Quasiparticle and superfluid dynamics in Magic-Angle Graphene

Abstract

Magic-Angle Twisted Bilayer Graphene (MATBG) shows a wide range of correlated phases which are electrostatically tunable. Despite a growing knowledge of the material, there is yet no consensus on the microscopic mechanisms driving its superconducting phase. A major obstacle to progress in this direction is that key thermodynamic properties, such as specific heat, electron-phonon coupling and superfluid stiffness, are challenging to measure due to the 2D nature of the material and its relatively low energy scales. Here, we use a gate-defined, radio frequency-biased, Josephson junction to probe the electronic dynamics of MATBG. We demonstrate evidence for two processes determining the low-frequency dynamics across the phase diagram: thermalization of electronic quasiparticles through phonon scattering and inductive response of the superconducting condensate. A phenomenological approach allows us to relate the experimentally observed dynamics to several thermodynamic properties of MATBG, including electron-phonon coupling and superfluid stiffness. Our findings support anisotropic or nodal superconductivity in MATBG and demonstrate a broadly applicable method for studying properties of 2D materials with out-of-equilibrium nanodevice dynamics.