First-principles study of the magnetic state of Iron-Based Superconductivity in LiFe_1−xCo_xAs

Jia-Xin Yin¹, Songtian S. Zhang¹, Guangyang Dai², Yuanyuan Zhao³, Andreas Kreisel⁴, Gennevieve Macam^5*, Xianxin Wu^2,14, 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 Hasan^2,13

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, email:mmgennevieve@gmail.com

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 LiFe_1-xCo_xAs, 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