Quantum Science Across Scales

Materials science is undergoing a paradigm shift. Classifications previously based on symmetries—whether, for example, atoms are held fixed in a crystalline solid, like table salt, or freely flowing as a liquid, like water—are now being enriched by concepts from topology, a prominent branch of mathematics that deals with properties that remain fixed no matter how something is stretched, twisted, or otherwise deformed. 

Suppose you’re given a strip of paper, said Aravind Devarakonda, who joined Columbia Engineering’s Department of Applied Physics and Applied Mathematics as an assistant professor in January, and are asked to turn it into a loop. Of course, with a piece of tape, you could connect the two ends. But you could also twist the strip before taping the ends, turning it into a Möbius loop. The number of twists is a so-called topological invariant that won’t change, no matter how you push or pull on a given loop. 

Devarakonda doesn’t work with strips of paper but with quantum materials, where he studies the often surprising behavior that emerges from the interactions amongst the astronomically large number of electrons within them and their more recently identified topological properties. As Devarakonda, who was recently named a Gordon and Betty Moore Foundation Fellow in Materials Synthesis, gets his new lab up and running, he has ambitious plans to synthesize new quantum materials with interesting electronic features that more closely resemble Möbius strips as opposed to simple loops. By combining physics with chemistry, he hopes to reveal new twists in our understanding of materials’ quantum properties.

Crystal Creator

Devarakonda joins the Columbia Engineering faculty with extensive experience in material synthesis. Raised in New Jersey, his first exposure to the subject was as an undergraduate at Rutgers University, where he observed the growth of newly discovered topological insulators one atomic layer at a time with physicist Seongshik Oh. “Looking back, I can better appreciate what a feat of engineering it is to control materials at this atomic scale, and how it lets us advance the boundaries of fundamental physics,” he said. “I found this ability to study new physics by physically growing a new material you can hold in your hands to be really beautiful.” 

As a graduate student at MIT, in the physics lab of Joseph Checkelsky, he picked up synthetic chemistry and materials science techniques to grow and study the structure of crystals and learned the art of “low-temperature physics” to tease out their quantum mechanical properties. 

In 2021, Devarakonda joined Cory Dean’s physics lab at Columbia as a Simons Junior Fellow to learn more recently developed techniques (most of them pioneered at Columbia) to stack layers of 2D materials together to craft quantum materials that are essentially impossible to grow or find in nature. He also collaborated closely with Columbia chemist Xavier Roy on a quintessentially Columbia collaboration revolving around a layered metal that shows unusual quantum behavior. 

“Synthesizing and studying materials has been the common thread in my work, either by naturally creating crystals from mixing different elements or designing devices from stacked layers that maybe nature won’t give you,” he said. “I plan to do both in my lab, and we believe we will enable something really powerful by combining these two techniques.” 

High-temperature Furnaces Meet Low-temperature Physics

Of the materials he has grown and worked with, Devarakonda is especially excited about bringing a new class of superconductors from his time in Boston to New York. These materials feature strong electron interactions and built-in topology. “That is a really cool combination,” he said, noting that they seem to be extremely tunable. “By exchanging a couple of elements,” he said, “we can transform the structure and the material’s quantum mechanical behavior.” He thinks there should be at least a dozen members of this unusual family of materials.

Similar to how metallurgists examined different mixtures of iron and carbon to find the perfect steel for their application, Devarakonda hopes to synthesize and study new materials like these to unravel how interactions and topology come together to create fascinating electronic behavior. “At this point, we know a lot about how to make and use steel by first figuring out what happens when we combine iron and carbon. I think we can reach a similar point with quantum materials,” he said. 

Among the things we can do with this understanding is realize groundbreaking applications in quantum information and computing. For example, quantum states tend to be fragile and fleeting in the face of even slight environmental variations, like a change in temperature or pressure. Topological materials, by contrast, are notably robust—it takes concerted effort (and a pair of scissors) to cut, untwist, and reattach a Möbius loop into a simple loop, Devarakonda noted. With the right material, we could, in a sense, make quantum states impervious to their noisy environments. 

The work is not without its touches of serendipity, though. “In creating these new superconductors, I was targeting an entirely different compound when I noticed crystals from a side reaction, which I now realize are remarkable materials,” he recalled. “I think the key was recognizing that we had an interesting material in our hands, and that insight comes from working at this intersection between chemistry and physics.” 

With a new crystal, Devarakonda looks to link macroscopic chemistry with nanoscopic physics principles. “From creating the material in a furnace, we can ask what the atomic structure of the crystal is, and what we can then say about the quantum mechanical behavior of its electrons at temperatures near absolute zero?” he explained. “We’re connecting all these different scales to try and reveal something entirely new about the complex, quantum world within materials that we can hold in our hand.”