Transport Gap in Suspended Bilayer Graphene at Zero Magnetic Field

TL;DR

This study investigates the transport gap in suspended bilayer graphene at zero magnetic field, revealing a spontaneous valley splitting and a spin-polarized antiferromagnetic ground state through resistance measurements and magnetic field analysis.

Contribution

It provides experimental evidence for a spin-polarized layer antiferromagnetic state as the ground state in bilayer graphene at zero magnetic field, highlighting the role of symmetry breaking and exchange interactions.

Findings

Transport resistance varies from a few kΩ to several MΩ near CNP.

Transport gap of 8 meV observed at 0.3 K.

Weak linear decrease of resistance with increasing magnetic field.

Abstract

We report a change of three orders of magnitudes in the resistance of a suspended bilayer graphene flake which varies from a few k$\Omega$s in the high carrier density regime to several M$\Omega$s around the charge neutrality point (CNP). The corresponding transport gap is 8 meV at 0.3 K. The sequence of appearing quantum Hall plateaus at filling factor $\nu=2$ followed by $\nu=1$ suggests that the observed gap is caused by the symmetry breaking of the lowest Landau level. Investigation of the gap in a tilted magnetic field indicates that the resistance at the CNP shows a weak linear decrease for increasing total magnetic field. Those observations are in agreement with a spontaneous valley splitting at zero magnetic field followed by splitting of the spins originating from different valleys with increasing magnetic field. Both, the transport gap and $B$ field response point toward spin polarized layer antiferromagnetic state as a ground state in the bilayer graphene sample. The observed non-trivial dependence of the gap value on the normal component of $B$ suggests possible exchange mechanisms in the system.