近日， 东南大学的施智祥&孙悦及其研究团队取得一项新进展。经过不懈努力，他们揭示FeSe基超导体中伴随两个超导穹顶的体态和表面狄拉克态。相关研究成果已于2024年11月21日在国际知名学术期刊《美国科学院院刊》上发表。

在本研究中，研究人员通过电磁传输测量建立了完整的相图，并成功在FeSe_1-xS_x（0 ≤ x ≤ 0.25）和FeSe_1-xTe_x（0 ≤ x ≤ 1）超导体中观察到了两个超导穹顶。第一个超导穹顶（SC1）的正常态电阻率呈现出奇异金属态，其幂指数约等于1（ρ(T) ∝ Tⁿ，其中n ~ 1），而第二个超导穹顶（SC2）的幂指数则小于1。

在SC1上观察到了一个与奇异金属行为完全同步的体狄拉克态，表明它们之间存在密切关系。而在SC2上则观察到了一个拓扑表面狄拉克态，该态在接近纯向列量子临界点时发生了符号变化。狄拉克态的演变表明，两个超导穹顶的出现可能源于费米面的重构。研究结果突出了两个超导穹顶中不同的狄拉克态和正常态电阻率，为FeSe基超导体中存在两种不同的配对机制提供了有力证据。

据悉，近期对FeSe基超导体的研究表明存在两个超导穹顶，并暗示可能存在不同的配对机制。两个超导穹顶通常在非常规超导体中被发现，并展现出独特的正常态和电子结构。

附：英文原文

Title: Bulk and surface Dirac states accompanied by two superconducting domes in FeSe-based superconductors

Author: Hou, Qiang, Wei, Wei, Zhou, Xin, Liu, Wenhui, Wang, Ke, Xing, Xiangzhuo, Zhang, Yufeng, Zhou, Nan, Pan, Yongqiang, Sun, Yue, Shi, Zhixiang

Issue&Volume: 2024-11-21

Abstract: Recent investigations of FeSe-based superconductors have revealed the presence of two superconducting domes and suggest possible distinct pairing mechanisms. Two superconducting domes are commonly found in unconventional superconductors and exhibit unique normal states and electronic structures. In this study, we conducted electromagnetic transport measurements to establish a complete phase diagram, successfully observing the two superconducting domes in FeSe_1-xS_x (0 ≤ x ≤ 0.25) and FeSe_1-xTe_x (0 ≤ x ≤ 1) superconductors. The normal state resistivity on SC1 shows the strange metal state, with a power exponent approximately equal to 1 (ρ(T) ∝ Tⁿ with n ~ 1), whereas the exponent on SC2 is less than 1. A bulk Dirac state observed on SC1, completely synchronized with the strange metal behavior, indicating a close relationship between them. While a topological surface Dirac state is witnessed on SC2 and undergoes a sign change near the pure nematic quantum critical point. The evolution of the Dirac states indicates that the appearance of the two superconducting domes may originate from the Fermi surface reconstruction. Our findings highlight distinct Dirac states and normal state resistivity across the two superconducting domes, providing convincing evidence for the existence of the two different pairing mechanisms in FeSe-based superconductors.

DOI: 10.1073/pnas.2409756121

Source: https://www.pnas.org/doi/abs/10.1073/pnas.2409756121