1. Optical studies of two-dimensional materials
Two-dimensional (2D) nanostructures (graphene, boron nitride, and transition metal dichalcogenides) have received enormous attention in recent years. These 2D structural and electronic-confined systems are ideally suited for fundamental studies of their physical properties and for the fabrication of the optoelectronic nanodevices. In this proposal, micro-optical spectroscopies such as the infrared to vacuum ultraviolet reflectivity and transmission as well as inelastic light scattering are used to study the frequency- and temperature-dependent excitation spectra of monolayer graphene and monolayer MoS2, MoSe2, WS2, WSe2, and PtSe2.
2. Optical studies of strongly correlated electron systems
Complex oxide systems such as high temperature superconducting cuprates, manganese perovskites, hydrated sodium cobaltate, 4d (ruthenates) and 5d (iridium) transition metal oxides, and spinel lithium-based oxides have generated intense study over the past few years, in an effort, first, to clarify the relationship between the exotic phases of the materials; and, second, to elucidate the origin and the nature of the rich phenomena these compounds exhibit, such as unconventional superconductivity, colossal magnetoresistance, and charge and orbital ordering. It is now generally believed that a strong coupling among the charge, lattice, and spin degrees of freedom plays an essential role in the remarkable and varied properties of these strongly correlated systems. In this proposal, optical spectroscopies such as infrared reflectivity and inelastic light scattering are used to study the phase transitions and low- and high-frequency excitation spectra of novel oxides. Measurements performed while pressures or magnetic fields tuning the phase behavior of a material are particularly valuable for carefully exploring the evolution of exotic phase behavior in complex materials.