[Zurück]

F. Libisch:
"Graphene quantum dots - confining Dirac electrons";
Hauptvortrag: ROSOV pinn 2017, Belgrad (Serbien) (eingeladen); 01.06.2017 - 02.06.2017.

Graphene, the first truly two-dimensional solid, attracts considerable attention due to its
unique electronical properties. With a nearly linear dispersion relation, the dynamics of
electrons near the Fermi energy of graphene closely mimics that of a massless Dirac
Hamiltonian. Moreover, the regular honeycomb lattice gives rise o a pseudospin degeneracy,
suggesting an analogy to Dirac four spinors. Envisioned applications range from high-speed
electronics to spintronic and valleytronic devices that profit from the long spin-lifetime and
the additional valley degree of freedom in the bandstructure of graphene.
Exploiting the special properties of the charge carriers in graphene requires precise
manipulation of Dirac electrons. Quantum dots present an essential building block, yet
providing tailored confinement in graphene has remained challenging: purely electrostatic
confinement fails due to the gapless band structure of graphene while patterning graphene
nanostructures leads to edges that strongly affect the properties of the highly symmetric
graphene lattice. I will review recent experimental efforts and our large-scale tight-binding
simulations to realize nanostructured graphene quantum dots and constrictions highlighting
the dominant role of edge effects. Sandwiching graphene by hexagonal boron nitride strongly
reduces bulk disorder, yet transport measurements and simulations still consistently show
strongly broken valley symmetries. A promising alternative combines electrostatic
confinement with magnetic fields to achieve smooth confinement yielding well-defined spin
and valley symmetries in experiment and theory. Such an approach provides an ideal scaffold
for future graphene-based valleytronic and spintronic devices.