Strongly fluctuating moments in the high-temperature magnetic superconductor RbEuFe4As4
K. Willa, R. Willa, J.-K. Bao, A. E. Koshelev, D. Y. Chung, M. G. Kanatzidis, W.-K. Kwok, U. Welp
DOI 10.1103/PhysRevB.99.180502 · Physical Review B
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Abstract
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 high-temperature 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 high-temperature expansion, both of which agree qualitatively and quantitatively with the experimental findings.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| RbEuFe4As4 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 37 | Pressure unresolved | onset |
| RbEuFe4As4 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 36.8 | Pressure unresolved | onset |
| CsEuFe4As4 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 35 | Pressure not reported | unknown |
| EuFe2As2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 23 | Pressure not reported | unknown |
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