New tetragonal magnetic phase in (Ba,K)Fe$_2$As$_2$

ORAL

Abstract

The recently discovered C$_4$-symmetric magnetic phase in (Ba,Na)Fe$_2$As$_2$ \footnote{Avci et al., Nature Commun. 5, 3845 (2014)} is a rare exception among iron-based superconductors, which usually display a stripe-type spin-density wave (SDW) ground state at low doping. We re-examine the phase diagram of the closely related (Ba,K)Fe$_2$As$_2$ in great detail, using high-quality single crystals and thermodynamic (thermal-expansion and specific-heat) measurements. We find a small region of a, previously missed, C$_4$-symmetric phase in the ambient-pressure phase diagram, likely related to an unidentified phase transition observed under hydrostatic pressure\footnote{Hassinger et al., Phys. Rev. B 86 140502 (2012)}. We investigate the remarkable interplay of the new C$_4$ phase with superconductivity and with the SDW phase by studying the electronic entropy and the effect of uniaxial pressure on the phase diagram.

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Authors

  • Anna B\"{o}hmer

    Institut f\"{u}r Festk\"{o}rperphysik, Karlsruhe Institute of Technology, Germany

  • Fr\'{e}d\'{e}ric Hardy

    IFP, Karlsruhe Institute of Technology, Institut f\"{u}r Festk\"{o}rperphysik, Karlsruhe Institute of Technology, Germany

  • Liran Wang

    Institut f\"{u}r Festk\"{o}rperphysik, Karlsruhe Institute of Technology, Germany

  • Peter Schweiss

    Institut f\"{u}r Festk\"{o}rperphysik, Karlsruhe Institute of Technology, Germany

  • Thomas Wolf

    Karlsruher Institut fur Technologie, Institut fur Festkorperphysik, 7602, Karlsruhe, Germany, Karlsruher Institut fuer Technologie, Institut fuer Festkoerperphysik, D-76021 Karlsruhe, Germany, Institut f\"{u}r Festk\"{o}rperphysik, Karlsruhe Institute of Technology, Germany

  • Christoph Meingast

    IFP, Karlsruhe Institute of Technology, Institut f\"{u}r Festk\"{o}rperphysik, Karlsruhe Institute of Technology, Germany, Institute for Solid State Physics, Karlsruhe Institute of Technology, Germany