Tunable extra Dirac points in one-dimensional graphene superlattice induced by periodic ferroelectric domains*

In this work, we investigate the transport signature of one-dimensional superlattice (SL) in monolayer graphene induced by pre-patterned periodic domains in an interfacial ferroelectric bottom layer. We work with 50 nm single crystaline ferroelectric Pb(Zr,Ti)O₃ (PZT) films deposited on (La,Sr)MnO₃ buffered SrTiO₃ substrates, and create periodic polarization up (P_up) and down (P_down) stripe domains on PZT using conductive atomic force microscopy. The domain periodicity varies from 200 nm to 300 nm, and the number of periods changes from 60 to 100. We then transfer hBN-graphene stacks onto the pre-patterned domains and fabricate them into top-gated field-effect devices. The difference in carrier density between the two polarization regions reaches around 3×10¹³ cm^-2 at 2 K due to the pyroelectric effect. We observe extra Dirac points in R(V_g) by applying voltage to the hBN top gate, which is attributed to the SL modification of the band structure. We discuss the effects of the SL period and the width ratio between the P_up and P_down domains on the position of the extra Dirac points, and the magnetotransport properties of these SLs.