Extended Data Fig. 10: Exciton transport in 2L and other few-layer crystals at 4 K.

a Left: Schematic of the sample chip mounted on top of a small disk magnet with in-plane magnetization. Right: Optical microscope image of a 2L and a 3L crystal on the chip, which is glued onto the magnet such that the b–axis of the crystals aligns with the magnetization axis with an estimated precision of ± 10^∘. b PL emission of the 2L crystal when the chip is mounted together with the magnet (red), or directly on top of the cold finger of the cryostat (blue). The spectral shift of the PL indicates a field-induced transition of the magnetic order into an FM state⁶. c Integrated PL signal of the 2L crystal (B = 0, AFM) shows only a weak dependence on excitation energy. d Fluence dependence of Δσ²(t) measured along the b–axis of the 2L crystal for 30 (orange), 55 (yellow), 150 (light blue), 310 (dark blue) μJ/cm² in the AFM phase without the magnet at B=0. Dashed lines are guides to the eye. Inset: Δσ²(t) measured along a and b–axis in the FM phase on top of the magnet (B∥b) with 310 μJ/cm². e,f Analogous to a,b on a second sample. g PL emission of a 1L and a 4L crystal when the chip is mounted together with the magnet (red), or directly on top of the cold finger of the cryostat (blue), illustrating the lack of energy shifts, as expected⁵¹. h Measurement of Δσ²(t) along the b–axis of a 2L (blue) and a 4L (orange) crystal for 500 μJ/cm² on top of the magnet. The magnetic configuration is FM for the 2L crystal but because of the larger switching field required remains AFM for the 4L crystal. Dashed lines are guides to the eye. Inset: Magnified view of the negative transport measured in the 4L crystal. All data recorded at 4 K.