Prof. Xianhui Chen [from USTC]

Title: Superconductivity and Antiferromagnetism in the Novel (Li0.8Fe0.2)OHFeSe Superconductor

Time: 14:00 - 15:00, December 12
Place: Conference Room 201, Building 6, HPSTAR (Shanghai)
Host: Xiaojia Chen

Abstract:
Iron selenide superconductors exhibit a number of unique characteristics that are helpful in understanding the mechanism of superconductivity in high-Tc iron-based superconductors. However, in the case of AxFe2Se2 (A=K, Rb, Cs), the presence of an intergrown antiferromagnetic insulating phase makes the study of the underlying physics problematic. Moreover, FeSe-based systems intercalated with alkali metal ions, NH3 molecules or organic molecules are extremely sensitive to air, which prevents the further investigation of their physical properties. It is therefore desirable to find a stable and easily accessible FeSe-based superconductor to study its physical properties in detail. In this lecture, I will report on a newly synthesized air-stable FeSe-derived superconductor, (Li0.8Fe0.2)OHFeSe, which shows superconducting transition at temperatures up to ~40 K. The crystal structure is unambiguously determined by a combination of X-ray (XRD) and neutron powder diffraction (NPD) and nuclear magnetic resonance (NMR). Specific heat data under various magnetic fields and magnetic susceptibility indicate that there exists antiferromagnetic order coexisting with superconductivity. NMR spectra of 7Li and 77Se reveal that magnetic order locates in (Li0.8Fe0.2)OH layer rather than FeSe layer, which was further confirmed by the unchanged AFM transition temperature with S substitution. Field-dependent NMR spectrum and T2 suggests a ferromagnetic component can be induced by external magnetic field. Finally, the detailed investigation on the relationships between Tc and the crystallographic facts in S-substituted samples suggests a very different dependence of Tc on anion height from Fe2 layer or Ch-Fe2-Ch angle from those in FeAs-based superconductors. Our work opens a path for exploring superconductivity in other related systems, and confirms the appeal of iron selenides as a platform for understanding superconductivity in iron pnictides more broadly.

References:

1. X.F. Lu et al. Nat. Mater. (in press).

2. Y.P. Wu et al., submitted.

3. X.F. Lu et al., Phys. Re. B (accepted).

4. X.F. Lu et al. Phys. Rev. B 89, 020507(R) (2013).

Biography of the Speaker:

Prof. Xianhui Chen works at USTC as a professor in Physics Department and the director of Key Laboratory of Strongly-coupled Quantum Matter Physics, Chinese Academy of Sciences. He was supported by National Science Fund for Distinguished Young Scholars of China in 1998. He was employed as “Chair Professor of Chang Jiang Scholars Program” in 2003. His research focuses on the exploration for new materials and studies on physics of the novel functional materials which show superconductivity, novel magnetism, thermoelectricity, etc. He published more than 300 papers, including 3 in Nature, 3 in Nat. Mater., 2 in Nat. Phys., 2 in Nat. Nanotechnol., 3 in Nat. Commun., 3 in JACS and 27 in PRL. During his research tenure, he has received many prestigious awards, including Chang Jiang Scholars Achievement Award (2009), Qiushi Outstanding Science & Technology Team Achievement Award (2009), Ye Qisun Physics Prize (2008-2009), and the first place of The National Natural Science Award (2013) and so on.