Researchers at the University of Maryland, along with collaborators from the National Institute of Standards and Technology (NIST), have developed a theoretical model that demonstrates how to shape and stretch graphene to create a powerful, adjustable and sustainable magnetic force. This discovery could also be a major step in understanding how electrons move in extremely high magnetic fields.

Graphene's electrons react to stretching or straining by behaving as if they are in a strong magnetic field. This so-called pseudomagnetic effect could open up new possibilities in graphene electronics, but so far, researchers have only been able to induce limited pseudofields that are far from to realizing in practice. However, Maryland researchers may have explained how to shape a graphene ribbon so that simply pulling its two ends produces a uniform pseudomagnetic field.The team is confident that they will soon be able to transition their theoretical model to a design reality.

The researchers found that the graphene sheet needed to not only be stretched, but that the sheet must also be shaped in a specific way - a simple rectangle or square of graphene, when stretched, would not create a pseudomagnetic field. A tapered shape of graphene, like a trapezoid or pennant, however, reacts by producing a strain that steadily increases along the length of the ribbon, and this constant strain gradient gives a uniform, and controllable, pseudomagnetic field. Furthermore, the more strain applied to the material, the greater the magnetic force. The team's model, which was verified across three computational models, predicts a tunable field magnitude from zero to 200 Tesla.

This type of controlled pseudomagnetic field open the door to new ways of studying the motion of electrons in a controllable high magnetic field. Currently, there is no sustainable method for generating magnetic fields of this magnitude. The induced fields – if made more spatially uniform – could potentially enable new concepts of electronics, such as "valleytronics," in which electrons separate between different valleys in the graphene band structure. 

Source: phys.org via Physical Review Letter



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