Strain-induced valley polarization in monolayer graphene*

We use nearly strain-free PECVD-grown graphene [1] to induce controllable strain and pseudo-magnetic fields by nanoscale strain engineering [2]. By placing strain-free monolayer graphene and monolayer h-BN on architected silicon nanostructures fabricated by electron-beam lithography, we demonstrate broken global inversion symmetry and provide experimental evidences for strain-induced giant pseudo-magnetic fields and valley polarization by scanning tunneling spectroscopic studies at room temperature. Here we report transport properties of monolayer graphene devices using both DC and low-frequency lock-in techniques. Non-local resistance and non-local magnetoresistance are measured on both strained and unstrained graphene devices to confirm the strain-induced valley Hall effect. We further use different circularly-polarized light to enhance or suppress the valley Hall effect via selectively exciting electrons in the corresponding valley. Our approach thus paves a new way to realize scalable graphene-based valleytronics.
1. D. A. Boyd et al. Nat. Comm. 6, 6620 (2015).
2. N.-C. Yeh et al. Acta Mech. Sin. 32, 497 (2016).