Anisotropy in the upper critical field of FeSe and FeSe 0.33 Te 0.67 single crystals

J. L. Her, Y. Kohama, Y. H. Matsuda, K. Kindo, W. H. Yang, D. A. Chareev, E. S. Mitrofanova, O. S. Volkova, A. N. Vasiliev, Jiunn-Yuan Lin

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The electric resistivity of single crystalline Fe-based superconductors FeSe and FeSe0.33Te0.67 was measured in pulsed magnetic fields up to 55 T. Te-doped iron selenide, FeSe0.33Te0.67, shows rather isotropic behavior in both magnetoresistance (MR) and upper critical fields (H c2 (0)/ H c2 (0) = 48 T/ 42 T ∼ 1.14), when an external magnetic field is applied parallel and perpendicular to the crystallographic c-axis. These isotropic behaviors are frequently observed in an iron-based superconductor, and the isotropy in H c2 can likely be described by the Pauli effect. In contrast, our measurements elucidate that the undoped iron selenide, FeSe, exhibits a clear anisotropy in both MR and H c2 (H c2 (0)/ H c2 (0) = 27 T/ 15 T ∼ 1.8). This behavior occurs because the clean in-plane conduction (RRR = 35) allows to form a closed electron orbit within the twodimensional Fermi sheets only for the magnetic field parallel to the c-axis, which results in an appearance of an intrinsic (orbital-effect limited) upper critical field for the undoped FeSe. Doping of Te breaks the clean in-plane conduction and leads to a crossover from an orbital limit dominating behavior to a Pauli limit dominating one.

Original languageEnglish
Article number045013
JournalSuperconductor Science and Technology
Issue number4
StatePublished - 1 Apr 2015


  • phase diagrams
  • pnictides and chalcogenides
  • superconductivity phase diagrams
  • transition temperature variations


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