Long dephasing time and high temperature ballistic transport in an InGaAs open quantum dot

We report on measurements of the magnetoconductance of an open circular InGaAs quantum dot between 1.3 and 204 K. We observe two types of magnetoconductance fluctuations: universal conductance fluctuations (UCFs), and "focusing" fluctuations related to ballistic trajectories between openings. The electron phase coherence time extracted from UCFs amplitude is larger than in GaAs/AlGaAs quantum dots and follows a similar temperature dependence (betwe en T-1 and T-2). Below 150 K, the characteristic length associated with "focusing" fluctuations shows a slightly different temperature dependence from that of the conductivity. (C) 2002 Elsevier Science B.V. All rights reserved.