Figure 2: Transient angle-resolved photoemission spectrum.
(a–h) tr-ARPES spectral intensity of irradiated graphene at peak field (delay time Δt=0) versus binding energy ω and momentum (k−K)x near the Dirac K point (vertical dashed lines) with Dirac point energy at −0.5 eV (horizontal dashed lines) on a momentum cut along the Γ−K−K′ direction. The colour scheme varies between 0 (white) and maximal (red) spectral intensity. The pump laser field is linearly polarized in panels (a) and (b), and circularly polarized in panels (c–h). The pump-pulse field strength Amax is varied between panels, with Amax values and laser polarizations as indicated. The driving frequency is 1.5 eV for all panels. The solid curves show the corresponding quasi-static Floquet band structures. The linearly polarized laser in panels (a) and (b) does not induce a band gap, whereas the circularly polarized laser in panels (c–h) first induces a band gap at the Dirac point and then leads to a sequence of level crossings (panels (d) and (f)) and gap closing (g) as the field strength is increased.
