Fig. 1: Continuously tunable phase patterning in a van der Waals heterostructure.
From: Beam steering at the nanosecond time scale with an atomically thin reflector
a Schematic of our approach: patterned electrostatic doping of atomically thin transition metal dichalcogenides (TMDs) allows for spatial control of the exciton resonance (inset). Thus, a continuously tunable phase profile is imparted on the reflected wavefront, enabling wide-ranging possibilities for beam control. b Schematic of SG-FET structure. Since the bottom gate only covers part of the device, the phase can be tuned independently in the two sides. The phase discontinuity in the reflected wavefront causes the two halves to constructively interfere at an angle in the far field. Inset: zoomed-in optical microscope image of the device, with gate edge indicated by white dashed line. c Representative reflection spectrum (orange) from left side of gate edge in intrinsic regime (VBG = 0 V and VTG = 0.5 V), with asymmetric resonance fit (black), which allows for extracting the phase (red). d, e Gate dependence of λleft and λright, respectively (locations indicated by circles in inset of b). The exciton resonance blue-shifts upon electrostatic doping. While λleft depends on 8VTG+ VBG, λright is largely independent of VBG. The intrinsic regime appears at an offset of VTG = 0.5 V, likely due to charge collection at the top gate. The small voltage range of the intrinsic regime suggests some doping via in-gap states. f Reflection spectra from left (orange) and right (blue) side of gate edge at different gate voltage combinations shown as correspondingly colored crosses in g. Dashed gray line indicates λ0 = 755.6 nm. g Gate dependence of phase difference Δϕ between the right and left side at λ0 = 755.6 nm, computed from fits as in (c). A tunable Δϕ-range of 42° is achieved. Large positive Δϕ is achieved when λleft < λ0 < λright (blue cross), while large negative Δϕ is achieved when λright < λ0 < λleft (green). Δϕ is closer to zero when either both sides are doped (λleft, λright < λ0; yellow) or both are intrinsic (λ0 < λleft, λright; red).
