Progress in Superconductivity

The Korean Superconductivity Society (한국초전도학회)
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Temperature and magnetic field dependent optical properties of superconducting $MgB_2$ thin film

초전도 $MgB_2$ 박막의 온도와 장기장의 변화에 따른 광학적 성질

  • Jung, J. H. (School of Physics and Research Center for Oxide Electronics, Seoul National University) ;
  • Lee, H. J. (School of Physics and Research Center for Oxide Electronics, Seoul National University) ;
  • Kim, K. W. (School of Physics and Research Center for Oxide Electronics, Seoul National University) ;
  • Kim, M. W. (School of Physics and Research Center for Oxide Electronics, Seoul National University) ;
  • Noh, T. W. (School of Physics and Research Center for Oxide Electronics, Seoul National University) ;
  • Wang, Y. J. (National High Magnetic Field Laboratory at Florida State Universtiy) ;
  • Kang, W. N. (National Creative Research Initiative Center for Superconduclivity, Department of Physics, Pohang University of Science and Technology) ;
  • Jung, C. U. (National Creative Research Initiative Center for Superconduclivity, Department of Physics, Pohang University of Science and Technology) ;
  • Lee, Sung-Ik (National Creative Research Initiative Center for Superconduclivity, Department of Physics, Pohang University of Science and Technology)
  • Published : 2001.01.01
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Abstract

We investigated the temperature and magnetic field dependent optical properties of a$ MgB_2$ thin film in the far-infrared region. In the superconducting state, i.e. 5 K, we obtained the values of superconducting gap $2\Delta$ ~ 5.2 meV and $2\Delta$ $_{k}$ $B/T_{c}$ ~1.8. Although the value of$ 2\Delta$$B/T_{c}$ was nearly half of the BCS value, the $2\Delta$ seemed to follow the temperature dependence of the BCS formula. Under the magnetic field (H), the superconducting state became suppressed. Interestingly, we found that the normal state area fraction abruptly increased at low field but slowly increased at high field. It did not follow the H-dependences predicted for a s-wave superconductor (i.e. a linear dependence) nor for a s-wave one (i.e. $H^{1}$2/ dependence). We discussed the complex gap nature of $MgB_2$ in comparison with two gap and anisotropic s-wave scenarios.ios.

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