SINGLE-ELECTRON TRANSISTORS IN THE REGIME OF HIGH CONDUCTANCE

摘要

We have studied high conductance single electron transistors with coupling strength up to α = 4.75. We measured the maximum and the minimum of the linear response conductance as a function of gate voltage U_g, called G_(max) and C_(min), respectively, in the temperature range from 25 mK to 18K. G_(max)(T) agrees almost perfectly with the second order perturbation theory up to α = 1.4. For larger values of α increasing deviations are observed, which have to be accounted for by more advanced techniques. The most promising approach, which has the power to describe the whole parameter range accessible to experiments, is the quantum Monte Carlo method, although the inclusion of higher orders might extend the range of validity for the perturbation theory. For G_(min) we get deviations from the second order result for all values of α investigated in this study, which is a surprising result as G_(min) is measured at a gate voltage where all charge states are far from degeneracy. Here perturbation theory does not have to deal with divergencies and is usually assumed to describe the data for moderate α. However, QMC results seem to show deviations from perturbative results similar to the ones we observe in our experiments. So also for G_(min) QMC data is the most promising candidate to describe our measurements at a quantitative level.