Light-Induced Tuning of Twisted Quantum Materials
By twisting stacks of atomically thin crystals, scientists have created structures called moiré materials, which can host useful, exotic electronic states. But switching between these states on ultrashort timescales remains a big challenge. Now Xiaoyang Zhu at Columbia University and his colleagues have demonstrated a way to use laser pulses to quickly inject charge into moiré materials and adjust their electronic behavior [1]. In a companion study, the team has shown that this process can induce certain metal-to-insulator phase transitions that had not previously been observed [2]. The new method could help scientists build ultrafast quantum devices based on moiré materials.
In the technique, the moiré material of interest is encapsulated in insulating layers and then sandwiched between two ultrathin graphite electrodes. A femtosecond-duration laser pulse strikes the device, driving charges in the electrodes out of thermal equilibrium. The charges then quickly thermalize, and some are imparted with enough energy to cross the insulating layers into the moiré material. Crucially, this injection process is both controllable and rapid, occurring on picosecond timescales.
In their first study, Zhu and his colleagues confirmed the charge injection by observing three different experimental signatures [1]. In their companion work, they found that the injection could drive transitions from metallic states to insulating ones in which electrons are strongly correlated [2]. Importantly, these correlated insulating states are metastable, as opposed to unstable, with lifetimes exceeding microseconds. The researchers argue that their approach could be used to induce, tune, and interrogate a wide variety of other electronic states and transitions.
–Ryan Wilkinson
Ryan Wilkinson is a Corresponding Editor for Physics Magazine based in Durham, UK
References
- Y. Li et al., “Ultrafast charge doping via photothermionic injection in van der Waals devices,” Phys. Rev. B 113, 195135 (2026).
- Y. Li et al., “Photoinduced metal-to-insulator transitions in 2D moiré devices,” Phys. Rev. Lett. 136, 206502 (2026).