Effect of iron content and potassium substitution in A 0.8 Fe 1.6 Se 2 ( A =K, Rb, Tl) superconductors: A Raman scattering investigation
Effect of iron content and potassium substitution in A 0.8 Fe 1.6 Se 2 ( A =K, Rb, Tl) superconductors: A Raman scattering investigation
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DOI：
10.1103/physrevb.86.134502
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发表时间：
2011-05
影响因子：
3.7
通讯作者：
A. Zhang;K. Liu;J. H. Xiao;J. He;D. M. Wang;G. Chen;B. Normand;Q. Zhang
中科院分区：
文献类型：
--
作者：
A. Zhang;K. Liu;J. H. Xiao;J. He;D. M. Wang;G. Chen;B. Normand;Q. Zhang
We have performed Raman-scattering measurements on high-quality single crystals of the superconductors K${}_{0.8}$Fe${}_{1.6}$Se${}_{2}$ (${T}_{c}=32$ K), Tl${}_{0.5}$K${}_{0.3}$Fe${}_{1.6}$Se${}_{2}$ (${T}_{c}=29$ K), and Tl${}_{0.5}$Rb${}_{0.3}$Fe${}_{1.6}$Se${}_{2}$ (${T}_{c}=31$ K) as well as of the insulating compound KFe${}_{1.5}$Se${}_{2}$. To interpret our results, we have made first-principles calculations for the phonon modes in the ordered iron-vacancy structure of K${}_{0.8}$Fe${}_{1.6}$Se${}_{2}$. The modes we observe can be assigned very well from our symmetry analysis and calculations, allowing us to compare Raman-active phonons in the $A$FeSe compounds. We find a clear frequency difference in most phonon modes between the superconducting and nonsuperconducting potassium crystals, indicating the fundamental influence of iron content. By contrast, substitution of K by Tl or Rb in $A$${}_{0.8}$Fe${}_{1.6}$Se${}_{2}$ causes no substantial frequency shift for any modes above 60 cm${}^{\ensuremath{-}1}$, demonstrating that the alkali-type metal has little effect on the microstructure of the FeSe layer. Several additional modes appear below 60 cm${}^{\ensuremath{-}1}$ in Tl- and Rb-substituted samples, which are vibrations of heavier Tl and Rb ions. Finally, our calculations reveal the presence of ``chiral'' phonon modes, whose origin lies in the chiral nature of the K${}_{0.8}$Fe${}_{1.6}$Se${}_{2}$ structure.
We have performed Raman-scattering measurements on high-quality single crystals of the superconductors K${}_{0.8}$Fe${}_{1.6}$Se${}_{2}$ (${T}_{c}=32$ K), Tl${}_{0.5}$K${}_{0.3}$Fe${}_{1.6}$Se${}_{2}$ (${T}_{c}=29$ K), and Tl${}_{0.5}$Rb${}_{0.3}$Fe${}_{1.6}$Se${}_{2}$ (${T}_{c}=31$ K) as well as of the insulating compound KFe${}_{1.5}$Se${}_{2}$. To interpret our results, we have made first-principles calculations for the phonon modes in the ordered iron-vacancy structure of K${}_{0.8}$Fe${}_{1.6}$Se${}_{2}$. The modes we observe can be assigned very well from our symmetry analysis and calculations, allowing us to compare Raman-active phonons in the $A$FeSe compounds. We find a clear frequency difference in most phonon modes between the superconducting and nonsuperconducting potassium crystals, indicating the fundamental influence of iron content. By contrast, substitution of K by Tl or Rb in $A$${}_{0.8}$Fe${}_{1.6}$Se${}_{2}$ causes no substantial frequency shift for any modes above 60 cm${}^{\ensuremath{-}1}$, demonstrating that the alkali-type metal has little effect on the microstructure of the FeSe layer. Several additional modes appear below 60 cm${}^{\ensuremath{-}1}$ in Tl- and Rb-substituted samples, which are vibrations of heavier Tl and Rb ions. Finally, our calculations reveal the presence of ``chiral'' phonon modes, whose origin lies in the chiral nature of the K${}_{0.8}$Fe${}_{1.6}$Se${}_{2}$ structure.