Local symmetry breaking in crystals: nature, origins and consequences
Simon Billinge a
a Columbia University and Brookhaven National Laboratory, USA
Proceedings of Atomic-level characterization of hybrid perovskites (HPATOM)
Online, Spain, 2021 January 26th - 28th
Organizers: Dominik Kubicki and Amita Ummadisingu
Invited Speaker, Simon Billinge, presentation 025
Publication date: 14th January 2021

Crystals are periodically long-range ordered arrays of atoms. But crystals are not always as they seem. For sure, they have a long-range ordered component that is encoded in their Bragg scattering signal.  But what if this is just an average over different local atomic arrangements. Does that happen? How does it happen? If it happens, how can we detect it and why is this only news now. And finally, if it does happen, who cares?  In this talk I will explore this phenomenon in a number of different systems and show that, (1) it happens much more often than we probably realize. (2) it does matter, it can turn metals into insulators for example, (3) it can have different origins, from boring steric effects to orbital degeneracy lifting, lone pair effects, local covalency, and even  interesting steric effects (the hybrid perovskites!).  Finally, I will discuss some (but not all) the methods we can use to detect it, and why we are only figuring this out now (spoiler alert, it is hard to detect).

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