First-principles study of the magnetic state of Iron-Based Superconductivity in LiFe1−xCoxAs
Jia-Xin Yin1, Songtian S. Zhang1, Guangyang Dai2, Yuanyuan Zhao3, Andreas Kreisel4, Gennevieve Macam5*, Xianxin Wu2,14, Hu Miao6, Zhi-Quan Huang5, Johannes H. J. Martiny7, Brian M. Andersen8, Nana Shumiya1, Daniel Multer1, Maksim Litskevich1, Zijia Cheng1, Xian Yang1, Tyler A. Cochran1, Guoqing Chang1, Ilya Belopolski1, Lingyi Xing2, Xiancheng Wang2, Yi Gao9, Feng-Chuan Chuang5, Hsin Lin10, Ziqiang Wang11, Changqing Jin3, Yunkyu Bang12, M. Zahid Hasan2,13
1Department of Physics, Princeton University, New Jersey, USA
2Institute of Physics, Chinese Academy of Sciences, Beijing, China
3School of Physics and Optoelectronic Engineering, Nanjing University of Information Science and Technology, Nanjing, China
4Institut für Theoretische Physik, Universität Leipzig, Leipzig, Germany
5Department of Physics, National Sun Yat-Sen University, Kaohsung, Taiwan
6Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, New York, USA
7Department of Physics, Technical University of Denmark, Lyngby, Denmark
8Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
9School of Physics and Technology, Nanjing Normal University, Nanjing, China
10Institute of Physics, Academia Sinica, Taipei, Taiwan
11Department of Physics, Boston College, Massachusetts, USA
12Asia Pacific Center for Theoretical Physics and Department of Physics, POSTECH, Gyeongbuk, Korea
13Materials Sciences Division, Lawrence Berkeley National Laboratory, California, USA
144Institut für Theoretische Physik und Astrophysik, Julius-Maximilians-Universität Würzburg, Würzburg, Germany
* Presenter:Gennevieve Macam,
High-Tc superconductors are highly sought for its promising pivotal technological applications, but its intricate physics has opened many questions that remain unsolved. Superconducting behavior can be understood by chemical substitution, a method that will disturb the system which can then break the Cooper pairing and suppress superconductivity but at the expense of generating other competing orders. Such drawback is not observed in LiFe1-xCoxAs, making it a unique case which provides more control in investigating the physics. Intriguingly, experimental observations show that Co dopants are nonmagnetic. These findings violate Anderson’s theorem in which nonmagnetic impurities have little to zero effect on superconductivity. Here, using systematic first-principles calculations we validate the nonmagnetic nature of Co. Without substitution, LiFeAs prefers the striped antiferromagnetic configuration. After 50 % Co substitution, ferromagnetic states become suppressed whereas striped antiferromagnetic states become degenerate with nonmagnetic states. Examining the local magnetic moments, Co doping substantially reduced the magnetic moments of Fe atoms. These results confirm the nonmagnetic nature of Co dopants in LiFeAs. Finally, from the density of states, we find Co has a weak scattering potential of -0.43 eV. With support from T-matrix theory, we conclude that the Born-limit nonmagnetic scattering of Co atoms is the culprit in destroying the superconductivity in LiFeAs.

Keywords: iron-based superconductor, first-principles, impurities