Coexistence of electron whispering-gallery modes and atomic collapse states in graphene/WSe2 heterostructure quantum dots

Abstract

The relativistic massless charge carriers with a Fermi velocity of about c/300 in graphene enable us to realize two distinct types of resonances (here, c is the speed of light in vacuum). One is the electron whispering-gallery mode in graphene quantum dots arising from the Klein tunneling of the massless Dirac fermions. The other is the atomic collapse state, which has never been observed in experiment with real atoms due to the difficulty of producing heavy nuclei with charge Z > 170; however, they can be realized near a Coulomb impurity in graphene with a charge Z ≥ 1 because of the “small” velocity of the Dirac excitations. Here we demonstrate that both the electron whispering-gallery modes and atomic collapse states coexist in graphene/WSe2 heterostructure quantum dots due to the Coulomb-like potential near their edges. By applying a perpendicular magnetic field, we explore the evolution from the atomic collapse states to unusual Landau levels in the collapse regime.

Recent progresses on graphene-based artificial nanostructures: a perspective from scanning tunneling microscopy

“…Another type of confinement state in graphene is atomic collapse states (ACSs), which arises from a Coulomb-like potential with a large local charge Z [38][39][40]. The fine structure constant of the atom is α = e 2 c ≈ 1 137 , where c is the speed of light, is the reduced Planck constant.…”

“…When the interaction strength, β ≡ Zα g (here α g is α( c κv F ),and κ is effective dielectric constant) is larger than the critical number 0.5, electrons tend to "collapse" into the nucleus due to quantum dot with a height of 0.8 nm and a width of 2.2 nm. Right panel: the calculated space-energy LDOS map for the dot with β = 2.4, r 0 = 9 nm [40]. (e) Left panel: dual-gate configurations for graphene.…”

Observation of Robust and Long-Ranged Superperiodicity of Electronic Density Induced by Intervalley Scattering in Graphene/Transition Metal Dichalcogenide Heterostructures

“…The atomically thin structure of graphene makes its electronic properties extremely sensitive to atomic adsorptions and supporting substrates. − To reveal the intrinsic electronic properties of graphene, scientists usually use two-dimensional (2D) h-BN and transition metal dichalcogenides (TMDs) as substrates because they are insulating, atomically flat, and without dangling bonds. − However, even in such a case, it has been demonstrated explicitly that the substrate will still affect the electronic properties of graphene dramatically when the moiré generated between graphene and the insulating/semiconducting substrates is large. − Then, a large band gap will be introduced in graphene by the substrate. It is believed that the low-energy electronic properties of graphene will remain unchanged when the moiré between them is small.…”

“…In our experiment, the graphene/TMD heterostructures with controlled interfacial twist angles are obtained by using the transfer technology of graphene monolayer onto mechanically exfoliated WSe 2 and WS 2 sheets ,, (see Figure a and Methods for details of the sample preparation). The obtained graphene/TMD heterostructures are systematically characterized by carrying out STM and STS measurements (see Supplemental Figure 1).…”

Kinetics of Nanobubbles in Tiny-Angle Twisted Bilayer Graphene

“…Figure a shows a schematic of our experimental device setup, and the TBG samples are obtained by wet transfer technology of graphene layer by layer on mechanical-exfoliated WSe 2 sheets, ,− which provide atomically flat substrate (see Supplemental Figures S1 and S2 for details). Figure b shows a representative STM image of the obtained TBG.…”