Modification of the Upper Critical Field of RbEuFe<sub>4</sub>As<sub>4</sub> due to Eu-Magnetism

ORAL

Abstract


ReEuFe4As4 is a Fe-base superconductor with a high transition temperature of Tc~37 K that enters into a magnetic state at 15 K in which Eu-4f moments are helically ordered. In this state, in-plane ferromagnetically ordered Eu-planes undergo 90 deg rotation between layers resulting in a commensurate helix with a period of 4 c-axis lattice constant. This structure is easily polarized in fields of the order of several kOe resulting in a field-induced ferromagnet with a moment of 7 µB/(unit cell) coexisting with superconductivity. Nevertheless, most measurements to date have yielded no or only very weak coupling between superconductivity and magnetism. Using specific heat measurements in fields up to 14 T, we show that the Hc2-line exhibits clear downwards curvature in a temperature range close to Tc where Ginzburg-Landau theory applies, amounting to a shift by δTc ~ 0.4 K in 14 T ||c. This effect can be captured quantitatively in a model in which the exchange fields from the field-induced polarization of the Eu-moments renormalize Tc(H).

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The work at Argonne National Laboratory was supported by the U.S. Department of Energy, Office of Science, Materials Sciences and Engineering Division. The PPMS used for specific heat measurements was funded by NSF MRI grant 1828387.

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Presenters

  • Ulrich Welp

    • Argonne National Laboratory
    • Argonne Natl Lab
    • Materials Science Division, Argonne National Laboratory
    • Materials Science Division, Argonne Natl Lab
    • Argonne National Lab

Authors

  • Ulrich Welp

    • Argonne National Laboratory
    • Argonne Natl Lab
    • Materials Science Division, Argonne National Laboratory
    • Materials Science Division, Argonne Natl Lab
    • Argonne National Lab

  • Alexei Koshelev

    • Argonne Natl Lab
    • Materials Science Division, Argonne National Laboratory
    • Materials Science Division, Argonne Natl Lab
    • Argonne National Lab

  • Roland Willa

    • Institute for Theory of Condensed Matter, Karlsruhe institute of Technology
    • Karlsruhe Institute of Technology

  • Clement Burns

    • Department of Physics, Western Michigan University

  • Matthew S. Cook

    • Department of Physics, Western Michigan University

  • Jinke Bao

    • Argonne Natl Lab
    • Materials Science Division, Argonne Natl Lab
    • Argonne National Laboratory

  • Duck Young Chung

    • Argonne Natl Lab
    • Materials Science Division, Argonne National Laboratory
    • Materials Science Division, Argonne Natl Lab
    • Argonne National Laboratory
    • Material Science, Argonne National Laboratory

  • Mercouri Kanatzidis

    • Northwestern University
    • Materials Science Division, Argonne National Laboratory
    • Department of Chemistry, Northwestern University
    • Chemistry, Northwestern Univ

  • Wai-Kwong Kwok

    • Argonne National Laboratory
    • Material Sciences, Argonne National Laboratory
    • Argonne Natl Lab
    • Materials Science Division, Argonne National Laboratory
    • Materials Science Division, Argonne Natl Lab
    • Argonne National Lab