Spin dynamics, electronic nematicity and superconductivity in FeSe1-xSx: A strain tuning study

by Prof. Xingye Lu (鲁兴业) (Beijing Normal University)

Wednesday 1 Apr 2026, 10:30 → 11:30 Asia/Shanghai

Tsung-Dao Lee Institute/N6F-N600 - Lecture Room (Tsung-Dao Lee Institute)

Host: Prof. Baiqing Lv  

Venue: TDLI Meeting Room N600

Tencent Meeting link: https://meeting.tencent.com/dm/TZCenHqi6etA

Meeting ID: 142534509, no password

 

Abstract:

The interplay between the electronic nematic state and superconductivity remains a central puzzle in iron-based superconductors. In this talk, I will present a comprehensive study of the spin dynamics and pairing symmetry in detwinned FeSe1-xSx, enabled by novel uniaxial strain devices and Cryogenic Digital Image Correlation (CDIC). Using inelastic neutron and x-ray scattering, we mapped the twin-free spin excitation spectrum, revealing that highly anisotropic, C2-symmetric stripe spin excitations persist up to ~200 meV. These dispersive high-energy excitations strongly suggest a local-moment, spin-driven origin for the nematicity. Furthermore, tracking these correlations across the nematic quantum critical point (NQCP) reveals that high-energy nematic spin fluctuations pervade the entire phase diagram. Finally, strain-tuning Tc reveals a sign reversal in the quadratic coefficient b across the NQCP, indicating pairing symmetry evolves from s-wave in pure FeSe to a mixed s+d state at higher doping.

 

References:

1.T. Chen, X. Lu, P. Dai et al, Nat. Mater. 18, 709 (2019);

2.X. Lu, et al., Nat. Phys. 18, 806 (2022);

3.R. Liu, X. Lu et al., Phys. Rev. Lett. 132, 016501 (2024);

4.R. Liu, X. Lu et al., Nat. Commun. 16, 5212 (2025);

5.R. Liu, X. Lu et al., Phys. Rev. B 112, 094514 (2025);

6.R. Liu, X. Lu et al., Chin. Phys. Lett. 41, 067401 (2024).

7.Z. Mo, X. Lu et al., Chin. Phys. Lett. 41, 107102 (2024);

 

Biography:

Xingye Lu is a Professor and Doctoral Advisor at the School of Physics and Astronomy, Beijing Normal University. He received his Ph.D. from the Institute of Physics, Chinese Academy of Sciences, in 2014. From November 2014 to December 2016, he conducted postdoctoral research at Rice University in the United States and the Swiss Light Source at the Paul Scherrer Institut (PSI) in Switzerland. He was also selected as a Marie Skłodowska-Curie Actions-funded PSI Fellow (2015–2017). He has been a faculty member at Beijing Normal University since 2017. His primary research focuses on neutron scattering and resonant inelastic X-ray scattering (RIXS) studies of correlated electron materials. His systems of interest include iron-based superconductors, cuprate superconductors, iridates, and low-dimensional quantum magnetic materials. To date, he has published 100 research papers in prominent academic journals such as Science, Nature sister journals, PRX, PRL, and PRB, with over 4,000 total citations.