Tuning superconductivity in twisted bilayer graphene

Abstract: Superconducting and correlating insulating states have recently been observed in twisted bilayer graphene (tBLG) with twist angle very near 1.1$^{\circ}$. At this angle, an isolated flat band emerges in which strong electron correlations dominate at low carrier density. Here, we demonstrate that these states can be manipulated by controlling the available degrees of freedom of this system, including interlayer electrical bias and interlayer electronic coupling. In particular, we demonstrate the ability to induce superconductivity in a device with twist angle larger than 1.1$^{\circ}$ --- in which correlated phases are otherwise absent --- by varying the interlayer spacing with hydrostatic pressure. Our devices also feature very low disorder, revealing new details about the superconducting phase diagram and its relationship to the nearby insulator. Our work demonstrates tBLG to be a uniquely flexible platform for exploring novel correlated states.