Pr pyrocholores - when muons perturb their host

Candidate quantum spin ice materials include Pr-based pyrochlores, but if you study them with muons you are in for a surprise. The ground state of the Pr ion is a non-Kramers doublet, meaning that it is not protected from non-magnetic perturbations (as a Kramers doublet would be) and we have been able to show that the anisotropic distortion field produced by the presence of the muon is enough to split the doublet. This leads to an enhancement of the nuclear coupling to the muon and this dominates the response. This effect was hinted at in earlier measurements by Doug MacLaughlin on Pr2Ir2O7, but our new experiments extend this to other Pr-based pyrochlores and using DFT and crystal-field calculations we are able to quantify this effect.

"Anisotropic local modification of crystal field levels in Pr-based pyrochlores: a muon-induced effect modeled using density functional theory", F. R. Foronda, F. Lang, J. S. Möller, T. Lancaster, A. T. Boothroyd, F. L. Pratt, S. R. Giblin, D. Prabhakaran and S. J. Blundell, Phys. Rev. Lett. 114, 017602 (2015)