Magnetoresistance in Quasi-One-Dimensional Weyl Semimetal (TaSe 4 ) 2 I
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Magnetoresistance in Quasi-one Dimensional Weyl Semimetal (TaSe4 )2 I I. A. Cohn, S. G. Zybtsev, A. P. Orlov, S. V. Zaitsev-Zotov 1) Kotelnikov Institute of Radioengineering and Electronics of Russian Academy of Sciences, 125009 Moscow, Russia Submitted 13 May 2020 Resubmitted 29 May 2020 Accepted 4 June 2020
Magnetic field effect on linear and nonlinear conductivity in a quasi-one-dimensional Weyl semimetal with a charge density wave (TaSe4 )2 I is studied. Longitudinal magnetoresistance in all known regimes of chargedensity wave motion (linear conduction, creep, sliding, “Fr¨ ohlich superconductivity”) is positive and does not exceed a fraction of per cent. Similar magnetotransport measurements were performed in samples profiled by focused ion beams is such a way that motion of the charge-density wave in them is accompanied by phase slip of the charge-density wave. In such samples, a peak-like non-parabolic negative magnetoresistance is observed in relatively small magnetic fields B 4 T in the nonlinear conduction regime in both longitudinal and transverse geometries. Our results differ significantly from ones obtained earlier and raise the question concerning conditions for observing the axion anomaly in Weyl semimetals in the Peierls state. DOI: 10.1134/S0021364020140040
Topological materials are currently some of the most interesting and intensively studied objects in solid state physics. Of great interest are Weyl semimetals, the transport properties of which are determined by the massless Weyl fermions. One of the most remarkable effects arising in such materials is the appearance of a chiral anomaly, which manifests itself as a negative longitudinal magnetoresistance (MR) [1–3]. At present, negative longitudinal MR has been observed in many Weyl and Dirac semimetals, such as TaAs [4], Cd3 As2 [5], etc. (TaSe4 )2 I has a monoclinic unit cell (space group I422) which consists of TaSe4 chains with helical symmetry that are placed in the middle of the faces and separated by chains of iodine atoms [6]. The calculations of the band structure (TaSe4 )2 I show that under normal conditions this material is a semimetal due to the interaction between the TaSe4 chains. This interaction leads to the splitting of the dz2 zones of tantalum into two intersecting near the boundary of the Brillouin zone at a distance of 0.44π/c, where c = 12.8 ˚ A is the unit cell size along the chains [7]. Subsequent analysis shows that this material is a Weyl semimetal in which numerous Weyl points are located at distances of 10–15 meV above and below the Fermi level and form pairs with the opposite chiral charge [8–11]. Moreover, (TaSe4 )2 I is a quasi-one-dimensional (quasi-1D) conductor with an incommensurate charge-density wave (CDW) forming at temperatures below the Peierls transition temperature TP ≈ 248−263 K [8, 11–17]. The Peierls gap covers the 1) e-mail:
entire Fermi surface. This means the disappearance of the Weyl cones in the Peierls state. The conductivity anisotropy at room temperature is A ≡ σ /σ⊥ ≈ 3×102, where σ and σ⊥ a
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