Comparison of temperature and angular dependence of the upper critical field in Mg1xAlxB2 single crystals in dirty-limit two-gap theory

Heon-Jung Kim, Hyan-Sook Lee, Byeongwon Kang, Woon-Ha Yim, Younghun Jo, Myung-Hwa Jung, and Sung-Ik Lee
Phys. Rev. B 73, 064520 – Published 28 February 2006

Abstract

We studied the temperature and the angular dependences of the upper critical field [Hc2(T,θ)] of Mg1xAlxB2 single crystals (x=0.12 and 0.21) and compared with the dirty-limit two-gap theory. We found that Hc2(T,θ)'s were well described in a unified way by this theory. The values of the parameters obtained by fitting experimental data to the theory indicated that as the Al concentration was increased, anisotropic impurity scattering increased, making the σ bands less anisotropic. Accordingly, the temperature dependence of the anisotropy ratio of Hc2 (γH) systematically decreased, and for x=0.21, γH was nearly independent of temperature. Our results imply that Mg1xAlxB2 single crystals are in the dirty limit and that the two-gap nature survives until x=0.21.

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  • Received 30 November 2005

DOI:https://doi.org/10.1103/PhysRevB.73.064520

©2006 American Physical Society

Authors & Affiliations

Heon-Jung Kim1, Hyan-Sook Lee1, Byeongwon Kang1,*, Woon-Ha Yim1, Younghun Jo2, Myung-Hwa Jung2, and Sung-Ik Lee1,2

  • 1National Creative Research Initiative Center for Superconductivity and Department of Physics, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea
  • 2Quantum Materials Research Laboratory, Korea Basic Science Institute, Daejeon 305-333, Republic of Korea

  • *Present address: Department of Physics, Chungbuk National University, Cheongju 361-763, Republic of Korea.

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Vol. 73, Iss. 6 — 1 February 2006

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