  In transition metal dichalcogenides, defects have been found to play an
important role, affecting doping, spin-valley relaxation dynamics, and
assisting in proximity effects of spin-orbit coupling. Here, we study localized
states in $\mathrm{WS}_2$ and how they affect tunneling through van der Waals
heterostructures of h-BN/graphene/$\mathrm{WS}_2$/metal. The obtained
conductance maps as a function of bias and gate voltage reveal single-electron
transistor behavior (Coulomb blockade) with a rich set of transport features
including excited states and negative differential resistance regimes. Applying
a perpendicular magnetic field, we observe a shift in the energies of the
quantum levels and information about the orbital magnetic moment of the
localized states is extracted.
