1 research outputs found
Decoherence in Disordered Conductors at Low Temperatures, the effect of Soft Local Excitations
The conduction electrons' dephasing rate, , is expected to
vanish with the temperature. A very intriguing apparent saturation of this
dephasing rate in several systems was recently reported at very low
temperatures. The suggestion that this represents dephasing by zero-point
fluctuations has generated both theoretical and experimental controversies. We
start by proving that the dephasing rate must vanish at the limit,
unless a large ground state degeneracy exists. This thermodynamic proof
includes most systems of relevance and it is valid for any determination of
from {\em linear} transport measurements. In fact, our
experiments demonstrate unequivocally that indeed when strictly linear
transport is used, the apparent low-temperature saturation of is
eliminated. However, the conditions to be in the linear transport regime are
more strict than hitherto expected. Another novel result of the experiments is
that introducing heavy nonmagnetic impurities (gold) in our samples produces,
even in linear transport, a shoulder in the dephasing rate at very low
temperatures. We then show theoretically that low-lying local defects may
produce a relatively large dephasing rate at low temperatures. However, as
expected, this rate in fact vanishes when , in agreement with our
experimental observations.Comment: To appear in the proceedings of the Euresco Conference on Fundamental
Problems of Mesoscopic Physics, Granada, September 2003, Kluwe