@article{DiracTheQT,
title={The quantum theory of the electron},
author={P. Dirac},
journal={Proceedings of The Royal Society A: Mathematical, Physical and Engineering Sciences},
volume={117},
pages={610-624}
}

Proceedings of The Royal Society A: Mathematical, Physical and Engineering Sciences

The new quantum mechanics, when applied to the problem of the structure of the atom with point-charge electrons, does not give results in agreement with experiment. The discrepancies consist of “duplexity ” phenomena, the observed number of stationary states for an electron in an atom being twice the number given by the theory. To meet the difficulty, Goudsmit and Uhlenbeck have introduced the idea of an electron with a spin angular momentum of half a quantum and a magnetic moment of one Bohr… Expand