Designing the Gauge Potential for Dirac Fermions in Nanoscale Strain-Engineered Graphene*

Non-trivial strain in graphene is known to induce pseudomagnetic fields ($B_{s})$ that can significantly affect the properties of Dirac fermions. We have employed nearly strain-free PECVD-grown graphene$^{1}$ to induce controllable strain and gauge potentials by placing graphene on substrates with either lithographically prepared nanostructures or synthesized nanocrystals.$^{2}$ Here we report the use of Pd tetrahedron nanocrystals (55nm laterally and 45nm in height) for strain-engineering of graphene. The nanocrystals were spin-coated on a Si substrates and then covered by a monolayer of h-BN followed by a monolayer of graphene. Comparison between the Raman 2D band of strained-graphene and that of as-grown graphene confirmed an increase of average strain in the former. Molecular dynamics simulations revealed alternating signs of $B_{s}$ with three-fold symmetry, and the maximum magnitude of $B_{s}$ was up to \textasciitilde 2000 T. These results will be compared with scanning tunneling spectroscopic studies for spatially varying $B_{s}$ and alternating presence and absence of the zero mode at two inequivalent sites of graphene due to local time-reversal symmetry breaking.$^{3}$ \newline [1] D. A. Boyd \textit{et al. Nat. Comm.} \textbf{6}, 6620 (2015). \newline [2] N.-C. Yeh \textit{et al. Acta Mech. Sin.} \textbf{32}, 497 (2016). \newline [3] N.-C. Yeh \textit{et al. Surf. Sci.} \textbf{605}, 1649 (2011).