Optical phonons in YBa2Cu4O8 and Y2Ba4Cu7O15−δ

Abstract

We present Raman spectra of high-temperature superconducting single crystals of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_4$ ${\mathrm{O}}_8$ and ${\mathrm{Y}}_2$ ${\mathrm{Ba}}_4$ ${\mathrm{Cu}}_7$ ${\mathrm{O}}_{15\mathrm{-}\mathrm{\delta }}$, differing from the well-known ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ by having double CuO chains. By performing polarization-dependent measurements, we were able to identify the symmetry of the observed phonons. In both materials, we detected four out of six Raman-allowed modes of the double Cu(1)-O(1) chains and assign the peaks to Cu(1) ${\mathit{A}}_{\mathit{g}}$ (250 ${\mathrm{cm}}^{\mathrm{-}1}$), O(1) ${\mathit{A}}_{\mathit{g}}$ (605 ${\mathrm{cm}}^{\mathrm{-}1}$), Cu(1) ${\mathit{B}}_{3\mathit{g}}$ (314 ${\mathrm{cm}}^{\mathrm{-}1}$), and O(1) ${\mathit{B}}_{2\mathit{g}}$ (228 ${\mathrm{cm}}^{\mathrm{-}1}$) in addition to the 5 ${\mathit{A}}_{\mathit{g}}$ phonons (in ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_4$ ${\mathrm{O}}_8$ near 104, 153, 341, 438, and 500 ${\mathrm{cm}}^{\mathrm{-}1}$), which are also present in the well-known ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$. Contrary to previous reports of Raman scattering on double-${\mathrm{CuO}}_2$-plane superconductors, ${\mathit{B}}_{2\mathit{g}}$ and

Keywords

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• INLINE
• HTTP
• MSUB
• MROW
• PHONONS
• MI MATHVARIANT

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