authors: YJ
authors: Yan
authors: A F
authors: AF
authors: Wang
authors: M
authors: M
authors: Zhang
authors: G J
authors: GJ
authors: Ye
authors: P
authors: P
authors: Cheng
authors: J P
authors: JP
authors: Hu
authors: X H
authors: XH
authors: Chen