# A simple rule for finding Dirac Cones in Bilayered Perovskites

## TL;DR

This paper introduces a straightforward rule to identify Dirac cone electronic states in bilayered perovskites by focusing on active atom groups, demonstrated through DFT calculations on specific materials, revealing high Fermi velocities and potential for ultra-fast devices.

## Contribution

The paper presents a simple, general rule for locating Dirac cones in bilayered perovskites based on quasi-atom lattices, validated with DFT calculations.

## Key findings

- Both bilayers exhibit Dirac cones near the Fermi level.
- Fermi velocities reach approximately 0.2×10^6 m/s.
- The materials are promising for ultra-fast electronic devices.

## Abstract

We propose a simple rule for finding Dirac cone electronic states in solids, that is neglecting those lattice atoms inert to the particular electronic bands, and pursuing the two dimensional (2D) graphene-like quasi-atom lattices with s- and p-bindings by considering the equivalent atom groups in the unit cell as quasi-atoms. With CsPbBr$_3$ and Cs$_3$Bi$_2$Br$_9$ bilayers as examples, we demonstrate the effectiveness and generality of this rule with the density functional theory (DFT) calculations. We demonstrate that both bilayers have Dirac cones around the Fermi level and reveal that their corresponding Fermi velocities can reach as high as $\sim$ 0.2$\times$10$^6$m/s. That makes these new 2D layered materials very promising in making new ultra-fast ionic electronic devices.