The Aharonov–Bohm effect is a quantum-mechanical phenomenon in which an electrically charged particle is influenced by the vector potential in regions in which the magnetic field is zero. A beam of monoenergetic electrons passes through a double slit on opposite sides of a solenoid. The expected interference pattern of the waves going through the two slits is shifted by an additional phase difference when the solenoid encloses a magnetic field, despite the magnetic field being zero in the regions through which the electrons pass. This can be observed experimentally by the horizontal displacement of the interference fringes.[more]
The effect can also be observed in small disordered metallic conductors as conductance fluctuations in small (nonsuperconducting) rings and wires.
In this Demonstration, you can observe the electron diffraction pattern on a fluorescent screen as the electron momentum and solenoid magnetic field are varied.[less]
Reference: Y. Aharonov and D. Bohm, "Significance of Electromagnetic Potentials in the Quantum Theory," Physical Review Series II, 115, 1959 pp. 485–491.