A collaborative team of researchers from the Max Planck Institute for Structure and Dynamics of Matter (MPSD), Nanjing University, Songshan Lake Materials Laboratory (SLAB), and international partners has introduced a new method to regulate exotic electronic states in two-dimensional materials.
Building on the foundations laid by their previous work on twisted van der Waals materials, the team of physicists has now discovered a novel way to manipulate correlated electronic states in twisted double bilayer tungsten diselenide (TDB-WSe₂). This breakthrough offers new possibilities for developing advanced quantum materials and devices.
By precisely twisting two bilayers of WSe₂ near a 60-degree angle and applying a perpendicular electric field, the researchers have achieved control over the interaction between two distinct electronic bands, known as the K-valley and Γ-valley bands. This tuning has led to the observation of a “valley charge-transfer insulator”—an exotic state where electron movement is highly correlated, and electrical conductivity is suppressed.
“This work reveals that we can control the electronic phases of matter using the valley degree of freedom, which acts as a new ‘knob’ to adjust the material’s properties,” explains Lei Wang, professor of physics at Nanjing University and senior author of the study. “Our findings provide a deeper understanding of how to engineer correlated insulating states, which is crucial for future quantum technologies.”
The ability to manipulate these correlated states without altering the chemical composition or introducing significant disorder is a significant advancement. Traditionally, achieving such control required changing the material itself or applying large magnetic fields. The team’s approach offers a more straightforward and reversible method by using electric fields to adjust the relative position of the electronic bands and reveals a new form of flat band at the Γ-valley.
This research demonstrates a continuous transition from a Mott–Hubbard insulator to a valley charge-transfer insulator by shifting the K-valley band across the Γ-valley Hubbard bands using gate control. This tunable behavior opens the door to exploring new quantum phases, with potential applications in superconductors, quantum computers, and other next-generation technologies.
Published in Nature Communications, the study represents a collaborative effort among several international institutions and underscores the growing importance of twisted van der Waals materials in quantum materials research.
“This is just the beginning,” says Lede Xian, Professor and Group Leader of the Max Planck Partner Group at SLAB. “We believe that our work opens up new pathways for investigating and utilizing strongly correlated materials, which are essential for the next generation of quantum devices.”
“This discovery opens up new possibilities for controlling matter at the atomic level,” adds Angel Rubio, Director of the Theory Department at the MPSD. “We are excited to see potential applications and how it can be used to create unique functionalities.”
Further advancements in Moiré materials engineering could lead to new, tunable properties that are difficult to achieve through conventional methods, pushing the frontiers of material science. “This is a highly interesting situation where changes in structural registry lead to a new type of correlated phenomena,” concludes Rubio.
This latest research highlights the rapid progress in the field and builds upon the pioneering insights from earlier studies by the team on twisted van der Waals materials. As scientists continue to uncover new mechanisms of control, the potential for groundbreaking applications in quantum computing, energy-efficient electronics, and beyond remains vast and promising.
