Abstract
Materials where the electronic bands have unusual topologies allow for the realisation of novel physics and have a wide range of potential applications. When two electronic bands with linear dispersions intersect at a point, the excitations could be described as Weyl fermions, which are massless particles with a particular chirality. Here we report evidence for the presence of Weyl fermions in the ferromagnetic state of the low-carrier density, strongly correlated Kondo lattice system CeSb, from electronic structure calculations and angle-dependent magnetoresistance measurements. When the applied magnetic field is parallel to the electric current, a pronounced negative magnetoresistance is observed within the ferromagnetic state, which is destroyed upon slightly rotating the field away. These results give evidence for CeSb belonging to a new class of Kondo lattice materials with Weyl fermions in the ferromagnetic state.
Highlights
Topological materials have been found to demonstrate a variety of novel phenomena
When either time reversal or inversion symmetry is broken, such a Dirac point can be split into a pair of Weyl points, near which the states are well described by Weyl fermions.[6,7,8,9]
A third route would be for the Weyl points to arise due to time reversal symmetry breaking from a magnetically ordered state. This has been proposed to occur in YbMnBi2 due to a canted antiferromagnetic state on the basis of angle-resolved photoemission spectroscopy (ARPES),[21] while the presence of Dirac fermions was suggested from magnetotransport measurements.[22]
Summary
Topological materials have been found to demonstrate a variety of novel phenomena. For instance, topological insulators are fully gapped in the bulk but display a band inversion leading to distinct behaviour from simple band insulators, such as gapless conducting edge states.[1, 2] More recently gapless topological systems such as Dirac semimetals have been discovered, where the crystal symmetry prevents the opening of a gap at a point where the bands cross linearly, much like a three-dimensional analogue of graphene.[3,4,5] When either time reversal or inversion symmetry is broken, such a Dirac point can be split into a pair of Weyl points, near which the states are well described by Weyl fermions.[6,7,8,9] In addition to being massless, Weyl fermions have a chirality (either left or right handed) and while a Dirac point requires protection from the crystal symmetry to avoid a gap opening, an isolated Weyl point is topologically protected.The realisation of Weyl fermions requires either the breaking of inversion or time reversal symmetry. This has been proposed to occur in YbMnBi2 due to a canted antiferromagnetic state on the basis of angle-resolved photoemission spectroscopy (ARPES),[21] while the presence of Dirac fermions was suggested from magnetotransport measurements.[22]
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