Single-Electron Transistor
Coulomb blockade, charging energy, single-electron tunneling
Single-electron tunneling animation
Parameters
1. What is the physical cause of Coulomb blockade in a single-electron transistor?
A. Adding a single extra electron to the island costs a finite electrostatic energy $e^2/2C_\Sigma$, which is not accessible via thermal excitation at low temperature
B. Electrons magnetically repel each other
C. The island is fully insulating and cannot carry current at all
D. This is a quantum spin effect
2. Why does observing single-electron effects require either a very small island or a very low temperature?
A. Charging energy is inversely proportional to capacitance, and capacitance is inversely proportional to size — a small island gives a large $E_C$ that can exceed $k_BT$ even at high temperature
B. A large island holds more electrons
C. This is purely a manufacturing limitation with no physical basis
D. A small island destroys electrons
3. What do the Coulomb oscillation peaks vs gate voltage represent?
A. Points where two neighboring island charge states (n and n+1 electrons) are energetically degenerate, temporarily lifting the blockade
B. Random noise
C. Moments of transistor damage
D. Temperature changes
4. Why does Coulomb blockade disappear if the tunnel junction resistance becomes smaller than the quantum resistance $h/e^2$?
A. Low resistance means fast tunneling — the charge state's "lifetime" becomes so short that the energy uncertainty ($\Delta E\sim\hbar/\Delta t$) washes out $E_C$
B. Temperature automatically increases
C. The island melts
D. This is only a theoretical case that never actually happens