Phason Light Scattering in BaMnF4

  • K. B. Lyons
  • T. J. Negran
Part of the NATO Advanced Study Institutes Series book series (NSSB, volume 77)


In an incommensurate phase there exists a lattice distortion with a periodicity incommensurate with that of the ambient lattice. The distortion is the order parameter of the normal—incommensurate phase transition, and may be approximated symbolically as
$$ \psi = {\psi _{0}}{e^{{\overrightarrow {i{k_{0}}r} }}}{e^{{i\emptyset }}} $$
where \( \overrightarrow {{k_{0}}} \) is the reciprocal periodicity of the distortion and Φ is a constant phase. Since \( \overrightarrow {{k_{0}}} \) is incommensurate, a uniform change in Φ clearly costs no energy. Hence, long wave length fluctuations in Φ should obey a dispersion law with the property that ω→0 as q→0. Thus, even well below the phase transition, a slow mode may be present which can modify the order parameter dynamics in some ways analagous to the effect of “microdomains”1 near a commensurate phase transition. That is, the slow mode, the phason, is an intrinsic part of the order-parameter dynamics. The present paper addresses the dynamics of the phasons as observed experimentally by light scattering in BaMnF4.


Slow Mode Incommensurate Phase Temperature Dependent Term Light Scattering Spectrum Entropy Fluctuation 
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Copyright information

© Plenum Press, New York 1982

Authors and Affiliations

  • K. B. Lyons
    • 1
  • T. J. Negran
    • 1
  1. 1.Condensed Matter Physics DepartmentBell LaboratoriesMurray HillUSA

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