STM Imaging of Generalized Wigner Crystal Phase Transitions in AB-stacked MoSe₂

Generalized Wigner crystal and Mott-insulating states form as a result of strong electronic correlations at fractional and integer fillings in twisted transition metal dichalcogenide (TMD) moirè heterostructures. Previous scanning tunneling microscopy (STM) studies have imaged correlated insulating states at integer (v = 1, 2, 3) and fractional fillings v < 1. Here we report STM measurements on a variety of generalized Wigner crystal states at fractional electron fillings 1 < v < 3 in homobilayer MoSe₂ stacked with a twist angle 2-3° off of AB stacking. We observe apparent metal-insulator transitions that occur as electron density is continuously tuned near select filling factors. Our STM images can be correlated with scanning tunneling spectroscopy, demonstrating a one-to-one correspondence between observed charge gaps and transitions in real-space charge distribution.