On the search for the chiral anomaly in Weyl semimetals: the negative longitudinal magnetoresistance
By R. D. Reis, M. O. Ajeesh, Nitesh Kumar, F. Arnold, C. Shekhar, M. Naumann, M. Schmidt, M. Nicklas, E. Hassinger. 2016
169 citations recorded by the source corpus.
Recently, the existence of massless chiral (Weyl) fermions has been postulated in a class of semi-metals with a non-trivial energy dispersion. These materials are now commonly dubbed Weyl semi-metals (WSM). One predicted property of Weyl fermions is the chiral or Adler–Bell–Jackiw anomaly, a chirality imbalance in the presence of parallel magnetic and electric fields. In WSM, it is expected to induce a negative longitudinal magnetoresistance (MR). Here, we present experimental evidence that the observation of the chiral anomaly can be hindered by an effect called ‘current jetting’. This effect also leads to a strong apparent negative longitudinal MR, but it is characterized by a highly non-uniform current distribution inside the sample. It appears in materials possessing a large field-induced anisotropy of the resistivity tensor, such as almost compensated high-mobility semimetals due to the orbital effect. In case of a non-homogeneous current injection, the potential distribution is strongly distorted in the sample. As a consequence, an experimentally measured potential difference is not proportional to the intrinsic resistance. Our results on the MR of the Weyl semimetal candidate materials NbP, NbAs, TaAs, and TaP exhibit distinct signatures of an inhomogeneous current distribution, such as a field-induced ‘zero resistance’ and a strong dependence of the ‘measured resistance’ on the position, shape, and type of the voltage and current contacts on the sample. A misalignment between the current and the magnetic-field directions can even induce a ‘negative resistance’. Finite-element simulations of the potential distribution inside the sample, using typical resistance anisotropies, are in good agreement with the experimental findings. Our study demonstrates that great care must be taken before interpreting measurements of a negative longitudinal MR as evidence for the chiral anomaly in putative Weyl semimetals.
Subfields: Atomic and Molecular Physics, and Optics, Condensed Matter Physics, Materials Chemistry
View Paper: https://www.semanticscholar.org/paper/7b235b28817658ecf27dfd0d18520d5679d6be95
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Citations in the corpus
- Weyl and Dirac semimetals in three-dimensional solids (2017, background): “…large enough transverse magnetoresistance to have the effect corrupted by the classic “current jetting” phenomenon in compensated semiconductors (Dos Reis et al., 2016; Yuan et al., 2016b) in which current becomes narrowly directed along the applied field due to a very large field induced…”
- Giant anomalous Nernst effect and quantum-critical scaling in a ferromagnetic semimetal (2018, background): “Recently, it has been shown that this current jetting effect is the major origin for the negative LMR observed in several Weyl semimetals[22, 23].”
- Experimental Tests of the Chiral Anomaly Magnetoresistance in the Dirac-Weyl Semimetals Na3Bi and GdPtBi (2018, background): “However, the weakness of their LMR signals (50-100× weaker than in Na3Bi) and their fragility with respect to placement of contacts, together with the high mobilities of the Weyl semimetals (150,000 to 200,000 cm(2)/Vs) have raised concerns about current jetting artifacts [20, 21].”