By Dave DeFusco

Imagine a world where materials can do things that we’ve only dreamed of, like moving sound or bits of information in ways that seem to defy logic. That’s the promise of topological materials—special types of crystals that are changing the rules of scientific discovery and technological progress: Instead of making a material more durable, lighter or resistant, researchers are now focusing on making it very different.

In a recent study, “Observation of D-class Topology in an Acoustic Metamaterial,” published in Science Bulletin, a team of researchers, including Dr. Emil Prodan in the Katz School’s M.A. in Physics, has taken a big step forward by demonstrating a new type of material using sound waves, opening up exciting possibilities for future technologies.

Topological materials are special because they don’t behave like regular materials. Their properties are protected by mathematical rules related to symmetry and topology. These materials can guide bits of energy, charge or sound, along their edges without losing power, even if the path is blocked or damaged. This makes them useful for making more robust and efficient devices, like quantum computers or advanced communication systems.

One area of focus in this field is something called "D-class topological phases." These are important because they can host something called Majorana particles.

“Majorana particles are fascinating because they behave like their own opposites—a rare trait in the particle world,” said Dr. Prodan, senior author of the paper and professor of physics. “We believe they could one day be used to build quantum computers that are more stable and less error-prone than today’s models.”

Until now, D-class phases have been mostly theoretical. Scientists have struggled to create them in real-world experiments, particularly in two dimensions (2D), which is where they become most useful. In this new study, researchers used sound waves to create a topological material that mimics the behavior of D-class phases. They built a structure, called an acoustic crystal, made up of tiny cavities connected in a specific way. Using mathematics to design these connections, they created a material that behaves like it has the special symmetries needed for D-class phases.

“This is a big deal because it’s the first time anyone has managed to create a 2D version of this phase using sound,” said Shi-Qiao Wu, lead author and a professor at Soochow University in China. “We even measured the flow of sound along the edges of their material and found that it worked just as predicted. The sound moved in a robust, topological way, unaffected by obstacles.”

The major takeaways are: 

1. A Path to Quantum Computing: The ability to create materials that support Majorana particles brings scientists closer to building more robust quantum computers. These materials could make it easier to store and process quantum information. 
2. New Materials, New Technologies: The techniques used in this study could be applied to create other types of topological materials, potentially leading to breakthroughs in electronics, energy storage and communication. 
3. Understanding the Universe: This research also helps scientists better understand the fundamental rules of nature. By exploring these exotic materials, scientists are learning more about the hidden symmetries that govern the universe. 

The researchers want to further explore how to create “p-fluxes,” a feature that could stabilize Majorana particles even more effectively. They’re also interested in using these materials to process information, much like how a computer chip works.

“While there’s still a long way to go, this research represents an important step forward,” said Dr. Prodan. “Topological materials, especially those created with sound, offer a glimpse of a future where technology is smarter, faster and more reliable, all thanks to the power of physics and mathematics.”