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The origin of the planar Hall effect (PHE) in various nonmagnetic semimetals has become a subject of considerable interest, especially in regard to the chiral anomaly that several of these semimetals exhibit. Here, we report a large PHE that exceeds several mΩ cm over a wide range of temperature T and magnetic field B in micron-thick single-crystalline bismuth thin films grown by molecular beam epitaxy techniques. The angular dependence of the PHE and the related anisotropic magnetoresistance (AMR) show complex behaviors as a function of B and T. At high temperatures and in modest magnetic fields, the PHE and AMR can be quantitatively explained by a semiclassical transport model based on the well-established elongated electron and hole pockets of the Fermi surface in bismuth. Although these results establish an anisotropic electronic orbital origin of the PHE, we find that when the electric current is oriented along the binary axis of bismuth, the PHE and AMR behaviors can be well described by a model based on the chiral anomaly in Weyl or Dirac semimetals. However, this model cannot account for these behaviors when the current is rather oriented along the bisectrix axis. Thus, the anisotropy of the PHE is a useful test to check on the validity of the chiral anomaly in semimetals.

Magnetic Weyl semimetals with broken time-reversal symmetry are expected to generate strong intrinsic anomalous Hall effects, due to their large Berry curvature. Here, we report a magnetic Weyl semimetal candidate Co3Sn2S2 with a quasi-two-dimensional crystal structure consisting of stacked Kagome lattices. This lattice provides an excellent platform for hosting exotic quantum topological states. We observe a negative magnetoresistance that is consistent with the chiral anomaly expected from the presence of Weyl fermions close to the Fermi level. The anomalous Hall conductivity is robust against both increased temperature and charge conductivity, which corroborates the intrinsic Berry-curvature mechanism in momentum space. Owing to the low carrier density in this material and the significantly enhanced Berry curvature from its band structure, the anomalous Hall conductivity and the anomalous Hall angle simultaneously reach 1130 S cm-1 and 20%, respectively, an order of magnitude larger than typical magnetic systems. Combining the Kagome-lattice structure and the long-range out-of-plane ferromagnetic order of Co3Sn2S2, we expect that this material is an excellent candidate for observation of the quantum anomalous Hall state in the two-dimensional limit., 22 pages, 5 figures, and 1 supporting file

The anomalous Hall effect soars when Dirac quasiparticles meet frustrated magnetism., The anomalous Hall effect (AHE) is one of the most fundamental phenomena in physics. In the highly conductive regime, ferromagnetic metals have been the focus of past research. Here, we report a giant extrinsic AHE in KV3Sb5, an exfoliable, highly conductive semimetal with Dirac quasiparticles and a vanadium Kagome net. Even without report of long range magnetic order, the anomalous Hall conductivity reaches 15,507 Ω−1 cm−1 with an anomalous Hall ratio of ≈ 1.8%; an order of magnitude larger than Fe. Defying theoretical expectations, KV3Sb5 shows enhanced skew scattering that scales quadratically, not linearly, with the longitudinal conductivity, possibly arising from the combination of highly conductive Dirac quasiparticles with a frustrated magnetic sublattice. This allows the possibility of reaching an anomalous Hall angle of 90° in metals. This observation raises fundamental questions about AHEs and opens new frontiers for AHE and spin Hall effect exploration, particularly in metallic frustrated magnets.