Intrinsic negative magnetoresistance from the chiral anomaly of multifold fermions

TL;DR

This paper demonstrates the intrinsic negative magnetoresistance caused by the chiral anomaly in multifold fermions within CoSi, confirming higher-spin Weyl fermion behavior and expanding understanding of topological quantum phenomena.

Contribution

It provides experimental evidence of the chiral anomaly in multifold fermions and develops a semiclassical theory explaining the negative magnetoresistance despite orbital magnetic effects.

Findings

Intrinsic negative longitudinal magnetoresistance observed in CoSi

Chiral anomaly confirmed in higher-spin multifold fermions

Nonlinear Hall effect supports multifold fermion origin

Abstract

The chiral anomaly, a hallmark of chiral spin-1/2 Weyl fermions, is an imbalance between left- and right-moving particles that underpins both high and low energy phenomena, including 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 trivial extrinsic effects such as current jetting. Here we report the chiral anomaly of multifold fermions in CoSi, which features multifold bands within about 0.85 eV around the Fermi level. By excluding current jetting through the squeezing test, we measure an intrinsic, longitudinal negative magnetoresistance. We develop the semiclassical theory of magnetotransport of multifold fermions that shows that the negative magnetoresistance originates in their chiral anomaly, despite a sizable and detrimental orbital magnetic moment contribution, previously unaccounted for. A concomitant nonlinear Hall effect supports the multifold-fermion origin of magnetotransport. Our work confirms the chiral anomaly of higher-spin generalizations of Weyl fermions, currently inaccessible outside the solid-state.