Electron energy spectrum and the Berry phase in graphite bilayer

TL;DR

This paper analyzes the electron energy spectrum in graphite bilayer, revealing four Dirac points near K that influence the Berry phase, with implications for electronic properties.

Contribution

It identifies four Dirac points in graphite bilayer and clarifies their combined effect on the Berry phase, advancing understanding of its electronic structure.

Findings

Four Dirac points identified near K in graphite bilayer

Berry phase contributions from these points sum to 2π when orbit surrounds all

Distinct phases of π and -π from different Dirac points

Abstract

We emphasize that there exist four Dirac-type points in the electron-energy spectrum of a graphite bilayer near the point K of its Brillouin zone. One of the Dirac points is at the point K, and three Dirac points lie nearby. Each of these three points generates the Berry phase $\pi$, while the Dirac point at K gives the phase $-\pi$. It is these four points that determine the Berry phase in the bilayer. If an electron orbit surrounds all these points, the Berry phase is equal to $2\pi$.