Research Summary:

By exploration of smaller and still smaller length scales, much has been learned about the fundamental interactions in nature. At the other extreme, condensed matter physicists have studied the collective statistical behavior of large numbers of particles. In a merging of these two approaches, intermediate size systems with relatively small numbers of atoms have recently been fabricated and studied. Novel effects have been discovered in these so-called mesoscopic systems. Traditionally these are samples of extremely small volume. But model systems with enlarged "atoms", such as vortices in superconducting networks, may suffice. Recent advances in the understanding of disordered systems, critical phenomena, and non-linear dynamics have also made it irresistible to ask deeper questions about complexity. Professor Israeloff's approach is to probe model complex materials with novel mesoscopic techniques, with an emphasis on noise measurements and analyses.

Experiments in progress or under development include mesoscopic studies of superconducting, disordered, and biological materials. The detailed dynamics of vortices in superconductors and superconducting networks are of interest. The vortices are localized regions of magnetic field penetration, around which circulate super-currents. These vortices must be pinned or nailed down, else they dissipate energy destroying the superconductivity. Also of interest are exotic transitions between the various fluid, crystalline, and glassy vortex phases which have recently been discovered. Understanding strongly driven motion of vortices may shed light on other complex problems, such as friction, granular flow, invasion, and charge transport. Strongly-driven vortex motion and localization effects are currently being studied in artificially disordered superconducting networks.

A full understanding of the transition between a liquid and a disordered solid such as ordinary window glass remains as a major unsolved problem in physics. The slow relaxation of a glass toward equilibrium, though also poorly understood, serves as a prototype for phenomena found in a wide variety of complex systems such as neural networks, protein folding, magnetic materials, and superconductors. Recent ideas suggest the answers to these mysteries lie in the mesoscopic regime. Using novel atomc force microscopy (AFM) techniques, developed in his laboratory, mesoscopic scale (nanometer) fluctuations in dielectric and viscoelastic properties have been observed and are being investigated near the glass transition. The techniques are also being developed into non-invasive nano-scale probes of advanced integrated circuits and materials.

Professor Israeloff's research is supported by the National Science Foundation through an NSF Young Investigator award.

Recent Publications:

Crider, P. S. & Israeloff, N. E. Imaging Nanoscale Spatio-Temporal Thermal Fluctuations. Nano Letters 6, 887-889 (2006).

Sinnathamby, K. S., Oukris, H. & Israeloff, N. E. Local Polarization Fluctuations in an Aging Glass. Physical Review Letters 95, 067205 (2005).

Vidal Russell, E. & Israeloff, N. E. Direct observation of molecular cooperativity near the glass transition. Nature 408, 695-698 (2000).

Grigera, T. S. & Israeloff, N. E. Observation of Fluctuation-Dissipation-Theorem Violations in a Structural Glass. Physical Review Letters 83, 5038-5041 (1999).

Russell, E. V., Israeloff, N. E., Walther, L. E. & Gomariz, H. A. Nanometer Scale Dielectric Fluctuations at the Glass Transition. Physical Review Letters 81, 1461-1464 (1998).