with time domain capacitance spectroscopy

Time domain capacitance spectroscopy (TDCS) probes the density of states in 2D systems without electrical contact. The technique generates a purely out-of-plane tunneling current and thus eliminates the effects of in-plane transport, maintaining sensitivity over a wide range of compressibility, from metallic to highly insulating states. We use TDCS to measure the density of states in electrostatically gated WTe₂ embedded in a vertical tunnel structure and observed an asymmetric and “hard” (with very low density of states out to the gap edge) gap pinned to the Fermi level. The gap occurs over a range of electron densities and thus does not appear related to WTe2 band structure but instead may arise from electron-electron interactions within the WTe₂ layer.