Jasper Linnartz and Steffen Wiedmann, HFML Nijmegen.
A team of researchers from HFML-FELIX, Aarhus University, and the University of Bristol has investigated the high-field electronic transport properties of the semimetal WTe2. In quantum-oscillations measurements, they revealed peculiar magnetic-breakdown trajectories of charge carriers between nested pockets of the Fermi surface.
WTe2 is a material with extraordinary properties. Bound by weak van der Waals interaction, two-dimensional layers can be exfoliated down to a monolayer, leading to emergent phenomena such as superconductivity and the quantum spin Hall effect. In its bulk form (as studied here), the material’s resistance increases by more than 107% in the presence of a high magnetic field. Moreover, bulk WTe2 has also been identified as a type-II Weyl semimetal, which essentially means that its electronic bands form tilted Dirac cones giving rise to small electron and hole pockets containing highly mobile charge carriers. In quantum-oscillation measurements, the observed frequency of the 1/B-periodic oscillations is directly proportional to the extremal area of particular pockets of the Fermi surface. Key properties of the charge carriers such as their effective mass, quantum mobility, and nature (electrons or holes) can be determined from these experiments.
In high magnetic fields, the phenomeon of magnetic breakdown (MB) occurs, which is essentially a tunneling of charge carriers between different pockets of the Fermi surface. In quantum-oscillation measurements, MB orbits are characterized by the sum of individual areas (frequencies) of different pockets. By measuring quantum oscillations that originate from MB orbits at different tilt angles and temperatures and comparing those to band-structure calculations, it was found that the Fermi surface of WTe2 can be explained within the model of a Matryoshka-doll nested Fermi surface of electron and hole pockets, i.e., electron and hole pockets in WTe2 fit inside one another in precisely the same way. What is so peculiar is the fact that the onset of magnetic breakdown is solely determined by impurity scattering in contrast to magnetic-breakdown scenarios in other metallic systems, which depends exclusively on the strength of the applied magnetic field. In addition, unlike in other systems, the phenomenon of MB in this material persists upon changing the magnetic-field orientation with respect to the two-dimensional layers of WTe2.
Figure: (top) Cut of the Fermi surface in the kx-ky
plane highlighting the nested doll configuration. (bottom) Fast-Fourier
transform spectrum for the field range [8–28.7 T] for different
temperatures up to 6.5 K. The corresponding individual (α, β, γ, δ)
and breakdown orbits (sum of individual orbits) are labeled.
Fermi surface and nested magnetic breakdown in WTe2, J. F. Linnartz, C. S. A. Müller, Yu-Te Hsu, C.
Breth Nielsen, M. Bremholm, N. E. Hussey, A. Carrington, and S.
Wiedmann, Phys. Rev. Res. 4, L012005 (2022).
https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.4.L012005
Contact: Jasper.Linnartz@ru.nl, Steffen.Wiedmann@ru.nl
