Fig. 2: Helicity-dependent all-optical switching (HD-AOS) in a CrI₃(10 nm)/WSe₂(1L) heterostructure (sample 2).

a Schematic of the CrI₃/WSe₂ heterostructure. b Polar MOKE hysteresis loop with the Kerr signal integrated over the entire area of the flake (a_tot). The blue-red color scale represents a remanent Kerr signal ranging between magnetization orientations M_↑ and M_↓ obtained after saturation at +100 and −100 mT, respectively. c Remament monodomain states M_↑ and M_↓. The CrI₃ flake is partially overlapped with a WSe₂ monolayer, as indicated by the black dashed lines in the M_↓ domain state image. d Changes to the Kerr signal after optical pumping with circular polarization σ⁺ (shaded areas with dashed lines) and σ⁻ (transparent areas). N bunches of 10² pulses are applied. The Kerr signal is extracted from the domain structure images and is plotted for different parts of the flake: total area a_tot, CrI₃/WSe₂ only, and CrI₃ only. The measurements were performed at 35 K, with pump photon energy 1.67 eV, ~30 fs pulse duration and fluence F = 6.9 mJ/cm². The scale bar has 5 μm in length. e–g Schematic of the HD-AOS mechanism in the CrI₃/WSe₂ heterostructure for circular light polarizations σ⁻ (top panel) and σ⁺ (bottom panel). e Valley-dependent optical selection rules for monolayer WSe₂ and spin-dependent charge transfer between the WSe₂ and CrI₃ for the magnetic moment orientation of the CrI₃ pointing down. The optical helicity is defined by the wavevector pointing up, i.e., out of the surface plane and opposite to the CrI₃ magnetization direction. f Schematic of the spin-dependent charge transfer during demagnetization. g Outcome of the charge transfer on the AOS.