Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Seeing many-body effects in single- and few-layer graphene: Observation
  of two-dimensional saddle-point excitons   Significant excitonic effects were observed in graphene by measuring its
optical conductivity in a broad spectral range including the two-dimensional
{\pi}-band saddle-point singularities in the electronic structure. The strong
electron-hole interactions manifest themselves in an asymmetric resonance
peaked at 4.62 eV, which is red-shifted by nearly 600 meV from the value
predicted by ab-initio GW calculations for the band-to-band transitions. The
observed excitonic resonance is explained within a phenomenological model as a
Fano interference of a strongly coupled excitonic state and a band continuum.
Our experiment also showed a weak dependence of the excitonic resonance in
few-layer graphene on layer thickness. This result reflects the effective
cancellation of the increasingly screened repulsive electron-electron (e-e) and
attractive electron-hole (e-h) interactions.

21
The categories of this paper are: adap-org
25
The categories of this paper are: patt-sol
14
The categories of this paper are: math-ph
5
The categories of this paper are: gr-qc
18
The categories of this paper are: econ
12
The categories of this paper are: nucl-th
36
The categories of this paper are: cmp-lg
6
The categories of this paper are: astro-ph
2
The categories of this paper are: math
37
The categories of this paper are: supr-con
1
The categories of this paper are: cs
23
The categories of this paper are: solv-int
9
The categories of this paper are: nlin
24
The categories of this paper are: dg-ga
35
The categories of this paper are: mtrl-th
30
The categories of this paper are: q-alg