Data for Visualizing electrostatic gating effects in two-dimensional heterostructures

Abstract: The ability to directly monitor the states of electrons in modern field-effect devices, for example imaging local changes in the electrical potential, Fermi level and band structure as a gate voltage is applied, could transform understanding of the device physics and function. Here we show that submicrometre angle-resolved photoemission spectroscopy1–3 (-ARPES) applied to two-dimensional van der Waals heterostructures4 affords this ability. In two-terminal graphene devices we observe a shift of the Fermi level across the Dirac point, with no detectable change in the dispersion, as a gate voltage is applied. In two-dimensional semiconductor devices we see the conduction band edge appear as electrons accumulate, thereby firmly establishing its energy and momentum. In the case of monolayer WSe2 we observe that the band gap is renormalized downwards by several hundred meV, approaching the exciton energy, as the electrostatic doping increases. Both optical spectroscopy and -ARPES can be carried out on a single device, allowing definitive studies of the relationship between gate-controlled electronic and optical properties. The technique provides a powerful new means to study not only fundamental semiconductor physics but also intriguing phenomena such as topological transitions5 and many-body spectral reconstructions under electrical control.