A type of coupling in many-fermion systems, such as electrons in atoms and nucleons in nuclei, in which the energies associated with the spin–orbit interactions are much higher than the energies associated with electrostatic repulsion. Multiplets of many-electron atoms having a large atomic number are characterized by j-j coupling. Multiplets in the shell model of nuclei characterized by j-j coupling are invoked to explain the magic numbers of nuclei. The multiplets of many atoms are intermediate between j-j coupling and Russell–Saunders coupling, a state of affairs known as intermediate coupling.