Lyddane–Sachs–Teller relation

In condensed matter physics, the Lyddane–Sachs–Teller relation (or LST relation) determines the ratio of the natural frequency of longitudinal optic lattice vibrations (phonons) ( ω LO {\displaystyle \omega _{\text{LO}}} ) of an ionic crystal to the natural frequency of the transverse optical lattice vibration ( ω TO {\displaystyle \omega _{\text{TO}}} ) for long wavelengths (zero wavevector). The ratio is that of the static permittivity ε st {\displaystyle \varepsilon _{\text{st}}} to the permittivity for frequencies in the visible range ε ∞ {\displaystyle \varepsilon _{\infty }} .

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