##
Quantum transport of non-interacting 2D Dirac
fermions

Shinsei Ryu**,
KITP**
__Abstract:__
We discuss the quantum transport of the 2D non-interacting
Dirac Hamiltonian, which, e.g., underlies theoretical
descriptions of graphene and a surface state of 3D Z_2
topological insulators. For a random scalar potential
type disorder, a Z_2 topological term is derived in
the non-linear sigma model encoding the physics of
Anderson localization in the symplectic symmetry class.
Unlike the Pruisken term (Chern integer) in the IQHE,
the Z_2 topological term cannot be expressed, in general,
as an integral of a local quantity, but
as a sign of the Pfaffian of a family of Dirac operators.
The Z_2 topological term has a significant effect on
the renomalization group flow of the conductance.