Vibrations of Correlated Electrons and Spins

Oscillations can reveal secrets of nature, from the vibrational signature of a chemical bond to the gravitational wave recording the final waltz of two black holes. Here, we aim to understand 2D quantum phases of electrons and spins from their coherent oscillations. We apply pump-probe spectroscopy to 2D materials and interfaces where increasing number of ordered electron and spin phases have been discovered. In the first example, we probe coherent oscillation of ordered spins, i.e., spin waves, in the 2D layered magnetic semiconductor, CrSBr with intralayer ferromagnetic and interlayer antiferromagnetic order and with a semiconducting bandgap at ~ 1.5 eV. The presence of both semiconducting and magnetic properties led to our discovery of coupling between interlayer electronic hybridization to magnetic order. We take advantage of this to show the strong coupling of excitons to coherent magnons, opening the door to optically accessible spin information and quantum interconnects. In the second example, we take advantage of recently discovered band flattening at transition metal dichalcogenides (TMDs) moiré interfaces. In these systems, the much-reduced electron kinetic energy (bandwidth) results in the dominance of many-body and on-site Coulomb repulsion and the formation of ordered phases of electrons. We show the formation of ordered electronic phases from excitonic sensing at the WSe₂/WS₂ moiré interface. We successfully obtained collective oscillation frequencies represent the first quantitative probes of the many body potential energy landscape for 2D electron ordering.