Condensed-matter physics concerns atoms in close proximity to one another and interacting strongly, as in the liquid and solid states. Collective and cooperative phenomena that result from these interactions can produce a variety of unusual physical properties as represented by the superfluid phases of 3He or high-temperature superconductivity.  Research areas of particular strength at Cornell include nanostructure physics, low-temperature physics, x-ray physics, and soft condensed matter physics.

Nanostructure Physics
Nanostructure physics was pioneered at Cornell. More than twenty-five years ago Cornell was the site of the first national nanofabrication facility, funded by the United States government, and remains the leader in this field because of a unique and continually updated collection of advanced tools at the present-day Cornell NanoScale Science & Technology Facility (CNF). This facility draws academic and industrial researchers from around the world. Physicists at Cornell developed many “top-down” lithography techniques, now capable of building structures on scales less than 10 nm, as well as “bottom-up” guided-assembly techniques for incorporating nanometer-scale objects into functional devices. Current work involves understanding the effects of quantum mechanics on electron transport in carbon nanotubes, metal nanoparticles, organic crystals, and individual organic molecules. Nanometer-scale magnetic devices are an area of emphasis, with applications for using spin-polarized currents to control ultra-dense magnetic memories. The dynamics of high-quality mechanical oscillators made of silicon or carbon nanotubes are approaching the single-phonon quantum limit. Fluid flow on the nanometer scale is also under investigation in collaboration with biophysicists. The department is heavily invested in continuing to invent new tools to further understanding, including entirely new forms of scanning-probe microscopy for use in characterizing phenomena on the nanometer scale.

Since the discovery of superfluid 3He at Cornell in the 1970s (for which Richardson, Lee, and Osheroff won the Nobel Prize), the fundamental properties of superfluid helium systems have become sufficiently well understood that they can be used as models for testing a wide range of interesting theories. Current research focuses on the effects of disorder on superfluids and their phase transitions. The properties of a sharp quantum-phase transition of 3He in aerogel glass (analogous in many ways to a disordered electronic superconductor) are being studied using a battery of techniques including torsional oscillators, sound measurements, heat capacity, and nuclear magnetic resonance. Other ongoing projects include studies of spin supercurrents and precessing domains in superfluid 3He-B, investigation of Bose-Einstein condensation over a wide range of atomic density using 4He in vycor glass, superflow along grain boundaries in solid helium, and the development of new cooling technologies for space-based applications.

X-Ray Synchrotron Studies
X-ray synchrotron studies are conducted at the Cornell Electron Storage Ring (CESR), used for high-energy particle experiments. CHESS, the Cornell High Energy Synchrotron Source, provides high-intensity x-rays for use in determining the structure and dynamics of materials in a wide range of scientific fields. X-ray diffraction is used in the physics department (and by a national user community and other researchers at Cornell) to understand the growth modes of metallic thin films used in electronic devices, defects in protein crystals, motion of charge-density waves in quasi-one-dimensional metals, and the dynamics by which polymer materials self-assemble into controlled structures. New regimes of study are opening up with the development of high-speed detectors for measuring time-dependent phenomena with x-rays.  Cornell is pursuing a major expansion in our facilities for x-ray studies, with planning underway for the design, construction, and operation of an Energy Recovery Linac (ERL) x-ray source.  This is a next-generation source of more brilliant x rays, that should enable powerful new techniques in x-ray microscopy, coherent diffraction, and time-resolved studies.

Soft Condensed Matter Physics
Soft condensed matter physics deals with liquids, polymers, liquid crystals, and other ’squishy’ materials that are central to biology and many industrial processes, and which could provide entirely new applications based on their capacity to self-assemble into complex structures. Colloidal liquids made of micron-sized polymer spheres in solution are being studied by confocal microscopy to see directly their correlations within both liquids and sheared crystals. Self-assembly of polymer mixtures is being applied to build three-dimensional controlled structures with dimensions of tens of nanometers, such as the plumber’s nightmare (imagine very small plumbers.)  The process of understanding protein structure and function is limited by the bottleneck of making crystals of purified proteins for X-ray diffraction — we are studying the fundamental growth modes of protein crystals and their intrinsic defect structures with the goal of enabling better understanding of biological function. The physics of insect flight is also being investigated using high-speed photography together with large-scale simulations of the interactions between air flow and wing