• Theoretical Condensed-Matter Physics
• Theoretical Elementary Particle Physics
• Astrophysics and General Relativity
• Experimental Elementary Particle Physics
• Accelerator Physics
• Experimental Condensed-Matter Physics
• Biological Physics
• Multidisciplinary Research
• Major Research Facilities
• Resources for Researchers

B.S., 1977, California Institute of Technology. Thomas J. Watson Fellow, 1977-78. William Lowell Putnam Fellow, 1976. Ph.D., 1983, Harvard University. Postdoctoral Research Associate, Bell Laboratories, 1983-85. Research Associate, Cornell University, 1985-87. Assistant Professor, Physics, Boston University, 1987-89. Assistant Professor, Physics, Cornell University, 1989-93. Associate Professor, Physics, Cornell, 1993-2001. Professor of Physics, Cornell, 2001-present. Alfred P. Sloan Fellow, 1987-91. Fellow, American Physical Society. 

Research Areas
Theory of frustrated magnetism (classical and quantum), interacting electron systems, quasicrystals, and biological physics

Current Research
My research falls into the areas of frustrated magnetism (classical and quantum), interacting electron systems, quasicrystals, and statistical/biological physics.  Much of my work is geometrical, involving nontrivial patterns in space.

My current biological-physics research [grad Steve Hicks] is on what fixes the size and pattern of the capsid (exterior shell) of a virus, especially retroviruses; these exhibit quasi-equivalence, whereby identical protein building blocks are not all in symmetry-equivalent places. We also investigate the physical basis of left/right symmetry-breaking which is obvious in vertebrate animals and in some plants.

In magnetism, we pursue the statistical physics and/or the quantum ground state of highly frustrated antiferromagnets on the Pyrochlore and related lattices containing corner-sharing triangles [Hizi, Ph.D. 2006]. Part of this is finding the classical ground states for competing spin interactions [undergrad S. Sklan]. We also explore simpler, classical realizations of exotic "topological order" (which was usually considered inherently quantum) [grad Zach Lamberty]. In interacting electron systems, my focus is on the boundary of analytic theory and computational physics. One current project is to understand the (highly degenerate) ground states of a spinless fermion lattice model with "supersymmety" [with Dr. Stefanos Papanikolaou, a postdoc in the Sethna group].We work on the phenomenology of STM measurements on high-Tc cuprates as done by the Davis group [grad Sumiran Pujari].

In quasicrystals, we want to determine the atomic structure and understand why quasicrystals form. On the atomic scale, we try to use microscopically-derived effective potentials to predict details of the atomic arrangements [undergrad A. Bhagat and visitor Dr. Marek Mihalkovic]. Another side is the statistical physics of quasicrystals: the "random tiling models" which are a likely explanation of the well-ordered icosahedral quasicrystals, and close packings of unequal spheres as a mathematical toy model related to structure prediction.

Graduate Students  
Steve Hicks, Sumiran Pujari and Zach Lamberty

Undergraduate Students
Sophia Sklan '10 and Amulya Bhagat '10

Spotlight

Yan-Jiun Chen is a graduate student working with Professor Jim Sethna studying non-equilibrium statistical physics, in particular, the scaling properties of crackling noise in magnets.  As a magnet is magnetized, magnetic spins flip in avalanches of all different sizes, this is called the Barkhausen effect (or crackling noise). The properties of these avalanches exhibit self-similarity, and can be studied using powerful theoretical tools in the form of the renormalization group (RG).  This means that studying these avalanches can tell us ...
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