Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Second-order Dirac equation of graphene electrons in an electromagnetic
  field and their novel spin   The second-order Dirac equation (DE) and its velocity operator of graphene
electrons in an electromagnetic field are obtained according to tight-binding
k.p method. With extra terms included, they demonstrate the motion of graphene
electrons more completely through a more complete Ehrenfest theorem and present
finer properties of graphene electrons. Eigen-energy given by the second-order
DE for field-free graphene indicates that extra terms may affect the trembling
motion of graphene electrons. For graphene in a magnetic field, eigen-energy
given by the second-order DE suggests that graphene electrons have a new kind
of spin of a boson other than true electronic spin and pseudo-spin of Dirac
particles, which will modify graphene properties such as the optical spectra.

10
The categories of this paper are: q-bio
1
The categories of this paper are: cs
3
The categories of this paper are: physics
6
The categories of this paper are: astro-ph
8
The categories of this paper are: hep-ex
16
The categories of this paper are: stat
20
The categories of this paper are: acc-phys
18
The categories of this paper are: econ
19
The categories of this paper are: eess
14
The categories of this paper are: math-ph
35
The categories of this paper are: mtrl-th
33
The categories of this paper are: plasm-ph
36
The categories of this paper are: cmp-lg
29
The categories of this paper are: funct-an
0
The categories of this paper are: hep-ph
23
The categories of this paper are: solv-int