Symmetry breaking of the zero energy Landau level in bilayer graphene

TL;DR

This study investigates the lifting of degeneracy in the zero energy Landau level of bilayer graphene under high magnetic fields, revealing new quantum Hall states and insights into the underlying symmetry-breaking mechanisms.

Contribution

It provides experimental evidence of complete degeneracy lifting in bilayer graphene's zero energy Landau level and identifies the formation of a quantum Hall ferromagnet.

Findings

Degeneracy in the zero energy Landau level is fully lifted at high magnetic fields.

New quantum Hall states appear at filling factors 0, 1, 2, and 3.

The Landau level splitting at filling factors 1, 2, and 3 is independent of spin.

Abstract

The quantum Hall effect near the charge neutrality point in bilayer graphene is investigated in high magnetic fields of up to 35 T using electronic transport measurements. In the high field regime, the eight-fold degeneracy in the zero energy Landau level is completely lifted, exhibiting new quantum Hall states corresponding filling factors $\nu=$0, 1, 2, & 3. Measurements of the activation energy gap in tilted magnetic fields suggest that the Landau level splitting at the newly formed $\nu=$1, 2, & 3 filling factors are independent of spin, consistent with the formation of a quantum Hall ferromagnet. In addition, measurements taken at the $\nu$ = 0 charge neutral point show that, similar to single layer graphene, the bilayer becomes insulating at high fields.