A New Realization of an Electron Glass A. M. Goldman, University of Minnesota, DMR-0455121

1. A New Realization of an Electron GlassA. M. Goldman, University of Minnesota, DMR-0455121 Ultra-thin films of metals can be prepared with disorder on either atomic or mesoscopic scales. Superconductivity can be induced in these films from the insulating state, either by electrostatic doping, or by increasing film thickness. Super-conductivity, once established, can be destroyed by magnetic field. The direct transitions between superconductor and insulator are quantum phase transitions (see: Parendo et al., Phys.Rev B 73, 174527 (2006)). We have found that near the superconductor-insulator transition of mesoscopically disordered, granulara-Bi films, the low temperature beha-vior is glass-like, independent of whether the ground state is insulating or superconducting. Resistance fluctuations increase, and the spec-tral density of noise is pushed to low frequencies at temperatures below 400mK. Since this low temperature glassy behavior is not a property of the localized Cooper pairs, it therefore may be considered to be evidence of an electron, rather than Cooper pair or Bose glass. The low frequency noise spectral density S(V2)~ 1/f. The slopes of the plots of logV2 vs. log f determine . The temperatures 700, 600, 500, and 400 mK collapse onto each other with =1. At the lowest temperature =1.6. Graphs of the standard deviation of the resistance R (red) and  (blue) vs. temperature. An upturn is seen at 400mK. This behavior is found no matter whether the zero temperature limit of the resistance is insulating or superconducting.

2. A New Realization of an Electron GlassA. M. Goldman, University of Minnesota, DMR-0455121 Societal Impact: The films which are the subject of this research are examples of highly correlated nanostructured materials. The fundamental understanding of the properties of such materials is important in the broader context of materials and devices for computing and other forms of signal processing. In the particular case of mesoscopic systems, exhibiting transitions between superconducting and insulating behavior, fundamental questions of the establishment of phase coherence are in play, which have relevance to the understanding of macroscopic quantum behavior of mesoscopic superconducting systems. These are important in the development of quantum computing. Atomic Force Microscope scan over a 1 m x 1 m area showing textured struc- ture typical of a granular ultra- thin films. Homogenous films are featureless on this scale. Education: This research is being performed by Kevin Parendo, a postdoctoral associate and recent Ph.D. graduate of the pro-gram, and Sarwa Tan, a graduate student. Some enabling experiments were carried out by a former student, Melissa Eblen-Zayas, and a former postdoctoral associate, Dr. Anand Bhattacharya. Dr, Eblen-Zayas is cur-rently a tenure-track professor at Carleton College. Dr. Bhattacharya is now a member of the permanent staff of Argonne National Laboratory.