Balduini Federico, Molinari Alan, Rocchino Lorenzo, Hasse Vicky, Felser Claudia, Sousa Marilyne, Zota Cezar, Schmid Heinz, Grushin Adolfo G, Gotsmann Bernd
IBM Research Europe - Zurich, Säumerstrasse, Ruschlikon, Switzerland.
Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Strasse 40, Dresden, Germany.
Nat Commun. 2024 Aug 2;15(1):6526. doi: 10.1038/s41467-024-50451-5.
The chiral anomaly - a hallmark of chiral spin-1/2 Weyl fermions - is an imbalance between left- and right-moving particles that underpins phenomena such as particle decay and negative longitudinal magnetoresistance in Weyl semimetals. The discovery that chiral crystals can host higher-spin generalizations of Weyl quasiparticles without high-energy counterparts, known as multifold fermions, raises the fundamental question of whether the chiral anomaly is a more general phenomenon. Answering this question requires materials with chiral quasiparticles within a sizable energy window around the Fermi level that are unaffected by extrinsic effects such as current jetting. Here, we report the chiral anomaly of multifold fermions in CoSi, which features multifold bands within ~0.85 eV of the Fermi level. By excluding current jetting through the squeezing test, we measure an intrinsic, longitudinal negative magnetoresistance. We develop a semiclassical theory to show that the negative magnetoresistance originates in the chiral anomaly, despite a sizable and detrimental orbital magnetic moment contribution. A concomitant non-linear Hall effect supports the multifold-fermion origin of the magnetotransport. Our work confirms the chiral anomaly of higher-spin generalizations of Weyl fermions, currently inaccessible outside solid-state platforms.
手征反常——手征自旋1/2外尔费米子的一个标志——是左右移动粒子之间的不平衡，它是诸如外尔半金属中的粒子衰变和负纵向磁阻等现象的基础。手征晶体可以容纳没有高能对应物的外尔准粒子的高自旋推广，即所谓的多重费米子，这一发现提出了一个基本问题，即手征反常是否是一种更普遍的现象。要回答这个问题，需要在费米能级周围相当大的能量窗口内具有手征准粒子且不受诸如电流喷射等外在效应影响的材料。在此，我们报道了CoSi中多重费米子的手征反常，其在费米能级约0.85电子伏特范围内具有多重能带。通过挤压测试排除电流喷射，我们测量到了本征纵向负磁阻。我们发展了一种半经典理论来表明，尽管存在相当大且有害的轨道磁矩贡献，但负磁阻起源于手征反常。伴随的非线性霍尔效应支持了磁输运的多重费米子起源。我们的工作证实了外尔费米子高自旋推广的手征反常，目前在固态平台之外无法实现。
