53 research outputs found
Confinement and edge effects on atomic collapse in graphene nanoribbons
Atomic collapse in graphene nanoribbons behaves in a fundamentally different
way as compared to monolayer graphene, due to the presence of multiple energy
bands and the effect of edges. For armchair nanoribbons we find that bound
states gradually transform into atomic collapse states with increasing impurity
charge. This is very different in zig-zag nanoribbons where multiple
quasi-one-dimensional \emph{bound states} are found that originates from the
zero energy zig-zag edge states. They are a consequence of the flat band and
the electron distribution of these bound states exhibits two peaks. The lowest
energy edge state transforms from a bound state into an atomic collapse
resonance and shows a distinct relocalization from the edge to the impurity
position with increasing impurity charge
Tuning quantum non-local effects in graphene plasmonics
The response of an electron system to electromagnetic fields with sharp
spatial variations is strongly dependent on quantum electronic properties, even
in ambient conditions, but difficult to access experimentally. We use
propagating graphene plasmons, together with an engineered dielectric-metallic
environment, to probe the graphene electron liquid and unveil its detailed
electronic response at short wavelengths.The near-field imaging experiments
reveal a parameter-free match with the full theoretical quantum description of
the massless Dirac electron gas, in which we identify three types of quantum
effects as keys to understanding the experimental response of graphene to
short-ranged terahertz electric fields. The first type is of single-particle
nature and is related to shape deformations of the Fermi surface during a
plasmon oscillations. The second and third types are a many-body effect
controlled by the inertia and compressibility of the interacting electron
liquid in graphene. We demonstrate how, in principle, our experimental approach
can determine the full spatiotemporal response of an electron system.Comment: 8 pages, 4 figure
Loneliness and the Emotional Experience of Absence
In this paper, we develop an analysis of the structure and content of loneliness. We argue that this is an emotion of absence-an affective state in which certain social goods are regarded as out of reach for the subject of experience. By surveying the range of social goods that appear to be missing from the lonely person's perspective, we see what it is that can make this emotional condition so subjectively awful for those who undergo it, including the profound sense of being unable to realise oneself, in collaboration with others
Thermodynamic properties of the electron gas in multilayer graphene in the presence of a perpendicular magnetic field
Comment on "Chiral tunneling in trilayer graphene" [Appl. Phys. Lett. 100, 163102 (2012)]
Spin and valley polarization of plasmons in silicene due to external fields
The electronic properties of the novel two dimensional (2D) material silicene
are strongly influenced by the application of a perpendicular electric field
and of an exchange field due to adatoms positioned on the surface or
a ferromagnetic substrate. Within the random phase approximation, we
investigate how electron-electron interactions are affected by these fields and
present analytical and numerical results for the dispersion of plasmons, their
lifetime, and their oscillator strength. We find that the combination of the
fields and brings a spin and valley texture to the particle-hole
excitation spectrum and allows the formation of spin- and valley-polarized
plasmons. When the Fermi level lies in the gap of one spin in one valley, the
intraband region of the corresponding spectrum disappears. For zero and
finite the spin symmetry is broken and spin polarization is possible. The
lifetime and oscillator strength of the plasmons are shown to depend strongly
on the number of spin and valley type electrons that form the electron-hole
pairs
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