Optical readout and control of correlated electron phases in 2D semiconductor moiré superlattices

Abstract

Ever since the isolation of the first single layer of a van der Waals material in 2004, the field of2D materials has been continuously accelerating. The ever-growing list of correlated electronic phenomena observed in 2D materials, and in particular 2D moiré systems, has created a sandbox for fundamental condensed matter research. Combined with the unique optoelectronic properties of the transition metal dichalcogenides (TMDs), we now have unprecedented access to correlated electronic phases with optical probes and optical controls. In this dissertation two main projects will be presented. First, Raman scattering experiments on WS2/WSe2 moiré heterobilayers have revealed two emergent scattering modes that are as of now unidentified. These Raman modes show evidence of coupling with the underlying correlated physics in the moiré system in addition numerous unusual and uncommon Raman signatures, including an anti-symmetric Raman tensor and a distinct excitation power dependence for the scattering cross section of the modes. Second, optical probes, and more importantly optical control, of the integer and fractional Chern insulator states in tMoTe2 will be presented. By leveraging the unique spin-valley-polarization coupling of the TMDs, we demonstrate the ability to deterministically choose the magnetization direction and thus sign of the Chern number for a domain encompassed by our optical pump. This represents the first step in optically controlling correlated electron phases in 2D materials rather than just optically probing them.