Large–Area Graphene Electrode for Ferroelectric Control of Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ Single Crystal

Large-area monolayer graphene is utilized as a metallic electrode for a ferroelectric single-crystal [Pb(Mg_1/3Nb_2/3)O₃]_m–[PbTiO₃]_n (PMNPT). Unlike conventional metal, whose properties remain unaffected by field-induced charge carriers, graphene's unique Dirac-cone band structure causes its carrier density to vary in response to the polarization state of contacting dielectrics. PMNPT capacitors with graphene-only and graphene/Cr/Au electrodes exhibit similar polarization versus electric-field curves. However, polarization switching in PMNPT and corresponding charge-state conversion in the graphene electrode are observed in the device configuration of a graphene-ferroelectric field-effect transistor. Systematic analysis of graphene's source-drain current variation reveals that experimental results align well with a theoretical model considering the intrinsically doped state in graphene and ferroelectric surface charge state in PMNPT. Furthermore, interfacial charge trapping discussed in many previous reports is not observed. These findings suggest that large-area monolayer graphene effectively serves as an electrode for ferroelectric single-crystal materials, irrespective of its atomically thin structure and ambipolar metallic nature.