Direct measurements of diamagnetism in few-layer van der Waals superconductors*

Thermodynamic properties of few-layer van der Waals superconductors are not well characterized, due to the small volume of the exfoliated devices. Here, we report direct measurement of the diamagnetism of few-layer NbSe2 and ionic gated MoS2 devices. By utilizing a scanning SQUID susceptometer, we report the temperature, magnetic field, and frequency dependence of the susceptibility of the superconductor. We observe signatures suggestive of a broadened vortex binding unbinding transition, and discuss the relation of this transition to the Berenzinskii-Kosterlitz-Thouless (BKT) transition. We report efforts to extract superconducting parameters from the temperature dependence of the magnetic response.