(Nanowerk News) Rydberg states occur in a variety of physical systems including atoms, molecules, and solids. In particular, Rydberg excitations, which are highly energetic electron-hole pairs, were first discovered in Cu2O semiconductor materials in the 1950s.
Recent research published in Science (“Observation of Rydberg’s moiré excitability”) by dr. XU Yang and his team from the Institute of Physics (IOP) of the Chinese Academy of Sciences (CAS), and a group led by Dr. YUAN Shengjun of Wuhan University, reported observing Rydberg’s moiré excitability. This is moiré-limited Rydberg stimulation in WSe2 monolayer semiconductor, next to small angle bent bilayer graphene (TBG).
The solid-state nature of Rydberg excitations, their significant dipole moments, strong mutual interactions, and high interaction with the environment suggest potential applications in sensing, quantum optics, and quantum simulation. However, the full capacity of Rydberg’s excitability has not been realized because of the difficulty in efficiently trapping and manipulating it. The introduction of two-dimensional (2D) moiré superlattices with adjustable periodic potentials may provide a solution.
In recent years, Dr. XU Yang and colleagues have investigated the use of Rydberg excitation in 2D semiconductor transition metal dichalcogenides (such as WSe2). They have developed a Rydberg sensing technique that exploits the sensitivity of Rydberg excitations to dielectric environments to detect exotic phases in nearby 2D electronic systems.
In the study, the researchers used low-temperature optical spectroscopy measurements to detect Rydberg moiré excitations, as evidenced by multiple energy separations, a marked red shift, and narrowed line widths in the reflectance spectrum.
Through numerical calculations by a team from Wuhan University, the findings were associated with the spatially varying charge distribution in the TBG. This generates a landscape of periodic potentials (referred to as moiré potentials) for interactions with Rydberg stimuli.
The strong confinement of the Rydberg excitons is achieved due to the unequal interlayer interactions of the constituent electrons and holes of the Rydberg excitons. This is the result of the accumulation of spatial charges in the AA-stacked TBG region. This process causes Rydberg moiré excitations that exhibit electron-hole splitting and the long-lived nature of charge transfer excitations.
The team demonstrated a new method for manipulating Rydberg excitations, which is challenging in bulk semiconductors. The moiré superlattice with long wavelengths (tens of nm) in this study is similar to the optical lattice created by standing wave laser beams or optical clamping arrays used for Rydberg atom traps.
In addition, system control is improved due to the adjustable moiré wavelength, in-situ electrostatic gating and longer service life. These features, combined with the strong light-matter interaction, facilitate optical excitation and reading.
This research may offer new opportunities for further Rydberg-Rydberg interactions and coherent control of the Rydberg state, potentially leading to applications in quantum information processing and quantum computation.