Professor Andrew Millis

John Hopkins University

Physics & Astronomy Department

3400 North Charles Street

Baltimore, MD 21218

(410) 516-8586

millis@eta.pha.jhu.edu

General Remark: I think the proposed 'Institute for Complex Adaptive Matter' (ICAM) can be successful only if its core is a strong Los Alamos National Labs research effort. The Labs have the intellectual and technical resources to provide the needed leadership, in particular a deep and sophisticated understanding of materials synthesis (i.e. the design and growth of materials with nontrivial properties), an excellent group of scientists with particular expertise in the study of materials properties on short length scales and immediate access to unique user facilities, in particular the high magnetic field lab and LANSCE. An active LANL research program, driven by the intellectual interests of the scientists on-site, will attract (and focus) the attention and participation of the academic community. Without this core I fear that the program will dissipate into a series of individual research projects with little coordination and less long-term impact than one would like!

Proposed Research: I plan to undertake theoretical investigations of the effects of defects and surfaces on the properties of systems with strong, competing interactions. I have chosen three model systems that are amenable to theoretical analysis and experimental study. The proposed research makes most sense if it is performed in parallel with experimental investigations. The requisite experiments involve synthesis of materials and measurements of transport, thermodynamic and magnetic properties; key techniques include nuclear magnetic resonance, muon spin rotation, neutron scattering (especially the 'PDF' technique for examining local correlations) and EXAFS. These would seem to fit naturally with the capabilities and research interests available at LANL.

The three systems are materials near magnetic quantum critical points, materials with frustrated order, and CMR manganites. In all cases the nondisordered systems have been well studied, so clear theoretical and experimental starting points are available. Also in all cases, an experimentally tunable control parameter is available. Study of variation of properties with control parameter will be invaluable. I expect the crucial physics will involve formation of 'droplets' of ordered phase in nominally non-ordered regions, and the interesting questions will concern the size, dynamics and contributions to physical properties of these droplets. The connection to ICAM is that 'adaptive materials' seem generally to have two (or more) competing energy scales, which are for some reason finely balanced. In such cases disorder will have an unusually large effect because it will shift this balance locally. This is important to understand in its own right and will be crucial for interpretation of experiments and for design of materials with useful properties.