Quantum materials, which operate based on the strange rules of quantum mechanics, have the potential to revolutionize technology.
These materials can exhibit unusual behaviors, like superconductivity—where electricity flows without resistance—but to get the best performance out of them, they need to be precisely tuned.
This process is similar to how a race car needs fine adjustments to run at its best.
A team led by Professor Mingda Li at MIT’s Department of Nuclear Science and Engineering has developed a groundbreaking method to fine-tune these quantum materials with remarkable precision.
Their research, published in Applied Physics Reviews, focuses on a particular type of quantum material called Weyl semimetals, but their technique can be applied to many other materials as well.
Weyl semimetals are fascinating because of their unique electronic structures, known as Weyl nodes.
These nodes are special points within the material that give it unusual electrical properties, which are highly desirable for various advanced technologies.
One key advantage of topological materials, like Weyl semimetals, is that their beneficial properties are “topologically protected.” This means that even if the material has imperfections, it will still perform well.
The MIT team’s new technique is all about adjusting the Fermi level of these materials. The Fermi level is the highest energy level that electrons in a material can reach.
Think of it like the water level in a dam—you can raise or lower it to control how the material behaves.
For Weyl semimetals, getting the Fermi level just right is crucial because their special properties only emerge when the Fermi level aligns with the Weyl nodes.
To fine-tune the Fermi level, Li’s team used a method called doping. Doping involves introducing foreign particles into the material to change its properties.
In this case, the team added negative hydrogen ions (particles with one proton and two electrons) into a Weyl semimetal made of tantalum phosphide (TaP). These hydrogen ions effectively adjust the Fermi level by adding extra electrons.
The process requires extreme precision. The researchers used a powerful ion accelerator at MIT to bombard the TaP sample with hydrogen ions, carefully controlling how many ions were added.
The challenge was figuring out exactly how long to expose the material to the ion beam to reach the desired Fermi level. To solve this, the team developed a theoretical model that predicts how many ions are needed and how long the material should stay in the accelerator.
What’s impressive is that this new method can achieve the necessary precision in minutes, a task that used to take weeks with traditional methods—and often without achieving the required accuracy.
The ability to fine-tune the Fermi level so precisely opens up new possibilities for quantum materials.
For instance, it could help raise the temperature at which materials become superconducting, making them more practical for everyday use.
It could also improve the efficiency of thermoelectric materials, which convert heat into electricity, and play a significant role in the development of quantum computers.
This new approach has broad implications. As Professor Li notes, “When it comes to quantum materials, the Fermi level is practically everything.”
By mastering the fine-tuning of the Fermi level, we may be able to unlock the full potential of these materials, paving the way for new technologies in quantum computing, electronics, and beyond.
