Condensed Matter Physics Seminar

2 p.m., Thursday, November 13, 2003
Room 1201, Physics Building

 Exploring interactions and disorder using transport in low dimensional semiconductor systems

Mike Lilly

(Sandia National Laboratories)

Abstract:  Two examples of using transport measurements to explore low dimensional systems are presented.  First, low temperature transport measurements on 2D carriers in Si MOSFETs, p-type GaAs, Si/SiGe and several other material systems have been interpreted as an metal-insulator transition.  Our understanding of the metallic behavior is complicated by the presence of both strong electron interactions and disorder.   We report the temperature dependence of the resistivity in dilute 2D electrons in GaAs where the disorder is very low and electron interactions are strong.  For a range of densities, a dramatic nonmonotonic feature appears in the resistivity with “metallic-like” behavior at low temperature.  All of the data, however, can be qualitatively understood using detailed scattering calculations within the framework of Fermi liquid physics.  The experiment shows that when disorder is very low there is no evidence for a new metallic state at zero magnetic field.

Second, we have experiments in progress to study interacting double quantum wires.  While long term goals include measuring energy spectroscopy using tunneling and probing correlations with Coulomb drag, our initial efforts have focused on determining the nature of the ballistic to diffuse crossover in long single quantum wires.  Long wires are necessary for the more complicated coupled double wire geometries.  We have observed quantized plateaus in the conductance of 5 mm wires, clear steps in 8 mm wires and less organized structure in the conductance of wires as long as 20 mm.  Using a combination of conductance, magnetoresistance, nonlinear I-V measurements and tunable confinement potential, we explore the role of scattering in 1D and its impact on ballistic transport in nanostructures.

Host:  Das Sarma
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