Fig. 2: Valley polarized momentum-dark excitons.
a–d Energy and momentum resolved linecut along the Γ-K-M axis showing. At 0 ps time delay, the resonantly photoexcited bright exciton signal in the K valley shows an exciton-bound electron with negative dispersion, located 2.1 eV above the valence band (red). By 1 ps, in the same valley, this electron signal has relaxed to a lower energy state (blue). In the K′ valley, a weak electron population is observed at 0 ps at the photoexcitation energy of 2.1 eV (green). At 1 ps, it evolves into a much larger population that shows up at a lower energy (gray) (data around the exciton electron energy, 1.9–2.2 eV, were normalized at each k-vector). The corresponding energy distribution curves in (e) shows the energy difference between the bright exciton state which dominates at 0 ps and lower energy states that shows up at 1 ps. f Photoemission signals from electrons around the A exciton energy and from holes at the valence band during photoexcitation (0.1 ps). For the electrons, the ARPES signals were energy integrated between 1.9 and 2.2 eV and displayed in kx,ky momentum space. For the holes, we display the difference between negative time delay and after photoexcitation ARPES signals at the top of the valence band. The data were energy integrated over 100 meV (−0.05 to 0.05 eV) and a 120° rotating average around the center of the Γ valley was performed to clearly display the photoemission count loss corresponding to the presence of holes. g Photoemission signals from exciton bound electrons and holes around the A exciton energy at 1 ps using a similar analysis as in (f).
