An international team of researchers, led by The University of Hong Kong (HKU) and The University of Science and Technology (HKUST), has achieved a groundbreaking discovery in the realm of quantum materials. They have unveiled the ability to control the nonlinear Hall effect in twisted bilayer graphene, shedding new light on the exceptional characteristics of two-dimensional quantum moiré materials. This breakthrough has promising implications across various industries, from new materials to quantum information, enabling terahertz detection with remarkable sensitivity at room temperature.
The team, led by Ph.D. student Xu Zhang and guided by Dr. Zi Yang Meng from the Department of Physics at HKU, along with Professor Ning Wang from the Department of Physics at HKUST, alongside their postdoctoral researchers Meizhen Huang and Zefei Wu, and Professor Kai Sun from The University of Michigan, conducted an extensive study using a combination of theory, computation, and experiments.
Their research revealed that by adjusting the dispersion of the topological flat bands in twisted bilayer graphene, it becomes possible to easily control and manipulate the crucial Berry curvature dipole moments responsible for the Hall effect. By applying a vertical electric field, the team observed a clear nonlinear voltage response in the longitudinal direction when a transverse current was applied. This response varied significantly with adjustments in the applied field, strain, and twist angles, resulting in increases, decreases, and changes in direction.
These experimental observations confirmed that the nonlinear transport behavior is sensitive to the movement of Berry curvature hotspots in the topological flat bands, aligning perfectly with their theoretical calculations.
The researchers also delved into the influence of the moiré potential and twist angle in the controllable nonlinear Hall effect of twisted bilayer graphene. They discovered that the strength of the moiré potential played a pivotal role in determining the magnitude of the observed nonlinear response. By altering the twist angle between the graphene layers, they were able to manipulate the moiré potential, thus controlling the nonlinear transport behavior.
The discovery of the controllable nonlinear Hall effect in twisted bilayer graphene holds immense potential for realizing quantum Hall materials and nonlinear Hall effects in novel experimental platforms. Unlike conventional electronic devices, the nonlinear Hall effect in graphene, driven by low-frequency currents, does not have voltage threshold or transition time limitations. This opens up possibilities for applications in frequency multiplication and rectification, particularly in the terahertz frequency range, with a substantial response and ultra-high sensitivity at room temperature.
This groundbreaking finding regarding the controllable nonlinear Hall effect in twisted bilayer graphene represents a major advancement in the field of quantum materials, paving the way for further exploration and applications in condensed matter physics, new materials, and quantum information.
Source: The University of Hong Kong
