Ben Foutty: Mapping topology and Hofstadter subband phase transitions in twisted WSe2 homobilayers

"Mapping topology and Hofstadter subband phase transitions in twisted WSe2 homobilayers"

Abstract: Semiconductor moire superlattices have been shown to host a wide array of interaction-driven ground states. However, twisted homobilayers have been difficult to study in the limit of large moire wavelength, where interactions are most dominant. In this talk, I will discuss recent local electronic compressibility measurements of twisted bilayer WSe2 (tWSe2) at small twist angles. We demonstrate multiple topological bands which host a series of Chern insulators at zero magnetic field near a ‘magic angle’ around 1.23o which are highly sensitive to locally applied electric fields. Away from zero magnetic field, the long moire wavelength in our platform enables the study of Hofstadter subbands as a significant fraction of flux per moire unit cell is achievable with laboratory scale magnetic fields. The interplay of valley-contrasting Hofstadter spectra and large Zeeman coupling in transition metal dichalcogenides leads to a cascade of interaction-driven electronic phase transitions. These measurements establish tWSe2 as a tunable platform for strongly correlated topological phases. Additionally, they give insight into how to deterministically pursue and stabilize electronic behavior of interest in a system with numerous tuning knobs.