Detailed Study of the Fermi Surfaces of the Type-II Dirac Semimetallic Candidates XTe₂ (X =Pd, Pt)

We present a detailed quantum oscillatory study on the Dirac type-II semimetallic candidates PdTe₂ and PtTe₂ via the temperature and the angular dependence of the de Haas-van Alphen and Shubnikov-de Haas effects. In high-quality single crystals of both compounds, i.e., displaying carrier mobilities between 10³ and 10⁴ cm²/Vs, we observed a large nonsaturating magnetoresistivity which in PtTe₂ at a temperature T=1.3 K leads to an increase in the resistivity up to (5×10⁴)% under a magnetic field μ₀H=62 T. These high mobilities correlate with their light effective masses in the range of 0.04 to 1 bare electron mass according to our measurements. For PdTe₂ the experimentally determined Fermi surface cross-sectional areas show excellent agreement with those resulting from band structure calculations. Surprisingly, this is not the case for PtTe₂, whose agreement between calculations and experiments is relatively poor even when electronic correlations are included in the calculations. Therefore, our study provides strong support for the existence of a Dirac type-II node in PdTe₂ and probably also for PtTe₂. Band structure calculations indicate that the topologically nontrivial bands of PtTe₂ do not cross the Fermi level. In contrast, for PdTe₂ the Dirac type-II cone does intersect, although our calculations also indicate that the associated cyclotron orbit on the Fermi surface is located in a distinct k_z plane with respect to that of the Dirac type-II node. Therefore, it should yield a trivial Berry phase.