Ruishi Qi

2023-2024 Graduate Student Fellow

Faculty Advisor: Professor Feng Wang

ruishiqi@berkeley.edu

Ruishi Qi obtained his B.S. degree in physics from Peking University in China. He is currently a physics PhD student working in the research group of Professor Feng Wang. His research work mainly focuses on experimental condensed matter physics, and in particular, using advanced spectroscopic techniques to study strongly correlated two-dimensional systems. 
Ruishi’s recent research work aims to create and probe high-temperature exciton superfluids and exciton Bose-Einstein condensates (BECs) in transition metal dichalcogenide (TMD) heterostructures. Studies of BECs are motivated by macroscopic realizations of quantum phenomena that usually only occur at nanometer scale. While BEC was first realized in cold atom gases at extremely low temperatures, recent efforts have focused on realizing a BEC in a condensed matter system for increased accessibility. Dipolar excitons in TMD heterostructures are recently predicted to hold a superfluid phase at high or even room temperature with no magnetic field required. However, experimental evidence has been elusive owing to challenges in performing direct electrical transport measurements in TMD systems. 

During his fellowship, Ruishi will try to achieve electrical control and optical detection of interlayer exciton superfluids in TMD heterostructures. By creating a device with dual gates and separate electrical contacts to the TMD layers, we will have full electrical control of the electron and hole densities in each layer. We will measure the carrier and exciton chemical potentials with laser reflection spectroscopy, and utilize a novel spectroscopy technique to optically measure exciton resistance. When the system is electrically tuned into the superfluid phase, we expect dissipationless exciton transport with zero resistance, which should provide direct evidence of an exciton BEC.