2 research outputs found
Layer Polarizability and Easy-Axis Quantum Hall Ferromagnetism in Bilayer Graphene
We
report magnetotransport measurements of graphene bilayers at
large perpendicular electric displacement fields, up to ∼1.5
V/nm, where we observe crossings between Landau levels with different
orbital quantum numbers. The displacement fields at the studied crossings
are primarily determined by energy shifts originating from the Landau
level layer polarizability or polarization. Despite decreasing Landau
level spacing with energy, successive crossings occur at larger displacement
fields, resulting from decreasing polarizability with orbital quantum
number. For particular crossings we observe resistivity hysteresis
in displacement field, indicating the presence of a first-order transition
between states exhibiting easy-axis quantum Hall ferromagnetism
Tunneling Plasmonics in Bilayer Graphene
We report experimental signatures
of plasmonic effects due to electron tunneling between adjacent graphene
layers. At subnanometer separation, such layers can form either a
strongly coupled bilayer graphene with a Bernal stacking or a weakly
coupled double-layer graphene with a random stacking order. Effects
due to interlayer tunneling dominate in the former case but are negligible
in the latter. We found through infrared nanoimaging that bilayer
graphene supports plasmons with a higher degree of confinement compared
to single- and double-layer graphene, a direct consequence of interlayer
tunneling. Moreover, we were able to shut off plasmons in bilayer
graphene through gating within a wide voltage range. Theoretical modeling
indicates that such a plasmon-off region is directly linked to a gapped
insulating state of bilayer graphene, yet another implication of interlayer
tunneling. Our work uncovers essential plasmonic properties in bilayer
graphene and suggests a possibility to achieve novel plasmonic functionalities
in graphene few-layers