Cornell set in place several keystones of contemporary condensed matter physics. The renormalization-group approach to critical phenomena, the theoretical description of exotic ordered phases (inspired by the discovery of superfluid helium-3), and the defining textbook of our field (Ashcroft & Mermin), were all developed at Cornell.

These techniques are now being applied to new and exciting areas of research at Cornell. The onset of chaos in low-dimensional systems and spatially-extended dynamical systems are being studied using renormalization group methods. Ordering induced by disorder is being investigated through models of magnetism incorporating temperature, quantum fluctuations, and dirt. Hysteresis loops in magnets, sliding charge-density waves, and paper when crumpled are all being studied for their exhibition of crackling noise with fractal and self-similar avalanches of all sizes. On a more practical level, theories describing surface growth (such as the deposition of metal wires on computer chips) are rooted in renormalization-group ideas.

The concepts of order parameters, symmetry breaking, and topological defects that emerged from the theory of superfluid helium-3 are being stretched and broadened in various directions. Cornell has played a central role in the theory of defects in liquid crystals. The department is a world center for the theory of quasicrystals—new, exotic phases with pentagonal or icosahedral order coexisting with long-range but non-periodic translational order.

Traditional solid state theory remains vital here as it extends itself into new regimes. Condensed matter physicists explore the weirdness of quantum mechanics in directions relevant to quantum computation. They predict the behavior of simple materials under extreme conditions. And they pursue the quantum theory of mesoscopic devices, using random-matrix theory and many-body physics to model everything from quantum dots to bouncing buckyballs.

Computational condensed-matter physics is a growing area within the theory group. The development of elegant software design and algorithms (such as wavelets in electronic structure, design patterns in multiscale modeling environments, and linear programming for crystallography) are all emphasized. Graduate students can use these elegant computational methods to study everything from magnetic grain boundaries through simulating fracture and crackling noise to extracting the three-dimensional structures of proteins.