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

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


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 (US)
Article number180502
JournalPhysical Review B
Issue number18
StatePublished - May 23 2019

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics


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