Evidence of superconductivity-induced phonon spectra renormalization in alkali-doped iron selenides

M. Opačić; N. Lazarević; M. Šćepanović; Hyejin Ryu; Hechang Lei; C. Petrovic; Z. V. Popović

doi:10.1088/0953-8984/27/48/485701

paper

Evidence of superconductivity-induced phonon spectra renormalization in alkali-doped iron selenides

arXiv:1609.05541 · doi:10.1088/0953-8984/27/48/485701

Abstract

Polarized Raman scattering spectra of superconducting K $_{x}$ Fe $_{2 - y}$ Se $_{2}$ and nonsuperconducting K $_{0.8}$ Fe $_{1.8}$ Co $_{0.2}$ Se $_{2}$ single crystals were measured in a temperature range from 10 K up to 300 K. Two Raman active modes from the $I 4/ mmm$ phase and seven from the $I 4/ m$ phase are observed in frequency range from 150 to 325 cm $^{- 1}$ in both compounds, suggesting that K $_{0.8}$ Fe $_{1.8}$ Co $_{0.2}$ Se $_{2}$ single crystal also has two-phase nature. Temperature dependence of Raman mode energy is analyzed in terms of lattice thermal expansion and phonon-phonon interaction. Temperature dependence of Raman mode linewidth is dominated by temperature-induced anharmonic effects. It is shown that change of Raman mode energy with temperature is dominantly driven by thermal expansion of the crystal lattice. Abrupt change of the A $_{1 g}$ mode energy near $T_{C}$ was observed in K $_{x}$ Fe $_{2 - y}$ Se $_{2}$ , whereas it is absent in non-superconducting K $_{0.8}$ Fe $_{1.8}$ Co $_{0.2}$ Se $_{2}$ . Phonon energy hardening at low temperatures in the superconducting sample is a consequence of superconductivity-induced redistribution of the electronic states below critical temperature.

13 pages, 6 figures

Evidence of superconductivity-induced phonon spectra renormalization in alkali-doped iron selenides

Abstract

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