Fig. 1: The d.c. Stark effect of interlayer excitons.
From: Optical signatures of interlayer electron coherence in a bilayer semiconductor
a, A schematic of a dual-gated 2H-stacked MoS2 homobilayer (BL MoS2) encapsulated with hBN. Tuning of the top and bottom gates, composed of a few layers of graphene (FLG), allows independent control of the total electron density n and out-of-plane electric field Ez. Interlayer excitons (IXs), highly sensitive to Ez owing to their large dipole moments, are also depicted. b, A schematic of the electronic band structure near the K valleys (top) and \({K}^{{\prime} }\) valleys (bottom) showing the relevant excitonic levels, electron spin and corresponding AQNs of the electronic bands, which determine optical selection rules. Top and bottom layers are labelled as LT and LB, respectively. c, In the undoped case n = 0, the energies of interlayer excitons shift linearly with Ez (VBG = −1.15VTG − 1 V), as can be seen in the simple crossing of exciton branches in the measured reflectance map ΔR/R0 at T = 8 K. d, The system exhibits two well-separated branches at a finite Ez ≠ 0, becoming degenerate at Ez = 0, with doubled oscillator strength. e, The d.c. Stark effect for the doped sample with n ≈ 1.3 × 1012 cm−2 (VBG = −1.15VTG + 1.25 V), showing that the simple crossing in c turns into a stochastic avoided crossing (Fig. 2). f, The linecut at VTG = 0.50 V, corresponding to Ez = 0, displays a broad feature with reduced relative amplitude compared with the undoped case in d.
