### Abstract

A theorem on the existence of a gap in the energy spectrum of quantum systems, the exact ground state of which is known explicitly, is proved. The theorem is applied to a three-dimensional Heisenberg spin-1/2 ferromagnet, with anisotropic nearest-neighbour interactions, and to an alternating Heisenberg antiferromagnet, with nearest- and next-nearest-neighbour interactions.

Original language | English |
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Pages (from-to) | 6395 |

Journal | Journal of Physics C: Solid State Physics |

Volume | 16 |

Issue number | 33 |

DOIs | |

Publication status | Published - 1983 |

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## Cite this

Caspers, W. J., & Magnus, W. (1983). On the existence of a gap in the energy spectrum of quantum systems.

*Journal of Physics C: Solid State Physics*,*16*(33), 6395. https://doi.org/10.1088/0022-3719/16/33/012