The existence of two-inequivalent valleys in the band structure of graphene
has motivated the search of mechanisms that allow their separation and control
for potential device applications. Among the several schemes proposed in the
literature, strain-induced out-of-plane deformations (occurring naturally or
intentionally designed in graphene samples), ranks among the best candidates to
produce separation of valley currents. Because valley filtering properties in
these structures is, however, highly dependent on the type of deformation and
setups considered, it is important to identify the relevant factors determining
optimal operation and detection of valley currents. In this paper we present a
comprehensive comparison of two typical deformations commonly found in graphene
samples: local centro-symmetric bubbles and extended folds/wrinkles. Using the
Dirac model for graphene and the second-order Born approximation we
characterize the scattering properties of the bubble deformation, while
numerical transmission matrix methods are used for the fold-like deformations.
In both cases, we obtain the dependence of valley polarization on the
geometrical parameters of deformations, and discuss their possible experimental
realizations. Our study reveals that extended deformations act as better valley
filters in broader energy ranges and present more robust features against
variations of geometrical parameters and incident current directions.Comment: 17 pages, 16 figures, figures were adjusted, added a few references,
accepted by PR
