Kramers theorem

The Kramers degeneracy theorem states that the energy levels of systems with an odd number of electrons remain at least doubly degenerate in the presence of purely electric fields (ie. no magnetic fields).

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It is a consequence of the time reversal invariance of electric fields, and follows from an application of the antiunitary T-operator to the wavefunction of an odd number of electrons. The theorem is valid for any configuration of static or time-varying electric fields.

See also

• Hendrik Anthony Kramers
• T-symmetry#Kramers.27_theorem