Surface electron doping induced double gap opening in T _d-WTe₂

By using scanning tunneling microscopy, we investigated the electronic evolution of T d -WTe 2 via in-situ surface alkali K atoms deposition. The T d -WTe 2 surface is electron doped upon K deposition, and as the K coverage increases, two gaps are sequentially opened near Fermi energy, which probably indicates that two phase transitions concomitantly occur during electron doping. The two gaps both show a dome-like dependence on the K coverage. While the bigger gap shows no prominent dependence on the magnetic field, the smaller one can be well suppressed and thus possibly corresponds to the superconducting transition. This work indicates that T d -WTe 2 exhibits rich quantum states closely related to the carrier concentration.