Positive Magnetoresistance and Chiral Anomaly in Exfoliated Type-II Weyl Semimetal Td-WTe2

Abstract

Layered van der Waals semimetallic Td-WTe2, exhibiting intriguing properties which include non-saturating extreme positive magnetoresistance (MR) and tunable chiral anomaly, has emerged as a model topological type-II Weyl semimetal system. Here, ∼45 nm thick mechanically exfoliated flakes of Td-WTe2 are studied via atomic force microscopy, Raman spectroscopy, low-T/high-μ0H magnetotransport measurements and optical reflectivity. The contribution of anisotropy of the Fermi liquid state to the origin of the large positive transverse MR⊥ and the signature of chiral anomaly of the type-II Weyl Fermions are reported. The samples are found to be stable in air and no oxidation or degradation of the electronic properties is observed. A transverse MR⊥∼1200 % and an average carrier mobility of 5000 cm2V−1s−1 at T=5K for an applied perpendicular field μ0H⊥=7T are established. The system follows a Fermi liquid model for T≤50K and the anisotropy of the Fermi surface is concluded to be at the origin of the observed positive MR. Optical reflectivity measurements confirm the anisotropy of the electronic behaviour. The relative orientation of the crystal axes and of the applied electric and magnetic fields is proven to determine the observed chiral anomaly in the in-plane magnetotransport. The observed chiral anomaly in the WTe2 flakes is found to persist up to T=120K, a temperature at least four times higher than the ones reported to date.

Ultrafast Coherent THz Lattice Dynamics Coupled to Spins in the van der Waals Antiferromagnet FePS3

“…This configuration allows to fully focus both beams into spots on different parts of the flake, so that homogeneous regions can be addressed in samples with lateral size larger than 5 µm. [44] First, we now focus on the optically excited dynamics in the bulk crystal. For these experiments the probe photon-energy was kept constant at 1.45 eV, which is just below the band-gap energy of 1.5 eV [33,34] while the pump photon energy was tuned from below to above the band gap of FePS 3 in the 0.83-1.9 eV range.…”

“…This configuration allows to fully focus both beams into spots on different parts of the flake, so that homogeneous regions can be addressed in samples with lateral size larger than 5 µm. [ 44 ]…”

High-Mobility Topological Semimetals as Novel Materials for Huge Magnetoresistance Effect and New Type of Quantum Hall Effect

“…The main source of MR in semimetals is related to the deviation of the charge carrier (both electrons and holes) trajectory due to the Lorentz force (Hall effect). In recent years, great attention has been devoted to the MR effect in high-mobility semimetals, and it has been found that topological semimetals exhibit an extremely large MR effect [108,109,[139][140][141][142][143][144] as occurs for topological insulators [145]. Quantitatively, the MR can be expressed in percentage units as:…”

Observation of Linear Magnetoresistance in MoO2

“…In particular, Dirac physics in topological insulators, semimetals, or spatial inhomogeneities can induce pronounced linear magnetoresistance behavior. Recently, linear magnetoresistance under high fields was observed in some Dirac or Weyl semimetals such as Bi [ 18 ], InSb [ 19 ], Cd 3 As 2 [ 20 ], NbP [ 21 ], LaSb [ 22 ], and ZrSiS [ 23 ]; and compensated semimetals such as WTe 2 [ 24 , 25 ], TaAs 2 , and NbAs 2 [ 26 ]. There have also been reports of linear magnetoresistance in layered charge density wave and spin density wave compounds, such as iron pnictides [ 27 , 28 ], 2H-NbSe 2 , and 2H-TaSe 2 [ 29 ].…”