In situ Raman spectroscopy across superconducting transition of liquid-gated MoS2

Semiconducting group-VI-B transition metal dichalcogenides (TMDs) with the triangular prism crystal structure exhibit unique features. A particularly striking recent example is the observation of an Ising superconducting transition at high carrier densities induced through the field effect in an electric double layer transistor (EDLT). So far, this phenomenon has been accounted for by assuming that the original triangular prismatic bulk crystal structure is unaffected by the heavy doping. However, this assumption has not been verified so far, even though other crystal phases of these layered materials were shown to host Ising superconductivity as well. Here, we provide experimental evidence that the initial triangular prismatic crystal structure of the MoS2, which serves here as a representative member of the TMD family, is not altered during operation of the EDLT even when the carrier density is large enough to induce the superconducting transition. The latter is monitored via transport measurements, while the crystal structure is simultaneously examined in situ with micro-Raman spectroscopy at low temperature.