近日，美国耶鲁大学的Eduardo H. da Silva Neto及其研究团队取得一项新进展。经过不懈努力，他们揭示了FeSe_1-xS_x向列量子临界点附近的高各向异性超导隙。相关研究成果已于2024年11月13日在国际知名学术期刊《自然—物理学》上发表。

本研究测定了接近量子临界点的FeSe_0.81S_0.19，在布里渊区中心附近的超导能隙的动量结构，发现其具有各向异性且近乎节点状。能隙最小值出现在相对于Fe-Fe方向旋转了45°的方向上，这与其他四方晶系铁基超导体中，由自旋介导配对所产生的通常各向同性能隙不同。

相反，研究人员发现该能隙结构，与由向列涨落介导的超导电性的理论预测相符，这表明在FeSe_1-xS_x的相图中配对机制发生了变化。

据悉，在一些非常规超导体家族中存在着向列相，在这种相中，固体中的电子会自发地破坏旋转对称性，同时保持平移对称性。理论上，由向列涨落介导的超导电性已经得到了充分的论证，但实验上尚未明确证实。

一个主要挑战是，向列性与磁性和电荷序等其他自由度往往相互交织。FeSe_1-xS_x超导体家族为研究这一概念提供了机会，因为它具有一个孤立的向列相，该相可以通过硫替代在量子临界点处被抑制，而在该量子临界点处向列涨落最为强烈。

附：英文原文

Title: Highly anisotropic superconducting gap near the nematic quantum critical point of FeSe_1-xS_x

Author: Nag, Pranab Kumar, Scott, Kirsty, de Carvalho, Vanuildo S., Byland, Journey K., Yang, Xinze, Walker, Morgan, Greenberg, Aaron G., Klavins, Peter, Miranda, Eduardo, Gozar, Adrian, Taufour, Valentin, Fernandes, Rafael M., da Silva Neto, Eduardo H.

Issue&Volume: 2024-11-13

Abstract: Nematic phases, in which electrons in a solid spontaneously break rotational symmetry while preserving translational symmetry, exist in several families of unconventional superconductors. Superconductivity mediated by nematic fluctuations is well established theoretically, but it has yet to be unambiguously identified experimentally. One major challenge is that nematicity is often intertwined with other degrees of freedom, such as magnetism and charge order. The FeSe_1-xS_x family of superconductors provides an opportunity to explore this concept, as it features an isolated nematic phase that can be suppressed by sulfur substitution at a quantum critical point where the nematic fluctuations are the largest. Here we determine the momentum structure of the superconducting gap near the centre of the Brillouin zone in FeSe_0.81S_0.19—close to the quantum critical point—and find that it is anisotropic and nearly nodal. The gap minima occur in a direction that is rotated 45° with respect to the Fe–Fe direction, unlike the usual isotropic gaps due to spin-mediated pairing in other tetragonal Fe-based superconductors. Instead, we find that the gap structure agrees with theoretical predictions for superconductivity mediated by nematic fluctuations, indicating a change in the pairing mechanism across the phase diagram of FeSe_1-xS_x.

DOI: 10.1038/s41567-024-02683-x

Source: https://www.nature.com/articles/s41567-024-02683-x