Electron dynamics in strained graphene

TL;DR

This paper provides a theoretical framework for understanding how out-of-plane strain deformations in graphene influence charge distribution, electron transport, and valley polarization, revealing phenomena like sublattice symmetry breaking and resonant states.

Contribution

It introduces a continuum Dirac model combined with elasticity theory to analyze strain effects, highlighting charge localization, sublattice symmetry breaking, and valley filtering in deformed graphene.

Findings

Local charge accumulation favors one sublattice in deformed regions.

Resonant states emerge as discrete levels in band structure.

Extended deformations serve as effective valley filters.

Abstract

The paper presents a theoretical description of the effects of strain induced by out-of-plane deformations on charge distributions and transport on graphene. A review of a continuum model for electrons using the Dirac formalism is complemented with elasticity theory to represent strain fields. The resulting model is cast in terms of scalar and pseudo-magnetic fields that control electron dynamics. Two distinct geometries, a bubble, and a fold are chosen to represent the most commonly observed deformations in experimental settings. It is shown that local charge accumulation regions appear in deformed areas, with a peculiar charge distribution that favors the occupation of one sublattice only. This unique phenomenon that allows distinguishing each carbon atom in the unit cell, is the manifestation of a sublattice symmetry broken phase. For specific parameters, resonant states appear in localized charged regions, as shown by the emergence of discrete levels in band structure calculations. These findings are presented in terms of intuitive pictures that exploit analogies with confinement produced by square barriers. In addition, electron currents through strained regions are spatially separated into their valley components, making possible the manipulation of electrons with different valley indices. The degree of valley filtering (or polarization) for a specific system can be controlled by properly designing the strained area. The comparison between efficiencies of filters built with this type of geometries identifies extended deformations as better valley filters. A proposal for their experimental implementations as a component of devices and a discussion for potential observation of novel physics in strained structures are presented at the end of the article.