Generation of Anisotropic Massless Dirac Fermions and Asymmetric Klein Tunneling in Few-Layer Black Phosphorus Superlattices

TL;DR

This paper demonstrates that anisotropic massless Dirac fermions can be generated in patterned few-layer black phosphorus superlattices, exhibiting tunable anisotropic properties and asymmetric Klein tunneling, expanding control over 2D electronic states.

Contribution

It introduces a method to generate and control anisotropic massless Dirac fermions in black phosphorus superlattices, a novel approach in 2D material engineering.

Findings

Massless Dirac fermions with tunable anisotropy are realized in black phosphorus superlattices.

These quasiparticles exist within an isolated energy window and inherit black phosphorus's anisotropic properties.

The states show asymmetric Klein tunneling with significant deviation from normal incidence.

Abstract

Artificial lattices have been employed in many two-dimensional systems, including those of electrons, atoms and photons, in a quest for massless Dirac particles with flexibility and controllability. Periodically patterned molecule assembly and electrostatic gating as well as moir\'e pattern induced by substrate, have produced electronic states with linear dispersions from isotropic two-dimensional electron gas (2DEG). Here we demonstrate that massless Dirac fermions with tunable anisotropic characteristics can, in general, be generated in highly anisotropic 2DEG under slowly varying external periodic potentials. For patterned few-layer black phosphorus superlattices, the new chiral quasiparticles exist exclusively in an isolated energy window and inherit the strong anisotropic properties of pristine black phosphorus. These states exhibit asymmetric Klein tunneling with the direction of incidence for wave packet with perfect transmission deviating from normal incidence by more than 50{\deg} under an appropriate barrier orientation.