| Speaker: Alastair Rucklidge Affiliation: University of Leeds Time: 2 pm Thursday, 6 April, 2017 Location: 303-257 |
| Regular crystals are ordered arrangements of atoms or molecules with rotation and translation symmetries, having a discrete X-ray diffraction pattern, or equivalently, a discrete spatial Fourier transform. Crystals are in some ways like periodic tilings, in which an area can be filled with (for example) square or hexagonal tiles. Pentagonal tiles don't fit together, so when quasicrystals, which have five-fold rotation symmetry, were discovered in 1982, they led to a rewriting of the definition of crystal, and to a Nobel Prize for Chemistry for their discoverer. In this talk, I will discuss the formation and stability of icosahedral quasicrystals using a three-dimensional phase field crystal model, which is a reasonable model for soft-matter systems. I show that nonlinear interactions between density waves at two length scales are responsible for stabilizing three-dimensional quasicrystals. |