Effects of quantum noise on dephasing in mesoscopic systems

• Applicant: Professor Dr. Jan von Delft
• Subject Area: Theoretical Condensed Matter Physics
• Term: from 2010 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 185960027

We propose to study the effects of quantum noise on dephasing due to electronelectron interactions in mesoscopic disordered systems, in the context of weak localization (WL) and universal conductance fluctuations (UCFs). In such systems, interactions can be described via a fluctuating effective noise field affecting the quantum mechanical phase of electron wave functions. The phase space for energy transfer between conduction electrons and this noise field, however, is restricted by Pauli blocking and hence depends on the temperature T. This very fundamental effect can be accounted for by using an effective quantum noise field with a nonzero noise correlation time, TT 1/T (whereas the commonly-used classical noise field has TT = 0). We will study two types of systems for which using TT ≠ 0 is essential: (i) Complex geometries such as rings and grids constructed from quasi-1D wires, characterized by a Thouless energy ETh (the inverse time for traversing a ring or a grid plaquette); and (ii) dephasing in external AC fields, characterized by an AC frequency ωac. For these, the temperature-dependence of the dephasing time Tφ(T) changes qualitatively once T drops below ETh or ωac, with experimentally measurable consequences for phenomena involving WL and UCFs.

• DFG Programme: Research Grants