Electronic quantum effects in disordered conductors are controlled by the conduction electrons dephasing rate. It is well known that elastic scattering does not destroy phase coherence, so it takes inelastic scattering to do that. The resulting phase breaking rate generically vanishes when the temperature goes to zero.
These well established theoretical results have been challenged in recent experiments showing a saturation of the dephasing rate at low temperature .
Here I discuss new theoretical developments. There have been attempts to explain the saturation of the dephasing time from interaction with zero point motion of the electromagnetic environment but these have been severely criticized by various groups. On the other hand it has been demonstrated that a weakly temperature dependent or even temperature independent dephasing rate is possible in presence of ``dynamic defects'' which may be modeled by two level systems [2,3]. It has been pointed out that the dynamics which is responsible for dephasing is related to the low frequency conductance noise. Measuring noise and the dephasing rate at the same samples then provides a test for this scenario.
Furthermore the dephasing rate for the electron-electron interaction correction to the conductivity has been calculated . It has been found that the dephasing rates for the interaction correction and for weak localization need not be identical, and the ratio depends on the explicit microscopic dephasing mechanism. A saturation of the interaction correction has indeed been observed at low temperature in the gold wires of Ref. .
 P. Mohanty, E.M. Jariwala, R.A. Webb, Phys. Rev. Lett. 77, 3366
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