Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Rientrant metallicity in the Hubbard model: the case of honeycomb
  nanoribbons   Based on the Cluster Perturbation solution of the Hubbard hamiltonian for a
2-D honeycomb lattice we present quasiparticle band structures of nanoribbons
at half filling as a function of the on-site electron-electron repulsion. We
show that at moderate values of e-e interaction ribbons with armachair shaped
edges exhibit an unexpected semimetallic behavior, recovering the original
insulating character only at larger values of $U$.

11
The categories of this paper are: hep-lat
13
The categories of this paper are: quant-ph
0
The categories of this paper are: hep-ph
30
The categories of this paper are: q-alg
8
The categories of this paper are: hep-ex
33
The categories of this paper are: plasm-ph
3
The categories of this paper are: physics
15
The categories of this paper are: nucl-ex
7
The categories of this paper are: hep-th
23
The categories of this paper are: solv-int
19
The categories of this paper are: eess
29
The categories of this paper are: funct-an
20
The categories of this paper are: acc-phys
1
The categories of this paper are: cs
9
The categories of this paper are: nlin
22
The categories of this paper are: chao-dyn