Progress in Superconductivity and Cryogenics (한국초전도ㆍ저온공학회논문지)

The Korean Society of Superconductivity and Cryogenics (한국초전도저온학회)
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Optical properties of LK-99 and Cu2S

  • Hong Gu Lee (Department of Physics, Sungkyunkwan University) ;
  • Yu-Seong Seo (Department of Physics, Sungkyunkwan University) ;
  • Hanoh Lee (Department of Physics, Sungkyunkwan University) ;
  • Yunseok Han (Department of Physics, Sungkyunkwan University) ;
  • Tuson Park (Department of Physics, Sungkyunkwan University) ;
  • Jungseek Hwang (Department of Physics, Sungkyunkwan University)
  • Received : 2024.03.25
  • Accepted : 2024.04.16
  • Published : 2024.06.30
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Abstract

We investigated Pb10-xCux(PO4)6 (0.9 < x < 1.1) (LK-99) and Cu2S, presumed to be contained as an impurity in LK-99, in a wide spectral range from far infrared to ultraviolet using optical spectroscopy. The optical conductivity spectra of both samples were obtained from measured reflectance spectra at various temperatures from 80 to 434 K. Both samples showed several infrared-active phonons in the far and mid-infrared regions. LK-99 showed typical insulating features with a band gap of ~1 eV. Cu2S showed a nonmonotonic temperature-dependent trend and two energy gaps: one energy gap of ~93 meV and a band gap of 2.42 eV. Our results indicate that LK-99 cannot be a superconductor because it is an insulator with a large band gap.

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Acknowledgement

This study was supported by the National Research Foundation of Korea (NRFK Grant Numbers: 021R1A2C101109811, 2021R1A2C2010925, RS-2023-00248099, and 2021R1A2C1014319).

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