A dilution refrigerator and a high field solenoid system are requested for application of scanning probe microscopy techniques to the study and manipulation of disorder in quantum transport at millikelvin temperatures. The coherence of the electron wavefunction at very low temperatures can make the transport properties of such systems uniquely sensitive to the exact distribution of defects and scattering centers in the sample. Experiments which involve the measurement of some bulk property (e.g., conductivity) as a function of some external variable (e.g. magnetic field) can only reveal information about the net contribution of all the defects in the system. In contrast, scanned probe microscopies offer a unique opportunity to investigate these systems at the single defect level. The ability to probe and manipulate disorder in small scale systems, in combination with more standard probes of transport should provide: 1) important tests of the theoretical understanding of the role that disorder plays in these systems, and 2) signific ant insight into such long standing problems as 1/f noise and electromigration in small metal wires, and the nature of two level tunneling centers in disordered materials. The extension of a variety of scanned probe techniques to operation at very low temperatures will also allow the spatially resolved investigation of such buried systems, as the 2-dimensional electron gas in semiconductor heterostructures, and allow new insights into transport in the integer and fractional quantum Hall effect regimes. %%% Over the past decade, there has been great deal of interest and activity in two areas of condensed matter physics: electrical transport in nanometer scale devices and systems, and the study of surfaces with the scanning tunneling microscope and related microscopies. These new tools have found wide use in the study of the structure, and defects, on surfaces, study of complex molecules and magnetic systems, and fabrication of very small st ructures through the manipulation of single-atom-building blocks. This research, for which a dilution refrigerator and a high field solenoid system are requested, seeks to apply scanning probe microscopy techniques to the study and manipulation of disorder in quantum transport at very low, millikelvin temperatures. The aim is to probe the microscopic origins of the effects of disorder on the bulk electronic properties of metals.
