Dephasing in disordered systems at low temperatures

The transition from quantum to classical behavior of complex
systems, known as dephasing, has fascinated physicists during the
last decades. Disordered systems provide an insightful environment
to study the dephasing time \tau_\varphi, since electron
interference leads to quantum corrections to classical quantities,
such as the weak- localization correction \Delta g to the
conductance, whose magnitude is governed by \tau_\varphi. In this
thesis, we study one of the fundamental questions in this field:
How does Pauli blocking influence the interaction-induced dephasing
time at low temperatures? In general, Pauli blocking limits the
energy transfer \omega of electron interactions to \omega \ll T,
which leads to an increase of \tau_\varphi. However, the so-called
0D regime of dephasing, reached at T \ll E_{Th}, is practically the
only relevant regime, in which Pauli blocking significantly
influences the temperature dependence of \tau_\varphi. Despite of
its fundamental physical importance, 0D dephasing has not been
observed experimentally in the past. We investigate several
possible scenarios for verifying its existence: (1) We analyze the
temperature dependence of \Delta g in open and confined systems and
give detailed instructions on how the crossover to 0D dephasing can
be reliably detected. Two concrete examples are studied: an almost
isolated ring and a new quantum dot model. However, we conclude
that in transport experiments, 0D dephasing unavoidably occurs in
the universal regime, in which all quantum corrections to the
conductance depend only weakly on \tau_\varphi, and hence carry
only weak signatures of 0D dephasing. (2) We study the quantum
corrections to the polarizability \Delta \alpha of isolated
systems, and derive their dependence on \tau_\varphi and
temperature. We show that \tZeroD dephasing occurs in a temperature
range, in which \Delta \alpha depends strongly (as a power-law) on
\tau_\varphi, making the quantum corrections to the polarizability
an ideal candidate to study dephasing at low temperatures and the
influence of Pauli blocking.