Coulomb screening and thermodynamic measurements in magic-angle twisted trilayer graphene (2108.03338v2)

Abstract: The discovery of magic-angle twisted trilayer graphene (tTLG) adds a new twist to the family of graphene moir\'e. The additional graphene layer unlocks a series of intriguing properties in the superconducting phase, such as the violation of Pauli limit and re-entrant superconductivity at large in-plane magnetic field. In this work, we integrate magic-angle tTLG into a double-layer structure to study the superconducting phase. Utilizing proximity screening from the adjacent metallic layer, we examine the stability of the superconducting phase and demonstrate that Coulomb repulsion competes against the mechanism underlying Cooper pairing. Furthermore, we use a combination of transport and thermodynamic measurements to probe the isospin order, which points towards a spin-polarized and valley-unpolarized isospin configuration at half moir\'e filling, and for the nearby fermi surface. 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.