Doping induced topological phase transition in WTe2*

WTe2 exibits diverse phenomena including non-saturating magnetoresistance in its bulk with predicted type-II Weyl semimetal electronic structure, superconductivity under hydrostatic pressure, quantum spin hall insulator (QSHI) in its monolayer limit, and superconductivity in the gated monolayer. In many of these transformations, the tuning of the carrier density plays an important role. We report two non-monotonic changes in the electronic structure of WTe2 upon in-situ electron doping, realizing occupation near the chemical potential as a pathway for tuning structure and behavior of 2D materials. The first phase transition is understood in terms of the extra charge inducing a shear mode that triggers the recombination of the Weyl points, lifting the topological nature of the bands. This topological switching behavior is relevant for gate-controlled topological transistors or for producing lateral interfaces within a single material host via differential doping. The second phase transition is most consistent with a electrons in a 2D K-overlayer hybridizing with the WTe2 host, broadly relevant to understanding interactions with metallic contacts in devices constructed from 2D materials.