题   目：Orbital Fulde–Ferrell–Larkin–Ovchinnikov state in an Ising superconductor

报告人：袁凡奇   副教授    哈尔滨工业大学（深圳）

时   间：2023年12月20日（星期三) 上午10：00

地   点：虎溪校区理科楼LE201

Abstract: In superconductors possessing both time and inversion symmetries, the Zeeman effect of an external magnetic field can break the time-reversal symmetry, forming a conventional Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) state characterized by Cooper pairings with finite momentum. In superconductors lacking (local) inversion symmetry, the Zeeman effect may still act as the underlying mechanism of FFLO states by interacting with spin–orbit coupling (SOC). Specifically, the interplay between the Zeeman effect and Rashba SOC can lead to the formation of more accessible Rashba FFLO states that cover broader regions in the phase diagram. However, when the Zeeman effect is suppressed because of spin locking in the presence of Ising-type SOC, the conventional FFLO scenarios are no longer effective. Instead, an unconventional FFLO state is formed by coupling the orbital effect of magnetic fields with SOC, providing an alternative mechanism in superconductors with broken inversion symmetries. Here we report the theoretical mechanism [1] and experimental discovery [2] of such an orbital FFLO state in the multilayer Ising superconductor 2H-NbSe2. Transport measurements show that the translational and rotational symmetries are broken in the orbital FFLO state, providing the hallmark signatures of finite-momentum Cooper pairings. We establish the entire orbital FFLO phase diagram, consisting of a normal metal, a uniform Ising superconducting phase and a six-fold orbital FFLO state. This study highlights an alternative route to achieving finite-momentum superconductivity and provides a universal mechanism to preparing orbital FFLO states in similar materials with (local) broken inversion symmetries.

Refs: 1. arXiv:2305.02006, Phys. Rev. Research in press; 2. Nature 619, 46 (2023)

About the speaker: Noah F. Q. Yuan got his PhD at the Hong Kong University of Science and Technology in 2017. After that he went to Massachusetts Institute of Technology as a Postdoc from 2017 to 2020. He becomes an Associate Professor at the Harbin Institute of Technology (Shenzhen) since 2021. His interests are mainly the theory of unconventional superconductivity, such as finite-momentum superconductivity, two-dimensional superconductivity and topological superconductivity.