"Coherent Oscillations of Correlated Electrons and Spins in 2D"

Xiaoyang Zhu, Columbia University

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 of doped moiré interfaces of transition metal dichalcogenides (TMDs), the much-reduced electron kinetic energy results in the dominance of Coulomb repulsion and the formation of ordered phases of electrons. We probe correlated electron crystals at the WS₂/WSe₂ moiré interface using excitonic sensing and successfully observed their collective oscillations. The oscillation frequencies of the electron crystals provide unprecedented insight into manybody potential landscape responsible for correlated electron ordering. In the second 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. 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.