Fermiology of the Dirac type-II semimetal candidates (Ni,Zr)<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">Te</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math> using de Haas–van Alphen oscillations

Abstract

We have investigated the Fermi surface properties of the Dirac type-II semimetal candidates (Ni,Zr)${\mathrm{Te}}_{2}$ using torque magnetometry with applied fields up to 35 T. Magnetization shows clear de Haas--van Alphen (dHvA) oscillations above 20 T. The dHvA oscillations are smooth and well defined and consist of one distinct frequency (${F}_{\ensuremath{\alpha}}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}530$ T) in $\mathrm{Zr}{\mathrm{Te}}_{2}$ and three (${\overline{F}}_{\ensuremath{\alpha}}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}72$ T, ${\overline{F}}_{\ensuremath{\beta}}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}425$ T, and ${\overline{F}}_{\ensuremath{\gamma}}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}630$ T) in $\mathrm{Ni}{\mathrm{Te}}_{2}$. The Berry phase $\ensuremath{\phi}$ was determined by constructing the Landau level fan diagram. It is found that $\ensuremath{\phi}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}$ 0 and $\ensuremath{\pi}$ for ${F}_{\ensuremath{\alpha}}$ and ${\overline{F}}_{\ensuremath{\beta}}$, respectively, for $\mathrm{Zr}{\mathrm{Te}}_{2}$ and $\mathrm{Ni}{\mathrm{Te}}_{2}$. This strongly suggests that the Dirac fermions make a dominant contribution to the transport properties of $\mathrm{Ni}{\mathrm{Te}}_{2}$, whereas topologically trivial fermions dominate those in $\mathrm{Zr}{\mathrm{Te}}_{2}$. The presence of lighter effective mass ${m}^{*}=0.13{m}_{e}$ in $\mathrm{Ni}{\mathrm{Te}}_{2}$ compared to ${m}^{*}=0.26{m}_{e}$ in $\mathrm{Zr}{\mathrm{Te}}_{2}$, where ${m}_{e}$ is an electron's rest mass, further confirms the presence of Dirac fermions in $\mathrm{Ni}{\mathrm{Te}}_{2}$. Our density functional theory calculations find that while both systems host type-II Dirac dispersions along the out-of-plane direction, their relative positions and the natures of the dispersions are different. The Dirac cone is closer to the Fermi energy ${E}_{F}$ ($\ensuremath{\sim}100$ meV above) in $\mathrm{Ni}{\mathrm{Te}}_{2}$, whereas it is far ($\ensuremath{\sim}500$ meV) above ${E}_{F}$ for $\mathrm{Zr}{\mathrm{Te}}_{2}$. This is consistent with our experimental finding of a nontrivial Berry phase and dominant contribution from lighter electrons in the quantum oscillation signal for only $\mathrm{Ni}{\mathrm{Te}}_{2}$. These findings suggest that the proximity of the Dirac cone to ${E}_{F}$ in topological compounds is crucial for observing the effect from Dirac quasiparticles in their electrical transport or magnetic properties.

Topics & Concepts