Influence of Fermi arc states and double Weyl node on tunneling in a Dirac semimetal

摘要

Most theoretical studies of tunneling in Dirac and the closely related Weylsemimetals have modeled these materials as single Weyl nodes described by thethree-dimensional Dirac equation $H = v_f \vec{p}\cdot\vec{\sigma}$. Theinfluence of scattering between the different valleys centered around differentWeyl nodes, and the Fermi arc states which connect these nodes are hence notevident from these studies. In this work we study the tunneling in a thin filmsystem of the Dirac semimetal $\text{Na}_3\text{Bi}$ consisting of a centralsegment with a gate potential, sandwiched between identical semi-infinitesource and drain segments. The model Hamiltonian we use for$\text{Na}_3\text{Bi}$ gives, for each spin, two Weyl nodes separated in$k$-space symmetrically about $k_z=0$. The presence of a top and bottom surfacein the thin film geometry results in the appearance of Fermi arc states andenergy subbands. We show that (for each spin) the presence of two Weyl nodesand the Fermi arc states result in enhanced transmission oscillations, andfinite transmission even when the energy falls within the \textit{bulk} bandgap in the central segment respectively. These features are not evident insingle Weyl node models.