The topological properties of fermions arise from their low-energy Dirac-like band dispersion and associated chirality. Initially confined to points, extensions of the Dirac dispersion to lines, and even loops, have now been uncovered, and semimetals hosting such features have been identified. However, experimental evidence for the enhanced correlation effects predicted to occur in these topological semimetals has been lacking. Here, we report a quantum oscillation study of the nodal-loop semimetal ZrSiS in high magnetic fields that reveals significant enhancement in the effective mass of the quasiparticles residing near the nodal loop. Above a threshold field, magnetic breakdown occurs across gaps in the loop structure with orbits that enclose different windings around its vertices, each winding accompanied by an additional π Berry phase. The amplitudes of these breakdown orbits exhibit an anomalous temperature dependence. These findings demonstrate the emergence of novel, correlation-driven physics in ZrSiS associated with the Dirac-like quasiparticles.

费米子的拓扑特性是由其低能量的狄拉克样带分散和相关的手性引起的。最初仅限于点，现在已经发现Dirac色散扩展到线，甚至是环，并且已经识别出具有这种特征的半金属。然而，缺乏关于在这些拓扑半金属中预计会发生的增强相关效应的实验证据。在这里，我们报告了在高磁场中节点环半金属ZrSiS的量子振荡研究，该结果表明驻留在节点环附近的准粒子的有效质量显着提高。在阈值场以上，磁击穿会发生在环形结构的间隙中，其轨道围绕其顶点围绕不同的绕组，每个绕组都伴有一个额外的πBerry相。这些击穿轨道的振幅表现出反常的温度依赖性。这些发现证明了ZrSiS中与狄拉克型准粒子有关的新颖的，相关驱动的物理学的出现。