Energy gaps, topological insulator state and zero-field quantum Hall effect in graphene by strain engineering

TL;DR

This paper demonstrates that strain engineering in graphene can induce strong gauge fields, creating topological insulator states and quantum Hall effects without external magnetic fields, and can open energy gaps in its electronic spectrum.

Contribution

It reveals how designed strain in graphene induces pseudo-magnetic fields and topological states, enabling quantum Hall effects and energy gap opening through strain engineering.

Findings

Strain induces gauge fields equivalent to magnetic fields exceeding 10 T.

Strain creates topological insulator states with edge conduction.

Strain can open significant energy gaps in graphene's spectrum.

Abstract

Among many remarkable qualities of graphene, its electronic properties attract particular interest due to a massless chiral character of charge carriers, which leads to such unusual phenomena as metallic conductivity in the limit of no carriers and the half-integer quantum Hall effect (QHE) observable even at room temperature [1-3]. Because graphene is only one atom thick, it is also amenable to external influences including mechanical deformation. The latter offers a tempting prospect of controlling graphene's properties by strain and, recently, several reports have examined graphene under uniaxial deformation [4-8]. Although the strain can induce additional Raman features [7,8], no significant changes in graphene's band structure have been either observed or expected for realistic strains of approx. 10% [9-11]. Here we show that a designed strain aligned along three main crystallographic directions induces strong gauge fields [12-14] that effectively act as a uniform magnetic field exceeding 10 T. For a finite doping, the quantizing field results in an insulating bulk and a pair of countercirculating edge states, similar to the case of a topological insulator [15-20]. We suggest realistic ways of creating this quantum state and observing the pseudo-magnetic QHE. We also show that strained superlattices can be used to open significant energy gaps in graphene's electronic spectrum.