We are exploring both static and dynamic properties of interesting condensed matter systems at very high pressures using diamond anvil cells (DACs). In particular we are interested in transitions between different phases of matter as temperature (T), pressure (P), and applied fields are varied. With appropriate furnaces and cryogenic equipment we can do combined T- and P-dependent studies. Several optical techniques such as Raman, tandem Brillouin, dynamic light scattering (DLS) and ruby fluorescence are used to probe materials under these extreme conditions.

A primary goal is to deepen our understanding of the mechanisms underlying the liquid to glass transition. This is currently a topic of intense interest for both fundamental and technological reasons. As a liquid melt is supercooled to the glassy state, its viscosity and structural relaxation time increase by up to 17 orders of magnitude, requiring several techniques to probe this enormous range in dynamical behavior.

By combining T- and P-dependent Brillouin scattering we can probe the low-viscosity (high-T or low-P) limit where relaxation times are short (10-12s). As the glass transition is approached at low T or high P, however, relaxation times approach experimentally long times and lower frequency probes such as DLS are needed. A current goal is to combine this technique with DACs to explore low fre-quency glass transition dynamics at high pressure.

We are also studying glassy behavior in magnetic spin-glass systems using a Quantum Design SQUID instrument. In particular, we are exploring the intriguing paramagnetic (PM) to ferromagnetic (FM) to reentrant PM to spin-glass sequence of transitions in the binary alloy Fe0.7Al0.3, as well as FM to spin-glass transitions in ternary Fe1-xAl0.3Mx alloys where M=Co, Mn, Ti, V. High-P studies of unusual reentrant behavior in oxide ferroelectric materials are also in progress.

This research is supported by several grants from the NSF. We also have an active collaboration with the Exxon Research and Engineering Company, where world record high-P viscosity measurements have been achieved.