FERMI SURFACE STUDIES OF THE DIRAC TYPE-II SEMIMETAL CANDIDATES (Ni, Zr)Te2 USING HIGH FIELD TORQUE MAGNETOMETRY

We have studied the Fermi surface characteristics of two Dirac type-II semimetal candidates (Ni, Zr)Te2 using the torque magnetometry technique under the magnetic field up to 35 T and temperature as low as 0.32 K. The torque signal shows clear de Haas-van Alphen (dHvA) oscillations above 20 T for both ZrTe2 and NiTe2 samples. Frequency analysis reveals one major frequency for ZrTe2 at 530 T; whereas there are three distinct frequencies Fα ∼ 72 T, Fβ ∼ 425 T, and Fγ ∼ 630 T for NiTe2. From the analyses of temperature-dependent dHvA oscillations data using the Lifshitz- Kosevich (LK) formula, we observed the effective masses charge carriers to be m*= 0.26me and m* = 0.13me for ZrTe2 and NiTe2, respectively, where me is the free electron mass. The Berry phase (Φ) is calculated to identify the topological nature of ZrTe2 and NiTe2 by constructing the Landau level fan diagram. It is found that Φ ∼ 0 and π for ZrTe2 and NiTe2, respectively. These results strongly suggest that ZrTe2 is a topologically trivial system, whereas NiTe2 is a topologically non-trivial system. These materials’ electronic band structure and Fermi surface were calculated using the density functional theory (DFT). Our DFT results show that the Dirac point is closer to the Fermi level in NiTe2 as compared to that for ZrTe2. Therefore, our torque results could only detect the signal from Dirac quasi-particles for NiTe2, not for ZrTe2.