Superfluid and Quasiparticle Dynamics of Magic-Angle Twisted Bilayer Graphene

The phase diagram of Magic-Angle Twisted Bilayer Graphene contains several correlation-driven phases, including superconductivity. Their nature and driving mechanisms remain an outstanding open question. However, key thermodynamic properties, such as specific heat, electron-phonon coupling and superfluid stiffness, are extremely challenging to measure due to the 2D nature of the material and its relatively low energy scales.

We relate the dynamical properties of gate-defined Josephson junctions in MATBG to intrinsic properties of MATBG. 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 access to the electron-phonon coupling in the different phases of MATBG, while favoring a strongly anisotropic or nodal pairing.