Current Research

We are developing optical devices that generate superfluorescence (SF) of quantum properties. SF is a highly desirable optical phenomenon that occurs when the light emitters synchronously behave under a single-mode electromagnetic field (Figure below, left). The quantum states of SF based on the cooperative effect are robust because it does not rely on fragile single emitters. The recent observations of SF in quasi-two-dimensional (2D) perovskite thin films and supper-lattices of perovskite nanocrystals have inspired us to engineer the output quantum properties of SF at room temperatures. This project is intended to control SF-lasing phase transitions in quasi-2D perovskite-incorporated distributed feedback (DFB) structures. We perform (1) time-resolved photoluminescence spectroscopy on ultrashort time scale to examine the dynamical characteristics of the SF emission from quasi-2D perovskite DFB cavities; (2) measurements of second-order correlation functions that can reveal the wavelength-dependent photon statistics of SF emission; (3) search for the non-classical photon states of SF such as displaced number or displaced squeezed states (Figure below, right) using homodyne detection tomography.    

Bose-Einstein condensation (BEC) is one of the macroscopic, emergent quantum pheonomena where the wavefunctions of gaseous atoms or bosonic quasiparticles start to overlap by lowering the temperature or by incresing the density of bosons. Exciton-polariton condensation is a successful solid-state analog of BEC, typically observed at standard cryogenic temperatures of only tens of Kelvin. The exciton-polariton BEC systems rely on light effective mass of exciton-polaritons trapped in micro- or nano-cavity structures. We make use of lattice plasmon polaritons that have even lighter effective mass than that of exciton-polaritons, and thus enable room-temperature BEC. Towards the realization of plasmonic BEC, we employ arrays of sodium (Na) nanoparticles (Figure below, left), which have much less optical losses in the near-infrared, compared to conventional plasmonic metals such as Au or Ag.  We identify lattice plasmon polariton modes by measuring the energy dispersion diagrams (Figure below, right). We also perform time-resolved photoluminescence and photon correlation spectroscopy in order to examine the dynamical properties of plasmonic BEC at room temperature.

 

In collaboration with 2DCC at Penn State University, we grow and fabricate twisted bilayer two-dimensional (2D) materials. We investigate their electronic and optical properties by means of low-frequency Raman scattering (Figure below), time-resolved photoluminescence, and photo correlation spectroscopy. In twisted bilayers of TMDs, the electronic flat bands appear at relatively small angles close to 0  and 60 degrees. Studying linear and nonlinear optical properties at these twist angles enables a great deal of understanding of the physics behind the singularities appearing at the magic angles. Importantly, stacking of two monolayers can generate so called Moire excitons with Moire patterns. Vertical stacking of TMDs homostructures and heterostructures with precise control of twist angles as well as ultra clean and large-area samples, thereby, would provide us with a great testbed to study a tailored interlayer coupling and their effect on the nonlinear optical properties.