Phonon dephasing temperature dependence

The pseudolocal phonon approach to dephasing, in the field of micro-wave and electronic spectroscopy rests on the assumption that insertion of a guest in a host crystal leads to formation of phonons which are substantially localized at the guest sites. There seems to be an urgent need for a model system where the pseudolocal phonons themselves are accessible for a direct relaxation study. Specifically the lifetime of this phonon and its temperature dependence are crucial quantities in a test of the dephasing... 

Tn denotes the dephasing time of the optical transition, T the lifetime of the excited state (fluorescence hfetime) and the pure dephasing time. At low temperatures T is essentially independent on temperature while shows a strong dependence on temperature. The actual value of at a given temperature depends on the excitation of low frequency modes (phonons, librations) that couple to the electronic transition of the chromophore. In crystalline matrices at low temperatures (T <2 K) Tl approaches infinity as host phonons and local modes are essentially quenched and the linewidth is solely determined by the lifetime contribution. 

We conclude, therefore, that it is possible to measure the temperature dependence of the dephasing time of LO phonons in GaP and ZnSe and to account for the observation in terms of the simple Bose-Einstein dependence on phonon occupation numbers. Although this procedure does indeed yield quite good agreement between experiment and theory, no theoretical apparatus exists for the prediction of the magnitude of T2 at T=0K. 

I have demonstrated that it is possible to determine experimentally the dephasing times of optical phonons and their temperature dependence, and that it is equally possible to determine experimentally all components of the third order nonlinear electronic susceptibility. The measurements reported here were taken in the temporal domain. Similar measurements of T2 and X taken in the spectral domain had previously been reported for other crystal systems. 

Indeed, Eq. (129) allowing for the bilinear electron-phonon-tunnelon interaction can easily explain a linear temperature broadening at kT > e. Hence, the temperature dependence of dephasing time in Fig. 27 results from the interaction with a tunnelon having e< lcm and the difference between experimental data found over various timescales is due to the temperature independent SD effect. At T > 15 K, the third term Ypi, in Eq.(130) exceeds... 

Ti is the level depletion lifetime and T2 is the pure dephasing time associated with the phase destructive events (e.g., by phonons and intermolecular interactions). This point will be taken up in more detail in Chapter 7. Here we merely note that the pure dephasing time is temperature dependent. 

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