Electric field tunable unconventional superconductivity in alternating twist magic-angle trilayer graphene

Abstract

We construct a van der Waals heterostructure consisting of three graphene layers stacked with alternating twisting angles $\pm \theta$. At the average twist angle $\theta \sim 1.56^{\circ }$, a theoretically predicted magic angle for the formation of flat electron bands, narrow conduction and valence moiré bands appear together with a linearly dispersing Dirac band. Upon doping the half-filled moiré valence band with holes, or the half-filled moiré conduction band with electrons, displacement field tunable superconductivity emerges, reaching a maximum critical temperature of 2.1 K at optimal doping and displacement field. By tuning the doping level and displacement fields, we find that superconducting regimes occur in conjunction with flavour polarization of moiré bands bounded by a van Hove singularity (vHS) at high displacement fields. This experimental observation is found to be inconsistent with a weak coupling description, suggesting that the observed moiré superconductivity has an unconventional nature.

35 pages, 14 figures. Supplementary materials added

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