Research on light-matter interaction could help improve electronic and optoelectronic devices

October 10, 2018

Basic research highlights new multi-particle quantum physics in atomically thin semiconductors

By SCER Staff

An article published in Nature Communications By Sufei Shi, an assistant professor of chemical and biological engineering at Rensselaer, deepens our understanding of how light interacts with atomically thin semiconductors and creates unique excitonic complex particles, multiple electrons, and highly interconnected holes. These particles possess a new degree of quantum freedom, called "spin of the valley". The "spin of the valley" is similar to the spin of electrons, which has been widely used in the storage of information such as hard drives and is also a promising candidate for quantum computing. .

The paper, titled "Revealing Biexciton and Trion-exciton Complexes in WSe2 Encapsulated in BN," was published on September 13, 2018 in the edition of Nature Communications. The results of this research could lead to new applications in electronic and optoelectronic devices, such as solar energy recovery, new types of lasers and quantum detection.

Shi's research focuses on small-dimensional quantum materials and their quantum effects, with a particular interest in materials with strong light-matter interactions. These materials include graphene, transition metal (TMD) dichacides, such as tungsten diselenide (WSe2), and topological insulators.

TMDs represent a new class of atomically thin semiconductors with superior optical and optoelectronic properties. The optical excitation on single-layer two-dimensional TMDs will generate a highly-bonded electron-hole pair called exciton, instead of electrons and freely moving holes as in traditional bulk semiconductors. This is due to the giant binding energy in monolayer TMDs, which is much larger than that of conventional semiconductors. As a result, the exciton can survive at room temperature and can therefore be used for the application of excitonic devices.

As the density of the exciton increases, more electrons and holes come together, thus forming excitonic complexes at four and even five particles. The understanding of multi-particle excitonic complexes gives not only a fundamental understanding of the two-dimensional light-matter interaction, but also opens up new applications, since the multi-particle excitonic complexes better maintain spin properties. of valley "the exciton. However, despite recent developments in the understanding of excitons and trions in DMTs, said Shi, an unambiguous measure of biexciton binding energy has remained elusive.

"Now, for the first time, we have revealed the true state biexciton, a unique four-particle complex that reacts to light," said Shi. "We also revealed the nature of the charged biexciton, a five-particle complex."

At Rensselaer, Shi's team developed a way to build an extremely clean sample to reveal this unique light-matter interaction. The device was constructed by stacking several atomically thin materials, including graphene, boron nitride (BN) and WSe2, through a van der Waals (vdW) interaction, representing the advanced manufacturing technique of two-dimensional materials.

This work was done in collaboration with the National High-Magnetic Field Laboratory in Tallahasee, Florida, and researchers at Japan's National Institute of Materials Science, as well as with Shengbai Zhang, a professor at the Kodosky constellation in Japan. Department of Physics, Applied Physics, and Astronomy at Rensselaer, whose work has been instrumental in acquiring a theoretical understanding of biexciton.

The results of this research could potentially lead to robust multi-particle optical physics, and illustrate possible new applications based on 2D semiconductors, Shi said. Shi received funding from the Air Force Scientific Research Bureau. Zhang was supported by the Department of Energy, Office of Science.

The research was also recently presented in Nature Nanotechnology.

Shi joined Rensselaer's Chemical and Biological Engineering Department in July 2015. He received his B.Sc. from Nanjing University, and his Ph.D. from Cornell University. He was then a postdoctoral fellow at UC Berkeley. Shi also holds a joint position with Rensselaer's Electrical, Computer and Systems Engineering Department.