Topological excitonic insulator monolayer WTe2 and the negative compressibility surface of MoS2

Two-dimensional materials can exhibit extraordinary and unique electronic properties due to their reduced dimensionality. The electronic properties of monolayer tungsten ditelluride (WTe2) and the quasi-two-dimensional surface of molybdenum disulphide (MoS2) were studied. In monolayer WTe2, the ‘smoking-gun’ signature of a unique low temperature insulating state known as an excitonic insulator was discovered. In MoS2, the counterintuitive movement of the electronic energy of the surface of the material with the addition of charges known as negative electronic compressibility was observed. These discoveries inform the design of next-generation two-dimensional electronic devices with engineered electronic properties.