W. M. Keck Microfabrication Facility |
CSM MSU PA MSU |
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Research Projects |
Electron-Electron Interactions in Mesoscopic Wires
Frédéric Pierre, Adel Gougam and Norman O. Birge
Department of Physics and Astronomy, Michigan State University
 Figure 1. Photograph with a scanning electron microscope of a sample used to deduce the phase coherence time tf from the low field magnetoresistance. The wire is 270 mm long, 100 nm width and 45 nm thick. The magnetic field is applied perpendicularly to the plane of the wire. |
 Figure 2. Open symbols: measured phase coherence time as a function of temperature in a silver, gold and copper wire. Solid line: fit of the phase coherence time measured on the silver wire using the predicted temperature dependence. Dashed line: theoretical prediction of screened Coulomb interaction for the silver wire. |
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In metallic thin films, the screening of Coulomb interactions is less efficient than in bulk metals, because of electron elastic scattering from film boundaries, lattice defects, and impurities. As a consequence, at sub-Kelvin temperatures, electron-electron interactions are expected to be the dominant inelastic process undergone by electrons, which determines energy exchange and limits the electronic phase coherence. In order to find out the mechanism of inelastic collisions experienced by electrons at low temperature, we measured the temperature dependence of the phase coherence time of electrons tf, from the weak localization corrections to the magnetoresistance of long metallic wires made of silver, gold and copper (see figure 1). The phase coherence of electrons is limited by all inelastic collisions, independently of the energy exchanged.
We found that the phase coherence time shows a saturation in some samples, and follows the predictions tfaT-2/3 of the screened Coulomb interaction in others (see figure 2) [1-3]. These results contradict the very controversial explanation by Mohanty et al. [4], who invoked a fundamental phenomenon, the zero point fluctuations of the electromagnetic field, to account for the saturation of tf observed in many samples.
These results were compared to the measured rate at which electrons exchange energy in similarly fabricated copper, gold and silver wires [3, 5-6]. This comparison allowed us to point out the unexpected importance of magnetic impurities for energy exchange [3].
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