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

TL;DR

This study demonstrates that alternating twist magic-angle trilayer graphene exhibits tunable unconventional superconductivity at a specific magic angle, with superconducting properties controlled by doping and displacement fields, and suggests a non-weak coupling mechanism.

Contribution

The paper reports the experimental realization of superconductivity in alternating twist trilayer graphene and reveals its unconventional nature, expanding understanding of moiré superconductor systems.

Findings

Superconductivity reaches 2.1 K at optimal doping and displacement field.

Superconducting regimes are associated with flavor polarization and van Hove singularities.

The observed superconductivity is inconsistent with weak coupling theories.

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 moir\'e bands appear together with a linearly dispersing Dirac band. Upon doping the half-filled moir\'e valence band with holes, or the half-filled moir\'e 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 moir\'e 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 moir\'e superconductivity has an unconventional nature.