Opačić M, Lazarević N, Šćepanović M, Ryu Hyejin, Lei Hechang, Petrovic C, Popović Z V
Center for Solid State Physics and New Materials, Institute of Physics Belgrade, University of Belgrade, Pregrevica 118, 11080 Belgrade, Serbia.
J Phys Condens Matter. 2015 Dec 9;27(48):485701. doi: 10.1088/0953-8984/27/48/485701. Epub 2015 Nov 16.
Polarized Raman scattering spectra of superconducting K(x)Fe(2-y)Se2 and non-superconducting K0.8Fe1.8Co0.2Se2 single crystals were measured in the temperature range from 10 K up to 300 K. Two Raman active modes from the I4/mmm phase and seven from the I4/m phase are observed in the frequency range from 150 to 325 cm(-1) in both compounds, suggesting that the K0.8Fe1.8Co0.2Se2 single crystal also has a two-phase nature. The temperature dependence of the Raman mode energy is analyzed in terms of lattice thermal expansion and phonon-phonon interaction. The temperature dependence of the Raman mode linewidth is dominated by temperature-induced anharmonic effects. It is shown that the change in Raman mode energy with temperature is dominantly driven by thermal expansion of the crystal lattice. An abrupt change of the A1g mode energy near T(C) was observed in K(x)Fe(2-y) Se2, whereas it is absent in non-superconducting K0.8Fe1.8Co0.2Se2. Phonon energy hardening at low temperatures in the superconducting sample is a consequence of superconductivity-induced redistribution of the electronic states below the critical temperature.
在10K至300K的温度范围内测量了超导K(x)Fe(2 - y)Se2和非超导K0.8Fe1.8Co0.2Se2单晶的偏振拉曼散射光谱。在这两种化合物中，在150至325 cm(-1)的频率范围内观察到来自I4/mmm相的两个拉曼活性模式和来自I4/m相的七个拉曼活性模式，这表明K0.8Fe1.8Co0.2Se2单晶也具有两相性质。根据晶格热膨胀和声子 - 声子相互作用分析了拉曼模式能量的温度依赖性。拉曼模式线宽的温度依赖性主要由温度诱导的非谐效应主导。结果表明，拉曼模式能量随温度的变化主要由晶格的热膨胀驱动。在K(x)Fe(2 - y)Se2中观察到A1g模式能量在T(C)附近的突然变化，而非超导的K0.8Fe1.8Co0.2Se2中则没有这种现象。超导样品在低温下的声子能量硬化是临界温度以下超导诱导的电子态重新分布的结果。
