Optical Spectroscopy of Two-Dimensional Superatomic Semiconductors and Magnetic Materials

Since the first discovery of atomically thin sheets of carbon, two-dimensional (2D) materials have captured the interest from scientific community to expand the understanding in fundamental physics and chemistry at low dimensional systems. With extraordinary phenomena only possible at atomically thin limits, there has been high demand to reveal new and unique 2D materials and manipulate their structures and properties. Structural tunability of superatomic solids motivates us to control dimentionality of the materials and construct layered structures which could be exfoliated to 2D materials. The layered crystal [Co6Se8(PEt2phen)6][C60]5 can be used as a template to create a 2D C60-based material with an optical gap in mid-infrared. Re6Se8Cl2 and Mo6S3Br6, are presented as the first examples of covalently linked 2D superatomic solids built from nanoscale building blocks with hierarchical structures and semiconducting properties. We further demonstrate the emergence of hierarchical coherent phonons in a 2D superatomic semiconductor Re6Se8Cl2. Lastly, we explore complex magnetic phases in 2D ferromagnetic semiconductor CrSBr using second harmonic generation and Raman spectroscopy. 2D superatomic semiconductors and 2D magnetic materials provide additional sets of design principles to manipulate structural, electronic, phononic, and magnetic properties at the atomically thin limits. These materials hold promises as model systems to study fundamental physical principles as well as platform for applications with phonon engineering and magnetic optoelectronic devices.