报告题目：Recent progresses on superconductivity in twisted cuprates, Li_xFeSe, and NbSe₂ 

报告时间：2025年3月20日（周四）15:30

报告地点：鼓楼校区唐仲英楼 B501

报  告 人：张定（清华大学）

摘      要：

In this talk, I will present our recent progresses in three superconducting systems: twisted high-T_c cuprates, lithium intercalated FeSe, and 20-30 nm thick NbSe₂. In the first part, I will discuss the Josephson effect in c-axis twisted cuprates ^[1,2]. In junctions with atomically flat interfaces, we observe pronounced Josephson tunneling across the twisted boundary at different twist angles. The latest findings include the observation of ac Josephson effect with both integer and fractional Shapiro steps, as well as the on-demand realization of superconducting diode effect. In the second part, I will present the surprising observation of the coexistence of high temperature superconductivity and ferromagnetism in FeSe after lithium intercalation ^[3]. We identify their coexistence through magneto-transport and magnetic imaging. Interestingly, superconductivity seems to be enhanced under an in-plane magnetic field, suggesting non-trivial interplay between the two usually antagonistic phenomena. Lastly, I will talk about the tunneling spectroscopy on exfoliated NbSe₂ thin flakes under an in-plane magnetic field ^[4]. This layered system with strong spin-orbit couplings is expected to host a novel state of matter—the orbital Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. We demonstrate its existence by reporting the observation of a first-order phase transition between the uniform superconducting state and the orbital FFLO state.

References:

[1] Y. Zhu, et al., Phys. Rev. X 11, 031011 (2021).

[2] H. Wang, et al., Nat. Commun. 14, 5201 (2023).

[3] Y. Hu, et al., arXiv: 2405.10482.

[4] Z. Cao, et al., arXiv: 2409.00373.

报告人简介：

Ding Zhang is an associate professor at Department of Physics, Tsinghua University. He did his PhD study in Max Planck Institute for Solid State Research, Stuttgart, Germany from 2008 to 2014. He then joined Tsinghua University as a post-doc. Since 2016, Ding Zhang started the tenure-track in Tsinghua University and got tenured in 2022. He is an experimentalist in condensed matter physics, with the current interest in low-dimensional/high-temperature superconductivity, and low-temperature/high magnetic field transport techniques.

直播信息：