Independent Superconductors and Correlated Insulators in Twisted Bilayer Graphene

Twisted bilayer graphene (tBLG) is a moiré heterostructure containing two sheets of graphene stacked on top of each other. At twist angle of θ ≈ 1.1°, theory predicts the formation of a nearly-flat electronic band in tBLG and experiments have successfully shown correlated insulating and superconducting states when the flat band is partially filled. The proximity of superconductivity to correlated insulators suggested a close relationship between these states. In this talk, I will describe our “cut-and-stack” technique to fabricate highly homogeneous tBLG devices, and survey our transport measurements of the intrinsic properties of these devices with a focus on superconductivity. Through transport measurements from five tBLG devices, we show that superconductivity can appear even in the absence of correlated insulating states. Although both superconductivity and correlated insulating behavior are strongest near the flat-band condition, superconductivity survives to larger detuning of the angle.