Super-Klein tunneling and electron-beam collimation in the honeycomb superlattice

Abstract

The honeycomb superlattice model from the nearly commensurate charge-density-wave phase of $1\mathrm{T}\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$ has been shown to host multiple robust flat bands that depends on the number $(m)$ of extra atoms residing on each edge of the hexagon [Lee et al., Phys. Rev. Lett. 124, 137002 (2020)]. In this work we numerically study the transport phenomenon of the single-valley Dirac electrons around the band center $E=0$ where a flat band crosses. A super-Klein tunneling (SKT) phenomenon is found for $m=1$ that the Dirac electrons can tunnel through a rectangle barrier with a unity transmission irrespective of the incident angle of electrons. For the case of $m=3$, a super electron-beam collimation instead of the SKT phenomenon is identified that the Dirac electrons are allowed to tunnel through the barrier only within nearly zero incident angle, and such perpendicular transmission probability is optimal in the low-energy regime but suppressed in the high-energy regime.