Displacive relaxor ferroelectrics as soft pseudo-spin glasses - some speculations

David Sherrington (Rudolf Peierls Centre for Theoretical Physics, University of Oxford and Santa Fe Institute)

Displacive ferroelectrics are ionic solids that undergo spontaneous displacements from higher temperature higher symmetry paraelectric structures to lower temperature lower symmetry structures with spontaneous overall ferroelectric moments.
Relaxors are related ionic alloys which exhibit a different kind of behaviour which is still not fully understood more than 50 years after their discovery, despite much study and application. Characteristic features are (i) significantly frequency-dependent peaks (in contrast to sharp and largely frequency-independent susceptibility peaks for the para-ferro transition), (ii) observation of polar nano-regions for a range above the peak temperature, but (iii) no change in global average lattice structure.
In this talk I shall use simple models and mappings to argue that displacive relaxors are physically analogous to spin glasses, but with soft pseudo-spins and induced-moment dipoles in place of the more common (hard) local moments of conventional experimental and model spin glasses, with the PNRs related to Anderson localization, without need for effective random fields in certain cases but with such fields probably also relevant in others.
If I have time, I may also relate these observations to (less studied) itinerant spin glasses.

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