Temperature dependence of phase breaking in ballistic quantum dots

Ballistic conductance fluctuations are measured in a zero-dimensional (0D) GaAs quantum dot and are used to measure the phase coherence lifetime ${\mathrm{\tau }}_{\mathit{c}\mathit{p}\mathit{h}\mathit{i}}$(T) based on a semiclassical ‘‘extra lead’’ model of phase breaking. Above 300 mK, the measured ${\mathrm{\tau }}_{\mathit{c}\mathit{p}\mathit{h}\mathit{i}}$ decreases as a power law, ${\mathrm{\tau }}_{\mathit{c}\mathit{p}\mathit{h}\mathit{i}}$(T)=a(T [K]${)}^{\mathrm{-}\mathrm{\zeta }}$, with ζ∼1.2 and a∼3.5×${10}^{\mathrm{-}11}$ s, and appears to saturate below this temperature. Variance of fluctuations increases from zero with dot conductance for few conducting channels in the leads, then saturates once several channels are open. Above 150 mK, variance decreases with temperature as a power law with an exponent between -1.2 and -1.6 depending on 〈g〉.