Fig. 1: Device response to AC and DC biases.

a Schematics of the device. The device is depicted by a cross section schematics. The vertical red dashed lines represent the central (C) region highlighted in (b). b Top-view simplified schematics with the gold contacts on the side, connected by a stripe of magic-angle twisted bilayer graphene (MATBG). The central region, of length 100 nm, is highlighted. The leads are superconducting (SC). c I/V characteristic of the junction at a density of  −2.8 × 10¹² cm⁻². In blue, solid line, a trace for increasing DC bias is shown. The dashed line represents the trace for decreasing bias. The green line is an extrapolation of the resistive part of the characteristic at 0 voltage. The green arrow highlights what is defined as excess current. d Switching (blue), retrapping (blue, dashed) and excess (green) currents as a function of density in the central region. The colors on the x-axis correspond to the filling of the band structure schematics shown in the inset. The upper part indicates whether the I/V characteristic shows a junction-like or bulk superconductor-like behavior. The black star, circle and square indicate, respectively, the densities at which is taken the data shown in (e, c, f). e I/V traces of the junction for AC bias of increasing frequency and fixed amplitude (red arrow) as a function of DC bias (horizontal axis). Solid lines show positive bias directions while dashed ones show negative directions. Curves are offset vertically for readability. f I/V traces at bias AC amplitude 1.4 nA and frequencies of 0.1 MHz and 20 MHz when the sample is tuned to all-bulk configuration see panel (d).