Semiconductor structures in the form of superconducting moiré supercrystals have proven to be highly interesting for investigating correlated electron states and quantum physics phenomena. These structures consist of artificial arrangements of atoms in what is known as a moiré configuration. They are characterized by strong electron interactions and significant modifiability.
Recently, a research group from the Massachusetts Institute of Technology (MIT) conducted studies on superconducting moiré supercrystals and their underlying physics. In their publication in the journal Physical Review Letters, the scientists present new theoretical frameworks that can be used to study large moiré supercrystals with weak inter-electron interactions.
“Our group has been working on two-dimensional moiré materials for the past five years. In these systems, electrons move in a periodic potential (moiré supercrystal) and interact with each other through electrostatic repulsion,” said Liang Fu, co-author of the publication.
The main advantage of superconducting moiré supercrystals is their ease of manipulation under experimental conditions. Researchers can control the electron density to modify the properties of their ground state.
“Most previous studies focused on situations where there was one or fewer than one electron per moiré unit,” Fu added. “We decided to investigate the multi-electron regime and see if any innovations emerge in this field.”
Predicting the behavior of multi-electron materials is extremely challenging. The main reason is that these systems often involve competing energy scales.
“Kinetic energy favors an electron liquid, while interaction and potential energy favor a solid state,” explained Aidan Reddy, the first author of the publication. “An interesting feature of moiré materials is that the relative values of different energy scales can be adjusted by changing the moiré period. Utilizing this flexibility, we developed a theoretical framework for studying large moiré systems where electrons at different potentials interact weakly.”
The newly presented theoretical model by the research team focuses on the behavior of individual atoms in the moiré supercrystal. It was discovered that this relatively simple approach can provide insights into many intriguing quantum physics phenomena.
The researchers presented novel physical phenomena that can be observed in semiconductor-based superconducting moiré supercrystals. For instance, at a filling factor of n=3 (meaning each moiré atom in the supercrystal contains three electrons), electrostatic interactions lead to the formation of so-called “Wigner molecules”. Moreover, under certain conditions (if their size is comparable to the moiré period), it was found that these Wigner molecules can form a unique structure known as an emergent Kagome lattice.
The interesting electron configurations presented in this publication may soon become the subject of further research. Additionally, the discovered structures can provide inspiration for other physicists, enabling the study of charge and quantum magnetism in previously unexplored territories for conventional materials.
“The most important conclusion from our research is that at specific filling factors, electrons self-assemble into astonishing configurations (Wigner molecules) due to energetic balance. Our prediction of Wigner solids has been experimentally confirmed,” Trithep added.
In the near future, the researchers plan to investigate the phase transition between the Wigner solid and the electron liquid in the quantum scale.
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