Pairing and Superconductivity in TMD Moire Materials

Transition metal dichalcogenide (TMD) bilayers are a new class of highly-tunable moire materials. I will discuss a remarkably simple and analytically-controlled model for how charge pairing and superconductivity could occur in twisted TMD homobilayers. When tuning twist angle, gate voltages, and distance to screening gates, we can predict when holes will pair up to form tightly-bound charge-2e excitations. When charge pairing occurs, a pair of holes are bound to a dipolar charge-transfer exciton, resulting in a composite "trimer" excitation, which lowers the total electrostatic repulsion. For small twist angles, the hole bandwidth is small and trimers crystallize into insulating generalized Wigner crystals at a sequence of commensurate charge fractions. For larger twist angles, itinerant holes and charge-2e trimers can interact resonantly, leading to unconventional superconductivity similar to superfluidity in an ultracold Fermi gas near Feshbach resonance.