Metric, Myth & Quasicrystals

Metric, Myth & Quasicrystallography describes the first measurement of the metric in quasicrystals and the first measurement at atomic scale. Quasicrystals are ordinary as window glass, but they have been mistified owing to their sharp diffraction patterns with 5-fold symmetries, impossible in crystals. Out of the fog, the patterns are not in Bragg order; the series is not properly Fibonacci: simplified indexation of the pattern is used to simulate a structure due to a single, aligned, edge-sharing unit-cell that is consistent with all data. Since it is unlikely that the sharp diffraction pattern is due to unmeasured poly polyhedra, does the International Union of Crystallography have to redefine crystals yet again? In modern physics, the metric relates the covariant components of invariant vectors with corresponding contravariant components. In crystallography it relates dimensions in momentum space to atomic locations in real space. In quasicrystals, the pattern in momentum space is logarithmic. Theory and simulation show why this has to be. Consequences follow. In particular, we show not only 'where the atoms are' but also 'why they are there'. A debate is reported so that the reader will be encouraged to make his own mind. When logarithmic periodicity is discovered and explained in one branch of physics, it should be expected in others.