Device fabrication The MATBG devices were fabricated using a cut-and-stack technique. All flakes were first exfoliated on a Si/SiO2 (285 nm) substrate and later picked up using a polycarbonate (PC)/polydimethylsiloxane (PDMS) stamp. All of the layers were picked up at a temperature of T ≈ 100 °C. We used an atomic force microscope tip to cut the graphene to avoid strain during the pick-up process. The PC/PDMS stamp first picked up the top graphite layer, the top hBN and the first graphene layer. Before picking up the second graphene layer, we rotated the stage by an angle of θ = 1.1°. Finally, the stamp picked up the bottom hBN and bottom graphite gates. We dropped the finalized stack onto a Si/SiO2 substrate by melting the PC at T ≈ 180 °C. The resulting stack was etched into a Hall bar using a CHF3/O2 plasma and one-dimensional contacts were formed by evaporating Cr (5 nm)/Au (50 nm) (Supplementary Fig. 1b). We etched a narrow channel of width d ≈ 150 nm in the top gate using an O2 plasma. Before etching the top gate, the device was characterized in transport using a four-probe configuration at TL = 35 mK to identify the pair of contacts closest to the magic angle of θ = 1.1°. The junction was made between this pair of contacts.

Transport measurements Transport studies for the characterization of the two samples were carried out in a dilution refrigerator (BlueFors SD250) with a base temperature of 20 mK and a VTI cryostat (ICEOxford) with a base temperature of 1.55 K. Further transport measurements were performed in situ in the optical cryostat (Attodry 800, base temperature 6 K) used for the optoelectronic measurements. All transport measurements were performed using a standard low-frequency lock-in technique (Stanford Research SR860 amplifiers) with frequency f = 17.177 Hz.

Optoelectronic measurements We studied the optoelectronic response of the MATBG p–n junctions using standard d.c. and low-frequency a.c. transport measurements combined with scanning laser microscopy. All optoelectronic measurements were performed in an Attodry 800 cryostat with free-space optical access.