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Kumar part of superconductivity research team

Barry McNamara
09/12/2011
One of Monmouth College’s newest faculty members, assistant professor of physics Ashwani Kumar, is already in the news, contributing to an article that was recently published in Nature Physics.

While doing his doctoral work at Florida State University, Kumar was part of a research team that studied superconductivity and quantum phase transitions in ultrathin metal films.

“These films mimic the super-current carrying planes of the high-temperature superconductors,” said Kumar.

In the article, titled “Enhancement of Superconductivity By a Parallel Magnetic Field in Two-dimensional Superconductors,” Kumar and his colleagues report the observation of “pronounced increases in the mean-field critical temperature on application of a parallel magnetic field in two different two-dimensional superconducting systems.”

The authors state that the observations they made “mark a radical departure from the current understanding of the interactions between magnetic fields and superconductivity.”

For those who need an entry-level version of the research to fully grasp its significance, Kumar was happy to oblige.

Widely regarded as one of the great scientific discoveries of the 20th century, superconductivity is the passing of electricity without loss.

“When electrons move inside a wire, they hit atoms, impurities and each other, resulting in a loss of electricity in the form of heat,” Kumar explained. “For example, nearly 10 percent of electric power is lost before it reaches your home.”

What value is there in superconductivity? An electric current flowing in a loop of superconducting wire can persist indefinitely with no power source, enabling a range of technology applications.

“At very low temperatures, electrons with opposite spins pair up to form Cooper pairs, which can carry electricity without any loss,” Kumar said. “The material is this state is called a superconductor. Magnetic fields break those pairs, thus weakening and eventually destroying superconductivity. What we found in our research is that a magnetic field can actually help strengthen superconductivity, if applied in a certain orientation.”

Kumar and his colleagues showed that when the magnetic field was applied in a parallel manner to the metal film, it actually enhanced superconductivity.

“A research group had observed this before, but the change was less than one percent,” he said. “What our research showed was an enhancement of 13.5 percent, which is very convincing. It is not merely an alleviation of some destructive effect such as magnetic-pair breaking but an enhancement of the intrinsic superconductivity by a parallel field.”

In the time since Kumar’s Ph.D. project, which spanned from 2004-2009, he said “the same effect of increase in critical temperature was observed in a very different system, commonly known as two-dimensional electron gas system.”

Explaining why the research is only now appearing in a journal, Kumar said, “We had compelling evidence, and we wanted to put in a good journal. It was worth the wait.”

The entire article can be found online at http://www.nature.com/nphys/journal/vaop/ncurrent/abs/nphys2075.html. It will appear in the actual journal later this week.

“At present, there is no theory that offers a thorough understanding of the experimental observation” said Kumar. “Our systematic study provides compelling evidence that spin-orbit coupling is playing an essential role and therefore should be the centerpiece of any viable theoretical model.”

Understanding the underlying physics will pave the way to design and fabricate better high-temperature superconductors, added Kumar, who is setting up a lab at the college to explore the exotic properties of nanostructures and superconducting materials.