Of swords, stars and superconductors

Robert Cava weaves physicists’ dreams into exotic new materials

By Bennett McIntosh

ROBERT CAVA PULLS A LONG CURVED steel blade from its ornate sheath, revealing a rippling pattern of light and dark metal. The sword is a Japanese katana made from steel of such legendary strength and sharpness that it was said to be able to cut a hair as it fell to the ground.

In his office where the shelves are lined with mineral samples and crystal structures, Cava, Princeton’s Russell Wellman Moore Professor of Chemistry, recounts the sword’s role in his destiny. He’d entered the Massachusetts Institute of Technology (MIT) wanting to study applied physics. “Someone at MIT interpreted ‘applied physics’ as being about materials science,” he said. “So, I ended up in a freshman seminar about samurai swords.”

Samurai swords derive their mythic properties from distinctive arrangements of iron and carbon atoms, Cava learned. His fascination with the atomic structure of the ancient metal turned into a career arranging atoms into materials for a more modern age: batteries, superconductors and materials with strange and exotic properties that could become the basis for future electronic devices.

In the 1970s, when Cava was a student, these technologies were far off in the future. Captivated by the science of materials, Cava stayed at MIT to earn his Ph.D. in ceramics. “Now I know how to make toilet bowls,” Cava quipped. In fact, ceramics have a wide range of electrical properties that make them useful in computers, televisions and communications devices. After graduation and a postdoctoral fellowship at the National Bureau of Standards, Cava took a job at Bell Laboratories, the research arm of the then-dominant AT&T telephone company.

Renowned for hiring the best and giving its researchers intellectual freedom, Bell Labs was at the time brimming with new ideas. “Collaborations were built by sitting with random people in the cafeteria,” Cava recalled. One day in 1986, one of these collaborators invited Cava to a seminar on high temperature superconductors, which were newly discovered materials that conducted electricity with no energy loss, but required less of the expensive refrigeration conventional superconductors needed.

Sitting in the seminar, Cava contemplated how the atoms in the new materials could be arranged to improve their performance. “I went back to the lab and four days later I had made a better superconductor,” he said. He would co-author more than 30 papers on superconductors in 1987 alone. One former colleague, Bertram Batlogg, now at the Swiss Federal Institute of Technology in Zurich (ETH Zurich), recalled being so excited about one discovery that they wrote the paper in one night, fueled by “European-strength coffee and fresh home-baked cornbread.”

In 1996, as AT&T broke up and spun off Bell Labs, Cava moved to Princeton, where he established a reputation of being able to weave physicists’ dreams into exotic new materials. When his collaborators in the Department of Physics come to him with theoretical predictions, he can often make a material that exhibits the desired properties. Some of the new materials he has conjured are topological insulators, materials that act like superconductors on their surface but conduct no electricity at all under the surface. “It is dark magic,” said B. Andrei Bernevig, a Princeton professor of physics and a frequent collaborator of Cava’s.

Cava is more understated in explaining what he calls his “chemical intuition.” The properties of a material depend as much upon the geometrical arrangement of its atoms as on the specific kinds of atoms. Cava approaches designing a new material first by finding the right geometry — how many other atoms of each kind should each atom connect to, and in which orientations — and then finding the right atoms to fit this geometry. All the while, he bounces ideas off his students and collaborators. “In the end, science is very personal,” Cava said.

The move to Princeton from Bell Labs brought more than new collaborators and projects. “At Princeton, I have to be more than a scientist,” Cava said. He had to become a teacher and, often, a performer, to engage the 100-plus students in his first-year general chemistry course.

To share the inspiration he has felt every day since his first materials-science class, Cava peppers his lessons with references to ancient alchemists and demonstrations of the power of their discoveries. Slicing a pumpkin — often adorned with a Harvard cap — with his Samurai sword is perhaps the tamest demonstration. “He’s always blowing something up, or lighting something on fire,” said Marisa Sanders, a Ph.D. student in Cava’s lab.

The antics cross over to his lab, where the lab rules encourage taking experimental risks, and where he can sometimes be spotted walking the lab in a Darth Vader costume, which he wears when he administers final exams, to, as he puts it, “relieve some of the students’ tension.” He is a patient teacher, willing to sit for hours with students to work through a difficult problem or an unexpected result.

But, especially in materials chemistry, such logical teaching only goes so far. The most harebrained ideas will either succeed or teach in their failure, according to Cava. “If he thinks something is not going to work, he won’t tell you not to do it,” said Elizabeth Seibel, a doctoral student in Cava’s lab. “But he might make a bet with you.”

When Cava isn’t conjuring crystals, he pursues his first scientific love, astronomy. Growing up on Long Island during the 1960s Space Race, Cava swapped his model-train set for another student’s home-built telescope just to get a good look at the moon. Now his students laugh at him for having so many telescopes in his garage that there is no room for a car. “I love to sit under the night sky and appreciate how beautiful the universe is,” he said. He shares this love with others, setting up a telescope outside the chemistry building to share eclipses and solar flares with colleagues and students. “It’s something that a bunch of us from the lab really look forward to,” Seibel said.

Beyond his passions for chemistry and astronomy, Cava hopes his mentorship and example help his students find something they love to do. “You have to be passionate about something,” he said. “In the end, you don’t want to look back and think, ‘I didn’t do anything with my life.’” He certainly will not have to worry about that.