We report a new, cleavable, strong topological metal, ${\mathrm{Zr}}_2{\mathrm{Te}}_2\mathrm{P}$, which has the same tetradymite-type crystal structure as the topological insulator $\mathrm{B}{\mathrm{i}}_2\mathrm{T}{\mathrm{e}}_2\mathrm{Se}$. Instead of being a semiconductor, however, ${\mathrm{Zr}}_2{\mathrm{Te}}_2\mathrm{P}$ is metallic with a pseudogap between 0.2 and 0.7 eV above the Fermi energy $\left(E_F\right)$. Inside this pseudogap, two Dirac dispersions are predicted: one is a surface-originated Dirac cone protected by time-reversal symmetry (TRS), while the other is a bulk-originated and slightly gapped Dirac cone with a largely linear dispersion over a 2 eV energy range. A third surface TRS-protected Dirac cone is predicted, and observed using angle-resolved photoemission spectroscopy, making ${\mathrm{Zr}}_2{\mathrm{Te}}_2\mathrm{P}$ the first system, to our knowledge, to realize TRS-protected Dirac cones at $\overline{M}$ points. The high anisotropy of this Dirac cone is similar to the one in the hypothetical Dirac semimetal $\mathrm{Bi}{\mathrm{O}}_2$. We propose that if $E_F$ can be tuned into the pseudogap where the Dirac dispersions exist, it may be possible to observe ultrahigh carrier mobility and large magnetoresistance in this material.

• Received 1 December 2015

DOI:https://doi.org/10.1103/PhysRevB.93.045315