Progress in Superconductivity

The Korean Superconductivity Society (한국초전도학회)
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Optical Properties of Infinite-Layer Superconductors $Sr_{0.9}$$Ln_{0.1}$Cu$O_2$ (LnLa, Gd, Sm)

무한층 초전도체 $Sr_{0.9}Ln_{0.1}CuO_2$(Ln=La, Gd, Sm)의 광학적 성질

  • Mun, Mi-Ock (Institute of Physics and Applied Physics and Department of Physics, Yonsei University) ;
  • Park, Young-Sub (Institute of Physics and Applied Physics and Department of Physics, Yonsei University) ;
  • Kim, Kibum (Institute of Physics and Applied Physics and Department of Physics, Yonsei University) ;
  • Kim, Jae H. (Institute of Physics and Applied Physics and Department of Physics, Yonsei University) ;
  • A. B. Kuzmenko (Material Science Center, University of Groningen, Nijenborgh)
  • Published : 2001.01.01
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Abstract

We have measured the reflectivity of superconducting infinite-layer compounds $Sr_{0.9}$ $Ln_{0.1}$ Cu $O_2$ (Ln=La, Gd, Sm) with $T_{c}$ : 39 K using a Fourier-transform infrared spectrometer. We have identified the optical phonon modes from their infrared reflectivity and conductivity spectra and have proposed possible displacement patterns. The La- and the Gd-doped compounds exhibited only four ($2A_{2u}$ $+2E_{u}$) out of the five ($2A_{2u}$ $3E_{u}$) infrared-active phonons predicted by a group theoretical analysis whereas the Sm-doped compound exhibited all five modes. For the La-doped sample, we investigated the temperature dependence of the optical response functions in a wide temperature range of 7 - 300 K. In FIR region, the reflectivity is apparently enhanced below ~120 $cm^{-1}$ as temperature decreases across $T_{c}$. The value of $2$\Delta$/k_{B}$ $T_{c}$ is about 4.5, which is consistent with maximum gap value of d-wave $high- T_{c}$ cuprates.> c/ cuprates.uprates.s.

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