The Physics & Astronomy Colloquium Series presents Frances Hellman from University of California Berkeley, discussing "Hidden Order in Amorphous Materials: From Gravitational Wave Detectors to Topological Materials" on October 18.

Abstract: Amorphous (glassy) materials lack structural order, making them difficult to describe or to calculate their properties compared to crystalline materials which consist of spatially repeated atoms.  This difficulty, however, does not preclude their applicability or scientific impact.  Various properties, including topological electronic states, seem to rely on the periodicity of the lattice for their derivation, yet are found in amorphous materials; recent advances have enabled explanation. Intriguingly, there exists the notion of an "ideal glass", which while remaining thoroughly disordered, lacks imperfections in that disorder and thus approaches the uniqueness of a crystal, including low entropy.  LIGO (laser interferometric gravitational observatory) relies on amorphous coatings for their mirrors; mechanical losses in these coatings are the limiting noise factor and are associated with universal yet poorly understand atomic motions associated with defects in the amorphous structure.  Amorphous silicon (a-Si) is the single material where these losses can be tuned over several decades, from below detectable limits to high in the range commonly seen in glassy systems, in a way seemingly connected with creating a near-ideal glass.

I will discuss the underlying phenomena of these results, which lie in a hidden order.