超導材料 Fe(Se,Te) 系統之拉曼散射光譜研究
Abstract
我們研究摻雜不同碲離子濃度 FeSexTe1-x ( x = 1.0 、 0.7 、 0.5 、0.3 、 0.0 ) 與 RFeSexTe1-x ( R = Cu 、 Co 、 Ni ) 單晶樣品之拉曼散射光譜。首先， FeSexTe1-x 具有四個拉曼活性振動模，其頻率位置分別在 122 cm-1(Eg(1) 對稱性)、 178.9 cm-1(A1g 對稱性)、 194.3 cm-1(B1g 對稱性) 及 253 cm-1(Eg(2) 對稱性) ，隨著摻雜碲離子濃度增加，這些拉曼峰展現紅移變化，符合簡易彈力公式的預測。 FeSe 低溫拉曼散射光譜顯示：(i)隨著溫度下降， B1g 振動模藍移量約為 A1g 振動模的三倍，此現象與兩種振動模的剛性特質不同有關； (ii)結構相轉變的 γ 鍵角變化並未影響拉曼峰參數值。有趣地是，在磁性及結構相轉變溫度下，FeTe A1g 與 B1g 拉曼峰發生紅移現象，推測與自旋-聲子交互作用有關； FeSe0.5Te0.5 室溫拉曼散射光譜，顯示額外三個拉曼峰，可能是紅外光活性振動模 (Eu 對稱性) 與多聲子振動模，當在超導相變溫度之下， FeSe0.5Te0.5 A1g 與 B1g 拉曼峰藍移，其與 YBa2Cu3O7-δ 的自洽能效應不相符合。
最後，RFeSexTe1-x ( R = Cu 、 Co 、 Ni ) 拉曼散射光譜顯示 B1g 振動模的偏移量比 A1g 振動模大，應該與鐵離子部分被取代有關。
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.
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.
Description
Keywords
Fe(Se, Te), 超導, 拉曼散射光譜, Fe(Se, Te), superconducting, Raman-scattering