Isospin order in superconducting magic-angle twisted trilayer graphene

The discovery of magic-angle twisted trilayer graphene unlocks various properties of the superconducting phase, such as violation of the Pauli limit and re-entrant superconductivity at large in-plane magnetic fields 1 – 3 . Here we integrate magic-angle twisted trilayer graphene into a double-layer structure to study the superconducting phase. Using proximity screening from the adjacent metallic layer, we examine the stability of superconductivity and demonstrate that Coulomb repulsion competes with the mechanism underlying Cooper pairing. Furthermore, we use a combination of transport and thermodynamic measurements to probe the ground-state order 4 – 6 , which points towards a spin-polarized and valley-unpolarized configuration at half moiré filling and for the Fermi surface at doping levels close to that point. Our findings provide important constraints for theoretical models aiming to understand the nature of superconductivity. A possible scenario is that electron–phonon coupling stabilizes a superconducting phase with a spin-triplet, valley-singlet order parameter 7 – 13 .