Long dephasing time and high-temperature conductance fluctuations in an open InGaAs quantum dot

We measure the electron phase-coherence time ${\tau }_{\phi }$ up to 18 K using universal fluctuations in the low-temperature magnetoconductance of an open InGaAs quantum dot. The temperature dependence of ${\tau }_{\phi }$ is quantitatively consistent with the two-dimensional model of electron-electron interactions in disordered systems. In our sample, ${\tau }_{\phi }$ is two to four times larger than previously reported in GaAs quantum dots. We attribute this enhancement to a larger value of the Fermi energy and the lower electron effective mass in our sample. We also observe a distinct type of conductance fluctuation due to ballistic electron focusing inside the dot up to 204 K.