Giant pseudo-magnetic fields and valley polarization by nanoscale strain engineering of graphene

We report the use of nearly strain-free PECVD-grown graphene¹ to induce controllable strain and pseudo-magnetic fields (B_S) by placing graphene on synthesized tetrahedron nanocrystals (55nm laterally and 45nm in height).² The nanocrystals were spin-coated on a Si substrates and then covered by a monolayer of h-BN followed by a monolayer of graphene. Scanning tunneling spectroscopic studies revealed giant B_S values up to ~25000T in isolated tetrahedrons. In contrast, the maximum B_S value became reduced to ~600T along the ridge of two correlated tetrahedrons. The effect of pseudo-magnetic field-induced local time-reversal symmetry breaking on valley polarization was confirmed by the alternating presence and absence of zeroth Landau level at two inequivalent sublattice sites.³ These empirical results were compared with Molecular Dynamics (MD) simulations for the magnitude and spatial distribution of strain-induced pseudo-magnetic fields, and the consistency ensured that properly designed arrays of nanostructures could induce the desirable B_S values and spatial distributions to yield realistic valleytronic devices.

1. D. A. Boyd et al. Nat. Comm. 6, 6620 (2015).
2. N.-C. Yeh et al. Acta Mech. Sin. 32, 497 (2016).
3. N.-C. Yeh et al. Surf. Sci. 605, 1649 (2011).