Strongly fluctuating moments in the higherature magnetic superconductor RbEuFe4As4

K. Willa, R. Willa, J. K. Bao, A. E. Koshelev, D. Y. Chung, M. G. Kanatzidis, W. K. Kwok, U. Welp

Research output: Contribution to journalArticlepeer-review

12 Citations (Scopus)


The iron-based superconductor RbEuFe4As4 undergoes a magnetic phase transition deep in the superconducting state. We investigate the calorimetric response of RbEuFe4As4 single crystals of the magnetic and the superconducting phase and its anisotropy to in-plane and out-of-plane magnetic fields. Whereas the unusual cusplike anomaly associated with the magnetic transition is suppressed to lower temperatures for fields along the crystallographic c axis, it rapidly transforms to a broad shoulder shifting to higher temperatures for in-plane fields. We identify the cusp in the specific-heat data as a Berezinskii-Kosterlitz-Thouless transition with fine features caused by the three-dimensional effects. The higherature shoulder in high magnetic fields marks a crossover from a paramagnetically disordered to an ordered state. This observation is further supported by Monte Carlo simulations of an easy-plane two-dimensional Heisenberg model and a fourth-order higherature expansion, both of which agree qualitatively and quantitatively with the experimental findings.

Original languageEnglish
Article number180502
JournalPhysical Review B
Issue number18
Publication statusPublished - May 23 2019

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

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