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Visualizing how radiation bombardment boosts superconductivity

A precision spectroscopic-imaging scanning tunneling microscope (SI-STM) developed by Davis is the first tool that can map out those three characteristics on the same material. Under Davis' guidance, Brookhaven Lab postdoctoral fellow Freek Massee (now at University Paris-Sud in France) and Cornell University graduate student Peter Sprau -- the two lead co-authors on the paper -- used the instrument's fine electron-tunneling tip to scan over the material's surface, imaging the atomic structure of the landscape below and the properties of its electrons, atom by atom. The precision allows the scientists to scan the same atoms repeatedly under different external conditions -- such as changes in temperature and ramped up magnetic fields -- to study the formation, movement, and effects of quantum vortices.

Their atomic-scale imaging studies reveal that vortex pinning -- the ability to keep those disruptive eddies in place -- depends on the shape of the high-energy ion damage tracks (specifically whether they are point-like or elongated), and also on a form of "collateral damage" discovered by the researchers far from the primary route traversed by each ion. Collaborating theorists at the University of Illinois are now using the experimental results to develop a descriptive framework the scientists can use to predict and test new approaches for materials design.

"These studies will really help us solve at which temperature which type of defects will be best for carrying a particular current," Kwok said. "The ability to achieve critical current by design is one of the ultimate goals of the Center for Emergent Superconductivity."

 

High-energy gold ions impact the crystal surface from above at the sites indicated schematically by dashed circles.

David Mermin Elected to American Philosophical Society

Congratulations to N. David Mermin for being elected to the American Philosophical Society! One of 25 Cornellians elected since 1865. Previous Cornell physicists in the APS were Hans Bethe, Michael Fisher, Bob Richardson, Ed Salpeter, and R. R. Wilson.

David Mermin

Sethna group featured in Through the Wormhole with Morgan Freeman

Jim Sethna's group is featured in an episode of "Through the Wormhole with Morgan Freeman." The episode "Are We Here for a Reason?" premiers on May 13 and explores new ideas about evolution. The Sethna group along with Barbara Baird's group illustrate crackling noise, critical fluctuations, and optimization of living systems.

Through the Wormhole

Paul McEuen elected to American Academy of Arts and Sciences

The American Academy of Arts and Sciences has named three Cornell faculty members, including KIC Director Paul McEuen, among its 197 new fellows for 2015.  The fellows are among “The world’s most accomplished scholars, scientists, writers, artists and civic, business and philanthropic leaders.” Read more in the Cornell Chronicle.

Charter Day Weekend: A Festival of Ideas and Imagination

Happy 150th Cornell!

Check out the list of events: http://150.cornell.edu/events/charterday

Charter Day

Vinay Ambegaokar awarded 2015 John Bardeen Prize

By Siv Schwink
Illinois Department of Physics

Theoretical condensed-matter physicist Vinay Ambegaokar has been selected for the 2015 John Bardeen Prize, in recognition of his theoretical research that substantially advanced our understanding of certain unique and fundamental features of superconductivity. Ambegaokar is Goldwin Smith Professor of Physics Emeritus at Cornell University’s Laboratory of Atomic and Solid State Physics (LASSP) in Ithaca New York.

The award citation reads “for his contributions to the statics, dynamics and kinetics of Josephson junctions and nanowires.”

The prize will be presented to Ambegaokar on August 24 during the 11th International Conference on Materials and Mechanisms of Superconductivity (M2S), in Geneva, Switzerland.

Ambegaokar received his bachelor of science and master of science degrees in mechanical engineering from the Massachusetts Institute of Technology in 1956 and his doctoral degree in theoretical physics from the Carnegie Institute of Technology in 1960. He completed a postdoctoral research appointment at the Bohr Institute in Copenhagen, Denmark prior to joining the faculty at Cornell University in 1962.

In June 1963, just a year after Brian Josephson—then a Cambridge graduate student—applied the BCS theory of superconductivity to predict a phenomenon that would come to be known as the Josephson current, Ambegaokar, with his student Alexis Baratoff, published the first calculation of the temperature dependence of the Josephson current. Interestingly, Ambegaokar had originally set out to disprove Josephson’s calculations—after learning of John Bardeen’s skepticism over the same—but Ambegaokar’s calculations agreed with Josephson’s. Prior to publishing what he found, Ambegaokar corresponded with Bardeen about this finding, and received a letter from Bardeen that called his calculation elegant but incorrect. The Josephson current was experimentally detected later that summer, and Bardeen conceded.

In his long career, Ambegaokar produced seminal theoretical work in condensed matter and low temperature physics,studying homogenous films and wires, metallic films, and quantum dots. Prior to his retirement in July 2007, Ambegaokar enjoyed several visiting appointments, including at Bell Laboratories; North American-Rockwell Science Center; Brookhaven National Laboratory; IBM Watson Research Center; Institute for Theoretical Physics at University of California, Santa Barbara; Collège de France; University of Karlsruhe; NORDITA, Copenhagen; University of Florida; All Souls College, Oxford; Bohr Institute, Copenhagen; and Raman Research Institute, Bangalore.

Among his professional honors, Ambegaokar was selected an Alfred P. Sloan Fellow from 1965 to 1967. In 1971, he received the medal of the University of Helsinki, Finland, after serving as the director of the Research Institute for Theoretical Physics at the university from 1969 to 1971. He was elected a Fellow of the American Physical Society in 1979 and a J. S. Guggenheim Fellow in 1983/84. In 1986, he received the Medal of the Collège de France. He served as a Humboldt Foundation Senior U.S. Scientist in 1986 and 1990.

 

The John Bardeen Prize was established in 1991 by the organizers of the M2S Conference, in honor of Dr. John Bardeen, the only person to have won the Nobel Prize in Physics twice, first for his part in the invention of the transistor, then for his part in developing the theory of superconductivity. The prize is presented triennially at the conference to a member of the international superconductivity research community for theoretical work that has provided significant insights on the nature of superconductivity and has led to verifiable predictions.

The list of previous distinguished winners includes four Nobel laureates: the late Vitaly L. Ginzburg of the Moscow Technical Institute of Physics; Alexei A. Abrikosov of Argonne National Laboratory; Anthony J. Leggett, the John D. and Catherine T. MacArthur Professor of Physics at the University of Illinois at Urbana-Champaign; and Philip Anderson, the Joseph Henry Professor of Physics, Emeritus, at Princeton University.

The award is sponsored by the Department of Physics of the University of Illinois at Urbana-Champaign and by the Friends of Bardeen.

Also see coverage of the award in the Chronicle.

Vinay Ambegaokar