Speaker: Ben Foutty, Stanford University

“Mapping topology and magnetic phase transitions in semiconductor moiré homobilayers”

Abstract

Semiconductor moiré superlattices host a wide array of correlated ground states arising from the interplay of strong electronic interactions and topological bands. In this talk, I will discuss local electronic compressibility measurements of twisted bilayer WSe2 (tWSe2) at small twist angles, where interactions are most prominent. We demonstrate multiple topological bands which host a series of Chern insulators at zero magnetic field near a ‘magic’ angle around 1.23 degrees. Using a locally applied electric field, we induce a topological quantum phase transition at one hole per moiré unit cell. Furthermore, by measuring in different spatial locations at a variety of twist angles, we characterize how the interacting ground states of the underlying honeycomb superlattice depend on the moiré wavelength. Finally, I will describe measurements at high magnetic field which reveal a cascade of magnetic transitions in the Hofstadter regime. These provide spin-resolved spectroscopic information about the Hofstadter and moiré bands, and they also strongly affect the realized insulating states. Our work establishes tWSe2 as a tunable platform for strongly correlated topological phases and clarifies how distinct experimental parameters dictate the nature of its ground states.