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 (1D) superlattice (SL) in monolayer graphene induced by pre-patterned periodic domains in a ferroelectric bottom gate. We work with 50 nm single-crystalline 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 30 to 50. 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 a 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 1D SLs.