Phason is a
quasiparticle
In physics, quasiparticles and collective excitations are closely related emergent phenomena arising when a microscopically complicated system such as a solid behaves as if it contained different weakly interacting particles in vacuum.
For exa ...
existing in
quasicrystal
A quasiperiodic crystal, or quasicrystal, is a structure that is ordered but not periodic. A quasicrystalline pattern can continuously fill all available space, but it lacks translational symmetry. While crystals, according to the classical ...
s due to their specific, quasiperiodic lattice structure. Similar to
phonon
In physics, a phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, specifically in solids and some liquids. A type of quasiparticle, a phonon is an excited state in the quantum mechanical ...
, phason is associated with atomic motion. However, whereas phonons are related to ''translation'' of atoms, phasons are associated with atomic ''rearrangements''. As a result of these rearrangements, waves, describing the position of atoms in crystal, change phase, thus the term "phason".
In the superspace picture, aperiodic crystals are obtained from the section of a periodic crystal of higher dimension (up to 6D) cut at an irrational angle. While phonons change the position atoms relative to the crystal structure in space, phasons change the position of atoms relative to the quasi-crystal structure and the cut through superspace that defines it. Phonon modes are therefore excitations of the "in plane" real (also called parallel or external) space whereas phasons are excitations of the perpendicular (also called internal) space.
The hydrodynamic theory of the quasicrystals predicts that the conventional (phonon) strain relaxes rapidly. On the contrary, relaxation of the phason strain is diffusive and is much slower.
Therefore, metastable quasicrystals grown by rapid quenching from the melt exhibit built-in phason strain associated with shifts and anisotropic broadenings of X-ray and
electron diffraction
Electron diffraction refers to the bending of electron beams around atomic structures. This behaviour, typical for Wave (physics), waves, is applicable to electrons due to the wave–particle duality stating that electrons behave as both particle ...
peaks.
References
Freedman, B., Lifshitz, R., Fleischer, J. et al. Phason dynamics in nonlinear photonic quasicrystals. Nature Mater 6, 776–781 (2007). https://doi.org/10.1038/nmat1981
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Quasicrystal
A quasiperiodic crystal, or quasicrystal, is a structure that is ordered but not periodic. A quasicrystalline pattern can continuously fill all available space, but it lacks translational symmetry. While crystals, according to the classical ...
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Quasiparticle
In physics, quasiparticles and collective excitations are closely related emergent phenomena arising when a microscopically complicated system such as a solid behaves as if it contained different weakly interacting particles in vacuum.
For exa ...
Quasiparticles
Crystallography
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