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Eun-Ah Kim group finds new insights to entanglement entropy

Eun-Ah Kim's group reported in May 22 issue of Physical Review Letters that the poster child non-Fermi liquid state found at filling factor ν = ½ shows strongly enhanced quantum entanglement as a result of strong correlations in the system. The ν = ½ composite fermion non-Fermi liquid state occurs when extremely clean two dimensional electron gas is subject under magnetic field such that there are two flux quanta per electron. This state has long been viewed as a prototypical example of fermions coupled to emergent gauge field which mediates strong interaction. However the state does not show any broken symmetry and hence cannot be described using conventional order parameter formalism. Kim group and collaborators used state of art numerical scheme to calculate the bi-partite entanglement entropy which measures the quantum mechanical entanglement between a sub-region and the rest of the system. They report two unforeseen aspects: 1) there is no change in the scaling of the entaglement 2) the scaling factor which counts number of free channels for free fermions is greatly enhanced. The results can be found at:

 Entanglement entropy scaling

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:

Charter Day