Coulomb blockade
In mesoscopic physics, a Coulomb blockade (CB), named after Charles-Augustin de Coulomb's electrical force, is the decrease in electrical conductance at small bias voltages of a small electronic device comprising at least one low-capacitance tunnel junction. Because of the CB, the conductance of a device may not be constant at low bias voltages, but disappear for biases under a certain threshold, i.e. no current flows.
Coulomb blockade can be observed by making a device very small, like a quantum dot. When the device is small enough, electrons inside the device will create a strong Coulomb repulsion preventing other electrons to flow. Thus, the device will no longer follow Ohm's law and the current-voltage relation of the Coulomb blockade looks like a staircase.
Even though the Coulomb blockade can be used to demonstrate the quantization of the electric charge, it remains a classical effect and its main description does not require quantum mechanics. However, when few electrons are involved and an external static magnetic field is applied, Coulomb blockade provides the ground for a spin blockade (like Pauli spin blockade) and valley blockade, which include quantum mechanical effects due to spin and orbital interactions respectively between the electrons.
The devices can comprise either metallic or superconducting electrodes. If the electrodes are superconducting, Cooper pairs (with a charge of minus two elementary charges ) carry the current. In the case that the electrodes are metallic or normal-conducting, i.e. neither superconducting nor semiconducting, electrons (with a charge of ) carry the current.
