| Summary: | 碩士 === 國立臺灣師範大學 === 物理學系 === 99 === We report a Raman-scattering study of Fe(Se,Te) single crystals at temperatures between 10 and 330 K. Room-temperature Raman-scattering spectrum of FeSe exhibits four phonon modes at about 122(Eg(1)), 178.9(A1g), 194.3 (B1g) and 253 cm-1(Eg(2)). When doped with Te on Se, the frequency positions of these phonon peaks redshift, in consistent with the prediction of simple spring constant model. With decreasing temperature, for FeSe, the amount of blue shift in B1g mode is three times larger than that in A1g, which is likely associated with the difference of rigidity of these two modes. Moreover, these two phonons are insensitive with the tetragonal to triclinic phase transition. Interestingly, anomalies of phonon parameters for FeTe are observed near the structural and magnetic phase transition temperatures, suggesting a spin-phonon coupling. FeSe0.5Te0.5 shows additional three phonon modes, which can be related with symmetry-breaking infrared mode (Eu) and multiphonons. The superconducting phase transition in this compound manifests itself as a blue shift in A1g and B1g phonon modes, betraying the self-energy effect (red shift) observed in YBa2Cu3O7-δ. Finally, Cu, Co, and Ni doping have a strong effect in the energy of B1g phonon mode.
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