Raman phonons of $\alpha \text{-FeTe}$ and ${\text{Fe}}_{1.03}{\text{Se}}_{0.3}{\text{Te}}_{0.7}$ single crystals

The polarized Raman-scattering spectra of nonsuperconducting $\alpha \text{-FeTe}$ and of As-free superconductor ${\text{Fe}}_{1.03}{\text{Se}}_{0.3}{\text{Te}}_{0.7}$ are measured at room temperature on single crystals. The phonon modes are assigned by combining symmetry analysis with first-principles calculations. In the parent compound $\alpha \text{-FeTe}$, the $A_{1g}$ mode of the Te atom and the $B_{1g}$ mode of the Fe atom are observed clearly, while in superconducting ${\text{Fe}}_{1.03}{\text{Se}}_{0.3}{\text{Te}}_{0.7}$, only a softened $\text{Fe}{B}_{1g}$ mode can be seen. No electron-phonon coupling feature can be distinguished in the spectra of the two samples. By contrast, the spectra of the superconducting system show a slight enhancement below $300{\text{cm}}^{-1}$, which may be of electronic origin.

Figure 1

(Color online) Room-temperature Raman spectra of (a) ${\text{FeTe}}_{0.92}$ and (b) ${\text{Fe}}_{1.03}{\text{Se}}_{0.3}{\text{Te}}_{0.7}$ for different polarized scattering geometries in the $ab$ plane. (c) Extended spectrum of ${\text{FeTe}}_{0.92}$ in polarization configuration $Z\left(XX\right)\overline{Z}$. (d) Schematic illustration of two sample polarization configurations, $Z\left(XX\right)\overline{Z}$ and $Z\left(X^{\prime }{Y}^{\prime }\right)\overline{Z}$ (see also Fig. 2).

Figure 2

(Color online) Displacement patterns for the Raman-active modes of $\alpha \text{-FeTe}$, obtained from LDA calculations. [(a) and (b)] $E_g$ modes, (c) $A_{1g}$ mode of Te atoms, and (d) $B_{1g}$ mode of Fe atoms.

Figure 3

(Color online) Room-temperature Raman-scattering spectra of the surface from samples exposed to air for several days and from one fixed point of the cleaved sample surface held under continuous laser irradiation. The polarization is $Z\left(XX\right)\overline{Z}$.