2D materials stressed for quantum investigation

Researchers at Rice University, led by materials theorist Boris Yakobson, have produced models that demonstrate unique properties of 2D materials stressed by contoured substrates. They theorised that altering the contour of a layer of 2D material, thereby changing the relationships between its atoms, could be more straightforward than otherwise thought, a breakthrough that could lead to greater investigation of many-body effects, and the interactions between many microscopic particles, including quantum systems.

The concept originated from the idea that a flat sheet of paper cannot be wrapped around a ball without crumpling due to their different topographies. Without tearing, the paper has to be deformed to fully stick to the surface of the ball. In the same way, a flat 2D material when either grown or stamped on a substrate with different topography will be strained and its electronic property modulated. By combining topographical deformations in a 2D material, it is possible to produce new quantum phases, such as flat electronic bands and strongly correlated 1D electronic states.

Electrons in a 1D system flow collectively and not individually. As the charge can be manipulated to flow in a particular direction, the path it takes is a model for 1D systems that can then be used to explore properties of 1D quantum systems that cannot be accessed through twisted graphene. In fact, it is more straightforward to form a bumpy substrate using an electron beam than it is to twist 2D bilayers of graphene or other heterostructures to less than a single degree of accuracy.

While twisting two layers of materials stacked together, known as 2D bilayers, to change their topology has already being achieved, here computation showed that growing or stamping single-layer 2D materials on a designed bumpy surface allows for effective control over their magnetic and electronic properties. As reported in Nature Communications [Gupta et al. Nat. Commun. (2022) DOI: 10.1038/s41467-022-30818-2], the models demonstrate that instead of twisting, just stamping or growing a 2D material such as hexagonal boron nitride (hBN) onto an undulating surface works to strain the material’s lattice to form pseudo-electric and pseudo-magnetic fields, as well as potentially showing physical effects akin to those in twisted materials.

This deformation would be highly controllable through the surface bumps since substrates can be precisely patterned using electron-beam lithography. As researcher Sunny Gupta said: “This will also allow one to controllably change the electronic states and quantum effects by designing substrates with different topography”.

Such 2D materials could be positioned on a contoured surface, and be manipulated to form 1D bands that take on electronic or magnetic properties useful for studying quantum systems. Future research is expected to focus on experimental validation of these predictions, as well as the properties of undulated 2D materials.

“This will also allow one to controllably change the electronic states and quantum effects by designing substrates with different topography”Sunny Gupta