How to manipulate the excitonic “Hulk”?Chinese scientists complete experimental observation for the first time in the world

The movie “Hulk” assumes that after being exposed to strong radiation, a mysterious force in the body is induced to become a “Hulk” with super strength. Things that are difficult to achieve in reality can be achieved in solids through exquisitely constructed materials. How to manipulate the exciton “Hulk” and complete experimental observations has always been one of the goals that physicists are concerned about and diligently pursuing.

Offers a potential route to applications such as quantum technology

According to the latest news from the Institute of Physics, Chinese Academy of Sciences (Institute of Physics, Chinese Academy of Sciences), Xu Yang’s team and collaborators from the Nanophysics and Devices Laboratory of the Institute have completed the experimental observation of Rydberg Mohr excitons for the first time in the world, and systematically demonstrated the importance of The controllable adjustment and spatial confinement of Rydberg excitons provide a potential way to realize the application of Rydberg states in solid-state systems in quantum science and technology.

This important research progress paper on the fundamentals of physics, completed by Chinese scientists, was recently published in the internationally renowned academic journal Science (Science) published online.

The research team said that atoms are the basic microscopic particles that make up matter. The electrons of atoms are arranged in layers. When electrons are excited to outer orbits, the atoms formed are called Rydberg atoms. This kind of excited atom is vividly called the “giant” of the atomic world because of its larger “body size”. In semiconductor materials, the particles composed of positive and negative charges attracting each other are called excitons. Correspondingly, the excited state of excitons is called Rydberg excitons, which are also giants in the exciton world. Just like the “Hulk” has super strength, the excitons in the Rydberg state have many interesting properties, such as being able to move freely in semiconductors, and being able to produce greater responses to changes in the surrounding environment.

In the 1950s, scientists first discovered an electron-hole pair in an excited state, that is, Rydberg excitons, in the semiconductor material cuprous oxide. Although such Rydberg excitons are more compatible with modern semiconductor technology, in a three-dimensional solid system, if you want to construct a stable and practical device by manipulating the Rydberg excitons, you still face many problems such as easy loss of excitonic states and few control parameters. challenges, while the Rydberg excitons in two-dimensional semiconductor materials provide a new direction for related research due to the reduction of dimensions and the enhancement of interface effects.

Development of an Optical “Rydberg Exciton Detection” Method

In recent years, the Institute of Physics, Chinese Academy of Sciences/Beijing National Research Center for Condensed Matter Physics Key Laboratory of Nanophysics and Devices Xu Yang and his collaborators have developed a set of optical “Rydberg exciton detection” methods, that is, using two-dimensional semiconductor The Rydberg excitonic state of tungsten diselenide is sensitive to the dielectric shielding of the surrounding environment, which enables the effective detection of novel electronic states in adjacent two-dimensional systems. However, in the system using this method, the interlayer interaction between the Rydberg excitons and the surrounding dielectric layer is weak. How to regulate the Rydberg excitons to form a strong coupling state and realize spatial confinement has become an urgent need to solve. The problem.

However, a magic-angle rotation method for two-dimensional materials in the field of condensed matter physics brings new opportunities to manipulate Rydberg excitonic states. Based on this, Hu Qianying, a doctoral student at the Institute of Physics, Chinese Academy of Sciences, under the guidance of Xu Yang, a special-appointed researcher, has prepared a two-dimensional van der Waals heterojunction device sample formed by single-layer tungsten diselenide and corner graphene in the past two years. The exciton state in the system was measured and the gate voltage doping regulation was studied by the method of photoluminescence spectroscopy. Experiments have found that in the samples of large-angle rotation graphene and magic-angle graphene, the spectral signal of tungsten diselenide is dominated by the “Rydberg exciton detection” mechanism, which mainly reflects the change of the dielectric function in the system, such as at the magic angle A series of symmetry-broken correlated electronic states were detected in graphene samples, while in small-angle corner graphene samples, the Rydberg excitonic states (about 7 nanometers in size) showed multiple The splitting and pronounced redshift are called Rydberg Moiré exciton states.

Provides highly tunable binding potential fields for Rydberg excitons

Xu Yang’s team combined with the real-space large-scale computational physics method newly developed by the Wuhan University research team, they found that the space charge distribution in the Moiré superlattice adjusted with the grid voltage may play a key role in the generation of this experimental phenomenon . In this system, the periodic Moiré potential field generated in the angled graphene is similar to the optical lattice in the cold atom system, providing a highly tunable binding potential field for Rydberg excitons and bringing electron- Interlayer Coulomb interactions with severe hole asymmetry.

In addition, they also systematically studied the evolution of the interlayer coupling strength with the rotation angle (or Moiré period) in the system. This coupling strength is directly reflected in the magnitude of the energy redshift of the Rydberg Moiré excitons, and these features become more pronounced with the increase of the Moiré period (decrease of the rotation angle), and the space-bound Reed The physical picture of Fort excitons is consistent.

The research team said that just as Rydberg atoms can have strong interactions and sensitivity to external fields, the optical levitation arrays formed by them can be used in quantum simulation and quantum computing, and the Rydberg Moore excitonic state Experiments have found that the system demonstrates controllable adjustment and spatial confinement of Rydberg excitons, which can provide a potential way to realize applications in quantum science and technology based on Rydberg states in solid-state systems.

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