Superfluid stiffness of twisted trilayer graphene

Twisted graphene is a paradigmatic example of how complex electronic behavior, including superconductivity, may emerge from a fundamentally simple system of Carbon atoms arranged in a Moiré lattice. Finite-frequency AC responses, as measured through microwave conductivity offer a new probe to investigate the emergent complexity of these systems. In this talk, I will describe our measurements of one such response, the superfluid stiffness, in magic angle twisted trilayer graphene (TTG) devices. Superfluid stiffness quantifies the phase rigidity of the superconducting condensate and serves as a direct probe of the superconducting order parameter. The variation of superfluid stiffness as a function of carrier density, temperature, and current bias reveals a nodal superconducting order that obeys Uemura's law and displays a robust non-linear Meissner effect within the entire superconducting dome. These observations, together with estimates of the Cooper pair coupling strength and the nodal velocity, suggest an "unconventional", possibly geometric, origin of superconductivity in TTG.