Pseudo-Goldstone Gaps and Order-by-Quantum Disorder in Frustrated Magnets.

  title={Pseudo-Goldstone Gaps and Order-by-Quantum Disorder in Frustrated Magnets.},
  author={Jeffrey G. Rau and Paul A. McClarty and Roderich Moessner},
  journal={Physical review letters},
  volume={121 23},
In systems with competing interactions, continuous degeneracies can appear which are accidental, in that they are not related to any symmetry of the Hamiltonian. Accordingly, the pseudo-Goldstone modes associated with these degeneracies are also unprotected. Indeed, through a process known as "order-by-quantum disorder," quantum zero-point fluctuations can lift the degeneracy and induce a gap for these modes. We show that this gap can be exactly computed at leading order in 1/S in spin-wave… 

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