2 research outputs found
Resolving the Spatial Structures of Bound Hole States in Black Phosphorus
Understanding
the local electronic properties of individual defects
and dopants in black phosphorus (BP) is of great importance for both
fundamental research and technological applications. Here, we employ
low-temperature scanning tunnelling microscope (LT-STM) to probe the
local electronic structures of single acceptors in BP. We demonstrate
that the charge state of individual acceptors can be reversibly switched
by controlling the tip-induced band bending. In addition, acceptor-related
resonance features in the tunnelling spectra can be attributed to
the formation of Rydberg-like bound hole states. The spatial mapping
of the quantum bound states shows two distinct shapes evolving from
an extended ellipse shape for the 1s ground state to a dumbbell shape
for the 2p<sub><i>x</i></sub> excited state. The wave functions
of bound hole states can be well-described using the hydrogen-like
model with anisotropic effective mass, corroborated by our theoretical
calculations. Our findings not only provide new insight into the many-body
interactions around single dopants in this anisotropic two-dimensional
material but also pave the way to the design of novel quantum devices
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