Figure 91: Experimental data: current as a function ofVbandVG.Figure 92: Coulomb staircase.Figure 92 shows the so-called Coulomb staircase at different gate voltages and different temperatures.
The first picture shows the current depending on the bias voltage at different gate voltages. The
second one shows that at high temperatures like room temperature the Coulomb staircase disappears
and the current-bias voltage line looks like the one of a resistor. We can say that the staircase gets
washed out when you increase the temperature which can be explained with the thermal fluctuations.
Because at high temperatures the thermal energy is bigger than the charging energy
e^2
2 CΣ kBT (201)and the thermally activated electrons can tunnel easily on the island.
But the Coulomb blockade can also be suppressed by quantum fluctuations. The Heisenberg uncer-
tainty relation for energy looks like
∆E·∆t∼~ (202)and the average time of a quantum fluctuation of the order of the charging energy is then
∆t∼~ 2 CΣ
e^2