Abstracts

=Abstracts=

Ariel Amir
We present a model, that while simple to define, shows rich behavior that accounts for a variety of physical phenomena, such as localization of phonons, anomalous diffusion, and slow relaxations in glassy systems. The 'crux of the matter' lies in the fact that the rate of many process es in nature is exponential in the relevant distance: quantum tunneling is a common example. If we think about a particle diffusing in a random environment, its dynamics will be described by a matrix A where the i,j'th element is exponential in the distance between points i and j. This leads us naturally to the model of exponential random matrices, which is a different ensemble of random matrices, with interesting properties. We solve the model exactly in the low density, and discuss the implications on the various physical problems.
 * Localization, anomalous diffusion and slow relaxations in disordered systems**

Stefano Borini
Some typical hallmarks of glasses, such as slow non exponential relaxation and aging, can be clearly observed by measuring the electrical conductivity of porous silicon at room temperature. I will report some experimental results, discussing similarities and differences with respect to other glassy systems.
 * Glassy dynamics in porous silicon electrical conductivity**

Sushanta Dattagupta
The general problem of Quantum Dissipation will be stated in the context of an electron in a magnetic field. We will show how dissipation makes the system move from the Landau regime to the Bohr-Van Leeuwen regime, which may be viewed as a coherence to decoherence transition. We will also discuss the specific heat and make some remarks on the Third Law of Thermodynamics. The problem allows us to also compare and unify two different approaches to Statistical Mechanics: the Gibbs and the Einstein (Quantum Brownian Motion) approaches.
 * Quantum Dissipation of an Electron in a Magnetic Field**

Arthur F. Hebard
Using an apparatus in which thin films can be deposited and then immediately transferred without exposure to air into an adjoining cryostat, we present results on the disorder-induced changes in conductivity and magnetic behavior of thin-film ferromagnets. The experiments are motivated by the question of how disorder, which is known to localize spin-oriented carriers, affects magnetism in itinerant (band) ferromagnets. For Fe films we find a weak-localization quantum correction to the anomalous Hall effect, whereas in Gd films we observe an additional localizing, linear in temperature quantum correction to the conductivity due to scattering off spin waves. At higher stages of disorder, evidence will be presented for two distinct and rather surprising behaviors: for Gd films, a scale-dependent conductivity that collapses onto separate curves on each side of a metal-insulator transition, and for Fe and Co films, an anomalous Hall insulator behavior that can be ascribed to granularity.
 * Disorder-tuned approach to critical behavior in thin-film ferromagnets**

Peter Nalbach
In recent years, experiments (Fleming group in Berkeley) showed that excitonic energy transfer in photosynthesis is quantum coherent for several hundreds of femto-seconds and thus for a big part of the total transfer time. I show how coherence can survive despite strongly coupled environmental fluctuations, namely due to two features of the fluctuation spectra: spatial correlations and/or suppression of fast fluctuations. These findings raise many questions regarding the use of quantum coherence by nature in living things.
 * Quantum coherent energy transfer in photosynthesis**

Michael Pollak
A brief survey of current activity will be presented, addressing also outstanding problems and open questions.
 * Electron-Glass Opening Talk**