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$Stuart Solin, Ph.D. (right), discusses graduate student Jian Wu’s research with a novel crystalline material. They stand behind a six-circle diffractometer, an instrument that uses high-intensity X-rays to determine the position of atoms in crystals. Solin is “imaginative, he’s clever, and he has an amazing breadth of knowledge in solid-state physics,” says Kenneth F. Kelton, Ph.D., chair of physics in Arts & Sciences.$

Stuart Solin, Ph.D. (right), discusses graduate student Jian Wu’s research with a novel crystalline material. They stand behind a six-circle diffractometer, an instrument that uses high-intensity X-rays to determine the position of atoms in crystals. Solin is “imaginative, he’s clever, and he has an amazing breadth of knowledge in solid-state physics,” says Kenneth F. Kelton, Ph.D., chair of physics in Arts & Sciences.

Abstract:
Solin lives by the scientific code of honesty and respect for evidence

Stuart Solin, physicist: the peer-reviewed life

St. Louis, MO | Posted on January 19th, 2010

In the middle of a Scientific American article about a new nanoscopic magnetic device his team had invented, Stuart Solin admitted that the prototype shouldn't have worked. It worked only because the fabrication process had accidentally produced ripples in the sidewall of the layered device that pushed its physics in the right direction. He even included a photo of the ripples for the readers' benefit.

It's the kind of thing only a scientist would do, someone who had made the unbending commitment to the values of honesty, doubt, respect for evidence and accountability that characterize science at its best.

"I'm a brutally objective observer," he says, "especially about my own stuff."

Down to atoms

Solin, Ph.D., the Charles M. Hohenberg Professor of Experimental Physics in Arts & Sciences, was hired seven years ago as the founding director of the university's Center for Materials Innovation.

The choice of a solid-state physicist to lead a materials center is itself a comment on how the field of materials science has changed in the past 20 years. "Materials science used to be mostly macroscopic — stretching rods to measure their tensile properties and so on," Solin says. "But as it evolved toward the microscopic and then toward the atomistic, it sort of met up with solid-state physics, which is my specialty."

Solid-state physicists use tools such as quantum mechanics to understand how the bulk properties of solid materials arise from their atomic properties. Their discipline is the theoretical basis of materials science and, in recent years, has led to many breakthrough applications, from transistors to superconducting magnets.

The Center for Materials Innovation's emphasis currently is on nanoscience, magnetic materials, amorphous solids and medical biomaterials.

Solin was picked for this position because he had led several materials science centers already: He had been co-director at the Materials Research Laboratory at the University of Chicago, now the Chicago Materials Research Center, and had started centers at Michigan State University and at the information technology company NEC.

Scientist to the bone

But what made him really stand out is his habit of thought. His colleagues say he is smart, meticulous, well-prepared, analytical, argumentative and self-critical. You could say he has a peer-review process continually running in his head, he has so internalized the standard that keeps science on the straight and narrow.

"He's very, very bright," says Kenneth F. Kelton, Ph.D., the Arthur Holly Compton Professor of Physics and chair of physics. "I've never gone to a colloquium where he didn't seem right on top of what is being discussed and able to ask really penetrating questions."

Solin knew quite early that he wanted to do something technical. He went to an elite technical high school that was the Baltimore equivalent of the Bronx High School of Science, and of his 30 classmates, 15 went to the Massachusetts Institute of Technology. He completed a bachelor's of science degree at MIT in three years and earned a master's degree and doctorate at Purdue University, a school nationally recognized for its strength in solid-state physics.

Kelton says that Solin has been a bold and decisive center director, and by way of examples tells the story of how he once purchased an electron microscope for a fraction of the usual price.

"We had come up with some money," Kelton says, "and we planned to get the National Science Foundation to make a matching grant. We were sitting around before the meeting with the manufacturer's representative, and someone said, ‘Maybe they'll just take our matching, and we won't have to go to the NSF.'

"I thought, ‘Well, that's ridiculous because it was such a small amount of money.' But Solin brought it up during the meeting, and we got this incredible deal — an unbelievable deal," Kelton says. "Basically, all we had to do was put up a plaque to give them credit for helping with the microscope."

