Characterizing Spatial Variation of Uniaxial Strain in Monolayer Graphene by Polarized Raman Spectroscopy

Moiré quantum matter has emerged as a new platform for investigating strongly correlated physics. The band structure of twisted bilayer graphene (TBG), which exhibits both superconductivity and orbital ferromagnetism at specific twist angles, is strong sensitivity to heterostrain. Though the twist angle can be approximately set via mechanical rotation during stacking, there is currently no means of controlling heterostrain. Because the twist and strain parameters of most TBG devices cannot be tuned after stacking, these devices are plagued by limited experimental repeatability.

One probable method of reproducibly creating heterostrain in TBG is by stacking an intentionally strained monolayer graphene (MLG) with an unstrained MLG. We describe a method to extract absolute values of uniaxial strain to within 0.01% with sub-micron spatial resolution over large area exfoliated and intentionally strained MLG flakes using Raman spectroscopy and determine an upper bound on the sub-micron spatial variation of uniaxial strain.