Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Magnetism and correlations in fractionally filled degenerate shells of
  graphene quantum dots   When an electron is confined to a triangular atomic thick layer of graphene
[1-5] with zig-zag edges, its energy spectrum collapses to a shell of
degenerate states at the Fermi level (Dirac point) [6-9]. The degeneracy is
proportional to the edge size and can be made macroscopic. This opens up the
possibility to design a strongly correlated electronic system as a function of
fractional filling of the zero-energy shell, in analogy to the fractional
quantum Hall effect in a quasi-two-dimensional electron gas[10], but without
the need for a high magnetic field. In this work we show that electronic
correlations, beyond the Hubbard model[6,7] and mean-field density functional
theory (DFT) [7,8] play a crucial role in determining the nature of the ground
state and the excitation spectrum of triangular graphene quantum dots as a
function of dot size and filling fraction of the shell of zero-energy states.
The interactions are treated by a combination of DFT, tight-binding,
Hartree-Fock and configuration interaction methods (TB-HF-CI) and include all
scattering and exchange terms within second nearest neighbors as well as
interaction with metallic gate. We show that a half filled charge neutral shell
leads to full spin polarization of the island but this magnetic moment is
completely destroyed by the addition of a single electron, in analogy to the
effect of skyrmions on the quantum Hall ferromagnet [11-14] and spin
depolarization in electrostatically defined semiconductor quantum dots[15-18].
The depolarization of the ground state is predicted to result in blocking of
current through a graphene quantum dot due to spin blockade (SB) [18].

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The categories of this paper are: nlin
20
The categories of this paper are: acc-phys
13
The categories of this paper are: quant-ph
16
The categories of this paper are: stat
32
The categories of this paper are: atom-ph
6
The categories of this paper are: astro-ph
27
The categories of this paper are: comp-gas
34
The categories of this paper are: chem-ph
24
The categories of this paper are: dg-ga
36
The categories of this paper are: cmp-lg
29
The categories of this paper are: funct-an
5
The categories of this paper are: gr-qc
33
The categories of this paper are: plasm-ph
23
The categories of this paper are: solv-int
15
The categories of this paper are: nucl-ex
31
The categories of this paper are: ao-sci