The Potential of Rydberg Excitons in 2D Semiconductors

The field of quantum physics has long been fascinated with the Rydberg state, a highly excited Coulomb-bound state of electron-hole pairs. These states have been observed in various physical platforms such as atoms, molecules, and solids. One of the earliest discoveries of Rydberg excitons was made in the 1950s in the semiconductor material Cu2O. These excitons exhibit solid-state properties and possess unique characteristics that make them highly promising for applications in sensing, quantum optics, and quantum simulation. However, researchers have faced significant challenges in efficiently trapping and manipulating Rydberg excitons.

In recent years, scientists have turned their attention to two-dimensional (2D) moiré superlattices as a potential solution to the challenges associated with Rydberg excitons. These superlattices are characterized by highly tunable periodic potentials, offering a new avenue for studying and manipulating Rydberg excitons. Dr. Xu Yang and his collaborators from the Institute of Physics of the Chinese Academy of Sciences (CAS) and Wuhan University have been at the forefront of this research.

Dr. Yang and his colleagues recently published a groundbreaking study in Science, in collaboration with researchers led by Dr. Yuan Shengjun of Wuhan University. Their study focused on the observation of Rydberg moiré excitons in the monolayer semiconductor WSe2 adjacent to small-angle twisted bilayer graphene (TBG). By utilizing low-temperature optical spectroscopy measurements, the researchers were able to detect the presence of Rydberg moiré excitons through multiple identifiable energy splittings, a pronounced red shift, and a narrowed linewidth in the reflectance spectra.

The Influence of Moiré Potential

The observations made by the researchers were attributed to the spatially varying charge distribution in TBG, which creates a periodic potential landscape known as the moiré potential. This potential interacts with Rydberg excitons, resulting in their strong confinement. Additionally, the unequal interlayer interactions of the constituent electron and hole of a Rydberg exciton, caused by spatially accumulated charges in the AA-stacked regions of TBG, contribute to the long-lived charge-transfer excitons exhibited by Rydberg moiré excitons.

One of the notable achievements of Dr. Yang and his team was the demonstration of a novel method for manipulating Rydberg excitons in a 2D system. Previously, such control was challenging to achieve in bulk semiconductors. The long-wavelength moiré superlattice, analogous to the optical lattices formed by standing-wave laser beams or arrays of optical tweezers used for Rydberg atom trapping, served as a key tool for controlling the Rydberg moiré excitons. With tunable moiré wavelengths, in-situ electrostatic gating, and longer lifetimes, researchers have greater control over the system, enabling convenient optical excitation and readout.

Potential Applications

The discovery of Rydberg moiré excitons opens up a wide range of opportunities in the field of quantum physics. The ability to study Rydberg-Rydberg interactions and achieve coherent control of Rydberg states can have profound implications for quantum information processing and quantum computation. As researchers delve deeper into the realm of 2D semiconductors and moiré superlattices, the potential applications of Rydberg excitons continue to expand.

With their groundbreaking study, Dr. Xu Yang and his collaborators have shed light on the potential of Rydberg excitons in 2D semiconductors. By leveraging the unique properties of moiré superlattices, they have successfully observed and manipulated Rydberg moiré excitons, paving the way for future advancements in this field of study. As researchers continue to explore the fascinating realm of Rydberg excitons, the possibilities for breakthroughs in sensing, quantum optics, and quantum simulation are endless.