Changing his mind

Decisive though Solin may be, he'll change his mind if you come up with a better argument. It just has to be a really good argument.

Mark Lee, Ph.D., a physicist at Sandia National Laboratories who did postdoctoral research under Solin, had the classic Mac/PC argument with him.

"As is Stuart's style," Lee says, "he usually opened such discussions with a statement that the PC system was better and waited for me to knock holes in his argument. But he started showing increasing curiosity about the Mac's operating system and user interface.

"At some point, after maybe a year of consideration, Stuart turned around and bought a Mac to replace his PC," Lee says.

An accidental discovery

Characteristically, Solin made the discovery he describes in the Scientific American article because something went wrong in the lab, and he was driven to understand exactly what and why.

His team was studying a semiconductor superlattice, a solid-state confection that consisted of alternating layers of what are called III-V semiconductors. They immersed the superlattice in a magnetic field and discovered that its resistance increased dramatically when the field grew stronger. This was a completely unexpected manifestation of an effect called "magnetoresistance."

It turned out the resistance jumped because the superlattice wasn't perfect. The layers weren't continuous sheets but were instead chunks of sheet with distortions or kinks. In other words, the effect was strong because the superlattice was flawed.

Physicists are taught to design experiments that minimize this kind of extrinsic effect and to concentrate on the intrinsic, or fundamental, properties of a material. "People go way out of their way to remove the so-called geometrical contributions, such as where the electrical contacts are placed, so they can just measure intrinsic properties," Solin says.

But he realized that the superlattice had exhibited such a strong response because of its geometrical properties and also — here's where the imaginative leap was made — that it might be possible to design novel devices by emphasizing rather than downplaying geometrical properties.

His first "geometrical" device was a magnetoresistive sensor consisting of a metal disk embedded in a doughnut-shaped slab of semiconductor. Modern computer hard drives rely on "giant magnetoresistive" (GMR) devices, whose resistance at room temperature changes by about 100 percent as they move into and out of strong magnetic fields. Devices based on Solin's effect, which he called "extraordinary magnetoresistance" (EMR), change resistance by as much as 1 million percent in the same fields at room temperature.

In a letter nominating Solin for the Academy of Science of St. Louis' James B. Eads Award, Ramanath Cowsik, Ph.D., professor of physics and director of the McDonnell Center for the Space Sciences in Arts & Sciences, says that two scientists won the Nobel Prize in physics in 2007 for GMR, and "Stuart's discovery of EMR is expected to spearhead the next generation of storage devices far beyond the technological limit of GMR technology."

Solin went on to design a series of metal/semiconductor sensors, all of which depend on the geometry of the metal inclusion. "The other EXX (extraordinarily sensitive) sensors are extraordinary piezoconductance devices (EPC), which are much more sensitive than present silicon pressure gauges," says L. R. Ram-Mohan, Ph.D., professor of physics and electrical and computer engineering at Worcester Polytechnic Institute, "and something called extraordinary optoconductance (EOC), which is an extremely sensitive way of measuring the intensity of light.

"He's still exploring how geometry influences the properties of these devices," Ram-Mohan says, "and there is still the promise of greater sensitivity in all of them."

Putting the discovery to work

Solin wants his work to impact a broad community, so together with Sam Wickline, M.D., professor of medicine, of biomedical engineering, of cell biology and physiology, and of physics and director of the Consortium for Translational Research in Advanced Imaging and Nanomedicine (C-TRAIN), he has started a new company, called PixelEXX Systems. The goal of the company is to incorporate the new EXX sensors in disposable arrays that can produce high-resolution images of cells.

Since nobody ever has produced images of a cell's properties at the resolution they envision, they're not sure how the arrays will be used.

They're entering "unchartered territory," Solin says, but he and Wickline believe there is a good chance they'll discover major differences between normal cells and cancerous ones.

"Stuart is a classic physics thinker," Wickline says. "I cannot tell you how many times he has delighted in exegesis of an abstruse concept with supreme confidence and pluck, only later to be informed that the data are totally backwards, then bursting forth with: ‘I can explain that! It's even better!' "