Research

Two-dimensional (2D) materials display an impressive set of electronic and optical properties. Most notably, they can serve as semimetals with exceptional charge carrier mobility and direct band-gap emitters offering high quantum yields. For these reasons, they are now actively explored as a new material platform for next-generation low-dimensional electronics and optoelectronics. Fundamentally, thanks to the reduced available states as compared with their 3D counterparts, they provide an exciting playground for the study of quantum and correlated electron physics.

Given the fact that the state-of-the-art optical nano-resonators are capable of providing an on-demand electromagnetic-field distribution with nanometer resolution, here we aim to employ optical nano-resonators as a tool to probe, study, and control the quantum properties of 2D materials. 2D materials are typically studied in the far field with advanced optical microscopes and imaging systems. However, important optical signatures never make it to the far field and can only be accessed by placing nanoresonators in very close proximity to these materials. When nano-resonators are optically coupled to a material of interest, they can selectively interact with desired quantum states, break selection rules, and employ the Purcell effect to enhance signal radiated to the far field. 

Believe it or not, the miniaturization process for optics has gone much behind electronics in the past one hundred years.  Until recently, thanks to the rapid development of the emerging field called metasurfaces, we now foresee an unprecedented opportunity to match the dimensions of functional optical elements again with that of nano /micro-electronics. This opens up exciting avenues to co-engineer and merge the optical and electronic functional layers into one, and create novel concepts in optoelectronic device designs.

Exemplified by photonic crystals, the similarity between wave optics and quantum mechanics has inspired optics researchers to borrow concepts from solid-state physics in the past few decades. For a single optical nano-resonator with cylindrical/spherical symmetry, Mie-solutions are the eigenmodes of the resonator. The structure of such a solution also shares considerable similarities with the wave functions of a Hydrogen atom. However, when optical nano-resonators are arranged into an array, their non-Hermitian nature will lead to critical radiative coupling between neighboring nano-resonators, creating photonic bands beyond the conventional chemical bonding model. The additionally created photonic bands offer an extra degree of freedom to interact with incident light fields, and therefore play an important role in better controlling the wavefronts.  However, such an optical crosstalk also induces intrinsic complexities in estimating the response of a spatially variant nano-resonator array. How to smartly harness this optical coupling determines the performance of many designed nanophotonic devices.

Starting from the 1970s, great efforts have been made in the community of optics to miniaturize bulky optical devices. This progress accelerated significantly over the last decade due to the emerging field of metasurfaces. These planar nanophotonic devices, made from judiciously engineered, subwavelength-thick optical nano-resonators, are capable of controlling the emission, propagation, and absorption of the light fields at the nanoscale, and therefore have the potential to revolutionize the design of optical elements with versatile and on-demand flat optics.