Condensed Matter Physics
	Prof. Stuart Brown NMR Techniques
	In our laboratory we study the physical properties of correlated electron systems using pulsed NMR techniques. Materials that we work on include high temperature superconductors and organic conductors. In both of these cases, the ground state can be tuned in the laboratory by changing the carrier density or by applying high pressure. For example, small changes in pressure could change a superconductor to an insulating antiferromagnet. NMR is sensitive to these changes through the hyperfine coupling to the electronic spins. The REU student will participate in probe development for a new cryostat and magnet, and measurements using the new hardware.
	Prof. W. Gilbert Clark High Performance Superconducting Cable for Nuclear Magnetic Resonance (NMR) Experiments at Very High magnetic Fields and Very Low Temperatures
	The goal of this project is to construct and characterize transmission lines that have both a high electrical performance and very low thermal conductivity for use in our NMR probes and those of other groups. The general approach is to make a transmission line of a type-II superconducting material. Such a material should have both low electrical losses and a low thermal conductivity. The most challenging part of the project is to characterize both the electrical conductivity and the thermal conductivity of the material at low temperatures and over a wide range of magnetic fields. This characterization will be the main activity of the REU participant. It will involve participating in the assembly of the instrumentation needed for the electrical and thermal measurements, carrying them out at low temperatures over a range of magnetic fields, analyzing the results, and applying them to the design and construction of superconducting transmission line segments that will be inserted at the appropriate place into a conventional transmission line. This work will be carried out in close collaboration with others in the research group. It is likely that the results will be published in the scientific literature. Topics the student will learn include how to measure the thermal conductivity at low temperatures, measure electrical conductivity at zero frequency, measure transmission line performance up to ~ 2 GHz., and learn the physical principles of heat conduction in normal and superconducting metals at low temperature in a magnetic field. It is reasonable to expect that with reasonable diligence, this work can be carried out on the time scale of the REU program in the summer.
	Soft Condensed Matter
	Prof. Douglas Durian Granular Materials
	Granular materials are all around us, and are crucial in many industries, yet their physics is poorly understood. Over last several years there has seen an explosion of interest in this field, owing to advances in theoretical and experimental tools. In this REU project, we shall explore granular mechanics (ie how they resist or respond to applied forces) in terms of impact craters. One project is to explore the role of dimensionality in order to distinguish possible dissipation mechanisms. Another project is to explore finite-size effects in order to test for the importance of force chains. Both can be accomplished within 10 weeks, and are expected to lead to publication.
	Prof. Gary Williams Luminescence from Laser-Induced Bubbles in Liquids
	This is a project to study the fast luminescence pulse emitted from a laser-created bubble in water and other liquids. To create the bubble a pulse from a YAG laser is focused to a point in the liquid, where the absorbed energy vaporizes the liquid, and creates a bubble that then expands to a maximum radius of order 1- 2 mm. The bubble then collapses and adiabatically compresses the gas inside, heating it sufficiently that an ionized plasma is formed, which then emits the luminescence. Our measurements have established that the maximum temperature is about 8000 K, hotter than the surface of the sun (5000 K). The figure shows multiple images of the collapsing bubble as a function of time from the minimum-radius collapse point; the bubble remains spherical during the collapse, and the white dot at the middle is the luminescence pulse at the collapse point t = 0. The goal of the summer project would be to investigate what happens to the luminescence when different salts such as NaCl and KCl are dissolved in the water. We have already seen an unusual effect with adding NaCl: the light emitted from the sodium D-line atomic transition comes out as much as 50 nanoseconds earlier than the plasma emission pulse. It appears that the sodium is heating up and emitting even without the plasma formation, which might be a nice diagnostic for understanding the emission process. We would like to make measurements of this in greater detail, and then extend this to other ionic salts and perhaps other types of liquids. Further references: Our experiment was chosen for a Physical Review Focus article: http://focus.aps.org/story/v7/st23 A conference paper of ours on the web gives an overview of the phenomenon: O. Baghdassarian, H. Chu, B. Tabbert, and G. A. Williams, “Spectrum of Luminescence from Laser-Induced Bubbles in Water and Cryogenic Liquids”, Proceedings of CAV2001, http://cav2001.library.caltech.edu/archive/00000324/ Two reasearch articles by our group: O. Baghdassarian, B. Tabbert, and G. A. Williams, "Luminescence Characteristics of Laser- Induced Bubbles in Water," Phys. Rev. Lett. 83, 2437 (1999). O. Baghdassarian, H. Chu, B. Tabbert, and G. A. Williams, "Spectrum of Luminescence from Laser-Created Bubbles in Water,", Phys. Rev. Lett. 86, 4934 (2001). more...