Emergence of Two-Dimensional Massless Dirac Fermions, Chiral Pseudospins, and Berry's Phase in Potassium Doped Few-Layer Black Phosphorus

TL;DR

Potassium doping in few-layer black phosphorus induces 2D massless Dirac fermions with chiral pseudospins and Berry's phase, potentially enabling graphene-like electronic transport properties in a tunable semiconductor.

Contribution

First-principles calculations predict the emergence of Dirac cones with linear dispersion in all directions in K-doped black phosphorus, revealing new topological electronic features.

Findings

Dirac cones appear beyond critical K doping levels.

Electronic states exhibit chiral pseudospins and Berry's phase.

Features are robust against spin-orbit interaction.

Abstract

Thin flakes of black phosphorus (BP) are a two-dimensional (2D) semiconductor whose energy gap is predicted being sensitive to the number of layers and external perturbations. Very recently, it was found that a simple method of potassium (K) doping on the surface of BP closes its band gap completely, producing a Dirac semimetal state with a linear band dispersion in the armchair direction and a quadratic one in the zigzag direction. Here, based on first-principles density functional calculations, we predict that, beyond the critical K density of the gap closure, 2D massless Dirac Fermions (i.e., Dirac cones) emerge in K-doped few-layer BP, with linear band dispersions in all momentum directions, and the electronic states around Dirac points have chiral pseudospins and Berry's phase. These features are robust with respect to the spin-orbit interaction and may lead to graphene-like electronic transport properties with greater flexibility for potential device applications.