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Dr. Freericks works to ensure his students understand the concepts behind the physics he teaches. (Photo: Roland Dimaya)
A poster on his door explains Dr. Freericks' work on nonlinear and nonequilibrium systems. (Photo: Roland Dimaya)
Dr. Freericks' computational work focuses on thermoelectricity, strongly correlated materials, nonlinear and nonequilibrium physics, and ultracold atomic systems. (Photo: Roland Dimaya)
Dr. Freericks developed this image during research on nanostructures. Like the ripples that appear in a pond after a stone is dropped, the quantum mechanical wavefunctions of a metal also develop ripples (yellow and black region in the center) when they are connected to an insulator of finite thickness. (Courtesy Jim Freericks)
In this version of the previous image, done by Georgetown student Sean Boocock with Dr. Freericks, oscillations present in the data are more clearly seen. Boocock and Dr. Freericks amplified the oscillations by subtracting out the "background." (Courtesy Jim Freericks)
Dr. Freericks uses graphics in his book to explain a part of his research. (Photo: Roland Dimaya)

"We're trying to solve problems you can't solve with pen and paper: the tedious, repetitive calculations that a computer is very good at doing."
--Dr. Jim Freericks

By LiAnna Davis

Thirty years ago, NASA launched two Voyager spacecrafts to explore Jupiter and Saturn. The space probes proved so effective that they are now in the outermost edge of the sun’s domain. The success of the Voyager program is due partially to research on thermoelectricity, the principle that differences in temperature can be used to drive an electrical current that can then power a device. Thermoelectricity is the power source that keeps the Voyager spacecrafts operating to this day; indeed, it is the only power source that could operate over such a long period of time.

Thermoelectricity is one of the key areas of research for Dr. Jim Freericks, professor of Physics at Georgetown. Dr. Freericks looks specifically at solid-state refrigeration, in which cooling can take place without the use of such items as compressors, whose subtle vibrations can disrupt the operation of certain devices—sensors, for example—which need to remain still but cool. His solution? Artificially engineered materials, built from different layers of atoms. Dr. Freericks’ work is computational in nature, as he harnesses the power of technology to examine what materials can grow together, how thick layers should be, and what arrangement improves the thermoelectric cooling. His lab equipment consists solely of powerful computers. What would take lifetimes for humans to discover by hand his computers can analyze in mere weeks.

“We’re trying to solve problems you can’t solve with pen and paper: the tedious, repetitive calculations that a computer is very good at doing,” Dr. Freericks explains. “We try to interpret the results that come out of the computer in the real world. To do this, we find ways to quantify the abstract problem so the computer can solve it efficiently. It’s easy to have a computer work on a problem inefficiently, but a challenge to make it efficient.”

Dr. Freericks also focuses his computational attention on strongly correlated materials, nonlinear and nonequilibrium physics, and ultracold atomic systems.

Strongly correlated materials are those in which the electrons feel the presence of other electrons. One example of a strongly correlated material is the rare-earth-based magnets used in most in-ear headphones like the iPod’s ear buds. Dr. Freericks estimates that only 5 percent of materials are strongly correlated; in the other 95 percent, the electrons essentially act independently of each other. For strongly correlated materials, the electrons are acutely aware of what other electrons are doing while they are moving; this trait makes the quantum mechanical description of strongly correlated materials—the electrons’ blueprint for movement—significantly more complex. Dr. Freericks is specifically interested in using X-rays to determine the underlying properties of strongly correlated materials.

“If you can measure how often the X-rays that scatter off the material change color and by how much, you can learn about the inner workings of the material,” he explains. Many scientists use resonant inelastic X-ray scattering, or RIXS, as a technique for determining information about a material. While RIXS is accurate, scientists do not fully understand how it works, so Dr. Freericks and his students are trying to determine its quantum mechanical description in hopes of better understanding it.

For his research on electric fields in nonlinear and nonequilibrium systems, Dr. Freericks worked with a quantum mechanical methodology developed in the 1960s. Computers then were not powerful enough to solve the resulting equations, but Dr. Freericks’ lab was able to solve them with thousands of processors running on the problem for six straight weeks. The problem that was solved examined how electrical current changes in a material when it is subjected to electrical fields many times larger than what is seen in a lightning strike. In the presence of such large fields, the electrical current oscillates and decays in time. The character of the oscillations changes when the electrons interact strongly enough with each other to undergo a transition from a metal to an insulator. Understanding the details of how this works had been one of the longest standing unsolved problems in the field. Dr. Freericks’ solution involved significant computer work; the total computer time used was the equivalent of one computer running nonstop for more than 250 years.

Dr. Freericks’ work with ultracold atomic systems looks at the patterns the atoms form at very low temperature. The atoms sit on a lattice made out of laser light, residing at the bottom of the corrugations like eggs sitting in an egg carton. But in this case, available spaces outnumber the eggs, so the eggs can arrange themselves into different kinds of patterns. Since nature chooses the patterns that have the lowest energy, experimental measurements of these patterns tell us about how the atoms interact with each other and could be used as a means to determine their temperature. No conventional thermometers work at these low temperatures (the lowest known in the universe), so Dr. Freericks has to be clever to find ways to determine what the temperature actually is. Once he determines how to measure the temperature, he may focus future research on how to cool these atomic systems to even lower temperatures.

Dr. Freericks is also interested in the field of physics pedagogy, examining how students learn physics best. He teaches quantum mechanics courses for everyone from non-science majors to graduate students.

“I teach students the conceptual ideas behind science rather than having them just memorize equations,” he says. “Students who understand what the equations mean learn how to think in a conceptual way rather than relying on equations as a crutch.”

Dr. Freericks has found a happy union between the aspects of physics that excite his curiosity and the funding available from numerous sources, including the National Science Foundation, the Defense Advanced Research Projects Agency, and the Civilian Research and Development Foundation.

“I like having the freedom in the university environment to choose research and explore things I find interesting,” he says. “I also enjoy working with students, especially when they understand complicated phenomena and can explain it simply and easily to others. Georgetown, with its outstanding students, is a great place to see that happen.”

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