Quantum transport studies the flow of particles, electric charge or energy when quantum states, their occupation and their transmission probabilities determine the flow. In a short quantum wire, transverse quantum confinement permits only discrete transverse electronic modes, even though motion along the wire remains possible.
The Landauer formula treats two contacts as reservoirs supplying incident electrons. Their different occupations drive an electric current; a potential barrier changes the transmission probability of each incident mode. At low temperature, opening one perfectly transmitted spin-resolved mode increases the electrical conductance by the spin-resolved conductance quantum . Quantum tunnelling, interference and Coulomb blockade explain departures from a simple classical resistor picture.
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