Superfluid and Quasiparticle Dynamics of Magic-Angle Twisted Bilayer Graphene II

Magic-Angle Twisted Bilayer Graphene shows a wide range of correlated phases to which it can be tuned electrostatically. Despite a growing knowledge of the material, there is yet no consensus on the microscopic mechanisms driving these phases, in particular superconductivity.

We analyze the properties of MATBG measured with gate-defined, radio frequency-biased, Josephson junctions. We bias our junction with both DC and AC current and observe a frequency-dependent drift in the retrapping and switching critical currents of the hysteretic current-voltage characteristic. The frequency scales for the retrapping and switching contain information about quasiparticle specific heat, electron-phonon coupling as well as superfluid stiffness. Changing the junction gate voltage allows us to probe these properties across the phase diagram of MATBG. The results give direct evidence for large electron-phonon coupling in the flat bands of MATBG but favor strongly anisotropic or nodal pairing.